GGA-based analysis of the metformin adsorption on BN nanotubes

Density functional theory (DFT) studies are done to investigate structural and electronic properties of (5,5) chirality single walls boron nitride nanotubes (BNNTs) in the armchair model interacting with metformin (MF) on the surface and ends. Our calculations consider the exchange-correlation energies with the Hamprecht–Cohen–Tozer–Handy functional within the generalized gradient approximation (HCTH-GGA) and the double polarized DNP base function. The geometry optimization follows the minimum energy criterion for all six geometries we have considered. Results show that the MF is adsorbed through the groups NH₂–NH at one end of the nanotube. The system polarity is increased which indicates the possible dispersion and solubility. Moreover the interaction between these species induces an increase in the chemical reactivity of the order of 0.42 eV. Meanwhile the solvation in water keeps the semiconductor characteristics of both nanotube and MF. The work function of the BNNT-MF is drastically reduced respect to the pristine system when the BN nanotube is doped at its surface and ends with carbon. This means that the functionalized BN nanotube facilitates conditions to improve field emission.     

Environment of the P b center at the Si(111)/oxide interface

We assess several models for the environment of the P _b center (Si dangling bond center) at the interface of Si(111) with its oxide. The comparison of hyperfine constants observed with those predicted using large cluster models favors a local structure in which there is an Si-Si bond within the oxide close to the Si dangling bond. Such Si-Si bonds are also suggested by a number of other experiments and are consistent with the reactive layer model proposed to rationalize a range of oxidation studies.     

Study on electrical defects level in single layer two-dimensional Ta_2O_5

Two-dimensional atomic-layered material is a recent research focus, and single layer Ta_2O_5 used as gate dielectric in field-effect transistors is obtained via assemblies of Ta_2O_5 nanosheets. However, the electrical performance is seriously affected by electronic defects existing in Ta_2O_5. Therefore, spectroscopic ellipsometry is used to calculate the transition energies and corresponding probabilities for two different charged oxygen vacancies, whose existence is revealed by x-ray photoelectron spectroscopy analysis. Spectroscopic ellipsometry fitting also calculates the thickness of single layer Ta_2O_5,exhibiting good agreement with atomic force microscopy measurement. Nondestructive and noncontact spectroscopic ellipsometry is appropriate for detecting the electrical defects level of single layer Ta_2O_5.     

透镜初级球差的横向剪切干涉条纹研究

利用玻璃平行平板构成简单的横向剪切干涉仪可以观察到单薄透镜形成的准直光束的剪切干涉条纹,由干涉条纹分布求出对应的几何像差和离焦量.用焦距为190 mm的单薄透镜做实验,实验结果与计算机模拟结果符合,说明可以从剪切干涉条纹的分布求出透镜的轴向调整误差和初级球差.     

硅单粒子位移损伤多尺度模拟研究

本文结合分子动力学方法和动力学蒙特卡罗方法, 研究了单个粒子入射硅引起的位移损伤缺陷的产生和演化过程; 基于Shockley-Read-Hall理论计算了单个粒子入射引起的位移损伤缺陷导致的泄漏电流增加及其演化过程, 比较了缺陷退火因子与泄漏电流退火因子之间的差异, 并将计算结果与实验值进行了对比. 结果表明, 计算泄漏电流时, 仅考虑一种缺陷的情况下缺陷退火因子与泄漏电流退火因子相同, 考虑两种缺陷类型情况下二者在数值上有所区别, 但缺陷退火因子仍能在一定程度上反映泄漏电流的退火行为. 分子动力学模拟中采用Stillinger-Weber势函数和Tersoff势函数时缺陷退火因子和泄漏电流退火因子与实验结果一致, 基于Stillinger-Weber势函数的计算结果与实验值更为接近.     

Thermodynamic aspects of carbon redistribution during ageing and tempering of Fe–Ni–C alloys

Carbon redistribution is known to occur during martensite ageing. The two associated processes most discussed in the literature are spinodal decomposition and carbon segregation to defects. In order to elucidate the topic, the ageing and tempering of two Fe–Ni–C alloys have been characterised by means of atom probe tomography and synchrotron radiation diffraction. Upon ageing at room temperature, carbon redistribution is clearly observed, where the process of carbon segregation to defects appears to be most likely to occur. Nevertheless, the possibility of spinodal decomposition is not entirely discarded, and the current work presents a series of discussion points that challenge our current understanding of the thermodynamic of ferrite in steels.     

Determination of thermal wave reflection coefficient to better estimate defect depth using pulsed thermography

Thermography is a promising method for detecting subsurface defects, but accurate measurement of defect depth is still a big challenge because thermographic signals are typically corrupted by imaging noise and affected by 3D heat conduction. Existing methods based on numerical models are susceptible to signal noise and methods based on analytical models require rigorous assumptions that usually cannot be satisfied in practical applications. This paper presents a new method to improve the measurement accuracy of subsurface defect depth through determining the thermal wave reflection coefficient directly from observed data that is usually assumed to be pre-known. This target is achieved through introducing a new heat transfer model that includes multiple physical parameters to better describe the observed thermal behaviour in pulsed thermographic inspection. Numerical simulations are used to evaluate the performance of the proposed method against four selected state-of-the-art methods. Results show that the accuracy of depth measurement has been improved up to 10% when noise level is high and thermal wave reflection coefficients is low. The feasibility of the proposed method in real data is also validated through a case study on characterising flat-bottom holes in carbon fibre reinforced polymer (CFRP) laminates which has a wide application in various sectors of industry.     

一种基于共轭节面的图像畸变分析方法

无像差的光学相机的成像模型可由其共轭节面模型等效表示。针孔模型本身忽略了偏离该等效模型的误差,也无法表示平板玻璃的平移误差、光轴的安装误差以及实际相机光学系统的像差,这四个因素都会引起图像畸变。基于此利用共轭节面的性质建立了一种图像畸变几何模型,并与广泛采用的像差模型进行了对比,从理论上解释了像差模型各个系数的物理意义。对某实际针孔相机进行仿真分析,该几何模型给出的相对径向畸变、角度误差在设计参数的范围以内,并且可以模拟图像的非对称畸变。该几何模型需要辨识包含主面相关参数、光轴倾斜角和平板玻璃的轴向球差在内的4个参数,辨识参数较少,理论上可以作为一种新的图像畸变校正方法。     

有效质量差异和电场对GaN/AlxGa1-xN球形量子点电子结构的影响

用平面波展开法对GaN/Al_xGa_1-xN球形量子点中类氢杂质态能级随量子点半径、Al组分以及结合能随Al组分的变化规律进行了详细讨论.计算了量子点内外有效质量差异对杂质态能级和结合能的修正,结果表明对于Al组分较高的GaN/Al_xGa_1-xN球形量子点,电子有效质量差异对杂质能级和结合能的修正不能忽略.考虑电子有效质量差异后,进一步具体计算了杂质结合能随量子点半 关键词： 球形量子点 平面波展开法 有效质量     

掺铁铌酸锂晶体中光致散射的锂组分和温度依赖关系研究

研究了单掺铁铌酸锂晶体的光致散射行为随锂组分以及温度的变化关系.实验表明,随晶体组分的升高,光致散射得到了大幅抑制;不同组分晶体光致散射被完全抑制的温度不同.由此提出掺铁铌酸锂晶体在48.9 mol%-49.3 mol%范围内可能存在一临界锂组分,当晶体组分超过这一临界组分时,晶体光致散射被大幅抑制,而光致散射行为的温度依赖关系明显改变.