Article
Chemistry, Multidisciplinary
Machi Kanna, Hikaru Oyama, Tomoyuki Ichikawa, Keita Yamamoto, Hiroki Miyaoka, Yoshitsugu Kojima, Takayuki Ichikawa
Summary: NaBH4 does not absorb NH3 below 100 kPa, while LiBH4 absorbs NH3 at lower pressures. Mixed borohydrides demonstrate a synergistic phenomenon where they absorb NH3 at low pressures and liquefy above 100 kPa. The kinematic viscosity of the liquefied state changes during NH3 absorption.
CHEMICAL COMMUNICATIONS
(2021)
Article
Chemistry, Physical
J. Paez-Ornelas, R. Ponce-Perez, H. N. Fernandez-Escamilla, E. Murillo-Bracamontes, H. A. Borbon-Nunez, Joseph P. Corbett, Ma Guadalupe Moreno Armenta, J. Guerrero-Sanchez
Summary: Theoretical models identified two stable reconstructions for oxygen-poor limits with oxygen vacancies, potentially explaining the experimentally observed (1 x 3) reconstruction. The striped pattern from the double oxygen vacancy model is consistent with experimental measurements, supporting the formation of Zn atomic wires in the [1000] direction.
JOURNAL OF PHYSICAL CHEMISTRY C
(2021)
Article
Materials Science, Multidisciplinary
Fatima Al-Quaiti, Alexander A. Demkov
Summary: Using density functional theory, the study examines the surface reconstructions and electronic properties of bulk-terminated GaN (0001), concluding that a laterally contracted Ga bilayer is the most energetically favorable surface arrangement under Ga-rich conditions. The study also suggests LaGa2 and LaN as potential materials for forming a transition layer to facilitate epitaxial integration of oxides on GaN.
PHYSICAL REVIEW MATERIALS
(2021)
Article
Chemistry, Physical
Davide Ripepi, Boaz Izelaar, Dylan D. van Noordenne, Peter Jungbacker, Martin Kolen, Pranav Karanth, Daniel Cruz, Patrick Zeller, Virginia Perez-Dieste, Ignacio J. Villar-Garcia, Wilson A. Smith, Fokko M. Mulder
Summary: Hydrogen permeable electrodes are a promising route for sustainable ammonia synthesis. The interaction of adsorbing N and permeating H at the catalytic interface is critical for the optimization of this process. The study shows that Ni oxide surface layer blocks the chemisorption of gaseous dinitrogen, but electrochemically driven permeating atomic hydrogen effectively reduces the Ni surface at ambient temperature. Surface oxide and nitride on iron block the H permeation, while on ruthenium, the stronger Ru-N bond favors the recombination of permeating hydrogen to H2 over the hydrogenation of adsorbed nitrogen.
Article
Chemistry, Multidisciplinary
Remi Cavallotti, Jacek Goniakowski, Gregory Cabailh, Remi Cavallotti, Jacques Jupille, Nicolas Trcera, Pierre Lagarde
Summary: This paper investigates the atomic structure of the Ag/alpha-Al2O3(0001) interface using X-ray absorption spectroscopy and numerical simulations. The results show that the structure of Ag clusters changes with decreasing cluster size, and the adhesion energy at the interface decreases accordingly.
Article
Energy & Fuels
Yaxin Liu, Hong Zhang, Xinlu Cheng
Summary: In this study, the catalytic potential of boron nitride nanotubes (BNNTs) embedded with transition-metal (TM) atoms as electrocatalysts for nitrogen reduction reaction (NRR) was systematically explored. Three single-atom catalysts (SACs) and two dual-atom catalysts (DACs) were selected through density functional theory (DFT) calculations. The results showed that Fe/BNNT, Mn/BNNT, and Pd/BNNT have good catalytic activity for N-2 reduction to NH3, and FeFe/BNNT and MnMn/BNNT can significantly improve the catalytic performance. This work provides a new idea for constructing high-efficiency electrocatalysts with BNNT as a new carrier.
