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1. First-principles investigation of oxidized Si- and Ge-terminated diamond (100) surfaces.

Author

Gomez Jr., H., Cruz, J., Milne, C., Debnath, T., Birdwell, A. G., Garratt, E. J., Pate, B. B., Rudin, S., Ruzmetov, D. A., Weil, J. D., Shah, P. B., Ivanov, T. G., Lake, R. K., Groves, M. N., and Neupane, M. R.

Subjects
ELECTRON affinity, DIAMOND surfaces, POSITRONS, SEMICONDUCTOR materials, SURFACE stability
Abstract

Diamond is a semiconductor material with remarkable structural, thermal, and electronic properties that has garnered significant interest in the field of electronics. Although hydrogen (H) and oxygen (O) terminations are conventionally favored in transistor designs, alternative options, such as silicon (Si) and germanium (Ge), are being explored because of their resilience to harsh processing conditions during fabrication. Density-functional theory was used to examine the non-oxidized and oxidized group-IV (Si and Ge)-terminated diamond (100) surfaces. The (3 × 1) reconstructed surfaces feature an ether configuration and show relative stability compared with the bare surface. Hybrid-functional calculations of the electronic properties revealed reduced fundamental bandgaps (<1 eV) and lower negative electron affinities (NEAs) than those of H-terminated diamond surfaces, which is attributed to the introduction of unoccupied Si (Ge) states and the depletion of negative charges. Furthermore, oxidation of these surfaces enhanced the stability of the diamond surfaces but resulted in two structural configurations: ether and ketone. Oxidized ether configurations displayed insulating properties with energy gaps of ∼4.3 ± 0.3 eV, similar to H-terminated diamond (100) surfaces, whereas bridged ether configurations exhibited metallic properties. Oxidization of the metallic ketone configurations leads to the opening of relatively smaller gaps in the range of 1.1–1.7 eV. Overall, oxidation induced a shift from NEAs to positive electron affinities, except for the reverse-ordered ketone surface with an NEA of −0.94 eV, a value comparable to the H-terminated diamond (100) surfaces. In conclusion, oxidized group-IV-terminated diamond surfaces offer enhanced stability compared to H-terminated surfaces and display unique structural and electronic properties that are influenced by surface bonding. [ABSTRACT FROM AUTHOR]

Published
2024
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2. Effect of the Factor XIa Inhibitor Asundexian According to Baseline Infarct Pattern and on MRI Covert Infarct Outcomes

