能量分析器型真空电离规性能研究

电子激励脱附(ESD)效应和软X射线效应是影响电离真空计测量下限的两大重要因素。基于能量分析器研制了电离真空规,在极高真空校准装置上对其开展性能研究,包括不同压力或不同阴极发射电流下的离子流、ESD效应和软X射线影响。结果表明,系统压力介于10^-8Pa和10^-6 Pa之间,当气体发生电离,能量分析器电压在低于阳极电压约25 V时收集极能得到最大的气相离子流。系统压力在10^-7~10^-8 Pa量级,采用2.5 mA的发射电流可得到比1 mA更大的气相离子流值。分离气相离子与ESD离子的能量筒电压差约为30 V,规管栅极除气后可降低ESD效应至除气前的37.5%。电离规的软X射线带来的本底干扰对应等效压力约为9×10^-11 Pa。     

不同压力下碳纳米管的电弧法合成及其表征

采用电弧放电法在氦气/乙炔混合气氛中,在不同压力下合成了碳纳米管.运用场发射扫描电镜、场发射透射电镜、X-射线衍射仪和拉曼光谱对碳纳米管的形貌进行了表征.采用可见发射光谱对碳纳米管的形成过程进行了原位诊断研究.场发射扫描电镜结果表明,在氦气/乙炔气氛中合成的碳纳米管的长度大于50微米,许多碳颗粒沉积在碳纳米管壁上.场发射透射电镜结果表明,在0.100MPa下合成的碳纳米管的壁厚明显大于0.035MPa下合成的碳纳米管的壁厚.可见发射光谱诊断结果表明,CH和C2物种可能作为碳纳米管形成的前驱体,其中,以H原子作为无定形炭的刻蚀物种.阳极消耗速率和产物在阴极的沉积速率随着反应器中压力的增加而增加.因此,可以通过加强阳极和乙炔的蒸发速率及CH和C2物种的沉积速率而增加碳纳米管的形成速率.     

圆柱形阳极层霍尔推进器的工作特性与离子束流研究

主要对圆柱形阳极层霍尔推进器进行实验研究,得到推进器的工作特性、离子束分布、束流中电子的含量等结果。并且给出圆柱形阳极层霍尔推进器的最佳工作参数:工作电压在700~1000 V之间,电流在0.15~0.65 A,气体流量低于8 ml/min。从离子束流的径向分布可知:高电压、低电流、小气量时离子束的发散角较小。     

Field-emission diode with tangential current takeoff from thin-film nanodiamond/graphite emitter

Dependence on the performance characteristics of a field-emission diode with tangential current takeoff from thin-film nanodiamond/graphite (NDG) emitter on the design parameters has been studied. Thin-film NDG emitter structures were formed in the plasma of microwave low-pressure gas discharge. Field-emission current densities up to 20 A/cm² at a voltage of 300 V were obtained. For the optimum diode design parameters, the tangential current takeoff scheme allows the threshold electric field strength for the onset of field emission to be decreased to less than half of the value typical of the planar field emission from the same NDG structures.     

Low operating voltage single ZnO nanowire field-effect transistors enabled by self-assembled organic gate nanodielectrics

The development of nanowire transistors enabled by appropriate dielectrics is of great interest for flexible electronic and display applications. In this study, nanowire field-effect transistors (NW-FETs) composed of individual ZnO nanowires are fabricated using a self-assembled superlattice (SAS) as the gate insulator. The 15-nm SAS film used in this study consists of four interlinked layer-by-layer self-assembled organic monolayers and exhibits excellent insulating properties with a large specific capacitance, 180 nF/cm2, and a low leakage current density, 1 x 10(-8) A/cm2. SAS-based ZnO NW-FETs display excellent drain current saturation at Vds = 0.5 V, a threshold voltage (Vth) of -0.4 V, a channel mobility of approximately 196 cm2/V s, an on-off current ratio of approximately 10(4), and a subthreshold slope of 400 mV/dec. For comparison, ZnO NW-FETs are also fabricated using 70-nm SiO2 as the gate insulator. Implementation of the SAS gate dielectric reduces the NW-FET operating voltage dramatically with more than 1 order of magnitude enhancement of the on-current. These results strongly indicate that SAS-based ZnO NW-FETs are promising candidates for future flexible display and logic technologies.     

