天然钻石与合成钻石的特异性光谱初步研究

通过紫外-可见-近红外(UV-Vis-NIR) 吸收光谱、傅里叶变换红外(FTIR)光谱及钻石观测仪( DiamondViewTM)对天然钻石、经辐照或热处理的天然钻石、高温高压(HTHP)合成钻石及化学气相沉积(CVD)合成钻石进行了较系统的谱图及微区生长结构的对比研究。结果表明：天然钻石、经辐照或高温退火处理后的天然钻石、高温高压(HTHP)合成钻石的UV-Vis-NIR吸收谱图在200～1 100 nm区间谱图的反射率变化明显。相比之下,CVD合成钻石的反射率的变化相对较小。基于钻石样品的红外光谱分析,在其图谱中的800～1 600 cm-1区间,合成钻石样品、特别是CVD合成钻石在上述区间无明显的特征吸收峰位。此外,DiamondViewTM检测表明：一般而言,经HTHP处理后的CVD合成钻石出现平行的位错线,并呈现淡蓝色荧光。部分天然钻石可见典型的八面体生长线或称为树的年轮状图像,且因样品经辐照与高温高压处理后其荧光图像的颜色发生改变。高温高压合成钻石呈现出块状几何生长图像。限于钻石样品类别的多样性及合成钻石工艺的复杂且不断更新特征,天然钻石与合成钻石 的UV-Vis-NIR或FTIR光谱特征存在一定的相似性,因此不具有典型天然钻石图谱特征的样品需进一步辅以DiamondViewTM、光致发光光谱等其他检测仪器予以综合分析。     

Critical behavior of a one-dimensional contact process with time-uncorrelated disorder

In this work, the critical behavior of the one-dimensional contact process with time-uncorrelated disorder is investigated. We develop simulations on finite chains and explore the finite size scaling hypothesis to obtain estimates for the relevant parameters associated with static and dynamical critical quantities. We use an auto-adaptative technique that has been recently shown to provide reliable results for the standard contact process transition. We compare the main results with those derived from the usual short-time dynamics scaling. We found that, contrary to the behavior of the contact-process with quenched disorder which displays an infinite randomness critical point with activated scaling, the contact process with time-uncorrelated disorder belongs to the usual universality class of directed percolation.     

Annealed Importance Sampling for Ising Models with Mixed Boundary Conditions

This note introduces a method for sampling Ising models with mixed boundary conditions. As an application of annealed importance sampling and the Swendsen-Wang algorithm, the method adopts a sequence of intermediate distributions that keeps the temperature fixed but turns on the boundary condition gradually. The numerical results show that the variance of the sample weights is relatively small.     

On the repulsion of an interface above a correlated substrate

We analyze a model of an interface fluctuating above a rough substrate. It is based on harmonic crystals, or lattice free fields, indexed by ^d , d 3. The phenomenon for which we want to get precise quantitative estimates is the repulsion effect of the substrate on the interface: the substrate is itself a random field, but its randomness is quenched (this generalizes the widely considered case of a flat deterministic substrate). With respect to [2] in which the substrate has been taken to be an IID field, here the substrate is an harmonic crystal, as the interface, and as such it is strongly correlated. We obtain the leading asymptotic behavior of the model in the limit of a very extended substrate: we show in particular that, to leading order, the effect of an IID substrate cannot be distinguished from the effect of an harmonic crystal substrate. We observe however that, unlike in the IID substrate case, annealed and quenched models display sharply different features.     

Central limit theorems for biased randomly trapped random walks on Z

We prove CLTs for biased randomly trapped random walks in one dimension. By considering a sequence of regeneration times, we will establish an annealed invariance principle under a second moment condition on the trapping times. In the quenched setting, an environment dependent centring is necessary to achieve a central limit theorem. We determine a suitable expression for this centring. As our main motivation, we apply these results to biased walks on subcritical Galton–Watson trees conditioned to survive for a range of bias values.     

On Markov Chain Approximations to Semilinear Partial Differential Equations Driven by Poisson Measure Noise

We consider the stochastic model of water pollution, which mathematically can be written with a stochastic partial differential equation driven by Poisson measure noise. We use a stochastic particle Markov chain method to produce an implementable approximate solution. Our main result is the annealed law of large numbers establishing convergence in probability of our Markov chains to the solution of the stochastic reaction-diffusion equation while considering the Poisson source as a random medium for the Markov chains.     

A Conditional CLT which Fails for Ergodic Components

We show that the conditional central limit theorem can take place for a stationary process defined on a nonergodic dynamical system while this last does not satisfy the central limit theorem for any ergodic component. There exists an ergodic Markov chain such that the conditional central limit theorem is satisfied for an invariant measure but fails to hold for almost all starting points.      

磁控溅射制备纳米TiO_2半导体薄膜的工艺研究与光谱分析

通过射频反应磁控溅射在玻璃基片上制备TiO2薄膜。采用X射线衍射仪和Raman光谱仪研究退火温度对薄膜晶体结构的影响;还探讨了磁控溅射氧分压对薄膜性能的影响。结果表明：磁控溅射制备的薄膜在不同温度下退火。300℃退火时薄膜没有结晶;400℃退火出现锐钛矿结构;500℃退火后薄膜锐钛矿结构更完善,（101）方向开始优先生长,是因为锐钛矿结构更完整。随着退火温度的升高晶粒长大拉曼光谱出现红移,拉曼光谱所反应的锐钛矿信息增强,500℃退火时197cm-1出现了Eg振动模式。和标准的单晶TiO2体材料相比,拉曼峰位置都略有红移是纳米量子尺寸效应造成的。氩氧比分别为9∶1、7∶3和6∶4溅射制备的薄膜通过400℃退火后的XRD衍射谱没有明显的区别,但拉曼光谱显示氩氧比为7∶3时结晶要完善些。     

High-Resolution Solid-State NMR Characterization of Morphology in Annealed Polylactic Acid

Single-pulse ¹³C NMR spectra and spin-lattice relaxation times T₁(¹H), detected indirectly via ¹³C carbons, and T₁(¹³C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the ¹³C NMR lines and proton spin-lattice relaxation times T₁(¹H). The spin-lattice relaxation times T₁(¹³C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study.     

水分辅助对无机钙钛矿CsPbI3薄膜结晶的影响

利用水分辅助晶粒溶解重结晶策略提高全无机铯铅碘钙钛矿(CsPbI₃)薄膜的质量, 探究了退火过程中不同湿度条件对薄膜结晶质量的影响, 并从形貌结构、 缺陷复合以及光伏性能等方面进行了研究. 结果表明, 相比于相对湿度(RH)为0%组CsPbI₃薄膜明显的晶界空隙, 适当的湿度退火有助于晶粒间更致密地结合, 晶界的减少进而可抑制载流子非辐射复合; 湿度过大则会形成较粗糙的表面形貌, 影响界面接触. 实验结果表明, 7%RH下CsPbI₃薄膜中缺陷明显减少, 非辐射复合得到抑制, 载流子寿命增加; 光伏性能测试结果显示, 开路电压(V_oc)和填充因子(FF)显著增大, 并获得了15.28%的光电转换效率(PCE).