Investigation of structural and optoelectronic properties of annealed nickel phthalocyanine thin films

Thin films of nickel phthalocyanine (NiPc) were prepared by thermal evaporation and the effects of annealing temperature on the structural and optical properties of the samples were studied using different analytical methods. Structural analysis showed that the grain size and crystallinity of NiPc films improved as annealing temperature increased from 25 to 150 °C. Also, maximum grain size (71.3 nm) was obtained at 150 °C annealing temperature. In addition, NiPc films annealed at 150 °C had a very smooth surface with an RMS roughness of 0.41 nm. Optical analysis indicated that band gap energy of films at different annealing temperatures varied in the range of 3.22–3.28 eV. Schottky diode solar cells with a structure of ITO/PEDOT:PSS/NiPc/Al were fabricated. Measurement of the dark current density–voltage (J–V) characteristics of diodes showed that the current density of films annealed at 150 °C for a given bias was greater than that of other films. Furthermore, the films revealed the highest rectification ratio (23.1) and lowest barrier height (0.84 eV) demonstrating, respectively, 23% and 11% increase compared with those of the deposited NiPc films. Meanwhile, photoconversion behavior of films annealed at 150 °C under illumination showed the highest short circuit current density (0.070 mA/cm²) and open circuit voltage of (0.55 V).     

The preparation of oxygen-deficient ZnO nanorod arrays and their enhanced field emission

Vertical and uniform zinc oxide (ZnO) nanorod arrays (NRAs) with sharp tips were fabricated on Zn substrate by a straightforward hydrothermal method without the assistance of seed layer, template or surfactant. Whereafter, the as-synthesized ZnO NRAs were successfully doped with oxygen vacancies by sodium borohydride (NaBH₄) solution reduction, aiming to generate donor energy levels below the conduction band. More importantly, the doped concentration of oxygen vacancies could be effectively controlled by adjusting the reduction temperature, and we have ultimately achieved the purpose of controllable tailoring the energy band structure of ZnO NRAs. As with design, the oxygen-deficient ZnO NRAs present a lower turn-on field of 0.67 V/μm, higher field enhancement factor of 64601 and better field emission stability. Such excellent FE performance of the as-prepared emitter should originate from the optimization of geometry, the efficient electron transport, as well as the decreased work function.     

图形化氧化锌阵列的制备及其场发射性能研究

为了减小场发射的屏蔽效应,采用图形化技术对氧化锌(ZnO)纳米枝阵列进行调控,并研究图形化ZnO枝阵列的性能。首先采用光刻法在ITO导电玻璃上制备图形化ZnO种子层,再用电沉积法在图形化种子层上生长ZnO纳米枝阵列。利用扫描电子显微镜(SEM)、X射线衍射(XRD)研究所制备的图形化ZnO阵列形貌、结构等,并测试其场发射性能。研究结果表明,制备的图形化ZnO纳米枝是圆阵列,直径为330μm左右,纳米ZnO主干平均直径为400~500nm,发现主干上有一些精细的类似锥状的纳米量级微细枝结构,并且具有良好的场发射性能,开启场强为2.15V/μm,场增强因子为16 109。该图形化生长ZnO阵列阴极的方法是一种能较好改善材料场发射性能的方法,在场发射应用领域表现出较好的前景。     

Observation of Ni silicide formations and field emission properties of Ni silicide nanowires

The Ni silicide nanowires were grown by physical vapor deposition. The morphological changes of silicide formation were observed on a gradient Ni film thickness, which visualized the critical thickness is 60-80 nm to grow nanowires. The field emission measurement provided uniform characteristics and high field enhancement factors were obtained to be 3180 and 3002 from the Ni silicide nanowires grown on a Si substrate and a tungsten plate, respectively. By using a conductive tungsten plate, the emission current was enhanced to be 172.5 μA/cm² comparing to 76.5 μA/cm² from a Si substrate at 5 V/μm.     

