Flow cells for liquid-phase transmission electron microscopy and methods

Abstract

In one aspect, a flow cell (100) for liquid-phase transmission electron microscopy comprising an imaging portion (140) and a surrounding portion (150) in fluid communication with the imaging portion is provided. A height (153) of the channel (130) in the surrounding portion is configured to be greater than a height (143) of the channel in the imaging portion; and a length (164, 174) of the imaging portion is selected to achieve mass transport of the one or more fluids preponderantly by diffusion in the imaging portion. In a further aspect, a method of manufacturing the flow cell is provided.

Description

[0001] FLOW CELLS FOR LIQUID-PHASE TRANSMISSION ELECTRON MICROSCOPY AND METHODS

[0002] The present disclosure relates to flow cells for use in liquid-phase transmission electron microscopy, methods of manufacturing the flow cells thereof, and methods of imaging a sample in a liquid and I or gaseous environment in an electron microscope.

[0003] BACKGROUND

[0004] Electron microscopy uses an electron beam as a source of illumination to illuminate and to perform imaging of a sample. Therefore, analysis of the sample may be carried out. Electron microscopy refers to e.g., transmission electron microscopy, scanning transmission electron microscopy, or scanning electron microscopy.

[0005] Particularly, transmission electron microscopy (TEM) requires a sample and a sample receiving device that are vacuum compatible. To image the sample, the thickness of the imaging area of the sample receiving device needs to be inferior to the mean free path to avoid inelastic scattering, which results in low-resolution information of the sample.

[0006] Typically, sample preparation is required to obtain structure information of the sample (i.e., conventional TEM) or in-situ structure information of the sample (i.e., cryo-TEM). In the latter, the sample undergoes cryogenic temperatures which prevent the observation of in-situ processes.

[0007] Liquid-phase TEM enables imaging and analysis of liquid-phase processes (e.g., in- situ processes) with nanometer-scale resolution.

[0008] Particularly, liquid-phase TEM can use external flow control systems to supply fluids through supply lines to the sample receiving device where imaging is performed. Supply lines are integrated into TEM sample holders.

[0009] In liquid-phase TEM, the sample receiving device may be a liquid cell. Liquid cells can be based on the enclosure of a thin liquid layer in a channel made of two opposing semiconductor devices, e.g., MEMS devices. The two opposing semiconductor devices comprise electron transparent membranes for imaging the sample. The sample is arranged on the membrane so that the sample may be imaged by a transmission electron microscope. Incorrect sample fixation and positioning in the limited field of view of the windows may prevent imaging of the sample.

[0010] As mentioned above, the two semiconductor devices (i.e., chips) forming the liquid cell, are arranged on the tip of a sample holder. Typically, the channel height of liquid cells is a few hundreds of nanometers resulting in high flow resistances, which leads to membrane bulging and potential rupture of the liquid cell. Membrane bulging may limit the spatial resolution of liquid-phase TEM.

[0011] Sample receiving devices such as liquid cells can be used to receive the sample to be imaged and to control the sample's environment. Liquid environment in the liquid cell may be controlled e.g., by replacing the fluids flowing through the liquid cell or by mixing the fluids within or outside the liquid cell. However, fluid replacement within the imaging portion of the liquid cell is slow (i.e., several minutes, typically more than 30 minutes), meaning that the liquid environment of the sample may be changed in a time window that is incompatible e.g., with the observation of in-situ processes, nanoscale dynamics, or fast kinetics (i.e., in the range of seconds).

[0012] Currently, flow cells for liquid-phase transmission electron microscopy may have an increased bulging and slow fluids exchange dynamics. Examples of the present disclosure seek to at least partially reduce one or more of the aforementioned problems.

[0013] SUMMARY

[0014] In a first aspect, a flow cell such as a liquid cell, for liquid-phase transmission electron microscopy is provided. The flow cell comprises an inlet configured to receive one or more fluids; an outlet configured to exit the one or more fluids; and a channel in fluid communication with the inlet and the outlet. The channel comprises an imaging portion and a surrounding portion in fluid communication with the imaging portion. The imaging portion comprises a first electron transparent membrane; and a second electron transparent membrane opposing the first electron transparent membrane. The first electron transparent membrane or the second electron transparent membrane are configured to receive a sample. A height of the channel in the surrounding portion is configured to be greater than a height of the channel in the imaging portion; and a length of the imaging portion is selected to achieve mass transport of the one or more fluids preponderantly by diffusion in the imaging portion.

[0015] In this configuration, by selecting the height of the channel in the surrounding portion greater than the height of the channel in the imaging portion, the overall flow resistance of the flow cell is decreased, and membrane bulging may be reduced. Particularly, selecting the height of the channel in the surrounding portion and the length of the imaging portion involves a synergistic effect resulting in mass transport, which is dominated by diffusion, of the one or more fluids in the imaging portion; and a decay time compatible with the observation of e.g., in-situ processes, nanoscale dynamics, or fast kinetics, which is in the range of seconds. This configuration allows obtaining a flow cell in which the fluids flowing through the channel are controlled preponderantly by convection along the surrounding portion and preponderantly by diffusion along the imaging portion. Being preponderantly or predominantly controlled by diffusion along the imaging portion, means that the fluids flowing through the channel mainly do so by diffusion.

[0016] In some examples, because transport of fluids may be governed by diffusion along the imaging portion rather than convection like in the surrounding portion, a first fluid of the one or more fluids may be mixed at least in part with a second fluid of the one or more fluids in the imaging portion, with a decay time below a threshold. The decay time refers to the gradual (exponential) decrease or increase of the concentration of a solute (at a given location) with time. Decay times are determined by decay time constants (unit: 1 / s). In one example, the decay times (e.g., the decay time constants) relate to the imaging portion (e.g., the centre of the imaging portion).

[0017] Similarly, in some examples, because of the configuration resulting in diffusion driven fluid exchange in the imaging portion and a low flow resistance in the surrounding portion, a first fluid of the one or more fluids may be replaced at least in part with a fluid a second fluid of the one or more fluids in the imaging portion, with a decay time below a threshold.

[0018] Depending on the use of the flow cell, in the former example, the flow cell may be operated for mixing the first fluid with the second fluid whereas in the latter example, the flow cell may be operated for flowing fluids where the first fluid may be replaced at least in part with the second fluid in the imaging portion. In both examples, the decay time may be below a threshold which is in the range of seconds, e.g.., less than 60 seconds. As a result, the flow cell according to this aspect may enable replacing the fluids (i.e., reagents and I or unwanted compounds that may be continuously supplied or removed) flowing through the flow cell or mixing the fluids (i.e., introduction of reagents or compounds in a timescale compatible with dynamics such as nucleation, growth and self-assembly at the nanoscale).

[0019] In some examples, the length of the imaging portion and the height of the channel in the surrounding portion may be selected to achieve a decay time below a threshold, the threshold being less than 60 seconds, specifically below 10 seconds, and more specifically below 5 seconds, and in some examples the threshold may be less than 1 second. As mentioned, there is an interplay of convective and diffusive mass transport depending on the selection of the length of the imaging portion and the height of the surrounding portion which may result in decay times compatible with the observation of e.g., in-situ processes, nanoscale dynamics, or fast kinetics.

[0020] In some examples, the length of the imaging portion may be comprised between 1 pm and 2 mm, specifically between 0.05 mm and 2 mm, and more specifically between 0.2 mm and 2 mm. Particularly, in some of these examples, the length of the imaging portion may be comprised between 1 pm and 10 pm. As a result, a flow cell with a reduced length along the imaging portion may be obtained. Decreasing the length of the imaging portion may accelerate fluid exchange dynamics which scales with the square of the imaging portion length): where D is the diffusion coefficient of a solute in a medium such as a fluid, lIPis the length of the imaging portion, and tdis the elapsed time since diffusion began. Particularly, the diffusion coefficient determines the time it takes a solute to diffuse a given distance in the medium. D has the units of area / time (m2 / s). The diffusion coefficient may be: measured with e.g., dynamic light scattering measurements, calculated with Fick’s law of diffusion, or retrieved from the state of the art. It may be noted that in this equation, diffusion length has been considered as being equal to half the length of the imaging portion.

[0021] In some examples, the height of the channel in the surrounding portion may be comprised between 150 nm and 50 pm. Therefore, a flow cell with a surrounding portion comprising up to pm2-sized cross-sections may be obtained. As a result, the surrounding portion may flow the one or more fluids around or about the imaging portion, thereby avoiding high operating pressures, and reducing membrane bulging as well as the risk of flow cell rupture.

