铌镁酸铅-钛酸铅铁电阴极电子发射特性

研究了铌镁酸铅-钛酸铅铁电材料的铁电、介电性能对阴极发射阈值电压的影响, 以及铁电阴极发射电流与激励脉冲电压和抽取电压之间的关系, 并分析了其发射机理. 结果表明, 室温介电常数高、极化强度变化量大的弛豫铁电体0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃具有较小的发射阈值电压; 铁电阴极电子发射与快极化反转和等离子体的形成有关; 由极化反转所致电子发射的自发射电流随激励脉冲电压的增大呈幂律增长关系, 其发射电流开始于激励脉冲电压的下降沿; 在抽取电压较大时, 发射电流随抽取电压的增大呈线性增长关系, 说明大电流主要取决于抽取电压; 其发射电流开始于激励脉冲电压的上升沿, 与“三介点”处的场增强效应和等离子体的形成有关; 当抽取电压为2500 V 时, 得到的发射电流幅值为210 A, 相应的电流密度为447 A/cm².     

基于Ni电极和ZrO_2/SiO_2/ZrO_2介质的MIM电容的导电机理研究

研究了基于Ni电极和原子层淀积的ZrO_2/SiO_2/ZrO_2对称叠层介质金属-绝缘体-金属(MIM)电容的电学性能.当叠层介质的厚度固定在14nm时,随着SiO_2层厚度从0增加到2nm,所得电容密度从13.1 fF/μm~2逐渐减小到9.3fF/μm~2,耗散因子从0.025逐渐减小到0.02.比较MIM电容的电流-电压(I-V)曲线,发现在高压下电流密度随着SiO_2厚度的增加而减小,在低压下电流密度的变化不明显,还观察到电容在正、负偏压下表现出完全不同的导电特性,在正偏压下表现出不同的高、低场I-V特性,而在负偏压下则以单一的I-V特性为主导.进一步对该电容在高、低场下以及电子顶部和底部注入时的导电机理进行了研究.结果表明,当电子从底部注入时,在高场和低场下分别表现出普尔-法兰克(PF)发射和陷阱辅助隧穿(TAT)的导电机理;当电子从顶部注入时,在高、低场下均表现出TAT导电机理.主要原因在于底电极Ni与ZrO_2之间存在镍的氧化层(NiO_x),且ZrO_2介质层中含有深浅两种能级陷阱(分别为0.9和2.3 eV),当电子注入的模式和外电场不同时,不同能级的陷阱对电子的传导产生作用.     

Plasma and heat flux characteristics of a supersonic ammonia or nitrogen/hydrogen-mixture direct-current plasma jet impinging on a flat plate

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics with or without a titanium plate under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle in a low-pressure environment. Heat fluxes into the plate from the plasma were also evaluated with a Nickel slug and thermocouple arrangement. Ammonia and mixtures of nitrogen and hydrogen were used as a working gas. The NH/sub 3/ and N/sub 2/+3H/sub 2/ plasmas in the nozzle and in the downstream plume without a substrate plate were in thermodynamical nonequilibrium states. As a result, the H-atom electronic excitation temperature and the N/sub 2/ molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. Each temperature was kept in a small range in the plume without a substrate plate except for the NH rotational temperature for NH/sub 3/ working gas. On the other hand, as approaching the titanium plate, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one because the plasma flow tended to stagnate in front of the plate. The electron temperature had a small radial variation near the plate. Both the electron number density and the heat flux decreased radially outward, and an increase in H/sub 2/ mole fraction raised them at a constant radial position. In cases with NH/sub 3/ and N/sub 2/+3H/sub 2/, a radical of NH with a radially wide distribution was considered to contribute to the better nitriding as a chemically active and non heating process.     

