Vacuum packaging for photonic crystals and methods thereof

Abstract

The present disclosure is generally related to photonic crystals, for example, for thermophotovoltaic power generation or other applications. Some aspects are directed to articles having multiple substrates that are used to contain vacuum or interior regions, for example, containing a photonic crystal. These articles may be heated in some embodiments by substantial amounts, without allowing leaks to occur into such regions. For instance, in some cases, the substrates may have similar coefficients of thermal expansion, which may expand in a substantially uniform manner to maintain physical contact without leaking. In some cases, a substrate may comprise sapphire and / or another IR-transparent material, e.g., to transmit emissions from the photonic crystal. In some cases, a substrate may comprise niobium and / or another metal, which may exhibit similar thermal expansion as sapphire. Other aspects are generally directed to methods of making or using the articles, kits including such articles, or the like.

Description

[0001] VACUUM PACKAGING FOR PHOTONIC CRYSTALS AND METHODS THEREOF

[0002] RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 457,183, filed April 5, 2023, entitled “Vacuum Packaging for Photonic Crystals and Methods Thereof,” by Chan, et al., incorporated herein by reference in its entirety.

[0004] GOVERNMENT FUNDING

[0005] This invention was made with Government support under FA864922P0754 awarded by the US Air Force. The Government has certain rights in the invention.

[0006] TECHNICAL FIELD

[0007] The present disclosure is generally related to photonic crystals, for example, for thermophotovoltaic power generation or other applications.

[0008] BACKGROUND

[0009] Photonic crystals promise near-arbitrary control of both angular and spectral emission profiles, and have been suggested for use for thermophotovoltaic power generation, or other applications. However, certain types of photonic crystals are also relatively reactive, and can be oxidized upon exposure to a variety of reactive species such as oxygen and water, rendering them nonfunctional. However, oxygen and water are common in the atmosphere, which accordingly can make it quite difficult to use phonetic crystals in many applications. Thus, techniques for preventing the exposure of photonic crystals to atmospheric conditions are needed.

[0010] SUMMARY

[0011] The present disclosure is generally related to photonic crystals, for example, for thermophotovoltaic power generation or other applications. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0012] Some aspects of the invention are related to articles. In some cases, the article comprises a first substrate comprising sapphire, a second substrate comprising niobium in physical contact with the first substrate, a third substrate comprising titanium in physical contact with the second substrate, and a photonic crystal positioned to emit radiation through the first substrate. In another aspect, the article comprises a first substrate comprising sapphire and defining an interior region having a pressure of less than or equal to 80 kPa, a second substrate comprising niobium in physical contact with the first substrate, and a third substrate comprising titanium in physical contact with the second substrate.

[0013] In some aspects, the article comprises a first substrate comprising sapphire, a second substrate comprising niobium in physical contact with the first substrate, a third substrate comprising titanium in physical contact with the second substrate, and a thermophotovoltaic cell positioned to receive radiation passing through the sapphire.

[0014] In another aspect, the article comprises a first substrate comprising an IR- transparent material and having a first coefficient of thermal expansion, a second substrate in physical contact with the first substrate and having a second coefficient of thermal expansion, wherein the second coefficient is between 0.9 and 1.1 times the first coefficient, a third substrate in physical contact with the second substrate and having a third coefficient of thermal expansion, wherein the third coefficient is between 0.8 and 1.2 times the second coefficient, and a photonic crystal positioned to emit radiation through the first substrate.

[0015] In one aspect, the article comprises a first substantially tube-shaped substrate comprising sapphire and defining an interior region, a second substantially tube-shaped substrate comprising niobium, bonded to an end portion of the first substrate, a third substantially tube-shaped substrate comprising titanium, bonded to an end portion of the second substrate, an inner substantially tube-shaped substrate, positioned at least partially within the interior region of the first substrate, a photonic crystal comprising Ta and able to emit radiation, the photonic crystal positioned on at least a portion of an outer surface of the inner substrate, and a thermophotovoltaic cell positioned to receive the radiation emitted by the photonic crystal passing through the sapphire, wherein the interior region of the first substrate has a pressure less than or equal to 80 kPa.

[0016] Some aspects are related to methods. In some cases, the method comprises emitting radiation from a photonic crystal, passing the radiation through a region having a pressure less than or equal to 80 kPa, and passing the radiation through sapphire.

[0017] In one aspect, the method comprises providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa, and emitting radiation from a photonic crystal positioned at least partially within the interior region. In some aspects, the method comprises providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa, and heating the interior region without increasing the pressure of the interior region above 300 kPa.

[0018] In one aspect, the method comprises providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa, and heating the interior region without exposing the interior region to a gas external of the substrate.

[0019] In another aspect, the method comprises providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa, and heating the interior region without exposing the interior region to a gas having a pressure of 101.3 kPa.

[0020] Other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the disclosure when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale unless otherwise indicated. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the figures:

[0023] FIG. 1 is a schematic illustration of a photonic crystal, substrates positioned in physical contact and / or around the photonic crystal, and a thermophotovoltaic cell, according to some embodiments;

[0024] FIG. 2 is a schematic illustration of a photonic crystal and substrates positioned in physical contact and / or around the photonic crystal, according to some embodiments. DETAILED DESCRIPTION

[0025] The present disclosure is generally related to photonic crystals, for example, for thermophotovoltaic power generation or other applications. Some aspects are directed to articles having multiple substrates that are used to contain vacuum or interior regions, for example, containing a photonic crystal. These articles may be heated in some embodiments by substantial amounts, without allowing leaks to occur into such regions. For instance, in some cases, the substrates may have similar coefficients of thermal expansion, which may expand in a substantially uniform manner to maintain physical contact without leaking. In some cases, a substrate may comprise sapphire and / or another IR-transparent material, e.g., to transmit emissions from the photonic crystal. In some cases, a substrate may comprise niobium and / or another metal, which may exhibit similar thermal expansion as sapphire. Other aspects are generally directed to methods of making or using the articles, kits including such articles, or the like.

