Thermal and electromagnetically induced switching of chirality in ferroelectrics

Abstract

Thermal and electromagnetic generation and switching of chirality in ferroelectrics is provided. A nanostructured ferroelectric is adapted to provide a high temperature state and a low temperature ferroelectric state. In the low temperature ferroelectric state, the nanostructured ferroelectric has a polarization state from a plurality of polarization states. The plurality of polarization states includes at least a first chirality polarization state having a first chirality and a second chirality polarization state having a second chirality different from the first chirality. A method for generating a nanostructured ferroelectric having a predefined chirality includes selecting the predefined chirality from a first chirality and a second chirality, selecting an electromagnetic field according to the predefined chirality, providing the nanostructured ferroelectric in a high temperature state, applying the electromagnetic field to the nanostructured ferroelectric in the high temperature state, and cooling the nanostructured ferroelectric from the high temperature state to a low temperature ferroelectric state while applying the electromagnetic field to establish a polarization state of the nanostructured ferroelectric having the predefined chirality.

Description

Technical Field

[0001] This disclosure relates to techniques for generating and switching the chirality of polarization fields in nanostructured ferroelectrics. Background Technology

[0002] Introduced by Lord Kelvin in 1894, chirality, or chirality, is a fundamental property describing non-mirror-symmetric objects. A typical example of a chiral object is the human hand. The left hand is a non-overlapping mirror image of the right hand. No matter how the two hands are oriented, they cannot coincide. Mathematically, an object is chiral (or possesses chirality) if it cannot be mapped to its mirror image by any combination of rotation and translation. Chirality distinguishes between left-handed and right-handed variants of a chiral object, also known as enantiomers. Given that a wide variety of organic substances, such as glucose, cellulose, and DNA molecules, are non-mirror-symmetric, molecular chirality is a key concept in stereochemistry and biochemistry. A chiral molecule is a molecule with a non-overlapping mirror image.

[0003] Chiral materials possess rare laser manipulation capabilities, such as chiral sensing, optical rotation, negative refractive index optical rotation, and circular dichroism, making chirality a focal point of modern materials science. Due to these capabilities, chiral materials have diverse applications in optoelectronics and plasmonics. However, fabricating chiral nanomaterials with tunable and switchable chirality—that is, designing nanoscale inorganic mixtures with controllable and configurable chirality—remains a challenge. Some examples of next-generation chiral nanomaterials include chiral metal particles and nanocrystals, DNA-assembled plasmon nanostructures, core-shell plasmon spheres, and chiral plasmon particles assembled on scaffolds. A problem arises because chiral nanomaterials are often fabricated as racemic mixtures of left-handed and right-handed particles, resulting in the loss of average chiral response in the racemic mixture. For practical applications, systems with monochirality are highly desirable.

[0004] One way to obtain single-chiral nanomaterials is through enantioselective synthesis. An alternative approach is to filter or sort the nanomaterials after production based on their chirality. Both methods significantly complicate the industrial manufacturing of nanoparticles.

[0005] Possible solutions to these problems are outlined in the following literature: Luk'yanchuk et al., “Hopfions emerge in ferroelectrics” Nat. Commun. 11, 2433 (2020) and Tikhonov et al., “Controllable skyrmion chirality in ferroelectrics” Sci. Rep. 10, 8657 (2020). Summary of the Invention

[0006] Given the high technological requirements, there is a need for methods to create single-chiral systems with switchable and adjustable chirality. Corresponding technologies allow for the fabrication of nanostructures with desired chirality, and most importantly, controllable chirality. Control can involve switching, adjusting, configuring, and reconfiguring the chirality. Specifically, a method is needed for reversibly and repeatedly switching the chirality of individual nanostructures after and independently of nanostructure fabrication.

[0007] This objective is achieved by the method according to claim 1. Claim 14 relates to an apparatus for generating nanostructured ferroelectrics with predefined chiral polarization states. Dependent claims relate to preferred embodiments.

[0008] Materials composed of chiral molecules have wide applications in fields ranging from nonlinear optics and spintronics to biology and pharmacology. However, chirality is usually an invariant intrinsic property of a given material and cannot be easily altered arbitrarily. This disclosure proposes a method that enables the configuration, switching, and tuning of the chirality of nanostructured ferroelectrics to ensure their wide utilization in various applications.

[0009] In a first aspect, the nanostructured ferroelectric is adapted to provide a high-temperature state and a low-temperature ferroelectric state. In the low-temperature ferroelectric state, the nanostructured ferroelectric has polarization states from a plurality of polarization states. These plurality of polarization states include at least a first chiral polarization state having a first chirality and a second chiral polarization state having a second chirality different from the first chirality. A method for generating a nanostructured ferroelectric with a predefined chirality includes: selecting a predefined chirality from a first chirality and a second chirality; selecting an electromagnetic field according to the predefined chirality; providing the nanostructured ferroelectric in a high-temperature state; applying the electromagnetic field to the nanostructured ferroelectric in the high-temperature state; and simultaneously applying the electromagnetic field while cooling the nanostructured ferroelectric from the high-temperature state to the low-temperature ferroelectric state to establish the polarization state of the nanostructured ferroelectric with the predefined chirality.

[0010] The polarization states of nanostructured ferroelectrics provide switchable chirality. Polarized structures with switchable chirality can be applied, for example, in storage and sensing applications, particularly for polarization-related optical control and / or readout. Temperature variation schemes allow the nanostructure to transition between ferroelectric and high-temperature states, where the energy barriers between polarization states with different chirities are lowered. Therefore, this method can reliably drive nanostructured ferroelectrics to polarization states with predefined chirality using an electromagnetic field selected according to a predefined chirality.

[0011] Therefore, this method can provide controllable chirality of the polarization state of nanostructured ferroelectrics. Controllable chirality can include adjustable, switchable, and / or reconfigurable chirality. In particular, controllable chirality can be tuned, switchable, and / or reconfigurable multiple times, and / or independent of the initial fabrication of the nanostructured ferroelectric.

[0012] Compared to methods without heat treatment, the disclosed method reduces the amplitude of the electromagnetic field required for reliable switching.

[0013] Nanostructured ferroelectrics can include lead titanate, lead zirconate titanate, zirconium oxide, hafnium oxide or hafnium oxide, especially doped hafnium oxide such as silicon.

[0014] Nanostructured ferroelectrics can include multiferroic materials.

[0015] According to some embodiments, any of the plurality of polarization states has first chirality or second chirality.

[0016] According to an embodiment, the first extension of the nanostructured ferroelectric material along a first direction is at most 1000 nm, particularly at most 200 nm, at most 100 nm, or at most 80 nm.

[0017] The second extension of the nanostructured ferroelectric material along the second direction can be at most 1000 nm, particularly at most 200 nm, at most 100 nm, or at most 80 nm. In particular, the second direction can be perpendicular to the first direction.

[0018] The third extension of the nanostructured ferroelectric material along a third direction can be up to 1000 nm, particularly up to 200 nm, up to 100 nm, or up to 80 nm. In particular, the third direction can be perpendicular to the first direction and / or the second direction.

[0019] The nanostructured ferroelectric material can be a layer, and the first extension can correspond to the thickness of the layer.

[0020] Nanostructured ferroelectrics can have a columnar shape, and the first extension can correspond to the height of the column.

[0021] Nanostructured ferroelectrics can have a rod shape. A first, second, or third extension can correspond to the height of the rod. A first, second, or third extension can correspond to the width of the rod. A first, second, or third extension can correspond to the length of the rod.

