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Your search keyword '"Rafael Gutierrez"' showing total 10 results
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10 results on '"Rafael Gutierrez"'

1. First principles study of field effect device through van der Waals and lateral heterostructures of graphene, phosphorene and graphane

Author

C. Rebolledo Espinoza, Rafael Gutierrez, Arezoo Dianat, Dmitry A. Ryndyk, and Gianaurelio Cuniberti

Subjects
Materials science, business.industry, Graphene, Band gap, Materials Science (miscellaneous), Schottky barrier, Field effect, Heterojunction, law.invention, chemistry.chemical_compound, Phosphorene, Tight binding, chemistry, Mechanics of Materials, law, Chemical Engineering (miscellaneous), Optoelectronics, Graphane, business
Abstract

Chemical modification and vertical stacking of two-dimensional materials are promising techniques for new nanoelectronic devices. We present Density Functional Tight Binding (DFTB) calculations of a field-effect device, based on lateral and vertical heterostructures of 2D materials. The device consists of a phosphorene channel protected by graphene sheets, which work as contacts and are divided into the source and drain by local hydrogenation of graphene, which gives insulating graphane. In this device composed of only 3 layers, single sheets of graphene-graphane can work as both leads and oxide gate, while also acting as protective layers for a phosphorene channel. We show how for perfect vdW heterostructures of graphane/phosphorene/graphane and graphene/phosphorene/graphene the Schottky barrier is deeply influenced by normal electric fields, and we characterize electronic transport of such a device. Finally, we characterize phosphorene channel doping and defects, which, at very high densities in the transport direction, enables transport inside the phosphorene bandgap.

Published
2022
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2. Organ doses in paediatric interventional cardiology. First values for patients in Costa Rica

Author

Diego Nocetti, Viviana Retana, Rafael Gutierrez, Luisa Salazar, Cristian Reyes, and Carlos Ubeda

Subjects
Paediatric cardiology, medicine.medical_specialty, Radiation, Interventional cardiology, business.industry, Monte carlo code, medicine, Dosimetry, Radiology, business, Paediatric patients
Abstract

The aim of this paper was to present the results of organ dose for paediatric patients in respect of diagnostic and therapeutic interventional cardiology procedures grouped by age and weight in Costa Rica. The data collection period was from July 2017 to July 2018. Monte Carlo software was used to calculate organ dose. The three organs for which the highest mean dose and range dose was recorded were lungs (9.5 mGy and 0.57 mGy–355.73 mGy), oesophagus (5.0 mGy and 0.36 mGy–167.88 mGy) and breast (5.0 mGy and 0.19 mGy–52.06 mGy) independent the type of procedure. The ranges of mean organ dose values by age and weight band and divided into procedure type were 0.03 (brain, 5–9 years) to 8.70 mGy (lungs, 1–4 years) for diagnostic procedures and 0.08 (brain

Published
2019
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3. Time-dependent framework for energy and charge currents in nanoscale systems

Author

Gianaurelio Cuniberti, Rafael Gutierrez, Thomas Lehmann, and Alexander Croy

Subjects
Range (particle radiation), Condensed Matter - Mesoscale and Nanoscale Physics, Chemistry, Charge current, Energy current, FOS: Physical sciences, General Physics and Astronomy, Charge (physics), 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, Mesoscale and Nanoscale Physics (cond-mat.mes-hall), 0103 physical sciences, Nano, Statistical physics, Physical and Theoretical Chemistry, 010306 general physics, 0210 nano-technology, Nanoscopic scale, Energy (signal processing)
Abstract

The calculation of time-dependent charge and energy currents in nanoscale systems is a challenging task. Nevertheless it is crucial for gaining a deep understanding of the relevant processes at the nanoscale. We extend the auxiliary-mode approach for time-dependent charge transport to allow for the calculation of energy currents for arbitrary time dependencies. We apply the approach to two illustrative examples, a single-level system and a benzene ring, demonstrating its usefulness for a wide range of problems beyond simple toy models, such as molecular devices.