[0026] Photonic crystals may exhibit optical properties that are desirable for certain applications, for example, for power generation. For instance, in some cases, photonic crystals may selectively emit radiation when heated, which may be useful for applications such as thermophotovoltaic power generation, in which a fuel can be burned to produce power, for example, by heating the photonic crystal to produce radiation which can then be converted, e.g., using a photovoltaic cell, to produce power. In some applications, however, when heated to relatively high temperatures (e.g., to at least 800 °C), certain photonic crystals may be susceptible to oxidative degradation in the presence of reactive species such as oxygen and / or water.

[0027] Accordingly, it may be advantageous in some cases to limit the exposure of the photonic crystal to oxygen and water. This may be achieved, in some embodiments, by positioning a photonic crystal within an interior region of a device having little to no oxygen and / or water vapor. For example, the interion region may contain a vacuum, and / or may contain gases that have very low concentrations of oxygen and / or water vapor. However, in some cases, during use, there can be very large changes in temperature, e.g., by at least 600 °C, at least 800 °C, at least 1000 °C, or more, and different substrates may expand at different rates, which may result in leaks or gaps between such substrates, e.g., allowing gases to flow into and / or out of the interior region. The breakdown of the sealing of the interior region and the introduction of reactive species such as oxygen and / or water vapor (e.g., from the surrounding atmosphere) may result in an adverse reaction of the photonic crystal with such reactive species.

[0028] Thus, certain embodiments as discussed herein are generally directed to systems and methods for maintaining a relatively airtight seal around an interior space containing a photonic crystal, even when the system is heated to relatively high temperatures for thermophotovoltaic power generation, or other applications. For example, some aspects of the present disclosure are directed to using certain substrates to enclose an interior region of a device, even when heated to relatively high temperatures. In some cases, the coefficients of thermal expansion (CTE) of the substrates may be relatively low and / or may be sufficiently matched such that these materials expand to a limited degree and / or expand in a substantially uniform manner. One non-limiting example of such a combination is sapphire, niobium, and titanium; other examples are discussed in more detail herein.

[0029] As an example, consider FIG. 1, which is a non-limiting, cross-sectional schematic illustration of article 100. In this example, a photonic crystal 110 may comprise tantalum (or other materials such as those described herein), and may be positioned within an interior region 115 on an inner substrate 105. The inner substrate may be used to heat the photonic crystal, e.g., by burning a fuel. For example, the inner substrate may be a tube formed out of Inconel, where a fuel may be burned to heat the Inconel and thus the photonic crystal. The inner region 115 may contain a vacuum, for example, having a pressure less than the ambient (atmospheric) pressure, and / or contain one or more gases that are not reactive species such as water or oxygen.

[0030] Inner substrate 105 and photonic crystal 110 may be at least partially surrounded by a first substrate 120, which may in some cases serve to at least partially define the interior region 115. In some cases, the first substrate may comprise sapphire or another IR-transparent material like quartz, which may be used since such materials may not substantively obstruct any radiation emitted 125 by the photonic crystal when the crystal is heated (e.g., heated by burning a fuel), which may allow the radiation emitted by the photonic crystal to pass through the sapphire and to be utilized elsewhere. In some cases, for instance, such radiation may be directed towards a thermophotovoltaic cell 150 for thermophotovoltaic power generation.

[0031] The first substrate may further be supported by a second substrate 130. The first substrate and the second substrate may have CTEs that are similar or approximately match. As a non-limiting example, if the first substrate comprises sapphire, the second substrate may comprise niobium. Due to having similar CTEs, when heated, the sapphire and the niobium expand in a relatively uniform manner and may maintain the airtight seal of the interior region, and thus the vacuum or gases, etc. remains present within inner region 115. In some cases, it may be beneficial to further support the second substrate 130 with a third substrate 140, for example, comprising titanium or another material, which may allow it to interface with other materials, as represented by fourth substrate 145 (e.g., stainless steel components forming other parts of the device).

[0032] The above discussion is a non-limiting example of one embodiment of the present disclosure that can be used to contain an interior space, e.g., in an airtight or sealed environment. However, other embodiments are also possible. Accordingly, more generally, various aspects are directed to various systems and methods for containing a photonic crystal, for example, in a vacuum or other environment.

[0033] Photonic crystals may comprise any of a variety of suitable materials, in accordance with some embodiments. In some cases, it may be advantageous to use a photonic crystal comprising a refractory metal (e.g., niobium, molybdenum, tantalum, tungsten, osmium, iridium, ruthenium, zirconium, titanium, vanadium, chromium, rhodium, hafnium, and / or rhenium) so that the photonic crystal can withstand the relatively high temperatures without degrading, for example, by melting. In some embodiments, it may be particularly advantageous to use a photonic crystal comprising tantalum.

