Photothermal Beam Deflection Spectroscopy for the Determination of Thermal Diffusivity of Soils and Soil Aggregates

Photothermal beam deflection spectroscopy (BDS) with a red He–Ne laser (632.8 nm, 35 mW) as an excitation beam source and a green He–Ne laser (543.1 nm, 2 mW) as a probe was used for estimating thermal diffusivity of several types of soil samples and individual soil aggregates with small surfaces (2?×?2 mm). It is shown that BDS can be used on demand for studies of changes in properties of soil entities of different hierarchical levels under the action of agrogenesis. It is presented that BDS clearly distinguishes between thermal diffusivities of different soil types: Sod-podzolic [Umbric Albeluvisols, Abruptic], 29?±?3; Chernozem typical [Voronic Chernozems, Pachic], 9.9?±?0.9; and Light Chestnut [Haplic Kastanozems, Chromic], 9.7?±?0.9 cm²·h^?1. Aggregates of chernozem soil show a significantly higher thermal diffusivity compared to the bulk soil. Thermal diffusivities of aggregates of Chernozem for virgin and bare fallow samples differ, 53?±?4 cm²·h^?1 and 45?±?4 cm²·h^?1, respectively. Micromonoliths of different Sod-podzolic soil horizons within the same profile (topsoil, depth 10–14 cm, and a parent rock with Fe illuviation, depth 180–185 cm) also show a significant difference, thermal diffusivities are 9.5?±?0.8 cm²·h^?1 and 27?±?2 cm²·h^?1, respectively. For soil micromonoliths, BDS is capable to distinguish the difference in thermal diffusivity resulting from the changes in the structure of aggregates.     

Optical Energy Gap and Below Gap Optical Absorption of Fullerene Films Measured by the Constant Photocurrent Method and Photothermal Deflection Spectroscopy

The CPM spectra of fullerene films was measured to obtain the below gap absorption. The optical energy gap E_o was obtained by using the Tauc's plots. E_o did not change greatly with intercalated impurities. The absorption due to intercalated impurities was found below 1.6eV.     

Potical Energy Gap and Below Gap Optical Absorption of Fullerene Films Measured By Constant Photocurrent Method and Photothermal Deflection Spectroscopy

CPM spectra of the fullerene film was measured to obtain the below gap absorption. The optical energy gap E_o was obtained by using the Tauc's plots. E_o did not change so much with the intercalated impurities. The absorption due to intercalated impurities was found below 1.6eV.     

Photoluminescence Quenching Probes Spin Conversion and Exciton Dynamics in Thermally Activated Delayed Fluorescence Materials

Fluorescent materials that efficiently convert triplet excitons into singlets through reverse intersystem crossing (RISC) rival the efficiencies of phosphorescent state‐of‐the‐art organic light‐emitting diodes. This upconversion process, a phenomenon known as thermally activated delayed fluorescence (TADF), is dictated by the rate of RISC, a material‐dependent property that is challenging to determine experimentally. In this work, a new analytical model is developed which unambiguously determines the magnitude of RISC, as well as several other important photophysical parameters such as exciton diffusion coefficients and lengths, all from straightforward time‐resolved photoluminescence measurements. From a detailed investigation of five TADF materials, important structure–property relationships are derived and a brominated derivative of 2,4,5,6‐tetrakis(carbazol‐9‐yl)isophthalonitrile that has an exciton diffusion length of over 40 nm and whose excitons interconvert between the singlet and triplet states ≈36 times during one lifetime is identified.     

用弹性电子测量能谱仪能量分辨率和电子倍增器的工作曲线

重点介绍了利用弹性二次电子方便快捷地测量多功能电子能谱的能量分辨率和通道倍增器的工作曲线。并与常规方法进行了比较 ,结果一致。测量发现当电子束流增大到一定程度时 ,测出的弹性电子峰严重畸变 ,电子倍增器工作在饱和状态。对出现饱和的机理进行了讨论     

Optimized Photothermal Lens Determination of Nonlinear Absorption

An optimized pump–probe mode-mismatched photothermal lens experiment aimed at determination of nonlinear absorption of an optical sample is reported. The pump beam generates a local thermal gradient or thermal lens that is tested by the probe light. The pump beam is tightly focused, and the probe beam is highly collimated. Changes in the probe light transmission through a small aperture located at some distance from the sample provide the signal. Scanning of the sample around the focal point yields a single-peaked Z-scan signature with a width several times larger than the pump Rayleigh range for linear absorption. If nonlinear absorption is dominant, the width of the peak is significantly smaller and of the order of the Rayleigh range of the pump field. If linear and nonlinear absorption are present simultaneously, a double-peaked Z-scan signature is obtained. In this situation, the linear and nonlinear absorption contributions can be easily separated and compared to each other for calibration purposes. Using the known values of linear absorption, nonlinear absorption coefficients can be estimated with good accuracy. The method is tested by studying nonlinear absorption in nitrobenzene and iron oxide water colloids. The values of the effective nonlinear absorption coefficients are determined. The physical origin of nonlinear absorption in both types of samples is also discussed.     

激光诱导击穿光谱测量土壤重金属污染研究

针对传统的土壤重金属污染检测方法的不足, 本文基于激光诱导击穿光谱 LIBS(Laser-induced Breakdown Spectroscopy) 技术对土壤重金属污染物的检测进行了研究. 利用 Nd:YAG 激光器在脉冲重复频率为 5 Hz, 脉冲宽度为 8 ns, 单脉冲能量为 80 mJ 的实验条件下, 使用美国 ACTON 公司的 AM-566 单色仪和美国 Stanford Research Systems 公司的 SR250 Boxcar 对 9 个自采样土壤样品光谱进行了测量分析; 对实验装置的标定方法进行了探索研究, 并以镉元素为例给出了浓度反演曲线, 其相对误差为 7%.     

Energy Spectroscopy of Josephson Supercurrent

In this paper we review recent microscopic studies ofsupercurrent flow in Josephson junctions. In particular, wediscuss a method that allows direct measurements of thecontribution given to the supercurrent by electrons whichoccupy quantum states at different energies. Relevanttheoretical concepts are explained, with a particular emphasison the relation between Andreev bound states and supercurrent.The experimental system developed to perform these studies, anew kind of four terminal Josephson junctions, is described indetail. Measurements and theoretical predictions are comparedand a very good qualitative agreement is found. In conclusion,possible future directions of research in this area arementioned.     

Au纳米粒子的束缚能

利用从头计算法计算了一定粒径下Au纳米量子点的谐振子束缚能的大小。根据对波函数的分析发现，谐振子势是描述量子点的一个较好的势模型。     

Measurement of the Thermal Conductivity of Si and GaAs Wafers Using the Photothermal Displacement Technique

Thermal conductivity and thermal diffusivity of Si and GaAs wafers were measured using the photothermal displacement technique, and the temperature dependence of these two quantities was investigated. Thermal diffusivity was obtained from the phase difference between the heating source and the signal, and thermal conductivity was determined from the maximum value of the signal amplitude in the temperature range 80 to 300 K. It was verified that an increase in doping concentration gives rise to a decrease in thermal conductivity at low temperatures. The experimental results obtained on samples with different types and doping concentrations are consistent with those expected from theoretical considerations.