Silicon Carbide: A Playground for 1D-Modulation Electronics

2006 ◽  
Vol 527-529 ◽  
pp. 355-358 ◽  
Author(s):  
Peter Deák ◽  
Adam Buruzs ◽  
Adam Gali ◽  
Thomas Frauenheim ◽  
Wolfgang J. Choyke
Keyword(s):  
Density Functional ◽  
Spatial Separation ◽  
Atomic Layer ◽  
Periodic Variation ◽  
Optical Nonlinearity ◽  
Double Layers ◽  
Hybrid Functional ◽  
Free Electrons ◽  
Functional Theory ◽  
Molecular Source

Optoelectronic devices with 1D modulation of the potential through hetero-structure or doping superlattices have so far been the privilege of III-V semiconductors. Based on the fact that SiC can be grown monolayer by monolayer, and that Si–Si and C–C double layers have been observed in it, we suggest the possibility of a stress-free polarization superlattice, consisting of the periodic variation of Si-face and C-face domains along the hexagonal axis of 4H-SiC. Such a structure could, in principle, be grown by molecular source atomic layer epitaxy. Investigating such superlattices by density functional theory, using a hybrid functional, we show that Si–Si and C–C double layers at the antiphase boundaries confine electrons within ~0.5 nm, and the periodic polarization field causes zig-zag shaped band edges which gives rise to tunable absorption, to spatial separation of free electrons and holes, as well as to optical nonlinearity. These properties could allow the application of SiC also in optoelectronics and photonics.

scholarly journals Intercalated architecture of MA2Z4 family layered van der Waals materials with emerging topological, magnetic and superconducting properties

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Lei Wang ◽  
Yongpeng Shi ◽  
Mingfeng Liu ◽  
Ao Zhang ◽  
Yi-Lun Hong ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Layer Structure ◽  
Atomic Layer ◽  
Type I ◽  
Hybrid Functional ◽  
Functional Theory ◽  
Valence Electrons ◽  
Nonmagnetic Metals ◽  
Standard Density

AbstractThe search for new two-dimensional monolayers with diverse electronic properties has attracted growing interest in recent years. Here, we present an approach to construct MA2Z4 monolayers with a septuple-atomic-layer structure, that is, intercalating a MoS2-type monolayer MZ2 into an InSe-type monolayer A2Z2. We illustrate this unique strategy by means of first-principles calculations, which not only reproduce the structures of MoSi2N4 and MnBi2Te4 that were already experimentally synthesized, but also predict 72 compounds that are thermodynamically and dynamically stable. Such an intercalated architecture significantly reconstructs the band structures of the constituents MZ2 and A2Z2, leading to diverse electronic properties for MA2Z4, which can be classified according to the total number of valence electrons. The systems with 32 and 34 valence electrons are mostly semiconductors. Whereas, those with 33 valence electrons can be nonmagnetic metals or ferromagnetic semiconductors. In particular, we find that, among the predicted compounds, (Ca,Sr)Ga2Te4 are topologically nontrivial by both the standard density functional theory and hybrid functional calculations. While VSi2P4 is a ferromagnetic semiconductor and TaSi2N4 is a type-I Ising superconductor. Moreover, WSi2P4 is a direct gap semiconductor with peculiar spin-valley properties, which are robust against interlayer interactions. Our study thus provides an effective way of designing septuple-atomic-layer MA2Z4 with unusual electronic properties to draw immediate experimental interest.

A Rare Low Spin Co(IV) Bis-Silyldiamide with High Thermal Stability: Exploring the Origin of an Unusual S = 1/2 Configuration

2020 ◽  
Author(s):  
David Zanders ◽  
Goran Bačić ◽  
Dominique Leckie ◽  
Oluwadamilola Odegbesan ◽  
Jeremy M. Rawson ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Density Functional ◽  
Atomic Layer ◽  
Epr Spectrum ◽  
Functional Theory ◽  
Cluster Calculations ◽  
Layer Deposition ◽  
Starting Point ◽  
Higher Spin ◽  
Surface Saturation

Attempted preparation of a chelated Co(II) β-silylamide re-sulted in the unprecedented disproportionation to Co(0) and a spirocyclic cobalt(IV) bis(β-silyldiamide): [Co[(NtBu)2SiMe2]2] (1). Compound 1 exhibits a room temperature magnetic moment of 1.8 B.M and a solid state axial EPR spectrum diagnostic of a rare S = 1/2 configuration. Semicanonical coupled-cluster calculations (DLPNO-CCSD(T)) revealed the doublet state was clearly preferred (–27 kcal/mol) over higher spin configurations for which density functional theory (DFT) showed no energetic preference. Unlike other Co(IV) complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self-limiting monolayer in initial atomic layer deposition (ALD) surface saturation tests. The ease of synthesis and high-stability make 1 an attractive starting point to begin investigating otherwise inaccessible Co(IV) intermediates and synthesizing new materials.