Author

Smith, Eric E., Shoamanesh, Ashkan, Xu, Lizhen, Heenan, Laura, Saad, Feryal, Colorado, Pablo, Chen, Chih-Hao, Lemmens, Robin, De Marchis, Gian Marco, Caso, Valeria, Masjuan, Jaime, Hirano, Teruyuki, Milanov, Ivan, Campbell, Bruce C.V., Mas, Jean-Louis, Connolly, Stuart J., Mundl, Hardi, Hart, Robert G., Bailey, P., Kleinig, T., Cordato, D., Choi, P., Garcia-Esperon, C., Chew, A., Cloud, G., Stanislaus, V., Krause, M., Priglinger, M., Grimley, R., Ghia, D., Sahathevan, R., Brown, H., Kwan, C., Devlin, M., Greisenegger, S., Bonelli-Nauer, S., Rath, J., Langer, A., Marko, M., Ferrari, J., Bernegger, A., Baumgartinger, M., Vigl, M., Krebs, S., Lang, W., Knoflach, M., Dejakum, B., Kiechl, S., Töll, T., Domig, L., Mutzenbach, J.S., Ganser, B., Hecker, C., Rösler, C., Bubel, N., Pikija, S., Zellner, T., Leitner, U., Berger, O., Surböck, B., Beirer, S., Staykov, D., Schrammel, D., Halilovic, A., Frattner, M., Barmherzigen, D., Lampl, C., Höfer, C., Nagl, S., Bocksrucker, C., Demeestere, J., Desfontaines, P., Ciobanu, C., De Pauw, A., Terwecoren, A., Hasenbroekx, M.C., Clement, F., De Klippel, N., Soors, P., Hermans, S., De Raedt, S., Vandervorst, F., Seynaeve, L., Fockaert, N., Smet, S., Rutgers, M., Del Gaudio, N., Paindeville, P., Staikov, I., Simeonova, A., Stoyanova, I., Cholakova, M., Mihnev, N., Petrova, T., Koralova, A., Dimov, D., Kuzev, Y., Danovska, M., Marinova, D., Marinova-Trifonova, D., Ovcharova, E., Mladenovski, I., Yanakieva, M., Stoev, P., Dimitrova, M., Todorova-Georgieva, S., Haralanov, L., Milkov, B., Solakov, D., Petkova, N., Ignatova-Valkova, V., Karabinov, V., Marinova, V., Miteva, Y., Andonova, V., Kasabova, D., Kostadinova, E., Shopova-Vrabcheva, Y., Gatev, D., Semova, D., Halil, E., Kaprelyan, A., Ivanov, B., Panov, G., Grudkova, M., Syuleyman, N., Kalpachki, R., Alexiev, F., Ivanova, I., Kancheva, K., Sakelarova, T., Maslarov, D., Drenska, D., Georgiev, V., Petrova, K., Petrova, N., Ivanova, I., Semerdjieva, N., Zhelyazkov, P., Spasova-Markova, S., Dong, X., Wang, D., Wang, S., Huang, W., Zhao, H., Wang, C., Jie, L., Xinyang, Y., Ping, Z., Dong, Q., Wang, Y., Fuling, Y., Yue, W., Liu, R., Yang, Y., Stetkarova, I., Mikulenka, P., Vasko, P., Peisker, T., Bar, M., Roubec, M., Mikulik, R., Cabukova, M., Vinklarek, J., Kovar, M., Pansky, M., Mencl, P., Skoda, O., Carek, M., Pernicka, M., Skodova, M., Geier, P., Cepkova, J., Drlik, J., Prax, T., Herzig, R., Krajickova, D., Vitkova, E., Haluskova, S., Vaclavik, D., Martinkova, J., Blejcharova, K., Tkacova, M., Pavlik, O., Nevšímalová, M., Rosol, J., Nevsimalova, M., Hruby, R., Iversen, H., Andersen, A.V., Rahimi, D., Christensen, H., Grundtvig, J., Hjort, N., Andersen, G., Sandal, B., Stilund, M., Modrau, B., Strade, A., Porobic, M., Andersen, S.D., Kruuse, C., Ölmestig, J., Kolmos, M., Parvez, A., Christensen, T., Stokholm, J., Jensen, H.B., Putaala, J., Strbian, D., Sibolt, G., Tiainen, M., Martinez-Majander, N., Curtze, S., Raty, S., Kraemer, Y., Roine, R., Aivo, J., Ruuskanen, J., Ylikotila, P., Roine, S., Hallikainen, M., Jakala, P., Kurl, S., Julkunen, V., Sibon