Published
2018
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4. The role of structural symmetry on proton tautomerization: A DFTB/Meta-Dynamics computational study

Author

Antonios Raptakis, Rafael Gutierrez, Arezoo Dianat, Alexander Croy, and Gianaurelio Cuniberti

Subjects
010304 chemical physics, Proton, Hydrogen, Chemistry, Dynamics (mechanics), Metadynamics, General Physics and Astronomy, Molecular electronics, chemistry.chemical_element, 010402 general chemistry, 01 natural sciences, Tautomer, 0104 chemical sciences, Chemical physics, 0103 physical sciences, Molecule, Physical and Theoretical Chemistry, Quantum
Abstract

Porphyrins, phthalocayanines and their derivatives have found interesting applications in various fields such as molecular electronics, optoelectronics, and sensorics. Common to this class of molecules with a metal-free core is the existence of hydrogen tautomerization reactions. Since the reaction only involves the motion of a pair of hydrogen atoms, it provides a rather simple, yet non-trivial test bed for advanced simulation tools. In this investigation, we exploit state-of-the-art quantum Metadynamics simulations complemented with Nudged Elastic Band (NEB) calculations, to study the effect of structural symmetry on the proton transfer tautomerism of functionalized porphyrins and porphyrazines. Calculated activation barriers using Metadynamics and NEB show a rather good quantitative agreement. We also demonstrate that the set of chosen collective variables in the Metadynamics simulations plays an important role for the appropriate description of the reaction path and dynamics of the system.

Published
2021
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5. Reverse breakdown behavior in organic pin-diodes comprising C60 and pentacene: Experiment and theory

Author

Hans Kleemann, Rafael Gutierrez, Gianaurelio Cuniberti, Karl Leo, Stanislav M. Avdoshenko, and Björn Lüssem

Subjects
Materials science, Zener effect, Organic solar cell, business.industry, General Chemistry, Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Biomaterials, Pentacene, Organic semiconductor, chemistry.chemical_compound, chemistry, Electric field, Materials Chemistry, OLED, Optoelectronics, Charge carrier, Zener diode, Electrical and Electronic Engineering, business
Abstract

Charge carrier transport under reverse voltage conditions is of major relevance in devices like organic photo-detectors, organic solar cells (tandem cells), organic light emitting diodes (generation contacts), and organic Zener diodes. We present organic pin-diodes comprising molecular doped layers of pentacene and C60 with an adjustable and reversible reverse breakdown behavior. We discuss the electric field and temperature dependence of the breakdown mechanism and propose a coherent charge transport scenario to describe the experimental findings. Within this model a field assisted tunneling of charge carriers over a rather large distance from valence to conductance states (and vice versa) governs the breakdown behavior. This is in accordance to experimental observations where charge carriers can overcome a layer thickness of 110 nm in the breakdown regime.

Published
2013
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6. Safety and tolerability of subcutaneous trastuzumab for the adjuvant treatment of human epidermal growth factor receptor 2-positive early breast cancer: SafeHer phase III study's primary analysis of 2573 patients

