Qimin Yan

Qimin Yan
Temple University | TU · Department of Physics

PhD

About

81
Publications
15,631
Reads
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4,049
Citations
Additional affiliations
July 2016 - present
Temple University
Position
  • Professor (Assistant)
January 2013 - July 2016
Lawrence Berkeley National Lab and University of California, Berkeley
Position
  • PostDoc Position
September 2007 - December 2012
University of California, Santa Barbara
Position
  • PostDoc Position

Publications

Publications (81)
Article
Full-text available
Being atomically thin and amenable to external controls, two-dimensional (2D) materials offer a new paradigm for the realization of patterned qubit fabrication and operation at room temperature for quantum information sciences applications. Here we show that the antisite defect in 2D transition metal dichalcogenides (TMDs) can provide a controllabl...
Article
In the search for photoanode materials with band gaps suitable for utilization in solar fuel generation, approximately 1.2–2.8 eV, theory-guided experiments have identified a variety of materials that meet the band gap requirements and exhibit operational stability in harsh photoelectrochemical environments. In particular, M-V-O compounds (M is a t...
Preprint
Full-text available
Being atomically thin and amenable to external controls, two-dimensional (2D) materials offer a new paradigm for the realization of patterned qubit fabrication and operation at room temperature for quantum information sciences applications. Here we show that the antisite defect in 2D transition metal dichalcogenides (TMDs) can provide a controllabl...
Article
Full-text available
Incorporation of physical principles in a machine learning (ML) architecture is a fundamental step toward the continued development of artificial intelligence for inorganic materials. As inspired by the Pauling’s rule, we propose that structure motifs in inorganic crystals can serve as a central input to a machine learning framework. We demonstrate...
Article
Full-text available
Recent years have witnessed the rapid increase in the application of deep learning in atomistic systems including both molecules and solid-state materials. The use of graphs and associated design of message passing strategies have enabled multiple deep learning frameworks to achieve reliable and efficient predictions of materials properties with a...
Article
Full-text available
Mo2C AND TI3C2 MXenes were investigated as earth-abundant electrocatalyts for the the CO2 reduction reaction (CO2RR). Mo2C and Ti3C2 exhibited faradaic efficiencies of 90% (250 mV overpotential) and 65% (650 mV overpotential), respectively, for the reduction of CO2 to CO in acetonitrile using an ionic liquid electrolyte. The use of ionic liquid 1-e...
Article
Discovery and design of two-dimensional (2D) materials with suitable band gaps and high carrier mobility are of vital importance for the photonics, optoelectronics, and high-speed electronics. In this work, based on first principles calculations using density functional theory with Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhoffunctionals, we i...
Article
Full-text available
Recent years have witnessed tremendous success in the discovery of topological states of matter. Particularly, sophisticated theoretical methods in time-reversal-invariant topological phases have been developed, leading to the comprehensive search of crystal database and the prediction of thousands of topological materials. In contrast, the discove...
Article
Full-text available
Auxetic two-dimensional (2D) materials provide a promising platform for biomedicine, sensors, and many other applications at the nanoscale. In this work, utilizing a hypothesis-based data-driven approache, we identify multiple materials with remarkable in-plane auxetic behavior in a family of buckled monolayer 2D materials. These materials are tran...
Article
Based on the first‐principles calculations, we designed a novel two‐dimensional Ce2C monolayer with ferromagnetic behavior. Ce2C monolayer has an anti‐site structure of the 1T‐MoS2 sheet, where carbon atoms hexagonally coordinated by neighboring Ce atoms. Both calculations of phonon dispersion and molecular dynamics show that the Ce2C monolayer has...
Article
We propose a novel class of two-dimensional (2D) Dirac materials in the MX family (M = Be, Mg, Zn and Cd, X = Cl, Br and I), which exhibit graphene-like band structures with linearly-dispersing Dirac-cone states over large energy scales (0.8–1.8 eV) and ultra-high Fermi velocities comparable to graphene. Spin-orbit coupling opens sizable topologica...
Article
A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of...
Preprint
Incorporation of physical principles in a network-based machine learning (ML) architecture is a fundamental step toward the continued development of artificial intelligence for materials science and condensed matter physics. In this work, as inspired by the Pauling rule, we propose that structure motifs (polyhedral formed by cations and surrounding...
Preprint
Discovery and design of two-dimensional (2D) materials with suitable band gaps and high carrier mobility is of vital importance for photonics, optoelectronics, and high-speed electronics. In this work, based on first principles calculations using density functional theory (DFT) with PBE and HSE functionals, we introduce a family of monolayer isostr...
