Controlled Synthesis of a High-Mobility Bi3O2.5Se2 Semiconductor by Oxidation of Bi2Se3 for Fast and Highly Sensitive Photodetectors

The search of new high-mobility two-dimensional (2D) semiconductors is crucial for the development of next-generation photodetectors, since current photodetectors based on single 2D semiconductors usually cannot simultaneously own ultrafast response rate and ultrahigh sensitivity. Here, using a facial method of sequentially oxidizing Bi₂Se₃ at optimal O content, a series of bismuth oxyselenide semiconductors (Bi₃O_2.5Se₂, Bi₂O₂Se, Bi₂SeO₅) with appealing electronic applications are successfully synthesized. The crystal and band structures of a superlattice-free Bi₃O_2.5Se₂ phase are resolved by 3D electron diffraction and density functional theory calculations, showing a unique non-neutral layered structure, moderate band gap, and small effective mass. More importantly, the concept of Bi₂Se₃ + O₂ can be extended to synthesize the superlattice-free Bi₃O_2.5Se₂ ultrathin films by chemical vapor deposition, whose room-temperature mobility can be as high as ≈150 cm² V⁻¹ s⁻¹ based on Hall measurements. The ultrathin Bi₃O_2.5Se₂ photodetectors with a simple device configuration simultaneously own ultrafast response time (≈31 µs), ultrahigh responsivity (≈8 × 10⁴ A/W), and large detectivity (≈8 × 10¹³ Jones). This work not only introduces a facile way to regulate the phase in the bismuth oxyselenide family, but also provides an alternative candidate for ultrafast and ultrasensitive photodetectors.     

Scalable fabrication of Bi_2O_2Se polycrystalline thin film for near-infrared optoelectronic devices applications

We present a controlled, stepwise formation of layered semiconductor Bi_2O_2 Se thin films prepared via the vapour process by annealing topological insulator Bi_2Se_3 thin films in low oxygen atmosphere for different reactions. Photodetectors based on Bi_2O_2 Se thin film show a responsivity of 1.7×10~4 A/W at a wavelength of 980 nm. Field-effect transistors based on Bi_2O_2 Se thin film exhibit n-type behavior and present a high electron mobility of 17 cm~2/V·s. In addition, the electrical properties of the devices after 4 months keeping in the air shows little change, implying outstanding air-stability of our Bi_2O_2 Se thin films. From the obtained results, it is evident that low oxygen annealing is a surprisingly effective method to fabricate Bi_2O_2 Se thin films for integrated optoelectronic applications.     

Edge assisted epitaxy of CsPbBr3 nanoplates on Bi2O2Se nanosheets for enhanced photoresponse

Bi$_{2}$O$_{2}$Se has been proved to be a promising candidate for electronic and optoelectronic devices due to their unique physical properties. However, it is still a great challenge to construct the heterostructures with direct epitaxy of hetero semiconductor materials on Bi$_{2}$O$_{2}$Se nanosheets. Here, a two-step chemical vapor deposition (CVD) route was used to directly grow the CsPbBr$_{3}$ nanoplate-Bi$_{2}$O$_{2}$Se nanosheet heterostructures. The CsPbBr$_{3}$ nanoplates were selectively grown on the Bi$_{2}$O$_{2}$Se nanosheet along the edges, where the dangling bonds provide the nucleation sites. The epitaxial relationships between CsPbBr$_{3}$ and Bi$_{2}$O$_{2}$Se were determined as ${[200]}_{\rm Bi_{2}O_{2}Se}||{[110]}_{\rm CsPbBr_{3}}$ and ${[110]}_{\rm Bi_{2}O_{2}Se}||{[200]}_{\rm CsPbBr_{3}}$ by transmission electron microscopy characterization. The photoluminescence (PL) results reveal that the formation of heterostructures results in the remarkable PL quenching due to the type-I band arrangement at CsPbBr$_{3}$/Bi$_{2}$O$_{2}$Se interface, which was confirmed by ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe measurements, and makes the photogenerated carriers transfer from CsPbBr$_{3}$ to Bi$_{2}$O$_{2}$Se. Importantly, the photodetectors based on the heterostructures exhibit a 4-time increase in the responsivity compared to those based on the pristine Bi$_{2}$O$_{2}$Se sheets, and the fast rise and decay time in microsecond. These results indicate that the direct epitaxy of the CsPbBr$_{3}$ plates on the Bi$_{2}$O$_{2}$Se sheet may improve the optoelectronic performance of Bi$_{2}$O$_{2}$Se based devices.     

