Engineering Zeolitic‐Imidazolate Framework (ZIF) Thin Film Devices for Selective Detection of Volatile Organic Compounds

Thin films of sodalite‐type zeolitic‐imidazolate frameworks (ZIFs, ZIF‐7, 8, 9, 67, 90, and ZIF‐65‐Zn) with different metal centers and functional moieties are fabricated on SiO₂ coated quartz crystal microbalance (QCM) substrates using automatic program controlled repeated direct growth method. The repeated direct growth procedure manipulated here shows great applicability for rapid growth of uniform ZIF thin films with controllable thickness. The fabricated ZIF/QCM devices are used to detect vapor phase volatile organic compounds including alcohol/water, BTEX compounds (benzene, toluene, ethylbenzene and xylene isomers), and hexane isomers. The ZIF/QCM devices exhibit selective detection behavior upon exposure to these chemical vapors. The effects of ZIF pore size, limited pore diameter, surface functionality, and structural flexibility on the sensing performances of ZIF/QCM devices are systematically investigated, which would be beneficial for the practical application of ZIF sensors based on array‐sensing technology. Furthermore, the selective adsorption behavior suggests that these ZIF materials have great potentials in the applications of biofuel recovery and the separation of benzene/cyclohexane, xylene, and hexane isomers.     

Nanosized Copper Selenide Functionalized Zeolitic Imidazolate Framework‐8 (CuSe/ZIF‐8) for Efficient Immobilization of Gas‐Phase Elemental Mercury

A key challenge in elemental mercury (Hg⁰) decontamination from flue gas lies in the design of a sorbent with abundant reactive adsorption sites that exhibit high affinity toward Hg⁰ to simultaneously achieve rapid capture and large capacity. Herein, zeolitic imidazolate framework‐8 (ZIF‐8) supported copper selenide (CuSe) nanocomposites are synthesized by a newly designed two‐step surfactant‐assisted method. The as‐prepared CuSe/ZIF‐8 with CuSe to ZIF‐8 mass ratio of 80% (0.8NC‐ZIF) exhibits unparalleled performance toward Hg⁰ adsorption with equilibrium capacity and average rate reaching 309.8 mg g^?1 and 105.3 µg g^?1 min^?1, respectively, surpassing all reported metal sulfides and traditional activated‐carbon‐based sorbents. The impressive performance of 0.8NC‐ZIF for Hg⁰ immobilization is primarily attributed to the adequate exposure of the Se‐terminated sites with high affinity toward Hg⁰ resulted from the layered structure of CuSe. The adsorbed mercury selenide exhibits even higher stability than the most stable natural mercury ore—that is, mercury sulfide—hence minimizing its environmental impact when the CuSe/ZIF‐8 sorbent is dumped. This work provides a new mindset for future design of sorbents for efficient Hg⁰ capture from industrial flue gas. The results also justify the candidature of CuSe/ZIF to be applicable for mercury pollution remediation in real‐world conditions.     

MOCVD法氧化锌单晶薄膜生长

介绍了氧化锌材料的一些突出特性以及生长氧化锌的方法。并通过金属有机化学气相沉积 (MOCVD)方法制备了优良的氧化锌薄膜。使用X射线衍射 (XRD)谱和室温光致发光(PL)光谱对所生长氧化锌薄膜的晶体质量和光学特性进行了研究。X射线衍射谱图显示仅在2θ =34.72°处有一个很陡峭的ZnO (0 0 2 )晶面衍射峰 ,说明所制备的氧化锌薄膜c轴取向高度一致。此衍射峰的半高宽为 0 .2 82° ,显示出较好的晶体质量。在室温光致发光谱中 ,薄膜的紫外发光强度与深能级复合发光的强度比超过 10∶1,表明薄膜的光学质量较高     

反应压力对MOCVD法沉积ZnO薄膜性质的影响

研究了反应压力对金属有机化学气相沉积(MOCVD)技术制备未掺杂ZnO薄膜的微观结构和光电特性影响.X射线衍射(XRD)和扫描电子镜(SEM)的研究结果表明,随着反应压力的降低,ZnO薄膜(002)择优峰的强度呈现相对减弱趋势,并且出现了较强的(110)峰;Hall测量表明,低的反应压力有助于提高薄膜电学特性.200 Pa时制备出的ZnO薄膜具有明显的"类金字塔"状绒面结构,电阻率为1.28×10-2 Ω·cm.实验中沉积的ZnO薄膜在600～2 600 nm内平均透过率超过80%,而短波长范围由于光散射作用,ZnO薄膜的垂直透过率有所下降.     