[0022] In some embodiments, the nanostructured ferroelectric may have a disk shape. A first extension or a second extension may correspond to the diameter of the disk. A first extension or a second extension may correspond to the height of the disk.

[0023] The column can be a rectangular column, and the second extension can correspond to the side length of the rectangular base of the rectangular column.

[0024] In some embodiments, the nanostructured ferroelectric may have a spherical shape, and the first extension may correspond to the diameter of the sphere.

[0025] In other embodiments, the nanostructured ferroelectric material may have a pyramid shape, and the first extension may correspond to the side length of the pyramid.

[0026] A high-temperature state can be a paraelectric state.

[0027] At high temperatures, nanostructured ferroelectrics can exhibit chiral polarization.

[0028] Cooling can include cooling the nanostructured ferroelectric from a temperature above the Curie temperature of the nanostructured ferroelectric to a temperature below the Curie temperature of the nanostructured ferroelectric.

[0029] The low-temperature state can correspond to the room-temperature state of nanostructured ferroelectrics.

[0030] Applying an electromagnetic field can include irradiating nanostructured ferroelectrics with electromagnetic waves.

[0031] Electromagnetic waves can include microwaves, terahertz waves, infrared radiation, visible light, ultraviolet radiation, or X-ray radiation.

[0032] The center wavelength of the electromagnetic wave can be at least 190 nm, especially at least 250 nm, especially at least 370 nm, especially at least 700 nm.

[0033] The center wavelength of electromagnetic waves can be up to 3000 nm, especially up to 1400 nm, up to 1100 nm, or up to 980 nm.

[0034] The center wavelength can correspond to the weighted average of all wavelengths of the electromagnetic wave.

[0035] Electromagnetic waves can be pulsed electromagnetic waves, with pulse durations of at most 1 ns, at most 300 ps, ​​at most 100 ps, ​​at most 40 ps, ​​at most 10 ps, ​​or at most 2 ps.

[0036] According to the embodiments, the energy per unit area of ​​the pulsed electromagnetic wave at the nanostructured ferroelectric material does not exceed 100 mJ / cm². 2 Especially not exceeding 70 mJ / cm 2 or not exceeding 40 mJ / cm 2 .

[0037] Providing nanostructured ferroelectrics at high temperatures may include heating the nanostructured ferroelectrics using electromagnetic waves.

[0038] Electromagnetic waves can be elliptically polarized. The chirality of elliptically polarized electromagnetic waves can correspond to a predefined chirality.

[0039] Electromagnetic waves can be circularly polarized. The chirality of a circularly polarized electromagnetic wave can correspond to a predefined chirality.

[0040] Elliptically or circularly polarized electromagnetic waves can provide stimulation that makes the first-chiral polarization state, possessing primary chirality, more energetically superior to the second-chiral polarization state, possessing secondary chirality. This enhances the likelihood that nanostructured ferroelectrics will develop a first-chiral polarization state after cooling to a cryogenic ferroelectric phase.

[0041] The method may further include, particularly, supporting the nanostructured ferroelectric material with a substrate while applying an electromagnetic field and / or while cooling the nanostructured ferroelectric material.

[0042] The substrate can be in direct contact with the nanostructured ferroelectric and can be adapted to induce stress or strain in the nanostructured ferroelectric; particularly in embodiments, the nanostructured ferroelectric comprises lead titanate and / or lead zirconate titanate, and / or the substrate comprises strontium titanate.

[0043] The substrate can induce strain or stress in the nanostructured ferroelectric, which can be used to customize the (multiple) chiral ground states of the nanostructured ferroelectric.

[0044] In some embodiments, the substrate may be adapted to absorb heat from the nanostructured ferroelectric during a process step of cooling the nanostructured ferroelectric.

[0045] The substrate can be adapted to absorb energy from electromagnetic waves and provide energy to the nanostructured ferroelectric in the process steps that provide the nanostructured ferroelectric at high temperature.

[0046] In some embodiments, the substrate may be adapted to guide electromagnetic waves, particularly to reflect electromagnetic waves toward the nanostructured ferroelectric material.

[0047] Nanostructured ferroelectrics can be ferroelectric layers arranged on a substrate.

[0048] At least one additional layer, particularly at least one non-ferroelectric additional layer, can be arranged on the nanostructured ferroelectric material.

[0049] A second nanostructured ferroelectric material can be arranged on top of at least one additional layer. The second nanostructured ferroelectric material can be a second ferroelectric layer.

[0050] In some embodiments, an intermediate layer, particularly a dielectric intermediate layer, such as a non-ferroelectric dielectric intermediate layer, may be disposed between the substrate and the ferroelectric layer.

[0051] Ferroelectric layers can be included in a stacked multilayer structure comprising multiple ferroelectric layers and multiple additional layers. In particular, the additional layers can be nonferroelectric.

[0052] In some embodiments, the stacked multilayer structure may include alternating ferroelectric layers and additional layers.

[0053] The substrate can be adapted to transfer heat to the nanostructured ferroelectric during process steps that provide the nanostructured ferroelectric at high temperatures.

[0054] While cooling nanostructured ferroelectrics, the nanostructured ferroelectrics can be surrounded by a solid matrix or a liquid matrix.

[0055] In some embodiments, a solid or liquid matrix may be adapted to absorb heat from the nanostructured ferroelectric during a process step of cooling the nanostructured ferroelectric.

[0056] Solid or liquid matrices can be adapted to be transparent to electromagnetic waves.

[0057] Solid or liquid matrices can be suitable for transferring heat to nanostructured ferroelectrics during process steps that provide nanostructured ferroelectrics at high temperatures.

[0058] Electromagnetic fields can be non-uniform electromagnetic fields.

[0059] The method may further include, during and / or after cooling the nanostructured ferroelectric from a high-temperature state to a low-temperature ferroelectric state, applying a non-uniform electromagnetic field to the nanostructured ferroelectric to transport the nanostructured ferroelectric to a location associated with a predefined chirality.

[0060] Applying a non-uniform electromagnetic field can include focusing electromagnetic waves at or near a focal point located on or near a nanostructured ferroelectric material.

[0061] The method may further include using a non-uniform electromagnetic field to lift the nanostructured ferroelectric material from the surface.

[0062] In some embodiments, the method may further include applying a non-uniform electromagnetic field to a second nanostructured ferroelectric having a chirality different from a predefined chirality, to transport the second nanostructured ferroelectric to a second location different from the location associated with the predefined chirality.

[0063] In particular, the method may include simultaneously applying a non-uniform electromagnetic field to a nanostructured ferroelectric and a second nanostructured ferroelectric to separate the nanostructured ferroelectric and the second nanostructured ferroelectric.

[0064] The substrate can be conductive, and applying a non-uniform electromagnetic field can induce plasmon excitations in the substrate, particularly at the substrate surface. Plasmon excitations can be adapted to separate nanostructured ferroelectrics and second nanostructured ferroelectrics with chirality different from a predefined chirality based on the chirality of the polarization state of the nanostructured ferroelectric and the second nanostructured ferroelectric.

[0065] Applying a non-uniform electromagnetic field can include using optical tweezers.

[0066] In some embodiments, applying a non-uniform electromagnetic field may include using plasmonic tweezers, particularly plasmonic tweezers with a plasmonic trap stiffness in the range of 0.1fN / (μm·W) to 5fN / (μm·W) or in the range of 0.1fN / (μm·W) to 1fN / (μm·W).