Article
Physics, Applied
Kenta Chokawa, Kenji Shiraishi, Atsushi Oshiyama
Summary: First-principles molecular dynamics simulations revealed that dangling bonds are completely absent at the interfaces of amorphous mixed oxide and GaN polar surfaces. This indicates the superiority of the mixed oxide films for use as gate oxides in GaN-metal-oxide-semiconductor field effect transistors.
APPLIED PHYSICS LETTERS
(2021)
Article
Chemistry, Multidisciplinary
Aneesa Ahmad, Natalia Martsinovich
Summary: The study shows that certain organic functional groups, particularly amine, amide, and carboxylic acids, bind more strongly to the α-Al2O3(0001) surface than water, suggesting their potential adsorption on this mineral surface under ambient conditions and providing stability for adsorbed OC.
Article
Physics, Applied
Ranim Mohamad, Pierre Ruterana
Summary: First-principle calculations were used to investigate the adsorption and diffusion of indium and aluminum atoms on (0001) and (0001) In (18%) AlN surfaces. The results showed that the surfaces are most stable when complex defects are present, with indium strongly bound to the surface in the presence of vacancies. The enhanced diffusion of indium and limited diffusion of aluminum around defects may contribute to the crystallographic degradation observed in InAlN epitaxial layers during epitaxial growth.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Chemistry, Physical
Bo Han, Yuxiao Jia, Jianchuan Wang, Xuezhang Xiao, Lixin Chen, Lixian Sun, Yong Du
Summary: In this work, the structural and kinetic properties of pure and Ti-doped Mg(0001)/MgH2(110) interfaces were studied using first principles methods. It is found that Ti doping can improve the stability of the interface, promote hydrogen atom migration, and enhance the hydrogen desorption process mainly within the interface.
JOURNAL OF MATERIALS CHEMISTRY A
(2023)
Article
Chemistry, Multidisciplinary
Remi Lazzari, Jacek Goniakowski, Gregory Cabailh, Remi Cavallotti, Jacques Jupille, Nicolas Trcera, Pierre Lagarde
Summary: This paper investigates the atomic structure of the Ag/alpha-Al2O3(0001) interface and reveals the size-dependent interface structure and properties. The experimental results show that as the size of Ag clusters decreases, the Ag-Ag distance and coordination number decrease. At low coverage, Ag atoms predominantly sit on Al sites to form buckled monolayer-thick islands.
Article
Chemistry, Physical
Mukesh Singh, Alok Shukla, Brahmananda Chakraborty
Summary: In this study, the hydrogen-storage properties of Zr-decorated g-graphyne monolayer were investigated using Density Functional Theory (DFT). The results predict that each Zr atom can adsorb up to seven H2 molecules with a hydrogen gravimetric density of 7.95 wt% and a desorption temperature of 574 K, making it suitable for fuel-cell applications. The strong attachment between decorated Zr atom and graphyne sheet is due to charge transfer, while hydrogen molecules adsorb on Zr decorated graphyne through Kubas type of interactions. The stability of Zr+g-graphyne was confirmed through ab-initio molecular dynamics simulations. Overall, these findings suggest that Zr functionalized on g-graphyne could be a promising solid-state hydrogen storage material.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2023)
Article
Chemistry, Physical
Alejandra Granja-DelRio, Maite Alducin, J. Inaki Juaristi, Maria J. Lopez, Julio A. Alonso
Summary: Experimental evidence shows that doping porous carbons with metal nanoparticles, such as palladium, enhances the hydrogen storage capacity. However, simulations reveal that high activation barriers prevent hydrogen spillover from anchored Pd clusters to the carbon substrate, as hydrogen atoms prefer to absorb within the Pd cluster rather than migrate to the carbon substrate.
