2002年IEEE国际可靠性物理年会论文集论文摘要（2）——假同晶GaAs HEMT上的创新氮化物钝化及其对器件性能的影响

22. 特邀论文:带铝盖铜垫的探测和线焊(InvitedPaper:Probing and Wire Bonding of AluminumCapped Copper Pads)-2002 International Relia-bility Physics Symposium pp. 140-143. 微电子制造已经开始发展并促进了用铜互连为首选金属的圆片制造工艺过程。由于裸铜线焊接被认为不是可靠和高产量的工艺过程,因而集成电路制造商在铜的顶部使用了铝盖,以方便焊接。

Etching Behavior of GaN/GaAs(001) Epilayers Grown by MOVPE

Wet etching characteristics of cubic GaN (c GaN) thin films grown on GaAs(001) by metalorganic vapor phase epitaxy (MOVPE) are investigated.The samples are etched in HCl,H 3PO 4,KOH aqueous solutions,and molten KOH at temperatures in the range of 90～300℃.It is found that different solution produces different etch figure on the surfaces of a sample.KOH based solutions produce rectangular pits rather than square pits.The etch pits elongate in 1 0] direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers. direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers.

Influence of preparation methods on the physicochemical properties and catalytic performance of MnO_x-CeO_2 catalysts for NH_3-SCR at low temperature

This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx‐CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3‐SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation,hydrothermal treatment, co‐precipitation, and a sol‐gel technique, were used to synthesizeMnOx‐CeO2 catalysts. The catalysts were characterized in detail, and an NH3‐SCR model reaction waschosen to evaluate the catalytic performance. The results showed that the preparation methodsaffected the catalytic performance in the order: hydrothermal treatment > sol‐gel > co‐precipitation> impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content,oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sitesand acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalystformed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalyticperformance, and good H2O resistance in NH3‐SCR reaction. This was attributed to incorporationof Mnn+ into the CeO2 lattice to form a uniform ceria‐based solid solution (containing Mn‐O‐Cestructures). Strengthening of the electronic interactions between MnOx and CeO2, driven by thehigh‐temperature and high‐pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment‐friendly route to synthesizing low‐temperature denitrification (deNOx) catalysts.

Advanced purification of filtered water by aerobic IBAC

Conventional water purified processes have low removal efficiencies for low concentrations of ammonia nitrogen, nitrite nitrogen and micro-pollutants. The efficiency and mechanisms of a novel immobilized biological activated carbon (IBAC) process to remove those pollutants from treated potable water was investigated. Operated at a hydraulic retention time of 24 minutes, the IBAC process achieved ammonia nitrogen, nitrite nitrogen and organic micro-pollutants (measured as COD equivalent) removal efficiencies of 95%, 96% and 37%, respectively. A GC/MS analysis of the organic micro-pollutants revealed that the initial 24 organic compounds in the in-coming water were reduced to 7 after the IBAC treatment. The organic micro-pollutant removal efficiency decreased with decreasing in-coming concentrations. Pollutant reduction in the IBAC process was achieved by a rapid physical adsorption on the activated carbon, which effectively retained the pollutants in the system despite the short hydraulic retention time, followed by a slower biological enzymatic degradation of the pollutants.

Boron Nitride Nanowires Produced on Commercial Stainless Steel foil

Chemical vapor deposition growth of one-dimensional nanomaterials usually demands substrates that have been coated with a layer of catalyst film. In this study, a green process to synthesize boron nitfide （BN） nanowires directly on commercial stainless steel foils was proposed by heating boron and zinc oxide powders under a mixture gas flow of N2 arid 15% H2 at 1100℃, and a large quantities of pure h-BN nanowires have been produced directly on commercial stainless steel foil. The stainless steel foils not only acted as the substrate but also the catalyst for the nanowire growth. The synthesized BN nanowires were characterized by X-ray diffraction, scanning and transmission electron microscopes, X-ray energy dispersive spectrometer and photoluminescence spectroscopy, The nanowires also possess strong PL emission bands at 515, 535, and 728 nm.