, I., Olindo, S., Richard, S., Larrue, V., Gollion, C., Catala, H., Henon, H., Lucie, D.S., Nelly, D., Calvet, D., Malbranque, A., Mazé, B., Barbieux-Ghitu, C., Rosso, C., Samson, Y., Vannier, S., Moulin, T., Bonnet, L., Reiner, P., Buffon, F., Denier, C., Amri, K., Legris, N., Chassin, O., Selli, N., Mariana, S., Berrouschot, J., Stoll, A., Klunk, D., Keilitz, J., Neustadt, M., Zerrenner, S., Veltkamp, R., Hajjar, K., Heeger, A., Winezki, E., Apel, L., Pompsch, M., Mueller, P., Rappard, P., Auer, R., Ringleb, P.A., Berberich, A., Heyse, M., Mundiyanapurath, S., Reiff, T., Poli, S., Gomez-Exposito, A., Mengel, A., Tünnerhoff, J., Adeyemi, K., Poli, K., Kusch, V., Pelz, J., Michalski, D., Wartenberg, K., Althaus, K., Tavares, F., Mueller, S., Soda, H., Rascher, A., Hiermann, E., Weinhardt, R., Weissenborn, K., Leotescu, A., Grosse, G., Worthmann, H., Ernst, J., Gabriel, M., Schuppner, R., Schäfer, J.H., Charisse, D., Gruber, K., Kurka, N., Reitz, S.C., Pfeilschifter, W., Lee, J.I., Gliem, M., Moll, M., Steiner, T., Segura, L., Szegedi, N., Barandi, D., Uhrinakova, L., Czencz, M., Pasztor, M., Gyuker, N., Bartha, N.E., May, Z., Simony, Z., Szasz, G., Kakuk, I., Pető, N., Panczel, G.F., Olah, A., Racz, O., Balla, T., Horvath, B., Tuba, K., Czinderi, V., Klivenyi, P., Annus, A., Hertelendy, P., Szapary, L., Bosnyak, E., Kalmar, P., Karadi, Z., Cziba, L., Olah, L., Berki, A., Hudak, L., Kozák, M., Babel, S., Nemeth, L., Molnár, B., Simon, Z., Roveri, L., Cerri, F., Giacalone, G., Zini, A., Mauro, G., Asioli, G.M., Forlivesi, S., Arnone, G., Fiaccadori, A., Maria Fontana Francesca, E., Allegra, G., Mosconi, M.G., Longoni, M., Terlizzi, R., Paolucci, M., Tassi, R., Franci, B., Lucani, B., Domenichelli, C., Paoletti, D., Acampa, M., Zedde, M.L., Pezzella, F.R., Mangiardi, M., Galizia, P., Anticoli, S., Scalise, S., Lattanzi, S., Norata, D., Cannuccia, M., Cavallini, A., Federica, F., Denaro, M.F., Tosi, P., Sonoda, K., Kawajiri, M., Kusano, Y., Haraguchi, K., Kawano, H., Terasaki, T., Kaneko, C., Murase, S., Kumagai, M., Murai, N., Miyazaki, Y., Mori, T., Hatano, T., Kawanishi, M., Ochiai, J., Ishihara, S., Uehara, T., Yasaka, M., Nakagawa, H., Makino, M., Yonehara, T., Fukushima, Y., Hirotsune, N., Sakai, N., Yamasaki, M., Coutinho, J., Wouters, A., den Hertog, H., Zwartbol, R., Beumer, D., Kerklaan, J., Hilkens, P., Schreuder, T., Propper, D., Slowik, A., Wlodarczyk, E., Wrona, P., Pulyk, R., Lasek-Bal, A., Kosarz-Lanczek, K., Puz, P., Bilik, M., Magielska, A., Zamiela – Żółciak, A., Ochocinska, L., Bahdasaryan, S., Stępień, A., Dębiec, A., Joanna, K., Pawel, M., Jacek, S., Daniel, P., Marta, S., Rejdak, K., Wojczal, J., Luchowski, P., Fryze, W., Wisniewska, A., Krzyzanowska, M., Skowron, P., Wolosz, A., Galan, A., Grzymala, K., Krajewska, M., Nowak, R., Kłos, M., Cruz, V., Castro, P., Ferro, J., Canhão, P., Gouveia, R., Inácio, N., Rodrigues, M., Rachão, A., Ionel, C., Pereira, L., Viana-Baptista, M., Machado, C., Fernandes, C., Sargento, J., Inácio, N., Timchenko, L., Mironova, J., Zhadan, O., Torgashova, A., Bazhenova, O., Barashenkova, M., Kireeva, M., Romadina, N., Stepanova, I., Lenskaya, L., Lukinykh, L., Vorontsova, T., Agafina, A., Fedorova, A., Yashina, A., Alasheev, A., Smolkin, A., Prazdnichkova, E., Lutskovich, O., Gonysheva, Y., Mordvintseva, E., Nechaev, A., Martynova, E., Fedoraeva, N., Vishnyakova, T., Popov, D., Merzliakova, A., Margarita, K., Rechkalova, L., Ilyina, A., Kurenkova, N., Barbarash, O., Bazdyrev, E., Zvereva, T., Hromova, A., Morkvenas, A., Postnikova, E., Kovalenko, G., Taran, I., Pavlov, L., Ott, M., Chernitsova, N., Vodopyanova, N., Drozdova, E., Korebo, E., Lobanova, M., Lazareva, N., Snegova, N., Nikolaeva, O., Kolesnikov, Y., Kosheleva, Y., Krastev, G., Tomasova, K., Danis, M., Mako, M., Jankovicova, Z., Stevkova, Z., Kovacik, M., Kubikova, T., Jarosova, A., Serdahely, V., Cilingova, I., Pribulova, I., Sedlak, J., Slebodova, K., Paldaufova, M., Risnovsky, R., Berndtova, B., Urbanova, I., Junas, R., Karapetian, S., Gurcik, L., Vantrobova, A., Verbovsky, F., Vanacka, K., Ferenc, M., Galik, P., Bucakova, S., Ferencova, M., Kubalova, P., Boksanska, Z., Zacharova, E., Mahundi, E., Judita, H., Bachnak, M., Turcani, P., Kvasnicova Kamenska, A., Jurik, M., Vestenicka, V., Kycina, M., Sagatova, E., Dvorak, M., Hlubekova, A., Kucera, C., Gernath, L., Ferenc, M., Frimmelova, P., Slebodnikova, J., Aksteinerova, N., Horny, V., Gregova, Z., Segura, T., Romero, C., Ayo, O., Masjuan Vallejo, J., Cruz, A., De felipe, A, Matute, M.C., Garcia, S., Tembl Ferrairo, J., Vielba, I., Morales Caba, L., Molina, C., Garcia-Tornel García-Camba, Á., Requena Ruiz, M., Noelia, R., Rodriguez-Yañez, M., Rodriguez Castro, E., Lopez, I., Santamaria, M., Arias, S., Purroy García, F., Vázquez Justes, D., Mauri Capdevila, G., Vicente Pascual, M., Martí Fabregas, J., Camps Renom, P., Rodríguez Campello, A., Giralt, E., Krupinski, J., Molina, J., Trillo Senin, C. Ramos Martin, S., De La Fuente Sanz, E., Moniche, F., Manuel, M.R., Pardo, B., Martínez, I., Hernández Pérez, M., Arenillas Lara, J.F., De Lera, M., Egido, J.A., Gomez Escalonilla, C., Guillan, M., Martinez, J., Lindgren, A., Andsberg, G., Wictor, L., Leonidou, M., Stenman, M., Dalberg, N., Laska, A.C., Grünfeldt, A., Lundström, A., Nadzjafov, E., Rooth, E., Dalenbring, I., Sandén, P., Johansson, E., Thomas, G., Zietz, A.V., Rudin, S., Dittrich, T.D., Lilian, K., Kägi, G., Vehoff, J., Arnold, M., Scutelnic, A., Clénin, L., Beyeler, M., Madlaine, M., Maamari, B., Siepen, B., Vynckier, J., Tarnutzer, A., Bertschi, D., Luciani, M., Cereda, C., Maulucci, F., Bianco, G., Shairin, S., Pihan, H.A., Salmen, S., Quinn, T., McAlpine, C., Wright, F., Kalladka, D., Taylor, E., Sohaa, J., Brown, Z., Dawson, J., Cameron, A., Muir, S., Dima, S., Khan, U., Zhang, L., Warburton, E., Chatterjee, K., Nallasivan, A., Curran, D., Haider, S., Ghani, U., Kenton, A., Dallol, B., Mirza, M., Menezes, B., Davies, R., Robinson, T.G., Manning, L., Sztriha, L., Phinney, T., Sethi, P., Altafullah, I., Sharaf, A., Ostrander, M., Renati, S., Burgin, W.S., Olds, K., Delio, P., Malek, A., Dissin, J., Khatri, P., Flaherty, M., Demel, S., and Dofitas, S.

