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Band gap semiconductor

Bingya Hou, Lang Shen, Haotian Shi, Jihan Chen, Bofan Zhao, Kun Li, Yi Wang, Guozhen Shen, Mai-Anh Ha, Fanxin Liu, Anastassia N Alexandrova, Wei-Hsuan Hung, Jahan M Dawlaty, Phillip Christopher, Stephen B Cronin
It has been known for several decades that defects are largely responsible for the catalytically active sites on metal and semiconductor surfaces. However, it is difficult to directly probe these active sites because the defects associated with them are often relatively rare with respect to the stoichiometric crystalline surface. In the work presented here, we demonstrate a method to selectively probe defect-mediated photocatalysis, through differential AC photocurrent (PC) measurements. In this approach, electrons are photoexcited from the valence band to a relatively narrow distribution of sub-bandgap states in the TiO2, and then subsequently to the ions in solution...
February 15, 2019: ACS Applied Materials & Interfaces
Yujuan Zhang, Weiyi Xia, Yabei Wu, Peihong Zhang
MXenes are a large family of layered transition metal carbide/nitride materials that possess a number of desired properties such as flexible chemical composition, high mechanical strength, and excellent structural stability. Although MXene based semiconductors have attracted considerable recent research attention in the search of novel 2D electronic materials, accurate understanding of their electronic properties has not been established. In this work, we carry out fully converged GW quasiparticle calculations for M2CO2 (M = Hf, Zr, and Ti) MXene based 2D semiconductors and alloys using newly developed accelerated GW methods...
February 15, 2019: Nanoscale
Paribesh Acharyya, Provas Pal, Pralok K Samanta, Arka Sarkar, Swapan K Pati, Kanishka Biswas
Two-dimensional (2D) perovskites recently attracted significant interest due to their unique and novel optoelectronic properties. CsPb2Br5, a 2D inorganic perovskite halide, is an indirect band gap semiconductor, and hence it is not supposed to be luminescent. However, a fundamental understanding of the origin of its luminescence properties is still lacking as there are contradictory literature reports present concerning its luminescence properties. Here, we demonstrate a single pot solution based transformation of 2D CsPb2Br5 nanosheets from the nanocrystals of 3D CsPbBr3 and investigate the origin of its luminescence properties by detailed experiments and density functional theory (DFT) calculations...
February 15, 2019: Nanoscale
Manila Sharma, Aymen Yangui, Vincent R Whiteside, Ian R Sellers, Dan Han, Shiyou Chen, Mao-Hua Du, Bayrammurad Saparov
Replacement of the toxic heavy element lead in metal halide perovskites has been attracting a great interest because the high toxicity and poor air stability are two of the major barriers for their widespread utilization. Recently, mixed-cation double perovskite halides, also known as elpasolites, were proposed as an alternative lead-free candidate for the design of nontoxic perovskite solar cells. Herein, we report a new nontoxic and air stable lead-free all-inorganic semiconductor Rb4 Ag2 BiBr9 prepared using the mixed-cation approach; however, Rb4 Ag2 BiBr9 adopts a new structure type (Pearson's code oP32) featuring BiBr6 octahedra and AgBr5 square pyramids that share common edges and corners to form a unique 2D layered non-perovskite structure...
February 15, 2019: Inorganic Chemistry
Khuong P Ong, Shunnian Wu, Tien Hoa Nguyen, David J Singh, Zhen Fan, Michael B Sullivan, Cuong Dang
Organo-lead halide perovskite solar cells represent a revolutionary shift in solar photovoltaics, introducing relatively soft defect containing semiconductors as materials with excellent charge collection for both electrons and holes. Although they are based on the nominally simple cubic perovskite structure, these compounds are in fact very complex. For example, in (CH3 NH3 )PbI3 the dynamics and ensuing structural fluctuations associated with the (CH3 NH3 )+ ions and the interplay with the electronic properties are still not fully understood, despite extensive study...
February 14, 2019: Scientific Reports
Hui Ling Tan, Fatwa F Abdi, Yun Hau Ng
The functionality of a photoactive semiconductor (i.e., photocatalysts, photoelectrodes, etc.) is largely dictated by three key aspects: (i) band gap; (ii) absolute potentials of the conduction band minimum and the valence band maximum; and (iii) bulk and surface charge carrier dynamics. Their relevance to governing the energetics and the photo(electro)chemical mechanisms of the semiconductor has prompted development of a multitude of characterization tools to probe the specific characteristic of the material...
