Effect of illlumination on thermionic emission from microfabricated silicon carbide structures

Lee, J.-H.; Bargatin, Igor; Provine, J.; Liu, F.; Seo, Myunghae; Maboudian, Roya; Brongersma, Mark L.; Melosh, Nicholas A.; Shen, Zhi‐Xun; Howe, Roger T.

doi:10.1109/transducers.2011.5969879

Cited by 16 publications

(28 citation statements)

References 2 publications

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“…It was early discovered that electron emission from a partially cesium covered tungsten filament resulted in an increase in electron emission (Ito and Cappelli, 2012). This phenomenon of work function reduction due to adsorbed alkali-metal atoms is still exploited in thermionic conversion research and applications with more recent interest in solar or photo-enhanced thermionic conversion (Langmuir and Kingdon, 1925;El-Genk and Momozaki, 2002;Zhang et al, 2003;Ogino et al, 2004;Lee et al, 2009;Makdisi et al, 2014). An extensive experimental investigation of various metal work functions under cesium coverage is presented in Table 2 ( Reck et al, 2014).…”

Section: Novel Materials For Thermionic Converter Electrodes Work Funmentioning

confidence: 99%

Advances in Thermionic Energy Conversion through Single-Crystal n-Type Diamond

Koeck

Nemanich

2017

Front. Mech. Eng.

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Thermionic energy conversion, a process that allows direct transformation of thermal to electrical energy, presents a means of efficient electrical power generation as the hot and cold side of the corresponding heat engine are separated by a vacuum gap. Conversion efficiencies approaching those of the Carnot cycle are possible if material parameters of the active elements at the converter, i.e., electron emitter or cathode and collector or anode, are optimized for operation in the desired temperature range. These parameters can be defined through the law of Richardson-Dushman that quantifies the ability of a material to release an electron current at a certain temperature as a function of the emission barrier or work function and the emission or Richardson constant. Engineering materials to defined parameter values presents the key challenge in constructing practical thermionic converters. The elevated temperature regime of operation presents a constraint that eliminates most semiconductors and identifies diamond, a wide band-gap semiconductor, as a suitable thermionic material through its unique material properties. For its surface, a configuration can be established, the negative electron affinity, that shifts the vacuum level below the conduction band minimum eliminating the surface barrier for electron emission. In addition, its ability to accept impurities as donor states allows materials engineering to control the work function and the emission constant. Singlecrystal diamond electrodes with nitrogen levels at 1.7 eV and phosphorus levels at 0.6 eV were prepared by plasma-enhanced chemical vapor deposition where the work function was controlled from 2.88 to 0.67 eV, one of the lowest thermionic work functions reported. This work function range was achieved through control of the doping concentration where a relation to the amount of band bending emerged. Upward band bending that contributed to the work function was attributed to surface states where lower doped homoepitaxial films exhibited a surface state density of ∼3 × 10 11 cm −2 . With these optimized doped diamond electrodes, highly efficient thermionic converters are feasible with a Schottky barrier at the diamond collector contact mitigated through operation at elevated temperatures.

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Section: Novel Materials For Thermionic Converter Electrodes Work Funmentioning

confidence: 99%

Advances in Thermionic Energy Conversion through Single-Crystal n-Type Diamond

Koeck

Nemanich

2017

Front. Mech. Eng.

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“…There is a growing demand for devices made from a thin layer of SiC on a substrate [1][2][3] to enable lower-cost research in harsh environment MEMS applications. For example, we have recently been exploring the use of SiC structures for applications in thermionic energy converters (TECs), which can convert heat or solar energy directly to electricity.…”

Section: Introductionmentioning

confidence: 99%

“…For example, we have recently been exploring the use of SiC structures for applications in thermionic energy converters (TECs), which can convert heat or solar energy directly to electricity. [3][4][5] Microfabricated TECs include high-temperature components that need to be suspended to keep them electrically and thermally isolated from the substrate, which is typically close to room temperature. This suspension and isolation can be easily achieved by using a silicon oxide sacrificial layer beneath the SiC structural layer.…”

Section: Introductionmentioning

confidence: 99%

“…This suspension and isolation can be easily achieved by using a silicon oxide sacrificial layer beneath the SiC structural layer. 3,4 For some applications, it is important that the SiC be single crystal. For example, photon-enhanced thermionic energy converters 3,5 need a low-defect single-crystal cathode to reduce recombination and increase the conversion efficiency.…”

Section: Introductionmentioning

confidence: 99%

“…3,4 For some applications, it is important that the SiC be single crystal. For example, photon-enhanced thermionic energy converters 3,5 need a low-defect single-crystal cathode to reduce recombination and increase the conversion efficiency. A potential approach to obtaining a singlecrystal film of SiC on buried oxide is epitaxial growth; however, to the best of our knowledge, there have been no reports of hetero-epitaxially grown SiC on top of oxidized silicon substrates.…”

Section: Introductionmentioning

confidence: 99%

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Smart-cut layer transfer of single-crystal SiC using spin-on-glass

Lee

Bargatin

Park

et al. 2012

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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The authors demonstrate "smart-cut"-type layer transfer of single-crystal silicon carbide (SiC) by using spinon-glass (SoG) as an adhesion layer. Using SoG as an adhesion layer is desirable because it can planarize the surface, facilitate an initial low temperature bond, and withstand the thermal stresses at high temperature where layer splitting occurs (800-900 °C). With SoG, the bonding of wafers with a relatively large surface roughness of 7.5-12.5 Å rms can be achieved. This compares favorably to direct (fusion) wafer bonding, which usually requires extremely low roughness (<2 >Å rms), typically achieved using chemical mechanical polishing (CMP) after implantation. The higher roughness tolerance of the SoG layer transfer removes the need for the CMP step, making the process more reliable and affordable for expensive materials like SiC. To demonstrate the reliability of the smart-cut layer transfer using SoG, we successfully fabricated a number of suspended MEMS structures using this technology. Smart-cut layer transfer of single-crystal SiC using spin-on-glass The authors demonstrate "smart-cut"-type layer transfer of single-crystal silicon carbide (SiC) by using spin-on-glass (SoG) as an adhesion layer. Using SoG as an adhesion layer is desirable because it can planarize the surface, facilitate an initial low temperature bond, and withstand the thermal stresses at high temperature where layer splitting occurs (800-900 C). With SoG, the bonding of wafers with a relatively large surface roughness of 7.5-12.5 Å rms can be achieved. This compares favorably to direct (fusion) wafer bonding, which usually requires extremely low roughness (<2 Å rms), typically achieved using chemical mechanical polishing (CMP) after implantation. The higher roughness tolerance of the SoG layer transfer removes the need for the CMP step, making the process more reliable and affordable for expensive materials like SiC. To demonstrate the reliability of the smart-cut layer transfer using SoG, we successfully fabricated a number of suspended MEMS structures using this technology. Disciplines Mechanical Engineering

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Impact of thermal contact resistances on micro-gap heat losses for microthermionic power generators

Belbachir

Ono

2015

Microsyst Technol

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Effect of illlumination on thermionic emission from microfabricated silicon carbide structures

Cited by 16 publications

References 2 publications

Advances in Thermionic Energy Conversion through Single-Crystal n-Type Diamond

Advances in Thermionic Energy Conversion through Single-Crystal n-Type Diamond

Smart-cut layer transfer of single-crystal SiC using spin-on-glass

Impact of thermal contact resistances on micro-gap heat losses for microthermionic power generators

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