Characterization of fullerenes and carbon nanoparticles generated with a laser-furnace technique

The microstructure and field emission properties of films prepared from commercial powders of single-wall and multi-wall carbon nanotube films were investigated. In addition to nanotubes, these materials contained amorphous and crystalline carbon phases, and the single-wall powder also contained nano-particles of the Fe-Co catalysts. The turn-on fields were measured to be 2.3 V 7m^-1 for films prepared with the material containing single-wall nanotubes and 2.6 V 7m^-1 for those with multi-wall nanotubes. Long-term stability of emission current for these films was also investigated and correlated to their microstructure. Single-wall material showed a decrease in emission current that extended over several days and that was related to permanent degradation of emission sites. Emission current from the multi-wall material stabilized after an initial increase.     

Patterned uniformly orientated silicon nanocrystallite films and efficient field emission characteristics

Patterned uniformly (100)-orientated silicon nanocrystallite (SiNC) films were fabricated based on hydrogen ion implantation technique and typical electrochemical anodic etching method. The surface morphology and microstructure characteristics of the films were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and atomic force microscopy. The efficient field emission with low turn-on field of about 3.2 V/μm at current density of 0.1 μA/cm² was obtained. The emission current density from the SiNC films reached 1 mA/cm² under a bias field of about 11 V/μm. The experimental results demonstrate that the SiNC films have great potential applications for flat panel displays.     

Thinning and diluting aligned carbon nanotube films for uniform field emission

Aligned carbon nanotube (CNT) films are potential field emitters for large-area flat panel displays. However, the distribution of emission areas in the CNT films is quite non-uniform because of inhomogeneous nanotube growth, which is hard to avoid using the conventional chemical vapor deposition (CVD) method. Here we show that the emission uniformity of CNT films can be improved simply by reducing the film thickness (thinning) or the nanotube density (diluting). The thickness and density of CNT films could be controlled by controlling the CNT growth time and temperature. Received: 12 June 2001 / Accepted: 27 October 2001 / Published online: 23 January 2002     

Effect of temperature on the electron field emission from aligned carbon nanofibers and multiwalled carbon nanotubes

Effect of temperature and aspect ratio on the field emission properties of vertically aligned carbon nanofiber and multiwalled carbon nanotube thin films were studied in detail. Carbon nanofibers and multiwalled carbon nanotube have been synthesized on Si substrates via direct current plasma enhanced chemical vapor deposition technique. Surface morphologies of the films have been studied by a scanning electron microscope, transmission electron microscope and an atomic force microscope. It is found that the threshold field and the emission current density are dependent on the ambient temperature as well as on the aspect ratio of the carbon nanostructure. The threshold field for carbon nanofibers was found to decrease from 5.1 to 2.6 V/μm when the temperature was raised from 300 to 650 K, whereas for MWCNTs it was found to decrease from 4.0 to 1.4 V/μm. This dependence was due to the change in work function of the nanofibers and nanotubes with temperature. The field enhancement factor, current density and the dependence of the effective work function with temperature and with aspect ratio were calculated and we have tried to explain the emission mechanism.     

Ion-induced secondary electron emission from ZnS thin films deposited by closed-spaced sublimation

ZnS thin films were deposited on soda lime glass and aluminum substrates by close-spaced sublimation technique. The change in composition, structural and optical properties of the films was investigated as a function of the substrate temperature. The deposited films were stoichiometric and crystalline in nature having cubic structure oriented only along (1 1 1) plane. The energy band gap of the films deposited at the substrate temperature of 150, 250 and 350 °C was 3.52, 3.58 and 3.63 eV respectively. These films were then bombarded with 2-10 keV energy pulsed Ar⁺ beam and their electron yield was determined from impinging ion and emitted electron currents. The electron yield of ZnS films was much high as compared to the metals. The electron yield of ZnS films increased with energy of the incident ion and got saturated at about 8 keV. The most important result of this study was that the electron yield of ZnS films having same composition was different. Monte Carlo simulations performed to interpret these experimental findings showed that the dissimilar electron yields of ZnS films is due to the combined effect of energy band gap, surface barrier potential and density of the films.     