Carbon Nitride Thin Films Deposited by Plasma Assisted Nd:YAG Laser Ablation of Graphite in N2+H2 Atmosphere

Carbon nitride thin films are deposited on silicon wafers by 532 nm Nd:YAG laser ablation of graphite in the N2+H2 atmosphere assisted by a dc glow discharge plasma at a higher gas pressure of about 4.0 kPa. The properties of the thin films are investigated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray diffraction (XRD). The results show that the deposited films are composed of α-C3N4, β-C3N4 phase and have the N/C atomic ratio of 2.01. The optical emission spectroscopy (OES) studies indicate that the introduction of a dc glow discharge and the adoption of a higher gas pressure during the film deposition are favorable to the net generation of the atomic N, CN radicals and N+2 in B2Σ+u excited state in the plasma, which are considered to play a major role in the synthesis of carbon nitride.     

LaAlO_3/SrTiO_3界面增强光伏效应

探索LaAlO_3/SrTiO_3(LAO/STO)界面产生的新奇物理特性对理解关联电子系统中多自由度耦合和设计功能材料器件具有重要的价值.本文通过脉冲激光沉积方法在SrTiO_3基底上制备了LAO/STO薄膜,研究了正面照射LAO/STO膜面和侧面照射LAO/STO界面时的光伏效应,探讨了LAO/STO界面对光伏效应的影响.研究结果表明,在同样光照能量下侧面照射LAO/STO界面产生的光电压远高于正面照射LAO/STO膜面产生的光电压,说明LAO/STO界面对光伏效应有明显的增强作用.通过偏压调控可以进一步增强照射LAO/STO界面产生的光电压,当偏压为60 V时, LAO/STO样品的位置探测灵敏度达到了36.8 mV/mm.这些研究结果为设计场调控位置敏感探测器等新型光电子器件提供了新的思路.     

AlxGa1-x N/GaN调制掺杂异质结构的子带性质研究

通过低温和强磁场下的磁输运测量研究了Al_0.22Ga_0.78N/GaN调制掺杂异质结构中2DEG的子带占据性质和子带输运性质.在该异质结构的磁阻振荡中观察到了双子带占据现象，并发现2DEG的总浓度随第二子带浓度的变化呈线性关系.得到了该异质结构中第二子带被2DEG占据的阈值电子浓度为7.3×10¹²cm^-2.采用迁移率谱技术得到了不同样品的分别对应于第一和第二子带的输运迁移率.发现当样品产生应变弛豫时第一子带的电子迁移 关键词： AlGaN/GaN异质结 二维电子气 子带占据 输运迁移率     

N/Cu共掺杂锐钛矿型TiO2第一性原理研究

基于密度泛函理论的第一性原理平面波超软赝势法, 采用局域自旋密度近似加Hubbard U值方法研究了纯锐钛矿型TiO₂, N, Cu单掺杂TiO₂及N/Cu共掺杂TiO₂ 的晶体结构、电子结构和光学性质. 研究结果表明, 掺杂后晶格发生相应畸变, 晶格常数变大. N 和Cu的掺杂在TiO₂禁带中引入杂质能级, 禁带宽度发生相应改变. 对于N掺杂TiO₂禁带宽度减小较弱, 而Cu掺杂和N/Cu共掺TiO₂禁带宽度显著降低, 导致吸收光谱明显红移, 光学催化性增强, 有利于实际应用.     

Particle-in-cell/Monte Carlo simulation of radio frequencySiH4/H2 discharges

In this paper we report on a study of SiH₄/H₂ radio-frequency discharges using the particle-in-cell/Monte Carlo (PIC/MC) method. A special procedure based on the rate balance for negative ions has been developed to speed up the simulation for this kind of electronegative discharge. The electron energy distribution function and the angular and energy distribution function of ions arriving at the substrate have been studied at different discharge settings (frequency, pressure, voltage, and power). The simulations show that the electrons are heated ohmically, so the average electron energy can be increased only by increasing the voltage. A high radical density, a high and more directional ion flux, and a low average ion energy can be obtained by a combination of a high frequency and a low RF voltage. The behavior of the dissociation rate with the discharge parameters is consistent with the experimentally observed consumption of SiH₄. The simulated ion energy distribution functions are in good agreement with experimental results     