Electrical and Thermal Transport Properties of n-type Bi6Cu2Se4O6 (2BiCuSeO + 2Bi2O2Se)

New thermoelectric materials, n-type Bi₆Cu₂Se₄O₆ oxyselenides, composed of well-known BiCuSeO and Bi₂O₂Se oxyselenides, are synthesized with a simple solid-state reaction. Electrical transport properties, microstructures, and elastic properties are investigated with an emphasis on thermal transport properties. Similar to Bi₂O₂Se, it is found that the halogen-doped Bi₆Cu₂Se₄O₆ possesses n-type conducting transports, which can be improved via Br/Cl doping. Compared with BiCuSeO and Bi₂O₂Se, an extremely low thermal conductivity can be observed in Bi₆Cu₂Se₄O₆. To reveal the origin of low thermal conductivity, elastic properties, sound velocity, Grüneisen parameter, and Debye temperature are evaluated. Importantly, the calculated phonon mean free path of Bi₆Cu₂Se₄O₆ is comparable to the interlayer distance for BiO─CuSe and BiO─Se layers, which is ascribed to the strong interlayer phonon scattering. Contributing from the outstanding low thermal conductivity and improved electrical transport properties, the maximum ZT ≈0.15 at 823 K and ≈0.11 at 873K are realized in n-type Bi₆Cu₂Se_3.2Br_0.8O₆ and Bi₆Cu₂Se_3.6Cl_0.4O₆, respectively, indicating the promising thermoelectric performance in n-type Bi₆Cu₂Se₄O₆ oxyselenides.     

新型层状Bi2Se3的第一性原理研究

近年来,在石墨烯研究热潮的推动下,众多种类丰富、性能各异的二维化合物材料相继被发现,其中一些二维材料具有多种同素异构体,进而呈现出更丰富的性质.层状Bi2Se3由于其独特的物理性质,受到人们广泛的关注,而它的同素异构体尚未有人研究.本文采用基于密度泛函理论的结构搜索方法,预测了一个稳定的b-Bi2Se3新相,它具有良好...     

Topological surface states of Bi2Te2Se are robust against surface chemical modification

The robustness of the Dirac‐like electronic states on the surfaces of topological insulators (TIs) during materials process‐ing is a prerequisite for their eventual device application. Here, the (001) cleavage surfaces of crystals of the topological insulator Bi₂Te₂Se (BTS) were subjected to several surface chemical modification procedures that are common for electronic materials. Through measurement of Shubnikov–de Hass (SdH) oscillations, which are the most sensitive measure of their quality, the surface states of the treated surfaces were compared to those of pristine BTS that had been exposed to ambient conditions. In each case – surface oxidation, deposition of thin layers of Ti or Zr oxides, or chemical modification of the surface oxides – the robustness of the topological surface electronic states was demonstrated by noting only very small changes in the frequency and amplitude of the SdH oscillations. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Subsolidus phase relation in the Bi2O3-Fe203-La2O3 system

Bismuth-containing semiconductor material is a hot topic in photocatalysts because of its effective absorption under the visible light. In this paper, we expect to explore a new bismuth-based photocatalyst by studying the subsolidus phase relations of the Bi2O3-Fe2O3-La2O3 system. The X-ray diffraction data shows that in this ternary system the ternary compound does not exist, while seven binary compounds （including one solid solution series Bi1-xLaxO1.5 with 0.167 〈 x 〈 0.339） are obtained and eight compatibility triangles are determined.     

