Atomistic Character of Nanocrystalline and Mixed Phase Silicon

2003 ◽  
Vol 762 ◽  
Author(s):  
R. Biswas ◽  
B. C. Pan
Keyword(s):  
Crystalline Silicon ◽  
Electronic Band Structure ◽  
Nanocrystalline Silicon ◽  
Distribution Functions ◽  
Mixed Phase ◽  
Electronic Band ◽  
Nano Crystalline ◽  
Excess Density ◽  
Heterogeneous Phase ◽  
The Stability

AbstractMaterials grown close to the phase boundary of amorphous and microcrystalline growth have the best electronic properties for solar cells. Systematic molecular dynamics methods have generated such nano-crystalline silicon, consisting of a mixed phase of nano-crystallites in an amorphous matrix, using an embedding method. An excess density of H resides on the surface of the nanocrystallites. The structure of this heterogeneous phase will be characterized by atomic distribution functions and structure factors. The electronic band structure of smaller models of nanocrystalline silicon reveals no midgap states and is similar to a-Si:H. There is a highly strained region surrounding the crystallites. The presence of localized strain region may increase the stability of the material.

H Evolution from Nano-Crystalline Silicon- Comparison of Simulation and Experiment

2004 ◽  
Vol 808 ◽  
Author(s):  
R. Biswas ◽  
B. C. Pan
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Crystalline Silicon ◽  
Nanocrystalline Silicon ◽  
Temperature Peak ◽  
Nano Crystalline ◽  
Crystallite Surface ◽  
Excess Density ◽  
Simulation And Experiment ◽  
Higher Temperature

ABSTRACTThe temperature dependent H evolution from a-Si:H provides unique information on the H-bonding and microstructure. Traditional undiluted a-Si:H films show a high temperature H-evolution peak near 600°C. However device-quality compact nanocrystalline silicon films grown near the phase boundary of amorphous and microcrystalline growth show a new low temperature H- evolution peak near 400°C in addition to a second high temperature peak near 600°C. The origin of this peak cannot be attributed to microvoids or a substantial density of dihydride species typical of porous low-temperature films. We have simulated the H evolution using a molecular dynamics generated model of nanocrystalline silicon, where nano-crystallites reside in a background amorphous matrix. An excess density of H occurs at the crystallite surface. We find a low temperature evolution peak at 250-400°C, where the H-evolution starts from the surface of the nano-crystallite. In addition there is a higher temperature peak at 700-800°C providing good agreement with H-evolution measurements. The mobile H is found to exist in both the bond-centered type of species and H2 molecules – which has implications for H-diffusion models.

scholarly journals Importance of tailoring lattice strain in halide perovskite crystals

2020 ◽  
Vol 12 (1) ◽  
Author(s):  
Hui-Seon Kim ◽  
Nam-Gyu Park
Keyword(s):  
Residual Strain ◽  
Review Paper ◽  
Lattice Mismatch ◽  
Electronic Band Structure ◽  
Perovskite Phase ◽  
Energy State ◽  
Optoelectronic Properties ◽  
Electronic Band ◽  
Halide Perovskite ◽  
The Stability

AbstractIn this review paper, the residual strain of a polycrystalline halide perovskite film is systematically studied based on its structural inhomogeneity, which is closely correlated to the local carrier dynamics caused by a modulated electronic band structure. Long-range collective strain ordering is responsible for the overall structural properties, consequently determining the optoelectronic properties of the perovskite film. Notably, the perovskite phase stability is strongly affected by the internal strain, favoring a lower energy state. The important parameters affecting the residual strain in a real perovskite film, ranging from thermal stress to lattice mismatch and compositional inhomogeneity, are subsequently introduced along with their impacts on the optoelectronic properties and/or the stability of the crystals.

scholarly journals Scrutinizing the stability and exploring the dependence of thermoelectric properties on band structure of 3d-3d metal-based double perovskites Ba2FeNiO6 and Ba2CoNiO6

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shabir Ahmad Mir ◽  
Dinesh C. Gupta
Keyword(s):  
Crystal Structure ◽  
Electronic Structure ◽  
Band Structure ◽  
Room Temperature ◽  
Electronic Band Structure ◽  
Double Perovskites ◽  
Electronic Band ◽  
Half Metal ◽  
The Stability ◽  
Wasted Energy

AbstractThrough the conventional DFT computation, we have designed new oxide double perovskites Ba2FeNiO6 and Ba2CoNiO6. The structural and thermodynamic stabilities are predicted by optimizing the crystal structure and evaluation of enthalpy of formation, respectively. Then by using the optimized lattice constant, we have explored the different physical properties. The GGA + mBJ electronic band-structure illustrates Ba2FeNiO6 is a half-metal with 100% spin polarization at the Fermi level. While Ba2CoNiO6 shows a ferromagnetic semiconducting nature. The change in the electronic structure when Fe is replaced by Co is explained with the help of the orbital diagram and exchange interaction. The eg-eg hybridization that happens via O-p states is strong because Fe–O–Ni and Co–O–Ni bond angles are strictly 180°. The narrow bandgaps in the semiconducting channels prompted us to analyze the applicability of these materials towards thermoelectric technology. Besides this, we have investigated the dependency of transport properties on electronic band structure. The semiconducting nature in Ba2CoNiO6 results in a significant ZT around 0.8 at room temperature makes it suitable for wasted-energy regeneration

scholarly journals Effects of Chamber Pressures on the Passivation Layer of Hydrogenated Nano-Crystalline Silicon Mixed-Phase Thin Film by Using Microwave Annealing

