TECHNIQUES FOR CONTROLLING THE STEAM PRESSURE OF OBJECTIVE MATERIALS IN STEAM CELLS AND CORRESPONDING PROCEDURES

Abstract

A method for producing a steam cell includes forming a body of the steam cell with walls defining a cavity between them, the cavity containing an amount of object material. The method also includes forming a pore structure comprising a substrate material with pores of substantially uniform diameter, the pore structure being arranged along a section of one or more of the walls of the steam cell. The method further includes forming a lining material of uniform thickness over one or more internal surfaces of the pores, the object material having a reduced contact angle on the lining material that is less than the contact angle of the object material on the substrate material.

Description

CROSS-REFERENCE TO RELATED REGISTRATION

[0001] This application claims the benefit under 35 USC § 119(e) of the priority date of the preliminary US patent application with serial number 63 / 507,212, filed on June 9, 2023, for TECHNIQUES FOR CONTROLLING VAPOR PRESSURE OF SUBJECT MATERIALS IN VAPOR CELLS AND RELATED METHODS, the disclosure of which is fully incorporated herein by reference. DECLARATION REGARDING GOVERNMENT-FUNDED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under grant W911NF2120016, provided by the U.S. Army Research Laboratory. The government has certain rights to the invention. AREA

[0003] This disclosure relates generally to techniques for controlling the vapor pressure of object materials in vapor cells, such as for atomic clocks, atomic sensors, and other applications. More specifically, disclosed examples relate to structures and materials for controlling the vapor pressure of alkali metals, which can improve the operational reliability of vapor cells, such as those used in atomic clocks, atomic sensors, and other applications, over wider temperature ranges. BACKGROUND

[0004] The vapor pressure is influenced by the surface tension according to the Kelvin equation: PPsat=e2γVm / rRT, where P / P sat the ratio of vapor pressure to saturation pressure, γ the surface tension, V mwhere is the molar volume of the liquid, r is the radius of the droplet, R is the universal gas constant, and T is the absolute temperature. Vapor pressure is important in a variety of operational contexts, including, but not limited to, atomic clocks and atomic sensors. REVELATION

[0005] In some examples, a vapor cell encloses a body with walls that define a cavity between them, the cavity containing a quantity of an object material. The vapor cell also has a pore structure comprising a substrate material with pores of substantially uniform diameter formed therein, the pore structure being arranged along a section of one or more of the walls, and a lining material arranged over one or more internal surfaces of the pores.

[0006] In other examples, a method for fabricating a vapor cell includes forming a vapor cell body with walls defining a cavity, the cavity containing an amount of object material. The method also includes forming a pore structure enclosing a silicon substrate material with pores of substantially uniform dimensions of about 1,000 nanometers, the pore structure being arranged along a section of one or more of the vapor cell walls. The method further includes forming a platinum lining material of uniform thickness over one or more internal surfaces of the pores, the object material exhibiting a reduced contact angle on the lining material, which is less than the contact angle of the object material on the substrate material.

[0007] In some other examples, a system includes an emitter positioned and oriented to direct radiation through windows of a vapor cell, the vapor cell comprising a body with walls defining a cavity between them, and a quantity of object material arranged within the cavity. The vapor cell also includes a pore structure comprising a substrate material with pores of substantially uniform diameter formed therein, the pore structure being arranged along a section of one or more of the walls, and a lining material of uniform thickness arranged over the inner surfaces of the pores, the object material having a contact angle on the lining material that is less than the contact angle of the object material on the substrate material.The system also includes a detector that is positioned and aligned to detect the radiation passed through the windows of the steam cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] While this disclosure concludes with claims that particularly highlight and explicitly claim certain examples, various features and advantages of examples within the scope of this disclosure can be more readily derived from the following description when read in conjunction with the accompanying drawings. In the drawings: are Fig. 1A and Fig. 1B Schematic cross-sectional side views of examples of steam cells; are Fig. 2A, Fig. 2B and Fig. 2C Schematic cross-sectional side views of other examples of steam cells; is Fig. 3 an enlarged, schematic cross-sectional side view of an example of a pore structure including one or more pores of uniform pore dimensions exposed to a cavity of a steam cell; is Fig. 4 a flowchart illustrating an example of a procedure for using a steam cell; is Fig. 5 a flowchart illustrating an example of a process for manufacturing a steam cell; is Fig. 6. A flowchart illustrating a further example of a procedure for constructing a steam cell; and are Fig. 7A and Fig. 7B Schematic representations of illustrative systems that include a steam cell according to this disclosure. FORM(S) OF EXECUTION OF THE INVENTION

[0009] The disclosed examples generally relate to the design of micro- or nanoporous structures for vapor cells, as non-limiting examples, for atomic clocks and atomic sensors, which, as a non-limiting example, can increase the temperature range in which reliable operation can be achieved. More specifically, the disclosed examples relate to designs for porous structures for controlling (e.g., suppressing) the vapor pressure. For example, at least one section of at least one inner wall in a vapor cell can include a porous structure having one or more pores that are dimensioned, shaped, and positioned to control (e.g., suppress) the vapor pressure of an object material (e.g., alkali metal, strontium, ytterbium) in the vapor cell. Such vapor pressure control can increase the temperature range in which reliable operation can be achieved.Some specific, non-limiting disclosed examples of a porous structure may include modifying the surface roughness of at least the section of the inner wall(s) of a vapor cell to form pores. Additionally or alternatively, at least one pore structure having one or more pores formed therein may be arranged in a vapor cell to control (e.g., suppress) the vapor pressure of the object material contained therein (e.g., alkali metal, strontium, ytterbium). Other specific, non-limiting disclosed examples may additionally or alternatively reduce the performance degradation of atomic clocks and atomic sensors when operating in high ambient temperature environments.

[0010] The illustrations presented in this revelation are not to be understood as actual views of any particular steam cell, a system that includes a steam cell, a structure that includes one or more pores, or any component thereof, but are merely idealized representations used to describe illustrative examples. Therefore, the drawings are not necessarily to scale. Furthermore, certain actions in flowcharts are shown in dashed lines to clearly indicate that these actions are "optional"; however, such designation is not to be interpreted as meaning that the other actions in flowcharts, shown in solid lines, are required, critical, or otherwise necessary in connection with a given example.