N_2-H_2容性耦合等离子体电非对称效应的particle-in-cell/Monte Carlo模拟

H_2-N_2混合气体电容性耦合射频放电在有机低介电系数材料刻蚀中具潜在研究意义.采用paxticle-incell/Monte Carlo模型模拟了双频(13.56 MHz/27.12 MHz)电压源分别接在结构对称的两个电极上的H_2-N_2容性耦合等离子体特征,研究了其电非对称效应.模拟结果表明,通过调节两谐波间的相位角θ,可以改变其电场、等离子体密度、离子流密度的轴向分布及离子轰击电极的能量分布.当相位角θ为0°时,低频电极(晶片)附近主要离子(H_3~+)的密度最小,离子(H_3~+,H_2~+,H~+)轰击低频电极的流密度及平均能量最高;当θ从0°变化90°时,低频电极的自偏压从-103V到106V近似线性增加,轰击电极的离子流密度变化约±18%,H~+离子轰击低频电极的最大能量约减小2.5倍,轰击电极的平均能量约变化2倍,表明氢离子能量和离子流几乎能独立控制.     

Experimental study on parameters of dust plasma in SiH4/C2H4/Ar discharges

Measurements of dust plasma parameters were carried out in the discharges of （SiH4/C2H4/Ar） mixtures. Dust particles were formed in the capacitively coupled radio-frequency discharge of these reactive mixtures in a cylindrical chamber. Langmuir probe was employed for diagnosing and measuring the important plasma parameters such as electron density and electron temperature. The results showed that the electron density dropped, and in contrast the electron temperature rose when the dust particles formed. The curves of the electron density and temperature versus the RF power and pressure were presented and analysed. Further, it was found that the wriations of electron temperature and the size of dust void with the RF power followed the similar trends. These trends might be useful for understanding more about the characteristics of dusty voids.     

杂质S对Fe/Al_2O_3界面结合影响的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法,研究了杂质S对Fe/Al_2O_3界面结合的影响.计算结果表明:S在界面上Fe3原子处的界面偏析能最小,因此S易于向Fe3原子处偏析.Fe/Al_2O_3界面的结合主要受界面两侧Fe和O原子间相互作用控制.态密度、键重叠布居数和电子密度的计算结果均表明:S在界面处的偏析减弱了界面处Fe原子和O原子之间的相互作用,而且S的存在会引起Fe和O原子之间较强的静电排斥,这些导致了界面结合力的下降.研究结果可以使我们深入理解S在Fe-Cr-Al合金界面处的偏析造成氧化膜与合金基体结合减弱及氧化膜在S偏聚处剥离的机理.     

第一性原理研究O和S掺杂的石墨相氮化碳(g-C_3N_4)_6量子点电子结构和光吸收性质

利用密度泛函和含时密度泛函理论研究了氧(O)和硫(S)原子掺杂的石墨相氮化碳(g-C_3N_4)_6量子点的几何、电子结构和紫外-可见光吸收性质.结果表明:掺杂后(g-C_3N_4)_6量子点杂质原子周围的C-N键长发生了一定的改变,最高电子占据分子轨道-最低电子未占据分子轨道(HOMO-LUMO)能隙显著减小.形成能的计算表明O原子取代掺杂的(g-C_3N_4)_6量子点体系更稳定,且O原子更易取代N3位点,而S原子更易取代N8位点.模拟的紫外-可见电子吸收光谱表明,O和S原子的掺杂改善了(g-C_3N_4)_6量子点的光吸收,使其吸收范围覆盖了整个可见光区域,甚至扩展到了红外区.而且适当的杂质浓度使(g-C_3N_4)_6量子点光吸收在强度和范围上都得到明显改善.通过O和S掺杂的比较,发现二者在可见光区对(g-C_3N_4)_6量子点的光吸收有相似的影响,然而在长波长区域二者的影响有明显差异.总体而言,O掺杂要优于S掺杂对(g-C_3N_4)_6量子点光吸收的影响.     