Preprint
Full-text available
We propose a novel class of two-dimensional (2D) Dirac materials in the MX family (M=Be, Mg, Zn and Cd, X = Cl, Br and I), which exhibit graphene-like band structures with linearly-dispersing Dirac-cone states over large energy scales (0.8~1.8 eV) and ultra-high Fermi velocities comparable to graphene. The electronic and topological properties are...
Preprint
Recent years have witnessed tremendous success in the discovery of topological states of matter. Particularly, sophisticated theoretical methods in time-reversal-invariant topological phases have been developed, leading to the comprehensive search of crystal database and the prediction of thousands of new topological materials. In contrast, the dis...
Article
Alumina (Al2O3) is one of the most widely used ceramic materials for innumerable applications, due to its unique combination of attractive physical and mechanical properties. These intrinsic properties are dictated by the numerous phases that Al2O3 forms and its related phase transformations. Transition metal (TM) cation dopants [iron (Fe), cobalt...
Article
The surging demand for miniaturized compact devices has generated the need for new metal conductors with high current carrying ampacity, electric and thermal conductivity. Herein, we report carbon-metal conductors that exhibit a high breakdown current density (39% higher than copper) and electrical conductivity (e.g. 63% higher than that of copper...
Article
Biaxial deformation of suspended membranes widely exists and is used in nanoindentation to probe elastic properties of structurally isotropic two-dimensional (2D) materials. However, elastic properties and particularly fracture behaviors of anisotropic 2D materials remain largely unclarified in the case of biaxial deformation. MoTe2 is a polymorphi...
Article
In this short review, we introduce recent progress in the research field of data-driven material discovery and design for solar fuel generation. Construction of material databases under the materials genome initiative provides a great platform for material discovery and design by creating computational screening pipelines based on the materials’ de...
Article
Full-text available
Exciting advances have been made in artificial intelligence (AI) during recent decades. Among them, applications of machine learning (ML) and deep learning techniques brought human-competitive performances in various tasks of fields, including image recognition, speech recognition, and natural language understanding. Even in Go, the ancient game of...
Article
Unveiling both the presence and nature of point defects is one of the biggest challenges in condensed matter physics and materials science. Particularly in complex oxides, even a minute amount of unavoidable point defects could generate novel physical phenomena and functions, such as visible light emission and ferroelectricity, yet it remains elusi...
Article
Full-text available
Combinatorial (photo)electrochemical studies of the (Ni-Mn)Ox system reveal a range of promising materials for oxygen evolution photoanodes. X-ray diffraction, quantum efficiency, and optical spectroscopy mapping reveal stable photoactivity of NiMnO3 in alkaline conditions with photocurrent onset commensurate with its 1.9 eV direct band gap. The ph...
Article
Here, using solution based self-assembly, we contrast a three-dimensional co-crystal, where [1]benzothieno[3,2-b][1]benzothiophene (BTBT) based donor and tetracyanoquinodimethane (TCNQ) based acceptor leads to a mixed stacking sequence with pronounced intermolecular hybridization,...
Article
We present a combined experimental and theoretical study to demonstrate that the electrocatalytic activity of NiFe layered double hydroxides (NiFe LDHs) for the oxygen evolution reaction (OER) can be significantly enhanced by systematic cobalt incorporation using co-precipitation and/or intercalation. Electrochemical measurements show that cobalt m...
Article
The solar photoelectrochemical generation of hydrogen and carbon-containing fuels comprises a critical energy technology for establishing sustainable energy resources. The photoanode, which is responsible for solar-driven oxygen evolution, has persistently limited technology advancement due to the lack of materials that exhibit both the requisite e...
Article
Triply degenerate points (TDPs) in band structure of a crystal can generate novel TDP fermions without high-energy counterparts. Although identifying ideal TDP semimetals, which host clean TDP fermions around the Fermi level ($E_F$) without coexisting of other quasiparticles, is critical to explore the intrinsic properties of this new fermion, it i...
Article
Full-text available
The limited number of known low-band-gap photoelectrocatalytic materials poses a significant challenge for the generation of chemical fuels from sunlight. Using high-throughput ab initio theory with experiments in an integrated workflow, we find eight ternary vanadate oxide photoanodes in the target band-gap range (1.2–2.8 eV). Detailed analysis of...
Article
Solar fuel generators entail a high degree of materials integration, and efficient photoelectrocatalysis of the constituent reactions hinges upon the establishment of highly functional interfaces. The recent application of high throughput experimentation to interface discovery for solar fuels photoanodes has revealed several surprising and promisin...
Article
Point-defect formation energies calculated within the framework of density functional theory often depend on the choice of the exchange and correlation (xc) functional. We show that variations between the local density approximation (LDA), generalized gradient approximation (GGA), and hybrid functionals mainly arise from differences in the position...