[0022] In some examples, the height of the channel in the imaging portion may be comprised between 50 nm and 5 pm, specifically between 100 nm and 500 nm. The distance between the side of the first electron transparent membrane in contact with the one or more fluids and the side of the second electron transparent membrane in contact with the one or more fluids may correspond to the height of the imaging portion, thereby defining a window. As a result, liquid-phase transmission electron microscopy of a sample arranged on the first electron transparent membrane or on the second electron transparent membrane may be performed.

[0023] In some of these examples, the height of the channel in the surrounding portion is comprised between 150 nm and 50 pm; and the height of the channel in the imaging portion is comprised between 50 nm and 5 pm. Therefore, the height of the channel may be varied along the extent of the channel which may result in portions with decreased flow resistance (i.e., the surrounding portions) and portions for imaging a sample (i.e., the imaging portions).

[0024] In some examples, the first electron transparent membrane may comprise, at least in part, a first corrugated portion; and the second electron transparent membrane may comprise, at least in part, a second corrugated portion. Because the second electron transparent membrane may oppose the first electron transparent membrane, a plurality of imaging portions and a plurality of surrounding portions may be obtained along the extent of the channel. Therefore, the plurality of imaging portions and the plurality of surrounding portions across the extent of the channel may result in a flow cell with decreased flow resistance, improved flow velocity, and improved flow cell breakage besides mass transport of the one or more fluids by diffusion in the imaging portion and a decay time compatible with the observation of e.g., in-situ processes, nanoscale dynamics, or fast kinetics, which is of the order of seconds.

[0025] In some of these examples, the first corrugated portion may define a first plurality of upper portions, a first plurality of lower portions, and a first plurality of side walls connecting each of the first plurality of upper portions with each of the first plurality of lower portions, thereby defining a length of each of the first plurality of lower portions and a depth of corrugation of the first corrugated portion of the first electron transparent membrane. Similarly, the second corrugated portion may define a second plurality of upper portions, a second plurality of lower portions, and a second plurality of side walls connecting each of the second plurality of upper portions with each of the second plurality of lower portions, thereby defining a length of each of the second plurality of lower portions and a depth of corrugation of the second corrugated portion of the second electron transparent membrane.

[0026] In some of these examples, the first corrugated portion and the second corrugated portion may be configured so that the height and the length of the imaging portion may be defined. The height of the channel in the imaging portion may correspond to a distance between the side of the lower portions of the first corrugated portion which is in contact with the one or more fluids, and the side of the second plurality of upper portions of the second corrugated portion which is in contact with the one or more fluids. The length of the imaging portion may correspond to the length of the lower portion of the first corrugated portion of the first electron transparent membrane; or to the length of the upper portion of the second corrugated portion of the second electron transparent membrane. Likewise, the first corrugated membrane and the second corrugated membrane may be configured to define the height and a length of the surrounding portion. The height of the channel in the surrounding portion may correspond to the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion.

[0027] In some examples, the length of the surrounding portion may correspond to a distance between a first imaging portion and a second imaging portion.

[0028] In some of these examples, the length of the surrounding portion may correspond to the length of the upper portion of the first corrugated portion of the first electron transparent membrane; or to the length of the lower portion of the second corrugated portion of the second electron transparent membrane.

[0029] In some examples, each of the first plurality of lower portions may be configured to be opposed to the second plurality of upper portions. Therefore, a plurality of channels comprising a plurality of imaging portions and a plurality of surrounding portion may be obtained. As a result, a flow cell allowing multiple observation of the sample may be obtained. Consequently, a plurality of samples may be observed at the same time. In some of these examples, the plurality of samples may be a plurality of the same sample.

[0030] In some of these examples, the first corrugated portion and the second corrugated portion may extend in a direction perpendicular to each other. In some of these examples, the first corrugated portion and the second corrugated portion may be configured so that the height and the length of the imaging portion may be defined. The height of the channel in the imaging portion may correspond to a distance between the side of the lower portions of the first corrugated portion which is in contact with the one or more fluids, and the side of the second plurality of upper portions of the second corrugated portion which is in contact with the one or more fluids. The length of the imaging portion may correspond to the length of the lower portion of the first corrugated portion of the first electron transparent membrane, or to the length of the upper portion of the second corrugated portion of the second electron transparent membrane. Similarly, the first corrugated membrane and the second corrugated membrane may be configured to define the height and a length of the surrounding portion. The height of the channel in the surrounding portion may correspond to: the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion, or the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the height of the imaging portion, or the sum of the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion.

[0031] In some examples, the length of the surrounding portion may correspond to a distance between a first imaging portion and a second imaging portion.

[0032] In some of these examples, the length of the surrounding portion may correspond to the length of the upper portion of the first corrugated portion of the first electron transparent membrane, or to the length of the lower portion of the second corrugated portion of the second electron transparent membrane.

[0033] In some examples, the flow cell may comprise a thermostat configured to measure a temperature of the one or more fluids flowing through the channel. Therefore, control of the environment of the sample may be improved. In a further aspect, a sample holder for an electron microscope, the sample holder configured to receive the flow cell according to an example of the disclosure is provided. Therefore, disposition of the flow cell within the electron microscope for correctly imaging a sample within the flow cell may be improved.

[0034] In a further aspect, a method of imaging a sample in a liquid and I or gaseous environment in an electron microscope is provided. The method comprises inserting a sample within a flow cell according to an example of the disclosure; inserting the flow cell comprising the sample in a sample holder; inserting the sample holder in an electron microscope; and causing a liquid and I or gas to flow on the sample. Therefore, electron microscopy of a sample within the flow cell may be performed.

[0035] In a further aspect, a method of manufacturing a flow cell is provided. The method comprises providing a first electron transparent membrane; providing a second electron transparent membrane; opposing the second electron transparent membrane with the first electron transparent membrane to define an imaging portion and a surrounding portion, the surrounding portion in fluid communication with the imaging portion, whereby the imaging portion and the surrounding portion define a channel.

[0036] Advantages derived from this aspect may be similar to those mentioned regarding the flow cell of the first aspect. Namely, improved mass transport of one or more fluids in the imaging portion.

[0037] Because the height of the channel in the surrounding portion may be configured to be greater than the height of the channel in the imaging portion; and the length of the imaging portion may be selected to achieve mass transport of one or more fluids by diffusion in the imaging portion. The method of manufacturing a flow cell may result in manufacturing a flow cell in which the fluids flowing through the channel are controlled preponderantly by convection along the surrounding portion and preponderantly by diffusion along the imaging portion is provided.

[0038] In some examples, the method may comprise providing the first electron transparent membrane comprising, at least in part, a first corrugated portion; providing the second electron transparent membrane comprising, at least in part, a second corrugated portion. Therefore, the method of manufacturing a flow cell may result in manufacturing a flow cell with a plurality of imaging portions and a plurality of surrounding portions across the extent of the channel. As a result, the method of manufacturing may result in manufacturing a flow cell with decreased flow resistance, improved flow velocity, and improved flow cell resistance to rupture besides mass transport of the one or more fluids by diffusion in the imaging portion and a decay time compatible with the observation of e.g., in-situ processes, nanoscale dynamics, or fast kinetics, which is of the order of seconds. In some examples, the decay time may be below 60 seconds, specifically below 10 seconds, and more specifically below 5 seconds, and in some examples the threshold may be less than 1 second.

[0039] The term "cell" may refer to a structure that holds a sample for imaging. A cell may comprise an imaging portion and / or a surrounding portion. Cells may comprise one, more than one or even an array of imaging portions and I or surrounding portions, which may include integrated features such as electrodes, thermocouples, thermostats and I or calibration sites. One example of a cell may be a flow cell which is a cell for flowing liquids through the flow cell.

[0040] The term “window” may be understood as a physical, electron transparent barrier of the cell with the vacuum environment of an electron microscope.

[0041] The term "sample" may refer to an object or compound being studied with an electron microscope, placed within the cell in which liquid or gases are flowed through.

[0042] The term "membrane" may correspond to a layer comprising at least in part an electron transparent portion for supporting the at least one sample.

[0043] The term "channel" may refer to a portion of the cell defined by two opposing layers such as chips, wherein at least one liquid and I or gas may be flowed therethrough.

[0044] The term “mixing” may refer to combining a fluid with another fluid within the flow cell. Mixing may allow the substantially instantaneous introduction of compounds such as reagents being at least part of a fluid into the flow cell. Mixing of a fluid with another fluid may result in dynamics such as nucleation, growth and self-assembly, by replacing the solution surrounding the sample.