Author

Gligorov, J., primary, Ataseven, B., additional, Verrill, M., additional, De Laurentiis, M., additional, Jung, K.H., additional, Azim, H.A., additional, Al-Sakaff, N., additional, Lauer, S., additional, Shing, M., additional, Pivot, X., additional, Koroveshi, Dhurata, additional, Bouzid, Kamel, additional, Casalnuovo, Monica, additional, Cascallar, Diana, additional, Korbenfeld, Ernesto Pablo, additional, Bastick, Patricia, additional, Beith, Jane, additional, Colosimo, Maree, additional, Friedlander, Michael, additional, Ganju, Vinod, additional, Green, Michael, additional, Patterson, Kevin, additional, Redfern, Andrew, additional, Richardson, Gary, additional, Ceric, Timur, additional, Gordana, Kecman, additional, Beato, Carlos Augusto, additional, Ferrari, Marcela, additional, Hegg, Roberto, additional, Helena, Vanessa, additional, Ismael, Gustavo Fernando, additional, Lessa, Alvaro Edson, additional, Mano, Max, additional, Morelle, Alessandra, additional, Nogueira, Jose Alberto, additional, Timcheva, Konstanta, additional, Tomova, Antoaneta, additional, Tsakova, Maya, additional, Zlatareva-Petrova, Ani, additional, Asselah, Jamil, additional, Assi, Hazem, additional, Brezden-Masley, Christine, additional, Chia, Stephen, additional, Freedman, Ori, additional, Harb, Mohammed, additional, Joy, Anil Abraham, additional, Kulkarni, Swati, additional, Prady, Catherine, additional, Gaete, Alejandro Andres Acevedo, additional, Matamala, Luis, additional, Torres, Roberto, additional, Yanez, Eduardo, additional, Franco, Sandra, additional, Urrego, Marcela, additional, Gugić, Damir, additional, Vrbanec, Damir, additional, Melichar, Bohuslav, additional, Prausová, Jana, additional, Vyzula, Rostislav, additional, Pilarte, Rafael Gutierrez, additional, León, María Isabel, additional, Muñoz, Rene, additional, Ramos, Glenda, additional, Azeem, Hamdy Abdel, additional, Aziz, Amr Abdel, additional, El Zawahry, Heba, additional, Osegueda, Finlander Rosales, additional, Alexandre, Jerome, additional, Artignan, Xavier, additional, Barletta, Hugues, additional, Beguier, Emmanuel, additional, Berdah, Jean-François, additional, Marty, Chantal Bernard, additional, Bollet, Marc, additional, Bourgeois, Hugues, additional, Bressac, Claude, additional, Burki, Franck, additional, Campone, Mario, additional, Coeffic, David, additional, Cojocarasu, Oana Zveltlana, additional, Dagada, Corinne, additional, Dalenc, Florence, additional, Del Piano, Francesco, additional, Desauw, Christophe, additional, Desmoulins, Isabelle, additional, Dohollou, Nadine, additional, Egreteau, Joelle, additional, Ferrero, Jean-Marc, additional, Foa, Cyril, additional, Garidi, Reda, additional, Gasnault, Laurent, additional, Gligorov, Joseph, additional, Guardiola, Emmanuel, additional, Hamizi, Salima, additional, Jarcau, Rosana, additional, Jacquin, Jean-Philippe, additional, Jaubert, Dominique, additional, Jolimoy, Geneviève, additional, Mineur, Hortense Laharie, additional, Largillier, Remy, additional, Leduc, Bernard, additional, Martin, Philippe, additional, Melis, Adrien, additional, Monge, Jeremy, additional, Moullet, Isabelle, additional, Mousseau, Mireille, additional, Nguyen, Suzanne, additional, Orfeuvre, Hubert, additional, Petit, Thierry, additional, Pivot, Xavier, additional, Priou, Frank, additional, Bach, Isabelle Sillet, additional, Simon, Helene, additional, Stefani, Laetitia, additional, Uwer, Lionel, additional, Youssef, Ali, additional, Aktas, Bahriye, additional, von der