Characterization of Al2O3 /GaN/AlGaN/GaN metalinsulator-semiconductor high electron mobility transistors with different gate recess depths

In this paper,in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs),we demonstrate better performances of recessed-gate Al 2 O 3 MIS-HEMTs which are fabricated by Fluorine-based Si 3 N 4 etching and chlorinebased AlGaN etching with three etching times (15 s,17 s and 19 s).The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of AlGaN/GaN HEMT.Through the recessed-gate etching,the transconductance increases effectively.When the recessed-gate depth is 1.02 nm,the best interface performance with τ it =(0.20-1.59) μs and D it =(0.55-1.08)×10 12 cm 2 ·eV 1 can be obtained.After chlorine-based etching,the interface trap density reduces considerably without generating any new type of trap.The accumulated chlorine ions and the N vacancies in the AlGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices.By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times,it is found that a low power chlorine-based plasma etching for a short time (15 s in this paper) can enhance the performances of MIS-HEMTs effectively.     

The improvement of Al2O3/AlGaN/GaN MISHEMT performance by N2 plasma pretreatment

This paper discusses the effect of N 2 plasma treatment before dielectric deposition on the electrical performance of a Al2O3 /AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor(MISHEMT),with Al2O3 deposited by atomic layer deposition.The results indicated that the gate leakage was decreased two orders of magnitude after the Al2O3 /AlGaN interface was pretreated by N 2 plasma.Furthermore,effects of N 2 plasma pretreatment on the electrical properties of the AlGaN/Al2O3 interface were investigated by x-ray photoelectron spectroscopy measurements and the interface quality between Al2O3 and AlGaN film was improved.     

The electronic structure and properties of the C15 compounds CeAl2, LaAl2 and YAl2

Results of self-consistent band calculations are reported for the C15 structured XAl₂ materials (X = Y, La, and Ce) using the local spin density functional formalism for assumed ferromagnetic and antiferromagnetic states as well as the paramagnetic state. The X-atoms are found to be the dominant factor is determining the electronic structure near the Fermi energy and this is enhanced by the presence of f-bands close to (LaAl₂) or at (CeAl₂) the Fermi energy. In paramagnetic CeAl₂, the f-bands are about 1 eV wide and, although principally above the Fermi energy, extend down to accomodate the additional electron compared to LaAl₂. The ferromagnetic state is found not to be stable. By contrast, the antiferromagnetic state is found to be stable with a magnetic moment of 0.88μ_B per Ce atom in very good agreement with the maximum moment, 0.89μ_B found in the neutron measurements of Barbara et al. A significant narrowing of the f-bandwidth is observed in the antiferromagnetic state. The antiferromagnetic spin density ordering appears to be related to nesting features in this underlying Fermi surface in LaAl₂ (i.e., no 4f electron) rather than that of CeAl₂.     

Experimental study of CF4 conical theta pinch plasmaexpanding into vacuum

Langmuir probe, photodiode, and optical multichannel analyzer (OMA) measurements have been made on a pulsed CF₄ conical theta-pinch plasma. A cloud of CF₄ was puffed into a conical theta-pinch coil, converted to plasma, and propelled into the vacuum region ahead of the expanding gas cloud. At a position 67 cm away from the conical theta-pinch coil, the plasma arrived in separate packets that were about 20 μs in duration. The average drift velocity of these packets corresponded to an energy of about 3 eV. The OMA measurements showed that the second packet contained neutral atomic fluorine as well as charged particles. The electron temperature and ion density in the second packet were 2.0 eV and 1.5×10¹³ cm^-3, respectively. The electron temperature and ion density in the wake plasma were 8.3 eV and 4×10¹¹ cm^-3 , respectively. This device can be used for plasma processing or as a laboratory test of numerical and analytical models of the expansion of plasma into vacuum     