ZnO薄膜紫外探测器的光电性质

采用直流反应磁控溅射的方法制备ZnO薄膜, 用X射线衍射仪(XRD)、扫描电镜(SEM)和紫外-可见光谱仪(UV-Vis)分别表征ZnO薄膜的晶体结构和表面形貌等特征。并用此材料制备Au/ZnO/Au金属-半导体-金属(MSM)结构光电导型ZnO薄膜紫外光探测器。实验结果表明, ZnO探测器在360 nm出现明显光响应,其光电流为2.5 mA, 在5 V偏置电压下暗电流为250 μA; ZnO紫外探测器在250～380 nm的紫外波段, 探测器有很明显的光响应, 且光电流响应比较平坦; 在380～430 nm区域, 光响应明显下降; 其光响应的上升与下降弛豫时间分别为20 s与80 s。从光谱响应图中可以看出紫外(360 nm)比可见区(450 nm)的光响应高出3个数量级, 薄膜表面存在的缺陷(如氧空位)在ZnO紫外探测器的光电效应中有重要作用。     

溶胶-凝胶法制备ZnO薄膜及表征

采用溶胶-凝胶法在石英玻璃衬底上使用旋转涂覆技术生长了Zn O薄膜.对薄膜的XRD分析表明Zn O薄膜为纤锌矿结构并沿c轴取向生长.透射光谱表明薄膜的禁带宽度为3.2 8e V ,与Zn O体材料的禁带宽度3.30 e V基本相同.用光致发光谱分析了经过5 0 0～70 0℃热处理获得的Zn O薄膜,结果表明Zn O薄膜在室温下有较强的紫外带边发射,但当热处理温度高于70 0℃时,可见光波段发射明显增加     

A Three Component Self‐Assembled Epitaxial Nanocomposite Thin Film

A self‐assembled three phase epitaxial nanocomposite film is grown consisting of ≈3 nm diameter fcc metallic Cu nanorods within square prismatic SrO rocksalt nanopillars in a Sr(Ti,Cu)O_3‐δ perovskite matrix. Each phase has an epitaxial relation to the others. The core–shell‐matrix structures are grown on SrTiO₃ substrates and can also be integrated onto Si using a thin SrTiO₃ buffer. The structure is made by pulsed laser deposition in vacuum from a SrTi_0.75Cu_0.25O₃ target, and formed as a result of the limited solubility of Cu in the perovskite matrix. Wet etching removes the 3 nm diameter Cu nanowires leaving porous SrO pillars. The three‐phase nanocomposite film is used as a substrate for growing a second epitaxial nanocomposite consisting of CoFe₂O₄ spinel pillars in a BiFeO₃ perovskite matrix, producing dramatic effects on the structure and magnetic properties of the CoFe₂O₄. This three‐phase vertical nanocomposite provides a complement to the well‐known two‐phase nanocomposites, and may offer a combination of properties of three different materials as well as additional avenues for strain‐mediated coupling within a single film.     

Improved Stability of Atomic Layer Deposited ZnO Thin Film Transistor by Intercycle Oxidation

By inserting H₂O treatment steps during atomic layer deposition of a ZnO layer, the turn‐on voltage shift from negative bias stress (NBS) under illumination was reduced considerably compared to that of a device that has a continuously grown ZnO layer without any treatment steps. Meanwhile, treatment steps without introducing reactive gases, and simply staying under a low working pressure, aggravated the instability under illuminated NBS due to an increase of oxygen vacancy concentration in the ZnO layer. From the experiment results, additional oxidation of the ZnO channel layer is proven to be effective in improving the stability against illuminated NBS.     