[0011] As used herein, the terms “essentially” and “approximately” with respect to a given parameter, property, or condition mean that the given parameter, property, or condition is satisfied to a degree of variance, such as within acceptable manufacturing tolerances, and include this to an extent that would be understood by those skilled in the art. For example, a parameter that is essentially or approximately a specified value may be at least approximately 90% of the specified value, at least approximately 95% of the specified value, at least approximately 99% of the specified value, or even at least approximately 99.9% of the specified value.

[0012] The term "pore," as used herein, means and includes surface features with an average dimension (e.g., average diameter) of approximately 5 nanometers (nm) to approximately 5 micrometers (µm), where micrometers can also be called microns, measured exemplarily in a direction parallel to a surface (e.g., sidewall) that at least partially defines a cavity to which an object material is exposed in a vapor cell. For example, "pores" may include interconnected, three-dimensional networks of cavities in a material that may be filled with surrounding fluids (e.g., air, inert gas). "Pores" may also include, for example, depressions, indentations, pits, and other surface features with average dimensions (e.g., average diameter) of less than 500 micrometers that may be measurable as surface roughness.

[0013] The term "micropore," as used herein, means and includes pores with an average dimension (e.g., average diameter) of about 1 micron to less than about 5 microns, which can be measured in a direction parallel to a surface (e.g., sidewall) that at least partially defines the cavity to which the object material is exposed in the vapor cell. The term "nanopore," as used herein, means and includes pores with an average dimension (e.g., average diameter) of about 5 nm to less than about 1,000 nm (i.e., less than about 1 micron), which can be measured in a direction parallel to a surface (e.g., sidewall) that at least partially defines the cavity to which the object material is exposed in the vapor cell.

[0014] Unless otherwise indicated in the context, the removal of the materials or surface modifications described herein may be carried out by any suitable technique, including, but not limited to, etching (e.g., dry etching, wet etching, steam etching, deep reactive ion etching (DRIE)), ion milling, abrasive planarization (e.g., chemical-mechanical planarization (CMP)), or other known methods.

[0015] The upper operating temperature of atomic sensors and atomic clocks, such as chip-scale atomic clocks (CSACs), without limitation, can be restricted by excessive optical absorption and collisional line broadening due to the high density of object material vapor (e.g., alkali metal, strontium, ytterbium) at elevated temperatures. The vapor pressure above a liquid can be suppressed by altering the shape of the liquid's outer surface, such as by confining the liquid within a pore of a porous structure (e.g., a porous structure). Such a process can be applied to lower the vapor pressure of the object material (e.g., alkali metal, strontium, ytterbium). According to the Kelvin equation, the radius of a droplet is positive when the curvature of the object liquid is convex, as is the case, for example, when the vapor pressure is greater than the saturation pressure.If the droplet's curvature is concave, its radius is negative, as is the case, for example, when the vapor pressure is lower than the saturation pressure. If the vapor pressure is lower than the saturation pressure, the vapor cell can operate over a wider temperature range (e.g., from approximately -45 degrees Celsius (°C) to approximately 250 °C), such as at high temperatures (e.g., 90 °C or higher), and ensure more consistent and reliable behavior of the object material.

[0016] Reducing the vapor pressure of an object material within vapor cells (e.g., atomic clocks, atomic sensors) can be achieved by introducing at least one pore. This pore, in combination with the surface tension of the object material within the pore, alters the shape of the object material within that pore. In other words, the interaction between the object material and the size and shape of a pore causes the shape of a surface of the object material to change in a desired manner (e.g., introduce a disturbance), compared to the shape of a surface of the object material on a substantially flat, non-porous surface.

[0017] Fig. 1A and Fig. Figure 1B shows schematic cross-sectional side views of examples of steam cells 100. The steam cell 100 can, for example, enclose a body 101 which in turn encloses a cavity 102. The cavity 102 can be dimensioned and shaped to contain an object material 104 (e.g., an alkali metal, strontium, ytterbium). For example, the body 101 can include transparent or see-through windows 106 that form one or more walls (e.g., boundaries) of the body 101, which at least partially define the cavity 102, with the remaining side walls 105 being opaque and further defining the cavity 102. Thus, the transparent or see-through windows 106 forming one or more walls and the remaining side walls 105 can define the cavity 102 between them.More precisely, the windows 106 can, for example, enclose a transparent or see-through borosilicate glass material, allowing a beam of radiation to pass through the windows 106 and into the cavity 102 of the vapor cell 100. The side walls 105 of the vapor cell 100 can enclose an opaque material (e.g., a silicon material), for example, if the vapor cell 100 is integrated into an atomic sensor, a chip-scale atomic clock, or a chip-scale atomic magnetometer.

[0018] The transparency of the material of window 106 can, for example, be approximately 10% or more at the wavelengths of the radiation directed at the cavity. More precisely, the transparency of the material of window 106 can, for example, range from approximately 10% to approximately 99% at the wavelengths of the radiation directed at the cavity. As a specific, non-limiting example, the transparency of the material of window 106 can, for example, range from approximately 20% to approximately 95% (e.g., approximately 25%, approximately 50%, approximately 75%).

[0019] A steam cell 100 according to the examples of the disclosure encloses one or more pores 103. The one or more pores 103 can be arranged on an inner section of one or more of the side walls 105 of the steam cell 100, such that the one or more pores 103 are exposed to the object material 104 contained in the cavity 102, as shown in Fig. Figure 1A shows that the inner section or sections of the respective side wall 105, which at least partially define the cavity 102, may enclose one or more pores 103 that are exposed to the object material 104 contained in the cavity 102. For example, the material of the section or sections of the respective side wall 105 may itself be porous, and at least some of the pores 103 of the section of the respective side wall 105 may be exposed to the object material 104 contained in the cavity 102. More specifically, the section of the respective side wall 105 may be subjected to a process different from the processing of a remainder of the side wall 105 to introduce porosity into the section of the respective side wall 105, such as by forming an array of micropores, an array of nanopores, or an array of micropores and nanopores.As a specific, non-limiting example, the section or sections of the respective sidewall 105 can be surface roughened or otherwise subjected to a material removal process (e.g., sandblasted, etched, ground) to form one or more pores 103 in the section or sections of the respective sidewall 105, whereby this process is not carried out for the remainder of the respective sidewall 105, such that the remainder of the respective sidewall 105 is at least substantially free of pores 103. The selective formation of pores in a particular section of a respective sidewall 105 can be achieved, for example, by using an aluminum hard mask to form the at least one pore in the respective sidewall 105 with the desired size, shape, and configuration.In a non-restrictive example, the surface roughness of the section of the respective side wall 105 which has one or more pores 103 can range from about 5 nm to about 1 micrometer.