Article
Deployment of solar fuels technology requires photoanodes with long term stability, which can be accomplished using light absorbers that self-passivate under operational conditions. Several copper vanadates have been recently reported as promising photoanode materials, and their stability and self-passivation is demonstrated through a combination o...
Article
Solar photoelectrochemical generation of fuel is a promising energy technology yet the lack of an efficient, robust photoanode remains a primary materials challenge in the development and deployment of solar fuels generators. Metal oxides comprise the most promising class of photoanode materials, but no known material meets the demanding requiremen...
Article
Full-text available
A compositionally step-graded (CSG) InGaN barrier is designed for the active region of c-plane blue light-emitting diodes (LEDs). High external quantum efficiencies of 45, 42, 39 and 36% are achieved at current densities of 100, 200, 300 and 400 A/cm2, respectively. Compared with GaN barrier devices, LEDs with CSG InGaN barriers showed higher power...
Article
Complex oxide β-Mn2V2O7 is identified as exhibiting near-optimal band energetics for solar fuel applications among known metal oxides. Experiments, corroborated by theory, indicate a bandgap near 1.8 eV. The calculations predict that β-Mn2V2O7 has well-aligned band edge energies for the hydrogen evolution reaction and oxygen evolution reaction. Pho...
Article
Full-text available
We present a first-principles study of MnNiO3, a promising oxygen-evolution photocatalyst. Using density functional theory with the PBE+U functional and the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE), we compute and analyze the ground-state geometry and electronic structure. We find that MnNiO3 is a ferrimagnetic semiconducto...
Article
Full-text available
To aid the development of AlN-based optoelectronics, it is essential to identify the defects that cause unwanted light absorption and to minimize their impact. Using hybrid functional calculations, we investigate the role of native defects and their complexes with oxygen, a common impurity in AlN. We find that Al vacancies are the source of the abs...
Article
Full-text available
Based on accurate band structures of AlN, GaN, and InN, we report physical quantities related to high-field electron transport, including effective masses, energies of inflection points, and satellite valleys in the conduction band. The band structures are obtained from density functional theory with a hybrid functional, as well as many-body pertur...
Article
Full-text available
We present a systematic study of strain effects on the electronic band structure of the group-III-nitrides (AlN, GaN and InN) in the wurtzite phase. The calculations are based on density functional theory with band-gap-corrected approaches including the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and quasiparticle G0W0 methods. We study strain...
Article
Full-text available
We investigate the impact of incorporating realistic In profiles in simulations of c-plane InGaN/GaN light-emitting diodes. Simulations based on a drift-diffusion model typically overestimate the onset voltage, but have usually been based on the assumption of ideal quantum wells with a square In profile. We demonstrate that more realistic profiles...
Article
Full-text available
We develop a practical first-principles methodology to determine nonradiative carrier capture coefficients at defects in semiconductors. We consider transitions that occur via multiphonon emission. Parameters in the theory, including electron-phonon coupling matrix elements, are computed consistently using state-of-the-art electronic structure tech...
Article
Elastic properties of materials are an important factor in their integration in applications. Chemical vapor deposited (CVD) monolayer semiconductors are proposed as key components in industrial-scale flexible devices and building blocks of 2D van der Waals heterostructures. However, their mechanical and elastic properties have not been fully chara...
Conference Paper
Full-text available
First-principles calculations show that phonon-assisted Auger recombination and its interplay with the polarization fields in polar nitride LEDs play an important role in the efficiency-droop and green-gap problems of these devices.
Article
Full-text available
The interest in SnTe has recently increased due to its topological crystalline insulator nature, despite the fact that SnTe is always heavily p type. Here, using first-principles calculations, we identify the microscopic origin of the p-type conductivity of SnTe. It is found that the negatively charged Sn vacancy (V2−Sn) dominates the electronic pr...
Article
Full-text available
Nitride light-emitting diodes are a promising solution for efficient solid-state lighting, but their performance at high power is affected by the efficiency-droop problem. Previous experimental and theoretical work has identified Auger recombination, a three-particle nonradiative carrier recombination mechanism, as the likely cause of the droop. In...
Article
This chapter discusses recent developments in first-principles computational methods for the study of nitride materials employed for solid-state lighting. The chapter also presents examples that show the wide range of applications of first-principles calculations in this field, ranging from the basic structural and electronic properties of the nitr...
Article
Full-text available
Using first-principles methods and 8-band k·p simulations, we study the electronic structure of an ultrathin quantum-well system consisting of a single layer of InN inserted in GaN matrix. Experimental photoluminescence and electroluminescence emission peaks for such structures have been reported in the wavelength region between 380 to 450 nm. In c...