[0034] Photonic crystals may have a micro structure that, in some cases, has 1- dimensional periodicity. In some embodiments, the photonic crystal may have 2- dimensional periodicity. One of ordinary skill in the art would be able to determine the dimensionality of the periodicity of a photonic crystal upon inspection. For example, 1- dimensionally periodic photonic crystals include materials arranged in such a way that the index of refraction within the volume of the photonic crystal varies along one coordinate direction and does not substantially vary along two orthogonal coordinate directions. For example, a 1 dimensionally periodic photonic crystal can include two or more materials arranged in a stack within the emitter such that there is substantially no variation in the index of refraction along two orthogonal coordinate directions. 2- dimensionally periodic photonic crystals include materials arranged in such a way that the index of refraction within the volume of the photonic crystal varies along two coordinate directions and does not substantially vary along 1 coordinate direction orthogonal to the other two coordinate directions. The periodicity of the photonic crystal may result in some of the desirable optical properties exhibited by the photonic crystal, as described above. For example, in some cases, photonic crystals can be configured such that the emittance of radiation about a cutoff wavelength changes significantly. That is, in some cases, the photonic crystal may have an emittance of radiation having a wavelength longer than a cutoff wavelength of no more than 0.4, no more than 0.3, nor more than 0.2, no more than 0.1, or nor more than 0.05, whereas the emittance exhibited by the photonic crystal for radiation having a shorter wavelength may be at least 0.5, at least 0.6, at least 0.7, at least 0.8, at least 0.9, or at least 0.95.

[0035] The cutoff wavelength, wherein the emittance of radiation from the photonic crystal is significantly different for radiation having shorter wavelengths than for radiation having longer wavelengths, may not be a discrete wavelength in radiation. For example, the cutoff wavelength may represent a 10 nm band. For example, the wavelength cutoff may be from 1 micron to 1.01 microns, wherein emittance is relatively low for radiation having a wavelength longer than 1.01 microns and emittance is relatively low for radiation having a wavelength shorter than 1 micron. In some cases, the cutoff wavelength may represent a band of at least 5 nm, at least 10 nm, at least 50 nm, or at least 100 nm. In some cases, the cutoff wavelength may represent a band of no more than 150 nm, no more than 100 nm, no more than 50nm, or no more than 10 nm.

[0036] Such optical properties may be useful for efficient power generation using thermophotovoltaic cells. That is, the photonic crystal may primarily emit radiation having a wavelength short than the cutoff wavelength, in some cases. In some cases, if the wavelength cutoff is equal to or shorter than light corresponding to the band gap of a thermophotovoltaic cell. Light with a wavelength longer than the band gap of the thermophotovoltaic cell may not be emitted by the photonic crystal, and accordingly not lost as waste energy, for example, as heat.

[0037] When heating a photonic crystals to relatively high temperatures (e.g., at least 800 °C, at least 1000 °C, at least 1500 °C, at least 2000 °C, or other temperature such as those described herein), the materials of the photonic crystal may react in the presence of oxygen and / or water vapor, or other reactive species. For example, in some embodiments, when the photonic crystal comprises tantalum, the photonic crystal may be susceptible to oxidative degradation when heated in the presence of oxygen and / or water. Accordingly, in some embodiments, it may be advantageous to position the photonic crystal within an interior region that helps to avoid or minimize the exposure of the photonic crystal to reactive species such as oxygen and water, e.g., to avoid oxidative degradation of the photonic crystal, and / or extend the lifetime of the photonic crystal.

[0038] The interior region may contain a vacuum, and / or may contain gases that have very low concentrations of oxygen and / or water vapor. One of ordinary skill in the art will understand the meaning of vacuum. In some cases, vacuum indicates a region with a pressure lower than atmospheric or ambient pressure, but the vacuum is not required to be a “perfect” vacuum (i.e., containing zero molecules).

[0039] For example, according to some embodiments, the vacuum may have a pressure (absolute) of less than 100 kPa, less than 10 kPa, less than 10'1kPa, less than 10'2kPa, less than 10'3kPa, less than 10'4kPa, less than 10'5kPa, less than 10'6kPa, less than 10'7kPa, or less than 10'8kPa at room temperature. In some embodiments, the partial pressure of water vapor and / or oxygen within the vacuum may be less than 100 kPa, less than 10 kPa, less than 10'1kPa, less than 10'2kPa, less than 10'3kPa, less than 10'4kPa, less than 10'5kPa, less than 10'6kPa, less than 10'7kPa, or less than 10'8kPa at room temperature, etc.

[0040] As mentioned, it should be understood that the vacuum need not be a perfect vacuum (i.e., it need not have a pressure of 0 kPa), and in various embodiments, the vacuum may have some gas present, but that gas may be at a pressure lower than atmospheric or ambient pressure. For instance, in certain embodiments, the interior space (e.g., around the photonic crystal) may contain any of a variety of gases, and the gases may be present at vacuum pressures (e.g., at a pressure lower than atmospheric or ambient pressure), or other pressures (e.g., at or even above atmospheric or ambient pressure in some cases).

[0041] In some embodiments, when the device is heated relatively high temperatures (e.g., at least 800 °C, at least 1000 °C, at least 1500 °C, at least 2000 °C, etc.) the pressure within the interior region may be less than or equal to 102kPa, less than or equal to 80 kPa, less than or equal to 101kPa, less than or equal to 10° kPa, less than or equal to 10'1kPa, less than or equal to 10'2kPa, less than or equal to 10'3kPa, less than or equal to 10’4kPa, less than or equal to 10'5kPa, or less than or equal to 10'6kPa, etc..