APPLIED SURFACE SCIENCE
(2021)
Article
Nanoscience & Nanotechnology
Sean Brown, Saleh Ahmat Ibrahim, Brandon R. Robinson, Ashley Caiola, Sarojini Tiwari, Yuxin Wang, Debangsu Bhattacharyya, Fanglin Che, Jianli Hu
Summary: A novel reactor methodology was developed for chemical looping ammonia synthesis using microwave plasma for pre-activation of dinitrogen. The reactions benefit from higher production of activated species, modularity, quick startup, and lower voltage input. Simple, economical, and environmentally benign metallic iron catalysts were used, and both surface mediated and bulk-mediated reaction domains were found to exist. Transition metal catalysts and their kinetics were also evaluated.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Thermodynamics
Qi Wang, Xuetao Shi, Xiaoyuan Zhang, Can Shao, S. Mani Sarathy
Summary: In recent years, the blending of ammonia with hydrocarbons as a carbon-neutral fuel additive has gained attention. However, the chemical effects of blending ammonia with hydrocarbons, particularly on polycyclic aromatic hydrocarbon (PAH) formation, are not well understood. This study systematically investigates the reaction pathways of nitrogen-containing polycyclic aromatic compounds (NPACs) and their comparison with the hydrogen-abstraction-acetylene (HACA) mechanism. The findings suggest that while the formation of nitrogen-embedded PAHs is less favored at high temperatures, a substantial amount of NPACs can still be formed.
COMBUSTION AND FLAME
(2023)
Article
Materials Science, Multidisciplinary
Pawel Strak, Ashfaq Ahmad, Pawel Kempisty, Jacek Piechota, Konrad Sakowski, Grzegorz Nowak, Yoshihiro Kangawa, Jan Lazewski, Stanislaw Krukowski
Summary: Ab initio calculations were used to investigate the physical properties of AlN(0001) surface under Al coverage, revealing the adsorption behavior and energy dependence on coverage for Al adatoms. The adlayer undergoes structural changes from disordered and corrugated to ordered and atomically flat with increasing Al coverage, affecting the Al bonding energy. Thermodynamic analysis identified equilibrium regions with Al vapor, crucial for physical vapor transport AlN growth.
COMPUTATIONAL MATERIALS SCIENCE
(2022)
Article
Physics, Condensed Matter
Akira Kusaba, Romeo Marcel Kurniawan, Pawel Kempisty, Yoshihiro Kangawa
Summary: Understanding the impact of magnesium doping on the unintentional oxygen incorporation into GaN and AlN during epitaxial growth is crucial for the development of optical and electronic devices. The study reveals that magnesium doping energetically promotes unintentional oxygen incorporation, even when complex defect structures are present. The mechanism is discussed based on charge neutrality or electron-counting model in the growth surface.
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS
(2022)
Article
Chemistry, Physical
Roman Hrytsak, Pawel Kempisty, Ewa Grzanka, Michal Leszczynski, Malgorzata Sznajder
Summary: This paper investigates the migration energy barriers of point defects in the AlN/GaN heterointerface and their effect on energy bands. It reveals that metal vacancies have a lower potential barrier to cross the interface compared to nitrogen vacancies, and demonstrates the electric field inversion effect in the presence of charged point defects. The findings contribute to the design and quality control of AlN/GaN heterostructures.
Article
Engineering, Electrical & Electronic
Kacper Sierakowski, Rafal Jakiela, Michal Fijalkowski, Tomasz Sochacki, Malgorzata Iwinska, Pawel Kempisty, Marcin Turek, Michal Bockowski
Summary: The diffusion of beryllium in gallium nitride crystals grown in non-polar crystallographic directions was investigated. The diffusion profiles were found to be box-shaped and pre-exponential factors and activation energies were determined. A model based on point defect complexes was proposed to explain the profiles and visible differences between the two directions.
MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING
(2022)
Article
Chemistry, Physical
Kamil Koronski, Krzysztof P. Korona, Serhii Kryvyi, Aleksandra Wierzbicka, Kamil Sobczak, Stanislaw Krukowski, Pawel Strak, Eva Monroy, Agata Kaminska
Summary: This paper presents a comparative analysis of the optical properties of non-polar and polar GaN/AlGaN multi-quantum well (MQW) structures using time-resolved photoluminescence (TRPL) and pressure-dependent studies. The results show that the lack of internal electric fields in non-polar structures leads to an improved electron and hole wavefunction overlap, resulting in shorter decay times. On the other hand, polar structures with electric fields exhibit reduced emission energy and wavefunction overlap, leading to a decrease in recombination rate with increasing well width. The study also explores the energy dependence of radiative and non-radiative recombination processes and the influence of electric fields on pressure behavior.