[0045] “In situ" electron microscopy may involve applying stimulus to a sample during imaging. The stimulus may be a thermal stimulus (e.g., heating or cooling), an electrical stimulus (e.g.., applying a voltage or a current), a mechanical stimulus (e.g., applying stress or strain), a chemical stimulus (e.g., containing a sample in a specific chemical environment or mixing one or more fluids), or different stimulus at once.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Non-limiting examples of the present disclosure will be described in the following, with reference to the appended drawings, in which:

[0048] Figure 1a is a schematic view of a flow cell for electron microscopy according to an example of the present disclosure;

[0049] Figure 1b is a cross-section view of a flow cell for electron microscopy according to an example of the present disclosure;

[0050] Figures 2a - h show hydrodynamic parameters of a flow cell for electron microscopy according to an example of the present disclosure;

[0051] Figure 3 shows a cross-section view of a flow cell for electron microscopy according to an example of the present disclosure;

[0052] Figures 4a - b show a schematic view of a flow cell for electron microscopy according to an example of the present disclosure;

[0053] Figures 4c shows a cross-section view of a flow cell for electron microscopy according to an example of the present disclosure;

[0054] Figure 5 schematically shows a block diagram of a method of imaging a sample arranged within a flow cell according to an example of the present disclosure; and

[0055] Figure 6 schematically shows a block diagram of a method of manufacturing a flow cell for electron microscopy according to an example of the present disclosure.

[0056] DETAILED DESCRIPTION OF EXAMPLES

[0057] In these figures, the same reference signs have been used to designate matching elements. Figure 1a is a schematic view of one example of a flow cell 100 for electron microscopy such as liquid-phase transmission microscopy. The flow cell 100 may be e.g., a liquid cell. The flow cell 100 comprises an inlet 110 configured to receive one or more fluids; an outlet 120 configured to exit the one or more fluids; and a channel 130 in fluid communication with the inlet 110 and the outlet 120.

[0058] Figure 1b is a cross-section view of the flow cell 100 for electron microscopy according to a vertical plane A - A’ of figure 1a. The vertical plane A - A’ of figure 1a passes through the channel 130.

[0059] In figure 1b, the channel 130 comprises an imaging portion 140 and a surrounding portion 150 in fluid communication with the imaging portion 140. The imaging portion 140 comprises a first electron transparent membrane 141 ; and a second electron transparent membrane 142 opposing the first electron transparent membrane 141. The first electron transparent membrane 141 or the second electron transparent membrane 142 may be configured to receive a sample. Therefore, the sample may be arranged on the first electron transparent membrane 141 or on the second electron transparent membrane 142. Particularly, a height 153 of the surrounding portion 150 may be configured to be greater than a height 143 of the imaging portion 140; and a length 144 of the imaging portion 140 may be selected to achieve mass transport of the one or more fluids by diffusion in the imaging portion 140.

[0060] In figure 1b, the height 153 of the channel 130 in the surrounding portion 150 may correspond to a distance between a top side 151 of the channel 130 in the surrounding portion 150 and a bottom side 152 of the channel 130 in the surrounding portion 150, the top side 151 and the bottom side 152 being in contact with the one or more fluids. The height 143 of the channel 130 may correspond to a distance between the side of the first electron transparent membrane 141 in contact with the one or more fluids and the side of the second electron transparent membrane 142 in contact with the one or more fluids.

[0061] In figure 1b, the imaging portion 140 comprises a first end 145 and a second end 146, and the imaging portion 140 of the channel 130 extends from the first end 145 to the second end 146. The distance between the first end 145 and the second end 146 may correspond to the length 144 of the imaging portion 140. It may be noted that the walls of the channel 130 are made of the first electron transparent membrane 141 and made of the second electron transparent membrane 142, at least in the imaging portion 140.

[0062] It may be noted that the channel 130 may enclose the one or more fluids received by the inlet 110, thereby forming a fluid layer across the channel 130.

[0063] Volumetric flow of the channel 130 along the imaging portion 140 may be defined by the ratio of the flow resistance of the surrounding portion 150 and the flow resistance of the imaging portion 140:

[0064] „ _ (RSP / RIP) ' Q , ,

[0065] Q,p~ (1 + RSP / RIP)(where Q is the total volumetric flow of the channel 130, QIPis the volumetric flow through the imaging portion 140, RSPand RIPare flow resistances of the surrounding portion 150 and the imaging portion 140 respectively.

[0066] By increasing the height 153 of the surrounding portion 150, the flow resistance RSPof the surrounding portion 150 may be decreased. Therefore, when the height 153 of the surrounding portion 150 is increased, the volumetric flow QIPthrough the imaging portion 140 may be decreased. Decreasing the volumetric flow QIPalong the imaging portion 140 may improve the observation of the sample that may be located within the channel 130 along the imaging portion 140.

[0067] Because the height 153 of the surrounding portion 150 is greater than the height 143 of the imaging portion 140, the overall flow resistance of the flow cell 100 may be decreased and membrane bulging may be reduced.

[0068] In addition, the pressure drop developed in the flow cell 100 due to the flow may be where Q is the total volumetric flow of the channel 130, AP is the pressure drop of the flow cell 100, RSPand RIPare flow resistances of the surrounding portion 150 and the imaging portion 140 respectively. By selecting the height 153 of the surrounding portion 150 greater than the height 143 of the imaging portion 140, the flow resistance RSPof the surrounding portion 150 may be decreased which may result in a reduction of the pressure drop AP. Therefore, higher flow rates may be applied to the flow cell 100.

[0069] Particularly, a synergistic effect may take place when selecting the height 153 of the surrounding portion 150 and the length 144 of the imaging portion 140. As a result, mass transport of the one or more fluids may be dominated by diffusion in the imaging portion 140 and a decay time compatible with the observation of e.g., in-situ processes, nanoscale dynamics, or fast kinetics, which is in the range of seconds, may be obtained. Therefore, a flow cell 100 in which the mass transport through the channel 130 may be controlled preponderantly by convection along the surrounding portion 150 and preponderantly by diffusion along the imaging portion 140, may be obtained.

[0070] In some examples, the length 144 of the imaging portion 140 and the height 153 of the surrounding portion 150 may be selected to achieve a decay time below a threshold, the threshold being less than 5 seconds, and more particularly less than 2 seconds. There may be an interplay of convective and diffusive mass transport depending on the selection of the length 144 of the imaging portion 140 and the height 153 of the surrounding portion 150 which may result in decay times compatible with the observation of e.g., in-situ processes, nanoscale dynamics, or fast kinetics.

[0071] In some examples, because of the one or more fluids flowing through the channel 130 may be governed by diffusion along the imaging portion 140 rather than convection, a first fluid of the one or more fluids may be mixed at least in part with a second fluid of the one or more fluids in the imaging portion 140, with a decay time below a threshold. Similarly, a first fluid of the one or more fluids may be replaced at least in part with a second fluid of the one or more fluids in the imaging portion, with a decay time below a threshold.

[0072] Depending on the operation of the flow cell 100, the flow cell 100 may be operated for mixing the first fluid with the second fluid within the imaging portion 140, or for flowing fluids where the first fluid may be replaced at least in part with the second fluid within the imaging portion 140. In some examples, the length 144 of the imaging portion 140 may be comprised between 0.05 mm and 2 mm, and more specifically between 0.2 mm and 2 mm. As a result, the flow cell 100 with a reduced length of the imaging portion may be obtained. Decreasing the length 144 of the imaging portion 140 may accelerate fluid exchange dynamics which scales with the square of the length 144 of the imaging portion 140: where D is the diffusion coefficient of a solute in a medium such as a fluid, lIPis the length 144 of the imaging portion 140, and tdis the elapsed time since diffusion began. Particularly, the diffusion coefficient determines the time it takes a solute to diffuse a given distance in the medium. D has the units of area / time (m2 / s). The diffusion coefficient may be measured with e.g., dynamic light scattering measurements, calculated with Fick’s law of diffusion, or retrieved from the state of the art. It may be noted that in this equation, diffusion length has been considered as being equal to half the length of the imaging portion.

[0073] It may be noted that: where lIPis the length of the imaging portion, and tcis the elapsed time since convection began, QIPis the volumetric flow through the imaging portion 140, and AIPis the cross-section of the channel 130 along the imaging portion 140.

[0074] In some examples, the cross-section of the channel 130 along the imaging portion 140 may correspond to the length 144 of the imaging portion 140 and a width of the imaging portion (i.e., the lateral expansion of the imaging portion 140).

[0075] Therefore, when the height 153 of the surrounding portion 150 may be selected so that the flow resistance RSPof the surrounding portion 150 and the volumetric flow QIPthrough the imaging portion 140 may be decreased (see equation 1), the time tcmay be decreased (see equation 4).