[0042] A variety of different gases may be present within the interior space, and such gases may be present at pressures that are less than atmospheric pressure (e.g., a vacuum), or at pressures that are at or greater than atmospheric pressure in certain cases. For example, the interior space may include gases such as nitrogen, argon, helium, krypton, xenon, hydrogen, or the like. One or more than one gas may be present, including these and / or other gases. In some embodiments, the gases may create an inert or reducing atmosphere. In addition, in certain cases, the gases may be selected to be relatively transparent to radiation, such as infrared radiation. Non-limiting examples of such gases are nitrogen, krypton, and xenon. Thus, as a non-limiting example, the nitrogen may be present in the interior space at at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% by volume of the total gas within the interior space.

[0043] In some embodiments, the gases in the interior space may be substantially free of oxygen and / or water vapor. For example, the partial pressure of oxygen may be less than or equal to 80 kPa, less than or equal to 101kPa, less than or equal to 10° kPa, less than or equal to 10'1kPa, less than or equal to 10'2kPa, less than or equal to 10'3kPa, less than or equal to 10'4kPa, less than or equal to 10'5kPa, or less than or equal to 10'6kPa. As another example, the partial pressure of water may be less than or equal to 80 kPa, less than or equal to 101kPa, less than or equal to 10° kPa, less than or equal to 10'1kPa, less than or equal to 10'2kPa, less than or equal to 10'3kPa, less than or equal to 10'4kPa, less than or equal to 10'5kPa, or less than or equal to 10'6kPa.

[0044] The vacuum or other interior region may be present within an enclosed or sealed environment, e.g., to prevent leakage of gases from occurring into or out of the interior region. In some cases, for example, a first substrate at least partially encloses an interior region having a pressure of no more than 80 kPa, or other pressures such as those described herein. Accordingly, in some embodiments, the first substrate may at least partially enclose an interior region, wherein the photonic crystal is partially or completely positioned within the interior region of the first substrate.

[0045] Any of a variety of materials may be suitable for use as the first substrate. For example, the material may be selected to maintain a substantially airtight seal, e.g., when heated to relatively high temperatures (e.g., at least 200 °C, at least 300 °C, at least 400 °C, at least 500 °C, at least 600 °C, or other temperatures such as those described herein). In some cases, the seal may be sufficient to maintain the pressure of the enclosed vacuum (e.g., without equilibrating with atmospheric pressure), e.g., over a period of time of at least a day, a week, four weeks, a year, 10 years, or more years, for example, to maintain the pressure at at least 80%, at least 90%, or at least 95% of its initial value.

[0046] Additionally, in some embodiments, it may be advantageous for the first substrate to comprise an IR-transparent material. In certain embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of the first substrate may comprise one or more IR-transparent materials. In some cases, the transmittance of the material of the first substrate may be at least 0.5, at least 0.6, at least 0.7, at least .75, at least 0.8, at least 0.85, at least 0.9, at least 0.95, or at least 0.99 for radiation corresponding to IR radiation (e.g., radiation having a wavelength of at least 700 nm, at least 800 nm, at least 900 nm, at least 1 micron, at least 1.2 microns, at least 1.5 microns, at least 1.8 microns, or at least 2 microns, etc.). Thus, in some cases, the photonic crystal may be heated and selectively emit radiation, where the photonic crystal may be positioned to emit the radiation through the interior region and / or through the first substrate enclosing the interior region. Thus, in accordance with some embodiments, the first substrate may at least partially comprise an IR-transparent material so that the radiation emitted by the photonic crystal may not be substantively impeded by the first substrate (e.g., absorbed and / or reflected by the first substrate), for example, having transmittances such as those described herein.

[0047] In some cases, the first substrate may comprise a ceramic material. In some embodiments, the first substrate may comprise sapphire. In some cases, the first substrate may comprise quartz. In certain embodiments, the first substrate comprises sapphire and at least partially defines an interior region having a pressure of no more than 80 kPa, or other pressures as those described herein, e.g., a vacuum as described elsewhere herein. In some cases, the sapphire may be present as a portion of a substrate that defines a region having a pressure of no more than 80 kPa.

[0048] When heated, the first substrate may expand, as quantified with a first coefficient of thermal expansion. The first coefficient of thermal expansion may be relatively low in certain embodiments such that, as described herein, the material of the first substrate can maintain a substantially airtight seal when heated to relatively high temperatures. The coefficient of thermal expansion of the materials of the first substrate, in some cases, may be less than or equal to 5xl0'5°C'1, less than or equal to 10'5°C'1, or less than or equal to 5xl0'6°C'1. In some embodiments, the coefficient of thermal expansion of the materials of the first substrate may be greater than or equal to 10'6°C'1, greater than or equal to 5xl0'6°C1, or greater than or equal to 10'5°C'1. Combinations of the foregoing ranges are possible (e.g., greater than or equal to 5xl0'6°C'1and less than or equal to 10'5°C'1). Other ranges are also possible.

[0049] The first substrate may be in physical contact with a second substrate, e.g., to define an interior region. As a non-limiting example, as discussed above, FIG. 1 shows an embodiment wherein the first substrate 120 may at least partially enclose an interior region 115 having a pressure corresponding to a vacuum, where a photonic crystal 110 is positioned on an inner substrate 105 within the interior region 115. The second substrate 130 may be in physical contact with the first substrate 120 and may at least partially enclose a portion of the interior region 115 having a pressure corresponding to a vacuum.

