Effect of interface on mid-infrared photothermal response of MoS2 thin film grown by pulsed laser deposition

This study reports on the mid-infrared (mid-IR) photothermal response of multilayer MoS2 thin films grown on crystalline (p-type silicon and c-axisoriented single crystal sapphire) and amorphous (Si/SiO2 and Si/SiN) substrates by pulsed laser deposition (PLD).The photothermal response of the MoS2 films is measured as the changes in the resistance of the MoS2 films when irradiated with a mid-IR (7 to 8.2 μm) source.We show that enhancing the temperature coefficient of resistance (TCR) of the MoS2 thin films is possible by controlling the film-substrate interface through a proper choice of substrate and growth conditions.The thin films grown by PLD are characterized using X-ray diffraction,Raman,atomic force microscopy,X-ray photoelectron microscopy,and transmission electron microscopy.The high-resolution transmission electron microscopy (HRTEM) images show that the MoS2 films grow on sapphire substrates in a layer-by-layer manner with misfit dislocations.The layer growth morphology is disrupted when the films are grown on substrates with a diamond cubic structure (e.g.,silicon) because of twin growth formation.The growth morphology on amorphous substrates,such as Si/SiO2 or Si/SiN,is very different.The PLD-grown MoS2 films on silicon show higher TCR (-2.9％ K-1 at 296 K),higher mid-IR sensitivity (△R/R =5.2％),and higher responsivity (8.7 V·W-1) compared to both the PLD-grown films on other substrates and the mechanically exfoliated MoS2 flakes transferred to different substrates.     

Probing the intrinsic optical quality of CVD grown MoS<Subscript>2</Subscript>

Optical emission efficiency of two-dimensional layered transition metal dichalcogenides (TMDs) is one of the most important parameters affecting their optoelectronic performance.The optimization of the growth parameters by chemical vapor deposition (CVD) to achieve optoelectronic-grade quality TMDs is,therefore,highly desirable.Here,we present a systematic photoluminescence (PL) spectroscopic approach to assess the intrinsic optical and crystalline quality of CVD grown MoS2 (CVD MoS2).We propose the use of the intensity ratio between the PL measured in air and vacuum as an effective way to monitor the intrinsic optical quality of CVD MoS2.Low-temperature PL measurements are also used to evaluate the structural defects in MoS2,via defect-associated bound exciton emission,which well correlates with the field-effect carrier mobility of MoS2 grown at different temperatures.This work therefore provides a sensitive,noninvasive method to characterize the optical properties of TMDs,allowing the tuning of the growth parameters for the development of optoelectronic devices.     

粘结MoS2基钼固体润滑膜的抗承载能力和耐速度性能研究

为了探讨粘结MoS2基固体润滑膜在干摩擦条件下的抗承载能力和耐速度性能,使用国产的环一块摩擦磨损试验机在干摩擦下对粘结MoS2基固体润滑膜在不同载荷和不同速度试验条件下的摩擦磨损性能进行了研究.试验结果表明:粘结MoS2基固体润滑膜的承载能力有高达2100N,在0.512～3.84m/s的滑动速度范围内具有良好的抗磨减摩性能.对转移膜的研究结果表明高载高速试验条件有利于促进对偶表面生成高质量的转移膜.粘结MoS2基固体润滑膜具有良好的抗承载能力和耐速度性能的机理应归结于在摩擦过程中对偶表面高质量转移膜的生成.     

MoS2含量对聚酰亚胺复合膜摩擦性能的影响

为降低PI膜的摩擦系数,在PI中加入不同质量比例的MoS2作为减摩相制备复合润滑膜.考察不同MoS2含量复合膜的机械性能和摩擦性能,研究复合膜表面Mo元素分布.结果显示加入量为30%的MoS2在复合膜表面富集,且分布较为均匀,在此配比下的复合膜能够在保证机械性能的基础上有效降低摩擦系数,随载荷的增加,摩擦系数稳定.     