[0076] In some examples, the height 153 of the surrounding portion 150 may be comprised between 150 nm and 50 pm. Therefore, the surrounding portion 150 may flow the one or more fluids about the first end 145 and / or the second end 146 of the imaging portion 140, thereby avoiding high operating pressures and reducing membrane bulging as well as the risk of flow cell rupture.

[0077] Referring to the electron transparent membranes (141, 142), in some examples, a thickness of each of the electron transparent membranes (141, 142) may be less than 15 nm.

[0078] In figure 1b, the first electron transparent membrane 141 and the second electron transparent membrane 142 may define a top window and a bottom window so that electron microscopy (e.g., liquid-phase transmission electron microscopy) of the sample may be performed.

[0079] The top window and the bottom window may enclose the one or more fluids flowing through the flow cell 100, thereby defining the imaging portion 140 of the channel 130. The top window and the bottom window may be separated by a distance such that an electron beam that enters from the top window may propagate through the imaging portion 140 and exit from the bottom window. As a result, electron microscopy (e.g., liquid-phase transmission electron microscopy) of a sample arranged about the first electron transparent membrane 141 or about the second electron transparent membrane 142 may be performed. Particularly, to image the sample, the height of the channel in the imaging portion may be inferior to the mean free path to avoid inelastic scattering and low-resolution information of the sample.

[0080] In some examples, the height of channel 130 in the imaging portion 140 may be comprised between 50 nm and up to few pm, for example between 50 nm and 5 pm. In some of these examples, the height of channel 130 in the imaging portion 140 may be comprised between 100 nm and 500 nm. The distance between the side of the first electron transparent membrane 141 in contact with the one or more fluids and the side of the second electron transparent membrane 142 in contact with the one or more fluids may correspond to the height 143 of the imaging portion 140. As a result, liquid-phase transmission electron microscopy of the sample arranged on the first electron transparent membrane or on the second electron transparent membrane may be performed.

[0081] It may be noted that the upper limit of the height of channel 130 in the imaging portion 140 (in the preceding example, the upper limit is up to few pm) is less than the lower limit of the surrounding portion 150. The upper limit of the height of channel 130 in the imaging portion 140 may be further defined by the transparency for the electron beam.

[0082] Therefore, as represented in figure 1a or 1b, the height of the channel 130 varies across the extent of the channel 130 which result in portions with decreased flow resistance (i.e., along the surrounding portion 150) and portions for imaging the sample (i.e., along the imaging portion 140).

[0083] In some examples, the channel 130 may comprise a first height along the surrounding portion 150 corresponding to the height 153 of the surrounding portion 150 and a second height along the imaging portion 140 corresponding to the height 143 of the imaging portion 140.

[0084] In some examples, the flow cell 100 may comprise structures such as spacers along the channel 130 for maintaining the height of the channel 130 in the surrounding portion 150 and I or in the imaging portion 140. For example, the spacers may be structures disposed between the top side 151 of the channel 130 in the surrounding portion 150 and the bottom side 152 of the channel 130 in the surrounding portion 150, or between the first electron transparent membrane 141 and the second electron transparent membrane 142. Consequently, in some of these examples, a height of the spacers may correspond either to the height 153 of the channel 130 in the surrounding portion 150 or to the height 143 of the channel 130 in the imaging portion 140.

[0085] The flow cell 100 may be manufactured by top-down fabrication methods to obtain two semiconductor devices, e.g., MEMS devices. Electron transparent membranes (141, 142) may be made of a material suitable for electron microscopy imaging such as silicon nitride SiN. Electron transparent membranes (141, 142) may be deposited by e.g., low pressure chemical vapor deposition or by atomic layer deposition. Surrounding portions 150 may be engraved on the semiconductor devices (e.g., made of silicon dioxide SiCh) using reactive ion etching methods. Spacers may be located across the channel 130 to support the electron transparent membranes (141, 142), or to support the top side 151 of the channel 130 in the surrounding portion 150 and the bottom side 152 of the channel 130 in the surrounding portion 150.

[0086] Because the flow cell 100 may be manufactured by contacting the two semiconductor devices, simple sample deposition in the imaging portion may be achieved. Therefore, access of the e.g., reactants, sample may be achieved which may enable the operation of the flow cell for imaging catalytic reactions.

[0087] Figures 2a - h represent hydrodynamic parameters of the flow cell 100. The depicted crosses of figures 2 a - h represent state-of-the-art values hydrodynamic parameters of state-of-the-art flow cells. Features of figures 2 a - h may be described in combination with the features of any of the examples shown in figures 1a - b.

[0088] Figures 2a, c, e, and g represent hydrodynamic parameters of the flow cell 100 depending on the length 144 of the imaging portion 140 which is comprised between 2 mm and 0.2 mm (i.e., 2 mm > lIP> 0.2 mm), for a fixed value of the height 153 of the surrounding portion (i.e., hSP= 10pm).

[0089] Figures 2b, d, f, and h represent hydrodynamic parameters of the flow cell 100 depending on the height 153 of the surrounding portion 150 which is comprised between 150 nm and 50 pm for a fixed length 144 of the imaging portion 140 (i.e., lIP= 0.2 mm).

[0090] For calculating the hydrodynamic parameters of the flow cell 100 represented in figures 2a - h, the total volumetric flow Q of the channel 130 may be equal to 300 pL / h (i.e., Q = 300 pL / h), and the diffusion coefficient D of a solute in a medium such as a fluid, may be equal to 6.1O'10m2 / s (i.e., D = 6.1O'10m2 / s).

[0091] Figures 2a - b show the pressure drop AP [mbar], which is dependent on the flow resistances RSPand RIPof the surrounding portion 150 and the imaging portion 140 respectively, either as a function of the length 144 (i.e., lIP[mm]) of the imaging portion 140 or as a function of the height 153 (i.e., hSP[pm]) of the surrounding portion 150. The pressure drop AP [mbar] is obtained by considering the total volumetric flow Q of the channel 130 equal to 300 pL / h (i.e., Q = 300 pL / h).

[0092] Figure 2a shows that the pressure drop AP decreases by decreasing the length 144 of the imaging portion (i.e., lIP[mm]). The pressure drop AP decreases from 92 mbar for lIP= 2 mm to 6 mbar for lIP= 0.05 mm.

[0093] Figure 2b shows that the pressure drop AP (and inherently the flow resistance of the channel 130, i.e., Rc=Rsp'Rlp) decreases by increasing the height 153 (i.e., h

[0094] RSPSP+RIP

[0095] [pm]) of the surrounding portion 150. The pressure drop AP decreases from 92 mbar for hSP= 150 nm to 0.12 mbar for hSP= 50 m. Therefore, by increasing the crosssection of the surrounding portion 150, the pressure drop AP and the flow resistance Rcof the channel may be decreased.

[0096] Figure 2b shows that for hSP= 50 pm, the pressure drop AP of the flow cell 100 is 3 orders of magnitude smaller than the state-of-the-art value (represented with a cross in figure 2b).

[0097] Flow cells with reduced flow resistance may require lower working pressures which may reduce window bulging. Particularly, flow cells with reduced flow resistance may operate at higher flow rates Q which may increase convective mass transport through the channel 130 of the flow cell 100. Therefore, higher flow rates Q of the one or more fluids flowing through the flow cell 100 may e.g., avoid the accumulation of compounds such as radiolytic compounds, or remove gas bubbles within the channel 130.

[0098] Figures 2c - d show the flow velocity vIP[pm / s] through the imaging portion 140, either as a function of the length 144 (i.e. , lIP[mm]) of the imaging portion 140 or as a function of the height 153 (i.e., hSP[pm]) of the surrounding portion 150.

[0099] Figure 2c shows that the flow velocity vIP[pm / s] through the imaging portion 140 decreases by decreasing the length 144 (i.e., lIP[mm]) of the imaging portion 140. The flow velocity vIPdecreases from 15 pm / s for lIP= 2 mm to 2 pm / s for lIP= 0.05 mm.

[0100] Figure 2d shows that the flow velocity vIP[pm / s] decreases by decreasing the height 153 (i.e., hSP[pm]) of the surrounding portion 150. The flow velocity vIPdecreases from 15 pm / s for hSP= 150 nm to 0.03 pm / s for hSP= 50 pm.

[0101] Figure 2d shows that for hSP= 50 pm, the flow velocity vcof the flow cell 100 is 3 orders of magnitude smaller than the state-of-the-art value (represented with a cross in figure 2d).