[0050] In some cases, when the first and second substrates are heated to relatively high temperatures, it may be advantageous for the coefficient of thermal expansion of the first and second substrates to approximately match. This is because when the first and second substrates are heated, the approximately matching coefficients of thermal expansion may indicate that the first and second substrates expand in a substantially uniform manner, which may at least reduce the possibility of a leak forming between the substrates during heating, e.g., due to uneven thermal expansion. For example, the first substrate may have a first coefficient of thermal expansion, and the second substrate may have a second coefficient of thermal expansion, where the second coefficient is between 0.5 and 1.5, between 0.6 and 1.4, between 0.7 and 1.3, between 0.8 and 1.2, or between 0.9 and 1.1 times the first coefficient. Thus, the first and second substrate may together preserve the seal of the interior region and maintain the vacuum and / or gases therein, in certain embodiments, even during or after heating as discussed herein. In some cases, for example when the first substrate comprises sapphire, the second substrate may comprise niobium, which have approximately matching coefficients of thermal expansion. In some cases, for instance, the first substrate comprising sapphire may be in physical contact with the second substrate comprising niobium.

[0051] According to some embodiments, as discussed, a photonic crystal can be heated and configured to selectively emit radiation through the first substrate. For example, the photonic crystal may be positioned within an interior region of the first substrate and allowed to emit radiation through the interior region and through the first substrate, for example, during thermophotovoltaic power generation. The heat used to heat the photonic crystal may also heat the first and / or second substrates, which, as described above, may have similar coefficients of thermal expansion and thus may maintain physical contact and / or a seal when heated, even to relatively high temperatures. Accordingly, in some such cases, a difference in pressure between the interior region and exterior region may be sustained, even when heated. In some cases, for example, the photonic crystal may be protected by being contained in an interior region, e.g., having a vacuum or gases such as discussed herein. According to some embodiments, the second substrate may comprise a material have a second coefficient of thermal expansion that approximately matches the first coefficient of thermal expansion of the first substrate. In some cases, the second coefficient of thermal expansion may be less than or equal to 5xl0'5°C , less than or equal to 10'5°C1, or less than or equal to 5xl0'6°C'1. In some embodiments, the coefficient of thermal expansion of the materials of the first substrate may be greater than or equal to I O’6°C- l, greater than or equal to 5x1 O'6°C-1, or greater than or equal to 10'5°C . Combinations of the foregoing ranges are possible (e.g., greater than or equal to 5xl0'6°C and less than or equal to 10'5°C ). Other ranges are also possible.

[0052] According to some embodiments, the first and second substrates may enclose an interior region comprising a vacuum or certain gases, where the photonic crystal may be positioned within the interior region. In some cases, a third substrate may be in physical contact with the second substrate and support (e.g., hold in place) the first and / or second substrate. In some cases, the third substrate does not enclose a portion of the vacuum. In some embodiments, the third substrate encloses at least a portion of the vacuum. The third substrate may be used, in certain embodiments to connect the first substrate and / or the second substrate to other components of the device, e.g., to stainless steel or other materials. According to some embodiments, the third substrate may comprise titanium. Other materials for the third substrate are also possible.

[0053] According to some embodiments, the third substrate may comprise a material have a third coefficient of thermal expansion. In some embodiments, the third coefficient of thermal expansion may be less than or equal to 5xl0'5°C'1, less than or equal to 10'5°C'1, or less than or equal to 5xl0'6°C'1. In some embodiments, the coefficient of thermal expansion of the materials of the first substrate may be greater than or equal to 10'6°C'1, greater than or equal to 5xl0'6°C'1, or greater than or equal to 10'5°C'1. Combinations of the foregoing ranges are possible (e.g., greater than or equal to 5xl0'6°C'1and less than or equal to 10'5°C'1). In some embodiments, the third substrate may have a third coefficient of thermal expansion, where the third coefficient is between 0.5 and 1.5, between 0.6 and 1.4, between 0.7 and 1.3, between 0.8 and 1.2, or between 0.9 and 1.1 times the second coefficient of the second substrate, and / or between 0.5 and 1.5, between 0.6 and 1.4, between 0.7 and 1.3, between 0.8 and 1.2, or between 0.9 and 1.1 times the second coefficient of the first substrate.

[0054] According to some embodiments, there may also be a fourth substrate in physical contact with the third substrate. The fourth substrate may be a portion of other parts of the device, e.g., structural components. Any of a variety of materials are suitable for the fourth substrate. For example, in some cases, the fourth substrate may comprise stainless steel be in physical contact with the third substrate comprising titanium.

[0055] The first, second, and / or third substrates may independently be any of a variety of suitable 3-dimensional shapes. In some cases, the shape of the first and / or second substrates may be able to enclose the vacuum. For example, the first substrate may be cylindrical, cubic, pyramidal, or any other regular or irregular 3-dimensional shape. In some cases, it may be particularly advantageous for the first, second, and / or third substrates to have a substantially circular profile, e.g., a cross section. In some embodiments, the first, second, and / or third substrates may be substantially tube-shaped (e.g., cylindrical). In some cases, when each of the first, second, and third substrates are substantially tube-shaped, it may facilitate the physical contact between each of the substrates.

