气相传输法制备大尺寸单晶Bi2Se3纳米片、纳米带

低维Bi₂Se₃纳米材料是最新研究发现的一种新型三维拓扑绝缘体材料, 在微电子器件和传感器领域具有广阔的应用前景。本研究采用气相传输法在真空石英管中合成了大尺寸单晶Bi₂Se₃纳米片、纳米带。通过XRD、EDS、Raman、SEM等手段对Bi₂Se₃纳米片、纳米带的物相结构、组成、表面形貌等进行表征。测试结果表明: 气相传输法合成的单晶Bi₂Se₃纳米片、纳米带相纯度高, 结晶性能好, 均是{001}取向; Bi₂Se₃纳米片水平尺寸大, 约为15~180 μm; Bi₂Se₃纳米带长度达860 μm, 宽度约5 μm。根据不同温度下制备的Bi₂Se₃纳米片、纳米带SEM照片及其不同方向结合能的差异, 分析了其可能的生长机制: 在较高温度下沿<001>和方向生长速度快, 生成大尺寸单晶Bi₂Se₃纳米片; 在较低温度下, 沿方向生长速度快, 生成大尺寸单晶Bi₂Se₃纳米带。这些研究结果完善了大尺寸Bi₂Se₃纳米材料的制备工艺, 有望在微电子器件领域得到商业化应用。     

铁掺杂诱导二维硒化铟的多铁性（英文）

多铁材料具有巨大的潜力,可应用于新型磁电设备,如高密度非易失性存储等.在本工作中,我们报道了一种具有铁电性和铁磁性共存特性的新型二维铁掺杂硒化铟.实验结果显示,Fe原子在In原子位点进行了替位掺杂,Fe的含量约为3.22%,其化学式为Fe0.16In1.84Se3.基于密度泛函理论第一性原理计算预测,当Fe替代硒化铟中In的位置时,每个Fe原子的磁矩为5μB.我们通过量子干涉超导测试进一步证实了理论预测.磁性测量表明纯硒化铟是抗磁性的,而Fe0.16In1.84Se3表现出铁磁行为,在2 K时具有平行各向异性,居里温度约为8 K.此外,压电力响应测试表明Fe原子掺杂进入铁电硒化铟纳米薄片后仍保持稳定的室温铁电性.研究结果表明,层状多铁材料Fe0.16In1.84Se3在未来的纳米电子、磁性和光电器件中具有潜在的应用前景.     

Sb2Se3管状化合物的制备和表征

用固相烧结法合成了管状Sb2Se3相变材料,并通过扫描电子显微镜（SEM）、X射线衍射仪（XRD）、透射电镜（TEM）、拉曼光谱仪（Raman）、热重分析（DSC）进行表征测试,结果表明成功制备出了正交晶系的Sb2Se3,计算所得晶格常数为a：11．6445A,b=11．792A,c=3．981A,;透射电镜结果说明Sb2Se3微米管晶体结构沿[001]方向择优生长;DSC测试Sb2Se3的熔点为624．5℃。同时本试验用固相烧结法制备了不同配比的Sb—Se材料,并用XRD和Raman表征测试了晶体结构.     

多元醇法制备和表征Sb2Se3纳米线

以自制的NaHSe乙醇溶液为硒源,在PEG-400无水体系中采用多元醇法,在180℃生长10h制备了直径100～200nm,长度可达十几微米的纳米线.产物通过XRD、TEM、HRTEM、FESEM、EDS和UV-Vis等手段进行了表征,并研究了不同多元醇对产物形貌的影响.研究表明,PEG-400作为结构导向剂在制备一维Sb₂Se₃纳米线中发挥着至关重要的作用,并且无水环境为纳米晶的生长提供了更加纯净的条件,有利于制备高质量的纳米晶.     