[0067] Non-uniform electric fields can have field polarization, and the method can further include selecting the field polarization according to a predefined chirality. The field polarization can be linear, elliptical, or circular.

[0068] Choosing field polarization can include selecting the chirality of circular or elliptical polarization, or selecting the direction of linear polarization.

[0069] Applying an electromagnetic field can include applying a voltage to electrodes arranged on the opposite side of the nanostructured ferroelectric.

[0070] Electrodes can be arranged on opposite sides of multiple nanostructured ferroelectrics, including the nanostructured ferroelectric. In particular, the multiple nanostructured ferroelectrics can be a racemic mixture of nanostructured ferroelectrics.

[0071] According to an embodiment, exactly one nanostructured ferroelectric material is arranged between the electrodes.

[0072] According to some embodiments, at least one of the electrodes has a first electrode extending along a first direction, the first electrode extension being at most 1000 nm, particularly at most 200 nm, at most 100 nm, or at most 80 nm.

[0073] According to an embodiment, at least one of the electrodes has a second electrode extending along a second direction, the second electrode extension being at most 1000 nm, particularly at most 200 nm, at most 100 nm, or at most 80 nm, wherein the second direction may be different from the first direction, particularly perpendicular to the second direction.

[0074] At least one electrode may be a tip, particularly a conductive tip, especially a tip suitable for providing a scanning tunneling microscope tip or a conductive atomic force microscope tip.

[0075] According to the embodiment, the absolute value of the electric field does not exceed 100 kV / cm, and in particular does not exceed 10 kV / cm.

[0076] At least one electrode may have a chiral shape.

[0077] In some examples, chiral molecules can be adsorbed onto at least one electrode near the nanostructured ferroelectric. In particular, the chiral molecules can be nanotubes, such as carbon nanotubes.

[0078] The at least one electrode can be a tip with chiral distortion, particularly a conductive tip with chiral distortion, such as a scanning tunneling microscope tip or a conductive atomic force microscope tip with chiral distortion.

[0079] Chiral molecules at the tip or chiral distortion at the tip can provide a chiral electric field, which can be used as a stimulus to drive nanostructured ferroelectrics into a predefined chiral polarization state during cooling.

[0080] Providing a nanostructured ferroelectric material at a high temperature state may further include: providing a nanostructured ferroelectric material at a low temperature state and possessing primary chirality; and heating the nanostructured ferroelectric material to a high temperature state. The predefined chirality may be secondary chirality.

[0081] The method according to this disclosure can provide reversible and repeatable switching between different polarization states.

[0082] Heating nanostructured ferroelectrics to high temperatures can include using a resistance heater.

[0083] The resistance heater can be in direct contact with the nanostructured ferroelectric, or with the substrate supporting the nanostructured ferroelectric, or with the solid or liquid matrix surrounding the nanostructured ferroelectric.

[0084] Heating nanostructured ferroelectrics to high temperatures can include using microwave heaters.

[0085] Heating nanostructured ferroelectrics to high temperatures allows the use of energy absorbed from electromagnetic waves. Energy can be absorbed from electromagnetic waves by the nanostructured ferroelectrics.

[0086] Alternatively or additionally, energy may be absorbed from electromagnetic waves by a substrate supporting the nanostructured ferroelectric or by a solid or liquid matrix surrounding the nanostructured ferroelectric, and the method may further include transferring energy to the nanostructured ferroelectric by a substrate supporting the nanostructured ferroelectric or by a solid or liquid matrix surrounding the nanostructured ferroelectric.

[0087] In a second aspect, an apparatus for generating a nanostructured ferroelectric material with a predefined chirality includes a holding element, a heating element, a field applying element, and a cooling element. The holding element is adapted to receive the nanostructured ferroelectric material. The heating element is adapted to heat the nanostructured ferroelectric material to a high-temperature state. The field applying element is adapted to apply an electromagnetic field to the nanostructured ferroelectric material while it is in the high-temperature state. The cooling element is adapted to cool the nanostructured ferroelectric material to a low-temperature ferroelectric state with a predefined chirality polarization state while simultaneously applying the electromagnetic field to the nanostructured ferroelectric material using the field applying element.

[0088] Nanostructured ferroelectrics can be characterized by one or all of the features described above in the context of the method according to the first aspect.

[0089] The holding element may include a substrate suitable for supporting the nanostructured ferroelectric, particularly a conductive substrate. The cooling element may include a substrate.

[0090] In particular, the substrate may be adapted to absorb heat from the nanostructured ferroelectric, and / or the substrate may be adapted to have direct thermal contact with the nanostructured ferroelectric.

[0091] Alternatively or additionally, the holding element may include a solid or liquid matrix suitable for surrounding the nanostructured ferroelectric. The cooling element may include a solid or liquid matrix.

[0092] In particular, a solid or liquid matrix may be suitable for absorbing heat from the nanostructured ferroelectric, and / or a solid or liquid matrix may be suitable for direct thermal contact with the nanostructured ferroelectric.

[0093] Heating elements may include resistance heaters, particularly resistance heaters that are in direct thermal contact with holding elements and / or resistance heaters suitable for direct thermal contact with nanostructured ferroelectrics.

[0094] The field-applying element may include an electrode arranged on the opposite side of the nanostructured ferroelectric.

[0095] An electrode may be characterized by one or all of the features described above in the context of an electrode according to the method of the first aspect.

[0096] The device may further include a monitoring element adapted to monitor the polarization state of the nanostructured ferroelectric, particularly the helicity or chirality of the polarization state of the nanostructured ferroelectric.

[0097] The monitoring element may include a device suitable for determining the polarization of the detected electromagnetic wave, particularly a polarimeter for detecting electromagnetic waves. The monitoring element may further include a detection light source adapted to generate the detected electromagnetic wave, direct the detected electromagnetic wave to the nanostructured ferroelectric, and, after the detected electromagnetic wave is reflected from or transmitted through the nanostructured ferroelectric, direct the detected electromagnetic wave to a device suitable for determining the polarization of the detected electromagnetic wave.

[0098] The device may further include a radiation source adapted to generate electromagnetic waves and irradiate the nanostructured ferroelectric material with the electromagnetic waves.

[0099] The radiation source wave can provide heating elements and / or field application elements. Electromagnetic waves can include microwaves, terahertz waves, infrared or visible light radiation, or can be microwaves, terahertz waves, infrared or visible light radiation.

[0100] The radiation source can be included in optical tweezers. The optical tweezers can be adapted to transport the nanostructured ferroelectric to a location associated with a predefined chirality. Alternatively or additionally, the optical tweezers can be adapted to separate the nanostructured ferroelectric from a second nanostructured ferroelectric having a chirality different from the predefined chirality.

[0101] The radiation source can be included in plasmonic tweezers. The plasmonic tweezers can be adapted to irradiate a conductive substrate of the nanostructured ferroelectric to induce plasmonic excitation in the conductive substrate. The plasmonic excitation in the conductive substrate can be adapted to separate the nanostructured ferroelectric and a second nanostructured ferroelectric having a chirality different from a predefined chirality. Alternatively or additionally, the plasmonic excitation in the conductive substrate can be adapted to generate a plasmonic trap. The plasmonic trap can be adapted to separate the nanostructured ferroelectric from the second nanostructured ferroelectric.

[0102] Electromagnetic waves can be used to provide detection electromagnetic waves.

[0103] The device may further include focusing optics for focusing electromagnetic waves onto the nanostructured ferroelectric material. In particular, the focusing optics may include a lens or a microscope objective.

