银掺杂对MoS_2薄膜特性的影响

二硫化钼(MoS2)是一种具有类似石墨烯结构和性能的新型二维层状化合物,近年来因其独特的物理化学特性而成为研究热点。采用化学气相沉积法(CVD),以掺杂银的MoS2饱和溶液为原料,氩气为输运气体,在p-Si衬底上制备MoS2薄膜,并研究了银掺杂对MoS2薄膜的表面形貌、晶体结构、光吸收特性以及电学特性的影响。研究发现,银掺杂并未改变MoS2薄膜的晶体结构,而使MoS2薄膜的结晶度更好;银掺杂的MoS2薄膜反射率降低,光吸收增强,进而可以提高器件的光电转换效率。另外,银掺杂的MoS2薄膜表面更均匀平整,同时具有更良好的电学特性,其电子迁移率高达1.154×104 cm2·V-1·s-1,可用于制造一些晶体管和集成电路等半导体器件。     

二硫化钼-石墨烯垂直异质结的制备与表征

以采用化学气相沉积法(CVD)生长的单层石墨烯为导电电极、四硫代钼酸铵水溶液为电解质,通过电化学沉积法合成了二硫化钼/石墨烯(MoS2/graphene)垂直异质结。将合成的MoS2/graphene垂直异质结通过CVD在氢气(H2)和氩气(Ar)环境下进行退火处理。利用拉曼光谱、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)系统地分析了样品的物质成分、表面形貌和厚度等。这种简单、环保、低成本的制备大面积MoS2/graphene垂直异质结的方法具有普遍适用性,为其他垂直异质结的制备开辟了新途径。     

氮气退火对NiO/ZnO薄膜PN结的影响

利用磁控溅射法,在ITO玻璃基底上沉积NiO薄膜和ZnO:Al（Al掺杂的ZnO或AZO）薄膜,制备具有半导体特性的NiO/ZnO透明异质结二极管。使用UV—1700型分光光度计、KEITHLEY4200-SCS半导体测试仪、JSM-6490LV型扫描电子显微镜等分析氮气退火对NiO/ZnO薄膜性能的影响。实验结果表明： 500℃退火范围内,NiO薄膜的透过率随退火温度的升高单调上升,500℃时透过率在80%以上,NiO/ZnO薄膜的透过率明显提高;在400℃时,NiO/ZnO薄膜整流特性最佳。     

氮气退火对NiO/ZnO:Al薄膜PN结的影响

利用磁控溅射法,在ITO玻璃基底上沉积NiO薄膜和ZnO:Al(Al掺杂的ZnO或AZO)薄膜,制备具有半导体特性的NiO/ZnO:Al透明异质结二极管。使用UV-1700型分光光度计、KEITHLEY4200-SCS半导体测试仪、JSM-6490LV型扫描电子显微镜等分析氮气退火对NiO/ZnO:Al薄膜性能的影响。实验结果表明:500℃退火范围内,NiO薄膜的透过率随退火温度的升高单调上升,500℃时透过率在80%以上,NiO/ZnO:Al薄膜的透过率明显提高;在400℃时,NiO/ZnO:Al薄膜整流特性最佳。     

一种NiO薄膜的新型制备方法及其应用

利用热氧化法,在紫外线光源催化作用下,在N型硅衬底上沉积氧化镍(NiO)薄膜,制备具有半导体特性的NiO/Si异质结二极管。使用JASCO NRS-3100测量薄膜拉曼散射频谱,分析不同氧化时间、不同紫外线光源、不同退火条件对NiO薄膜性能的影响。实验结果表明:氧化时间为60 min时,金属Ni能够充分氧化;含臭氧水银灯比金属卤化物灯更有助于金属Ni的氧化反应;氮气下退火30 min,有助于消除晶格损伤,改善薄膜特性。通过Phillips X'Pert衍射仪分析NiO薄膜的晶体结构,Keysight B1500A半导体参数测量仪测量NiO/Si二极管的I-V特性,当二极管两端电压分别为2 V和-2 V时,电流密度相差3个数量级,表现出良好的整流特性。     

基于电纺纤维的CuO/SnO_2薄膜及其气敏特性

研究了一种基于静电纺丝纳米纤维制备异质结薄膜的方法。采用静电纺丝技术在硅衬底上依次沉积PVP/CuCl2.2H2O和PVP/SnCl4.5H2O纳米纤维,经过氧等离子体刻蚀并高温退火处理后得到了基于多孔纳米纤维的CuO/SnO2异质结薄膜。利用扫描电子显微镜(SEM)和X射线衍射技术(XRD)对纤维的形貌和结晶状态进行了表征。电学特性及气敏特性测试结果表明,该异质结薄膜具有明显的整流特性,在100℃的工作温度下,对H2S气体响应和恢复速度快、检测限低、选择性好。     