Se及Cu2Se纳米线的大面积合成及其纳米电子学器件性能

通过液相化学反应制备了高质硒(Se)纳米线,同时以Se纳米线为模板,合成了CuzSe纳米线.利用透射电镜(TEM)、高分辨透射电镜(HRTEM)以及X射线衍射仪(XRD)研究了纳米线的形貌结构特征.结果显示,Se纳米线为单晶结构,生长方向沿其[001]面.结合先进的光刻技术及磁控溅射,成功制备了Se和Cu2Se纳米电子学器件.初步测试表明,这种Se纳米线为P型半导体,而Cu2Se纳米线则表现出明显的相变行为.这些发现有利于开发纳米线场效应晶体管以及相变存储器件方面的应用.     

纳米Cu_2Se的制备及其生长机理分析

采用一种新的合成技术,在复合氢氧化物熔融体中,以CuCl2·2H2和Se粉为原料在200℃下合成了Cu2Se纳米晶体,X射线衍射谱表明合成的Cu2Se纳米晶体属立方晶系结构,格点对称群为Fm3m(225),格点参数a=0.5765nm.扫描电子显微镜(SEM)和透射电子显微镜(TEM)图表明Cu2Se纳米晶体为厚度为10～20nm,宽度为200～300nm的片状结构.生长时加入少量的水会导致棒状非晶产生,水量越多棒状非晶的尺寸越大,使得Cu2Se晶体的均匀性和品质变差.根据配位多面体生长机理模型,计算了生长基元的稳定能,并探讨了在复合氢氧化物熔融中纳米Cu2Se晶体的形成机理.     

Facile Synthesis of γ‐In2Se3 Nanoflowers toward High Performance Self‐Powered Broadband γ‐In2Se3/Si Heterojunction Photodiode

An effective colloidal process involving the hot‐injection method is developed to synthesize uniform nanoflowers consisting of 2D γ‐In₂Se₃ nanosheets. By exploiting the narrow direct bandgap and high absorption coefficient in the visible light range of In₂Se₃, a high‐quality γ‐In₂Se₃/Si heterojunction photodiode is fabricated. This photodiode shows a high photoresponse under light illumination, short response/recovery times, and long‐term durability. In addition, the γ‐In₂Se₃/Si heterojunction photodiode is self‐powered and displays a broadband spectral response ranging from UV to IR with a high responsivity and detectivity. These excellent performances make the γ‐In₂Se₃/Si heterojunction very interesting as highly efficient photodetectors.     

Metabolizable Ultrathin Bi2Se3 Nanosheets in Imaging‐Guided Photothermal Therapy

Poly(vinylpyrrolidone)‐encapsulated Bi₂Se₃ nanosheets with a thickness of 1.7 nm and diameter of 31.4 nm are prepared by a solution method. Possessing an extinction coefficient of 11.5 L g^?1 cm^?1 at 808 nm, the ultrathin Bi₂Se₃ nanosheets boast a high photothermal conversion efficiency of 34.6% and excellent photoacoustic performance. After systemic administration, the Bi₂Se₃ nanosheets with the proper size and surface properties accumulate passively in tumors enabling efficient photoacoustic imaging of the entire tumors to facilitate photothermal cancer therapy. In vivo biodistribution studies reveal that they are expelled from the body efficiently after 30 d. The ultrathin Bi₂Se₃ nanosheets have large clinical potential as metabolizable near‐infrared‐triggered theranostic agents.     

Preparation of monodisperse Se colloid spheres and Se nanowires using Na2SeSO3 as precursor

Nearly monodisperse spherical amorphous Se colloids are prepared by the dismutation of Na₂SeSO₃ solution at room temperature; by altering the pH of the solution, amorphous Se colloid spheres with sizes of about 120 nm, 200 nm, 300 nm, and 1 μm can be obtained. Se@Ag₂Se core/shell spheres are successfully synthesized by using the obtained amorphous Se (a-Se) spheres as templates, indicating the potential applications of these Se nanomaterials in serving as soft templates for other selenides. Meanwhile, selenium nanowires are obtained through a “solid-solution-solid” growth process by dispersing the prepared Se spheres in ethanol. This simple and environmentally benign approach may offer more opportunities in the synthesis and applications of nanocrystal materials. This article is published with open access at Springerlink.com     

Highly Anisotropic Sb2Se3 Nanosheets: Gentle Exfoliation from the Bulk Precursors Possessing 1D Crystal Structure