MoS_2电子屏蔽长度和等离激元

通过有效哈密顿量求解了单层MoS_2低能量区的电子薛定谔方程,分析得出电子能量本征值以及波函数、电子态密度以及电子间的屏蔽长度.发现电子能带分裂成两支导带和两支价带,并且其能带是准线性的.MoS_2的电子间的屏蔽长度非常大,高达10~8cm~(-1).利用费曼图形自洽方法,在无规相近似的基础上研究了单层二硫化钼电子系统的多体相互作用产生的等离激元.研究发现二硫化钼系统由于自旋的劈裂使得导带中存在两支自旋频率不同的等离激元,该元激发的特征与单层石墨烯和传统二维电子气的等离激元对波矢q的依赖关系是一样的,激发频率都正比于q~(1/2),并且随着电子浓度的增加激发频率增大.由于其准线性的能量色散关系,该系统等离激元的频率与电子浓度的变化关系非常不同于石墨烯和二维电子气的关系.自旋-轨道耦合对单层二硫化钼的能带结构和电子性质有重要的影响.研究发现,通过调控二硫化钼系统的电子浓度可以有效地调节该系统两支等离激元的频率.研究结果对理解二硫化钼的电子结构和性质,以及开发二硫化钼为基础的等离子器件有重要的研究和参考价值.     

(CH3)2和(NH2)2基团修饰的齐聚苯乙炔分子电子输运性质研究

采用密度泛函理论和非平衡格林函数相结合的方法研究了S原子作为单、双端基的(CH₃)₂-OPE (齐聚苯乙炔)和(NH₂)₂-OPE分子在金电极间的电子输运性质. 通过第一性原理优化计算获得分子部分稳定结构, 再置于Au电极之间构成两极系统, 然后再优化整个两极系统获得稳定结构. 另外, 通过非平衡格林函数方法计算了两极系统的电子输运性质. 计算结果表明, 不同的修饰基团和桥接方式可以导致两极系统的开关效应、负微分电阻行为和整流行为等不同的电子输运性质. 通过计算不同偏压下的分子体系投影轨道电子分布、透射谱、态密度, 对这些新异的电输运性质出现的机理进行了解释.     

合成温度和N2/O2流量比对碳纤维衬底上生长的SnO2纳米线形貌及场发射性能影响

采用化学气相沉积法系统研究了合成温度和N₂/O₂流量对生长在碳纤维衬底上的SnO₂纳米线形貌及场发射性能的影响规律. 利用扫描电镜(SEM)、透射电镜(TEM), X射线衍射(XRD)及能谱仪(EDS)对产物细致表征, 结果表明, SnO₂纳米线长径比随反应温度的升高而增大; 随N₂/O₂流量比值的增大先增大后变小, 场发射测试表明, 合成温度780 ℃, N₂/O₂流量比为300 : 3 时SnO₂纳米线阵列具有最佳的场发射性能, 开启电场为1.03 V/μm, 场强增加到1.68 V/μm时, 发射电流密度达0.66 mA/cm², 亮度约2300 cd/m².     

NH3 adsorption on Ni(110) and the production of the NH2 species by electron irradiation

The adsorption of NH₃ on Ni(110) has been examined using electron stimulated desorption ion angular distribution (ESDIAD), low energy electron diffraction (LEED) and thermal desorption spectrometry (TDS). At ～ 85 K the NH₃ molecule enters into a series of chemisorption and physisorption states whose structures have been partially characterized by means of ESDIAD and LEED. Upon heating, these NH₃ states desorb without dissociation; for adsorption below 300 K there is essentially no thermal decomposition. The ammonia adiayer was found to be extremely sensitive to electron irradiation effects. Evidence was found to support the irradiation induced conversion of NH₃(ads) to an amido intermediate, nh_2(ads). The NH₂ adsorbs with its C_2v axis normal to the surface and its NH bonds aligned along the [001] and [001?] directions. In the absence of further electron irradiation the nh_2(ads) species is stable to 375 K whereupon it dissociates to N_(ads)and H_2(g). The remaining N_(ads) desorbs near 750 K with significant attractive N…N interaction. No evidence is found for an imido intermediate, nh_(ads). nh_2(ads) also undergoes a disproportionation/recombination reaction upon heating to produce an additional NH₃ desorption state. A significant isotope effect for NH versus ND scission, sensitive to the adsorption state of the ammonia, is found to occur upon electron irradiation.