Assen, Albert, additional, Augustin, Doris, additional, Balser, Christina, additional, Bauer, Lelia-Eveline, additional, Bechtner, Christina, additional, Beyer, Greta, additional, Brucker, Cosima, additional, Bückner, Ute, additional, Busch, Steffi, additional, Christensen, Bernd, additional, Deryal, Mustafa, additional, Farrokh, Andre, additional, Faust, Elke, additional, Friedrichs, Kay, additional, Graf, Heiko, additional, Griesshammer, Martin, additional, Grischke, Eva-Maria, additional, Hänle, Claudia, additional, Heider, Andrea, additional, Henschen, Stephan, additional, Hesse, Tobias, additional, Jackisch, Christian, additional, Kisro, Jens, additional, Köhler, Andreas, additional, Kuemmel, Sherko, additional, Lampe, Dieter, additional, Lantzsch, Tilmann, additional, Latos, Kunibert, additional, Lex, Benno, additional, Liedtke, Cornelia, additional, Luedders, Doerte, additional, Maintz, Christoph, additional, Müller, Volkmar, additional, Overkamp, Friedrich, additional, Park-Simon, Tjoung-won, additional, Paul, Marion, additional, Prechtl, Anita, additional, Ringsdorf, Uta, additional, Runnebaum, Ingo, additional, Ruth, Sylvia, additional, Salat, Christoph, additional, Scheffen, Iris, additional, Schilling, Jörg, additional, Schmatloch, Sabine, additional, Schmidt, Marcus, additional, Schneeweiss, Andreas, additional, Schrader, Iris, additional, Seipelt, Gernot, additional, Simon, Elke, additional, Stefek, Andrea, additional, Stickeler, Elmar, additional, Thill, Marc, additional, Tio, Joke, additional, Tuczek, Anna, additional, Warm, Mathias, additional, Weigel, Michael, additional, Wischnik, Arthur, additional, Wojcinski, Sebastian, additional, Ziegler-Löhr, Katja, additional, Aravantinos, Gerasimos, additional, Ardavanis, Alexandros, additional, Fountzilas, George, additional, Gogas, Helen, additional, Kakolyris, Stylianos, additional, Mavroudis, Dimitris, additional, Papadimitriou, Christos, additional, Papandreou, Christos, additional, Papazisis, Konstantinos, additional, Castro, Hugo, additional, Hernandez-Monroy, Cesar Estuardo, additional, Ngan, Roger, additional, Yeo, Winnie, additional, Bittner, Nora, additional, Boer, Katalin, additional, Csejtei, Andras, additional, Horvath, Zsolt, additional, Kocsis, Judit, additional, Mangel, László Csaba, additional, Mezei, Klara, additional, Nagy, Zsuzsanna, additional, Szanto, Janos, additional, Atmakusuma, Djumhana, additional, Fadjari, Heri, additional, Kurnianda, Djohan, additional, Prayogo, Nugroho, additional, Tanggo, Eddie Herman, additional, Coate, Linda, additional, Hennessy, Bryan, additional, Kelly, Cathy, additional, Martin, Michael, additional, Nasim, Saira, additional, O'Connor, Miriam, additional, Aieta, Michele, additional, Allegrini, Giacomo, additional, Amadori, Dino, additional, Bidoli, Paolo, additional, Biti, Giampaolo, additional, Bordonaro, Roberto, additional, Bottini, Alberto, additional, Carterni, Giacomo, additional, Cavanna, Luigi, additional, Cazzaniga, Marina, additional, Cognetti, Francesco, additional, Contu, Antonio, additional, Cruciani, Giorgio, additional, Donadio, Michela, additional, Falcone, Alfredo, additional, Farci, Daniele, additional, Forcignanò, R. Chiara, additional, Frassoldati, Antonio, additional, Gaion, Fernando, additional, Gamucci, Teresa, additional, Giotta, Francesco, additional, de Laurentiis, Michele, additional, Livi, Lorenzo, additional, Lorusso, Vito, additional, Maiello, Evaristo, additional, Marchetti, Paolo, additional, Mariani, Gabriella, additional, Mion, Marta, additional, Moscetti, Luca, additional, Musolino, Antonino, additional, Pazzola, Antonio, additional, Pedrazzoli, Paolo, additional, Pigi, Andrea, additional, de Placido, Sabino, additional, Caremoli, Elena Rota, additional, Santoro, Armando, additional, Tienghi, Amelia, additional, Ahn, Jin-Seok, additional, Jung, Kyung Hae, additional, Lee, Keun Seok, additional, Lee, Soo Hyeon, additional, Seo, Jae Hong, additional, Sohn, Joo-Hyuk, additional, Cesas, Alvydas, additional, Juozaityte, Elona, additional, Cheah, Nellie Lay