[0104] Focusing optics and radiation sources can be adapted to generate non-uniform electromagnetic fields at the receiving element, particularly at locations suitable for receiving nanostructured ferroelectrics. These non-uniform electromagnetic fields can be adapted to transport the nanostructured ferroelectrics to locations associated with their polarization states, particularly to locations associated with the chirality of their polarization states.

[0105] Focusing optics and radiation sources can provide optical tweezers that are suitable for moving nanostructured ferroelectrics according to their polarization state, and in particular, according to the chirality of their polarization state.

[0106] In some embodiments, the retaining element may include a conductive substrate.

[0107] Radiation sources and focusing optics can be adapted to induce plasmon excitation in conductive substrates, particularly at the surface of the conductive substrate.

[0108] Focusing optics, radiation sources, and conductive substrates can provide plasmonic tweezers suitable for moving nanostructured ferroelectrics according to their polarization state, particularly plasmonic trap stiffness in the range of 0.1 fN / (μm·W) to 5 fN / (μm·W), or in the range of 0.1 fN / (μm·W) to 1 fN / (μm·W). Attached Figure Description

[0109] The technology of this disclosure and the advantages associated with these technologies will become most apparent from the description of exemplary embodiments with reference to the accompanying drawings, in which:

[0110] Figure 1a Illustrative examples of hand-shaped left-handed and right-handed enantiomers are shown;

[0111] Figure 1b Illustrative examples of left-handed and right-handed enantiomers in a helical shape are shown;

[0112] Figure 2 The chiral domain walls of the ferroelectric material are shown;

[0113] Figure 3a A nanostructured ferroelectric material in the form of a ferroelectric thin film is shown, which has a chiral polarization state including skyrmions;

[0114] Figure 3b A nanostructured ferroelectric material in the form of a multilayer structure is shown. The nanostructured ferroelectric material has a ferroelectric thin film with a chiral polarization state with vortices.

[0115] Figure 4The potential energy surface of the nanostructured ferroelectric is shown;

[0116] Figure 5 The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to an embodiment;

[0117] Figure 6a The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0118] Figure 6b The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0119] Figure 7a The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0120] Figure 7b The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0121] Figure 8 A nanostructured ferroelectric in the form of nanodots is shown, which has a chiral polarization structure associated with domain walls;

[0122] Figure 9a A nanostructured ferroelectric material in the form of nanoparticles is shown, which has a chiral polarization structure and no domain walls.

[0123] Figure 9b A nanostructured ferroelectric in the form of nanodots is shown, which has a different chiral polarization structure and no domain walls.

[0124] Figure 10a The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0125] Figure 10b The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0126] Figure 11a The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0127] Figure 11b The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0128] Figure 12a The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0129] Figure 12b The illustration shows a method and apparatus for generating predefined chirality of nanostructured ferroelectrics according to another embodiment;

[0130] Figure 13 The illustrations depict a method and apparatus according to embodiments for generating predefined chirality of nanostructured ferroelectrics using enantioselective transport; and

[0131] Figure 14 The illustration shows a method and apparatus according to another embodiment for generating predefined chirality of nanostructured ferroelectrics using enantioselective transport. Detailed Implementation

[0132] The technology of this disclosure will now be described with reference to several different embodiments from the field of materials science. Although some features will be described with respect to only some of these embodiments, those skilled in the art will understand that these embodiments can be combined, and thus these features can generally be present in some or all of the described embodiments.

[0133] Figure 1a and Figure 1b Two examples of chiral structures are shown, namely, Figure 1a The manpower of 104L, 104R and Figure 1b The helices 106L and 106R exist as two distinct enantiomers. These enantiomers are mirror images of each other with respect to mirror plane 100. The mirror images 104R and 106R differ from their prototypes 104L and 106L, respectively, in their rotation direction 102R or chirality. In this context, the enantiomers with a counterclockwise rotation direction 102R are referred to as the right-handed enantiomers 104R and 106R, while the enantiomers with a clockwise rotation direction 102L are referred to as the left-handed enantiomers 104L and 106L.

[0134] Figure 2 Chiral ferroelectric domain walls 200L and 200R between two ferroelectric domains 202U and 202D are shown. Ferroelectrics are characterized by remanent polarizations 204U and 204D. The long-range electric fields associated with polarizations 204U and 204D are very energy-intensive. Therefore, bulk ferroelectrics typically exhibit domain walls 200L and 200R, which reduce the long-range field and associated energy.

[0135] Near the domain walls 200L and 200R, polarizations 204U and 204D are typically oriented parallel to the surface defined by the domain walls 200L and 200R. For a long time, it was thought that the polarizations would maintain their orientation and only change their values ​​across the domain walls, for example, changing from negative to positive about an axis parallel to polarization 204U (Ising domain wall). However, recent experiments have shown that polarizations 204U and 204D at the ferroelectric domain walls 200L and 200R rotate around the surface normal 208 of the domain walls 200L and 200R, as... Figure 2 As shown. This type of domain wall is called a Bloch domain wall 200L or 200R. The rotation direction 102L or 102R can be clockwise 102L or counterclockwise 102R, producing a left-handed Bloch domain wall 200L or a right-handed Bloch domain wall 200R. Bloch domain walls 202L and 202R are chiral and cannot overlap with themselves through mirror reflection and / or spatial rotation transformations.

[0136] In bulk ferroelectrics, ferroelectric domains and domain walls are formed at random locations with random orientations. However, for many practical applications, controlled orientation and arrangement may be preferred. For this purpose, ferroelectrics are nanostructured along at least one direction.

[0137] In the context of this disclosure, a nanostructured ferroelectric can be understood as having an extension confined to the nanoscale (e.g., confined to 1 μm or less) along at least one direction. Such a ferroelectric can also be referred to as nano-confined.

[0138] One example is a thin layer that is confined in a direction perpendicular to the layer.

[0139] Figure 3a A ferroelectric thin layer 300 on a substrate 302 is shown. Due to the geometry of the nanostructure, polarization 304 is preferably oriented either within (in-plane) or perpendicular to the ferroelectric thin layer 300 (out-of-plane). The choice of the ferroelectric material of the ferroelectric thin layer 300 and the material providing its environment (e.g., substrate 302) provides control over the orientation of polarization 304.

[0140] The selection of the ferroelectric material of the ferroelectric thin layer 300, the material providing its environment (e.g., the substrate), and the growth conditions are also used to control the topology of the domain walls 306. Typically, the ferroelectric thin layer may include chiral (e.g., Ising) domain walls and chiral domain walls (such as those in...). Figure 2 (The Bloch domain wall described in the context).

[0141] For layers that include various types of chiral and achiral domain walls, chirality can be defined as a sign of helicity. in, The value represents the polarization intensity, and the integral is performed over the volume of the nanostructured ferroelectric material (e.g., ferroelectric thin layer 300).

[0142] Figure 3a A ferroelectric thin layer 300 of lead titanate (PbTiO3) deposited with a thickness of 50 nm on a dielectric strontium titanate (SrTiO3) substrate 302 is depicted. Lattice mismatch induces strain in the ferroelectric layer 300. The ferroelectric thin layer 300 develops polarization 304 with out-of-plane orientation.

[0143] Ferroelectric thin films are grown using pulsed laser deposition, but physical vapor deposition, atomic layer deposition, or molecular beam epitaxy can also be used alternatively. Details of the growth conditions can be found in the following literature: Das et al., “Localnegative permittivity and topological phase transition in polar skyrmions”, Nat. Mater. 20, 194 (2021).

