bluuebunny/crossref_metadata_2025 huggingface dataset:
Friends in High Places
Authors: Richardson Damone
Published: August 2004

During the first year of his term as president, George W. Bush has worked hard to further tip the balance of financial power against working families. Bush has creatively used his influence to elevate the quest for airline‐industry profitability to the top of his agenda. September 11 changed many things, but not the focus of Bush's regressively profit‐centered political and legislative agenda. However, the tragedy has done much to change how he goes about the “business of business.”
Reviews
Authors: Reese Ellen , Lynd Staughton , Doyle Kevin
Published: August 2004

Welfare Racism: Playing the Race Card Against America's Poor.By KennethJ. Neubeck andNoelA. Cazenave.

After Capitalism: From Managerialism to Workplace Democracy.By SeymourMelman.

Unions and Legitimacy.By GaryChaison andBarbaraBigelow.
Review
Authors: Early Steve
Published: August 2004

Three Strikes: Labor's Heartland Losses and What They Mean for Working Americans. By Stephen Franklin.

Three Strikes: Miners, Musicians, Salesgirls, and the Fighting Spirit of Labor's Last Century. By Howard Zinn, Dana Frank, and Robin D.G. Kelley.
Syntaxin 1A regulation of weakly inactivating N‐type Ca2+ channels
Authors: Hurley Joyce H. , Cahill Anne L. , Wang Meijing , Fox Aaron P.
Published: August 2004

N‐ and P/Q‐type Ca2+ channels are abundant in nerve terminals where they interact with proteins of the release apparatus, including syntaxin 1A and SNAP‐25. In previous studies on N‐ or P/Q‐type Ca2+ channels, syntaxin 1A co‐expression reduced current amplitudes, increased voltage‐dependent inactivation and/or enhanced G‐protein inhibition. However, these studies were conducted in Ca2+ channels that exhibited significant voltage‐dependent inactivation. We previously reported that N‐type current in bovine chromaffin cells exhibits very little voltage‐dependent inactivation and we identified the Ca2+ channel subunits involved. This study was undertaken to determine the effect of syntaxin 1A on this weakly inactivating Ca2+ channel. Co‐expression of syntaxin 1A with the weakly inactivating bovine N‐type Ca2+ channels in Xenopus oocytes did not appear to alter inactivation but dramatically reduced current amplitudes, without changing cell surface expression. To further understand the mechanisms of syntaxin 1A regulation of this weakly inactivating channel, we examined mutants of the α1B subunit, β2a subunit and syntaxin 1A. We determined that the synprint site of α1B and the C‐terminal third of syntaxin 1A were necessary for the reduced current amplitude. In addition we show that enhanced G‐protein‐dependent modulation of the Ca2+ current by syntaxin 1A cannot explain the large suppression of Ca2+ current observed. Of most significance, syntaxin 1A increased voltage‐dependent inactivation in channels containing mutant β2a subunits that cannot be palmitoylated. Our data suggest that changes in inactivation can not explain the reduction in current amplitude produced by co‐expressing syntaxin and a weakly inactivating Ca2+ channel.
Cochlear function in Prestin knockout mice
Authors: Cheatham M. A. , Huynh K. H. , Gao J. , Zuo J. , Dallos P.
Published: August 2004

