Heat capacity of crystalline GaN

The heat capacity of gallium nitride has been measured by DSC method using DuPont Thermal Analyst 2100, DSC 951 unit in the temperature range (300–850 K). The temperature dependence of the heat capacity can be presented in the following form: C _p=32.960+0.162·10⁻¹ T+2360170T ⁻²-775370000T ⁻³.     

丙烷氧化反应中多组分氧化物Bi－V－Mo－O催化作用的红外光谱研究

迄今对于含有铝、秘复合氧化物催化剂的活性中心和作用机理存在不同看法,本文采用红外光谱法,探讨了复合氧化物钥钒酸秘在丙烷选择氧化反应中的催化作用机理.     

Wettability of Polyhedral Oligomeric Silsesquioxane Nanostructured Polymer Surfaces

Summary: Some model structures of waterborne polyurethane anionomers containing various amounts (ca. 3–20%) of a diol functionalized polyhedral oligomeric silsesquioxane (POSS) nanofiller were prepared. X‐ray diffraction showed the formation of a nanocrystalline structure in all copolymers considered. Static contact angle measurements indicated a significant enhancement of surface hydrophobicity as well as reduction in surface tension components even at the least POSS level (3%). Dynamic contact angle cycles allowed the evaluation of the hysteresis, which was found to be large and kinetically increasing in POSS‐modified samples. Film topography was analyzed by AFM, showing a more pronounced roughness in the nanostructured surface.

The AFM image showing a moderate roughness increase.     

甘氨酸铝锆的制备与红外光谱研究

以结晶氯化铝、氧氯化锆、甘氨酸为原料,通过分步溶解再混溶制备了甘氨酸铝锆水溶液,讨论了其稳定性,确定了较佳原料配比m(结晶氯化铝)/m(氧氯化锆)/m(甘氨酸)=12.46/8.00/16.39。并采用分步升温的烘干方法制得固体。进行了铝形态分布分析,测定了红外光谱,指认了其主要红外吸收带的归属。计算了羧基的反对称和对称伸缩振动频率的差值Δυ=154.73cm-1,说明甘氨酸通过羧基与金属离子配位形成的化学键为离子键。     

Density Functional Theory Study on the Optical Properties of Mn-doped GaN

The absorption and emission spectra of the wurtzite Mn-doped GaN were calculated with cluster models.The predicted lattice parameters become slightly larger than those of undoped cluster.The average bond length of Mn-N is longer than that of Ga-N.Spin density shows that one Mn atom in these clusters has four single electrons with the same direction of the spin polarity.The new energy level with light Mn-doping appears at 1.37 eV above the valance band.The absorption spectra of Mn-doped GaN cover the visible light region.The calculated emission spectra show that the green luminescence of GaN material in experiment did not result from Mn dopant.With the increase of Mn doping,the emission intensity of yellow or blue band increases to different extent and the band-to-band emission band shows red shift from peak at 3.34 to 3.24 eV.     

The First Principles Investigations of the Thermoelectric Properties of GaN with p- and n-Type Doping

We investigate the thermoelectric properties of GaN with p-and n-type doping by the first principles calculation and the semi-classical Boltzmann theory. We find that the power factors (S2σof p-type GaN (-3500 W/mK2) is about twice that of the n-type (-1750 W/mK2), which indicates the thermoelectric properties of p-type GaN would be better. Thermal conductivity of GaN crystal decreases rapidly as the temperature increases, but it is still too large for thermoelectric applications. The figure of merit (ZT) estimated at 1500 K is 0.134 for p-type GaN crystal and 0.062 for the n-type.     

Theoretical Investigation on the Electronic and Geometric Structure of GaN2+ and GaN4+

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

GaN and GaxIn1−xN Nanoparticles with Tunable Indium Content: Synthesis and Characterization

Semiconducting GaN and Ga_xIn_1?xN nanoparticles (4–10 nm in diameter, depending on the metal ratio) with tunable indium content are prepared through a chemical synthesis (the urea‐glass route). The bandgap of the ternary system depends on its composition, and therefore, the color of the final material can be turned from bright yellow (the color of pure GaN) to blue (the color of pure InN). Transmission electron microscopy (TEM and HRTEM) and scanning electron microscopy (SEM) images confirm the nanoparticle character and homogeneity of the as‐prepared samples. X‐ray diffraction (XRD), electron diffraction (EDX), elemental mapping, and UV/Vis, IR, and Raman spectroscopy investigations are used to confirm the incorporation of indium into the crystal structure of GaN. These nanoparticles, possessing adjusted optical properties, are expected to have potential applications in the fabrication of novel optoelectronic devices.     

Etching characteristics of GaN by plasma chemical vaporization machining

A high‐quality bulk gallium nitride (GaN) substrate, which is suitable for high‐quality homoepitaxial growth, is indispensable for realizing high‐performance GaN devices. With improvement in the quality of the bulk GaN substrate, the removal of subsurface damage induced during surface polishing has become increasingly necessary. To remove the subsurface damage from the bulk GaN substrate, a chemical finishing method that does not produce further damage is required. We applied plasma chemical vaporization machining (CVM) to remove the subsurface damage from the bulk GaN substrate. In this study, we investigated the etching characteristics of GaN by plasma CVM applying atmospheric pressure Cl₂/He plasma. The maximum removal rate in the depth direction by plasma CVM was 9100 nm/min, which is seven times greater than that of reactive ion etching (RIE). The activation energy in plasma CVM was estimated to be 2.1 kcal/mol, which is 1.75 times greater than that in RIE. It is supposed that some of the energy required for the removal reaction in RIE is supplied by ion bombardment, but plasma CVM depends on only a chemical reaction without high‐energy ion collision. This result suggests that plasma CVM is a finishing method that causes less subsurface damage than RIE. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of repetition nanoindentation of GaN epilayers on a‐axis sapphire substrates