[0020] In other examples, such as the one in Fig. As shown in Figure 1B, at least substantially the entirety of at least one or more side walls 105, which at least partially define the cavity 102, can enclose one or more pores 103 that are exposed to the object material 104 contained in the cavity 102. For example, the material of a particular side wall 105 can itself be porous, and at least some of the pores 103 of the respective side wall 105 can be exposed to the object material 104 contained in the cavity 102. Alternatively, the entirety of at least one particular side wall 105 can be subjected to a process that differs from the treatment of one or more other side walls 105 in order to introduce porosity into the respective side wall 105.As a specific, non-restrictive example, the entirety of the at least one respective side wall 105, which at least partially defines the cavity 102, can be roughened or otherwise subjected to a material removal process (e.g. sandblasted, etched, ground) to form one or more pores 103 in the respective side wall 105, whereby this processing cannot be carried out on other side walls 105, so that other side walls 105 may be at least substantially free of pores.

[0021] In some examples, more than one of the sidewalls 105, which at least partially define the cavity 102, can enclose pores 103 to tune the vapor pressure of the object material 104 to a target performance. The pores 103 can be positioned so that they do not obstruct the light path between a source and a detector in a device such as a chip-scale atomic clock (CSAC). For example, the pores 103 can be located on opaque sidewalls 105 that at least partially define the cavity 102, while pores 103 can be omitted on transparent windows 106 that further define the cavity 102.

[0022] The steam cell 100 can be dimensioned and shaped such that a beam of radiation can pass through the body 101 and into the cavity 102. For example, the windows 106 of the body 101 can allow radiation of one or more wavelengths or wavelength spectra to pass through the windows 106 and into the cavity 102 when the steam cell 100 is in operation. More precisely, the windows 106 can enclose a material (e.g., borosilicate glass) that is permeable or transparent to radiation (e.g., in the visible spectrum, infrared radiation, ultraviolet radiation, microwave radiation) directed at the object material 104 in the cavity 102.

[0023] The cavity 102 can be dimensioned and shaped to contain the object material 104, at least a section of which can be in a vaporous state and onto which radiation incident through the windows 106 can act when the steam cell 100 is in operation. The cross-sectional shape of the steam cell 100 can have any suitable shape, such as square, oval, round, rectangular, polygonal, or irregular. The cavity 102 of the steam cell 100 can, for example, have a volume of approximately 1 × 10 4 cubic millimeters (mm 3 ) or less. More precisely, as a non-restrictive example, the volume of the cavity 102 of the steam cell 100 can be approximately 0.1 mm³. 3 up to about 1×10 4 mm 3 amount to (e.g., approximately 10 mm) 3 , approximately 100 mm 3 , approximately 1×10 3 mm 3 , approximately 1×10 4 mm 3 ). The cavity 102 can, for example, be hermetically sealed.

[0024] In the Fig. 1A and Fig. In the examples illustrated in Figure 1B, the cavity 102 of the steam cell 100 can be enclosed by the side walls 105 and the windows 106. As shown in the Fig. 1A and Fig. As illustrated in Figure 1B, the windows 106 can be positioned on opposite sides that define at least part of the cavity 102, with the side walls 105 oriented perpendicular to the windows 106 and extending between them. In other examples, the steam cell 100 can include more or fewer windows 106 (e.g., one window, all walls designed as windows); side walls 105 can be oriented at an oblique angle or can curve relative to the window or windows; one or more side walls 105 can be arranged in the same plane as one or more of the corresponding windows 106; or any combination or subcombination of these features can be present.

[0025] As in Fig. 1A and Fig. As illustrated in Figure 1B, the pores 103 can be located directly in one or more of the walls that define the cavity 102, at least partially, such as the side walls 105. In some examples, the material of the side walls 105 can define the pores 103. As another example, the material of the side walls 105 can be modified during the formation of the pores 103, so that the material defining the pores 103 can differ from the material that forms part of the side walls 105, the windows 106, or both. More precisely, a process for forming the pores 103 can change the material composition of the side walls 105 that define the pores 103, or the material of the side walls 105 that define the pores 103 can be deliberately changed after the pores 103 have been formed. As a specific, non-restrictive example, the material of the side walls 105 that define the pores 103 can include silicon dioxide (SiO2).

[0026] In some examples, the section of the side wall 105 enclosing the pore 103 or pores 103 may be concentrated in a single, discrete section of the side wall 105. In other examples, the side wall 105 may enclose pores 103 in several different sections of the side wall 105. A single discrete section, several different sections, the total surface area occupied by all sections, the shapes of the sections, the positions of the sections, the sizes and shapes of the pores 103 in the section or sections, or any combination or subcombination of these features may be selected to induce that the vapor pressure of an object material 104 in the cavity 102 remains within predetermined threshold values ​​under the expected operating conditions of the steam cell 100.

[0027] As in Fig. As illustrated in Figure 1B, one or more side walls 105 that define at least part of the cavity 102 can enclose pores 103 that are exposed to the object material 104 contained in the cavity 102, and one or more other side walls 105 that define at least part of the cavity 102 can be without pores 103. For example, one, some, or all of the side walls 105 can be porous and / or have a surface roughness to form pores 103 near the cavity 102, and one or some of the side walls 105 can be non-porous.