2D materials, particularly those bearing in‐plane anisotropic optical and electrical properties such as black phosphorus and ReS₂, have spurred great research interest very recently as promising building blocks for future electronics. However, current progress is limited to layered compounds that feature atomic arrangement asymmetry within the covalently bonded planes. Herein, a series of highly anisotropic nanosheets (Sb₂Se₃, Sb₂S₃, Bi₂S₃, and Sb₂(S, Se)₃), which are composed of 1D covalently linked ribbons stacked together via van der Waals force, is introduced as a new member to the anisotropic 2D material family. These unique anisotropic nanosheets are successfully fabricated from their polymer‐like bulk counterparts through a gentle water freezing‐thawing approach. Angle‐resolved polarized Raman spectroscopy characterization confirms the strong in‐plane asymmetry of Sb₂Se₃ nanosheets, and photodetection study reveals their high responsivity and anisotropic in‐plane transport. This work can enlighten the synthesis and application of new anisotropic 2D nanosheets that can be potentially applied for future electronic and optoelectronic devices.     

Bolometric Effect in Bi2O2Se Photodetectors

Bi₂O₂Se is emerging as a photosensitive functional material for optoelectronics, and its photodetection mechanism is mostly considered to be a photoconductive regime in previous reports. Here, the bolometric effect is discovered in Bi₂O₂Se photodetectors. The coexistence of photoconductive effect and bolometric effect is generally observed in multiwavelength photoresponse measurements and then confirmed with microscale local heating experiments. The unique photoresponse of Bi₂O₂Se photodetectors may arise from a change of hot electrons during temperature rises instead of photoexcited holes and electrons. Direct proof of the bolometric effect is achieved by real‐time temperature tracking of Bi₂O₂Se photodetectors under time evolution after light excitation. Moreover, the Bi₂O₂Se bolometer shows a high temperature coefficient of resistance (?1.6% K^?1), high bolometric coefficient (?31 nA K^?1), and high bolometric responsivity (>320 A W^?1). These findings offer a new approach to develop bolometric photodetectors based on Bi₂O₂Se layered materials.     

Thermally Phase‐Transformed In2Se3 Nanowires for Highly Sensitive Photodetectors

The photoresponse characteristics of In₂Se₃ nanowire photodetectors with the κ‐phase and α‐phase structures are investigated. The as‐grown κ‐phase In₂Se₃ nanowires by the vapor‐liquid‐solid technique are phase‐transformed to the α‐phase nanowires by thermal annealing. The photoresponse performances of the κ‐phase and α‐phase In₂Se₃ nanowire photodetectors are characterized over a wide range of wavelengths (300–900 nm). The phase of the nanowires is analyzed using a high‐resolution transmission microscopy equipped with energy dispersive X‐ray spectroscopy and X‐ray diffraction. The electrical conductivity and photoresponse characteristics are significantly enhanced in the α‐phase due to smaller bandgap structure compared to the κ‐phase nanowires. The spectral responsivities of the α‐phase devices are 200 times larger than those of the κ‐phase devices. The superior performance of the thermally phase‐transformed In₂Se₃ nanowire devices offers an avenue to develop highly sensitive photodetector applications.     

Chemical Vapor Deposition Growth of High Crystallinity Sb2Se3 Nanowire with Strong Anisotropy for Near‐Infrared Photodetectors

Low‐dimensional semiconductors have attracted considerable attention due to their unique structures and remarkable properties, which makes them promising materials for a wide range of applications related to electronics and optoelectronics. Herein, the preparation of 1D Sb₂Se₃ nanowires (NWs) with high crystal quality via chemical vapor deposition growth is reported. The obtained Sb₂Se₃ NWs have triangular prism morphology with aspect ratio range from 2 to 200, and three primary lattice orientations can be achieved on the sixfold symmetry mica substrate. Angle‐resolved polarized Raman spectroscopy measurement reveals strong anisotropic properties of the Sb₂Se₃ NWs, which is also developed to identify its crystal orientation. Furthermore, photodetectors based on Sb₂Se₃ NW exhibit a wide spectral photoresponse range from visible to NIR (400–900 nm). Owing to the high crystallinity of Sb₂Se₃ NW, the photodetector acquires a photocurrent on/off ratio of about 405, a responsivity of 5100 mA W^?1, and fast rise and fall times of about 32 and 5 ms, respectively. Additionally, owing to the anisotropic structure of Sb₂Se₃ NW, the device exhibits polarization‐dependent photoresponse. The high crystallinity and superior anisotropy of Sb₂Se₃ NW, combined with controllable preparation endows it with great potential for constructing multifunctional optoelectronic devices.     