In this work, gallium nitride (GaN) epilayers were deposited on a‐axis sapphire substrate by means of metal organic chemical vapor deposition (MOCVD). Berkovich nanoindentation was used to explore the repetition pressure‐induced impairment of the GaN film. The observation of load‐displacement vs stress‐strain curves concludes that basal slip is implicated in the deformation on the A plane GaN. The increase in the hardness (H) and elastic modulus (E) was determined from cyclic nanoindentation, and resulted in a crack due to the formation of incipient slip bands and/or the to‐and‐fro motion of mobile dislocation. It is indicated that the generation of individual dislocation and residual deformation of the GaN films are showed by CL mapping analysis. From the morphological studies, it is revealed that the crack was found by means of atomic force microscope (AFM) technique at nine loading/reloading cycles even after the indentation beyond the critical depth on the residual indentation impression. Copyright © 2010 John Wiley & Sons, Ltd.     

Al表面条纹状准有序纳米结构的AFM研究

用电化学抛光法在高纯铝表面生成纳米级条纹状的准有序结构.在原子力显微镜（AFM）下观察,条纹状结构的突起和凹槽部分线宽各为40～50 nm,峰 谷高度差为1.5～5.0 nm.随工艺条件的变化该纳米结构的尺寸和有序程度有较大差异,只有在很窄的参数范围内才可以得到大面积有序的条纹状结构.在用阳极氧化法制备多孔膜过程中该结构不能保持.对这种有序结构的形成机理提出了定性解释.     

Growth of GaN Layers on Sapphire by Low‐Temperature‐Deposited Buffer Layers and Realization of p‐type GaN by Magesium Doping and Electron Beam Irradiation (Nobel Lecture)

This Review is a personal reflection on the research that led to the development of a method for growing gallium nitride (GaN) on a sapphire substrate. The results paved the way for the development of smart display systems using blue LEDs. The most important work was done in the mid to late 80s. The background to the author’s work and the process by which the technology that enables the growth of GaN and the realization of p‐type GaN was established are reviewed.     

An Attenuated Total Reflection FT‐IR Spectroscopic Study of Polyamide 6/Clay Nanocomposite Fibers

Summary: An attenuated total reflection FT‐IR spectroscopic study of the hydrogen bonding, molecular orientation, and crystalline phase transitions in polyamide 6 (PA6)/clay nanocomposite (PA6CN) fibers is proposed. The nanoscale dispersed clay layers lowered the degree of order of hydrogen bonding, affected little the hydrogen bonding strength, and increased the degree of orientation of both γ crystalline and overall domains. A partial γ to α phase transition appeared with time.

Schematic representation of the attenuated total reflection FT‐IR dichroism measurements.     

Spectroscopic investigation (IR and NMR) and HOMO-LUMO analysis of aromatic imines using theoretical approach

In this work, the theoretical studies on the structure, FT-IR, NMR, and UV–Vis spectroscopy of (E)-N-benzylidenebenzenamine (A1) and (E)-N-(2, 4′-dichlorobenzylidene) propan-1-amine (A2) are presented. The optimized structure of the molecules, NMR and UV–Vis spectra analysis were determined by the Density Functional Theory (DFT) method using B3LYP/6-311G (d, p) basis set. For FT-IR analysis, both the HF and DFT methods were used in order to determine their accuracy and reliability in theoretical calculations. The computed result of DFT calculations in comparison with the experimental results showed that the DFT method gives a more accurate prediction. The infrared (IR) spectra for the imine molecules have been recorded in the region of 500–4000 cm^?1. The gauge-independent atomic orbital (GIAO) method has been used to evaluate the ¹³C and ¹H nuclear magnetic resonance (NMR) chemical shifts of the molecules. The computed results of NMR spectra of the molecules was found to be in good agreement with the experimental data. The UV–Vis spectra of the molecules were computed to determine the HOMO-LUMO energies in order to gain insight into their electronic properties. Mulliken population analysis on atomic charges of the molecules was also calculated using the HF (Hartree-Fock) and B3LYP method. All the computed results indicated that the B3LYP method provides satisfactory results and, therefore, can be employed to support experimental data. It also demonstrated a reliable approach towards characterization of molecules in chemical science.     

DFT Simulations of Water Adsorption and Activation on Low‐Index α‐Ga2O3 Surfaces

Density functional theory (DFT) calculations are used to explore water adsorption and activation on different α‐Ga₂O₃ surfaces, namely (001), (100), (110), and (012). The geometries and binding energies of molecular and dissociative adsorption are studied as a function of coverage. The simulations reveal that dissociative water adsorption on all the studied low‐index surfaces are thermodynamically favorable. Analysis of surface energies suggests that the most preferentially exposed surface is (012). The contribution of surface relaxation to the respective surface energies is significant. Calculations of electron local density of states indicate that the electron‐energy band gaps for the four investigated surfaces appears to be less related to the difference in coordinative unsaturation of the surface atoms, but rather to changes in the ionicity of the surface chemical bonds. The electrochemical computation is used to investigate the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on α‐Ga₂O₃ surfaces. Our results indicate that the (100) and (110) surfaces, which have low stability, are the most favorable ones for HER and OER, respectively.     

Formation and Thermal Decomposition of Gallium Oxynitride Compounds

The formation of a previously unknown crystalline phase was observed in the system Li–Ga–N–O. During the reactions of Ga₂O₃ with Li₃N and of LiGaO₂ with Li₃N, a new compound with the stoichiometry Li₄GaNO₂ was formed. The stages in thermal decomposition of the new phase were determined. This revised version was published online in July 2006 with corrections to the Cover Date.