[0028] Fig. 2A, Fig. 2B and Fig. Figures 2C are schematic cross-sectional side views of other examples of steam cells 200. The steam cells 200 can enclose a body 201 which has a cavity 202 within it. A large part of the side walls defining the body 201 can be formed from windows 206, as shown in the Fig. 2A, Fig. 2B and Fig. 2C shown. For example, the entire body 201 can be made of a material that is transparent to a predetermined wavelength of radiation, such that the body 201 consists of windows 206, as shown in the Fig. 2A and Fig. Figure 2B shows this. More precisely, the body 201 can, for example, enclose a discrete, uniform transparent material comprising windows 206 that enclose the cavity 202. As a specific, non-restrictive example, the body 201 can enclose a borosilicate glass that defines the cavity 202. As another example, all but one wall of the walls of the body 201 can be formed from the transparent material, so that the body 201 is largely composed of windows 206, as shown in Figure 2B. Fig. 2C shown. More precisely, the body 201 can, for example, enclose a transparent material that defines a first section (e.g., window 206) and forms a large part of the cavity 202, and an opaque material that defines a second, other section (e.g., side wall 205) and forms a minority of the cavity 202. As a specific, non-restrictive example, the body 201 can enclose a borosilicate glass arranged around and securing a silicon material, the silicon material forming only a side wall 205 that defines at least part of the cavity 202, as shown in Fig. 2C shown.

[0029] At least one pore structure 210, including one or more pores 203, can be introduced into the cavity 202. The pore structure 210 can include any material capable of defining one or more pores 203 and suitable for use with regard to the anticipated operating conditions in the cavity 202 of the steam cell 200. For example, the material of the pore structure 210 can be non-reactive with the object material 204 (e.g., alkali metal, strontium, ytterbium), the atmospheric material in the cavity 202, and the material of the body 201. More specifically, the pore structure 210 can, for example, include a silicon material. The pore structure 210 can include one or more pores 203 that are exposed to the object material 204 inside the cavity 202.

[0030] As in Fig. As illustrated in Figure 2A, the pore structure 210 can be mobile within the cavity 202. For example, the pore structure 210 can be enclosed within the cavity 202 by the body 201 and can otherwise be detached from and not restricted by the body 201 and other structures in the cavity. More precisely, the pore structure 210 can, for example, move freely within the cavity 202 without being physically, chemically, or otherwise attached to the walls of the body 201 that at least partially define the cavity 202. As a specific, non-restrictive example, the pore structure 210 can be detached from the body 201 and move freely relative to it, with the walls (e.g., window 206) of the body 201 defining at least partially the cavity 202, the body 201 being the only constraint on the movement of the pore structure 210 within the cavity 202.

[0031] As in Fig. As illustrated in Figure 2B, the pore structure 210 can be attached to the body 201 and be movable with it. The pore structure 210 can be attached, for example, by means of a holder 208, an adhesive 207, or a combination or subcombination of the two, and / or other techniques for attaching a pore structure 210 to a body 201 within a cavity 202 defined by the body 201.

[0032] As in Fig. As illustrated in Figure 2C, the pore structure 210 can be integrally formed in a side wall 205 that at least partially defines the cavity 202 and attached to a remainder of the body 201. For example, the material of the remainder of the body 201 can be provided in a deformable state around the pore structure 210 that is integrally formed in the respective side wall 205, and the material of the remainder of the body 201 can then be fixed in place around the pore structure 210 that is integrally formed in the respective side wall 205 to attach the pore structure 210 to the remainder of the body 201. More precisely, the material of the window 206 or windows 206 can be positioned in a deformable state around the material of the pore structure 210 that is integrally formed in the respective side wall 205 (e.g.,During the blowing of the window 206 (or windows 206) from a borosilicate glass material, the pore structure 210, which is integrally formed in the respective side wall 205, can be attached to a section of the window 206 (or windows 206) that surrounds a corresponding section of the pore structure 210. As the window 206 (or windows 206) cools, the pore structure 210, which is integrally formed in the respective side wall 205, can form a wall (e.g., the respective side wall 205) that at least partially defines the cavity 202, and the windows 206 can form the remainder of the walls that define the cavity 202 of the vapor cell 200. A geometry of the cavity 202 can constrain the position of the pore structure 210 to a specific location within the cavity 202.More specifically, the borosilicate glass of body 201 can be placed around and in contact with the pore structure 210 in a heated, viscous state, and body 201 can be cooled to a higher viscosity state or a solid state to attach the pore structure 210 to the rest of body 201. As a specific, non-limiting example, body 201 and pore structure 210 can be bonded together by anodic bonding.

[0033] In some examples, the size, shape, number, and porosity of the pore structure 210 can be selected such that the vapor pressure of the object material 204 is adjusted to the target performance. For example, a reduction in the size (e.g., average dimension, average diameter) of the pores 203 in the pore structure 210 can lead to a corresponding increase in the maximum temperature at which the vapor pressure in the vapor cell 200 can be within certain target values. As another example, an increase (e.g., average dimension, average diameter) of the pores 203 can lead to a corresponding decrease in the maximum temperature at which the vapor pressure in the vapor cell 200 can be within certain target values.

[0034] Fig. Figure 3 is an enlarged, schematic cross-sectional side view of a pore structure 310 defining one or more pores 303 exposed to an object material 304 contained in the cavity 302 of a steam cell. The pores 303 can have a substantially uniform pore dimension 312 (e.g., a substantially uniform pore diameter), for example, from about 10 nm to about 10,000 nm. More precisely, the substantially uniform pore dimension 312 (e.g., a substantially uniform pore diameter) of the pores 303 exposed to the object material 304 (e.g., alkali metal, strontium, ytterbium) contained in the cavity 302 of a vapor cell can, for example, range from about 500 nm to about 5,000 nm (e.g., about 500 nm, about 1,000 nm, about 1,500 nm, about 2,500 nm) as they are in a direction parallel to a wall (e.g., side wall 105). Fig. 1A and Fig. 1B)) can be measured, which at least partially defines the cavity 302 to which the pores 303 are exposed. As a specific, non-restrictive example, the substantially uniform pore dimension 312 (e.g., substantially uniform pore diameter) of the pores 303 exposed to the cavity 302 can be, for example, about 1,000 nm.

