Surface Carbonization of GaN and the Related Structure Evolution during the Annealing Process

To explain the stabilization mechanism of the carbon-ion-implanted GaN under the diamond growth environment,the luminescence characteristics and structure evolution correlative with sites' carbon atoms located for highfluence carbon-ion-implanted Ga N are discussed. GaN is implanted with carbon ion using fluence of 2×10~(17) cm~(-2) and energy of 45 keV. Then the implanted samples are annealed at 800℃ for 20 min and 1 h under the N_2 atmosphere. The luminescence characteristics of carbon-ion-implanted GaN are evaluated by photoluminescence spectrum at wavelength 325 nm. The lattice damage of Ga N is characterized by Raman spectrum and the corresponding vacancy-defect evolution before and after annealing is measured by slow positron annihilation. The results show that most of the carbon atoms will be located at the interstitial sites after carbon ion implantation due to the weak mobility. As the implanted samples are annealed, strong yellow luminescence is emitted and the vacancies for Ga(V_(Ga)) are reduced resulting from the migration of interstitial carbon(C_i) and formation of complexes(CGaand/or C_(Ga)-C_i) between them. As the annealing time is prolonged, the carbon ions accommodated by the vacancies are saturated, vacancy clusters with carbon atoms appear and the concentration of C_(Ga) diminishes, which will have an adverse effect on the diamond film nucleation and growth.     

Electrophysical Model of the Micro-Arc Oxidation Process

Russian Physics Journal - On the basis of the equivalent electrical circuit proposed by the authors, a mathematical model of the formation of protective coatings by the micro-arc oxidation method...     

环境对MgB_2氧化过程中MgO晶须生长形状的影响

用扫描电镜研究了在 Mg B2 氧化过程中环境对 Mg O晶须生长形状的影响。仅有 Mg B2 时 ,在 80 0℃左右空气气氛中 ,可生长出纳米尺寸的 Mg O晶须。若把 Mg B2 添加到氧化铝陶瓷基体中 ,则生长成竹节状晶须。Mg O晶须生长形状的差别可能是由于氧浓度以及位错等因素造成的。     

不同退化程度与人工恢复方式对草原土壤胡敏酸结构的影响

该研究主要探讨不同退化程度和人工恢复方式对草原土壤胡敏酸结构的变化特征,为退化草原恢复提供理论依据.在鄂尔多斯沙地不同退化样地与人工恢复草地,对草原土壤的腐殖酸进行了分离提取,采用元素分析、13核磁共振(NMR)等方法对荒漠草原土壤退化与恢复过程中土壤胡敏酸(HA)不同官能团的含量变化进行分析,并用因子分析法研究它们的结构特征和差异.结果表明:不同退化及恢复阶段HA碳骨架相似,但各类碳原子(官能团)的含量不同,芳香族和脂肪族结构在胡敏酸结构中发挥了重要作用.退化阶段,土壤HA的芳香碳减少,碳水化合物减少,土壤HA的氧化程度增加,疏水程度降低.恢复阶段土壤芳香碳含量增加,碳水化合物含量增加,疏水程度略有降低.土壤退化及恢复阶段,胡敏酸(HA)的结构变化最大的部分是芳香碳、取代脂肪碳结构,其次是羧基和酯基碳和未取代脂肪碳结构.植被恢复对腐殖酸结构的变化有重要的影响,本氏针茅区和本氏针茅+油蒿区的HA结构中芳香化程度和复合程度较高,氧化程度低.围栏样区内土壤胡敏酸(H A)的酸度相对较高,芳香化程度和复合程度仍然较低.因此,土壤胡敏酸结构特征的变化可以反映草原土壤的退化程度,进一步揭示草原土壤退化的机制.     

Structural Evolution of Compressing Amorphous Ice

Molecular dynamics simulation is employed to study structural evolution during compressing low density amorphous ice from one atmosphere to 2.5 GPa. The calculated results show that high density amorphous ice is formed under intermediate pressure of about 1.0GPa and O-O-O angle ranges from about 83°to 113° and O-H…O is bent from 112° to 160°The very high density amorphous ice is also formed under the pressure larger than 1.4 GPa and interstitial molecules are found in 0.3-0.4 A just beyond the nearest O-O distance. Low angle O-H… O disappears and it is believed that these hydrogen bonds are broken or re-bonded under high pressures.     