Giant Rashba spin splitting in Bi2Se3:Tl

First‐principles calculations are employed to demonstrate a giant Rashba spin splitting in Bi₂Se₃:Tl. Biaxial tensile and compressive strain is used to tune the splitting by modifying the potential gradient. The band gap is found to increase under compression and decreases under tension, whereas the dependence of the Rashba spin splitting on the strain is the opposite. Large values of α_R = 1.57 eV Å at the bottom of the conduction band (electrons) and α_R = 3.34 eV Å at the top of the valence band (holes) are obtained without strain. These values can be further enhanced to α_R = 1.83 eV Å and α_R = 3.64 eV Å, respectively, by 2% tensile strain. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

SrBi2Ta2O9/Bi4Ti3O12复合铁电薄膜的制备与特性研究

采用溶胶凝胶工艺在p-Si衬底上制备了SrBi2Ta2O9/Bi4Ti3O12复合铁电薄膜. 研究了SrBi2Ta2O9/Bi4Ti3O12复合薄膜的微观结构与生长行为、铁电性能和疲劳特性. 研究表明: Si衬底Bi4Ti3O12薄膜易于沿c轴择优生长,并有利于SrBi2Ta2O9/Bi4Ti3O12复合薄膜的生长.合理的SrBi2Ta2O9/Bi4Ti3O12厚度配比能获得较好的铁电性能和优良的抗疲劳特性,SrBi2Ta2O9/Bi4Ti3O12厚度配比为1∶3的复合薄膜的剩余极化强度和矫顽电场分别为8.1 μC/cm2 和 130 kV/cm,其无疲劳极化开关次数达1011以上.     

静电纺丝法制备Bi2Fe4O9及其磁学性能的研究

采用静电纺丝法合成了纤维状的Bi₂Fe₄O₉前驱体,再对前驱体进行热处理得到了棒状的Bi₂Fe₄O₉.通过X射线衍射、扫描电子显微镜及透射电子显微镜表征了合成样品的物相及形貌特征.结果表明合成的样品为Bi₂Fe₄O₉单相,属于正交晶系;退火处理导致纤维状的前驱体转变为棒状的Bi₂Fe₄O₉.紫外-可见吸收光谱表明制备的Bi₂Fe₄O₉对光的吸收范围广,不仅对紫外光具有较强吸收,而且对可见光也有一定的吸收.通过振动样品磁强计测定Bi₂Fe₄O₉磁滞回线研究其磁学特性,相应的矫顽力H_C≈82 Oe（1 Oe=79.5775 A/m）,剥离顺磁信号后的剩磁M_r≈0.25 emu/g,研究发现Bi₂Fe₄O₉样品具有弱铁磁性,并且软磁性能有所提高.     

溶胶-凝胶法制备Sr2Bi4Ti5O18薄膜及其铁电性能研究

采用溶胶-凝胶法,在氧气氛中和层层晶化的工艺条件下,成功地制备了沉积在Pt/Ti/SiO2/Si(100)衬底上的铁电性能优良的Sr2Bi4Ti5O18(SBTi)薄膜,并研究了SBTi薄膜的微结构、表面形貌、铁电性能和疲劳特性.研究表明:薄膜具有单一的层状钙钛矿结构,且为随机取向;薄膜表面光滑,无裂纹,厚度约为725nm;铁电性能测试显示较饱和、方形的电滞回线,当外电场强度为275kV/cm时,其剩余极化2Pr和矫顽场2Ec分别为24.0μC/cm2和137.8kV/cm;疲劳测试发现薄膜经过4.4×1010次极化反转后,基本没有显示疲劳.     