February 14, 2019: Chemical Society Reviews
Jianqiao Liu, Weiting Xue, Guohua Jin, Zhaoxia Zhai, Jiarong Lv, Wusong Hong, Yuzhen Chen
Tin oxide quantum dots (QDs) were prepared in aqueous solution from the precursor of tin dichloride via a simple process of hydrolysis and oxidation. The average grain size of QDs was 1.9 nm. The hydrothermal treatment was used to control the average grain size, which increased to 2.7 and 4.0 nm when the operating temperatures of 125 and 225 °C were employed, respectively. The X-ray photoelectron spectroscopy (XPS) spectrum and X-ray diffraction analysis (XRD) pattern confirmed a rutile SnO₂ system for the QDs...
February 11, 2019: Nanomaterials
Amin Azizi, Gabriel Antonius, Emma Regan, Rahmatollah Eskandari, Salman Kahn, Feng Wang, Steven G Louie, Alex Zettl
Alloying two-dimensional (2D) semiconductors provides a powerful method to tune their physical properties, especially those relevant to optoelectronic applications. However, as the crystal structure becomes more complex, it becomes increasingly difficult to accurately correlate response characteristics to detailed atomic structure. We investigate, via annular dark-field scanning transmission electron microscopy, electron energy loss spectroscopy, and second harmonic generation, the layered III-VI alloy GaSe0...
February 12, 2019: Nano Letters
S Rosy Christy, L Srimathi Priya, M Durka, A Dinesh, N Babitha, S Arunadevi
In this present study, semiconductor zinc oxide (ZnO) nanoparticles were successfully prepared by microwave irradiation (ZnO-MIM) and conventional combustion (ZnO-CCM) method, respectively using Aloe vera plant extract as reducing agent. Crystal structure, purity and surface morphology of the samples were examined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. UV-Visible diffuse reflectance (DRS) and photoluminescence (PL) spectral studies was used to analysis the optical property and band gap energy of the samples...
June 1, 2019: Journal of Nanoscience and Nanotechnology
Chao Liu, Tao Hu, Yabei Wu, Heng Gao, Yali Yang, Wei Ren
Combining the particle-swarm optimization (PSO) method with first-principles calculations, we explore a new category of two-dimensional (2D) monolayers composed of solely the element selenium. Three stable structures are screened from outputs of crystal search computations, namely T-Se (1T-MoS2-like), C-Se (tiled 1D helical chain), and S-Se (square structure). Phonon calculations, as well as formation energy calculations have been performed to confirm the stability of the three phases. The electronic structure calculations show that both T-Se and C-Se are indirect-band-gap semiconductors, with gap values of 1...
February 8, 2019: Journal of Physics. Condensed Matter: An Institute of Physics Journal
U N Roy, G S Camarda, Y Cui, R Gul, A Hossain, G Yang, J Zazvorka, V Dedic, J Franc, R B James
Because of its ideal band gap, high density and high electron mobility-lifetime product, cadmium zinc telluride (CdZnTe or CZT) is currently the best room-temperature compound-semiconductor X- and gamma-ray detector material. However, because of its innate poor thermo-physical properties and above unity segregation coefficient for Zn, the wide spread deployment of this material in large-volume CZT detectors is still limited by the high production cost. The underlying reason for the low yield of high-quality material is that CZT suffers from three major detrimental defects: compositional inhomogeneity, high concentrations of dislocation walls/sub-grain boundary networks and high concentrations of Te inclusions/precipitates...
February 7, 2019: Scientific Reports
Ghada Dushaq, Ammar Nayfeh, Mahmoud Rasras
Thin Ge films directly grown on Si substrate using two-step low temperature growth technique are subjected to low load nano-indentation at room temperature. The nano-indentation is carried out using a Berkovich diamond tip (R ~ 20 nm). The residual impressions are studied using ex-situ Raman Micro-Spectroscopy, Atomic Force Microscopy combined system, and Transmission Electron Microscopy. The analysis of residual indentation impressions and displacement-load curves show evidence of deformation by phase transformation at room temperature under a critical pressure ranging from 4...
February 7, 2019: Scientific Reports
Tianshuang Wang, Bin Jiang, Qi Yu, Xueying Kou, Peng Sun, Fangmeng Liu, Huiying Lu, Xu Yan, Geyu Lu
Understanding the effect of substitutional doping on gas-sensing performances is essential for designing high activity sensing nanomaterials. Herein, formaldehyde sensors based on gallium-doped In2O3 inverse opal (IO-(GaxIn1-x)2O3) microspheres were purposefully prepared by simple ultrasonic spray pyrolysis method combined with self-assembly sulfonated polystyrene spheres template. The well-aligned inverse opal structure, with three different-sized pores, plays dual roles of accelerating the diffusion of gas molecules and providing more active sites...