Electronics ◽  
2021 ◽  
Vol 10 (18) ◽  
pp. 2199
Author(s):  
Jia-Hao Lin ◽  
Hung-Wei Wu ◽  
Wei-Chen Tien ◽  
Cheng-Yuan Hung ◽  
Shih-Kun Liu
Keyword(s):  
Thin Film ◽  
Carrier Lifetime ◽  
Volume Fraction ◽  
Crystalline Silicon ◽  
Mixed Phase ◽  
Passivation Layer ◽  
Very High Frequency ◽  
Microwave Annealing ◽  
Symmetric Structure ◽  
Nano Crystalline

This paper proposes the effects of chamber pressures on the passivation layer of hydrogenated nano-crystalline silicon (nc-Si:H) mixed-phase thin film using microwave annealing (MWA) to achieve a high-quality thin film. The use of 40.68 MHz very-high-frequency plasma-enhanced chemical vapor deposition (VHFPECVD) deposited the nc-Si:H mixed-phase thin film on the top and bottom of the n-type crystalline silicon substrate. The chamber pressures (0.2, 0.4, 0.6, and 0.8 Torr) of the VHFPECVD were critical factors in controlling the carrier lifetime of the symmetric structure. By using the VHFPECVD to deposit the nc-Si:H and using the MWA to enhance the quality of the symmetric structure, the deposited nc-Si:H’s properties of a crystalline volume fraction of 29.6%, an optical bandgap of 1.744 eV, and a carrier lifetime of 2942.36 μs were well achieved, and could be valuable in thin-film solar-cell applications.

Microcrystalline and Nanocrystalline Silicon: Simulation of Material Properties

2005 ◽  
Vol 862 ◽  
Author(s):  
R. Biswas ◽  
B. C. Pan ◽  
V. Selvaraj
Keyword(s):  
Silicon Nanowires ◽  
Amorphous Matrix ◽  
Volume Fraction ◽  
Crystalline Silicon ◽  
Amorphous Region ◽  
Nanocrystalline Silicon ◽  
Nano Crystalline ◽  
Crystalline Core ◽  
Silicon Structures ◽  
Dynamics Simulations

AbstractWe have simulated nano-crystalline silicon and microcrystalline silicon structures with varying crystallite volume fractions, using molecular dynamics simulations. The crystallite regions reside in an amorphous matrix. We find the amorphous matrix is better ordered in nanocrystalline-Si than in the homogenous amorphous silicon networks, consistent with the observed higher stability of H-diluted films. There is a critical size above which the crystallites are stable and may grow. Sub-nm size crystallites in the protocrystalline phase are found to reduce the strain of the amorphous matrix. We simulated micro-crystalline silicon with a substantial crystallite volume fraction. Microcrystalline structures exhibit a crystalline core surrounded by an amorphous shell with similarities to silicon nanowires. We find a relatively uniform H distribution in the amorphous region and a crystal-amorphous phase boundary that is not welldefined.

The Pressure Dependence of Structural, Electronic, Mechanical, Vibrational, and Thermodynamic Properties of Palladium-Based Heusler Alloys

2017 ◽  
Vol 72 (9) ◽  
pp. 843-853 ◽  
Author(s):  
Cansu Çoban
Keyword(s):  
Thermodynamic Properties ◽  
Elastic Constants ◽  
Phonon Dispersion ◽  
Electronic Band Structure ◽  
Heusler Alloys ◽  
Dispersion Curves ◽  
Pressure Derivative ◽  
Electronic Band ◽  
Phonon Dispersion Curves ◽  
The Stability

AbstractThe pressure dependent behaviour of the structural, electronic, mechanical, vibrational, and thermodynamic properties of Pd2TiX (X=Ga, In) Heusler alloys was investigated by ab initio calculations. The lattice constant, the bulk modulus and its first pressure derivative, the electronic band structure and the density of states (DOS), mechanical properties such as elastic constants, anisotropy factor, Young’s modulus, etc., the phonon dispersion curves and phonon DOS, entropy, heat capacity, and free energy were obtained under pressure. It was determined that the calculated lattice parameters are in good agreement with the literature, the elastic constants obey the stability criterion, and the phonon dispersion curves have no negative frequency which shows that the compounds are stable. The band structures at 0, 50, and 70 GPa showed valence instability at the L point which explains the superconductivity in Pd2TiX (X=Ga, In).