Gross‐potential recordings in mice lacking the Prestin gene indicate that compound action potential (CAP) thresholds are shifted by ∼45 dB at 5 kHz and by ∼60 dB at 33 kHz. However, in order to conclude that outer hair cell (OHC) electromotility is associated with the cochlear amplifier, frequency selectivity must be evaluated and the integrity of the OHC's forward transducer ascertained. The present report demonstrates no frequency selectivity in CAP tuning curves recorded in homozygotes. In addition, CAP input–output functions indicate that responses in knockout mice approach those in controls at high levels where the amplifier has little influence. Although the cochlear microphonic in knockout mice remains ∼12 dB below that in wild‐type mice even at the highest levels, this deficit is thought to reflect hair cell losses in mice lacking prestin. A change in OHC forward transduction is not implied because knockout mice display non‐linear responses similar to those in controls. For example, homozygotes exhibit a bipolar summating potential (SP) with positive responses at high frequencies; negative responses at low frequencies. Measurement of intermodulation distortion also shows that the cubic difference tone, 2f1–f2, is ∼20 dB down from the primaries in both homozygotes and their controls. Because OHCs are the sole generators of the negative SP and because 2f1–f2 is also thought to originate in OHC transduction, these data support the idea that forward transduction is not degraded in OHCs lacking prestin. Finally, application of AM1‐43, which initially enters hair cells through their transducer channels, produces fluorescence in wild‐type and knockout mice indicating transducer channel activity in both inner and outer hair cells.
Inhibition of endogenous HIF inactivation induces angiogenesis in ischaemic skeletal muscles of mice
Authors: Milkiewicz Malgorzata , Pugh Christopher W. , Egginton Stuart
Published: August 2004

Hypoxia‐inducible factor (HIF) modulates transcriptional control of several genes involved in vascular growth and cellular metabolism. HIF activity can be enhanced by suppression of prolyl and asparaginyl hydroxylase activity by dimethyloxalylglycine (DMOG). We have compared the effects of DMOG treatment and femoral artery ligation individually or in combination on HIF‐1α protein level, HIF‐dependent gene expression and capillary‐to‐fibre ratio (C: F) in extensor digitorum longus and tibialis anterior muscles of mice. Immunohistochemical examination revealed that HIF‐1α is present in non‐ischaemic mouse skeletal muscles, but its amount increased profoundly in response to the combination of DMOG treatment and ischaemia. Combined treatment resulted in 39% increase in C: F in ischaemic muscles (P < 0.0001 versus controls) whereas individual treatments produced little effect under our conditions. Combined treatment led to a significant increase in endogenous HIF‐1α protein (6.14 ± 1.1 versus 1.17 ± 0.2 in controls; P < 0.05) that was not apparent in mice treated with DMOG or femoral artery ligation alone. Ischaemia increased vascular endothelial growth factor (VEGF) protein production by 2.5‐fold (P < 0.05 versus controls), irrespective of DMOG treatment. However, production of the VEGF receptor Flk‐1 was more enhanced in ischaemic + DMOG‐treated muscles (P < 0.001 and P < 0.05 compared with controls and untreated ischaemic muscles, respectively), which may explain the intensive growth of capillaries in those muscles. The findings indicate that treatment with DMOG has a potential therapeutic use in promoting angiogenesis in ischaemic diseases, and perhaps for improving muscle recovery after injury, exercise or training.
Activity‐dependent excitability changes in hippocampal CA3 cell Schaffer axons
Authors: Soleng A. F. , Baginskas A. , Andersen P. , Raastad M.
Published: August 2004

The membrane potential changes following action potentials in thin unmyelinated cortical axons with en passant boutons may be important for synaptic release and conduction abilities of such axons. In the lack of intra‐axonal recording techniques we have used extracellular excitability testing as an indirect measure of the after‐potentials. We recorded from individual CA3 soma in hippocampal slices and activated the axon with a range of stimulus intensities. When conditioning and test stimuli were given to the same site the excitability changes were partly masked by local effects of the stimulating electrode at intervals < 5 ms. Therefore, we elicited the conditioning action potential from one axonal branch and tested the excitability of another branch. We found that a single action potential reduced the axonal excitability for 15 ms followed by an increased excitability for ∼200 ms at 24°C. Using field recordings of axonal action potentials we show that raising the temperature to 34°C reduced the magnitude and duration of the initial depression. However, the duration of the increased excitability was very similar (time constant 135 ± 20 ms) at 24 and 34°C, and with 2.0 and 0.5 mm Ca2+ in the bath. At stimulus rates > 1 Hz, a condition that activates a hyperpolarization‐activated current (Ih) in these axons, the decay was faster than at lower stimulation rates. This effect was reduced by the Ih blocker ZD7288. These data suggest that the decay time course of the action potential‐induced hyperexcitability is determined by the membrane time constant.
Single‐shock LTD by local dendritic spikes in pyramidal neurons of mouse visual cortex
Authors: Holthoff Knut , Kovalchuk Yury , Yuste Rafael , Konnerth Arthur
Published: August 2004