[0035] The pores 303 enclose internal surfaces, for example pore sidewalls 305 and floors 306, as in Fig. 3 shown. In some examples, the inner surfaces of the respective pores 303 (i.e., pore sidewalls 305 and bottoms 306) form pores 303 with a cylindrical configuration (e.g., an essentially cylindrical configuration).

[0036] The pore structure 310 encloses a substrate material 311 that forms pore sidewalls 305 of the pores 303, as shown in Fig. Figure 3 shows. In some examples, the substrate material 311 can comprise silicon (e.g., silicon wafers), and the pores 303 can be formed in the substrate material 311 with substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters) of about 1,000 nm by a suitable removal method (e.g., deep reactive ion etching (DRIE), without limitation). The pores 303 formed in the substrate material 311 can have a depth 313, as also shown in Fig. Figure 3 shows that the depth of the pores can range from approximately 100 nm to approximately 100,000 nm.

[0037] The pores 303 have substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters) and are shaped such that a bead rim 309 of the object material 304 in a fluid state within the pores 303 also has a uniform shape, which differs from a shape that an exposed surface of the object material 304 in a liquid state on a flat, non-porous surface would have under the same operating conditions (e.g., temperature, pressure). For example, the radius of the bead rim 309 of the object material 304 in the fluid state within the pores 303 with substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters) can be negative (i.e., the bead rim 309 can be concave).More precisely, the size and shape of the uniform pores 303 can induce that the bead rim 309 of the object material 304 in the fluid state has a uniform concave shape due to capillary action (e.g., the pores 303 can enclose capillaries), such that the height of the object material 304 in the center of the pores 303 is less than the height of the object material 304 near the pore sidewalls 305 of the pores 303 with substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters), as in . Fig. 3 illustrated by example.

[0038] Changing the shape of the bead rim 309 of the object material 304 in the fluid state within the pores 303 changes the vapor pressure of the object material 304 within the cavity 302. For example, inducing a negative radius of the bead rim 309 of the object material 304 in the fluid state within the cavity 302 (e.g., a concave bead rim 309) can cause the vapor pressure of the object material 304 within the cavity 302 to be lower than a saturation pressure of the object material 304 in a vapor state within the cavity 302. More precisely, the size and shape of the pores 303 with substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters) and the corresponding size and shape of the bead rim 309 (e.g.,The concave rim 309) of the object material 304 within the pores 303 results in a larger proportion of the object material 304 being in the liquid state within the cavity 302 than a proportion of the object material 304 that would be in the liquid state without the pores 303.

[0039] A pore structure 310 can have a lining material 320 arranged over at least one section of the respective pores 303 of the pore structure 310. Amounts of the lining material 320 can be arranged over at least the extent of the pore sidewalls 305 of the respective pores 303 of the pore structure 310. Optional amounts of lining material 320 can be arranged over other sections of the respective pores 303, provided that the covering is substantially uniform over at least the extent of the pore sidewalls 305 beneath the respective pores 303 with substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters) of the pore structure 310.In some examples, a pore structure 310 can enclose a lining material 320 arranged over the pores 303 of the pore structure 310, wherein the lining material 320 can have a uniform thickness over the pore sidewalls 305 and bottoms 306 of the pores 303, as in . Fig. Figure 3 shows that a lining material 320 can have a uniform thickness in a range of about 10 nm to about 1,000 nm. In some examples, the lining material has a substantially uniform thickness over at least the pore sidewalls 305 of the pores 303 of the pore structure 310 to ensure that the pores 303 of the pore structure 310 have substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters).

[0040] The lining material 320 can be selected from a material on which the object material 304 exhibits a smaller contact angle (e.g., about 50% smaller, about 60% smaller, about 75% smaller) than the object material 304 on the underlying substrate material 311 under the same operating conditions (e.g., temperature, pressure). In some examples, the underlying substrate material 311 comprises silicon, and the object material 304 comprises an alkali metal (e.g., cesium) that exhibits a contact angle of about 70 degrees on the silicon substrate material 311. In other examples, the lining material 320 comprises a metal or metal alloy (e.g., a precious metal, platinum) on which the object material 304 (e.g., cesium) exhibits a reduced contact angle of about 30 degrees.

[0041] Reducing the contact angle of the object material 304 on the lining material 320 allows for an increase in the substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameter) while maintaining the desired vapor pressure suppression (e.g., corresponding to approximately 25 °C). Suppressing the vapor pressure of the object material 304 can reduce the accumulation of the object material 304 at the windows of the vapor cell itself. Increasing the achievable substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameter) enables reliable and repeatable automated fabrication (e.g., DRIE) of a pore structure 310 with pores 303 having substantially uniform pore dimensions 312 (e.g., substantially uniform pore diameters of approximately 1,000 nm).

[0042] is Fig. Figure 4 is a flowchart illustrating an example of an explanatory Method 400 for using a vapor cell. Method 400 may, for example, involve providing a vapor cell enclosing a body that defines a cavity within the body, as shown in Step 402. At least one section of at least one surface within the cavity includes one or more pores with a substantially uniform diameter of about 500 nm to about 5,000 nm. According to some examples, at least one section of at least one surface within the cavity includes one or more pores with a substantially uniform diameter of about 1,000 nm, as also shown in Step 402. In particular, one of the pores described in the Fig. 1A, Fig. 1B, Fig. 2A, Fig. 2B and Fig. The steam cells 100 and 200 shown in Figure 2C are provided. In some examples, the at least one surface within the cavity that encloses the pores can be a wall (e.g., side wall) of a body of the steam cell that defines the cavity at least partially. In other examples, the at least one surface within the cavity that encloses the pores can be a pore structure separate from the body and located within the cavity.