High-performance transparent inorganic-organic hybrid thin-film n-type transistors

High-performance thin-film transistors (TFTs) that can be fabricated at low temperature and are mechanically flexible, optically transparent and compatible with diverse substrate materials are of great current interest. To function at low biases to minimize power consumption, such devices must also contain a high-mobility semiconductor and/or a high-capacitance gate dielectric. Here we report transparent inorganic-organic hybrid n-type TFTs fabricated at room temperature by combining In2O3 thin films grown by ion-assisted deposition, with nanoscale organic dielectrics self-assembled in a solution-phase process. Such TFTs combine the advantages of a high-mobility transparent inorganic semiconductor with an ultrathin high-capacitance/low-leakage organic gate dielectric. The resulting, completely transparent TFTs exhibit excellent operating characteristics near 1.0 V with large field-effect mobilities of >120 cm2 V(-1) s(-1), drain-source current on/off modulation ratio (I(on)/I(off)) approximately 10(5), near-zero threshold voltages and sub-threshold gate voltage swings of 90 mV per decade. The results suggest new strategies for achieving 'invisible' optoelectronics.     

Anomalous kink behavior in the current-voltage characteristics of suspended carbon nanotubes

Electrically-heated suspended, nearly defect-free, carbon nanotubes (CNTs) exhibiting negative differential conductance in the high bias regime experience a sudden drop in current (or “kink”). The bias voltage at the kink (V _kink) is found to depend strongly on gate voltage, substrate temperature, and gas environment. After subtracting the voltage drop across the contacts, however, the kink bias voltages converge around 0.2 V, independent of gate voltage and gas environment. This bias voltage of 0.2 V corresponds to the threshold energy of optical phonon emission. This phenomenon is corroborated by simultaneously monitoring the Raman spectra of these nanotubes as a function of bias voltage. At the kink bias voltage, the G band Raman modes experience a sudden downshift, further indicating threshold optical phonon emission. A Landauer model is used to fit these kinks in various gas environments where the kink is modeled as a change in the optical phonon lifetime, which corresponds to a change in the non-equilibrium factor that describes the existence of hot phonons in the system.      

Gas ionization sensors with carbon nanotube/nickel field emitters

Gas ionization sensors based on the field emission properties of the carbon nanotube/nickel (CNT/Ni) field emitters were first developed in this work. It is found that the breakdown electric field (E(b)) slightly decreases from 2.2 V/microm to 1.9 V/microm as the pressure of H2 gas increases from 0.5 Torr to 100 Torr. On the contrary, E(b) obviously increases from 2.9 V/microm to 6.5 V/microm as O2 gas pressure increases from 0.5 Torr to 100 Torr. This may be explained by the depression of the electron emission that caused by the adsorption of the O2 gas on the CNT emitters. The Raman spectra of the CNT/Ni emitters also show that more defects were generated on the CNTs after O2 gas sensing. The Joule heating effect under high current density as performing H2 sensing was also observed. These effects may contribute the pressure dependence on the breakdown electric field of the CNT/Ni gas ionization sensors.     

High-performance nano-Schottky diodes and nano-MESFETs made on single CdS nanobelts

Nano-Schottky diodes and nanometal-semiconductor field-effect transistors (MESFETs) on single CdS nanobelts (NBs) have been fabricated and studied. The Au/CdS NB Schottky diodes have very low reverse current density ( approximately 3.0 x 10-5 A.cm-2 at -10 V reverse bias) and the highest on/off current ratio (approximately 108) reported so far for nano-Schottky diodes. The single CdS NB MESFETs exhibit n-channel normally on (depletion) mode, low threshold voltage (approximately -1.56 V), high transconductance ( approximately 3.5 microS), low subthreshold swing ( approximately 45 mV/dec), and the highest on/off current ratio (approximately 2 x 108) reported so far for nanofield-effect transistors. We also show that the absolute value of threshold voltage for a metal-insulator-semiconductor field-effect transistor made on a single CdS NB can be reduced from approximately 12.5 to approximately 0.4 V and its transconductance can be increased from approximately 0.2 to approximately 3.2 microS by adding an extra Au Schottky contact on the CdS NB, the mechanism of which is discussed.     