Published
2024
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3. New Optical Gating Technique for Detection of Electric Field Waveforms with Subpicosecond Resolution

Author

Muraviev, A., Gutin, A., Rupper, G., Rudin, S., Shen, X., Yamaguchi, Y., Aizin, G., and Shur, M.

Subjects
Condensed Matter - Materials Science
Abstract

We report on the new optical gating technique used for the direct photoconductive detection of short pulses of terahertz radiation with the resolution up to 250 femtoseconds. The femtosecond optical laser pulse time delayed with respect to the THz pulse generated a large concentration of the electron hole pairs in the AlGaAs/InGaAs High Electron Mobility Transistor (HEMT) drastically increasing the conductivity on the femtosecond scale and effectively shorting the source and drain. This optical gating quenched the response of the plasma waves launched by the THz pulse and allowed us to reproduce the waveform of the THz pulse by varying the time delay between the THz and quenching optical pulses. The results are in excellent agreement with the electro-optic effect measurements and with our hydrodynamic model that predicts the ultra-fast transistor plasmonic response at the time scale much shorter than the electron transit time, in full agreement with the measured data.

Published
2016
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7. Entropy driven stabilization of energetically unstable crystal structures explained from first principles theory

Author

Souvatzis, P., Eriksson, O., Katsnelson, M. I., and Rudin, S. P.

Subjects
Condensed Matter - Statistical Mechanics
Abstract

Conventional methods to calculate the thermodynamics of crystals evaluate the harmonic phonon spectra and therefore do not work in frequent and important situations where the crystal structure is unstable in the harmonic approximation, such as the body-centered cubic (bcc) crystal structure when it appears as a high-temperature phase of many metals. A method for calculating temperature dependent phonon spectra self consistently from first principles has been developed to address this issue. The method combines concepts from Born's inter-atomic self-consistent phonon approach with first principles calculations of accurate inter-atomic forces in a super-cell. The method has been tested on the high temperature bcc phase of Ti, Zr and Hf, as representative examples, and is found to reproduce the observed high temperature phonon frequencies with good accuracy., Comment: 4 pages 2 figurs

Published
2008
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8. Classical potential describes martensitic phase transformations between the $\alpha$, $\beta$ and $\omega$ titanium phases

Author

Hennig, R. G., Lenosky, T. J., Trinkle, D. R., Rudin, S. P., and Wilkins, J. W.

Subjects
Condensed Matter - Materials Science
Abstract

A description of the martensitic transformations between the $\alpha$, $\beta$ and $\omega$ phases of titanium that includes nucleation and growth requires an accurate classical potential. Optimization of the parameters of a modified embedded atom potential to a database of density-functional calculations yields an accurate and transferable potential as verified by comparison to experimental and density functional data for phonons, surface and stacking fault energies and energy barriers for homogeneous martensitic transformations. Molecular dynamics simulations map out the pressure-temperature phase diagram of titanium. For this potential the martensitic phase transformation between $\alpha$ and $\beta$ appears at ambient pressure and 1200 K, between $\alpha$ and $\omega$ at ambient conditions, between $\beta$ and $\omega$ at 1200 K and pressures above 8 GPa, and the triple point occurs at 8GPa and 1200 K. Molecular dynamics explorations of the dynamics of the martensitic $\alpha-\omega$ transformation show a fast-moving interface with a low interfacial energy of 30 meV/\AA$^2$. The potential is applicable to the study of defects and phase transformations of Ti., Comment: 10 pages, 6 figures

Published
2007
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9. An Empirical Tight-Binding Model for Titanium Phase Transformations

Author

Trinkle, D. R., Jones, M. D., Hennig, R. G., Rudin, S. P., Albers, R. C., and Wilkins, J. W.