[0056] In some cases, when the first, second, and / or third substrate is tube-shaped, the outer diameter of the circular profile of the first, second, and / or third substrate may be at least 10 mm, at least 15 mm, at least 20 mm, least 25 mm, at least 30 mm, at least 35 mm, at least 40 mm, at least 45 mm, at least 50 mm, at least 55 mm, at least 60 mm, at least 65 mm, at least 70 mm, at least 75 mm, at least 80 mm, at least 90 mm, at least 100 mm, at least 110 mm, at least 120 mm, at least 130 mm, at least 140 mm, at least 150 mm, at least 175 mm, at least 200 mm, at least 225 mm, at least 250 mm, at least 275 mm, at least 300 mm, at least 350 mm, at least 400 mm, at least 450 mm, at least 500 mm, at least 600 mm, at least 700 mm, at least 800 mm, at least 900 mm, at least 1000 mm, etc. In addition, in some embodiments, the outer diameter of the third substrate may be no more than 1000 mm, no more than 900 mm, no more than 800 mm, no more than 700 mm, no more than 600 mm, no more than 500 mm, no more than 450 mm, no more than 400 mm, no more than 350 mm, no more than 300 mm, no more than 275 mm, no more than 250 mm, no more than 250 mm, no more than 225 mm, no more than 200 mm, no more than 175 mm, no more than 150 mm, no more than 140 mm, no more than 130 mm, no more than 120 mm, no more than 110 mm, no more than 100 mm, no more than 90 mm, no more than 80 mm, no more than 75 mm, no more than 70 mm, no more than 65 mm, no more than 60 mm, no more than 55 mm, no more than 50 mm, no more than 45 mm, no more than 40 mm, no more than 35 mm, no more than 30 mm, no more than 25 mm, no more than 20 mm, no more than 15 mm, no more than 10 mm, etc.

[0057] Combinations of any of these are also possible in some cases. In some cases, there may be one or more materials positioned between the first, second, and / or third substrates, although in other embodiments, no materials may be positioned between the first, second, and / or third substrates (e.g., as disclosed above). As non-limiting examples, there may be one or more brazing materials (or brazes) positioned between the first substrate and the second substrate, e.g., at an interface. In some cases, the brazing material may comprise a metal. In some cases, the brazing material may be a material that has a lower melting point than either the first substrate on the second substrate, which may facilitate bonding of the first material and the second material. Non-limiting examples of brazing materials include metals such as nickel, aluminum, silicon, copper, silver, zinc, tin, gold, brass, bronze, or the like. In some cases, the brazing materials may be present in an amount of no more than 100 mg / m2, no more than 50 mg / m2, no more than 30 mg / m2, no more than 20 mg / m2, no more than 10 mg / m2, no more than 5 mg / m2, no more than 3 mg / m2, no more than 2 mg / m2, no more than 1 mg / m2, etc. of interface area.

[0058] The photonic crystal may be positioned on an inner substrate. In some cases, the photonic crystal is positioned on at least a portion of a surface of the inner substrate. According to some embodiments, the photonic crystal may be positioned on an inner substrate comprising a material that can be heated several hundred degrees, e.g., heated to a temperature of at least 800 °C, at least 900 °C, at least 1000 °C, at least 1100 °C, at least 1200 °C, at least 1300 °C, at least 1400 °C, at least 1500 °C, at least 1600 °C, at least 1700 °C, at least 1800 °C, at least 1900 °C, at least 2000 °C, etc. In addition, in some cases, the material may be heated such that it experiences a relatively large change in temperature. For instance, the material may be heated by a temperature of at least 800 °C, at least 900 °C, at least 1000 °C, at least 1100 °C, at least 1200 °C, at least 1300 °C, at least 1400 °C, at least 1500 °C, at least 1600 °C, at least 1700 °C, at least 1800 °C, at least 1900 °C, at least 2000 °C, etc.

[0059] In certain embodiments, the inner substrate is a metal. Non-limiting examples of metals include, but are not limited to, aluminum, lead, brass, silver, copper, gold, nickel, iron, steel, or the like. In some embodiments, the inner substrate may be a metal alloy of two or more metals, e.g., including these and / or other metals.

[0060] For example, in one set of embodiments, the inner substrate may be an Inconel or another metal superalloy, for example, an austenitic nickel-chromium-based superalloy. Non-limiting examples include Inconel 625, Inconel 617, Inconel 690, Inconel 600, Inconel 718, or Inconel X-750. In some cases, the metal may be an alloy of nickel and chromium, optionally including other metals or materials, such as iron, molybdenum, niobium, tantalum, cobalt, manganese, copper, aluminum, titanium, silicon, carbon, sulfur, phosphorous, boron, etc. According to some embodiments, the inner substrate may comprise at least 90% of a metal superalloy

[0061] The inner substrate may be any of a variety of suitable 3-dimensional shapes. For example, the inner substrate may be cylindrical, cubic, pyramidal, or any other regular or irregular 3-dimensional shape. In some cases, it may be particularly advantageous for the inner substrate to have a substantially circular profile, e.g., a cross section. For example, the inner substrate may be substantially tube-shaped (e.g., cylindrical). Other shapes are possible.

[0062] In some cases, when the inner substrate is tube-shaped, the outer diameter of the circular profile of the inner substrate may be at least 10 mm, at least 15 mm, at least 20 mm, least 25 mm, at least 30 mm, at least 35 mm, at least 40 mm, at least 45 mm, at least 50 mm, at least 55 mm, at least 60 mm, at least 65 mm, at least 70 mm, at least 75 mm, at least 80 mm, at least 90 mm, at least 100 mm, at least 110 mm, at least 120 mm, at least 130 mm, at least 140 mm, at least 150 mm, at least 175 mm, at least 200 mm, at least 225 mm, at least 250 mm, at least 275 mm, at least 300 mm, at least 350 mm, at least 400 mm, at least 450 mm, at least 500 mm, at least 600 mm, at least 700 mm, at least 800 mm, at least 900 mm, at least 1000 mm, etc. In addition, in some embodiments, the outer diameter may be no more than 1000 mm, no more than 900 mm, no more than 800 mm, no more than 700 mm, no more than 600 mm, no more than 500 mm, no more than 450 mm, no more than 400 mm, no more than 350 mm, no more than 300 mm, no more than 275 mm, no more than 250 mm, no more than 250 mm, no more than 225 mm, no more than 200 mm, no more than 175 mm, no more than 150 mm, no more than 140 mm, no more than 130 mm, no more than 120 mm, no more than 110 mm, no more than 100 mm, no more than 90 mm, no more than 80 mm, no more than 75 mm, no more than 70 mm, no more than 65 mm, no more than 60 mm, no more than 55 mm, no more than 50 mm, no more than 45 mm, no more than 40 mm, no more than 35 mm, no more than 30 mm, no more than 25 mm, no more than 20 mm, no more than 15 mm, no more than 10 mm, etc. Combinations of any of these are also possible in some cases.