[0102] Figures 2e - f show the delay time At [s], either as a function of the length 144 (i.e., lIP[mm]) of the imaging portion 140 or as a function of the height 153 (i.e., hSP[pm]) of the surrounding portion 150. Delay time At [s] may refer to the delay time for observing a change, i.e., the time frame for diffusion to smear out the interface of a moving concentration front of the one or more fluids flowing through the channel.

[0103] Figure 2e shows that the delay time At decreases by decreasing the length 144 (i.e., lIP[mm]) of the imaging portion 140.

[0104] The delay time At decreases from 114 s for lIP= 2 mm to 5 s for lIP= 0.05 mm.

[0105] Figure 2e shows that for lIP= 0.2 mm, the delay time At of the flow cell 100 is 2 orders of magnitude smaller than the state-of-the-art value (represented with a cross in figure 2e). For lIP= 0.2 mm, the delay time At is about 7 seconds. Therefore, fluids exchange dynamics may be accelerated.

[0106] Figure 2f shows that the delay time At decreases by reducing the height 153 (i.e., hSP[pm]) of the surrounding portion 150.

[0107] The delay time At decreases from 114 s for hSP= 150 nm to 5.4 s for hSP= 50 pm.

[0108] Figure 2f shows that for hSP= 50 pm, the delay time At of the flow cell 100 is 2 orders of magnitude smaller than the state-of-the-art value (represented with a cross in figure 2f). For hSP= 50 pm, delay time At is about 5 seconds. Therefore, fluids exchange dynamics may be accelerated.

[0109] Figures 2 g - h show the decay time T [S], either as a function of the length 144 (i.e., lIP[mm]) of the imaging portion 140 or as a function of the height 153 (i.e., hSP[pm]) of the surrounding portion 150.

[0110] Decay time T [S] may refer to the transition of replacing and I or mixing a first fluid with a second fluid. The decay time refers to the gradual (exponential) decrease or increase of the concentration of a solute (at a given location) with time. Decay times are determined by decay time constants (unit: 1 / s). In one example, the decay times (e.g., the decay time constants) relate to the imaging portion (e.g., the centre of the imaging portion).

[0111] Figure 2g shows that the decay time T decreases by decreasing the length 144 (i.e., lIP[mm]) of the imaging portion 140. The decay time T decreases from 360 s for lIP= 2 mm to 1.7 s for lIP= 0.05 mm.

[0112] Figure 2h shows that for lIP= 0.2 mm, the decay time T of the flow cell 100 is 2 orders of magnitude smaller than the state-of-the-art value (represented with a cross in figure 2e). For lIP= 0.2 mm, decay time T is about 4 seconds. Therefore, fluids exchange dynamics may be accelerated.

[0113] Figure 2h shows that the decay time T decreases by decreasing the height 153 (i.e., [pm]) of the surrounding portion 150.

[0114] The decay time T decreases from 360 s for hSP= 150 nm to 4 s for hSP= 50 pm.

[0115] Figure 2h shows that for hSP> 10 pm, the decay time T of the flow cell 100 is 2 orders of magnitude smaller than the state-of-the-art value (represented with a cross in figure 2f). For hSP> 10 pm, decay time T is about 4 seconds. Therefore, fluids exchange dynamics may be accelerated.

[0116] Decay times T obtained as a function of the length 144 (i.e., lIP[mm]) of the imaging portion 140 or as a function of the height 153 (i.e., hSP[pm]) of the surrounding portion 150 (see figures 2e - f) may correspond to 90% of a first fluid being replaced with a second fluid within 10 seconds (i.e., in less than 10 seconds).

[0117] State-of-the-art values of decay time may be about 20 times slower (see the depicted crosses of figures 2e - h), where 90% of a first fluid may be replaced with a second fluid within e.g., 193 seconds.

[0118] Figures 2e - h show that the delay time At and decay time T are dependent on the length 144 (i.e., lIP[mm]) of the imaging portion 140 and I or the height 153 (i.e., hSP[pm]) of the surrounding portion 150. Particularly, the delay time At and decay time T may be preponderantly dependent on the length 144 (i.e., lIP[mm]) of the imaging portion 140, which is inherently correlated to mass transport of the one or more fluid by diffusion through the imaging portion 140 of the channel 130.

[0119] By selecting the length 144 of the imaging portion 140 and I or the height 153 of the surrounding portion 150, a flow cell 100 with low flow resistance Rc, low pressure build-up, fast solution exchange dynamics with a delay time At and a decay time T in the range of seconds, may be obtained. Consequently, the obtained flow cell 100 may be operated at high volumetric flow Q.

[0120] Figure 3 is a cross-section view of a flow cell 100 for electron microscopy such as liquid-phase transmission microscopy. The flow cell 100 may be e.g., a liquid cell. Features of figure 3 may be described in combination with the features of any of the examples shown in figures 1 or 2.

[0121] Compared to figures 1a - b, the flow cell 100 represented in figure 3, the first electron transparent membrane 141 comprises, at least in part, a first corrugated portion 160; and the second electron transparent membrane 142 comprises, at least in part, a second corrugated portion 170.

[0122] The first corrugated portion 160 may define a first plurality of upper portions 161 , a first plurality of lower portions 162, and a first plurality of side walls 163 connecting each of the first plurality of upper portions 161 with each of the first plurality of lower portions 162, thereby defining a length 164 of each of the first plurality of lower portions 162 and a depth 165 of corrugation of the first corrugated portion 160 of the first electron transparent membrane 141.

[0123] The second corrugated portion 170 may define a second plurality of upper portions 171 , a second plurality of lower portions 172, and a second plurality of side walls 173 connecting each of the second plurality of upper portions 171 with each of the second plurality of lower portions 172, thereby defining a length 174 of each of the second plurality of upper portions 171 and a depth 175 of corrugation of the second corrugated portion 170 of the second electron transparent membrane 142.

[0124] Referring to the length 164 of each of the first plurality of lower portions 162, the length 164 of the lower portion 162 may correspond to a distance between a first end 162a and a second end 162b of each of the first plurality of lower portions 162 of the first corrugated portion 160.

[0125] Similarly, the length 174 of each of the second plurality of upper portions 171 may correspond to a distance between a first end 171a and a second end 171b of each of the second plurality of upper portions 171 of the second corrugated portion 170. In figure 3, the length 164 of the lower portions 162 of the first corrugated portion 160 is equal to the length 174 of the upper portion 171 of the second corrugated portion 170.

[0126] In some examples, the corrugated shape of the first corrugated portion 160 or the second corrugated portion 170 may be e.g., rounded, sinusoidal, triangular, trapezoidal, square-shaped, rectangular, or toroidal.

[0127] In figure 3, because the second electron transparent membrane 142 opposes the first electron transparent membrane 141, there is a plurality of imaging portions 140 and a plurality of surrounding portions 150 along the extent of the channel 130. Therefore, the plurality of imaging portions 140 and the plurality of surrounding portions 150 across the extent of the channel 130 may result in a flow cell 100 with decreased flow resistance, improved flow velocity, and improved flow cell resistance to rupture, in addition to mass transport of the one or more fluids by diffusion in the plurality of imaging portions 140 and a decay time compatible with the observation of e.g., in-situ processes, nanoscale dynamics, or fast kinetics, which is of the order of seconds.

[0128] In figure 3, the first corrugated portion 160 and the second corrugated portion 170 are configured to define at least in part the height 143 of the imaging portions 140, and the length 144 (not shown in figure 3) of the imaging portions 140.

[0129] The height 143 of the imaging portions 140 may correspond to a distance between the side of the lower portions 162 of the first corrugated portion 160 which is in contact with the one or more fluids, and the side of the second plurality of upper portions 171 of the second corrugated portion 170 which is in contact with the one or more fluids.

[0130] The length 144 of the imaging portions 140 may correspond to the length 164 of the lower portion 162 of the first corrugated portion 160 of the first electron transparent membrane 141; or to the length 174 of the upper portion 171 of the second corrugated portion 170 of the second electron transparent membrane 142.

[0131] In figure 3, because the electron transparent membranes (141, 142) comprise corrugated portions (160, 170), the length 144 of the imaging portions 140 may be comprised between 1 pm and 2mm, specifically between 1 pm and 10 pm. Corrugated portions of the electron transparent membranes (141, 142) may allow obtaining smaller lengths of the imaging portion 140. Consequently, fluid exchange dynamics may be further improved.

[0132] In figure 3, the first corrugated portion 160 and the second corrugated portion 170 are configured to define at least in part the height 153 of the surrounding portions 150, and a length 154 of the surrounding portion 150.