Effect of frequency and pulse-on time of high power impulse magnetron sputtering on deposition rate and morphology of titanium nitride using response surface methodology

Titanium nitride thin films were deposited on silicon by high power impulse magnetron sputtering(HiPIMS)method at different frequencies(162-637 Hz)and pulse-on time(60-322μs).Response surface methodology(RSM)was employed to study the simultaneous effect of frequency and pulse-on time on the current waveforms and the crystallographic orientation,microstructure,and in particular,the deposition rate of titanium nitride at constant time and average power equal to 250 W.The crystallographic structure and morphology of deposited films were analyzed using XRD and FESEM,respectively.It is found that the deposition rate of HiPIMS samples is tremendously dependent on pulse-on time and frequency of pulses where the deposition rate changes from 4.5 to 14.5 nm/min.The regression equations and analyses of variance(ANOVA)reveal that the maximum deposition rate(equal to(17±0.8)nm/min)occurs when the frequency is 537 Hz and pulse-on time is 212μs.The experimental measurement of the deposition rate under this condition gives rise to the deposition rate of 16.7 nm/min that is in good agreement with the predicted value.

Effect of Substrate Nitridation on Properties of Thick GaN Film Grown by Hydride Vapour Phase Epitaxy

Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The crystalline quality of GaN films revealed by high resolution X-ray diffraction were strongly dependent on the nitridation time, which determined substrate surface topography. The different nitridation schemes strongly affected the morphology of GaN overlayers resulting in the blue shift of the main excitonic peak in photoluminescence spectra at room temperature.

The relationship between nNOS and Cyt-c in mitochondria of glioma

Objective： The aim of this study was to investigate the association between neuronal nitric oxide synthase （nNOS） and the expression level of Cytochrome C （Cyt-c） in mitochondria. Methods： The pathological diagnosis of glioma and tumor classification was by HE staining, and we use immunohistochemistry method to analyse the level of nNOS in different pathological grade glioma and the expression level of Cyt-c in mitochondria meanwhile. Results： The levels of nNOS were highest in grade Ⅲ tumors, moderate in grade Ⅱ tumors, and lowest different in grade I tumors. There was significant difference of the nNOS levels among different pathological grade tumors （P 〈 0.05）. Furthermore, the similar phenomenon was observed in the expression level of Cyt-c in mitochondria （P 〈 0.05）. Conclusion： The expression level of nNOS and Cyt-c in mitochondria was significantly related to the pathological grade of glioma.

State-to-state Photoionization Dynamics of Vanadium Nitride by Two-color Laser Photoionization and Photoelectron Methods

We have conducted a two-color visible-ultraviolet （VIS-UV） resonance-enhanced laser pho- toionization and pulsed field ionization-photoelectron （PFI-PE） study of gaseous vana- dium mononitride （VN） in the total energy range of 56900-59020 cm-1. The VN molecules were selectively excited to single rotational levels of the intermediate VN（D3H0, v＇=0） state by using a VIS dye laser prior to photoionization by employing a UV laser. This two-color scheme allows the measurements of rovibronically selected and re- solved PFI-PE spectra for the VN＋（X2A; v＋=0, 1, and 2） ion vibrational bands. By simulating the rotationally resolved PFI-PE spectra, J＋=3/2 is determined to be the lowest rotational level of the ground electronic state, indicating that the symmetry of the ground VN＋ electronic state is 2A3/2. The analysis of the PFI-PE spectra for VN＋ also yields accurate values for the adiabatic ionization energy for the formation of VN＋（X2A3/2）, IE（VN）=56909.5＋0.8 cm-1 （7.05588±0.00010 eV）, the vibrational fre- quency wc＋=1068.0±0.8 cm-1, the anharmonicity constant wc＋Xe＋=5.8±0.8 cm-1, the rotational constants Be＋=0.6563±0.0005 cm-1 and ae＋=0.0069±0.0004 cm-1, and the equi-librium bond length, re＋=1.529A, for VN＋（X2A3/2）; along with the rotational constants Bc＋=0.6578i0.0028 cm-1 and a＋=0.0085±0.0028 cm-1, and the equilibrium bond length re＋=1.527A for VN＋（X2As/2）, and the spin-orbit coupling constant A=153.3±0.8 cm-1 for VN＋（X2/k5/2,3/2）. The highly precise energetic and spectroscopic data obtained in the present study are valuable for benchmarking the predictions based on state-of-the-art ab initio quantum calculations.