In2Se3/CuSe核壳结构微纳粉的合成及其喷涂热处理制备CuInSe2薄膜

分别采用超声微波溶剂热法、常压溶剂热法及高压溶剂热法制备In₂Se₃/CuSe粉体, 研究不同方法制备In₂Se₃/CuSe粉体的物相、形貌, 并利用涂覆-快速热处理法制作薄膜太阳电池吸收层。通过XRD、Raman、FESEM和TEM对样品的物相、形貌和组成进行了表征。结果表明: 超声微波溶剂热法和常压溶剂热法得到的产物是以In₂Se₃+CuSe混合相的形式存在, 高压溶剂热法合成的In₂Se₃/CuSe粉体则呈核壳结构, (以In₂Se₃为核, CuSe为壳)。涂覆-快速热处理法制备CIS薄膜的FESEM照片结果表明, 高压溶剂热法合成的In₂Se₃/CuSe更容易获得平整致密的薄膜。将该CIS薄膜直接用于电池器件的组装, 获得的光电性能参数: V_oc为50 mV, J_sc为8 mA/cm²。     

铁基超导体KxFe2-ySe2的研究进展

自2008年在F掺杂的LaOFeAs化合物中发现高达26 K的超导电性后,高温超导研究迎来了新一轮热潮。随后一系列不同结构的铁基超导材料被发现,到目前为止,铁基超导体的最高临界温度记录为56 K。在2010年末,临界温度高达32 K的KxFe2-ySe2这一新的铁硫族超导体被发现。与其他铁磷族超导体相比,这个系统有着许多不同寻常的性质。角分辨光电子谱实验与能带结构计算都表明此材料在费米能附近没有空穴型费米面。这一性质强烈地挑战了被广为接受的S±超导配对图像:理论物理学家提出在铁基超导体中,电子在空穴型费米面与电子型费米面之间散射,通过交换反铁磁自旋涨落来达到超导配对。不久之后,在此材料中又确定了相分离的性质。其中一个主要的相是具有K2Fe4Se5结构的反铁磁绝缘相,另一个是少量的超导相。闻海虎小组最近的一篇论文认定了此材料的超导相以三维网络状的细丝形态存在,相关实验数据表明每8个Fe原子位置中存在1个空位,并由此提出超导的母体相是由Fe空位形成的槡槡8×10这种有序平行四边形结构组成。文章比较全面地介绍这一快速发展领域的研究进展,包括晶体生长与淬火处理,Fe空位有序与块反铁磁相,相分离与超导相的探索,配对对称性与能隙结构。最后列举了一些重要的问题,并且展望了将来的研究内容。     

Thermoelectric properties of solution-synthesized n-type Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> nanocomposites modulated by Se: An experimental and theoretical study

We report the investigation of the thermoelectric properties of large-scale solution-synthesized Bi2Te3 nanocomposites prepared from nanowires hotpressed into bulk pellets. A third element, Se, is introduced to tune the carrier concentration of the nanocomposites. Due to the Se doping, the thermoelectric figure of merit (ZT) of the nanocomposites is significantly enhanced due to the increased power factor and reduced thermal conductivity. We also find that thermal transport in our hot-pressed pellets is anisotropic, which results in different thermal conductivities along the in-plane and cross-plane directions. Theoretical calculations for both electronic and thermal transport are carried out to establish fundamental understanding of the material system and provide directions for further ZT optimization with adjustments to carrier concentration and mobility.

Open image in new window