[0043] The vapor pressure of the object material within the cavity can be controlled, as described in step 404. Control of the vapor pressure can be achieved, for example, by providing a quantity of the object material within the cavity of the body containing the one or more pores, ensuring that the quantity of object material within the cavity is insufficient to fully saturate (e.g., completely fill) the one or more pores under the expected operating conditions. A pressure and temperature within the cavity can be controlled for this purpose (e.g.,by inducing a selected pressure within the cavity, by transferring heat to or from the cavity, or by exposing the vapor cell to operating conditions), to induce that a portion of the object material is in a vapor state within the cavity and another portion of the object material is in a liquid state within the one or more pores. In some examples, it can be induced that an exposed surface of the object material in a liquid state within the one or more pores has a different shape than the shape that the exposed surface of the object material would have in a fluid, liquid state on a flat, non-porous surface, as also specified in step 404.More specifically, in some examples, a bead edge of the object material can be induced to be concave in the liquid state, as indicated in step 406, in order to achieve a vapor pressure of the object material that is lower than a saturation pressure of the object material in the cavity. As a specific, non-limiting example, the uniform size, shape, and position of the one or more pores within the cavity can induce the object material to have a concave shape in the liquid state within the pores by capillary action.

[0044] In some examples, the radiation can be directed at the object material inside the vapor cell using a radiation source directed at the vapor cell, as specified in step 408.

[0045] In some examples, controlling the vapor pressure during operation of the steam cell can enable the reliable operation of an atomic sensor, atomic clock, magnetometer, or gyroscope with the steam cell at operating temperatures in the range of about -45 °C to about 250 °C, as specified in step 410.

[0046] In particular, according to this disclosure, steam cells can enable the reliable operation of an atomic sensor, an atomic clock, a magnetometer or a gyroscope with the steam cell at operating temperatures in the range of about -45 °C to about 250 °C.

[0047] When operating a vapor cell according to this disclosure, the cavity of the vapor cell can be placed in the beam path of a radiation source (i.e., such that an object material within the cavity can be influenced (e.g., excited) by incident radiation). By including one or more pores, the vapor pressure of the object material can be controlled relative to the saturation pressure of the object material. It can be induced that a bead edge of the object material in a liquid state within one or more pores has a different shape than the one the object material would have in a liquid state on a flat, non-porous surface, which can influence the vapor pressure of the object material.

[0048] Fig. Figure 5 is a flowchart illustrating an example of an illustrative procedure 500 for fabricating a steam cell. The procedure 500 may, for example, involve forming or providing a steam cell that includes a body defining a cavity within the body, as specified in step 502. The body of the steam cell may include an object material within the cavity. As specific, non-limiting examples, the body of the steam cell may take any of the shapes and include any of the materials previously mentioned in connection with the Fig. 1A, Fig. 1B, Fig. 2A, Fig. 2B and Fig. 2C were described.

[0049] One or more pores with a substantially uniform diameter can be formed in at least one section of at least one surface within the cavity, as specified in step 504. The pores are formed with a substantially uniform diameter, for example, a uniform diameter as measured in a direction parallel to the at least one surface, wherein the substantially uniform diameter may be from about 500 nm to about 5,000 nm. In accordance with some examples, the pores are formed with a substantially uniform diameter, for example, a uniform diameter of about 1,000 nm, as also specified in step 504.The one or more pores of the at least one surface can be substantially uniformly sized, shaped and positioned to control the vapor pressure of an object material when the object material is inside the cavity, such that it has a different shape than the shape that the exposed surface of the object material would have in a liquid state on a flat, non-porous surface, as specified in step 506.

[0050] In some examples, the one or more pores can be formed by controlling the average surface roughness of the at least one surface, as described in Step 508. The pores in the at least one surface can be formed, for example, by etching the surface. More specifically, deep reactive ion etching (DRIE) can be performed on the at least one surface to control its average surface roughness, as described in Step 510. A substantially uniform diameter of the pores, for example, as measured in a direction parallel to the at least one surface, can range from about 500 nm to about 5,000 nm. In some examples, Procedure 500 involves bringing the diameters of the one or more pores to a substantially uniform diameter of about 1,000 nm, as described in Step 512.The essentially uniform diameter of the pores can be selected such that a beaded edge of the object material in a liquid state within the pores retains a different shape than the shape that the exposed surface of the object material in a liquid state on a flat, non-porous surface would have under the same operating conditions (e.g., temperature, pressure).

[0051] In some examples, Procedure 500 includes placing the item material into the cavity, as specified in Step 514. The item material may be selected to include an alkali metal material, as also specified in Step 514. In some examples, the item material may be selected to include francium, cesium, rubidium, potassium, sodium, or a combination or subcombination thereof, as specified in Step 516. In other examples, the item material may be selected to include a non-alkali metal material, as also specified in Step 514. For example, the item material may include a mercury material (e.g., for use in a mercury-ion watch), as also specified in Step 516. In some examples, the item material may be selected to include a mixture of alkali metal materials.

[0052] In some examples, one or more surfaces (e.g., walls, sidewalls) of the steam cell body that define or partially define the cavity can be made porous, as described in step 522. For example, a material forming at least one section of the steam cell body itself and positioned near the cavity can define the pores with substantially uniform diameters. In particular, the surface roughness and / or porosity of the material of at least one section of the body exposed to the cavity can be modified to form the pores with substantially uniform diameters.

[0053] In other examples, at least one pore structure with one or more pores of substantially uniform diameters can be placed in the cavity, as described in step 518. For example, the pore structure can be attached to the body so that it cannot move relative to the body within the cavity, as described in step 520. More specifically, the pore structure can be attached to the body using a fixture, an adhesive, or a fixture and an adhesive.

[0054] Fig. Figure 6 is a flowchart that presents another example of an illustrative process 600 for manufacturing a steam cell. The process 600 may, for example, involve forming or providing a body of the steam cell with walls defining a cavity between them, the cavity containing an amount of an object material as specified in step 602. As specific, non-limiting examples, the body of the steam cell may take any of the shapes and include any of the materials previously mentioned in connection with the Fig. 1A, Fig. 1B, Fig. 2A, Fig. 2B and Fig. 2C were described.

[0055] In some examples, the process 600 also includes the formation of a pore structure comprising a silicon substrate material with pores formed therein of a substantially uniform dimension of about 1,000 nanometers, wherein the pore structure is arranged along a section of one or more of the walls of the vapor cell, as specified in step 604.