Subjects
Condensed Matter - Materials Science
Abstract

For a previously published study of the titanium hcp (alpha) to omega (omega) transformation, a tight-binding model was developed for titanium that accurately reproduces the structural energies and electron eigenvalues from all-electron density-functional calculations. We use a fitting method that matches the correctly symmetrized wavefuctions of the tight-binding model to those of the density-functional calculations at high symmetry points. The structural energies, elastic constants, phonon spectra, and point-defect energies predicted by our tight-binding model agree with density-functional calculations and experiment. In addition, a modification to the functional form is implemented to overcome the "collapse problem" of tight-binding, necessary for phase transformation studies and molecular dynamics simulations. The accuracy, transferability and efficiency of the model makes it particularly well suited to understanding structural transformations in titanium., Comment: 9 pages, 8 figures, 5 tables

Published
2005
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12. Tuning the configuration of quantum dot molecules grown on stacked multilayers of heteroepitaxial islands.

Author

Rudin, S. A., Zinovyev, V. A., Smagina, Zh. V., Novikov, P. L., Shklyaev, A. A., and Dvurechenskii, A. V.

Subjects
*QUANTUM dots, *SCANNING tunneling microscopy, *MOLECULAR beam epitaxy, *MONTE Carlo method, *MULTILAYERS, *MOLECULES
Abstract

Arrays of Ge quantum dot molecules were grown by molecular beam epitaxy using a template, composed of a multilayer structure with layers of vertically aligned three-dimensional (3D) Ge islands buried in an Si crystal matrix with the Si capping layer on top. Depending on preparation conditions, the molecules assume various configurations, including a square frame with [001]–[010]-oriented sides. It was shown by scanning tunneling microscopy that the 3D islands are located closer to the buried SiGe mound centers with the increase of the capping layer thickness. The mechanism of the quantum dot molecule formation is ascribed to strain relaxation. It was confirmed by Monte Carlo simulations of heteroepitaxial Ge growth on the template, containing the buried Ge mound. [ABSTRACT FROM AUTHOR]

Published
2022
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14. Leveraging patient-specific simulated angiograms to characterize cerebral aneurysm hemodynamics using computational fluid dynamics

Author

Chivukula, V, White, R, Shields, A, Davies, J, Mokin, M, Bednarek, D R, Rudin, S, and Ionita, C

Subjects
Article
Abstract

Cerebral aneurysms (CA) affect nearly 6% of the US population and its rupture is one of the major causes of hemorrhagic stroke. Neurointerventionalists performing endovascular therapy (ET) to treat CA rely on qualitative image sequences obtained under fluoroscopy guidance alone, and do not have access to crucial quantitative information regarding blood flow before, during and after treatment – partially contributing to a failure rate of up to 30%. Computational fluid dynamics (CFD) is a powerful tool that can provide a wealth of quantitative data; however, CFD has found limited utility in the clinic due to the challenges in obtaining hemodynamic boundary conditions for each patient. In this work, we present a novel CFD-based simulated angiogram approach (SAA) that resolves the blood flow physics and interaction between blood and injected contrast agent to extract quantitative hemodynamic parameters which can be used to design real-time parametric imaging analysis. The SAA enables correlating contrast agent transport to the underlying hemodynamic conditions via time-density curves (TDC) obtained at several points in the region of interest. The ability of the TDC and the SAA to provide critical hemodynamic parameters in and around CA anatomies, such as washout and local flow changes is explored and presented. This provides invaluable quantitative data to the clinician at the time of intervention, since it incorporates the physics of blood flow and correlates the contrast transport to hemodynamic parameters quantitatively – thereby enabling the clinician to take informed decisions that improve treatment outcomes.

Published
2022
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17. Sustained TREM2 stabilization accelerates microglia heterogeneity and Aβ pathology in a mouse model of Alzheimer’s disease

Author

Dhandapani R, Stefanie Joller, Marilisa Neri, Ivan Galimberti, Annick Waldt, Rachel Cuttat, Irena Brzak, Dominik Feuerbach, Rudin S, Guglielmo Roma, Derya R. Shimshek, Tatjana Schweizer, Ulf Neumann, Berth R, Caroline Gubser Keller, Mario Bernhard, Ulrike Naumann, and Fabrizio Gasparini