衬底对微米金刚石聚晶薄膜生长及场发射特性的影响

摘要：本文在陶瓷衬底上面利用磁控溅射的方法镀上一层厚金属钛,用不同方法对金属钛层进行表面处理,处理后的衬底放在微波等离子体化学气相沉积腔中,在相同的沉积条件下制备出不同微米金刚石薄膜。对不同的薄膜的微观表面形态、结构组成进行对比研究;对不同的薄膜用二极管型结构测试了它们的场致发射电子的性能,并对发射机理进行了深入的研究。最终分析出不同方法处理的衬底,对微米金刚石聚晶薄膜生长及场发射特性的影响的原因。     

碳纳米管场发射阴极电泳法制备及场发射特性研究

采用电泳沉积法在玻璃基板上成功制备出碳纳米管场发射阴极,采用扫描电子显微镜观察薄膜表面形貌,并对制备的碳纳米管阴极进行场发射测试.实验结果表明电泳2 min沉积的碳纳米管薄膜均匀连续且具有较好的场发射特性,其开启电场为3.1 V/μm,当外加电场强度为11.5 V/μm时场发射电流密度达到11.33 mA/cm2,经过10 V/μm的电场激活处理后样品具有较好的场发射稳定性.     

ZnO纳米线的快速生长机理及其场发射性能研究

为了快速制备具有优良场发射性能的ZnO纳米线,对ZnO纳米线的生长机理及场发射性能进行研究。首先采用优化的两步法制备出高长径比的ZnO纳米线,其次采用SEM对ZnO的微观形貌进行表征,然后,在分析形貌特点的基础上,说明了强碱体系下ZnO纳米线薄膜的快速生长机理。最后,对典型样品的场发射性能进行了测试。测试果表明,优化后的两步法,只需3h即可获得直径为40~50nm,长度为2.2~2.7μm,长径比高达54的纳米线。薄膜的开启电场为3.6V/μm,阈值场强为9.1V/um,场增强因子β高达3 391。研究表明,高pH值溶液可以加快ZnO纳米线沿C轴方向的择优生长,获得高长径比的ZnO纳米线,进而获得优良的场发射性能。     

分散定向碳纳米管阵列的制备及场发射性能

利用脉冲电化学沉积技术,以NiSO4·6H2O为电镀液在镀Cr硅基片上沉积低密度、直径在150nm左右的Ni催化剂颗粒,在此基础上,采用乙炔、氨气作为气源,采用等离子体增强化学气相沉积(PECVD)技术制备分散定向的碳纳米管阵列。研究了等离子体预处理技术对纳米管制备的影响以及该阵列的场发射性能,证明低密度的碳纳米管阵列阴极能有效地降低场屏蔽效应,进而提高场发射性能,其场发射的开启电场强度约为2.39V/μm。     

Synthesis,field emission and optical properties of ZnSe nanobelts,nanorods and nanocones by hydrothermal method

ZnSe nanostructures, such as nanobelts, nanorods and nanocones, were successfully synthesized on Zn foils via a hydrothermal method using EDTA as soft template at low temperature. EDTA played a significant role on the morphology of ZnSe nanomaterials. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) were carried out to characterize the microstructures and chemical compositions of the as-synthesized ZnSe samples. XRD patterns indicated that the as-synthesized ZnSe samples belonged to a cubic zinc blende structure. SEM observation obviously showed that the nanocones had very sharp tips compared to nanorods and nanobelts. The field emission (FE) measurement showed that the as-synthesized ZnSe nanocones had a lower turn-on field of ~1.6 V μm⁻¹ at the current density of 10 μA cm⁻². A high field enhancement factor of ~4514 was achieved for the ZnSe nanocones. The superior field emission properties were probably attributed to the sharp tips of the ZnSe nanocones. Room temperature photoluminescence (PL) spectroscopy of the ZnSe nanostructures showed a wide band emission from blue light to orange light. The as-prepared ZnSe nanomaterials have promising applications in optoelectronic devices. A possible formation mechanism of ZnSe nanobelts, nanorods and nanocones was also proposed and discussed.     

