Energetics of AlN Epitaxial Wetting Layers on SiC (0001)

1996 ◽  
Vol 449 ◽  
Author(s):  
R. Di Felice ◽  
J. E. Northrup ◽  
J. Neugebauer
Keyword(s):  
First Principles ◽  
Three Dimensional ◽  
Layer Growth ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Charge Accumulation ◽  
Wetting Layer ◽  
Interface Charge ◽  
Wetting Layers

ABSTRACTWe present a first-principles characterization of the initial stages of formation of AlN films on c-plane SiC substrates. Studying the competition between two-dimensional films and three-dimensional islands as a function of Al and N abundances, we find that a two-dimensional film can wet the surface in N-rich conditions. Ordered layer-by-layer growth can proceed to some extent on this wetting layer, and is improved by the formation of an atomically mixed interface which eliminates interface charge accumulation. Our results indicate that the stable AlN films grow in the (0001) orientation on the Si-terminated SiC(0001) substrate.

Structural Defects and Their Relationship to Nucleation of Gan Thin Films

1996 ◽  
Vol 423 ◽  
Author(s):  
Weida Gian ◽  
Marek Skowronski ◽  
Greg S. Rohrer
Keyword(s):  
Film Growth ◽  
Three Dimensional ◽  
Scanning Force Microscopy ◽  
Columnar Structure ◽  
Layer Growth ◽  
Buffer Layers ◽  
Structural Defects ◽  
Layer By Layer ◽  
Extended Defects ◽  
Edge Dislocations

AbstractMicrostructure and extended defects in α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AIN (or GaN) buffer layers have been studied using transmission electron microscopy. The types and distribution of extended defects were correlated with the film growth mode and the layer nucleation mechanism which was characterized by scanning force microscopy. The nature of the extended defects was directly related to the initial three-dimensional growth. It was found that inhomogeneous nucleation leads to a grain-like structure in the buffer; the GaN films then have a columnar structure with a high density of straight edge dislocations at grain boundaries which are less likely to be suppressed by common annihilation mechanisms. Layer-by-layer growth proceeds in many individual islands which is evidenced by the observation of hexagonal growth hillocks. Each growth hillock has an open-core screw dislocation at its center which emits monolayer-height spiral steps.

First-principles characterization of two-dimensional (CH3(CH2)3NH3)2(CH3NH3)n−1GenI3n+1 perovskite

2018 ◽  
Vol 6 (47) ◽  
pp. 24389-24396 ◽  
Author(s):  
Liyuan Wu ◽  
Pengfei Lu ◽  
Yuheng Li ◽  
Yan Sun ◽  
Joseph Wong ◽  
...  
Keyword(s):  
First Principles ◽  
Two Dimensional ◽  
Hybrid Perovskite ◽  
Optoelectronic Applications

A novel two-dimensional Ge-based hybrid perovskite is proposed for potential optoelectronic applications.

scholarly journals Structural diversity induced by ligand geometry: From two-dimensional to three-dimensional coordination polymers with pyridine

2020 ◽  
pp. 174751982096816
Author(s):  
Fang-Kuo Wang ◽  
Shi-Yao Yang ◽  
Hua-Ze Dong
Keyword(s):  
Coordination Polymers ◽  
Three Dimensional ◽  
Structural Diversity ◽  
Dimensional Structure ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Guest Molecules ◽  
X Ray ◽  
Benzenedicarboxylic Acid ◽  
Benzenetricarboxylic Acid