基于低温光声光谱技术的高Tc超导材料Bi2Sr2CaCu2O8

在光声光谱技术基础上,将不同仪器组装成一套系统,并成功测量出碳黑的光声光谱。利用低温检测系统测定高温超导材料Bi2Sr2CaCu2O8在室温和液氮温度下的光声光谱,发现室温时在598nm和695nm有峰值,液氮温度时在466nm出现峰值。以吸收系数近似为1的碳黑为参照,利用归一化方法得到了Bi2Sr2CaCu2O8相对吸收系数谱图,并进行了初步的探讨,得到了该超导材料的一些信息,为利用低温光声光谱技术,研究超导材料的超导特性提供了一种可行的途径。     

γ射线辐照与O2退火对Bi∶CdWO4单晶体光谱性能的影响

用500和800℃,在氧气下,对掺Bi钨酸镉晶体进行热退火处理,测定了处理后晶体的吸收光谱与发射光谱。随退火处理温度的升高晶体的吸收强度降低,吸收边带发生蓝移。在373与980nm的光激发下,分别观察到发光中心为528nm的CdWO4晶体本征发光与发光中心为1 078nm的Bi 5+发光。晶体样品通过高温氧气处理,发光中心为528nm的荧光带强度增强,但发光中心为1 078nm的荧光带强度变弱。这可能是由于氧退火使Bi 5+转化成Bi 3+所致。经退火处理后,晶体的颜色逐渐变浅,透光率明显提高,这是由于晶体中氧空位减少所致。经γ射线辐照处理后,528nm处的发光增强,而1 078nm处的发光减弱,这可能是由于γ射线辐照后导致Bi 5+变成Bi 3+。     

Bi2Sr2CaCu2O8超导单晶中的电阻反常行为

测量了Bi2 Sr2 CaCu2 O8单晶的ab面和c轴方向电阻 ,在其超导转变温度附近发现了反常的电阻峰出现 .其随外磁场 (>10 0Gs)和电流的增加而逐渐消失 .文章认为这个反常的电阻峰是由于单晶中超导相的不均匀分布而导致的准再进入行为 .     

Raman and IR spectra of the cation‐deficient Aurivillius layered crystal Bi2W2O9

Raman and IR spectra of Bi₂W₂O₉, the m = 2 member of the cation‐deficient Aurivillius phase, have been measured. The obtained spectra are discussed using the factor group approach for the orthorhombic Pna2₁(C_2v⁹) space group. The results are compared with those obtained for Bi₂WO₆ and some m = 2 members of Aurivillius family of bismuth layered ferroelectrics. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural,magnetic, and dielectric properties of Ni–Zn ferrite and Bi_2O_3 nanocomposites prepared by the sol-gel method

Ni–Zn ferrite and Bi_2O_3 composites were developed by the sol-gel method. The structural, magnetic, and dielectric properties were studied for all the prepared samples. X-ray diffraction(XRD) was performed to study the crystal structure.The results of field emission scanning electron microscopy(FE-SEM) showed that the addition of Bi_2O_3 can increase the grain size of the Ni–Zn ferrite. Magnetic properties were analyzed by a hysteresis loop test and it was found that the saturation magnetization and coercivity decreased with the increase of Bi_2O_3 ratio. In addition, the dielectric properties of the Ni–Zn ferrite were also improved with the addition of Bi_2O_3.     

Observation of π Berry phase in quantum oscillations of three‐dimensional Fermi surface in topological insulator Bi2Se3

We report the quantum transport studies on Bi₂Se₃ single crystal with bulk carrier concentration of ～10¹⁹ cm^–3. The Bi₂Se₃ crystal exhibits metallic character, and at low temperatures, the field dependence of resistivity shows clear Shubnikov–de Haas (SdH) oscillations above 6 T. The analysis of these oscillations through Lifshitz–Kosevich theory reveals a non‐trivial π Berry phase coming from three‐dimensional (3D) Fermi surface, which is a strong signature of Dirac fermions with three‐dimensional dispersion. The large Dingle temperature and non zero slope of Williamson–Hall plot suggest the presence of enhanced local strain field in our system which possibly transforms the regions of topological insulator to 3D Dirac fermion metal state. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)