Mammalian dendrites are active structures, capable of regenerative electrical activity. Dendritic spikes can mediate synaptic plasticity and could enrich the computational properties of neurons. Besides sodium‐based action potentials, which can propagate throughout the dendritic tree, neocortical pyramidal neurons also sustain dendritic spikes that are spatially restricted. The function of these ‘local’ dendritic spikes is unknown. We show that local spikes, which require activation of N‐methyl‐d‐aspartate receptors (NMDARs), induce long‐term synaptic depression (LTD) in layer 5 pyramidal neurons. This depression does not require somatic spiking and is input specific. Moreover, a single synaptic stimulus can evoke a dendritic spike and a brief local dendritic calcium transient, and is sufficient for the full induction of LTD.
High field-emission current of carbon nanotubes grown on TiN-coated Ta substrate for electron emitters in a microwave power amplifier
Authors: Han Jae-Hee , Lee Tae Young , Kim Do Yoon , Yoo Ji-Beom , Park Chong-Yun , Choi Jin Ju , Jung Taewon , Han In Taek , Jung J. E. , Kim J. M.
Published: August 2004

For field emitters as an electron source of traveling wave tube microwave power amplifiers, field-emission properties of multiwalled carbon nanotubes (MWNTs) grown in situ onto an electrically conducting substrate were systematically characterized. MWNTs grown on a TiN-coated Ta substrate with NH3 plasma pre-treatment exhibited the best field-emission property. The maximum current density and corresponding total emission current were 9.4 mA/cm2 and ∼5 mA at 18.8 V/μm, respectively. These enhanced field-emission properties are caused by the highly conducting buffer layer (TiN), the optimum metal substrate (Ta) that produces high field-emission current, and the control of site density of MWNTs by NH3 plasma pre-etching. Details on the correlation between the field-emission properties and the morphological parameters will be discussed.
Emission characteristics of NbC/Nb field emitters
Authors: Charbonnier F. M. , Southall L. A. , Mackie W. A.
Published: August 2004

For several years we have searched for emitter materials that are capable of high currents and are environmentally tolerant. Our studies have focused on the refractory carbides of transitions metals. We have reported promising results with HfC and ZrC at several International Vacuum Microelectronics Conference (IVMC) conferences. Then we reported at the two previous IVMCs, on studies of gated arrays with individually addressable emitters made of niobium carbide, other transition metal carbides, and platinum. Here we report on an extensive study of the emission characteristics (noise and stability) of individual NbC/Nb field emitters at currents of about 1 μA and at residual pressures ranging from 2×10−9 to 2×10−5 Torr, for five different residual gases (H2, CO, CH4, Ar, and Xe). We conclude that flicker noise amplitude at ∼10 Hz increases slowly with residual pressure, according to an empirical formula: μ(p)=μ0(p/p0)n with n≅0.2–0.3. For our studies of medium term stability, for given residual gas and pressure, we record about 30 consecutive I(V) characteristics and plot the corresponding points on a Fowler–Nordheim slope–intercept chart. We have developed different analytical expressions for slope and intercept for smooth emitters and for emitters with sharp protrusions. Analysis of slope–intercept charts leads to several conclusions, particularly that emission is dominated by small, sharp nano protrusions that are relatively unstable. Future plans include testing various tip conditioning techniques to improve stability.
Electron-beam induced initial growth of platinum films using Pt(PF3)4
Authors: Wang S. , Sun Y.-M. , Wang Q. , White J. M.
Published: August 2004