Chin, additional, Chong, Flora Li Tze, additional, Devi, Beena C.R., additional, Phua, Vincent, additional, Teoh, Darren, additional, Ching, Lee Wei, additional, Yusof, Mastura, additional, Corona, Jorge, additional, Dominguez, Adriana, additional, Mendoza, René Lazaro González, additional, Hernandez, Carlos Alberto, additional, Ramiro, Alejandro Juarez, additional, Santos, Juan Matos, additional, Espinosa, Paola Morales, additional, Villarreal Garza, Cynthia Mayte, additional, Errihani, Hassan, additional, Bakker, Sandra, additional, van den Berkmortel, Franchette, additional, Blaisse, R.J.B., additional, Huinink, Daan ten Bokkel, additional, van den Bosch, J., additional, Braun, J.J., additional, Dercksen, M.W., additional, Droogendijk, Helga, additional, Erdkamp, Frans, additional, Haringhuizen, Annebeth, additional, de Jongh, F.E., additional, Kok, T.C., additional, Los, Maartje, additional, Madretsma, Stanley, additional, Terwogt, Jetske M. Meerum, additional, van der Padt, Annemieke, additional, van Rossum-Schornagel, Quirine Clementine, additional, Smilde, T.J., additional, de Valk, Bart, additional, van der Velden, Annette, additional, van Warmerdam, Laurence, additional, van de Wouw, A.J., additional, North, Richard, additional, Kersten, Christian, additional, Mjaaland, Ingvild, additional, Wist, Erik, additional, Aziz, Zeba, additional, Masood, Nehal, additional, Rashid, Kamran, additional, Shah, Mazhar, additional, Alcedo, Juan Carlos, additional, Aleman, Diana, additional, Neciosup, Silvia, additional, Reategui, Rocio, additional, Valdiviezo, Natalia, additional, Vera, Luis, additional, Fernando, Gracieux, additional, Roque, Fernando, additional, Strebel, Heinrik Martin, additional, Krzemieniecki, Krzysztof, additional, Litwiniuk, Maria, additional, Mruk, Andrzej, additional, Pienkowski, Tadeusz, additional, Sawrycki, Piotr, additional, Slomian, Grzegorz, additional, Tomczak, Piotr, additional, Afonso, Noemia, additional, Cardoso, Fátima, additional, Damasceno, Margarida, additional, Nave, Monica, additional, Badulescu, Florinel, additional, Ciule, Larisa, additional, Curescu, Stefan, additional, Eniu, Alexandru, additional, Filip, Dumitru, additional, Grecea, Daniela, additional, Jinga, Dan-Corneliu, additional, Lungulescu, Dan, additional, Oprean, Cristina Marinela, additional, Stanculeanu, Dana Lucia, additional, Turdean, Maria, additional, Dvornichenko, Viktoria, additional, Emelyanov, Sergey, additional, Lichinitser, Mikhail, additional, Manikhas, Alexey, additional, Sakaeva, Dina, additional, Shirinkin, Vadim, additional, Stroyakovskiy, Daniil, additional, Abulkhair, Omalkhair, additional, Zekri, Jamal, additional, Filipovic, Sladjana, additional, Kovcin, Vladimir, additional, Nedovic, Jasmina, additional, Pesic, Jasna, additional, Vasovic, Suzana, additional, Ng, Raymond, additional, Bystricky, Branislav, additional, Leskova, Jaroslava, additional, Mardiak, Jozef, additional, Mišurová, Etela, additional, Wagnerova, Maria, additional, Takač, Iztok, additional, Demetriou, Georgia Savva, additional, Dreosti, Lydia, additional, Govender, Poovandren, additional, Jordaan, Johannes Petrus, additional, Veersamy, Petrosian, additional, Romero, Jose Luis Alonso, additional, Lopez, Norberto Batista, additional, Arias, Carmen Cañabate, additional, Chacon, Jose, additional, Aramburo, Antonio Fernandez, additional, Morales, Luis Antonio Fernandez, additional, Garcia, Mirta, additional, Estevez, Laura Garcia, additional, Garcia-Palomo Perez, Andres, additional, Garcia Saenz, Jose Angel, additional, Garcia Sanchis, Laura, additional, Cubells, Laia Garrigos, additional, Cortijo, Lucia Gonzalez, additional, Santiago, Santiago Gonzalez, additional, De Aranguiz, Blanca Hernando Fernandez, additional, Mañas, José Juan