Two coordination polymers with two-dimensional and three-dimensional structures are, {[Zn3(bdc)3(py)2]·2NMP}n (1) (H2bdc = 1,4-benzenedicarboxylic acid) and [Zn2(NO3−)(btc)(nmp)2(py)]n (2) (H3btc = 1,3,5-benzenetricarboxylic acid), synthesized by hot-solution reactions of Zn(NO3)2·6H2O, pyridine (py) and two different ligands in N-methylpyrrolidone (NMP). {[Zn3(bdc)3(py)2]·2NMP}n exhibits two-dimensional networks with trizinc subunits [Zn3(COO)6py2] stacking with a layer-by-layer alignment, and there are strong π–π interactions involving py from adjacent layers. [Zn2(NO3−)(btc)(nmp)2(py)]n has a three-dimensional structure containing two independent zinc ions, tetrahedral ZnO4 and octahedral ZnNO5. Based on X-ray studies, the coordination polymers {[Zn3(bdc)3(py)2]·2NMP}n (1) have a porous structure with NMP guest molecules. In contrast, X-ray studies revealed that coordination polymer [Zn2(NO3−)(btc)(nmp)2(py)]n (2) had a larger void that was inhabited by coordinated py and NMP. In addition, the form of the two coordination polymers changed from two-dimensional to three-dimensional with transformation of the ligand geometry.

scholarly journals Characterization of the translocon of the outer envelope of chloroplasts

2003 ◽  
Vol 160 (4) ◽  
pp. 541-551 ◽  
Author(s):  
Enrico Schleiff ◽  
Jürgen Soll ◽  
Michael Küchler ◽  
Werner Kühlbrandt ◽  
Roswitha Harrer
Keyword(s):  
Three Dimensional ◽  
Dependent Manner ◽  
Interior Structure ◽  
Two Dimensional ◽  
Outer Envelope ◽  
Core Complex ◽  
The Core ◽  
Precursor Proteins ◽  
Stable Core

The protein translocon of the outer envelope of chloroplasts (Toc) consists of the core subunits Toc159, Toc75, and Toc34. To investigate the molecular structure, the core complex was purified. This core complex has an apparent molecular mass of ∼500 kD and a molecular stoichiometry of 1:4:4–5 between Toc159, Toc75, and Toc34. The isolated translocon recognizes both transit sequences and precursor proteins in a GTP-dependent manner, suggesting its functional integrity. The complex is embedded by the lipids phosphatidylcholine and digalactosyldiacylglyceride. Two-dimensional structural analysis by EM revealed roughly circular particles consistent with the formation of a stable core complex. The particles show a diameter of ∼130 Å with a solid ring and a less dense interior structure. A three-dimensional map obtained by random conical tilt reconstruction of electron micrographs suggests that a “finger”-like central region separates four curved translocation channels within one complex.

Metal-Organic chemical vapor deposition of BN on sapphire and its heterostructures with 2D and 3D materials

MRS Advances ◽  
2016 ◽  
Vol 1 (32) ◽  
pp. 2273-2283
Author(s):  
Qing Paduano ◽  
Michael Snure
Keyword(s):  
Electron Mobility ◽  
Substrate Surface ◽  
Chemical Vapor ◽  
High Electron Mobility Transistor ◽  
Layer Growth ◽  
Organic Chemical ◽  
Layer By Layer ◽  
High Electron ◽  
Two Dimensional ◽  
Direct Growth

ABSTRACTWe studied MOCVD processing for direct growth of BN on 2” sapphire substrates as a template for heterostructures with two dimensional (2D) and three dimensional (3D) materials. The combined experimental evidence points to three growth modes for BN: self-terminating, 3D random, and layer-by-layer, all of which are dependent on V/III ratio, temperature, pressure, and substrate surface modification via nitridation. At moderate temperature (950-1050°C), BN growth using high V/III ratio is self-terminating, resulting in c-oriented films aligned in-plane with respect to the orientation of the sapphire substrate. BN films grown under low V/III ratios are 3D, randomly oriented, and nano-crystalline. At higher temperature (1100°C), self-terminating growth transitions to a continuous layer-by-layer growth mode. When BN growth is self-terminating, films exhibit atomically smooth surface morphology and highly uniform thickness over a 2” sapphire wafer. Using these BN/sapphire templates we studied the growth of 2D and 2D/3D heterostructures. To study direct growth of 2D on 2D layered material we deposited graphene on BN in a continued process within the same MOCVD system. Furthermore, we explore the growth and nucleation of 3D materials (GaN and AlN) on BN. AlGaN/GaN based high electron mobility transistor (HEMT) structures grown on BN/sapphire exhibited two-dimensional electron gas characteristics at the AlGaN/GaN heterointerface, with room-temperature electron mobility and sheet electron density about 1900cm2/Vs and 1x1013cm-2, respectively.