[0133] The height 153 of the surrounding portions 150 may correspond to a distance between the side of the first plurality of upper portions 161 of the first corrugated portion 160 which is in contact with the one or more fluids, and the side of the second plurality of lower portions 172 of the second corrugated portion 170 which is in contact with the one or more fluids. Therefore, the height 153 of the surrounding portions 150 may correspond to the sum of the depth 165 of corrugation of the first corrugated portion 160 and the depth 175 of corrugation of the second corrugated portion 170 and the height 143 of the imaging portion 140.

[0134] In figure 3, because the shape of the corrugated portions (160, 170) is sinusoidal, the height of the channel 130 in the surrounding portion 150 tapers from the upper portions 161 of the first corrugated portion 160 towards the lower portions 162 of the first corrugated portion 160. Similarly, the height of the channel 130 in the surrounding portion 150 tapers from the lower portions 172 of the second corrugated portion 170 towards the upper portions 171 of the second corrugated portion 170.

[0135] The length 154 of the surrounding portion 150 may correspond to a distance between the second end 162b of a first lower portion of the first corrugated portion 160 and the first end 162a of a second lower portion of the first corrugated portion 160; or to a distance between the second end 171b of a first upper portion of the second corrugated portion 170 and the first end 171a of a second upper portion of the second corrugated portion 170. Therefore, the length 154 of the surrounding portion 150 may correspond to the distance between a first imaging portion and a second imaging portion, where the first imaging portion and the second imaging portion are separated by the surrounding portion.

[0136] In some examples such as when the shape of the corrugated portions (160, 170) may be square, the length 154 of the surrounding portion 150 may correspond to a length 166 of the upper portion 161 of the first corrugated portion 160 of the first electron transparent membrane 141; or to a length 176 of the lower portion 172 of the second corrugated portion 170 of the second electron transparent membrane 142.

[0137] The length 166 of each of the first plurality of upper portions 161 may correspond to a distance between a first end 161a and a second end 161b of each of the first plurality of upper portions 161 of the first corrugated portion 160.

[0138] Similarly, the length 176 of each of the second plurality of lower portions 172 may correspond to a distance between a first end 172a and a second end 172b of each of the second plurality of lower portions 172 of the second corrugated portion 170.

[0139] In some examples, the first corrugated portion 160 may extend in a first direction and the second corrugated portion 170 may extend in a second direction. In some of these examples, the first direction may be perpendicular to the second direction.

[0140] Figure 4a - b is a schematic view of a flow cell 100 for electron microscopy such as liquid-phase transmission microscopy. Figure 4c is a cross-section view of the flow cell 100 for electron microscopy according to a vertical plane B - B’ of figure 4b. The vertical plane B - B’ of figure 4b passes through one channel of the plurality of channels 130. The flow cell 100 may be e.g., a liquid cell. Features of figure 4 may be described in combination with the features of any of the examples shown in figures 1 to 3.

[0141] Compared to figure 3, the flow cell 100 represented in figures 4a - b, the first corrugated portion 160 extends in a first direction A and the second corrugated portion 170 extends in a second direction B. Particularly, as shown in figure 4, the first direction A is perpendicular to the second direction B.

[0142] Referring to figures 4a - c, each of the first plurality of lower portions 162 of the first corrugated portion 160 of the first electron transparent membrane 141 may be configured to be opposed to the second plurality of upper portions 171 of the second corrugated portion 170 of the second electron transparent membrane 142.

[0143] Because the first corrugated portion 160, which extends in the first direction A, may face the second corrugated portion 170, which extends in the second direction B and the first direction A is perpendicular to the second direction B, a flow cell 100 comprising multiple channels 130 with a plurality of imaging portions 140 (represented with black squares in figures 4a - b) and a plurality of surrounding portions 150 may be obtained along the extent of each channel 130. Therefore, multiple beam-induced experiments, or screening of several samples and I or experimental conditions may be achieved with the flow cell.

[0144] Figure 4a shows the first corrugated portion 160 and the second corrugated portion 170 in an exploded view. Dotted lines in figure 4a show how the first corrugated portion 160 is opposed to the second corrugated portion 170 so that a plurality of imaging portions 140 (represented with black squares in figures 4a - b) and a plurality of surrounding portions 150 may be obtained along the extent of each channel.

[0145] Figure 4c is a cross-section view of the flow cell 100 according to the vertical plane B - B’ of figure 4b. The represented lengths and I or heights in figure 4c are exaggerated and not up-to-scale.

[0146] In figure 4c, the first corrugated portion 160 and the second corrugated portion 170 are configured to define the height 143 of the imaging portions 140, and the length 144 of the imaging portions 140.

[0147] The thickness of each of the first corrugated portion 160 and the second corrugated portion 170 may be equal to or less than 100 nm (e.g., 5 nm) where they form the imaging portions 140. This thickness ensures electron transparency.

[0148] The height 143 of the imaging portions 140 may correspond to a distance between the side of the lower portions 162 of the first corrugated portion 160 which is in contact with the one or more fluids, and the side of the second plurality of upper portions 171 of the second corrugated portion 170 which is in contact with the one or more fluids.

[0149] The length 144 of the imaging portion 140 may correspond to the length 164 of the lower portion 162 of the first corrugated portion 160 of the first electron transparent membrane 141; or to the length 174 of the upper portion 171 of the second corrugated portion 170 of the second electron transparent membrane 142.

[0150] Referring to the length 164 of each of the first plurality of lower portions 162, the length 164 of the lower portion 162 may correspond to a distance between a first end 162a and a second end 162b of each of the first plurality of lower portions 162 of the first corrugated portion 160.

[0151] Similarly, the length 174 of each of the second plurality of upper portions 171 may correspond to a distance between a first end 171a and a second end 171b of each of the second plurality of upper portions 171 of the second corrugated portion 170.

[0152] In figure 4b, the length 164 of the lower portions 162 of the first corrugated portion 160 is equal to the length 174 of the upper portion 171 of the second corrugated portion 170.

[0153] In figures 4a - c, because the electron transparent membranes (141, 142) comprise corrugated portions (160, 170), the length 144 of the imaging portions 140 may be comprised between 1 pm and 2 mm, specifically between 1 pm and 10 pm. Corrugated portion may allow obtaining smaller lengths of the imaging portion. Consequently, fluid exchange dynamics may be further improved.

[0154] In figures 4b - c, the first corrugated portion 160 and the second corrugated portion 170 are configured to define the height 153 of the surrounding portions 150, and a length 154 of the surrounding portion 150.

[0155] Where the first corrugated portion 160 and the second corrugated portion 170 form the surrounding portion 150, they may have a thickness of equal to or greater than 100 nm (e.g., up to 100 pm). Thus, where the first corrugated portion 160 and the second corrugated portion 170 form the imaging portions 140 and where first corrugated portion 160 and the second corrugated portion 170 form the surrounding portion 150 may have the same or different thicknesses. In the case of the thicknesses being different, the ability to image and structural integrity are, advantageously, simultaneously facilitated.

[0156] The height 153 of the surrounding portions 150 may correspond to a distance between the side of the first plurality of upper portions 161 of the first corrugated portion 160 which is in contact with the one or more fluids, and the side of the second plurality of lower portions 172 of the second corrugated portion 170 which is in contact with the one or more fluids. As shown in figure 4b, the first plurality of upper portions 161 of the first corrugated portion 160 faces against the second plurality of lower portions 172 of the second corrugated portion 170. Therefore, in this example the height 153 of the surrounding portion 150 may correspond to the sum of the depth 165 of corrugation of the first corrugated portion 160 and the depth 175 of corrugation of the second corrugated portion 170 and the height 143 of the imaging portion 140.

[0157] Similarly, as shown in figure 4b, the first plurality of upper portions 161 of the first corrugated portion 160 faces against the second plurality of upper portions 171 of the second corrugated portion 170. Therefore, in this example the height 153 of the surrounding portion 150 may correspond to the sum of the depth 165 of corrugation of the first corrugated portion 160 and the height 143 of the imaging portion 140.

[0158] Similarly, as shown in figure 4b, the first plurality of lower portions 162 of the first corrugated portion 160 faces against the second plurality of lower portions 172 of the second corrugated portion 170. Therefore, in this example the height 153 of the surrounding portion 150 may correspond to the sum of the depth 175 of corrugation of the second corrugated portion 170 and the height 143 of the imaging portion 140.

[0159] In figures 4a - c, because the shape of the corrugated portions (160, 170) is trapezoidal, the height of the channel 130 in the surrounding portion 150 tapers from the upper portions 161 of the first corrugated portion 160 towards the lower portions 162 of the first corrugated portion 160. Similarly, the height of the channel 130 in the surrounding portion 150 tapers from the lower portions 172 of the second corrugated portion 170 towards the upper portions 171 of the second corrugated portion 170.