A BN analog of two-dimensional triphenylene-graphdiyne: stability and properties

Nanoscale ◽  
2019 ◽  
Vol 11 (18) ◽  
pp. 9000-9007 ◽  
Author(s):  
Imran Muhammad ◽  
Huanhuan Xie ◽  
Umer Younis ◽  
Yu Qie ◽  
Waseem Aftab ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Band Structure ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Two Dimensional ◽  
Electronic Band ◽  
Functional Theory ◽  
The Stability ◽  
First Time ◽  
Recent Synthesis

Motivated by the feasibility of hybridizing C- and BN-units as well as the recent synthesis of a triphenylene-graphdiyne (TpG) monolayer, for the first time we explore the stability and electronic band structure of a Tp-BNyne monolayer composed of C-chains and the BN analog of triphenylene (Tp-BNyne) by using density functional theory.

Oxidation Reduction in Nanocrystalline Silicon Grown by Hydrogen-Profiling Technique

2016 ◽  
Vol 41 ◽  
pp. 9-17 ◽  
Author(s):  
Christopher J. Arendse ◽  
Theophillus F.G. Muller ◽  
Franscious R. Cummings ◽  
Clive J. Oliphant
Keyword(s):  
Amorphous Silicon ◽  
Hydrogen Concentration ◽  
Film Growth ◽  
Volume Fraction ◽  
Crystalline Silicon ◽  
Chemical Vapour ◽  
Silicon Layer ◽  
Nanocrystalline Silicon ◽  
Substrate Interface ◽  
Nano Crystalline

The deposition of a compact amorphous silicon/nano-crystalline silicon material is demonstrated by hot-wire chemical vapour deposition using a sequential hydrogen profiling technique at low hydrogen dilutions. Nano-crystallite nucleation occurs at the substrate interface that develops into a uniform, porous crystalline structure as the growth progresses. A further reduction in the H-dilution results in the onset of a dense amorphous silicon layer. The average crystalline volume fraction and nano-crystallite size in the sample bulk amounts to 30% and 6 nm, respectively, as probed by Raman spectroscopy using the 647 nm excitation. The change in hydrogen dilution is accompanied by a graded hydrogen concentration depth-profile, where the hydrogen concentration decreases as the growth progresses. The level of post-deposition oxidation is considerably reduced, as inferred from infrared spectroscopy. The presence of oxygen is mainly confined to the substrate interface as a result of thermal oxidation during thin film growth.

The Electronic Properties of Al-, P-Doped and Al, P Co-Doped Boron Nitride Nanotubes

2011 ◽  
Vol 399-401 ◽  
pp. 2215-2221 ◽  
Author(s):  
Miao Sun ◽  
Gong Lian Wu ◽  
Ting Ye ◽  
Hui Zhang ◽  
Zhao Di Yang ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Boron Nitride Nanotubes ◽  
Electronic Band ◽  
First Principle Calculation ◽  
Impurity Atoms ◽  
Impurity Doped ◽  
The Stability ◽  
Co Doped

The electronic properties of Al-, P-doped, and Al, P co-doped in a (6, 6) BN nanotubes were obtained using the first principle calculation based on the density functional theory. For the doped BNNTs, the structures are with ignorable deformation observed around the doping atoms. The analysis of the formation energies shows that aluminum replacement to be favorable, particularly in the case of the low concentration, and the stability of nanotubes has nothing to do with the doping position. The electronic band structure and DOS for the systems of Al-, and P-doped BNNTs all behave as impurity-doped widegap semiconductor. And as to the P-doped BNNTs, the conductivity becomes stronger with the higher concentration. Whereas, the results of the system of Al, P co-doped BNNTs illustrate that the electronic properties of nanotubes have nothing to do with the doping positions of impurity atoms.

scholarly journals Scrutinizing the Stability and Exploring the Dependence of Thermoelectric Properties on Band Structure of 3d Metal-Based Double Perovskites: An ab-initio Analysis

2021 ◽  
Author(s):  
Shabir Ahmad Mir ◽  
Dinesh C. Gupta
Keyword(s):  
Band Structure ◽  
Transport Properties ◽  
Exchange Interaction ◽  
Electronic Band Structure ◽  
Double Perovskites ◽  
Electronic Band ◽  
Band Profile ◽  
Strong Exchange ◽  
The Stability ◽  
Cohesive Energies

Abstract Through the conventional DFT computation, we have designed new oxide double perovskites Ba2BNiO6 (B = Fe and Co). The structural and thermodynamic stabilities are defined by optimizing the crystal energy and determination of tolerance factor and cohesive energies. Thereafter, at the optimized lattice constant, we have explored the different physical properties. The GGA+mBJ electronic band-structure depicts the semiconducting nature for Ba2CoNiO6 while half-metallic with 100% spin polarization for Ba2FeNiO6. The origin of such a diverse band profile upon changing Fe to Co is explained with the help of the orbital diagram and exchange interaction. The eg-eg interaction is strong in these perovskites compared to eg-t2g and t2g-t2g hybridization. The strong exchange interaction among eg states via O-p states happens because the B-O-Ni angle is strictly 180°. Furthermore, due to the narrow bandgaps, we have explored the transport properties to express the applicability of these materials towards thermoelectric technology. Also, herein we have investigated the dependency of transport properties on band profile. The semiconducting nature in Ba2CoNiO6 results in a high ZT~0.8 at room temperature makes it suitable for energy restoration.

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