Rheed Intensity Oscillation During Layer-by-Layer Growth of Bi-Sr-Ca-Cu-O Thin Films

1992 ◽  
Vol 275 ◽  
Author(s):  
K. Yoshikawa ◽  
N. Sasaki
Keyword(s):  
Thin Films ◽  
Buffer Layer ◽  
High Energy ◽  
Layer Growth ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Growth Interruption ◽  
Layer Deposition ◽  
Unit Cells ◽  
Layered Growth

ABSTRACTUsing in-situ reflection high-energy electron diffraction (RHEED), we studied the growth of Bi-Sr-Ca-Cu-O (BSCCO) thin films prepared by reactive evaporation using layer-by-layer deposition. Bi2Sr2CaCu2Ox(2212) tends to be grown three-dimensionally if it is grown directly on (100) SrTiO3, in contrast to Bi2Sr2CuOx(2201) which is easily grown two-dimensionally on SrTiO3. Two-dimensional 2212 growth can be realized, if a buffer layer of 2201 is deposited on (100) SrTiO3 and growth interruption is utilized after SrO layer deposition. A buffer layer of only two 2201 unit cells improved the surface crystallinity of the substrate for the epitaxial growth of 2212. Growth interruption for two minutes after the 2nd SrO layer in the half unit cell is necessary to keep two-dimensional layered growth. The resulting Tc (zero) is 76 K and Jc (at 4.2 K) is 1.5 × 106 (A/cm2) with these epitaxial films.

scholarly journals Realizable response matrices of multi-terminal electrical, acoustic and elastodynamic networks at a given frequency

2008 ◽  
Vol 464 (2092) ◽  
pp. 967-986 ◽  
Author(s):  
Graeme W Milton ◽  
Pierre Seppecher
Keyword(s):  
Three Dimensional ◽  
Complete Characterization ◽  
Two Dimensional ◽  
Response Matrix ◽  
Electrical Networks ◽  
Fixed Frequency ◽  
Symmetry Properties ◽  
Acoustic Networks ◽  
Mathematical Equivalence

We give a complete characterization of the possible response matrices at a fixed frequency of n -terminal electrical networks of inductors, capacitors, resistors and grounds, and of n -terminal discrete linear elastodynamic networks of springs and point masses, both in three-dimensional and two-dimensional cases. Specifically, we construct networks that realize any response matrix that is compatible with the known symmetry properties and thermodynamic constraints of response matrices. Owing to a mathematical equivalence, we also obtain a characterization of the response matrices of discrete acoustic networks.

Effects of Stress on Step Energies and Surface Roughness

MRS Bulletin ◽  
1996 ◽  
Vol 21 (4) ◽  
pp. 27-30 ◽  
Author(s):  
Christopher Roland
Keyword(s):  
Thin Films ◽  
Strain Relaxation ◽  
Three Dimensional ◽  
Layer Growth ◽  
Growth Mode ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Strained Layers ◽  
The Subject ◽  
Growth Changes

Strain relaxation in lattice-mismatched, heteroepitaxial systems is one of the classic problems in materials physics, which has gained new urgency with the increased applications of strained layers in microelectronic systems. In general both the structure and the integrity of the thin films are strongly influenced by strain. For instance it has long been known that under strain, the growth changes from an initial layer-by-layer growth mode to one with three-dimensional islanding. In the seminal works of van der Merwe, and Matthews and Blakeslee, this change in growth mode is explained in terms of the introduction of strain-relieving misfit dislocations, which appear when the film has reached some critical thickness. Recently it has become clear that this change in growth mode can take place even without the introduction of misfit dislocations. Such dislocation-free coherent islanding, or “roughening,” has been observed experimentally both in Ge/Si and in InGaAs/GaAs systems. Furthermore recent experiments show that in Ge/Si(100) systems, the thin films display a curious asymmetry with respect to the sign of the strain: Films under compression roughen by forming coherent islands while those under tension remain relatively smooth. A possible mechanism behind this strain-induced type of roughening is the subject of this article.

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