Crystal structure of pomalidomide Form I, C13H11N3O4

2021 ◽  
pp. 1-6
Author(s):  
James A. Kaduk ◽  
Amy M. Gindhart ◽  
Thomas N. Blanton
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Powder Diffraction ◽  
Density Functional ◽  
Double Layers ◽  
Carbonyl Groups ◽  
Hydrogen Atoms ◽  
Powder Diffraction File ◽  
Functional Theory ◽  
Amine Hydrogen

The crystal structure of pomalidomide Form I has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Pomalidomide Form I crystallizes in the space group P-1 (#2) with a = 7.04742(9), b = 7.89103(27), c = 11.3106(6) Å, α = 73.2499(13), β = 80.9198(9), γ = 88.5969(6)°, V = 594.618(8) Å3, and Z = 2. The crystal structure is characterized by the parallel stacking of planes parallel to the bc-plane. Hydrogen bonds link the molecules into double layers also parallel to the bc-plane. Each of the amine hydrogen atoms acts as a donor to a carbonyl group in an N–H⋯O hydrogen bond, but only two of the four carbonyl groups act as acceptors in such hydrogen bonds. Other carbonyl groups participate in C–H⋯O hydrogen bonds. The powder pattern has been submitted to ICDD® for inclusion in the Powder Diffraction File™ (PDF®).

scholarly journals Cryogenic Exfoliation of 2D Stanene Nanosheets for Cancer Theranostics

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Jiang Ouyang ◽  
Ling Zhang ◽  
Leijiao Li ◽  
Wei Chen ◽  
Zhongmin Tang ◽  
...  
Keyword(s):  
Biomedical Applications ◽  
Density Functional ◽  
Biomedical Application ◽  
Density Functional Theory Calculations ◽  
Free Electrons ◽  
Functional Theory ◽  
New Approach ◽  
New Type ◽  
Average Size ◽  
Cancer Theranostics

Abstract Stanene (Sn)-based materials have been extensively applied in industrial production and daily life, but their potential biomedical application remains largely unexplored, which is due to the absence of the appropriate and effective methods for fabricating Sn-based biomaterials. Herein, we explored a new approach combining cryogenic exfoliation and liquid-phase exfoliation to successfully manufacture two-dimensional (2D) Sn nanosheets (SnNSs). The obtained SnNSs exhibited a typical sheet-like structure with an average size of ~ 100 nm and a thickness of ~ 5.1 nm. After PEGylation, the resulting PEGylated SnNSs (SnNSs@PEG) exhibited good stability, superior biocompatibility, and excellent photothermal performance, which could serve as robust photothermal agents for multi-modal imaging (fluorescence/photoacoustic/photothermal imaging)-guided photothermal elimination of cancer. Furthermore, we also used first-principles density functional theory calculations to investigate the photothermal mechanism of SnNSs, revealing that the free electrons in upper and lower layers of SnNSs contribute to the conversion of the photo to thermal. This work not only introduces a new approach to fabricate 2D SnNSs but also establishes the SnNSs-based nanomedicines for photonic cancer theranostics. This new type of SnNSs with great potential in the field of nanomedicines may spur a wave of developing Sn-based biological materials to benefit biomedical applications.

scholarly journals Sn-Doped Hematite for Photoelectrochemical Water Splitting: The Effect of Sn Concentration

2020 ◽  
Vol 234 (4) ◽  
pp. 683-698 ◽  
Author(s):  
Siyuan Zhang ◽  
Hamidreza Hajiyani ◽  
Alexander G. Hufnagel ◽  
Jonathan Kampmann ◽  
Benjamin Breitbach ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Atomic Layer ◽  
Solubility Limit ◽  
Metallic State ◽  
Equilibrium Solubility ◽  
Functional Theory ◽  
Sn Doping ◽  
Layer Deposition

AbstractHematite-based photoanodes have been intensively studied for photoelectrochemical water oxidation. The n-type dopant Sn has been shown to benefit the activity of hematite anodes. We demonstrate in this study that Sn-doped hematite thin films grown by atomic layer deposition can achieve uniform doping across the film thickness up to at least 32 mol%, far exceeding the equilibrium solubility limit of less than 1 mol%. On the other hand, with the introduction of Sn doping, the hematite crystallite size decreases and many twin boundaries form in the film, which may contribute to the low photocurrent observed in these films. Density functional theory calculations with a Hubbard U term show that Sn doping has multiple effects on the hematite properties. With increasing Sn4+ content, the Fe2+ concentration increases, leading to a reduction of the band gap and finally to a metallic state. This goes hand in hand with an increase of the lattice constant.

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