硫掺杂纳米金刚石薄膜的图形化生长

利用电子增强热丝化学气相沉积(EACVD)技术,以CH4/H2/H2S/Ar为工作气体,SiO2/Si为衬底,制备了硫掺杂金刚石薄膜。研究了利用光刻技术实现薄膜的图形化生长。结果表明:以SiO2作掩模的光刻技术能够使得硫掺杂金刚石薄膜在光滑SiO2/Si基片上很好地图形化生长。Hall效应检测表明硫掺杂金刚石薄膜为n型,给出了n型金刚石/p-Si异质结的反向I-V特性曲线。     

简易化学水浴法制备SnO2/p-Si异质结光电性能

SnO2薄膜沉积在晶硅衬底上通过一种简单化学水浴法以制备n-SnO2/p-Si异质结光电器件,该化学水浴法非常便宜和方便。采用XRD、XPS、紫外-可见光分光光度计和霍尔效应测试系统表征了SnO2薄膜的微结构、光学和电学性能,对SnO2/p-Si异质结的I-V曲线进行测试并分析,获得明显的光电转换特性。     

LP-MOCVD法制作n-ZnO/p-Si异质结及其电致发光研究

采用低压-金属有机化学气相沉积法(LP-MOCVD)在(100)p-Si衬底上制备未掺杂n型ZnO薄膜,并制作了相应的n-ZnO/p-Si异质结器件.通过X射线衍射(XRD)、光致发光(PL)光谱和霍尔测试分别研究了所制备薄膜的结构、光学和电学特性.得到具有较高质量的n型ZnO薄膜.在室温条件下,测得了该类异质结器件正向注入电流下可见光和近红外区域的电致发光(EL).     

二维WS2薄膜的制备及光电特性

以硫化钨(WS2)水溶液为原料、氩气为携载气体、利用化学气相沉积(CVD)法在硅衬底上制备了二维WS2薄膜,并研究了其形貌、晶体结构、光吸收特性及光电特性等。发现利用该方法生长的WS2薄膜非常光滑均匀,并具有良好的结晶性。另外,发现WS2薄膜不仅在466 nm处有很强的蓝光发射,还在617和725 nm处有显著的红光发射,前者可能是由于量子尺寸效应引起的分立能级的发光,后者则分别对应WS2单层和多层的本征发射。最后,研究了WS2/Si异质结的光电效应和温度效应,发现随照射光功率或温度的增加,异质结的电流显著增大,说明WS2/Si异质结对光照和温度非常敏感,可用于制备太阳电池和光探测器等新型光电子器件。     

物理气相传输法制备层状MoS2薄膜

以化学气相沉积(CVD)方法在蓝宝石衬底上沉积一层较厚的MoS_2膜作为前驱体,使用物理气相传输(PVT)方法制备了层状MoS_2薄膜。用光学显微镜、扫描电子显微镜、喇曼光谱和光致发光光谱对制备的层状MoS_2膜表面形貌、层数、光学特性进行了研究。分析了源和衬底距离对MoS_2薄膜沉积的影响,发现距离较近有利于成核概率增大,形成连续膜,但是易引入不稳定因素导致立体生长的MoS_2纳米片,同时观察到出现树枝状生长,这是由于前驱体质量过剩引起的部分晶面生长速率过高导致的。喇曼光谱测试表明,薄膜大部分为单层膜和双层膜,有少量的多层膜,膜的光致发光光谱强度与层数有关,单层膜光致发光光谱强度最强。     

Lattice vibration and Raman scattering of two-dimensional van der Waals heterostructure

Research on two-dimensional(2D) materials and related van der Waals heterostructures(vdWHs) is intense and remains one of the leading topics in condensed matter physics.Lattice vibrations or phonons of a vdWH provide rich information,such as lattice structure,phonon dispersion,electronic band structure and electron–phonon coupling.Here,we provide a mini review on the lattice vibrations in vdWHs probed by Raman spectroscopy.First,we introduced different kinds of vdWHs,including their structures,properties and potential applications.Second,we discussed interlayer and intralayer phonon in twist multilayer graphene and MoS2.The frequencies of interlayer and intralayer modes can be reproduced by linear chain model(LCM)and phonon folding induced by periodical moiré potentials,respectively.Then,we extended LCM to vdWHs formed by distinct 2D materials,such as MoS2/graphene and hBN/WS2 heterostructures.We further demonstrated how to calculate Raman intensity of interlayer modes in vdWHs by interlayer polarizability model.     