[0056] With continued reference to Fig. 6 further comprises the process 600 for producing a steam cell forming a lining material of platinum having a uniform thickness over one or more internal surfaces of the pores, wherein the object material has a reduced wetting angle on the lining material which is less than a wetting angle of the object material on the substrate material as specified in step 606.

[0057] Fig. 7A and Fig.Figure 7B are schematic representations of Systems 711 and 717, respectively, which include a vapor cell 700 according to this disclosure. They differ in whether microwaves are applied directly to the vapor cell 700, as in a microwave-optical dual-resonance clock or an Mx magnetometer shown in System 711, or as modulation of the laser bias current, as in a clock based on coherent population trapping or a bell-bloom type magnetometer shown in System 717. Systems 711 and 717 can be, for example, atomic sensors, atomic clocks, magnetometers, or gyroscopes.

[0058] The vapor cell 700 can enclose a study area into which the vaporized atoms of the object material can be directed, and one or more emitters (e.g., a first emitter 714 (e.g., a laser) or a second emitter 715 (e.g., a microwave, an RF synthesizer)) or both the first emitter 714 and the second emitter 715 can direct energy of a known type and intensity toward the study area. A detector 716 can include a sensor that detects one or more properties of the vaporized atoms of the object material in response to the emitted energy. For example, the sensor of the detector 716 can be directed toward the study area and detect the transition of the object material between energy levels in response to the energy of the first emitter 714 (e.g., a laser), measured as a variation in signal strength relative to the frequency of the energy emitted by the second emitter 715 (e.g., a microwave, an RF synthesizer).Detect microwaves emitted by a microwave oven.

[0059] One or more signals representing the properties measured by the detector 716 can be provided as feedback to an oscillator 713. The oscillator 713 can generate a clock output 712, which can either be used as a clock signal itself or to check or synchronize another clock signal. In other words, the oscillator 713 can generate a clock output 712 clocked at a frequency corresponding to the rate at which the atoms of the object material transition between energy levels in response to changes in the frequency of the radiation from the second emitter 715 (e.g., a microwave, an RF synthesizer), which are detected by corresponding changes in the frequency of the energy from the first emitter 714 (e.g., a laser). The oscillator 713 can also be used to generate / synthesize radiation from the second emitter 715 (e.g., a microwave oven, an RF synthesizer).

[0060] Such a system 711 or 717 can be particularly useful for generating, verifying, or synchronizing clock signals with high accuracy and / or under extreme environmental conditions (e.g., near vacuum, low or microgravity, near Earth orbit, and / or in space). Systems 711 and 717 according to this disclosure may be used in the aerospace industry (e.g., for controlling clock signals in satellites and spacecraft), in the telecommunications and banking industries (e.g., for verifying or adjusting clock signals for relevant computer systems), and in standardization (e.g., for establishing time specifications for relevant standards). By reducing the vapor pressure of the object material in the vapor cell 700 of system 711 or 717, the vapor cell 700 can operate over a wider range of ambient temperatures.

[0061] Additional, non-restrictive examples of revelation include: Example 1: A vapor cell comprising: a body with walls defining a cavity between them, the cavity containing an amount of an object material; a pore structure comprising a substrate material with pores formed therein of a substantially uniform diameter, the pore structure being arranged along a section of one or more of the walls; and a lining material being arranged over one or more internal surfaces of the pores. Example 2: The steam cell according to Example 1, wherein the body includes at least one window located on another of the one or more walls. Example 3: The steam cell according to one of Examples 1 and 2, wherein the pore structure is arranged along the section of one of the one or more walls at a distance from the at least one window. Example 4: The steam cell according to one of Examples 1 to 3, wherein the pore structure is integrally formed in the section of one of the one or more walls. Example 5: The steam cell according to one of Examples 1 to 4, wherein the substrate material comprises silicon. Example 6: The steam cell according to one of Examples 1 to 5, wherein the pores in the substrate material are formed by deep reactive ion etching. Example 7: The steam cell according to one of Examples 1 to 6, wherein the substantially uniform diameter of the pores is from about 500 nanometers to about 5,000 nanometers. Example 8: The steam cell according to one of Examples 1 to 7, wherein the substantially uniform diameter of the pores is approximately 1,000 nanometers. Example 9: The steam cell according to one of Examples 1 to 8, wherein the pores have a cylindrical configuration. Example 10: The steam cell according to one of Examples 1 to 9, wherein the inner surfaces of the pores enclose a bottom and pore sidewalls. Example 11: The steam cell according to one of Examples 1 to 10, wherein the lining material is arranged over at least the pore sidewalls of the pores. Example 12: The steam cell according to one of Examples 1 to 11, wherein the lining material has a uniform thickness over at least the pore sidewalls of the pores. Example 13: The steam cell according to any of Examples 1 to 12, wherein the lining material comprises a metal or a metal alloy. Example 14: The steam cell according to one of Examples 1 to 13, wherein the lining material comprises platinum. Example 15: The steam cell according to one of Examples 1 to 14, wherein the object material comprises an alkali metal. Example 16: The steam cell according to one of Examples 1 to 15, wherein the object material has a contact angle on the lining material which is less than a contact angle of the object material on the substrate material. Example 17: The steam cell according to one of Examples 1 to 16, wherein sections of the object material arranged within the pores have a beaded edge with a uniform shape. Example 18: The steam cell according to one of Examples 1 to 17, wherein the sections of the object material arranged within the pores have a concave beaded edge. Example 19: The vapor cell according to one of Examples 1 to 18, wherein the concave beaded edge of the sections of the object material arranged within the pores results in a vapor pressure of the object material being less than a saturation pressure of the object material in a vapor state within the cavity of the vapor cell. Example 20: The steam cell according to one of Examples 1 to 19, wherein sections of the object material arranged within the pores have a concave beaded edge. Example 21: A method for producing a vapor cell, comprising: forming a body of the vapor cell with walls defining a cavity between them, the cavity containing an amount of object material; forming a pore structure comprising a substrate material of silicon with pores formed therein of a substantially uniform dimension of about 1,000 nanometers, the pore structure being arranged along a section of one or more of the walls of the vapor cell; and forming a lining material of platinum having a uniform thickness over one or more internal surfaces of the pores, the object material having a reduced wetting angle on the lining material that is less than a wetting angle of the object material on the substrate material. Example 22: The method according to Example 21, wherein forming the body of the steam cell comprises forming the body of the steam cell with at least one window arranged on another of the one or more walls. Example 23: The method according to one of Examples 21 and 22, wherein the formation of the pore structure comprises the formation of the pore structure with pores of substantially uniform dimensions formed in the substrate material by deep reactive ion etching. Example 24: The method according to any of Examples 21 to 23, wherein forming the lining material of uniform thickness over the one or more internal surfaces of the pores comprises forming the lining material over at least pore sidewalls of the pores. Example 25: The method according to any of Examples 21 to 24, wherein the formation of the lining material of uniform thickness over the one or more internal surfaces of the pores comprises the formation of the lining material by atomic layer deposition. Example 26: A system comprising: an emitter positioned and oriented to direct radiation through windows of a vapor cell, the vapor cell comprising: a body with walls defining a cavity between them, and an amount of object material arranged in the cavity; a pore structure comprising a substrate material with pores of substantially uniform diameter formed therein, the pore structure being arranged along a section of one or more of the walls; a lining material of uniform thickness arranged over inner surfaces of the pores, the object material having a wetting angle on the lining material that is less than a wetting angle of the object material on the substrate material; and a detector positioned and oriented to detect the radiation directed through the windows of the vapor cell.