Illarramendi, additional, Gallego, Pedro Jimenez, additional, Cussac, Antonio Llombart, additional, Ferrandiz, Cristina Llorca, additional, Garrido, Maria Lomas, additional, Alvarez, Pilar Lopez, additional, Vega, Jose Manuel Lopez, additional, Del Prado, Purificacion Martinez, additional, Jañez, Noelia Martinez, additional, Murillo, Serafin Morales, additional, Rosales, Adolfo Murias, additional, Jaso, Laura Murillo, additional, Fernandez, Ignacio Pelaez, additional, Martorell, Antonia Perello, additional, Carrion, Ramon Perez, additional, Simon, Sonia Pernas, additional, Alcibar, Arrate Plazaola, additional, Lorenzo, Jose Ponce, additional, Garcia, Vanesa Quiroga, additional, Asensio, Teresa Ramon y Cajal, additional, Maicas, Maria Dolores Torregrosa, additional, Villanueva Silva, Maria Jose, additional, Killander, Fredrika, additional, Svensson, Jan Henry, additional, Fehr, Mathias, additional, Hauser, Nik, additional, Müller, Andreas, additional, Pagani, Olivia, additional, Passmann-Kegel, Heike, additional, Popescu, Razvan, additional, Rabaglio, Manuela, additional, Rauch, Daniel, additional, Schlatter, Christina, additional, Zaman, Khalil, additional, Chang, Tsai-Wang, additional, Huang, Chiun-Sheng, additional, Wang, Hwei-Chung, additional, Yu, Jyh-Cherng, additional, Bandidwattanawong, Chanyoot, additional, Maneechavakajorn, Jedzada, additional, Seetalarom, Kasan, additional, Dejthevaporn, Thitiya (Sirisinha), additional, Somwangprasert, Areewan, additional, Vongsaisuwon, Mawin, additional, Akbulut, Hakan, additional, Altundag, Kadri, additional, Arican, Ali, additional, Bozcuk, Hakan, additional, Eralp, Yesim, additional, Idris, Mohamed, additional, Isikdogan, Abdurrahman, additional, Senol, Coskun Hasan, additional, Sevinc, Alper, additional, Uygun, Kazim, additional, Yucel, Eftal, additional, Yucel, Idris, additional, Yumuk, Fulden, additional, Shparyk, Yaroslav, additional, Voitko, Nataliia, additional, Jaloudi, Mohammed, additional, Adams, Jocelyn, additional, Agrawal, Rajiv, additional, Ahmed, Samreen, additional, Alhasso, Abdulla, additional, Allerton, Rozenn, additional, Anwar, Suhail, additional, Archer, Caroline, additional, Ashford, Richard, additional, Barraclough, Lisa, additional, Bertelli, Gianfilippo, additional, Bishop, Jill, additional, Branson, Tony, additional, Butt, Mohammed, additional, Chakrabarti, Amit, additional, Chakraborti, Prabir, additional, Churn, Mark, additional, Crowley, Clare, additional, Davis, Ruth, additional, Dhadda, Amandeep, additional, Eldeeb, Hany, additional, Fraser, Judith, additional, Hall, Julia, additional, Hickish, Tamas, additional, Hogg, Martin, additional, Howe, Theresa, additional, Joffe, Jonathan, additional, Kelleher, Muireann, additional, Kelly, Stephen, additional, Kendall, Anne, additional, Kristeleit, Hartmut, additional, Lumsden, Graeme, additional, Macmillan, Craig, additional, MacPherson, Iain, additional, Malik, Zafar, additional, Mithal, Natasha, additional, Neal, Anthony, additional, Panwar, Udaiveer, additional, Proctor, Andrew, additional, Proctor, Steven John, additional, Raj, Sanjay, additional, Rehman, Shazza, additional, Sandri, Ines, additional, Scatchard, Kate, additional, Sherwin, Elizabeth, additional, Sims, Eliot, additional, Singer, Julian, additional, Smith, Sarah, additional, Tahir, Saad, additional, Taylor, Wendy, additional, Tsalic, Medy, additional, Verrill, Mark, additional, Wardley, Andrew, additional, Waters, Simon, additional, Wheatley, Duncan, additional, Wright, Kathryn, additional, Yuille, Frances, additional, Alonso, Isabel, additional, Artagaveytia, Nora, additional, Rodriguez, Robinson, additional, Arbona, Esther, additional, Garcia, Yuraima, additional, Lion, Lorena, additional, Marcano, Dalila, additional, and Van Thuan, Tran, additional