磁控溅射MoS2/WS2复合薄膜的工艺与摩擦学性能研究

采用MoS2/WS2复合靶材在不锈钢和硅基片上溅射MoS2/WS2纳米薄膜,通过多次实验,得到溅射MoS2/WS2薄膜的最佳工艺如下:溅射气压4.0Pa,靶基距为70mm,溅射功率为150W,溅射时间为3h.使用X-射线衍射仪,能谱仪,扫描电子显微镜对薄膜的成分和结构进行分析.采用HH-3000薄膜结合强度划痕试验仪,纳米压痕测试系统,UNT-3摩擦磨损试验机对薄膜进行机械性能和摩擦磨损性能分析,结果表明:在大气环境中,WS2/MoS2 复合薄膜摩擦性能要优于纯MoS2薄膜.     

Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates

The two-dimensional layer of molybdenum disulfide (MoS(2)) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS(2) atomic thin layers is still rare. Here we report that the high-temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS(2) thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS(2) sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS(2) layer is comparable with those of the micromechanically exfoliated thin sheets from MoS(2) crystals. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS(2) films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.     

Single-layer MoS2 transistors

Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene, both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS(2) have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5-3 cm(2) V(-1) s(-1) range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS(2) mobility of at least 200 cm(2) V(-1) s(-1), similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10(8) and ultralow standby power dissipation. Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS(2) could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.     

离子束辅助沉积MoS2复合膜的XPS和ESR特性分析

通过IBAD技术制备了MoS2 Ag(Cu)复合膜 ,并利用XPS和ESR考察了复合膜的氧化情况。发现在RH为 6 0 %的大气环境下 ,Cu的掺入加速了MoS2 的氧化 ,相反Ag的加入却使MoS2 的氧化受到抑制 ;XPS发现MoS2 Cu复合膜中存在Mo6 ,ESR却并没发现中间态Mo5 ;而XPS没有检测到MoS2 Ag膜中有Mo6 ,ESR却发现Mo5 。这说明Mo5 受化学环境影响较大     

MoS_2与TiO_2一维纳米复合材料的制备与表征

本文采用气相还原法制备了MoS2包覆TiO2的一维纳米复合材料,首先用水热法制备TiO2纳米管,并制备前驱体(NH42)MoS4;用浸渍法将(NH4)2MoS4附着于TiO2纳米管表面;然后利用氢气还原前驱体得到MoS2包覆层。用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)表征所得产物的结构及微观形貌。结果表明当还原反应温度较高(≥600℃)时,产物呈烧结状态,而当反应温度为500℃时,可以得到表面均匀包覆MoS2的TiO2纳米管复合材料,其中包覆层MoS2的结晶程度较低。在此基础上,本文提出了该产物的生长模型,并对包覆前后的样品做荧光性能分析。     

磁控溅射MoS2＋Sb2O3防冷焊薄膜性能研究

MoS2溅射膜具有在潮湿大气中容易发生氧化而失去润滑作用的缺点.为了解决这个问题,将Sb2O3添加于MoS2中,用磁控溅射法制备了MoS2+Sb2O3薄膜,并利用球-盘式磨损试验机考察了它对薄膜摩擦特性的影响.通过XRD、XPS、AFM对MoS2+Sb2O3薄膜的微观结构和形貌及其化学状态进行了分析.实验结果表明薄膜的微观结构致密、晶粒小、分布均匀,有良好的润滑性、防冷焊性,特别适用于卫星活动部件的固体润滑.     

Self-assembled lamellar MoS2, SnS2 and SiO2 semiconducting polymer nanocomposites

Lamellar nanocomposites based on semiconducting polymers incorporated into layered inorganic matrices are prepared by the co-assembly of organic and inorganic precursors. Semiconducting polymer-incorporated silica is prepared by introducing the semiconducting polymers into a tetrahydrofuran (THF)/water homogeneous sol solution containing silica precursor species and a surface-active agent. Semiconducting polymer-incorporated MoS(2) and SnS(2) are prepared by Li intercalation into the inorganic compound, exfoliation and restack in the presence of the semiconducting polymer. All lamellar nanocomposite films are organized in domains aligned parallel to the substrate surface plane. The incorporated polymers maintain their semiconducting properties, as evident from their optical absorption and photoluminescence spectra. The optoelectronic properties of the nanocomposites depend on the properties of both the inorganic host and the incorporated guest polymer as demonstrated by integrating the nanocomposite films into light-emitting diodes. Devices based on polymer-incorporated silica and polymer-incorporated MoS(2) show no diode behaviour and no light emission due to the insulating and metallic properties of the silica and MoS(2) hosts. In contrast, diode performance and electroluminescence are obtained from devices based on semiconducting polymer-incorporated semiconducting SnS(2), demonstrating that judicious selection of the composite components in combination with the optimization of material synthesis conditions allows new hierarchical structures to be tailored for electronic and optoelectronic applications.     