Light Effects on the Bias Stability of Transparent ZnO Thin Film Transistors

We report on the bias stability characteristics of transparent ZnO thin film transistors (TFTs) under visible light illumination. The transfer curve shows virtually no change under positive gate bias stress with light illumination, while it shows dramatic negative shifts under negative gate bias stress. The major mechanism of the bias stability under visible illumination of our ZnO TFTs is thought to be the charge trapping of photo‐generated holes at the gate insulator and/or insulator/channel interface.     

衬底温度对磁控溅射法制备的ZnO:In薄膜光电性能的影响

以粉末靶为溅射源,采用射频磁控溅射法在玻璃衬底上制备掺铟氧化锌(ZnO:In)透明导电膜.利用X射线衍射仪、原子力显微镜、霍尔测试仪,以及分光光度计等对不同衬底温度下生长的ZnO:In薄膜的结构、光电性能进行表征.结果表明,所有制备的ZnO:In薄膜均为六角纤锌矿结构的多晶膜,具有(002)择优取向.ZnO:In薄膜的电阻率随着衬底温度的升高先减小后增大,当衬底温度为100℃时,薄膜的最低电阻率为3.18×10~(-3)Ω·cm.制备的薄膜可见光范围内透过率均在85%以上.

Abstract：

Indium doped zinc oxide (ZnO : In) films were deposited on glass substrates by RF magnetron sputtering method using a powder target.The influence of the substrate temperature on the structure,optical and electrical properties was investigated by X-ray diffraction (XRD),atom force microscope (AFM),Hall measurement and optical transmission spectroscopy.The results show all the obtained films are polycrystalline with a hexagonal wurtzite structure and grow preferentially in the (002) direction,and the grain size is about 22～29 nm.The conductivity of the ZnO : In films change with the substrate temperature,and the lowest electrical resistivity is about 3.18 × 10~3 Ω·cm for the samples deposited at substrate temperature 100 ℃.The transmittance of our films in the visible range is all higher than 85%.     

溅射功率对AlN/ZnO薄膜结构形貌的影响

采用直流反应磁控溅射法以ZnO为缓冲层在Si衬底上制备了AlN/ZnO薄膜。利用台阶仪、X线衍射(XRD)仪和原子力显微镜(AFM)对不同溅射功率下制备的AlN/ZnO薄膜的厚度、结构及表面形貌进行测试表征。结果表明,不同溅射功率下生长的AlN薄膜都沿(002)择优生长,且随着功率的增大,薄膜的沉积速率增加,晶粒长大,AlN薄膜的(002)取向性变好。同时还利用扫描电子显微镜(SEM)对在优化工艺下制得AlN/ZnO薄膜断面的形貌进行表征,结果显示AlN薄膜呈柱状生长。     

High‐Mobility ZnO Thin Film Transistors Based on Solution‐processed Hafnium Oxide Gate Dielectrics

The properties of metal oxides with high dielectric constant (k) are being extensively studied for use as gate dielectric alternatives to silicon dioxide (SiO₂). Despite their attractive properties, these high‐k dielectrics are usually manufactured using costly vacuum‐based techniques. In that respect, recent research has been focused on the development of alternative deposition methods based on solution‐processable metal oxides. Here, the application of the spray pyrolysis (SP) technique for processing high‐quality hafnium oxide (HfO₂) gate dielectrics and their implementation in thin film transistors employing spray‐coated zinc oxide (ZnO) semiconducting channels are reported. The films are studied by means of admittance spectroscopy, atomic force microscopy, X‐ray diffraction, UV–Visible absorption spectroscopy, FTIR, spectroscopic ellipsometry, and field‐effect measurements. Analyses reveal polycrystalline HfO₂ layers of monoclinic structure that exhibit wide band gap (≈5.7 eV), low roughness (≈0.8 nm), high dielectric constant (k ≈ 18.8), and high breakdown voltage (≈2.7 MV/cm). Thin film transistors based on HfO₂/ZnO stacks exhibit excellent electron transport characteristics with low operating voltages (≈6 V), high on/off current modulation ratio (～10⁷) and electron mobility in excess of 40 cm² V^?1 s^?1.     