Using an organometallic precursor, tetrakis(trifluorophosphine)platinum [Pt(PF3)4], electron-beam induced deposition of Pt thin films on a Cr-coated Si(100) substrate was investigated. Based on Auger electron spectroscopy, the Pt content reached 60 at. % for a 3 kV e-beam flux of 2.1×10−2 A cm−2, a precursor pressure of 2×10−5 Torr, and a substrate temperature of 80 °C. As the flux ratio (e-beam/precursor) increased above the optimized value of 10, the rate shifted from control by the e-beam flux to the precursor flux. The phosphorus content was reduced by adding O2.
Etching characteristics of platinum in inductively coupled plasma using Cl2/CO
Authors: Kim Jin Hong , Kim Ki Woong , Woo Seong Ihl
Published: August 2004

The effects of process parameters on etching properties were investigated for inductively coupled plasma etching of platinum with Cl2/CO mixed gas. The etch rates and selectivities of Pt against SiO2 depended significantly on the Cl2 concentration as the substrate temperature was raised. The volatile effect where the etch rates of Pt increase considerably above about 210 °C was not observed. The influence of O2 addition to a Cl2/CO gas mixture on the etch profile of patterned Pt films was evaluated. It was shown that the etch slope of patterned Pt was increased by enhancing the selectivity of Pt to the mask oxide. X-ray photoelectron spectroscopy and scanning electron microscope studies of the Pt surface etched partially with and without oxygen in a Cl2/CO gas mixture indicated that the etch slope may be increased by a reduction in the etch residues on Pt and by an enhancement in the selectivity of Pt against mask oxide. In the case of the addition of O2 at the substrate temperature lower than 120 °C, the fence polymer was observed at the patterned sidewall, but disappeared as the substrate temperature increased to 180 °C.
High-brightness GaN-based light-emitting diode with indium tin oxide based transparent ohmic contact
Authors: Kim Soo Young , Jang Ho Won , Lee Jong-Lam
Published: August 2004

We have fabricated GaN-based light-emitting diodes (LEDs) using Ni/Au with indium tin oxide (ITO) overlayer as a p-electrode. A Ni (20 Å)/Au (30 Å)/ITO (600 Å) contact with pre-annealing at 500 °C under an O2 ambient before ITO deposition (O-annealed contact) showed lower contact resistivity compared to the contact with pre-annealing under a N2 ambient (N-annealed contact) and without the pre-annealing (nonannealed contact). The pre-annealing under the O2 ambient produced NiO, which acted as the diffusion barrier for out-diffusion of N and Ga atoms and in-diffusion of In during the subsequent postannealing. Thus, the formation of a Au–In solid solution was effectively suppressed, resulting in the decrease of contact resistivity and enhancement in thermal stability. The LED with the O-annealed contact as a p-electrode showed lower operation voltage at 20 mA, better thermal stability, and enhanced light output than the LED with the N-annealed or nonannealed contact. The low operation voltage and better thermal stability originated from the low contact resistivity and low sheet resistance of ITO. The refractive index of ITO is between GaN and air, reducing the total reflection at the interface of GaN, thus enhancing the light output.
Structural characterization of nanocomposite Ti–Si–N coatings prepared by pulsed dc plasma-enhanced chemical vapor deposition
Authors: Ma Shengli , Ma Dayan , Xu Kewei , Jie Wanqi
Published: August 2004