The microstructure and physical properties of thin SnO2 films

Thin polycrystalline SnO₂ films were deposited on glass substrates by magnetron sputtering. Electrical, optical, and gas-sensing properties, as well as the structure and phase composition of the films, were studied. The electrical resistance of the films and the concentration and mobility of free charge carriers were determined by the four-point-probe and van der Pauw methods. The band gap and the type of optical transitions in the films were derived from optical absorption spectra. The sensitivity to toxic and explosive gases was measured. The composition, morphology, and crystal structure of the films annealed at 600°C were examined by X-ray diffraction and electron microscopy. The films were found to contain only a tetragonal SnO₂ phase and have good crystallinity. The average grain size in the annealed films is 11–19 nm. A model of the electrical conduction in the polycrystalline SnO₂ films is discussed.     

Solution flow rate influence on properties of copper oxide thin films deposited by ultrasonic spray pyrolysis

The present work is an investigation of the solution flow rate influence on copper oxide (CuO) thin film properties deposited by ultrasonic spray pyrolysis. A set of CuO thin films were deposited, with various solution flow rates, on glass substrate at 300 °C. The precursor solution is formed with copper salt dissolution in distilled water with 0.05 molarity. The solution flow rate was ranged from 10 to 30 ml/h. Films composition and structure were characterized by means of XRD (X Rays diffraction) and Raman scattering. The optical properties were studied using UV–visible spectroscopy. The electrical conductivity, carrier mobility and concentration were determined by Hall Effect measurements. The obtained results indicate that flow rate is a key parameter controlling CuO films growth mechanism and their physical properties. The prepared films are mainly composed with a CuO monophase, the crystallite size is reduced with increasing the flow rate. A ZnO/CuO heterojunction structure has been realized and its rectifying behavior is tested.     

Polarity‐Controlled Attachment of Cytochrome C for High‐Performance Cytochrome C/Graphene van der Waals Heterojunction Photodetectors

Biomolecule/graphene van der Waals heterojunction provides a generic platform for designing high‐performance, flexible, and scalable optoelectronics. A key challenge is, in controllable attachment, the biomolecules to form a desired interfacial electronic structure for a high‐efficiency optoelectronic process of photoabsorption, exciton dissociation into photocarriers, carrier transfer, and transport. Here, it is shown that a polarity‐controlled attachment of the Cytochrome c (Cyt c) biomolecules can be achieved on the channel of graphene field effect transistors (GFET). High‐efficiency charge transfer across the formed Cyt c/graphene interface is demonstrated when Cyt c attaches with positively charged side to GFET as predicted by molecular dynamics simulation and confirmed experimentally. This Cyt c/GFET van der Waals heterojunction nanohybrid photodetector exhibits a spectral photoresponsivity resembling the absorption spectrum of the Cyt c, confirming the role of Cty c as the photosensitizer in the device. The high visible photoresponsivity up to 7.57 × 10⁴ A W^?1 can be attributed to the high photoconductive gain in exceeding 10⁵ facilitated by the high carrier mobility in graphene. This result therefore demonstrates a viable approach in synthesis of the biomolecule/graphene van der Waals heterojunction optoelectronics using polarity‐controlled biomolecule attachment, which can be expanded for on‐chip printing of high‐performance molecular optoelectronics.     

Broadband polarized photodetector based on p-BP/n-ReS2 heterojunction

Two-dimensional(2D) atomic crystals,such as graphene,black phosphorus(BP) and transition metal dichalcogenides(TMDCs) are attractive for use in optoelectronic devices,due to their unique crystal structures and optical absorption properties.In this study,we fabricated BP/ReS2 van der Waals(vdWs) heterojunction devices.The devices realized broadband photoresponse from visible to near infrared(NIR)(400–1800 nm) with stable and repeatable photoswitch characteristics,and the photoresponsivity reached 1.8 mA/W at 1550 nm.In addition,the polarization sensitive detection in the visible to NIR spectrum(532–1750 nm) was demonstrated,and the photodetector showed a highly polarization sensitive photocurrent with an anisotropy ratio as high as 6.44 at 1064 nm.Our study shows that van der Waals heterojunction is an effective way to realize the broadband polarization sensitive photodetection,which is of great significance to the realization and application of multi-functional devices based on 2D vdWs heterostructures.     