激光和等离子体混合法氮化铁表面

采用激光和氮等离子体混合方法在大气气氛下对铁样品表面进行处理,获得了铁氮化合物表层。利用X射线衍射仪(XRD)对氮化处理样品测试,得到样品的相结构。分别使用混合方法与普通激光氮化方法,在相同条件下对样品表面进行氮化处理,结果表明通过混合方法提高了氮化物含量,并有效地抑制了氧化发生。利用扫描电镜(SEM)测量氮化后样品得出氮的最大质量分数可达34.44%,有效氮化层深度可达11.21μm。讨论激光功率密度、氮等离子体流量、扫描速度等参数对混合法氮化效果的影响。在实验条件下,激光功率密度和扫描速度分别与氮化物衍射峰相对强度成线性递增关系和二次方递减关系。而随着氮等离子体流量的增加,氮化物含量增加;但是当氮等离子体流量大于0.9 m3/h后,氮化所需活化氮达到饱和,氮化物含量不再增加。另外,氮化后样品的硬度得到了增强。

Accurate characterization of room-temperature long range magnetic order in GaN: Mn by magnetic force microscope

Room-temperature ferromagnetism with a Curie temperature higher than 380 K was studied in GaN: Mn thin films grown by metal-organic chemical vapor deposition. By etching artificial microstructures on the GaN: Mn layer,strong magnetic responses were observed in the magnetic force microscopy (MFM) measurement,which revealed that the films were independent of dopant particles and clusters. Numerical simulation on the data of atomic force microscope (AFM) and MFM measurements covering the whole microstructure validated the formation of long range magnetic order. This result excluded a variety of controversial origins of room-temperature ferromagnetism in the GaN: Mn and gave a strong evidence of our GaN: Mn as the intrinsic diluted magnetic semiconductor (DMS). The forwarded method for accurate characterization of long range magnetic order could be applied to a wide range of DMS and diluted magnetic oxide (DMO) systems.

A lightweight carbon nanofiber-based 3D structured matrix with high nitrogen-doping level for lithium metal anodes

Lithium metal is considered to be the most promising anode material for the next-generation rechargeable batteries. However, the uniform and dendrite-free deposition of Li metal anode is hard to achieve, hindering its practical applications. Herein, a lightweight, free-standing and nitrogen-doped carbon nanofiber-based 3D structured conductive matrix(NCNF), which is characterized by a robust and interconnected 3D network with high doping level of 9.5 at%, is prepared by electrospinning as the current collector for Li metal anode. Uniform Li nucleation with reduced polarization and dendrite-free Li deposition are achieved because the NCNF with high nitrogen-doping level and high conductivity provide abundant and homogenous metallic Li nucleation and deposition sites. Excellent cycling stability with high coulombic efficiency are realized. The Li plated NCNF was paired with LiFePO4 to assemble the full battery, also showing high cyclic stability.

Stability of BN/metal interfaces in gaseous atmosphere

Hexagonal boron nitride （h-BN） is often prepared by epitaxial growth on metals, and stability of the formed BN/metal interfaces in gaseous environment is a key issue for physicochemical properties of the BN overlayers. As an illustration here, the structural change of a BN/Ru（0001） interface upon exposure to 02 has been investigated using in situ photoemission electron microscopy （PEEM） and ambient pressure X-ray photoelectron spectroscopy （AP-XPS）. We demonstrate the occurrence of oxygen intercalation of the BN overlayers in 02 atmosphere, which decouples the BN overlayer from the substrate. Comparative studies of oxygen intercalation at BN/Ru（0001） and graphene/Ru（0001） surfaces indicate that the oxygen intercalation of BN overlayers happens more easily than graphene. This finding will be of importance for future applications of BN-based devices and materials under ambient conditions.

First way of enantioselective synthesis of moxifloxacin intermediate

A new method of enantioselective synthesis of （S,S）-2,8-diazobicyclo [4.3.0] nonane was found by using （R）-2-amino-2- phenyl-ethanol as chiral induction reagent. The entire synthetic process included 8 steps which were easy to operate with high yield. The purification method was only simple recrystallization or even used directly in the next step without further purifica- tion. The total yield was 29%.