磁控溅射防锈MoS2薄膜沉积工艺研究

介绍了磁控溅射制备防锈MoS2薄膜的沉积工艺,同时对影响膜层性能的几个因素进行了初步的探讨,并且制备了防锈性能优良的MoS2薄膜样品。     

射频溅射MoS2,WS固体润滑膜在脂润滑下的摩擦学特性

用球－盘试验机研究了射频溅射ＭｏＳ２，ＷＳ２固体润滑膜在脂润滑下的摩擦学特性，并用ＸＰＳ，ＳＥＭ和ＥＤＸ等方法进行了分析．结果指出，在锂基脂润滑下，表面溅射ＭＯＳ２薄膜后摩擦系数降低，擦伤载荷成几倍或几十倍增长，尤其在高滑动速度下效果更加明显，可在一定载荷范围内代替２＃主轴油进行润滑，摩擦中ＭＯＳ２膜表层组织很容易剥落，摩擦中与基体结合较牢的主要是表面下的有效膜厚。因而在本试验条件下两种厚度ＭＯＳ２膜的摩擦学性能基本无差别，溅射ＷＳ２膜中含氧量很高，且在整个膜层中均以ＷＯ３存在，因此减摩效果不理想。     

Real-time electrical detection of epidermal skin MoS<Subscript>2</Subscript> biosensor for point-of-care diagnostics

Various approaches have been proposed for point-of-care diagnostics,and in particular,optical detection is preferred because it is relatively simple and fast.At the same time,field-effect transistor (FET)-based biosensors have attracted great attention because they can provide highly sensitive and label-free detection.In this work we present highly sensitive,epidermal skin-type point-of-care devices with system-level integration of flexible MoS2 FET biosensors,read-out circuits,and light-emitting diode (LEDs) that enable real-time detection of prostate cancer antigens (PSA).Regardless of the physical forms or mechanical stress conditions,our proposed high-performance MoS2 biosensors can detect a PSA concentration of 1 pg.mL-1 without specific surface treatment for anti-PSA immobilization on the MoS2 surface on which we characterize and confirm physisorption of anti-PSA using Kelvin probe force microscopy (KPFM)and tapping-mode atomic force microscopy (tm-AFM).Furthermore,current modulation induced by the binding process was stably maintained for longer than 2-3 min.The results indicate that flexible MoS2-based FET biosensors have great potential for point-of-care diagnostics for prostate cancer as well as other biomarkers.     

MoS₂ nanosheet phototransistors with thickness-modulated optical energy gap

We report on the fabrication of top-gate phototransistors based on a few-layered MoS(2) nanosheet with a transparent gate electrode. Our devices with triple MoS(2) layers exhibited excellent photodetection capabilities for red light, while those with single- and double-layers turned out to be quite useful for green light detection. The varied functionalities are attributed to energy gap modulation by the number of MoS(2) layers. The photoelectric probing on working transistors with the nanosheets demonstrates that single-layer MoS(2) has a significant energy bandgap of 1.8 eV, while those of double- and triple-layer MoS(2) reduce to 1.65 and 1.35 eV, respectively.     

