Epitaxial thin films of topological insulator Bi2Te3 with two-dimensional weak anti-localization effect grown by pulsed laser deposition

We have grown high quality epitaxial topological insulator Bi₂Te₃ thin films on silicon (111) substrates by pulsed laser deposition. Systematic structural characterization of the films using X-ray diffraction and transmission electron microscopy has demonstrated that a low laser pulse rate is the key to achieving epitaxial films. The films show n-type metallic behavior, consistent with Te deficiency as determined by Rutherford backscattering spectrometry measurements. The A_1g longitudinal optical phonon mode of Bi₂Te₃ was detected by time-resolved reflectivity measurements. A 2-dimensional (2-D) weak-antilocalization effect was also observed at low temperatures, which indicates the existence of topologically protected 2-D surface states in our thin films. This growth and characterization effort paves the way to fabricate multi-layer heterostructures of topological insulators along with ferromagnetic oxides and high temperature superconductors by the same growth technique in the search for physics arising from their interfacial couplings.     

基片温度对射频磁控溅射碲化铋薄膜微结构和表面形貌的影响

碲化铋材料是目前已知的室温下性能优异的热电材料之一。本文利用射频磁控溅射在不同基片温度下制备了碲化铋薄膜。研究发现,基片温度对薄膜的微结构和表面形貌影响显著。随着温度的提高,薄膜内晶粒尺寸都不同程度地增加。基片温度100℃以上碲化铋薄膜为Bi2Te3相为主的多晶结构,并具有良好的c轴择优取向,形成了六角层状结构。基片温度250℃时薄膜转变为BiTe相,并在表面生成Te长条状颗粒。应力分析表明碲化铋薄膜与Si(100)基片之间的残余应力受温度影响明显。     

Synthesis and Thermoelectric Characterization of Bi2Te3 Nanoparticles

Here, a novel synthesis for near monodisperse, sub‐10 nm Bi₂Te₃ nanoparticles is reported. A new reduction route to bismuth nanoparticles is described, which are then applied as starting materials in the formation of rhombohedral Bi₂Te₃ nanoparticles. After ligand removal by a novel hydrazine hydrate etching procedure, the nanoparticle powder is spark plasma sintered to a pellet with preserved crystal grain sizes. Unlike previous works on the properties of Bi₂Te₃ nanoparticles, the full thermoelectric characterization of such sintered pellets shows a highly reduced thermal conductivity and the same electric conductivity as bulk n‐type Bi₂Te₃.     

Bi_2Te_3基半导体合金的结构与性能

采用粉末热挤压的方式制备出了n型Bi2Te3基块体材料,研究了烧结工艺对其微观结构、力学性能和热电性能的影响。结果表明,与区熔单晶相比热挤压试样的力学性能有了较大提高,挤压温度的提高有利于试样力学性能的改善,挤压温度为400℃时试样获得室温下最大的热电优值约为0.75。     

Abnormal conductivity behavior in porous lead telluride films

ABSTRACT: We report the experimental observation of the novel phenomenon of the resistivity decrease in porous PbTe layers during the pore formation process. Investigations were performed on the n-PbTe films with 2.3 micrometer thickness, which were near the point of the conductivity-type inversion at room temperature. Anodic electrochemical treatment for the porous layers with 41-52% porosity fabrication was performed using a KOH-based Norr electrolyte solution. For the porous lead telluride layers, the resistivity value at 300 K decreased 2.5-3 times. For the explanation of the observed phenomenon a physical model is proposed, which takes into account the Pb/Te ratio change during the anodic treatment.     

In situ analysis of bismuth telluride electrodeposition using combined spectroscopic ellipsometry and electrochemical quartz crystal microbalance

Electrodeposition of bismuth telluride (Bi₂Te₃) in an acidic medium with Arabic gum by galvanostatic polarization has been investigated. Simultaneous in situ spectroscopic ellipsometry and gravimetric measurements have been performed to study the morphological evolution of the compound. A progressive covering stage was demonstrated and revealed that a 40 nm thick film has already acquired morphological and optical behavior similar to that of thicker films. The optical thickness and electrochemical quartz crystal microbalance (EQCM) mass are coherent with a density of 7.06. Combined gravimetric and coulometric data confirm the formation of Bi₂Te₃ by determining the ratio m/z.