Published
2017
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7. Stoichiometric and non-stoichiometric (101̄0) and (112̄0) surfaces in 2H–SiC: a theoretical study

Author

Th. Frauenheim, Rafael Gutierrez, J. Elsner, and E. Rauls

Subjects
Range (particle radiation), Materials science, General Chemistry, Condensed Matter Physics, Surface energy, Metal, Crystallography, Low energy, Chemical physics, visual_art, Materials Chemistry, visual_art.visual_art_medium, Density functional theory, Electronic band structure, Stoichiometry, Surface reconstruction
Abstract

We examine the atomic geometries, energetics and electrical properties of a variety of reconstructions at (1010) and (1120) surfaces in 2H–SiC using the density functional theory. In agreement with previous studies we find the stoichiometric surfaces to be semiconducting. However, the non-stoichiometric Si and C terminated reconstructions are found to be stable over a wide range of growth conditions. Some of these low energy surfaces show metallic-like character. They might, therefore, negatively influence the electrical properties of the material, if they occur as internal surfaces in extended defects, e.g. as micropipes or dislocations.

Published
1999
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8. A theoretical study of O chemisorption on GaN (0001)/(0001̄) surfaces

Author

R. Jones, M. Haugk, Rafael Gutierrez, J. Elsner, Th. Frauenheim, and Benjamin Hourahine

Subjects
Surface (mathematics), Chemistry, Stereochemistry, chemistry.chemical_element, General Chemistry, Condensed Matter Physics, Oxygen, Crystallography, Adsorption, Chemisorption, Monolayer, Materials Chemistry, Ideal surface, Layer (electronics), Surface reconstruction
Abstract

We present a theoretical study of atomic structures and formation energies for a variety of possible oxygen induced reconstructions at the GaN (0 0 0 1) and (0 0 0 1) surfaces. We find that at the nominally Ga terminated (0 0 0 1) surface a coverage of Θ O =0.375 ML on top of the ideal surface is stable. Only in a very oxygen rich environment a full monolayer of O can be adsorbed at the ideal surface. On top of the Ga atop structure at the (0 0 0 1) surface, which consists of a Ga layer on top of the ideal surface, a full monolayer of oxygen is stable. At the nominally N terminated (0 0 0 1) surface which is usually found to exhibit the Ga atop reconstruction the most stable surfaces have oxygen coverages of Θ O =0.75 ML and Θ O =1.0 ML depending on the oxygen chemical potential. In all stable structures O is exclusively bound to Ga.

Published
1998
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9. Ionization energies and Coulomb explosion of highly charged C60

Author

Gotthard Seifert, Rafael Gutierrez, and Rüdiger Schmidt

Subjects
Physics, Chemical ionization, Ionization, Coulomb explosion, General Physics and Astronomy, Thermal ionization, Physics::Atomic Physics, Molar ionization energies of the elements, Atomic physics, Electron ionization, Ion source, Ion
Abstract

Ionization energies and the dynamics of fragmentation processes in highly charged C60m+ ions (m = 1–20) are studied using density functional calculations combined with molecular dynamics. The calculated ionization potentials increase linearly with increasing charge, and the charged clusters with m > 16 explode in less than 1 ps into small fragments containing up to seven atoms. Structural formation takes place during fragmentation, leading to an even-odd pattern of the final mass distribution similar to that found experimentally in the laser vaporization of graphite.

Published
1996
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10. The influence of structural instabilities and non-linear electron-phonon coupling on the isotope effect

Author

Jürgen Hesse, Rafael Gutierrez, and Jürgen Schreiber

Subjects
Physics, Superconductivity, Coupling, Condensed matter physics, Transition temperature, Energy Engineering and Power Technology, Soft modes, Electron, Condensed Matter Physics, Instability, Electronic, Optical and Magnetic Materials, Condensed Matter::Superconductivity, Kinetic isotope effect, Electrical and Electronic Engineering, Lattice model (physics)
Abstract

In the framework of a two-component Φ 4 -lattice model structural phase transitions are considered. It was found that both long-range ordered phases and glassy-like states can be described in this model. On the basis of the standard Eliashberg theory the phonon-driven superconducting transition of electrons in a single band is investigated. To do this, the electron-phonon coupling is taken linear and quadratic in the fluctuations of the lattice order parameters. The dependence of the superconducting transition temperature and the isotope effect on the defect concentration is discussed for various parameter sets. Different qualitative features are obtained. Tje La 2− x Sr x CuO 4 is taken as a reference system.

Published
1994
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