[0062] Although certain illustrative examples have been described in connection with the figures, the scope of protection of this revelation is not limited to the examples expressly presented and described herein. Rather, many additions, deletions, and modifications may be made to the examples described herein to create examples within the scope of protection of this revelation, such as those expressly claimed, including statutory equivalents. Furthermore, features of one disclosed example may be combined with features of another disclosed example and still fall within the scope of protection of this revelation.

Claims

[1] Steam cell, comprising: a body with walls that define a cavity between them, the cavity containing a quantity of an object material; a pore structure comprising a substrate material with pores formed therein of a substantially uniform diameter, wherein the pore structure is arranged along a section of one or more of the walls; and a lining material that is arranged over one or more internal surfaces of the pores. [2] Steam cell according to claim 1, wherein the body includes at least one window arranged on another of the one or more walls. [3] Steam cell according to claim 2, wherein the pore structure is arranged along the section of one of the one or more walls at a distance from the at least one window. [4] Steam cell according to claim 1, wherein the pore structure is integrally formed in the section of one of the one or more walls. [5] Steam cell according to claim 1, wherein the substrate material comprises silicon. [6] Steam cell according to claim 5, wherein the pores in the substrate material are formed by deep reactive ion etching. [7] Steam cell according to claim 1, wherein the substantially uniform diameter of the pores is from about 500 nanometers to about 5,000 nanometers. [8] Steam cell according to claim 1, wherein the substantially uniform diameter of the pores is about 1,000 nanometers. [9] Steam cell according to claim 1, wherein the pores comprise a cylindrical configuration. [10] Steam cell according to claim 1, wherein the inner surfaces of the pores enclose a bottom and pore sidewalls. [11] Steam cell according to claim 10, wherein the lining material is arranged over at least the pore sidewalls of the pores. [12] Steam cell according to claim 11, wherein the lining material comprises a uniform thickness over at least the pore sidewalls of the pores. [13] Steam cell according to claim 1, wherein the lining material comprises a metal or a metal alloy. [14] Steam cell according to claim 1, wherein the lining material comprises platinum. [15] Steam cell according to claim 1, wherein the article material comprises an alkali metal. [16] Steam cell according to claim 15, wherein the object material has a wetting angle on the lining material which is less than a wetting angle of the object material on the substrate material. [17] Steam cell according to claim 1, wherein sections of the object material arranged within the pores have a bead edge with a uniform shape. [18] Steam cell according to claim 17, wherein the sections of the object material which are arranged within the pores have a concave beaded edge. [19] Steam cell according to claim 18, wherein the concave bead edge of the sections of the object material which are arranged within the pores results in a vapor pressure of the object material being lower than a saturation pressure of the object material in a vapor state within the cavity of the steam cell. [20] Steam cell according to claim 1, wherein sections of the object material arranged within the pores have a concave beaded edge. [21] Method for producing a steam cell, comprising: Forming a body of the vapor cell with walls defining a cavity between them, the cavity containing an amount of object material; Forming a pore structure comprising a silicon substrate material with pores formed therein of a substantially uniform dimension of about 1,000 nanometers, wherein the pore structure is arranged along a section of one or more of the walls of the vapor cell; and Forming a platinum lining material of uniform thickness over one or more internal surfaces of the pores, wherein the object material has a reduced wetting angle on the lining material that is less than a wetting angle of the object material on the substrate material. [22] Method according to claim 21, wherein forming the body of the steam cell comprises forming the body of the steam cell with at least one window arranged on another of the one or more walls. [23] Method according to claim 21, wherein forming the pore structure comprises forming the pore structure with pores of substantially uniform dimensions that are formed in the substrate material by deep reactive ion etching. [24] Method according to claim 21, wherein forming the lining material of uniform thickness over the one or more inner surfaces of the pores comprises forming the lining material over at least pore sidewalls of the pores. [25] Method according to claim 21, wherein forming the lining material of uniform thickness over the one or more inner surfaces of the pores comprises forming the lining material by atomic layer deposition. [26] System, comprehensive: an emitter positioned and oriented to direct radiation through windows of a steam cell, the steam cell comprising: a body with walls that define a cavity between them, and a quantity of object material arranged in the cavity; a pore structure comprising a substrate material with pores formed therein of a substantially uniform diameter, wherein the pore structure is arranged along a section of one or more of the walls; a lining material of uniform thickness arranged over the inner surfaces of the pores, wherein the object material has a contact angle on the lining material that is less than a contact angle of the object material on the substrate material; and a detector positioned and aligned to detect the radiation passed through the windows of the steam cell.

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