[0144] Figure 3a The growth conditions for the ferroelectric layer 300 were optimized for polarization 304 to form a chiral polarization state with skyrmions 308. Skyrmions can be considered similar to those described above. Figure 2 The Bloch domain wall described in the context of Bloch domain walls 200L and 200R is one of the Bloch domain walls.

[0145] However, the curvature of skyrmion 308 leads to the formation of a self-closing structure 308. Depending on the chirality of the underlying Bloch domain wall, skyrmion 308 can be left-handed or right-handed. Figure 3a The diagram illustrates a skyrmion 308 with a counterclockwise rotation direction of 102R, i.e., a right-handed skyrmion 308. For example... Figure 3a The regular arrangement of skyrmion 308 described in the text is sometimes referred to as chiral bubble domains or cylindrical domains.

[0146] Figure 3b A multilayer structure 312 is shown, comprising an alternating sequence of ferroelectric thin layers 300a, 300b, 300c and paraelectric layers 302a, 303b. For example, the multilayer structure can be formed from alternating layers of ferroelectric lead titanate and dielectric strontium titanate, each layer having a thickness of 9 nm to 10 nm, as detailed in the following literature: Yadav et al., “Observation of polar vortices in oxide superlattices,” Nature 530, 198 (2016). Applications and applications in… Figure 3aThe same growth technique for forming a ferroelectric layer is described in the context of the ferroelectric thin layer 300.

[0147] Figure 3b The multilayer structure 312 includes three ferroelectric thin layers 300a, 300b, and 300c and two paraelectric layers 302a and 302b, but this is merely an example, and the number of layers can generally be freely adapted to the requirements of the application. For example, for optical applications, the number of ferroelectric layers can be increased to at least 10, at least 50, or at least 100 to generate a multilayer structure 312 with enhanced thickness and optical activity. In contrast, for storage applications, a single ferroelectric layer can be used to minimize the amount of polarization material and maximize switching speed.

[0148] The polarization of the ferroelectric thin layers 300a, 300b, and 300c in the multilayer structure 312 forms coreless vortices 314L and 314R. The coreless vortices 314L and 314R within each of the ferroelectric thin layers 300a, 300b, and 300c typically rotate alternately in opposite directions. The chirality of the vortices 314L and 314R occurs when the vortices have a coreless structure and the polarization escapes along the vortex axis in a third spatial direction, thus forming a helical chiral texture. Dashed lines 316 separate the region with left-handed vortices 314L from the region with right-handed vortices 314R.

[0149] Any chiral structure of a nanostructured ferroelectric (e.g., Bloch domain walls 200L, 200R, skyrmion 308, or vortex 314L, 314R, etc.) can be right-handed or left-handed, and the polarization states associated with the two chirities are generally energy degenerate. Therefore, when a nanostructured ferroelectric is cooled from a paraelectric high-temperature state to a ferroelectric room-temperature state, the two chirities may have equal probabilities of formation. This equal probability of formation of either chirality can be understood as a direct result of the energy degeneracy of the two states. However, the situation may change when a suitable external stimulus is applied, as will now be discussed in reference to… Figure 4 Further detailed description.

[0150] Figure 4 The energy E of the polarization state of a nanostructured ferroelectric is described as a function of the chirality χ of the nanostructured ferroelectric. Figure 4 Potential energy landscape 402 (dashed line) in the high-temperature paraelectric state, potential energy landscape 404 in the ferroelectric state without external stimulation, and potential energy landscape 404L and 404R in the presence of two different external stimuli are shown.

[0151] When cooled to the Curie temperature without external stimulation, the probability of the polarization state transitioning from the potential energy surface 402 of the paraelectric state to the energy minimum of the potential energy surface 404 of the ferroelectric state associated with both left-handed chirality (L) and right-handed chirality (R) is the same. However, applying a suitable stimulus can increase the energy degeneracy of the minimums associated with both chirality L and R. Ferroelectrics can thus become preferentially chiral or chiral. Figure 4 This is reflected by the lower energy of the minimum value associated with left-handed chirality L in the potential energy landscape 404L under the presence of external stimuli.

[0152] The modified external stimulus can cause the potential energy landscape 404R to have a lower energy minimum for right-handed chirality R. Therefore, if the ferroelectric is cooled from a high-temperature paraelectric state 402 to a low-temperature ferroelectric state in the presence of either of the two stimuli, the ferroelectric can achieve states with defined chirality L and R at the corresponding energy minimums of the potential energy surfaces 404L and 404R.

[0153] Stimuli can include electromagnetic radiation, electric fields, mechanical forces, structural stimuli, or chemical stimuli. One aspect of this disclosure relates to the design of suitable stimuli and the design of methods and apparatus for applying such stimuli.

[0154] Figure 5 The illustration shows a photo-assisted method and apparatus for generating nanostructured ferroelectrics and switching their chirality according to a first embodiment. Figure 5 In one embodiment, the chirality of the ferroelectric thin layer 300 on the substrate 302 is controlled, and the ferroelectric thin layer can be similar to Figure 3a A ferroelectric thin layer 300 on a substrate 302. However, this method can also be applied to other nanostructured ferroelectrics, such as those used in... Figure 3b The multi-layer structure of 312.

[0155] The apparatus includes a resistance heater 502 in thermal contact with a substrate 302. A supply voltage is applied to the heater 502, causing the temperature of the heater 502, the substrate 302, and the ferroelectric thin layer 300 to rise until the temperature of the ferroelectric layer 300 approaches or exceeds the Curie temperature of the ferroelectric material contained therein, for example, 400°C for BaTiO3 or 500°C for PbTiO3. During heating, the ferroelectric material undergoes a phase transition from a room-temperature ferroelectric phase to a high-temperature paraelectric phase.

[0156] Subsequently, the power supplied to heater 502 is reduced, and the ferroelectric thin layer 300 is cooled from a high-temperature paraelectric phase to a temperature far below the Curie temperature of the ferroelectric material contained in the ferroelectric thin layer 300. Radiative heat transfer from the surface of the ferroelectric thin layer 300 to the environment typically provides sufficient heat transfer for cooling. However, for thicker layers 300 and / or substrates 302, substrates 302 can be coupled to cooling devices such as Peltier elements to remove heat from the ferroelectric thin layer 300 more quickly.

[0157] When cooled to temperatures below the Curie temperature, the paraelectric phase can become unstable and the symmetry of local polarization can be disrupted, leading to the localized formation of remanent polarization 304 in the ferroelectric thin layer 300. For example... Figure 5 and Figure 3a As depicted, the ferroelectric thin layer 300 can achieve a polarization structure with out-of-plane polarization 304. To minimize the energy associated with the out-of-plane polarization 304, skyrmions 308 can be additionally formed around small regions (cores) of opposite polarization. The skyrmions 308 can be right-handed or left-handed. (As shown in...) Figure 4 In the context of any nanostructured ferroelectric, any chiral or chiral skyrmion 308 can have equal energy and therefore equal probability of formation during cooling in the absence of external stimuli.

