The non-linear refractive index of colloidal PbSe nanocrystals: Spectroscopy and saturation behaviour

A spectroscopic study of the optical non-linearities of PbSe colloidal solutions was performed with the Z-scan technique, at wavelengths between 1200 and 1750 nm. No non-linear absorption is observed, while the third-order non-linear refractive index n₂ shows clear resonances, somewhat blueshifted relative to the exciton transitions in the absorbance spectrum. The occurrence of thermal effects is ruled out by time-resolved measurements. At resonance, measured n₂ values exceed typical bulk semiconductor values by two orders of magnitude. At high optical intensity, the refractive index change saturates, indicating that state filling lies at the origin of the observed effect.     

Dielectrophoretic placement of quasi-zero-, one-, and two-dimensional nanomaterials into nanogap for electrical characterizations

DEP is one of promising techniques for positioning nanomaterials into the desirable location for nanoelectronic applications. In contrast, the lithography technique is commonly used to make ultra-thin conducting wires and narrow gaps but, due to the limit of patterning resolution, it is not feasible to make electrical contacts on ultra-small nanomaterials for a bottom-up device fabrication. Thus, integrating the lithography and dielectrophoresis, a real bottom-up fabrication can be achieved. In this work, the device with the nanogap in between two nanofinger-electrodes is made using electron-beam lithography from top down and the ultra-small nanomaterials, such as colloidal PbSe quantum dots, polyaniline nanofibers, and reduced-graphene-oxide flakes, are placed in the nanogap by DEP from bottom up. The threshold electric field for the DEP placement of PbSe nanocrystals was roughly estimated to be about 8.3 × 10(4) V/cm under our experimental configuration. After the DEP process, several procedures for reducing contact resistances are attempted and measurements of intrinsic electron transport in versatile nanomaterials are performed. It is experimentally confirmed that electron transport in both PbSe nanocrystal arrays and polyaniline nanofibers agrees well with Prof. Ping Sheng's model of granular metallic conduction. In addition, electron transport in reduced-graphene-oxide flakes follows Mott's 2D variable-range-hopping model. This study illustrates an integration of the electron-beam lithography and the DEP techniques for a precise manipulation of nanomaterials into electronic circuits for characterization of intrinsic properties.     

PbSe-MnSe纳米复合热电材料的微结构和电热输运性能

相比于常见的热电材料PbTe, 另一种硫族铅化合物PbSe具有熔点高、Se储量更丰富等优势, 从而越来越受到科学界的关注. 本文采用熔融淬火结合快速热压烧结工艺制备了Pb_0.98-xMn_xNa_0.02Se(0 ≤x ≤ 0.12)纳米复合热电材料, 系统地研究了不同Mn含量对材料微纳结构、机械性能和热电性能的影响规律. 发现纳米复合样品中有面心立方结构的MnSe球状和薄层状析出物, 显微硬度得到显著增强. 少量固溶的Mn增加了能带简并度, 使功率因子提高, 球状析出物使声子散射增强、热导率降低, 体系的热电优值ZT得到优化; 但是当Mn含量更高时, 赛贝克系数趋于饱和, 连续析出物使晶格热导率反常增大, ZT 没有得到进一步改善. 通过进一步调节Na含量优化了载流子浓度, 获得了ZT=0.65的PbSe-MnSe纳米复合热电材料.     

Studies on PbS and PbSe Detectors for IR System

It is of paramount importance to fully understand, characterize and specify each major component of the system by their wavelength and temperature characteristics, size and performance variation with time. In this paper, we present research results on PbS/PbSe detectors which characters vary with temperature.     

两种不同Pb源对PbSe纳米晶生长的影响

采用有机相合成法, 分别以PbO和醋酸铅[Pb(Ac)₂]作为铅源, 研究了在不同反应温度和反应时间下, 不同铅源对PbSe纳米晶生长的影响. 实验结果表明, 以PbO作为铅源, 油酸(OA)作为配体时, 在不同的反应温度下得到了球形PbSe纳米晶和截角八面体PbSe纳米晶; 选择Pb(Ac)₂作为铅源时, 在不同的温度下得到了PbSe纳米花和PbSe纳米星. 选择不同铅源得到的PbSe纳米晶形貌完全不同, 这主要是由于醋酸根的引入产生了不同的空间位阻, 引起纳米晶导向吸附并形成纳米花. 而随着反应温度的升高和反应时间的延长, 这些不同形貌的PbSe纳米晶最终会演变成纳米立方块, 这主要是由PbSe的晶体特性决定的.     

Solid‐State Chemistry on the Nanoscale: Ion Transport through Interstitial Sites or Vacancies?

How can ion‐exchange process occur in nanocrystals without the size and shape changing and why is the ion transport much faster than in classical interdiffusion processes in macrocrystalline solids? We have investigated these processes at the molecular level by means of high‐resolution and analytical electron microscopy in temperature‐dependent kinetic experiments for several model reactions. The results clearly show a diffusion process that proceeds exclusively through the interstitial lattice positions with a subsequent “kick out” to remove individual ions from lattice sites without the formation of vacancies. This mechanism has not been observed in nanocrystalline systems before.     

Te/Cr共掺提高PbSe的热电性能

采用高温固相法和快速热压工艺在PbSe的Pb位掺入Cr以调节载流子有效质量、在Se位掺入Te以调节载流子浓度,协同优化载流子迁移率以提高基体材料的热电优值ZT。最终获得的Pb0.97Cr0.03Se0.94Te0.06热电材料在673 K时ZT为0.44,是未掺杂样品PbSe的4.89倍。     

Effect of oxygen annealing on the photoresponse of PbSe thin films fabricated by the pulsed laser deposition method

In this work, we have fabricated lead selenide (PbSe) thin films by the pulsed laser deposition method on Si/SiO₂ substrates and investigated the effect of oxygen annealing (sensitization) in these films. The oxygen-sensitized films show high responsivity in the visible (VIS) and the near-infrared (NIR) region at room temperature without cooling. We also demonstrate the effective surface oxidation of PbSe thin films during the oxygen annealing process without treated with commonly used halogens that leads to a better photoresponse in these PbSe films.     

Sonocatalysis of a sulfa drug using neodymium-doped lead selenide nanoparticles

Undoped and Nd-doped PbSe nanoparticles with different Nd contents were successfully synthesized using a simple hydrothermal method. The prepared nanoparticles were thoroughly characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. Catalytic efficiency of undoped and Nd-doped PbSe samples was evaluated by monitoring the removal of sulfasalazine (SSZ) in aqueous solution under ultrasonic irradiations (sonocatalytic removal process). It was found that the presence of the K₂S₂O₈ accelerated the sonocatalytic removal of SSZ, but the presence of NaF, Na₂SO₄, NaCl, and NaHCO₃ obstructed it. The removal efficiency of 30.24% for PbSe and 86% for 12% Nd-doped PbSe was achieved at 90 min of reaction time, in the presence of peroxydisulfate. Also, the effect of operational parameters on the sonocatalytic removal efficiency and the dominant sonocatalytic removal mechanism were completely examined. It was found that removal of SSZ by sonocatalytic process was completed by the action of reactive oxygen species (ROS) rather than pyrolysis. An ecotoxicological test using an aquatic plant Lemna minor (L. minor) confirmed the negligible toxicity of the synthesized samples, which makes these nanoparticles appropriate for use as a sonocatalyst.