The fabrication and operation of fully printed Carbon nanotube field emission displays

Screen-printing is undoubtedly the most cost effective process for the fabrication of large-sized carbon nanotube field emission display (CNT-FED). A novel post-treatment method of mechnical crushing and blowing was presented to solve the problem of poor field emission properties of printed CNT films. The turn-on electric field of the treated film decreased and the emission current increased distinctly. Then a technique was developed to fabricate fully printed CNT-FED in which all the inner cells were fabricated by screen-printing process. Based on this technique, fully printed matrix-addressable diode CNT-FEDs, which can display moving image and be driven by the integrated drive circuits of commercial plasma display panel (PDP), were fabricated subsequently. A very high brightness of 1×10⁴ cd/m² can be achieved at 220 V.     

Field emission of vertically-aligned carbon nanotube arrays grown on porous silicon substrate

Vertically aligned arrays of multi-walled carbon nanotubes were grown by pyrolysis of acetylene on iron catalytic particles within a porous silicon template via chemical vapor deposition (CVD) at 700 °C. Using this method ordered nanotubes with diameters from 75 to 100 nm could be produced. The diode configuration field emission of the CNT arrays were performed and the onset electric field is 4 V/μm and the emission current can approach 1 mA/cm² at a electric field of 9.5 V/μm. The enhancement factor of the CNT arrays (4012) is derived from the F–N plot of the experiment data. To demonstrate the uniformity of the field emission, an ITO glass substrate with phosphor coated is used as anode in the field emission experiment. The average fluctuation of the emission current density was less than 5%. The result shows that the field emission of the CNT arrays on the silicon substrate is very uniform. These carbon nanotube arrays are useful for applications in field emission displays and sensors. The fabrication method shows the feasibility of integration between carbon nanotube arrays and silicon microelectronics.     

Enhanced field emission from printed CNTs by high-temperature sintering and plasma bombarding in hydrogen

A novel post-treatment, including high-temperature sintering and plasma bombarding in hydrogen ambient, was performed intentionally to improve the field emission capability and stability of screen-printed carbon nanotubes (CNTs). With this treatment, the organic bonding material covering on the CNTs was preferentially removed. And the CNTs were wetted and filled by silver at the interface between the CNTs and silver electrode so that a reliable ohmic contact was achieved. These effects improved the field emission capability and stability of CNT cathode. Moreover, the equal-high CNT emitters, after the removal of the excessively protruded CNT tips/or arches, would improve the luminescence uniformity. It is suggested that a high-temperature sintering and plasma bombarding in hydrogen may be a key technology for the commercialization of CNT field emission display.     

Enhanced field emission and hysteresis characteristics of aligned carbon nanotubes with Ti decoration

The field emission behavior of aligned carbon nanotubes (CNTs) is remarkably improved by decorating their surfaces with Ti nanoparticles through a sputtering process. The CNT/Ti(4 nm) sample shows a low turn-on field of 0.63 V/μm at 10 μA/cm², low threshold field of 1.06 V/μm at 1 mA/cm², and maximum field emission current density of 23 mA/cm² at 1.80 V/μm. The enhanced field emission properties of the CNT/Ti samples are attributed to the added defect sites and Ti nanoparticles, which increase the field enhancement factor and density of emission sites. Stability measurements indicate that the Ti coating, which acts as a protective layer, also strengthens the field emission stability of the CNT arrays. Moreover, the extent of hysteresis in the current–voltage sweep highly depends on the voltage-sweep speed.     

Electron field emission from ZnO self-organized nanostructures and doped ZnO:Ga nanostructured films

Self-organized ZnO nanostructures were grown by thermal decomposition of metalorganic precursors as well as by carbothermal reduction process. Nanostructured undoped and gallium-doped ZnO nanostructured films were deposited by plasma-enhanced chemical vapor deposition from metalorganic compounds. Electron field emission follows Fowler-Nordheim equation. Efficient electron emission was obtained from self-organized nanostructures due to their geometric shape. Enhanced field emission from ZnO:Ga nanostructured films in comparison with undoped ZnO films is obliged to lowering work function at doping by gallium.     