February 6, 2019: ACS Applied Materials & Interfaces
Tianxiang Zhang, Zhihui Chen, Yumeng Shi, Qing-Hua Xu
CsPb2Br5 is a new member of the all-inorganic lead halide perovskite family with unique structures and optoelectronic properties for various applications. As an indirect band gap semiconductor, the photoluminescence (PL) mechanism of CsPb2Br5 is still under debate. To resolve this issue, CsPb2Br5 microplates with strong green PL have been prepared by a hot-injection method. Characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis and ultraviolet-visible (UV-vis) absorption spectroscopy indicates the existence of a small amount of embedded CsPbBr3 phase...
February 6, 2019: Nanoscale
Chung-Yu Wang Wang, Peter Elliott, Sangeeta Sharma, John Kay Dewhurst
We demonstrate how the scissor correction to the optical band gap, common in linear-response time-dependent density functional theory (TD-DFT), may be extended to the domain of real-time TD-DFT. This requires modifying both the eigenvalues and momentum matrix elements of the underlying basis set. It provides a simple and computationally economical approach for calculating accurate electron dynamics in solids. We demonstrate the importance of this correction for prototypical semiconductors, diamond and silicon, where the energy absorption in both the linear and non-linear regimes is examined...
February 5, 2019: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Ehsan Hosseini, Mohammad Zakertabrizi, Asghar Habibnejad Korayem, Rouzbeh Shahsavari
Ternary 2D materials such as fused graphene-boron nitride (GBN) nanosheets exhibit attractive physics and tunable properties far beyond their parent structures. While these features impart several multifunctional properties in various matrices, a fundamental understanding on the nature of the interfacial interactions of these ternary 2D materials with host matrices and the role of their individual components has been elusive. Herein, we focus on intercalated GBN/ceramic nanocomposites as a model system and perform a series of density functional theory calculations to fill this knowledge gap...
February 5, 2019: ACS Applied Materials & Interfaces
Felix Huttmann, Nico Rothenbach, Stefan Kraus, Katharina Ollefs, Lucas M Arruda, Matthias Bernien, Danny Thonig, Anna Delin, Jonas Fransson, Kurt Kummer, Nicholas B Brookes, Olle Eriksson, Wolfgang Kuch, Thomas Michely, Heiko Wende
We investigate the magnetic and electronic properties of europium cyclooctatetraene nanowires (EuCot) by means of low-temperature x-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as a wide-band-gap semiconductor with a band gap of 2.3 eV. By means of Eu M5,4 edge XMCD, orbital and spin magnetic moments of (-0.1 ±0.3) μΒ and (+7.0 ±0.6) μΒ , respectively, were determined...
February 4, 2019: Journal of Physical Chemistry Letters
Feng Li, Hong Wu, Zhaoshun Meng, Ruifeng Lu, Yong Pu
Designing novel two-dimensional (2D) materials is highly desirable for the material innovation. Here, we proposed the monolayered calcium triarsenide (1L CaAs3) as a new 2D semiconductor with a series of encouraging functionalities. Contrast to ~33 meV small bandgap in bulk CaAs3, 1L CaAs3 possesses a large direct band gap of 0.92 eV with a high hole mobility of ~104 cm2 v1 s1. The electronic properties of 2D CaAs3 can be manipulated significantly by the layer thickness and external strains. Remarkably, 2D CaAs3 suggests a topologically nontrivial-trivial states transition under thickness reduction and strain engineering, which is attributed to the drastic surface relaxation and pinch-effect under compression...
February 4, 2019: Journal of Physical Chemistry Letters
Zhi-Yong Tao, Ting Liu, Chuan Zhang, Ya-Xian Fan
Heterojunctions between two crystalline semiconductor layers or regions can always lead to engineering the electronic energy bands in various devices, including transistors, solar cells, lasers, and organic electronic devices. The performance of these heterojunction devices depends crucially on the band alignments and their bending at the interfaces, which have been investigated for years according to Anderson's rule, Schottky-Mott rule, Lindhard theory, quantum capacitance, and so on. Here, we demonstrate that by engineering two different acoustic waveguides with forbidden bands, one can achieve an acoustic heterojunction with an extraordinary transmission peak arising in the middle of the former gaps...
January 31, 2019: Scientific Reports
Wanxing Lin, Shi-Dong Liang, Chunshan He, Wucheng Xie, Haiying He, Quanxiang Mai, Jiesen Li, Dao-Xin Yao
We predict three novel phases of the carbon nitride (CN) bilayer, denoted α-C2 N2 , β-C2 N2 and γ-C4 N4 , respectively. All of them consist of two CN sheets connected by C-C covalent bonds. The phonon dispersions reveal that all these phases are dynamically stable, because no imaginary frequency is present. The transition pathway between α-C2 N2 and β-C2 N2 is investigated, which involves bond-breaking and bond-reforming between C and N. This conversion is difficult, since the activation energy barrier is 1...
January 31, 2019: Scientific Reports
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