[0158] according to Figure 5 In the embodiment depicted, laser 504 irradiates ferroelectric thin film 300 with light or near-infrared radiation 506 having circular polarization 508. The laser provides external stimulation in this manner to break the energy degeneracy between polarization states 304 having left-handed and right-handed skyrmions 308. Depending on the chirality of the circular polarization 508 or the chirality of the light or near-infrared radiation 506, the polarization state having either left-handed or right-handed skyrmions 308 becomes a global energy minimum and forms during cooling. The emitted light or near-infrared radiation 506 is applied while cooling the ferroelectric thin film 300 from a high-temperature paraelectric state to a temperature well below the Curie temperature. As the nanostructured ferroelectric 300 cools, the polarization state of this nanostructured ferroelectric can achieve a global minimum of potential energy surfaces 504L, 504R with either left-handed or right-handed chirality, wherein the chirality is controlled by the helicity of the light or near-infrared radiation 506. In this way, polarization states with either left-handed or right-handed skyrmions 308 can be prepared in a controlled manner. By repeatedly heating, applying light or near-infrared radiation 506 with a selected helicity, and cooling, the polarization states with controlled chirality can be repeatedly rewritten.

[0159] Figure 5The embodiment depicted uses a laser 504 as a source of light or near-infrared radiation 506, more specifically a Ti:sapphire amplifier system that emits laser pulses with wavelengths ranging from 700 nm to 1200 nm at a repetition rate of 1 kHz. The emitted laser pulses can be second, third, or fourth harmonics. The laser pulses can also be provided by a laser amplifier using doped optical fibers. A value below 40 mJ / cm² can be selected. -2 Up to 70mJ cm -2 The excitation laser energy density is adjusted to avoid damaging the nanostructured ferroelectric 300. According to alternative embodiments, terahertz radiation emitted from a quantum cascade laser, microwave radiation emitted from a magnetron, or X-ray radiation emitted from an X-ray tube or synchrotron can be applied.

[0160] according to Figure 5 In the embodiments depicted, the energy for heating the nanostructured ferroelectric 300 is primarily provided by a resistance heater 502. Alternatively, a laser 504 or an alternative radiation source 504 as described above can provide a large portion, or even all, of the energy for heating, and the resistance heater can be omitted. The energy from the laser or radiation source 504 can be directly absorbed by the nanostructured ferroelectric 300, or it can be absorbed by the substrate and subsequently transported toward the nanostructured ferroelectric 300 through the substrate 302.

[0161] Figure 5 The apparatus 500 includes an additional laser 510 that acts as a probe light source, emitting probe light 512. A portion of the probe light 512 is reflected from the surface of the ferroelectric thin layer 300, while another portion is transmitted through the ferroelectric thin layer 300 and reflected from the substrate 302, then transmitted again through the ferroelectric thin layer 300. The polarization of the reflected and / or transmitted probe light 512 can be analyzed using a rotatable polarimeter 514, acting as a cyclotron, in conjunction with a photodetector (not shown). Measurement of the polarization of the reflected and / or transmitted probe light 512 allows for monitoring the polarization, and particularly the chirality, of the nanostructured ferroelectric. Instead of using the additional laser 510 as a probe light source, the polarization state can be monitored using light from laser 504 or a portion of near-infrared radiation 506.

[0162] Figure 6a The illustration shows a method and apparatus for generating desired chirality of nanostructured ferroelectrics according to a second embodiment. The apparatus includes a heater 502, which can be similar to... Figure 5The heater 502 is described in the context of the embodiments described above. Additionally, a counter electrode 602 is provided on the side of the ferroelectric thin layer 300 opposite to the substrate 302. By applying supply power to the heater 502, the ferroelectric thin layer 300 can be heated to a temperature close to or above the Curie temperature of the ferroelectric material contained in the ferroelectric thin layer 300. During subsequent cooling of the ferroelectric thin layer 300, a voltage U is applied between the substrate 302 and the counter electrode 602 to generate an electric field 604 through the ferroelectric thin layer 300. The electric field 604 can improve the energy degeneracy between local minima in the potential energy surface 404 of the ferroelectric thin layer 300. The amplitude of the electric field 604 can be as high as 10 kV / cm, or even as high as 100 kV / cm, depending on the ferroelectric material and its thickness. Depending on the sign of the voltage U or the direction of the electric field 604, a potential energy surface 404L with a global minimum of left-handed chirality L for the ferroelectric thin layer or a potential energy surface 404R with a global minimum of right-handed chirality R for the ferroelectric thin layer can be generated. Therefore, cooling the ferroelectric thin layer 300 in the presence of the electric field 604 can prepare a ferroelectric layer 300 with controlled chirality (left-handed or right-handed chirality) skyrmions 308.

[0163] Figure 6b The diagram illustrates the relationship with Figure 6a Similar embodiments to those described above. However, instead of a single counter electrode, a top electrode 602 and a bottom electrode 606 are provided. A voltage U is applied between the top electrode 602 and the bottom electrode 606 to generate an electric field 604. In this way, the electric field 604 can be applied to the nanostructured ferroelectrics 300a, 300b, and 300c without a conductive substrate.

[0164] Figure 7a The illustration shows the desired chirality and the method and apparatus for generating a nanostructured ferroelectric 300 according to a third embodiment. This embodiment is similar to... Figure 6a The embodiments described in the context of [the previous sentence are missing]. However, a strongly localized electric field 604' is achieved using a conductive atomic force microscope tip 602' as the counter electrode. This provides two advantages: First, due to the tip enhancement of the electric field 604', the reduced voltage U' is sufficient to provide a sufficiently large electric field 604' to reliably control the chirality of the polarization state 304 of the ferroelectric thin layer 300. Second, the electric field 604' is spatially confined to the nanoscale, thus providing the possibility of writing chiral structures 308 with nanoscale dimensions into the ferroelectric thin layer 300. This is particularly attractive for the generation of (optical) metamaterials or for storage applications.

[0165] Figure 7b The illustration is similar to Figure 7a This is an embodiment of the present invention, but the difference is that the conductive atomic force microscope tip 602 is chiral, and thus generates a chiral electric field 604. Figure 7b The right-handed chiral electric field 604” further reduces the energy 404R of the right-handed chiral polarization state of the skyrmions 308 of the ferroelectric thin film 300, and thus supports the formation of right-handed skyrmions 308 when the ferroelectric thin film 300 is cooled to the ferroelectric phase. The conductive atomic force microscope tip 602” can be generated before use in a scanning probe microscope, for example, by growing or etching an overall chiral shape of the tip 602’ or by applying torque to an initially achiral tip 602’. Alternatively, the conductive atomic force microscope tip 602” can have a wide range of achiral shapes, and these chiral molecules can be adsorbed at the tip, for example, by picking up chiral molecules such as chiral carbon nanotubes during scanning of the scanning probe microscope. Repositories of left-handed and right-handed chiral molecules can be provided in different regions on the substrate 302, and the chirality of the tip 604” can be changed by picking up chiral molecules from the corresponding regions.

[0166] Figure 8 Cylindrical nanodots 800 bearing skyrmions 308 are shown on substrate 302. Skyrmions 308 can be illustrated as curved and self-closing domain walls 306, as previously shown in... Figure 3a Described in the context of. Figure 8 The rotation direction 102R of the skyrmion 308 is right-handed. Compared with the ferroelectric material in the thin ferroelectric film 300, the ferroelectric material in the nanodots 800 is additionally restricted in a direction parallel to the surface of the substrate 302, the ferroelectric film 300, and / or the surface of the nanodots 800. This additional restriction can improve the control over the formation, position, and rotation direction of the skyrmion 308, while still allowing control via the environment, particularly via the selection of the substrate 302.

