A5088600905- Electronic and Structural Properties of Oxides
- Semiconductor materials and devices
- Chalcogenide Semiconductor Thin Films
- ZnO doping and properties
- Quantum Dots Synthesis And Properties
- Advanced Memory and Neural Computing
- Ferroelectric and Negative Capacitance Devices
- Copper-based nanomaterials and applications
- Catalytic Processes in Materials Science
- Advanced Photocatalysis Techniques
- Magnetic properties of thin films
- Advancements in Semiconductor Devices and Circuit Design
- nanoparticles nucleation surface interactions
- Magnesium Oxide Properties and Applications
- Quantum and electron transport phenomena
- Semiconductor materials and interfaces
- Magnetic Properties and Synthesis of Ferrites
- 2D Materials and Applications
- MXene and MAX Phase Materials
- Metal and Thin Film Mechanics
- X-ray Diffraction in Crystallography
- TiO2 Photocatalysis and Solar Cells
- Magnetic and transport properties of perovskites and related materials
- Iron oxide chemistry and applications
- Multiferroics and related materials
University of York
2015-2024
University of Leeds
2005-2022
Durham University
2022
University of Glasgow
2022
Natural History Museum
2022
Sci-Tech Daresbury
2022
Tohoku University
2009-2016
University College London
2007-2011
Institute for Materials Research, Tohoku University
2009-2011
London Centre for Nanotechnology
2007-2009
By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament (CF) features controlling TiN/HfO2/TiN resistive memory (RRAM) operations. The leakage current through the dielectric is found to be supported by oxygen vacancies, which tend segregate at hafnia grain boundaries. We simulate evolution of a path during forming operation employing multiphonon trap-assisted tunneling (TAT) electron transport model. process analyzed...
The diffusion and segregation of oxygen vacancies near a grain boundary in m-HfO2 is investigated by first principles calculations. We find that both neutral positive segregate to the boundary. Positive vacancies, which are mobile bulk with activation energies for ∼0.7 eV, have enhanced mobility parallel plane but once at face high barriers climb out.
The complex and intriguing properties of the ferrimagnetic half metal magnetite (Fe3O4) are continuing fundamental interest as well being important for practical applications in spintronics, magnetism, catalysis medicine. There is considerable speculation concerning role ubiquitous antiphase boundary (APB) defects magnetite, however, direct information on their structure has remained challenging to obtain. Here we combine predictive first principles modelling with high-resolution...
Magnetic tunnel junctions (MTJs) constitute a promising building block for future nonvolatile memories and logic circuits. Despite their pivotal role, spatially resolving chemically identifying each individual stacking layer remains challenging due to localized features that complicate characterizations limiting understanding of the physics MTJs. Here, we combine advanced electron microscopy, spectroscopy, first-principles calculations obtain direct structural chemical imaging atomically...
We present a computationally efficient and predictive methodology for modeling the formation properties of electron hole polarons in solids. Through nonempirical self-consistent optimization fraction Hartree-Fock exchange (α) hybrid functional, we ensure generalized Koopmans' condition is satisfied self-interaction error minimized. The approach applied to model polaron known stable metastable phases TiO2 including anatase, rutile, brookite, TiO2(H), TiO2(R), TiO2(B). Electron are predicted...
Polycrystalline materials are ubiquitous in technology, and grain boundaries have long been known to affect properties performance. First principles modeling electron microscopy methods powerful highly complementary for investigating the atomic scale structure of boundaries. In this review, we provide an introduction key concepts approaches using these methods. We also a number case studies providing examples their application understand impact range energy materials. Most presented interest...
Cu–Zn cation disorder plays a vital and controversial role in kesterite CuZnSn(S1–xSex)4 solar cells. We demonstrate using density functional theory nonadiabatic molecular dynamics simulations that the across different planes (i.e., Cu–Sn planes) is significantly more detrimental to device performance than case when confined only planes. The main reason plane induces significant elongation of Sn–S/Se bond lengths, leading downshift conduction band minimum, decreasing gap, reducing optical...
Abstract Photovoltaics (PVs) are a critical technology for curbing growing levels of anthropogenic greenhouse gas emissions, and meeting increases in future demand low-carbon electricity. In order to fulfill ambitions net-zero carbon dioxide equivalent (CO 2 eq) emissions worldwide, the global cumulative capacity solar PVs must increase by an magnitude from 0.9 TW p 2021 8.5 2050 according International Renewable Energy Agency, which is considered be highly conservative estimate. 2020, Henry...