Silicon enhanced carbon nanotube growth on nickel films by chemical vapor deposition

Silicon enhances carbon nanotube growth on nickel films by chemical vapor deposition using methane and hydrogen. Nanotube growth characteristic is significantly improved on nickel films patterned by argon plasma etching on silicon oxide layers. Auger electron spectroscopy shows that a reduced silicon phase forms in the surface silicon oxide layer by Ar ion bombardment used for patterning. The enhanced growth of carbon nanotubes could be ascribed to an oxygen removal effect by silicon in the process of synthesis.     

不同基底的GaN纳米薄膜制备及其场发射增强研究

采用脉冲激光沉积 (PLD) 方法在Si及SiC基底上制备了相同厚度的GaN纳米薄膜并对其进行了微结构表征及场发射性能测试分析. 结果表明: 基底对于GaN薄膜微结构及场发射性能具有显著的影响. 在SiC基底上所制备的GaN纳米薄膜相对于Si基底上的GaN纳米薄膜, 其场发射性能得到显著提升, 其场发射电流可以数量级增大. 场发射显著增强应源于纳米晶微结构及取向极化诱导增强效应. 本研究结果表明, 要获得优异性能场发射薄膜, 合适基底及薄膜晶体微结构需要重点考虑. 关键词： 基底 GaN 纳米薄膜 场发射     

The preparation and refractive index of BST thin films

Radio-frequency magnetron sputtering technique is used to deposit Ba_0.65Sr_0.35TiO₃ (BST) thin films on fused quartz substrates. In order to prepare the high-quality BST thin films, the crystallization and microstructure of the films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). More intense characteristic diffraction peaks and better crystallization can be observed in BST thin films deposited at 600 °C and subsequently annealed at 700 °C. The refractive index of the films is determined from the measured transmission spectra. The dependences of the refractive index on the deposition parameters of BST thin films are different. The refractive index of the films increases with the substrate temperature. At lower sputtering pressure, the refractive index increases from 1.797 to 2.197 with pressure increase. However, when the pressure increases up to 3.9 Pa, the refractive index reduces to 1.86. The oxygen to argon ratio also plays an important effect on the refractive index of the films. It has been found that the refractive index increases with increase in the ratio of oxygen to argon. The refractive index of BST thin films is strongly dependent on the annealing temperature, which also increases as the annealing temperature ascends. In a word, the refractive index of BST thin films is finally affected by the films’ microstructure and texture.     

Formation of nanocrystalline TiO2 by 100 MeV Au

Nanocrystalline TiO₂ structures are formed by irradiation of 100 MeV Au⁸⁺ ion beam on amorphous thin films of TiO₂. Surface morphology of the nanocrystals is studied by Atomic Force Microscopy (AFM). Amorphous to nanocrystalline phase transformation is identified by Glancing Angle X-ray Diffraction (GAXRD) and Raman spectroscopic studies. Optical characterization is carried out by UV-VIS spectroscopy technique. Blue shift observed in absorption band edge indicates the formation of nanophase TiO₂ after irradiation. The impinging swift heavy ion (100 MeV Au⁸⁺) induces nucleation of nanoparticles along the ion trajectory through inelastic collisions of the projectile with electrons of the material. It is observed that the shape and size of nanoparticles formed is dependant on the irradiation fluence.     

Characterization and field-emission property of aligned porous carbon nanotube film by hydrogen-ion implantation

To enhance the field emission of carbon nanotube (CNT) films, a novel technique that combines hydrogen-ion implantation used in the silicon-on-insulation smart-cut process and plasma-enhanced chemical vapor deposition was developed to produce an aligned porous carbon nanotube (AP-CNT) film on a Si substrate. All steps in the AP-CNT synthesis were carried out in vacuum, which reduced possible contamination. The morphology and the field-emission properties of the CNT films were investigated and results show that CNT holes with a diameter of 5 m and a depth of 30 m were produced in the AP-CNT film. The alignment of the CNTs is visibly improved. Due to the implantation treatment, the turn-on field of the CNT films decreased from 1.5 to 0.8 V/m, and the emission-current (and dot) density obviously increased. This field-emission improvement may mainly arise from the holes formed in the AP-CNT films. The edges of these holes not only intensified the electron emission but also increase the emission site density of the CNT films. PACS 81.05.Uw; 61.72.Tt; 85.45.Db     