垂直腔面发射激光器湿法氧化工艺的实验研究

为实现对垂直腔面发射半导体激光器氧化孔径的精确控制,提高其光电特性,对湿法氧化工艺进行了实验研究.在不同的氧化温度下,对相同结构的垂直腔面发射半导体激光器模拟片进行湿法氧化.采用X射线能谱分析仪,对氧化后模拟片的氧化层按不同的氧化深度对其氧化生成物进行检测.依据氧化生成物中氧元素组分浓度的变化,对氧化过程进行了分析与讨论,推导出在一定的温度下,氧化速率随时间变化的一般规律.提出了在垂直腔面发射半导体激光器的湿法氧化工艺过程中,适当降低氧化温度,延长氧化时间,可减小氧化限制孔径的控制误差,提高氧化工艺的准确性与稳定性.     

初始状态对自组织演化过程的影响

从实验上系统研究了在强电场下处于介质中的大量金属小球从不同初始状态通过自组织演化为分形的过程;用Sandbox方法定量分析了最终形成的稳定树枝状分形的维数。结果表明:不同初始状态形成分形的过程完全不同,但最终的树枝状分形的维数基本相同。分析认为,小球之间的相互作用存在临界作用距离,不同初始状态相邻小球之间的平均间距不同,因而演化过程不同;而维数相同正是系统耗散相同的体现。     

Modelling Moran Process with Network Dynamics for the Evolution of Cooperation

We introduce a simple model based on the Moran process with network dynamics. Using pair approximation, the cooperation frequencies at equilibrium states are deduced for general interactions. Three usual social dilemmas are discussed in the framework of our model. It is found that they all have a phase transition at the same value of cost-to-benefit ratio. For the prisoner＇s dilemma game, notably it is exactly the simple rule reported in the literature [Nature 441 （2006） 502]. In our model, the simple rule results from the parent-offspring link. Thus the basic mechanism for cooperation enhancement in network reciprocity is in line with the Hamilton rule of kin selection. Our simulations verify the analysis obtained from pair approximation.     

Study of the Evolution in the Iron Oxide Synthesis by Hydrothermal Process

Hyperfine Interactions - A solution of Fe(NO3)3 with a pH 9 was processed with a hydrothermal method in an autoclave. During the heating process samples were extracted at 140°C, 160°C,...     

Structural Evolution of Diisopropylammonium Chloride (DIPAC) Molecular Ferroelectric

Physics of the Solid State - Room-temperature changes in the structure of a new diisopropylammonium chloride (C6H16ClN, DIPAC) molecular ferroelectric have been investigated by high-resolution...     

Thermal Oxidation and Structural Changes of Degraded Polyethylene in an Oxygen Atmosphere

High-temperature bulk thermolysis of high density polyethylene was performed to obtain degraded polyethylene, which was then left in an oxygen atmosphere for oxidation reaction at 160°C at different oxidation times, yielding a series of polyethylene degradation–oxidation products. Using infrared spectroscopy, chemical titration, gel chromatography, and differential scanning calorimetry, the structural changes of the polyethylene degradation–oxidation products were investigated. Hydroxyl, carboxyl, ester, and other functional groups were introduced into the molecular chains of oxidation products, and the number of carboxyl groups sharply increased with increasing oxidation time. The breaking of molecular chains as well as combination reactions, such as esterfication, during the oxidation process lead to decrease of number-average molecular weight () and increase of both weight-average molecular weight () and molecular weight distribution, and an initial increase and leveling off of the carboxyl number per molecular chain. It is noteworthy that oxidation occurred primarily near weak bonds, mainly terminal vinyl unsaturations. Thus, compared with degraded polyethylene, the oxidation products showed little changes in the melting and crystallization behaviors; even when the oxidation time was up to 4 hr, the drop in the melting and crystallization temperature was less than 3°C. These results might lay a foundation for exploring tailored low molecular weight polymers to be used just as they are or after chemical modifications of olefinic functions.     