Ultrathin Non‐van der Waals Magnetic Rhombohedral Cr2S3: Space‐Confined Chemical Vapor Deposition Synthesis and Raman Scattering Investigation

Two dimensional (2D) magnetic materials display enormous application potential in spintronic fields. However, most of currently reported magnetic materials are van der Waals layered structure that is easy to be isolated via exfoliation method. By contrast, the studies on non‐van der Waals ultrathin magnetic materials are rare, largely due to the difficulty in fabrication. Rhombohedral Cr₂S₃, an intensively studied antiferromagnetic transition metal chalcogenide with Neel temperature of ≈120 K, has a typical non‐van der Waals structure. Restricted by the strong covalent bonding in all the three dimensions of non‐van der Waals structure, the synthesis of ultrathin Cr₂S₃ single crystals is still a challenge that is not achieved yet. Besides, the study on the Raman modes of rhombohedral Cr₂S₃ is also absent. Herein, by employing space‐confined chemical vapor deposition strategy, ultrathin rhombohedral Cr₂S₃ single crystals with a thickness down to ≈2.5 nm for the first time are successfully grown. Moreover, a systematically investigation is also conducted on the Raman vibrations of ultrathin rhombohedral Cr₂S₃. With the aid of angle‐resolved polarized Raman technique, the Raman modes of rhombohedral Cr₂S₃ for the first time based on crystal symmetry and Raman selection rules are rationally assigned.     

CIGS Thin Films for Cd-Free Solar Cells by One-Step Sputtering Process

Cu(In_1?x Ga _x )Se₂ (CIGS) thin films were deposited by a one-step radio frequency (RF) magnetron sputtering process using a quaternary CIGS target. The influence of substrate temperature on the composition, structure, and optical properties of the CIGS films was investigated. All the CIGS films exhibited the chalcopyrite structure with a preferential orientation along the (112) direction. The CIGS film deposited at 623 K showed significant improvement in film crystallinity and surface morphology compared to films deposited at 523 and 573 K. To simplify the manufacturing procedure of solar cells and avoid the use of the toxic element Cd, the properties of ZnS films prepared by RF sputtering were also investigated. The results revealed that the sputtered ZnS film exhibits good lattice matching with the sputtered CIGS film with significantly lower optical absorption loss. Finally, all-sputtered Cd-free CIGS-based heterojunction solar cells with the structure SLG/Mo/CIGS/ZnS/AZO/Al grids were fabricated without post-selenization. Furthermore, the results demonstrated the feasibility of using a full sputtering process for the fabrication of Cd-free CIGS-based solar cell.     

掺胺碳膜及其对甲酸蒸气传感特性

用射频等离子体化学沉积方法制备氢化非晶碳（a-C:H)膜。在等离子体气氛中引入胺基团,则能够在a-C:H薄膜沉积过程中将胺基团掺入薄膜的网络结构中。喇曼光谱表明薄膜具有无序态结构。红外分析表明薄膜中有胺基团存在,将掺胺a－C：H薄膜作为质量传感膜沉积到石英晶体表面制成气相质量传感器。测试表明掺胺a－C：H膜对甲酸蒸气具有高的响应灵敏度,好的线性相关系数和线性响应范围。     

Towards van der Waals Epitaxial Growth of GaAs on Si using a Graphene Buffer Layer

Van der Waals growth of GaAs on silicon using a two‐dimensional layered material, graphene, as a lattice mismatch/thermal expansion coefficient mismatch relieving buffer layer is presented. Two‐dimensional growth of GaAs thin films on graphene is a potential route towards heteroepitaxial integration of GaAs on silicon in the developing field of silicon photonics. Hetero‐layered GaAs is deposited by molecular beam epitaxy on graphene/silicon at growth temperatures ranging from 350 °C to 600 °C under a constant arsenic flux. Samples are characterized by plan‐view scanning electron microscopy, atomic force microscopy, Raman microscopy, and X‐ray diffraction. The low energy of the graphene surface and the GaAs/graphene interface is overcome through an optimized growth technique to obtain an atomically smooth low­ temperature GaAs nucleation layer. However, the low adsorption and migration energies of gallium and arsenic atoms on graphene result in cluster‐growth mode during crystallization of GaAs films at an elevated temperature. In this paper, we present the first example of an ultrasmooth morphology for GaAs films with a strong (111) oriented fiber‐texture on graphene/silicon using quasi van der Waals epitaxy, making it a remarkable step towards an eventual demonstration of the epitaxial growth of GaAs by this approach for heterogeneous integration.