[0160] The length 154 of the surrounding portion 150 may correspond to a distance between the second end 162b of a first lower portion of the first corrugated portion 160 and the first end 162a of a second lower portion of the first corrugated portion 160 (as shown in figure 4c); or to a distance between the second end 171b of a first upper portion of the second corrugated portion 170 and the first end 171a of a second upper portion of the second corrugated portion 170. Therefore, the length 154 of the surrounding portion 150 may correspond to the distance between a first imaging portion and a second imaging portion, where the first imaging portion and the second imaging portion are separated by the surrounding portion. In some examples such as when the shape of the corrugated portions (160, 170) may be square, the length 154 of the surrounding portion 150 may correspond to the length 166 of the upper portion 161 of the first corrugated portion 160 of the first electron transparent membrane 141; or to a length 176 of the lower portion 172 of the second corrugated portion 170 of the second electron transparent membrane 142.

[0161] The length 166 of each of the first plurality of upper portions 161 may correspond to a distance between a first end 161a and a second end 161b of each of the first plurality of upper portions 161 of the first corrugated portion 160.

[0162] Similarly, the length 176 of each of the second plurality of lower portions 172 may correspond to a distance between a first end 172a and a second end 172b of each of the second plurality of lower portions 172 of the second corrugated portion 170.

[0163] In some examples, the imaging portion 140 may be 1 pm2(i.e., corresponds to the surface of the cross-section of the imaging portion). In these examples, the length 144 may be 1 pm and the lateral expansion (i.e., the width) of the imaging portion may be 1 pm. In these examples, a distance 178 (as shown in figure 4c) between the second end 161b of a first upper portion of the first corrugated portion 160 and the first end 161a of a second upper portion of the first corrugated portion 160 may correspond to the sum of two times the depth of corrugation (165, 175) and the length 144 of the imaging portion. In some of these examples, the depth 165 of corrugation of the first corrugated portion 160 may be 5 pm and the length 144 of the imaging portion may be 1 pm. Consequently, the distance 178 between the second end 161b of the first upper portion and the first end 161a of the second upper portion may be: 2x5 pm + 1 pm = 11 pm.

[0164] It may be noted that the examples of figure 3 and 4, the surrounding portion 150 and the imaging portion may be within the window by construct. The surrounding portion 150 may be non-transparent because of the height 153 of the surrounding portion 150.

[0165] In some examples, a sample holder used for receiving the flow cell 100 comprising a sample to be imaged in an electron microscope, e.g., a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM) and variations of the scanning electron microscopes (SEM), may be provided. The sample holder may be configured to receive the flow cell 100 according to any example disclosed in the description of figures 1 to 4.

[0166] Referring to the description of figures 1 - 4, it may be noted that the flow cell 100 may be used for hard and soft X-ray methods (such as X-ray scattering; X-ray absorption spectroscopy; X-ray diffraction; scanning transmission X-ray microscopy; X-ray photoelectron spectroscopy), optical methods (such as Ultraviolet-visible-Near Infrared UV-vis-NIR spectroscopy, Scanning Near Field Optical microscopy).

[0167] Figure 5 schematically show a block diagram of a method of imaging a sample arranged within a flow cell according to an example of the present disclosure. Features of figure 5 may be described in combination with the features of any of the examples shown in figures 1 to 4. Particularly, figure 5 represents a method 200 of imaging a sample in a liquid and I or gaseous environment in an electron microscope.

[0168] At block 210, the block 210 may comprise inserting a sample within the flow cell 100 according to any example disclosed in the description of figures 1 to 4.

[0169] At block 220, the block 220 may comprise inserting the flow cell 100 comprising the sample in a sample holder.

[0170] At block 230, the block 230 may comprise inserting the sample holder in an electron microscope.

[0171] At block 240, the block 240 may comprise causing a liquid and I or gas to flow on the sample.

[0172] Therefore, imaging and analysis of the sample in a liquid and I or gaseous environment in an electron microscope may be achieved.

[0173] Figure 6 schematically shows a block diagram of a method 300 of manufacturing the flow cell 100 for electron microscopy according to an example of the present disclosure. Features of figure 6 may be described in combination with the features of any of the examples shown in figures 1 to 4.

[0174] At block 310, the block 310 may comprise providing the first electron transparent membrane 141. At block 320, the block 320 may comprise providing the second electron transparent membrane 142.

[0175] At block 330, the block 330 may comprise opposing the second electron transparent membrane 142 against the first electron transparent membrane to define the imaging portion 140 and the surrounding portion 150 in fluid communication with the imaging portion 140, whereby the imaging portion 140 and the surrounding portion 150 define the channel 130.

[0176] In some examples, the block 310 may further comprise providing the first electron transparent membrane 141 comprising, at least in part, a first corrugated portion 160. In some examples, the block 320 may further comprise providing the second electron transparent membrane 142 comprising, at least in part, a second corrugated portion 170.

[0177] In some of these examples, the first and second corrugated portion may be provided so that the first corrugated portion and the second corrugated portion may extend in a direction perpendicular to each other.

[0178] Regardless of the configuration of the sample holder, i.e., a sample holder with a premixing channel or a sample holder without a pre-mixing channel, similar values may be obtained for the hydrodynamic parameters of the flow cell 100 shown in Figures 2a - h.

[0179] Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and / or equivalents thereof are possible. Furthermore, all possible combinations of the described examples are also covered. Thus, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

[0180] For reasons of completeness, various aspects of the present disclosure are set out in the following numbered clauses:

[0181] Clause 1 : A flow cell for liquid-phase transmission electron microscopy comprising: an inlet configured to receive one or more fluids; an outlet configured to exit the one or more fluids; a channel in fluid communication with the inlet and the outlet, the channel comprising: an imaging portion comprising: a first electron transparent membrane; and a second electron transparent membrane opposing the first electron transparent membrane, the first electron transparent membrane or the second electron transparent membrane are configured to receive a sample; a surrounding portion in fluid communication with the imaging portion; and wherein a height of the channel in the surrounding portion is configured to be greater than a height of the channel in the imaging portion; and wherein a length of the imaging portion is selected to achieve mass transport of the one or more fluids preponderantly by diffusion in the imaging portion.

[0182] Clause 2: A flow cell for liquid-phase transmission electron microscopy comprising: an inlet configured to receive one or more fluids; an outlet configured to exit the one or more fluids; a first electron transparent membrane comprising a first corrugated portion; a second electron transparent membrane comprising a second corrugated portion; wherein the second electron transparent membrane faces the first electron transparent membrane to define an imaging portion and a surrounding portion, the surrounding portion in fluid communication with the imaging portion, whereby the imaging portion and the surrounding portion define a channel which is in fluid communication with the inlet and the outlet.

[0183] Clause 3: The flow cell according to clause 1 or 2, wherein the length of the imaging portion and the height of the surrounding portion are selected to achieve a decay time below a threshold, the threshold being less than 60 seconds.

[0184] Clause 4: The flow cell according to any of clauses 1 to 3, wherein the height of the surrounding portion is comprised between 150 nm and 50 pm. Clause 5: The flow cell according to any of clauses 1 to 4, wherein the height of the imaging portion is comprised between 50 nm and 5 pm.

[0185] Clause 6: The flow cell according to any of clauses 1 to 5, wherein the height of the channel in the surrounding portion is comprised between 150 nm and 50 pm; and wherein the height of the channel in the imaging portion is comprised between 50 nm and 5 pm.

[0186] Clause 7: The flow cell according to any of clauses 1 to 6, wherein the first electron transparent membrane comprises, at least in part, a first corrugated portion; and wherein the second electron transparent membrane comprises, at least in part, a second corrugated portion.

[0187] Clause 8: The flow cell according to clause 7, wherein the length of the imaging portion is comprised between 1 pm and 2 mm.

[0188] Clause 9. The flow cell according to clause 7 or 8, wherein the first corrugated portion defines a first plurality of upper portions, a first plurality of lower portions, and a first plurality of side walls connecting each of the first plurality of upper portions with each of the first plurality of lower portions, thereby defining a length of each of the first plurality of lower portions and a depth of corrugation of the first corrugated portion of the first electron transparent membrane; and wherein the second corrugated portion defines a second plurality of upper portions, a second plurality of lower portions, and a second plurality of side walls connecting each of the second plurality of upper portions with each of the second plurality of lower portions, thereby defining a length of each of the second plurality of lower portions and a depth of corrugation of the second corrugated portion of the second electron transparent membrane.