Fabrication and enhanced field emission properties of novel silicon nanostructures

We reported the fabrication and the field emission properties of two-tier novel silicon nanostructures. First, silicon nanopillars with ordered high aspect ratio were achieved by using conventional lithographic techniques to act as the field emission sources. Second, sharp-edged well-aligned silicon nanograss was fabricated on top of the nanopillars by means of hydrogen plasma dry etching to induce the field emission characteristics. The turn-on fields were obtained as 10.5 and 14.4 V/μm under current density of 0.01 mA/cm² for two-tier patterns separated by respective 5 μm and 2 μm spaces. The excellent field emission property from these novel nanostructures exhibited a great potential as high-performance field emitter arrays towards future nanoelectronic devices.     

Electronic and optoelectronic properties of zinc phthalocyanine single-crystal nanobelt transistors

ZnPc single-crystal nanobelts were grown by a physical vapor transport process with the length ranging from 20 to 150 μm and the width ranging from several tens of nanometers to several micrometers. Based on high crystalline ZnPc nanobelts, its single-crystal nanobelt transistors were realized. The field-effect mobility is as high as 0.75 cm²V⁻¹s⁻¹ with OTS modified SiO₂ as dielectric, which is the highest value for the reported ZnPc devices. In addition, ZnPc nanobelt transistors show the excellently photosensitive properties with the high photoswitching ratio (|I_light/I_dark|) of 7.34 × 10³ and the high photoresponsivity at 1.57 × 10⁴ AW⁻¹. These results indicate the future potential of ZnPc single-crystal transistors in organic electronic and optoelectronic applications.     

Tungsten oxide nanostructures:controllable growth and field emission

正Non-fully oxidized tungsten oxide(WO_(3-x)) nanostructures with controllable morphology were fabricated by adjusting the gas pressure in chemical vapor deposition.The comparative field emission(FE) measurements showed that the obtained W_(18)O_(49) nanowires have excellent FE property.The turn-on field was 7.1 V/μm for 10μA/cm~2 and the observed highest current density was 4.05 mA/cm~2 at a field of 17.2 V/μm.Good electron emission reproducibility was also observed during thermal evaporation and desorption testing.     

氧化钨纳米结构：可控制备及场发射性能

通过简单调控化学气相沉积反应气压制备了形貌尺寸可控的各种非化学计量比氧化钨纳米结构。场发射研究表明W18O49纳米线具有优异的场发射性能。对于10 μA/cm2的发射电流,其开启电压为7.1 V/μm。 实验中测得最高场发射电流密度4.05mA,对应场强为17.2 V/μm。场发射过程中的热蒸发和脱附测试表明该氧化钨纳米线的场发射再现性很高。     

Chemical modification of carbon nanotube for improvement of field emission property

In the present work, chemical modification of carbon nanotube was proposed for improvement of field emission property. Multi-wall carbon nanotubes (MWCNTs) were grown vertically on silicon substrate using catalytic chemical vapor deposition. Tips of grown MWCNTs were chemically modified using oxygen plasma, nitric acid, and hydrofluoric acid. Surface state and morphology of the chemically modified CNTs were investigated. CNT tips were opened and defects working as trap sites were generated on the CNT surface by the chemical modification process leading to improvement of field emission property. We suggest that two main factors determining the field enhancement factor are geometric factor and surface state of the CNT tips.     

Improved field emission characteristic of carbon nanotubes by an Ag micro-particle intermediation layer

An efficient way to improve field emission characteristic of carbon nanotubes (CNTs) through an Ag micro-particle intermediation layer is presented. In this way, the intermediation layer is deposited on an indium tin oxide glass substrate by electrochemical method and then the CNTs are covered onto surface of the intermediation layer by electrophoretic method as CNT field emitters. The field emission characteristic of the CNT field emitters with the intermediation layer is significantly improved compared to the one without the intermediation layer, including decreased turn-on electric field from 4.2 to 3.1 V/μm and increased emission current density from 0.224 to 0.912 mA/cm² at an applied electric field of 6 V/μm. The improved field emission characteristic may be attributed to gibbous surface of the CNT field emitters. This efficient way is much simple, low cost, and suitable for production of large scale CNTs–based field emission cold cathode.