摩擦表面MoS2润滑膜的显微结构分析

为探讨ＭｏＳ２／Ｎｉ复合材料的自润滑机理，采用薄膜分离技术从摩擦表面提取了ＭｏＳ２润滑膜，在透射电镜下研究其显微结构。结果表明，润滑膜中的ＭｏＳ２具有择优取向，其基础面科行于摩擦表观，形成了助于于润滑作用的织构。     

Morphology and current-voltage characteristics of nanostructured pentacene thin films probed by atomic force microscopy

Atomic force microscopy was used to study the growth modes (on SiO2, MoS2, and Au substrates) and the current-voltage (I-V) characteristics of organic semiconductor pentacene. Pentacene films grow on SiO2 substrate in a layer-by-layer manner with full coverage at an average thickness of 20 A and have the highest degree of molecular ordering with large dendritic grains among the pentacene films deposited on the three different substrates. Films grown on MoS2 substrate reveal two different growth modes, snowflake-like growth and granular growth, both of which seem to compete with each other. On the other hand, films deposited on Au substrate show granular structure for thinner coverages (no crystal structure) and dendritic growth for higher coverages (crystal structure). I-V measurements were performed with a platinum tip on a pentacene film deposited on a Au substrate. The I-V curves on pentacene film reveal symmetric tunneling type character. The field dependence of the current indicates that the main transport mechanism at high field intensities is hopping (Poole-Frenkel effect). From these measurements, we have estimated a field lowering coefficient of 9.77 x 10(-6) V-1/2 m1/2 and an ideality factor of 18 for pentacene.     

二维层状WS2/MoS2异质结中镧系近红外光子发射与能量转移（英文）

镧系离子由于其独特的光子特性而备受关注.二维层状范德华异质结的光电特性和器件性能受到界面耦合的极大影响,该异质结通常是由两层或多层过渡金属二硫化物(TMD)堆叠而成.本文通过两步合成构建了镧系离子掺杂的层状WS2/MoS2异质结.所制备的掺杂薄膜是在晶圆衬底上生长的高度织构纳米片.更重要的是,由于两个TMD层中镧系离子之间的能量转移,层状异质结的结构减少了因均匀掺杂或浓度猝灭而引起的无益交叉松弛,所制备的堆叠异质结能够在近红外通讯窗口产生高效的光子发射.镧系掺杂和能量转移的研究结果表明,镧系离子可以有效地扩展TMD薄膜的发射波段及其异质结构.本工作所发展的镧系掺杂TMD异质结有助于进一步研究原子级超薄近红外光子器件.     

Experimental obviousness of the necessity for a thin Ni interfacial layer to obtain highly ordered photoconductive MoS2 films

It is shown that photosensitive films can be obtained by solid state reaction, induced by annealing, between the constituents Mo and S sequentially deposited in thin film form if the substrate is coated with a thin (10–20 nm) NiCr layer. The thin Mo and S layers are deposited in the atomic ratio Mo : S=1 : 3. The substrates used are mica sheets. An annealing at 1073 K for 30 min under argon flow allows one to obtain highly 2H–MoS2 crystallized films. The thickness of the crystallites is similar to that of the films; they have their c-axes perpendicular to the plane of the substrate. After crystallization, X-ray photoelectron spectroscopy (XPS) depth profiles show that Ni is diffused all over the thicknesses of the films and that 1 at% of Ni is visible at the surfaces of the films. The direct current (d.c.) conductivity of these films is nearly similar to that of single crystals. The films are photosensitive. The room temperature photoconductivity, which results from interband transitions, allows one to measure the direct band gap that is similar to that of a single crystal. When bare mica substrates (without Ni) are used MoS2 films are obtained but they are poorly crystallized and not photoconductive, which shows an NiCr interfacial layer is necessary. Probably a melting phase NiSx forms, which increases the mobility of the atom at grain boundaries. This revised version was published online in November 2006 with corrections to the Cover Date.     

磁控溅射MoS2/Sb2O3复合膜的润滑失效分析

磁控溅射法制备了MoS2 /Sb2 O3 固体润滑复合膜 ,用CSEM摩擦试验机、CSEM纳米划痕仪和PHI- 5 70 2XPS/AES多功能电子能谱仪 ,考察了其摩擦磨损性能、抗损伤性能和抗氧化性能 ,侧重分析了薄膜失效的原因 ,探讨了该固体润滑复合膜润滑失效的微观机理