Article
Physics, Applied
Ashfaq Ahmad, Pawel Strak, Pawel Kempisty, Konrad Sakowski, Jacek Piechota, Yoshihiro Kangawa, Izabella Grzegory, Michal Leszczynski, Zbigniew R. Zytkiewicz, Grzegorz Muziol, Eva Monroy, Agata Kaminska, Stanislaw Krukowski
Summary: This work investigates the emergence of polarization doping in AlxGa1-xN layers with graded composition from a theoretical viewpoint. It shows that bulk electric charge density emerges in the graded concentration region and obtains the relation between the polarization bulk charge density and the concentration gradient. The study also demonstrates that a mobile charge appears due to the increase of the distance between opposite polarization-induced charges.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Ashfaq Ahmad, Pawel Strak, Konrad Sakowski, Jacek Piechota, Pawel Kempisty, Agata Kaminska, Stanislaw Krukowski
Summary: Ab initio simulations were used to study the properties of GaN/AlN superlattices with different widths for the first time. The results revealed significant differences between polar and nonpolar systems in terms of band diagrams, bandgaps, and oscillator strengths.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Multidisciplinary
Roman Hrytsak, Pawel Kempisty, Michal Leszczynski, Malgorzata Sznajder
Summary: This paper investigates the mechanism behind the 'green gap' problem and demonstrates that the Kirkendall effect may contribute to the thermal decomposition of InGaN/GaN MQWs structures.
NEW JOURNAL OF PHYSICS
(2022)
Article
Chemistry, Physical
Ashfaq Ahmad, Pawel Strak, Pawel Kempisty, Konrad Sakowski, Jacek Piechota, Yoshihiro Kangawa, Izabella Grzegory, Michal Leszczynski, Zbigniew R. R. Zytkiewicz, Grzegorz Muziol, Eva Monroy, Agata Kaminska, Stanislaw Krukowski
Summary: Polarization doping in a GaN-InN system with a graded composition layer was studied using ab initio simulations. The electric charge volume density in the graded concentration part was determined by spatial potential dependence. The polarization difference in the GaN-InN system was changed by piezoelectric effects and showed potential applications in blue and green laser and light-emitting diode design.
Article
Chemistry, Physical
Jacek Piechota, Stanislaw Krukowski, Bohdan Sadovyi, Petro Sadovyi, Sylwester Porowski, Izabella Grzegory
Summary: This study investigates the behavior of GaN crystal at high temperatures and pressures, revealing that it undergoes thermal decomposition and congruent melting. Simulation results are in excellent agreement with experimental data, providing valuable insights into the physical properties of GaN.
CHEMISTRY OF MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Pawel Kempisty, Ashfaq Ahmad, Pawel Strak, Konrad Sakowski, Anna Kafar, Jacek Piechota, Stanislaw Krukowski
Summary: Indium incorporation on the GaN surface was analyzed in the context of InGaN growth by MOVPE. The results showed that the adsorption energy strongly depends on the electronic properties of the surface, and the increase in hydrogen pressure leads to an increase in the equilibrium pressures of indium, resulting in reduced indium incorporation.
COMPUTATIONAL MATERIALS SCIENCE
(2023)
Article
Physics, Applied
S. Zoino, L. Borowik, B. Mohamad, E. Nowak, P. Kempisty
Summary: The formation of a two-dimensional electron gas (2DEG) at the GaN (0001)/AlN interface holds significant implications for GaN-based high-voltage and high-frequency (RF) devices. Recent ab initio simulations shed light on the role of polarizations in driving the formation of the 2DEG, and the study also investigates the impact of fixed charges and additional layers on the carrier concentration.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Physical
Pawel Kempisty, Karol Kawka, Akira Kusaba, Yoshihiro Kangawa
Summary: This paper presents an improved theoretical view of ab initio thermodynamics for polar GaN surfaces under gallium-rich conditions. The study uses density functional theory (DFT) calculations to systematically investigate the adsorption of gallium atoms on GaN polar surfaces, starting from the clean surface and progressing to the metallic multilayer. The analysis confirms that a monolayer of Ga adatoms on the GaN(000-1) surface is highly stable over a wide range of temperatures and provides a better thermodynamic description of the surface state under conditions typical for molecular beam epitaxy.