Article
We develop a computational methodology to determine nonradiative carrier capture rates at defects in wide-band-gap semiconductors. In our theoretical framework, we consider carrier capture via multiphonon emission as the dominant nonradiative mechanism for deep defects in wide-band-gap materials at low and moderate carrier densities. Our methodolog...
Article
We investigate the effects of different InGaN quantum well (QW) profiles in c-plane InGaN/GaN 3-QW blue light-emitting diodes (LEDs) by employing a semi-empirical drift-diffusion model. Our results show that changing the typically assumed square indium profile to one with a smoother interfacial transition leads to a significant modification of the...
Article
Full-text available
Linear polarized electroluminescence was investigated for semipolar (30 3 ¯ 1) and (30 3 ¯ 1 ¯ ) InGaN light-emitting diodes (LEDs) with various indium compositions. A high degree of optical polarization was observed for devices on both planes, ranging from 0.37 at 438 nm to 0.79 at 519 nm. The extracted valence band energy separation was consisten...
Article
Full-text available
We use theoretical modeling to investigate the effect of polarization fields and non-radiative Auger recombination on the efficiency-droop and green-gap problems of polar and nonpolar nitride light-emitting diodes. The dependence of radiative and nonradiative recombination rates on electron-hole wave-function overlap is analyzed. Device designs tha...
Article
Full-text available
Topological insulator (TI) states have been demonstrated in materials with narrow gap and large spin-orbit interactions (SOI). Here we demonstrate that nanoscale engineering can also give rise to a TI state, even in conventional semiconductors with sizable gap and small SOI. Based on advanced first-principles calculations combined with an effective...
Article
Full-text available
We have derived consistent sets of band parameters (bandgaps, crystal-field splittings, effective masses, Luttinger, and EP parameters) and strain deformation potentials for MgO, ZnO, and CdO in the wurtzite phase. To overcome the limitations of density-functional theory in the local-density and generalized gradient approximations, we employ a hybr...
Article
Full-text available
Triplet-polaron quenching by charges on guest molecules in phosphorescent organic light emitting devices Appl. Phys. Lett. 101, 063502 (2012) Blue-white tunable luminescence for white light-emitting diodes and wideband near-infrared luminescence from Sm3+-doped borophosphate glass Appl. Phys. Lett. 101, 061904 (2012) Transparent Ce:Y3Al5O12 ceramic...
Article
Full-text available
We investigate the influence of polarity on carrier transport in single-quantum-well and multiple-quantum-well (MQW) light-emitting diodes (LEDs) grown on the semipolar (201) and (20) orientations of free-standing GaN. For semipolar MQW LEDs with the opposite polarity to conventional Ga-polar c-plane LEDs, the polarization-related electric field in...
Article
Full-text available
We report indium incorporation properties on various nonpolar and semipolar free-standing GaN substrates. Electroluminescence characterization and x-ray diffraction (XRD) analysis indicate that the semipolar (20) and (112) planes have the highest indium incorporation rate among the studied planes. We also show that both indium composition and polar...
Article
Full-text available
Defects may cause compensation or act as recombination centers in Mg-doped GaN. Using hybrid functional calculations, we investigate the effects of nitrogen vacancies (V-N) and Mg-vacancy complexes (Mg-Ga-V-N) on the electrical and optical properties of GaN. We find that Mg-Ga-V-N are compensating centers in p-type but electrically inactive in n-ty...
Article
Full-text available
We perform self-consistent Schrödinger-Poisson simulations on (112) In-GaN/GaN quantum wells (QW). By solving the 6 × 6 k·p Hamiltonian, including strain and polarization fields, we study the separation, ordering, and wavefunction character of the topmost valence bands in the QW and their dependence on In composition and QW width. Our results show...
Article
Full-text available
We report the effects of Mg doping in the barriers of semipolar (2021) multiple-quantum-well light-emitting diodes (LEDs) with long emission wavelengths (>500 nm). With moderate Mg doping concentrations (3 × 1018-5 × 1018 cm-3) in the barriers, the output power was enhanced compared to those with undoped barriers, which suggests that hole transport...
Article
Full-text available
The optical polarization ratio of spontaneous emission was investigated by electroluminescence measurements for semipolar (2021) InGaN/GaN light-emitting diodes, covering the blue to green spectral range. Devices fabricated on semipolar (2021) substrates exhibit polarization ratios ranging from 0.46 at 418 nm to 0.67 at 519 nm. These polarization r...
Article
Full-text available
Band gaps and band alignments for AlN, GaN, InN, and InGaN alloys are investigated using density functional theory with the with the Heyd-Scuseria-Ernzerhof {HSE06 [J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 134, 8207 (2003); 124, 219906 (2006)]} XC functional. The band gap of InGaN alloys as a function of In content is calculated an...