Growth of Transparent and Conductive Polycrystalline (0001)‐ZnO Films on Glass Substrates Under Low‐Temperature Hydrothermal Conditions

Flat panel display technology seems to be an ever‐expanding field developing into a multibillion dollar market. A set of technical solutions involve a transparent conducting film (TCF) that is today still dominated by indium‐tin‐oxide (ITO). In a race to find alternatives that would avoid the indium pitfalls, mainly due to its increasing price and limited natural availablity, replacement materials have been extensively investigated. This work demonstrates that by exploiting basic principles of crystal growth in geometrically constrained conditions, zinc oxide (ZnO) could easily be utilized for this purpose. ZnO layers were grown on inexpensive glass substrates via low‐temperature citrate‐assisted hydrothermal (HT) method. It was shown that in the nucleation stage the crystal growth can be efficiently controlled by spatially confined oriented growth (SCOG) mechanism to produce smooth and dense (0001) oriented polycrystalline ZnO films with superb optical properties. Our products show optical transparency of 82% and surprisingly low sheet resistance for undoped ZnO, only in the order of few 100 Ω sq^?1. We believe that a very high degree of self‐organization between the ZnO crystals in our polycrystalline films grown under controlled SCOG conditions is main reason for the highest so far reported transparency to conductivity ratio for undoped ZnO thin film ceramics.     

RF磁控溅射法原位制备C轴择优取向ZnO薄膜

采用RF磁控溅射法在玻璃衬底上原位低温生长ZnO薄膜.生长出的薄膜对可见光具有高于90%的透射率,该薄膜具有良好的C轴取向.利用X射线衍射(XRD)的测试结果,分析了溅射工艺条件如衬底温度、氩氧比和溅射气压等对薄膜性能的影响,得到最佳的生长工艺条件为:衬底温度300 ℃,溅射气压1 Pa,氩氧比为25 sccm∶15 sccm.在此条件下生长的ZnO薄膜具有良好的C轴择优取向,并且薄膜的结晶性能良好.采用这种方法制备的ZnO薄膜适合用于制备平板显示器的透明薄膜晶体管和太阳电池的透明导电电极.     

Ultrathin Sticker‐Type ZnO Thin Film Transistors Formed by Transfer Printing via Topological Confinement of Water‐Soluble Sacrificial Polymer in Dimple Structure

To create ultrathin sticker‐type electronic devices that can be attached to unconventional substrates, it is highly desirable to develop printable membrane‐type electronics on a handling substrate and then transfer the printing to a target surface. A facile method is presented for high‐efficiency transfer printing by controlling the interfacial adhesion between a handling substrate and an ultrathin substrate in a systematic manner under mild conditions. A water‐soluble sacrificial polymer layer is employed on a dimpled handling substrate, which enables the topological confinement of the polymer residue inside and near the dimples during the etching and drying processes to reduce the interfacial adhesion gently, creating a high yield of transfer printing in a deterministic manner. As an example of an electronic device that was created using this method, a highly flexible sticker‐type ZnO thin film transistor was successfully developed with a thickness of 13 μm including a printable ultrathin substrate, which can be attached to various substrates, such as paper, plastic, and stickers.     

Self‐Polarized BaTiO3 for Greatly Enhanced Performance of ZnO UV Photodetector by Regulating the Distribution of Electron Concentration

ZnO film ultraviolet photodetectors (UV PDs) have always suffered from slow speed and low photosensitivity that restrict their broader applications. To break through those barriers, high‐performance ZnO UV PD based on self‐polarized BaTiO₃ (BTO) is first introduced through a facile one‐step spin‐coating method. Compared with pure ZnO film UV PD with low on/off ratio (65) and slow speed (4.1/7.5 s) at 3 V bias under 350 nm UV light, the BTO‐ZnO bilayer film device exhibits an ultrahigh on/off ratio (14 300) and ultrafast response speed (0.11/5.80 ms), which is much faster than that of the most reported ZnO film‐based UV PDs. The numerical simulation demonstrates that the spatial distribution of electron concentration of ZnO film is regulated by the self‐polarization of BTO film, resulting in low dark current and fast response time of the BTO‐ZnO PD. This work provides a new approach to fabricate high‐performance PDs based on self‐polarized ferroelectric materials.     