[0063] According to some embodiments, the article may further comprises a heat source. The heat source, in some cases, may be positioned to heat the inner substrate. In some cases, the inner substrate may be heated chemically, e.g., by burning or reacting a fuel, and the heat that is produced may heat the photonic crystal to emit electromagnetic radiation, which can be directed at a thermophotovoltaic cell to produce power. Nonlimiting examples of fuels that can be used include gasoline, ethanol, diesel, petroleum, naphtha, hydrogen, propane, methane, coal gas, water gas, or the like. Additional nonlimiting examples of fuel include heavy fuels, such as diesel, jet fuel, kerosene, or the like. Specific non-limiting examples of jet fuel include JP-8, Jet A-l, Jet-A, JP-4, Jet B, TS-1, JP-1, JP-2, JP-3, JP-5, JP-6, JP-7, JP-9, JP-10, JPTS, Zip fuel, syntroleum, or the like.

[0064] In accordance with some embodiments, the inner substrate may be configured to heat the photonic crystal to a temperature of at least 800 °C. In some cases, the inner substrate may be configured to heat the interior region to a temperature of at least 800 °C and / or by at least 800 °C. In accordance with some embodiments, heating the interior region may increase the pressure of the interior region. In some such cases, the pressure of the interior region may increase to no more than 10 kPa, no more than 50 kPa, no more than 100 kPa, no more than 500 kPa, no more than 1000 kPa, no more than 2000 kPa, or no more than 3000 kPa.

[0065] In some cases, when the first and second substrates have approximately matching coefficients of thermal expansion, heating the interior region may not expose the interior region to gas external of the first and / or second substrate. According to some embodiments, when the first and second substrates have approximately matching coefficients of thermal expansion, heating the interior region occurs without exposing the interior region to a gas having a pressure of 101.3 kPa.

[0066] As mentioned, the heat from the reaction may be used to heat a suitable thermal power generator to produce power. For example, a photonic crystal may be heated from the reaction. The photonic crystal may be part of an emitter that emits electromagnetic radiation, which can be directed at a thermophotovoltaic cell to produce power. In some cases, the thermophotovoltaic cell may be positioned to received radiation emitted from the photonic crystal. One of ordinary skill in the art will know of suitable thermophotovoltaic cells. It may be advantageous in certain embodiments to select a photonic crystal that emits radiation having a wavelength that is greater than or equal to radiation that can be absorbed by the thermophotovoltaic cell (e.g., matching the emittance of the photonic cell with the band gap of the thermophotovoltaic cell).

[0067] In one example embodiment, the first substrate may be substantially tubeshaped, comprise sapphire, and define an interior region, the interior region having a pressure of less than or equal to 80 kPa, or other pressures as described herein, the second substrate may be substantially tube-shaped, comprise niobium, and be bonded to an end portion of the first substrate, the third substrate may be substantially tube-shaped, comprise titanium, and be bonded to an end portion of the second substrate, the inner substrate may be substantially tube-shaped, comprise an Inconel alloy, and positioned at least partially within the interior region of the first substrate, wherein the photonic crystal comprising Ta may be positioned on at least a portion of an outer surface of the inner substrate and configured to emit radiation such that it passes through the first substrate and is directed to the thermophotovoltaic cell.

[0068] U.S. Pat. Apl. Ser. No. 63 / 339,617, entitled “Rapid Mixing Systems and Methods for Fuel Burners,” filed May 9, 2022, is incorporated herein by reference in its entirety. In addition, U.S. Pat. Apl. Ser. No. 63 / 457,179, entitled “Passivation Systems and Methods for Photonic Crystals,” and U.S. Pat. Apl. Ser. No. 63 / 457,176, entitled “Systems and Methods for Photonic Crystal Integration,” each filed on April 5, 2023, are also each incorporated herein by reference in its entirety. Also, U.S. Pat. Apl. Ser. No. 63 / 457,183, filed April 5, 2023, entitled “Vacuum Packaging for Photonic Crystals and Methods Thereof,” is incorporated herein by reference in its entirety

[0069] The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.

[0070] EXAMPLE 1

[0071] The following is an example of an article. FIG. 2 shows a schematic illustration of the article 200. Here, a tantalum photonic crystal 210 may be positioned on an Inconel burner tube 205. The photonic crystal 210 and Inconel burner tube 205 may be positioned within a vacuum 215 enclosed by a first substrate comprising sapphire 220 and a second substrate comprising niobium. In this case, the second substrate comprising niobium comprises a niobium washer 230 and a niobium tube 235. The first and second substrates 220, 230, and 235 are supported by a third substrate comprising titanium 240 and fourth substrate comprising stainless steel 245. In this example, the substrates are tube shaped, surrounding the Inconel burner tube 205. The first, second, third, and fourth substrates have CTEs as shown in Table 1.

[0072] Table 1. CTEs of the materials of the first, second, third, and fourth substrates

[0073] While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present invention is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present invention.

[0074] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0075] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and / or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0076] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0077] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0078] As used herein, “wt%” is an abbreviation of weight percentage. As used herein, “at%” is an abbreviation of atomic percentage.