Optical emission spectroscopy study of positive direct current bias enhanced diamond nucleation

High nucleation density and crystalline diamond films were deposited on a mirror-polished Si(100) substrate by horizontal microwave plasma chemical vapor deposition using a two step process consisting of positive direct current (dc) bias enhanced nucleation and growth. Optical emission spectroscopy was employed to investigate in situ the plasma emission characterization during positive biasing process. Emission lines from the Balmer series of atomic hydrogen, molecular hydrogen, CH, C₂, and Ar were observed in the visible and ultraviolet ranges when CH₄, H₂, and Ar were used as the reactant gases. The dependence of plasma emission spectra on the deposition parameters, such as biasing voltage, methane concentration and working pressure was investigated. The relative concentrations of neutral atomic hydrogen were estimated by using the Ar emission at 750.4 nm as an actinometer. A significant variation in the emission intensity of the radicals was measured with a change in the biasing voltage. The correlation between the spectra of some species and the quality of diamond films was studied. The results show that CH and C₂ both were important precursor in the diamond deposition, while C₂ was associated with the presence of amorphous phase in the films during positive dc biasing process.     

On the investigation of d.c. plasmatron discharges by optical emission spectrometry

We investigated the emission spectra resulting from high rate plasmatron sputtering in order to gain further information on the coating process. The measured relations between the peak intensities of the target material and such plasmatron discharge parameters as discharge current, discharge power and deposition rate were almost linear. However, the intensity showed a strong pressure dependence. In the case of reactive high rate sputtering there is a drastic drop in the spectral line intensity of the target material as the pressure of the reaction gas increases. The behaviour of both the line intensity and the discharge voltage clearly reflects the coverage of the target with reaction products as a function of the pressure ratio p_O2/p_tot. The effects of the residual gas on the metal sputter rate and the desorption of H₂O during r.f. substrate cleaning were verified. From these results it is seen that emission spectroscopy may be used to advantage for monitoring the process of high rate plasmatron sputtering.     

Nucleation and Oriented Textured Growth of Diamond Films on Si(100) via Electron Emission in Ho.t Filament Chemical Vapor Deposition

1. IntroductionIn recent years, there has been increasing illterest in the heteroepitaxial growth of diamond films'by chemicisl vapor deposition(CVD) owing to theirpromising applications for the electronic devices. Epitaxial diamond films have been successfully grown onc-BN and monocrystal diamond substrated~4]. However, it is a more imperative task to deposit heteroepitarial diamond films on St which was anticipated tobe as a low cost substrate to achieve synthesis of singlecrystalline diam…     

Electron Field Emission from Multiwall Carbon Nanotubes in Air Gas

Electron field emission (FE) from multiwall carbon nanotubes (CNTs) in air for excitation of atmospheric pressure microplasma was investigated in a scanning electron microscope (SEM). The results showed that, the FE properties of the CNTs in air at 10 kPa and lower pressures were the same as those in vacuum. At pressures more than 10 kPa, the FE threshold voltages in air were higher than those in vacuum and increased with increasing air pressures. When the FE threshold voltages became higher than those of the conventional gas breakdown voltage, microplasma was ignited before FE appearance. FE properties of the CNTs were stable in air before appearing the conventional gas discharges.     

A precision gas feeding system for a PIG heavy ion source

A precision gas feeding system aiming at stable and efficient operation of a small, cold-cathode PIG heavy ion source for the K = 50 MeV AVF cyclotron is described in detail. The system can regulate the supply gas pressure with a precision of 0.6 Torr and keep a constant gas flow rate with a stability of 0.010 ± 0.003 cm³/min. The ion source operating parameters such as the arc current, the arc voltage and the gas flow rate remain fairly constant through the lifetime of the source. By adopting this system in the routine accelerations of carbon or oxygen ions, the average beam current was increased by a factor of 2–3.     

脉冲调制射频容性耦合SiH/C2H4/Ar放电的发射光谱诊断

本文采用发射光谱法诊断了低气压下氩气(Ar)、硅烷(SiH4)及乙烯(C2H4)混合气体(SiH4/C2H4/Ar)脉冲调制射频放电等离子体特性,利用了Ar发射光谱中的五条谱线通过Boltzmann斜率法计算了电子激发温度,研究了占空比、调制频率、功率及气压等对电子激发温度和谱线相对强度的影响.     