Subjects
Transcriptome, Genetically modified mouse, Pathology, medicine.medical_specialty, medicine.anatomical_structure, Microglia, Cell surface receptor, TREM2, Chemistry, Cell, medicine, Neuroinflammation, Transmembrane protein
Abstract

SummaryTREM2 is a transmembrane protein expressed exclusively in microglia in the brain that regulates inflammatory responses to pathological conditions. Proteolytic cleavage of membrane TREM2 affects microglial function and is associated with Alzheimer’s disease, but the consequence of reduced TREM2 proteolytic cleavage has not been determined. We generated a transgenic mouse model of reduced TREM2 shedding (Trem2-IPD) through amino acid substitution of ADAM-protease recognition site. We found that Trem2-IPD mice displayed increased TREM2 cell surface receptor load, survival and function in myeloid cells. Using single cell transcriptomic profiling of mouse cortex we show that sustained TREM2 stabilization induces a shift of fate in microglial maturation and accelerates microglial responses to Aβ pathology in a mouse model of Alzheimer’s disease. Our data indicate that reduction of TREM2 proteolytic cleavage aggravates neuroinflammation during the course of AD pathology suggesting that TREM2 shedding is a critical regulator of microglial activity in pathological states.

Published
2021
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23. Nucleation sites of Ge nanoislands grown on pit-patterned Si substrate prepared by electron-beam lithography.

Author

Smagina, Zh. V., Zinovyev, V. A., Rudin, S. A., Novikov, P. L., Rodyakina, E. E., and Dvurechenskii, A. V.

Subjects
NUCLEATION, MONTE Carlo method, ELECTRON beam lithography, NANOTECHNOLOGY, SUBSTRATES (Materials science)
Abstract

Regular pit-patterned Si(001) substrates were prepared by electron-beam lithography followed by plasma chemical etching. The geometry of the pits was controlled by varying the etching conditions and the electron-beam exposure duration. It was shown that the location of three-dimensional (3D) Ge nanoislands subsequently grown on the pit-patterned Si substrates depends on the shape of the pit bottom. In the case of pits having a sharp bottom, 3D Ge islands nucleate inside the pits. For pits with a wide flat bottom, the 3D Ge island nucleation takes place at the pit periphery. This effect is attributed to the strain relaxation depending not only on the initial pit shape, but also on its evolution during the Ge wetting layer deposition. It was shown by Monte Carlo simulations that in the case of a pit with a pointed bottom, the relaxation is most effective inside the pit, while for a pit with a wide bottom, the most relaxed area migrates during Ge deposition from the pit bottom to its edges, where 3D Ge islands nucleate. [ABSTRACT FROM AUTHOR]

Published
2018
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36. Theory and measurement of plasmonic terahertz detector response to large signals.

Author

Rudin, S., Rupper, G., Gutin, A., and Shur, M.

Subjects
*PLASMONS (Physics), *EXCITON theory, *DETECTORS, *FIELD-effect transistors, *FIELD-effect devices
Abstract

Electron gas in the conduction channel of a Field Effect Transistor (FET) can support collective plasma oscillations tunable by the gate voltage. In the Dyakonov-Shur terahertz (THz) detector, nonlinearities in the plasma wave propagation in the gated channel of a FET lead to a constant source-to-drain voltage providing the detector output. We present the detector theory in the frame of the hydrodynamic model using the electron plasma Navier-Stokes and thermal transport equations, thus fully accounting for the hydrodynamic non-linearity, the viscosity, and pressure gradients in the detector response. Both resonant and broadband operations of the high electron mobility transistor (HEMT) based plasmonic detectors are described by this model. The relation between the electron channel density and gate voltage was modeled by the unified charge control model applicable both above and below the threshold voltage. The theoretical results are compared with the response measured in the short channel InGaAs HEMT and the analytical approximation. The THz source was operating at 1.63 THz, and the response was measured at varying signal intensities. The response of the detector operated in the open drain mode was measured above and below the threshold, and the theoretical and experimental results are shown to be in good agreement. [ABSTRACT FROM AUTHOR]

Published
2014
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