[0079] Some embodiments may be embodied as a method, of which various examples have been described. The acts performed as part of the methods may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include different (e.g., more or less) acts than those that are described, and / or that may involve performing some acts simultaneously, even though the acts are shown as being performed sequentially in the embodiments specifically described above.

[0080] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0081] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMSWhat is claimed is:

1. An article, comprising: a first substrate comprising sapphire; a second substrate comprising niobium in physical contact with the first substrate; a third substrate comprising titanium in physical contact with the second substrate; and a photonic crystal positioned to emit radiation through the first substrate.

2. The article of claim 1, wherein the first substrate is substantially tube-shaped.

3. The article of any one of claims 1 or 2, wherein the first substrate defines an interior region.

4. The article of claim 3, wherein the interior region has a pressure less than or equal to 80 kPa.

5. The article of any one of claims 3 or 4, wherein the interior region comprises an inert gas.

6. The article of any one of claims 3-5, wherein the photonic crystal is positioned at least partially within the interior region of the first substrate.

7. The article of any one of claims 1-6, wherein the photonic crystal comprises Ta.

8. The article of any one of claims 1-7, wherein the second substrate is substantially tube-shaped.

9. The article of any one of claims 1-8, wherein the third substrate is substantially tube-shaped.

10. The article of any one of claims 1-9, wherein the photonic crystal is positioned on an inner substrate.

11. The article of claim 10, wherein the inner substrate comprises at least 90% of a metal superalloy.

12. The article of any one of claims 10-11, wherein the inner substrate comprises an Inconel alloy.

13. The article of any one of claims 10-12, wherein the inner substrate is substantially tube-shaped.

14. The article of any one of claims 10-13, wherein the photonic crystal is positioned on at least a portion of a surface of the inner substrate.

15. The article of any one of claims 1-14, further comprising a photovoltaic cell positioned to receive radiation passing through the sapphire.

16. An article, comprising: a first substrate comprising sapphire and defining an interior region having a pressure of less than or equal to 80 kPa; a second substrate comprising niobium in physical contact with the first substrate; and a third substrate comprising titanium in physical contact with the second substrate.

17. An article, comprising: a first substrate comprising sapphire; a second substrate comprising niobium in physical contact with the first substrate; a third substrate comprising titanium in physical contact with the second substrate; and a thermophotovoltaic cell positioned to receive radiation passing through the sapphire.

18. An article, comprising: a first substrate comprising an IR-transparent material and having a first coefficient of thermal expansion; a second substrate in physical contact with the first substrate and having a second coefficient of thermal expansion, wherein the second coefficient is between 0.9 and 1.1 times the first coefficient; a third substrate in physical contact with the second substrate and having a third coefficient of thermal expansion, wherein the third coefficient is between 0.8 and 1.2 times the second coefficient; and a photonic crystal positioned to emit radiation through the first substrate.

19. An article, comprising: a first substantially tube-shaped substrate comprising sapphire and defining an interior region; a second substantially tube-shaped substrate comprising niobium, bonded to an end portion of the first substrate; a third substantially tube-shaped substrate comprising titanium, bonded to an end portion of the second substrate; an inner substantially tube-shaped substrate, positioned at least partially within the interior region of the first substrate; a photonic crystal comprising Ta and able to emit radiation, the photonic crystal positioned on at least a portion of an outer surface of the inner substrate; and a thermophotovoltaic cell positioned to receive the radiation emitted by the photonic crystal passing through the sapphire, wherein the interior region of the first substrate has a pressure less than or equal to 80 kPa.

20. The article of claim 19, further comprising a heat source, positioned to heat the inner substrate.

21. A method, comprising: emitting radiation from a photonic crystal;passing the radiation through a region having a pressure less than or equal to 80 kPa; and passing the radiation through sapphire.

22. The method of claim 21, further comprising receiving the radiation on a photovoltaic cell.

23. The method of any one of claims 21-22, wherein the sapphire is present as a portion of a substrate that defines the region having a pressure less than or equal to 80 kPa.

24. The method of any one of claims 20-23, further comprising heating the photonic crystal to a temperature of at least 800 °C.

25. A method, comprising: providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa; and emitting radiation from a photonic crystal positioned at least partially within the interior region.

26. The method of claim 25, wherein the IR-transparent material comprises sapphire.

27. The method of claim 25-26, further comprising a second substrate comprising niobium in physical contact with the first substrate, and a third substrate comprising titanium in physical contact with the second substrate.

28. The method of claim 25-27, further comprising passing the radiation emitted from the photonic crystal through the IR-transparent material.

29. A method, comprising: providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa; andheating the interior region without increasing the pressure of the interior region above 300 kPa.

30. The method of claim 29, comprising heating the interior region by at least 800 °C.

31. The method of any one of claims 29 or 30, comprising heating the interior region to at least 800 °C.

32. A method, comprising: providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa; and heating the interior region without exposing the interior region to a gas external of the substrate.

33. The method of claim 32, comprising heating the interior region by at least 800 °C.

34. The method of any one of claims 32 or 33, comprising heating the interior region to at least 800 °C.

35. A method, comprising: providing a compartment at least partially defined by a first substrate comprising an IR-transparent material, the compartment defining an interior region having a pressure of less than or equal to 80 kPa; and heating the interior region without exposing the interior region to a gas having a pressure of 101.3 kPa.

36. The method of claim 35, comprising heating the interior region by at least 800 °C.

37. The method of any one of claims 35 or 36, comprising heating the interior region to at least 800 °C.

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