Patterning of Flexible Transparent Thin‐Film Transistors with Solution‐Processed ZnO Using the Binary Solvent Mixture

Flexible transparent thin‐film transistors (TTFTs) have emerged as next‐generation transistors because of their applicability in transparent electronic devices. In particular, the major driving force behind solution‐processed zinc oxide film research is its prospective use in printing for electronics. Since the patterning that prevents current leakage and crosstalk noise is essential to fabricate TTFTs, the need for sophisticated patterning methods is critical. In patterning solution‐processed ZnO thin films, several points require careful consideration. In general, as these thin films have a porous structure, conventional patterning based on photolithography causes loss of film performance. In addition, as controlling the drying process is very subtle and cumbersome, it is difficult to fabricate ZnO semiconductor films with robust fidelity through selective printing or patterning. Therefore, we have developed a simple selective patterning method using a substrate pre‐patterned through bond breakage of poly(methyl methacrylate) (PMMA), as well as a new developing method using a toluene–methanol mixture as a binary solvent mixture.     

Steering the Growth of Metal Ad‐particles via Interface Interactions Between a MgO Thin Film and a Mo Support

The coincidence lattice formed between a crystalline MgO film and a Mo(001) support is found to be an ideal template to produce long‐range ordered ensembles of Fe and Cr particles for electronic, magnetic and chemical applications. The structural and electronic properties of this super‐lattice are analyzed by means of scanning tunnelling microscopy and density functional theory. The different registers of atoms at the interface induce periodic changes in the MgO lattice parameter, in the metal‐oxide binding length, and the workfunction. These variations modulate the adsorption landscape for Cr and Fe atoms and give rise to the observed ordering phenomena. Preferred nucleation and growth is revealed in those regions of the coincidence lattice that have a small lattice mismatch with the ad‐particles and enable electron‐transfer processes with the support.     

Growth of Heteroepitaxial ZnO Thin Films on GaN‐Buffered Al2O3 (0001) Substrates by Low‐Temperature Hydrothermal Synthesis at 90 °C

Heteroepitaxial ZnO films are successfully grown on nondoped GaN‐buffered Al₂O₃ (0001) substrates in water at 90 °C using a two‐step process. In the first step, a discontinuous ZnO thin film (ca. 200 nm in thickness) consisting of hexagonal ZnO crystallites is grown in a solution containing Zn(NO₃)·6 H₂O and NH₄NO₃ at ca. pH 7.5 for 24 h. In the second step, a dense and continuous ZnO film (ca. 2.5 μm) is grown on the first ZnO thin film in a solution containing Zn(NO₃)·6 H₂O and sodium citrate at ca. pH 10.9 for 8 h. Scanning electron microscopy, X‐ray diffraction, UV‐vis absorption spectroscopy, photoluminescence spectroscopy, and Hall‐effect measurement are used to investigate the structural, optical, and electrical properties of the ZnO films. X‐ray diffraction analysis shows that ZnO is a monocrystalline wurtzite structure with an epitaxial orientation relationship of (0001)[11 0]_ZnO∥(0001)[11 0]_GaN. Optical transmission spectroscopy of the two‐step grown ZnO film shows a bandgap energy of 3.26 eV at room temperature. A room‐temperature photoluminescence spectrum of the ZnO film reveals only a main peak at ca. 380 nm without any significant defect‐related deep‐level emissions. The electrical property of ZnO film showed n‐type behavior with a carrier concentration of 3.5 × 10¹⁸ cm^–3 and a mobility of 10.3 cm² V^–1 s^–1.