Fine-structured field emission images originating from coherently scattering of electrons within a multi-walled carbon nanotube

High resolution field emission image of a single multi-walled carbon nanotube was studied by field emission microscopy. The images contain patterns consisting of rather ordered bright fringes. We propose a model based on coherent electron scattering to explain the observed field emission image. The emitted electrons will undergo coherent scattering within the cap region of a multi-wall carbon nanotube, which may be viewed as elastic scattering by a polycrystalline structure with an infinite size. This study is helpful for understanding the physical mechanism of field emission of carbon nanotube.     

Structure, microstructure and photoluminescence properties of Fe doped SnO2 thin films

In this paper, effects of Fe doping on crystallinity, microstructure and photoluminescence (PL) properties of sol-gel derived SnO₂ thin films are reported. It is shown that doping of Fe³⁺ ions leads to crystallite size reduction and higher strain in SnO₂ thin films. The room temperature PL spectra show marked changes in intensity and blue-shift of the emission lines upon Fe doping. These observations have been correlated with structural changes and defect chemistry of Fe doped SnO₂ thin films.     

不同能级加速过滤电弧沉积四面体非晶碳膜的结构和性能

采用过滤阴极真空电弧技术，通过施加0—2000 V衬底负偏压使沉积离子获得不同能级的入射能量，在单晶硅上制备了四面体非晶碳薄膜.拉曼光谱分析表明，薄膜的结构为非晶sp³骨架中镶嵌着平面关联长度小于1 nm的sp²团簇.原子力显微镜研究表明：在低能级、富sp³能量窗口和次高能级，薄膜中sp³的含量越多，其表面就越光滑，应用sp³浅注入生长机制能够圆满地解释薄膜表面形态与离子入射能量之间的关系；但在高 关键词： 四面体非晶碳 过滤阴极真空电弧 能级     

Field emission properties of polymer-converted carbon films by heat treatment

Carbon films were prepared on single crystal silicon substrates by heat-treatment of a polymer-poly(phenylcarbyne) at 800 °C in Ar atmosphere. The heat-treatment caused the change of the polymer into carbon film, which exhibited good field emission properties. Low turn-on emission field of 4.3 V/μm (at 0.1 μA/cm²) and high emission current density of 250 μA/cm² (at 10 V/μm) were observed for the polymer-converted carbon films. This behavior was demonstrated to be mainly related to the microstructure of the carbon films, which consisted of fine carbon nanoparticles with high sp² bonding. The carbon films, which can be deposited simply with large areas, are promising for practical applications in field emission display.     

RF-PACVD of water repellent and protective HMDSO coatings on bell metal surfaces: Correlation between discharge parameters and film properties

Hexamethyldisiloxane (HMDSO) films have been deposited on bell metal using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) technique. The protective performances of the HMDSO films and their water repellency have been investigated as a function of DC self-bias voltage on the substrates during deposition. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. Optical emission spectroscopy (OES) analyses of the plasma during deposition reveal no significant change in the plasma composition within the DC self-bias voltage range of −40 V to −160 V that is used. Raman and X-ray photoelectron spectroscopy (XPS) studies are carried out for film chemistry analysis and indicate that the impinging ion energy on the substrates influences the physio-chemical properties of the HMDSO films. At critical ion energy of 113 qV (corresponding to DC self-bias voltage of −100 V), the deposited HMDSO film exhibits least defective Si-O-Si chemical structure and highest inorganic character and this contributes to its best corrosion resistance behavior. The hardness and elastic modulus of the films are found to be bias dependent and are 1.27 GPa and 5.36 GPa for films deposited at −100 V. The critical load for delamination is also bias dependent and is 11 mN for this film. The water repellency of the HMDSO films is observed to be dependent on the variation in surface roughness. The results of the investigations suggest that HMDSO films deposited by RF-PACVD can be used as protective coatings on bell metal surfaces.     