[0167] Nanodot 800 has a diameter of 60 nm and a height of 30 nm. It can be produced by depositing bismuth ferrite on strontium titanate on a porous anodic alumina scaffold, as described in detail in the following literature: Li et al., “High-density array of ferroelectric nanodots with robust and reversibly switchable topological domain states,” Sci. Adv. 3, e1700919 (2017). Alternatively, nanodot 800 can be produced by first depositing a continuous film of ferroelectric on a flat substrate, followed by using photolithography (e.g., photolithography, electron beam lithography, ion beam lithography, X-ray lithography) and etching techniques (e.g., wet etching, ion beam etching, reactive ion etching) to construct the continuous film. Figure 8The nanodot 800 is cylindrical, i.e., a column with a circular substrate. Using photolithography, nanodots with substrates having columnar shapes and a wide range of shapes can be produced, thus providing options to optimize the shape and size of the nanodot 800 according to the requirements of a specific application. For example, the substrate can be rectangular and extremely elongated (nanoring), square, triangular, or elliptical. The method and apparatus for generating the desired chirality of nanostructured ferroelectrics according to this disclosure are applicable to nanodots having any of these shapes.

[0168] Figure 9a and Figure 9b Nanoparticles 900a and 900b are shown. In the context of this disclosure, the polarization structure of nanodot 800 can have chirality depending on the presence of domain wall 306, while the polarization states of nanoparticles 900a and 900b can be chiral even in the absence of domain wall.

[0169] Figure 9a and Figure 9b The nanoparticles 900a and 900b described herein are spherical with a diameter of 30 nm. The nanoparticles can be fabricated using solvothermal and hydrothermal methods. Alternatively, nanoparticles 900a and 900b can be produced using sol-gel synthesis, peroxy-oxalate complexation, non-isothermal decomposition, or any combination of these techniques. The size and shape can be adjusted by selecting the ferroelectric material and preparation conditions. For example, shapes with facets that are approximately spherical, pyramidal, cubic, cuboid, icosahedral, or dodecahedral can be achieved. The nanoparticles can also have one of the shapes described in the context of nanodot 800.

[0170] Figure 9a and Figure 9b Two examples of nanoparticles 900a and 900b exhibiting chiral polarization state 304 are given. The polarization state of nanoparticles 900a and 900b can depend on the preparation conditions and / or on prior treatment using external stimuli such as an external electric field. The preparation conditions and external field treatment can be adjusted to achieve, for example, vortex states, Hopfion states, or skyrmion states. Details are given in the following reference: Luk'yanchuk et al., “Hopfions emerge inferroelectrics,” Nat. Commun. 11, 2433 (2020).

[0171] Figure 4 , Figure 5 , Figure 6a , Figure 6b , Figure 7a and Figure 7bThe method and apparatus described herein for generating desired chirality in nanostructured ferroelectrics can also be applied to nanodots 800 and nanoparticles 900a, 900b as nanostructured ferroelectrics to generate desired chirality. Figure 10a , Figure 10b , Figure 11a , Figure 11b , Figure 12a and Figure 12b Related disclosures are referenced to the corresponding portions of the above disclosures, and similar components will not be described again. Only aspects of methods and apparatus relevant to specific applications of nanodots 800 and nanoparticles 900a and 900b will be pointed out.

[0172] Figure 10a The illustration shows the desired chirality of nanodots 800 or nanoparticles 900a, 900b and a light-assisted method and apparatus 500' for switching their chirality, which is similar to... Figure 5 Examples described in the context refer to ferroelectric thin films. Figure 10a The paper describes nanodots 800 with a cylindrical shape, but this method can be applied to the above. Figure 8 , Figure 9a and Figure 9b The nanodot 800 or nanoparticle 900a, 900b described in the context of the above.

[0173] Figure 10b The diagram illustrates the relationship with Figure 10a Similar embodiments exist. In this embodiment, nanodots 800 or nanoparticles 900a, 900b are embedded in a solid or liquid matrix 302', rather than being supported by a substrate 302. Surrounding the nanodots 800 or nanoparticles 900a, 900b with a solid or liquid matrix 302' provides a highly efficient path for transferring heat away from the nanodots 800 or nanoparticles 900a, 900b and thus efficiently cooling them. Therefore, the material forming the solid or liquid matrix 302' can be selected to provide optimized thermal conductivity. According to an embodiment, a portion of the light or near-infrared radiation 506 from the laser 504 can be used by a polarimeter 514 to monitor the polarization state of the nanodots 800 or nanoparticles 900a, 900b. However, additional detection light sources, such as irradiating the nanodots 800 or nanoparticles 900a, 900b in a direction perpendicular to one of the light or near-infrared radiation 506, can also be provided.

[0174] Figure 11a and Figure 11b The diagram illustrates the relationship with Figure 6bSimilar embodiments to those described above. Top electrode 602 and bottom electrode 606 are arranged on opposite sides of nanodots 800 or nanoparticles 900a, 900b. A voltage U is applied between electrodes 602, 606 to generate an electric field 604, which can be used as a stimulus to generate a polarized state with desired chirality while cooling the nanodots 800 or nanoparticles 900a, 900b. Figure 11b In the process, the voltage -U applied between the top electrode 602 and the bottom electrode 606 is related to... Figure 11a The voltage U applied in the middle is opposite to that applied in the middle, which makes the polarization state of nanodot 800 or nanoparticles 900a and 900b have reverse chirality.

[0175] According to an embodiment, the bottom electrode 606 is provided by a conductive substrate.

[0176] According to embodiments, nanodots 800 or nanoparticles 900a, 900b can be deposited on the bottom electrode from a suspension or solution via dip coating or spin coating. The concentration of nanodots 800 or nanoparticles 900a, 900b in the suspension or solution can be selected to control the density of nanodots 800 or nanoparticles 900a, 900b deposited per unit area on the bottom electrode 606. In particular, if required by the application, the concentration can be selected to achieve a sufficiently low density, thereby resulting in a single nanodot 800 or nanoparticle 900a, 900b in the electric field 604. Other applications may require a larger number of nanodots 800 or nanoparticles 900a, 900b in the field, which can be easily achieved by applying a suspension or solution with a high concentration of nanodots 800 or nanoparticles 900a. A top electrode can be deposited on top of the deposited nanodots 800 or nanoparticles 900a, 900b. Prior to depositing the top electrode, a matrix, particularly a dielectric matrix, can be deposited around the nanodots 800 or nanoparticles 900a, 900b, specifically to provide a propagation path for electromagnetic radiation, thereby heating the nanodots 800 or nanoparticles 900a, 900b. The matrix can be optimized for high thermal conductivity to facilitate cooling of the nanodots 800 or nanoparticles 900a, 900b.

[0177] In alternative embodiments, electrodes 602, 606 may be arranged in a single plane, for example, as finger-like structures on a surface. Nanodots 800 or nanoparticles 900a, 900b may be deposited between electrodes 602, 606 from a suspension or solution. As described above, the density of the deposited nanodots 800 or nanoparticles 900a, 900b can be controlled via the concentration of the suspension or solution. Either or both of electrodes 602, 606 may also be used as resistance heaters to heat the nanodots 800 or nanoparticles 900a, 900b.

[0178] Figure 12a It shows the relationship with Figure 7a Similar embodiments to those described above. Using the tip 602' as the top electrode, an electric field 604' can be selectively applied to a single nanodot 800 or nanoparticle 900a, 900b among a plurality of nanodots 800 or nanoparticles 900a, 900b present on the substrate 302.