Evolution of the auroral oval during a weak substorm

The present paper deals with a detailed study of the dynamics of the polar cap boundaries. The study involves the data from two satellites of the APEX project, and the data from three DMSP satellites. The APEX (Active Plasma Experiment) satellites moving along the polar orbit provide charged particle measurements in a small spatial scale (due to variable distance between both spacecrafts), up to 2 000 km. The large scale changes are studied by the comparison of the APEX and the DMSP (Defense Meteorological Satellite Program) data. Different regions are identified using the characteristics of the precipitating particles in the energy range 0.1–20 keV which have been registered onboard all satellites. This satellite configuration allows us to determine the evolution of the small structures as well as the motion of the whole precipitating region. The main attention is concentrated on the rising phase of the substorms when the width of the auroral oval decreases with the increasing geomagnetic activity and the velocity of the auroral oval motion can reach 0.2° per minute. The observed phenomena are compared with the changes of the interplanetary magnetic field and the solar wind parameters as provided by the IMP-8 spacecraft.     

Characterizing the Evolution of Porosity during Controlled Drug Release

Nuclear magnetic resonance (NMR) techniques have been successfully used to characterize the evolving pore structure of partially soluble pharmaceutical pellets as they absorb water and release soluble components. The restricted diffusivity of water trapped within pellets, which have been immersed in water for differing times, has been measured by pulsed field gradient NMR. These measurements have been used to calculate the surface-to-volume ratio and tortuosity of the pore structure. A one-shot Carr–Purcell–Meiboom–Gill sequence has been used to measure the spin–spin (T ₂) relaxation time of water trapped within the pellets. These data have been regularized and then analyzed by the Brownstein–Tarr model to provide a pore size distribution for the pellets as a function of increasing immersion time. It has been found that pore structure changes significantly as water enters the pellet matrix. Two pellet formulations (herein referred to as placebo and drug-loaded) were studied and showed the same trends of a decreasing surface-to-volume ratio and tortuosity with increasing immersion time. At an immersion time of 10 min, both of these parameters decreased to approximately 70% of their values compared to an immersion time of 2 min. The placebo material tested consistently had both a higher tortuosity and surface-to-volume ratio than the drug-loaded material. At an immersion time of 2 min, the tortuosity for the placebo and drug-loaded materials were about 18 and about 10, respectively, and surface-to-volume ratios of about 6 μm⁻¹ and about 5 μm⁻¹, respectively. The materials tested also show changes in their pore size distribution with immersion time. In both formulations the mean and modal pore sizes increase with immersion time. The placebo material maintains an approximately similar mean and modal pore size, about 2 μm over the timescales studied, suggesting a more symmetric pore size distribution. In the drug-loaded pellets the mean pore size is much higher than the modal pore size, their values being 6.5 and 2.1 μm after 10 min immersion time, respectively. Authors' address: Michael D. Mantle, Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK     

Oxidation phenomena at the surface of iron alloys during laser treatments

An 1C-1.5Cr steel was laser treated under conditions suitable to obtain surface melting. The surface oxidizing phenomena and the laser-induced transformations were studied by means of surface Mössbauer measurements, X-ray diffraction and metallography. Significant modifications in the transformations, caused by surface oxidation, were correlated to the carbon availability at the surface during the treatments.     

Analysis of the Structural Evolution of Zinc Oxide Powders Obtained by Mechanical High-Energy Grinding

Technical Physics - Zinc oxide powders made by mechanical high-energy grinding have been investigated using the methods of scanning electron microscopy, thermal nitrogen desorption, and Raman...     

三氧化钨溶胶稳定机理及薄膜结构变化特征探讨

本文以钨酸钠阳离子树脂酸化法制备三氧化钨溶胶,采用提拉法成膜,并讲座了溶胶稳定和成膜的机理,通过TG－DTA和IR分析探讨了固体薄在热算是过程中的结构变化,实验结果表明,双氧水和乙醇与钨酸络合,使溶胶稳定,挥发性强的小分子配体（如乙醇）对成膜有利,TG－DTA和IR分析结果表明,随着热处理温度的提高,薄膜中多聚钨酸离子（或者产氧化钨分子簇）进一步缩合,WO6八面对称性逐渐增强。     

Numerical Simulation of the Structure and Mechanical Properties of Silicene Layers on Graphite during the Lithium Ion Motion

Physics of the Solid State - The molecular dynamics method is applied to study structural and mechanical effects appearing during the lithium ion motion in a dc electric field along a planar...     

Structural changes in CoPt during ordering

X-ray methods have been applied to CoPt (48. 6 at. Co) during ordering; new data from the superlattice peaks are presented on the shape, size, and orientation of the new phase. The diffraction effects for the main peaks are explained as the result of monoclinic distortion in the cubic matrix. The maximal hardness during ordering is considered to be due to the rotation of blocks produced by the elastic stresses rather than to the stresses themselves.