A planar excimer-halogen radiation source pumped by transverse RF discharge

We present the characteristics of a planar source of wideband shortwave radiation pumped by transverse RF (f=1.76 MHz) discharge in a Kr/Xe/Cl₂ mixture (P≤500 Pa). The spectral characteristics of the plasma emission were studied in the wavelength interval of 130–600 nm. The oscillograms of the voltage, current, and output radiation intensity and the diagrams of the output power depending on the gas pressure, partial composition of the working gas mixture, and discharge power are presented. It is established that the source produces emission predominantly in the spectral interval of 170–330 nm, representing a system of the molecular emission bands XeCl(D, B-X), KrCl(B-X), Cl₂(D′-A′), and Cl₂**. For a maximum output power in the UV-VUV range, the optimum working gas mixture is Kr/Xe/Cl₂ with the partial pressures P(Kr)/P(Xe)/P(Cl₂)=150–200/150–200/20–40 Pa. The maximum power irradiated within a solid angle of 4π via two output holes with a total area of S≤ 100 cm² reaches 30–40 W. In the region of a threshold with respect to the transverse discharge initiation, there are narrow peaks of plasma emission that are probably related to the jumps in the density of electrons and the positive and negative ions at the boundary between the plasma and the RF discharge layer.     

Nanocrystalline diamond films grown in nitrogen rich atmosphere: structural and field emission properties

The field emission behaviour of a series of nanocrystalline N-doped diamond films has been investigated and interpreted on the basis of the structural and compositional characteristics of the layers. The diamond films, formed by crystallites with grain size in the range 20-100 nm were produced from CH4/H2 mixtures using a HF-CVD apparatus. Nitrogen was added to the gaseous reactants in form of both N2 and of Urea. Micro-Raman spectroscopy and cathodoluminescence have been used to define the structure of the deposits on a nanometric scale. The field emission measurements have been carried out under a pressure of 10(-6) mbar using a sphere-to-plane anode-cathode configuration. The characteristics of the emission from the various nanodiamond samples and from different regions of the same sample are discussed in terms of field threshold, current density, current stability.     

Ar对N_2介质阻挡放电光谱的影响

采用光谱法研究了大气压下氮气、氩气以及氩气对氮气介质阻挡放电等离子体的光辐射特性的影响。研究结果表明：在氮气里添加少量氩气,氮气光谱谱线强度会有所增强,尤其是386.3 nm和418.9 nm谱线强度增强明显。在氩气体积分数为10%时,随着等离子体放电电压变化,氮气的386.3 nm和418.9 nm两条谱线强度在放电电压70 kV时迅速增强。因此,在氮气和氩气混合气体放电中,气体组成影响等离子体内部的能量传输特性以及放电的发光特性。     

Vakuummikro‐ und Vakuumnanoelektronik mit Feldemission

Vacuum microelectronics and nanoelectronics with field emission — features of breakdown voltage in vacuum gaps lower than 10 μm Further miniaturization in vacuum electronics will be possible only with field‐emitter cathodes. However in microscale vacuum gaps in the range 10 μm field emission is a dominant process in gas breakdown process, leading to signif icant deviations from the traditional Paschen's Law. At first a significant reduction of breakdown voltage is observed. The high surface‐to‐volume ratio in microscale dimensions 3 μm and in interactions with gas desorption, outgassing and gas ionization during electron field‐emission give a ignition and stabilization of micro plasmas (glow discharges) or/and micro arcs, which exist largely independent of surrounding vacuum, atmospheric or over pressure. In this range the Paschen's Law is invalid. This is an interesting approach which opens up new dimensions for basic research, field emission‐driven micro plasmas and for novel fieldemitter applications in vacuum electronics and plasma technology.     

Ne-Xe混合气体对荫罩式等离子体显示器放电影响的研究

本文使用7英寸荫罩式等离子体显示器(SM-PDP)的实验小屏,在真空系统上动态地改变混合气体中Xe浓度和气体压强,测量了着火电压、发射光光强、电子温度、电流、亮度和效率等参数,并分析了混合气体对(SM-PDP)放电的影响。结果表明,提高Xe浓度和气体压强虽然带来了着火电压的升高,但是同时也使得电流下降,亮度和效率大幅提高。通过提高Xe浓度和气体压强,导致电子和中性粒子的碰撞截面变大:一方面电子的碰撞几率增加,使得放电中电子温度降低,增加了基态Xe原子到低能级的直接激发;另一方面中性粒子的碰撞几率增加,使得173 nm的真空紫外线辐射增强,从而改善总的气体放电效率。