[0179] Figure 12b It shows the relationship with Figure 7b Similar embodiments to those described above. Using a chiral tip 602” as a top electrode, an electric field 604” can be selectively applied to a single nanodot 800 or nanoparticle 900a, 900b among a plurality of nanodots 800 or nanoparticles 900a, 900b present on the substrate 302.

[0180] Figure 13 An embodiment is shown that utilizes enantioselective transport of nanodots 800 or nanoparticles 900a, 900b from an ensemble 1304. The ensemble 1304 may comprise left-handed nanodots or nanoparticles 1304L and right-handed nanodots or nanoparticles 1304R. The optical tweezers 1300 consist of a light source (not shown) that generates light or near-infrared radiation 506 with circular polarization 508 and a microscope objective 1302 for tightly focusing the light or near-infrared radiation 506. Tight focusing can generate a gradient of the light or near-infrared radiation 506, thereby generating forces on the nanodots 800 or nanoparticles 900a, 900b of the ensemble 1304. The forces on nanodots 800 or nanoparticles 900a, 900b can depend on the chirality of nanodots 800 or nanoparticles 900a, 900b, and on the circular polarization 508 of light or near-infrared radiation 506. The circular polarization 508 can be selected to selectively transport nanodots 800 or nanoparticles 900a, 900b with pre-selected chirality. Figure 13 In the example shown, light or near-infrared radiation 506 with right-handed circular polarization 508 is transmitted only to those nanodots 800 or nanoparticles 1304R with right-handed chirality in the ensemble 1304.

[0181] According to Figure 13In the method of one embodiment, light or near-infrared radiation 506 heats the ensemble 1304 of nanodots 800 or nanoparticles 900a, 900b to a paraelectric state. Alternatively or additionally, a resistance heater 502 in thermal contact with the substrate 302 can be used to heat the ensemble 1304. The heating power can then be reduced, and the ensemble 1304 can be cooled down. The selected circular polarization 508 can determine the chirality of the polarization state of the generated nanodots 800 or nanoparticles 900a, 900b. When the nanodots 800 or nanoparticles 900a, 900b have been cooled to a ferroelectric state and a pre-selected chirality has been achieved, enantioselective transport can be applied to move nanodots 800 or nanoparticles 900a, 900b of the predetermined chirality to a target destination, or to remove nanodots 800 or nanoparticles 900a, 900b of the opposite chirality. This can further improve the chiral purity of the ensemble 1304 of nanodots 800 or nanoparticles 900a and 900b.

[0182] Figure 14 Another embodiment is shown that utilizes enantioselective transport of nanodots 800 or nanoparticles 900a, 900b from ensemble 1304 of nanodots 800 or nanoparticles 900a, 900b. This embodiment is similar to... Figure 13 The embodiment is described above. However, instead of optical tweezers 1300, plasmonic tweezers 1400 are used. Therefore, light or near-infrared radiation 506 with linear polarization 508' is focused onto the conductive substrate 302 using a microscope objective 1302. The linearly polarized light or near-infrared radiation 506 can induce plasmonic excitation in the conductive substrate 302, which can exert a force on the ensemble 1304 of nanodots 800 or nanoparticles 900a, 900b. Typical plasmonic trap stiffness can vary between 0.1 fN / (μm*mW) and 1 fN / (μm*mW) and up to 5 fN / (μm*mW). The forces experienced by nanodots 800 or nanoparticles 900a can differ for left-handed nanodots or nanoparticles 1304L and right-handed nanodots or nanoparticles 1304R. Therefore, left-handed nanodots or nanoparticles 1304L and right-handed nanodots or nanoparticles 1304R can be transported to different regions on surface 302 and thus can be separated.

[0183] The description and accompanying drawings of this embodiment are for illustrative purposes only and are not intended to imply any limitation. The scope of this disclosure will be determined by the appended claims.

Claims

1. A method for generating nanostructured ferroelectrics with predefined chirality, in, The nanostructured ferroelectric is suitable for providing both high-temperature and low-temperature ferroelectric states. In the low-temperature ferroelectric state, the nanostructured ferroelectric material has polarization states from multiple polarization states. The plurality of polarization states include at least a first chiral polarization state having first chirality and a second chiral polarization state having second chirality different from the first chirality; Wherein, the first extension of the nanostructured ferroelectric material along the first direction is at most 1000 nm; The method includes: The predefined chirality is selected from the first chirality and the second chirality; The electromagnetic field is selected according to the predefined chirality; Provides the nanostructured ferroelectric material under the aforementioned high-temperature condition; The electromagnetic field is applied to the nanostructured ferroelectric material at the high temperature; and While applying the electromagnetic field, the nanostructured ferroelectric material is cooled from the high-temperature state to the low-temperature ferroelectric state to establish the polarization state of the nanostructured ferroelectric material with the predefined chirality.

2. The method according to claim 1, wherein, The high-temperature state refers to the paraelectric or ferroelectric state at elevated temperatures.

3. The method according to claim 1, wherein, The low-temperature ferroelectric state corresponds to the room-temperature state of the nanostructured ferroelectric material.

4. The method according to claim 1, wherein, Applying the electromagnetic field includes irradiating the nanostructured ferroelectric with electromagnetic waves.

5. The method according to claim 4, wherein, The electromagnetic wave is elliptical polarized.

6. The method of claim 1, further comprising supporting the nanostructured ferroelectric with a substrate.

7. The method according to claim 1, wherein, While cooling the nanostructured ferroelectric, the nanostructured ferroelectric is surrounded by a solid matrix or a liquid matrix.

8. The method of claim 1, further comprising during and / or after cooling the nanostructured ferroelectric material from the high-temperature state to the low-temperature ferroelectric state: A non-uniform electromagnetic field is applied to the nanostructured ferroelectric to transport the nanostructured ferroelectric to a location associated with the predefined chirality.

9. The method according to claim 8, wherein, The non-uniform electromagnetic field has field polarization, and the method further includes selecting the field polarization according to the predefined chirality.

10. The method according to claim 1, wherein, Applying the electromagnetic field includes applying a voltage to electrodes arranged on the opposite side of the nanostructured ferroelectric.

11. The method according to claim 10, wherein, At least one of the electrodes has a chiral shape that provides a chiral electromagnetic field as the electromagnetic field.

12. The method according to claim 1, wherein, The nanostructured ferroelectric material provided at the high temperature includes: Provides the nanostructured ferroelectric material in the low-temperature ferroelectric state and possessing the first chirality; and The nanostructured ferroelectric material is heated to the aforementioned high temperature state; Wherein, the predefined chirality is the second chirality.

13. An apparatus for generating nanostructured ferroelectrics with predefined chirality, the apparatus comprising: A retaining element adapted to receive the nanostructured ferroelectric; A heating element, the heating element being adapted to heat the nanostructured ferroelectric to a high temperature; A field-applying element, the field-applying element being adapted to apply an electromagnetic field to the nanostructured ferroelectric body while the nanostructured ferroelectric body is in the high-temperature state; as well as A cooling element, adapted to cool the nanostructured ferroelectric material to a low-temperature ferroelectric state with the predefined chirality while the electromagnetic field is applied to the nanostructured ferroelectric material using the field application element. Wherein, the first extension of the nanostructured ferroelectric material along the first direction is at most 1000 nm.

14. The apparatus of claim 13, further comprising: A radiation source adapted to generate electromagnetic waves, and further adapted to irradiate the nanostructured ferroelectric with the electromagnetic waves.

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