Effects of gas composition on the growth of multi-walled carbon nanotube

This paper studies the effects of different gas compositions on the growth of multi-walled carbon nanotube (MWCNT) films by using an electron cyclotron resonance chemical vapor deposition (ECR-CVD) method. The Raman spectrum was employed to explore the composition of the MWCNT films grown under different mixtures of C₃H₈ and H₂. The results showed that the optimum relative intensity ratio of the D band to G band (i.e., I_D/I_G) is 2 for the cases considered in this study. In addition, the morphology and microstructure of the MWCNTs were examined by field emission scanning electron microscopy (FE-SEM) and field emission gun transmission electron microscopy (FEG-TEM). Furthermore, atomic force microscopy (AFM) and scanning thermal microscopy (SThM) were used to study the surface topography and thermal properties of the MWCNTs.     

Correlation between substrate bias, growth process and structural properties of phosphorus incorporated tetrahedral amorphous carbon films

We investigate the growth process and structural properties of phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) films which are deposited at different substrate biases by filtered cathodic vacuum arc technique with PH₃ as the dopant source. The films are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, Raman spectroscopy, residual stress measurement, UV/VIS/NIR absorption spectroscopy and temperature-dependent conductivity measurement. The atomic fraction of phosphorus in the films as a function of substrate bias is obtained by XPS analysis. The optimum bias for phosphorus incorporation is about −80 V. Raman spectra show that the amorphous structures of all samples with atomic-scaled smooth surface are not remarkably changed when PH₃ is implanted, but some small graphitic crystallites are formed. Moreover, phosphorus impurities and higher-energetic impinging ions are favorable for the clustering of sp² sites dispersed in sp³ skeleton and increase the level of structural ordering for ta-C:P films, which further releases the compressive stress and enhances the conductivity of the films. Our analysis establishes an interrelationship between microstructure, stress state, electrical properties, and substrate bias, which helps to understand the deposition mechanism of ta-C:P films.     

Formation of Pt-C films by ion beam assisted deposition for the application of suppression thermo-electron emission

Platinum and carbon were deposited onto the surface of molybdenum grids simultaneously by ion beam assisted deposition. The structure of the Pt-C films was studied by XRD and Raman spectroscopy. The XRD results showed that Pt exhibited mixed strong (1 1 1) and weak (2 0 0) orientations. The Raman spectra showed that the carbon existed in the form of graphite-like phase. Electron emission characteristics from the Mo grid with and without Pt-C films were measured using analogous diode method. The results showed that electron emission from the Mo grid coated with Pt-C films was much less than that from the Mo grid without Pt-C films. The obtained results demonstrated that the Pt-C films are effective grid-coating materials for the application of suppression thermo-electron emission.     

Columnar growth of crystalline silicon films on aluminium-coated glass by inductively coupled plasma CVD at room temperature

Silicon films were grown on aluminium-coated glass by inductively coupled plasma CVD at room temperature using a mixture of SiH₄ and H₂ as the source gas. The microstructure of the films was evaluated using Raman spectroscopy, scanning electron microscopy and atomic force microscopy. It was found that the films are composed of columnar grains and their surfaces show a random and uniform distribution of silicon nanocones. Such a microstructure is highly advantageous to the application of the films in solar cells and electron emission devices. Field electron emission measurement of the films demonstrated that the threshold field strength is as low as ～9.8V/μm and the electron emission characteristic is reproducible. In addition, a mechanism is suggested for the columnar growth of crystalline silicon films on aluminium-coated glass at room temperature.     

Field emission properties of carbon nanotube film using a spray method

We fabricated carbon nanotube (CNT) emitters by a spray method using a CNT suspension with ethanol. Indium with a low melting pointing metal or indium tin oxide (ITO) was deposited on the glass substrate. The CNTs were sprayed on these layers and thermally annealed. The sprayed CNTs on an ITO were obtained a high emission current density, field enhancement factor, and a uniform emission pattern than the sprayed CNTs on an ITO layer. We found that the sprayed emitters on the indium layer had good field emission characteristics because of the strong adherence between the metal layer and CNTs.