[0189] Clause 10: The flow cell according to clause 9, wherein the first corrugated portion and the second corrugated portion are configured to define: the height and the length of the imaging portion, wherein the height corresponds to a distance between the side of the lower portions of the first corrugated portion which is in contact with the one or more fluids, and the side of the second plurality of upper portions of the second corrugated portion which is in contact with the one or more fluids, and wherein the length corresponds to:

[0190] • the length of the lower portion of the first corrugated portion of the first electron transparent membrane, or

[0191] • the length of the upper portion of the second corrugated portion of the second electron transparent membrane; and the height and a length of the surrounding portion, wherein the height corresponds to the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion.

[0192] Clause 11: The flow cell according to clause 10, wherein the corrugated shape of the first corrugated portion or the second corrugated portion is square-shaped.

[0193] Clause 12: The flow cell according to clause 10 or 11 , wherein the length of the surrounding portion corresponds to a distance between a first imaging portion and a second imaging portion.

[0194] Clause 13: The flow cell according to clause 12, wherein the first imaging portion and the second imaging portion are separated by the surrounding portion.

[0195] Clause 14: The flow cell according to any of clauses 10 to 13, wherein the length of the surrounding portion corresponds to the length of the upper portion of the first corrugated portion of the first electron transparent membrane, or to the length of the lower portion of the second corrugated portion of the second electron transparent membrane.

[0196] Clause 15: The flow cell according to any of clauses 7 or 9, wherein the first corrugated portion and the second corrugated portion extend in a direction perpendicular to each other.

[0197] Clause 16: The flow cell according to clause 15, wherein the first corrugated portion and the second corrugated portion are configured to define: the height and the length of the imaging portion, wherein the height corresponds to a distance between the side of the lower portions of the first corrugated portion which is in contact with the one or more fluids, and the side of the second plurality of upper portions of the second corrugated portion which is in contact with the one or more fluids, and wherein the length corresponds to:

[0198] • the length of the lower portion of the first corrugated portion of the first electron transparent membrane, or

[0199] • the length of the upper portion of the second corrugated portion of the second electron transparent membrane; and the height and a length of the surrounding portion, wherein the height corresponds to:

[0200] • the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion, or

[0201] • the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the height of the imaging portion, or

[0202] • the sum of the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion.

[0203] Clause 17: The flow cell according to clause 16, wherein the corrugated shape of the first corrugated portion or the second corrugated portion is square-shaped.

[0204] Clause 18: The flow cell according to clause 16 or 17, wherein the length of the surrounding portion corresponds to a distance between a first imaging portion and a second imaging portion.

[0205] Clause 19: The flow cell according to clause 18, wherein the first imaging portion and the second imaging portion are separated by the surrounding portion.

[0206] Clause 20: The flow cell according to any of clauses 16 to 19, wherein the length of the surrounding portion corresponds to the length of the upper portion of the first corrugated portion of the first electron transparent membrane, or to the length of the lower portion of the second corrugated portion of the second electron transparent membrane.

[0207] Clause 21: A sample holder for an electron microscope, the sample holder configured to receive the flow cell according to any of clauses 1 to 20.

[0208] Clause 22: A method of imaging a sample in a liquid and I or gaseous environment in an electron microscope, the method comprising: inserting a sample within a flow cell according to clauses 1 to 20; inserting the flow cell comprising the sample in a sample holder; inserting the sample holder in an electron microscope; and causing a liquid and I or gas to flow on the sample.

[0209] Clause 23. A method of manufacturing a flow cell, the method comprising: providing a first electron transparent membrane; providing a second electron transparent membrane; and opposing the second electron transparent membrane with the first electron transparent membrane to define an imaging portion and a surrounding portion, the surrounding portion in fluid communication with the imaging portion, whereby the imaging portion and the surrounding portion define a channel.

[0210] Clause 24. A method of manufacturing a flow cell according to clause 23, wherein the first electron transparent membrane comprises, at least in part, a first corrugated portion; and wherein the second electron transparent membrane comprises, at least in part, a second corrugated portion.

Claims

CLAIMS1. A flow cell (100) for liquid-phase transmission electron microscopy comprising: an inlet (110) configured to receive one or more fluids; an outlet (120) configured to exit the one or more fluids; a channel (130) in fluid communication with the inlet and the outlet, the channel comprising: an imaging portion (140) comprising: a first electron transparent membrane (141); and a second electron transparent membrane (142) opposing the first electron transparent membrane, the first electron transparent membrane or the second electron transparent membrane are configured to receive a sample; a surrounding portion (150) in fluid communication with the imaging portion; and wherein a height (153) of the channel in the surrounding portion is configured to be greater than a height (143) of the channel in the imaging portion; and wherein a length (144) of the imaging portion is selected to achieve mass transport of the one or more fluids preponderantly by diffusion in the imaging portion.

2. The flow cell according to claim 1 , wherein the length of the imaging portion and the height of the surrounding portion are selected to achieve a decay time below a threshold, the threshold being less than 60 seconds.

3. The flow cell according to claim 1 or 2, wherein the height of the surrounding portion is comprised between 150 nm and 50 pm.

4. The flow cell according to any of claims 1 to 3, wherein the height of the imaging portion is comprised between 50 nm and 5 pm.

5. The flow cell according to any of claims 1 to 4, wherein the height of the channel in the surrounding portion is comprised between 150 nm and 50 pm; and wherein the height of the channel in the imaging portion is comprised between 50 nm and 5 pm.

6. The flow cell according to any of claims 1 to 5,wherein the first electron transparent membrane comprises, at least in part, a first corrugated portion (160); and wherein the second electron transparent membrane comprises, at least in part, a second corrugated portion (170).

7. The flow cell according to claim 6, wherein the length of the imaging portion is comprised between 1 pm and 2 mm.

8. The flow cell according to claim 6 or 7, wherein the first corrugated portion defines a first plurality of upper portions (161), a first plurality of lower portions (162), and a first plurality of side walls (163) connecting each of the first plurality of upper portions with each of the first plurality of lower portions, thereby defining a length of each of the first plurality of lower portions and a depth of corrugation of the first corrugated portion of the first electron transparent membrane; and wherein the second corrugated portion defines a second plurality of upper portions (171), a second plurality of lower portions (172), and a second plurality of side walls (173) connecting each of the second plurality of upper portions with each of the second plurality of lower portions, thereby defining a length of each of the second plurality of lower portions and a depth of corrugation of the second corrugated portion of the second electron transparent membrane.

9. The flow cell according to claim 8, wherein the first corrugated portion and the second corrugated portion are configured to define: the height and the length of the imaging portion, wherein the height corresponds to a distance between the side of the lower portions of the first corrugated portion which is in contact with the one or more fluids, and the side of the second plurality of upper portions of the second corrugated portion which is in contact with the one or more fluids, and wherein the length corresponds to:• the length of the lower portion of the first corrugated portion of the first electron transparent membrane, or• the length of the upper portion of the second corrugated portion of the second electron transparent membrane; and the height and a length of the surrounding portion,wherein the height corresponds to the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion.

10. The flow cell according to any of claims 6 to 8, wherein a longitudinal axis of the first corrugated portion and a longitudinal axis of the second corrugated portion extend in directions perpendicular to each other.

11. The flow cell according to claim 10, wherein the first corrugated portion and the second corrugated portion are configured to define: the height and the length of the imaging portion, wherein the height corresponds to a distance between the side of the lower portions of the first corrugated portion which is in contact with the one or more fluids, and the side of the second plurality of upper portions of the second corrugated portion which is in contact with the one or more fluids, and wherein the length corresponds to:• the length of the lower portion of the first corrugated portion of the first electron transparent membrane, or• the length of the upper portion of the second corrugated portion of the second electron transparent membrane; and the height and a length of the surrounding portion, wherein the height corresponds to:• the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion, or• the sum of the depth of corrugation of the first corrugated portion of the first electron transparent membrane and the height of the imaging portion, or• the sum of the depth of corrugation of the second corrugated portion of the second electron transparent membrane and the height of the imaging portion.

12. A method of manufacturing a flow cell (100), the method comprising: providing a first electron transparent membrane (141); providing a second electron transparent membrane (142); and opposing the second electron transparent membrane with the first electron transparent membrane to define an imaging portion (140) and a surrounding portion (150), the surrounding portion in fluid communication with the imaging portion, whereby the imaging portion and the surrounding portion define a channel (130).

13. A method of manufacturing a flow cell according to claim 12, wherein the first electron transparent membrane comprises, at least in part, a first corrugated portion (160); and wherein the second electron transparent membrane comprises, at least in part, a second corrugated portion (170).

Images