By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament features controlling TiN/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiN resistive memory operations. The forming process is found to define the geometry, which in turn determines temperature profile and, consequently, switching characteristics. findings point importance of dimensions during (polarity,...
The electronic structure of oxygen vacancy and proton defects close to grain boundaries in MgO are calculated using first principles methods. These defects, various charge states, favorably segregate can trap electrons. interplay between electron defect segregation provides a mechanism for build up at boundaries, example, under irradiation or applied electrical voltage. theoretical calculations presented provide insight into the complex properties metal-oxide that be difficult obtain by...
The excess volume associated with grain boundaries is one of the primary factors driving defect segregation and diffusion which controls electronic, mechanical chemical properties many polycrystalline materials. Experimental measurements boundary fcc metals Cu Ni have shown a difference over 40%. in lattice constant between only 3%, therefore this substantial currently lacking explanation. In article we employ high throughput computational approach to determine atomic structure, formation...
Abstract A model device based on an epitaxial stack combination of titanium nitride (111) and monoclinic hafnia (11) is grown onto a c ‐cut Al 2 O 3 ‐substrate to target the role grain boundaries in resistive switching. The texture transfer results 120° in‐plane rotated m ‐HfO grains, thus, defined subset allowed boundary orientations high symmetry. These engineered thread whole dielectric layer, thereby providing predefined breakdown paths for electroforming‐free random access memory...
We present first-principles theoretical predictions of the electronic properties {111} twin boundaries in pure formamidinium lead iodide (FAPI) as well a mixed-ion halide perovskite containing formamidinium, Cs, I, and Br. find that boundary is extremely stable FAPI but introduces no electron or hole trapping states presents relatively small barriers (<100 meV) to transport electrons holes, suggesting they are benign for solar cell performance. However, perovskite, serve nucleation site...
The crystal structure of Sb2Se3 gives rise to unique properties that cannot otherwise be achieved with conventional thin-film photovoltaic materials, such as CdTe or Cu(In,Ga)Se2. It has previously been proposed grain boundaries can made benign provided only the weak van der Waals forces between (Sb4Se6)n ribbons are disrupted. Here, it is shown non-radiative recombination suppressed even for cutting across ribbons. This due a remarkable self-healing process, whereby atoms at boundary relax...
We demonstrate that the three-dimensional (3D) binary monoclinic oxides ${\mathrm{HfO}}_{2}$ and ${\mathrm{ZrO}}_{2}$ exhibit quasi-2D polaron localization conductivity, which results from a small difference in coordination of two oxygen sublattices these materials. The transition between 2D large into zero-dimensional state requires overcoming energetic barrier. These how asymmetry lattice structure can determine qualitative character significantly broaden realm systems.
We employ a periodic plane-wave implementation of constrained density functional theory to describe electron tunnelling between oxygen vacancy defects in MgO. find that calculated transfer parameters, and therefore rates, depend sensitively on the fraction Hartree-Fock exchange (HFX) used approximate exchange-correlation functional. In particular, we show exponential decay constant for electronic coupling (β) is proportional square-root band gap Therefore, it essential use an which predicts...
Grain boundaries are shown to play a critical role in controlling electron mobility nanocrystalline titanium dioxide affecting material performance for applications such as solar energy generation and catalysis. Theoretical modelling demonstrates that can be reduced by several orders of magnitude result enhanced trapping at grain improved high current densities highly nonlinear trap filling effect. The electrons oxide materials underpins diverse range areas generation, catalysis, gas sensing...
The trapping of electrons at surfaces nanocrystalline titanium dioxide can be decisive in controlling performance for diverse applications photocatalysis, energy storage, and solar generation. Here, we employ first-principles calculations to elucidate the factors which influence electron all low index rutile TiO2. We show that different surface orientations exhibit markedly affinities: some preferring trap with others repelling electrons. demonstrate local variations are linked electrostatic...
The optical properties and charge trapping phenomena observed on oxide nanocrystal ensembles can be strongly influenced by the presence of interfaces. MgO powders represent a convenient system to study these effects due well-defined shape controllable size distributions nanocrystals. spectroscopic interfaces are investigated monitoring dependence absorption characteristics concentration in nanopowders. is found affect spectra nanopowders more significantly than changing constituent...