Ti–Si–N coatings have been investigated widely in recent years due to their unique nanocomposite microstructure and attractive properties of superhardness, fairly good oxidation-resistance nearly to 1000 °C, etc. In this study, Ti–Si–N coatings have been prepared by pulsed dc plasma-enhanced chemical vapor deposition in an industrial-scale chamber. Structural characterization of Ti–Si–N coatings was examined by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron micrograph, and transmission electron microscopy. The results show that: (1) The microstructure of Ti–Si–N coatings varies significantly with the processing parameters, (2) the microstructure can be confirmed as nanocomposite Ti–Si–N where nanocrystalline TiN and/or TiSi2 particles are embedded into an amorphous matrix of Si3N4, and (3) the nanocrystals have a multioriented microstructure. However, the silicon content in Ti–Si–N coatings and coating thickness as well as crystalline size all increase when the inlet gas ratio of X=[SiCl4/(TiCl4+SiCl4)]% increases. Whereas the microhardness of the coatings first increases with increased Si content, microhardness reaches a maximum value of about Hv5800 at 13 at. % Si and then decreases slightly.
Quantitative analysis of deuterium and tritium in erbium hydride films of neutron tube targets
Authors: Bach H. T. , Steinkruger F. J. , Chamberlin W. S. , Walthers C. R.
Published: August 2004

An apparatus for measuring the deuterium and tritium in erbium hydride films on neutron tube targets has been designed, constructed, and tested at the Tritium Science and Fabrication Facility at Los Alamos National Laboratory. The apparatus consists of a pumped thermal desorption inlet system (TDIS) and a high-resolution mass spectrometer (HRMS). The pumped TDIS has a unique capability to perform complete and rapid thermal desorption of gases from the erbium hydride film and pressure–volume–temperature measurement for accurate quantification of the total moles of released gas. The HRMS measures the partial pressures of the hydrogen isotopes in the released gas. From these two measurements, we can determine the total moles of each hydrogen isotope in erbium hydride films accurately. The optimum desorption time is 2 to 3 minutes; the optimum desorption temperature is 900 °C. Under these conditions, 99.98% of the total moles of deuterium in the hydride films of deuterated erbium (ErD2) targets are released in a single desorption step. The molar atomic ratios of total hydrogen isotopes to erbium (HDT/Er), deuterium to erbium (D/Er), and tritium to erbium (T/Er) of deuterated and tritiated erbium (ErDxT2−x) targets are measured with better than 2% precision.
Comparison of a new photoresist (DiaPlate 133) with SU-8 using both x-ray and ion beam lithographies
Authors: Gonin Yvan , Munnik Frans , Benninger Frédéric , Dias Francisco , Mikhaı̈lov Sergueı̈
Published: August 2004

We describe essentially the lithography performed on a new photoresist, called DiaPlate 133. This negative resin has been structured by an x-ray beam produced by a new high brightness synchrotron light source, the Swiss Light Source (SLS) located at Villigen, near Zurich, during a 8 h-run and compared with another well-known resin, SU-8. Then the resins have been structured with ions at CAFI and both techniques are compared. Results and comments are presented underneath. It can be noted that the x-ray and ion beam lithography tests we performed with DiaPlate 133 were the first ones ever realized.
Resist-pattern transformation studied by x-ray photoelectron spectroscopy after exposure to reactive plasmas. I. Methodology and examples
Authors: Pargon E. , Joubert O. , Posseme N. , Vallier L.
Published: August 2004

We have used x-ray photoelectron spectroscopy (XPS) to investigate the resist patterns’ transformation after exposure to reactive plasmas and we have correlated the resist modifications with the process performance obtained by scanning electron microscope (SEM) observations. The experimental procedure based on the chemical-topography analysis of resist patterns using XPS has been used to determine the chemical composition and thickness of the reactive layers that are formed both on the tops and sidewalls of the resist features during the plasma process. This method was then applied to a variety of processes used in integrated-circuit fabrication. For all the processes analyzed [resist-trimming process in high-density plasma, bottom-antireflective-coating (BARC) opening process in a medium-density plasma and thin SiO2 hard-mask-opening processes in both plasma sources], we have observed very good correlations between XPS results and the evolution of the resist-patterns’ dimensions during plasma exposure. In this study we show that variations in resist-patterns dimension can be easily generated by reactive plasmas and that they may induce some drastic consequences on plasma processes involved in advanced complementary-metaloxide-semiconductor (CMOS) device fabrication.
Optimization of post-N2 treatment and undoped-Si-glass cap to improve metal wring delamination in deep submicron high-density plasma-fluorinated silica glass intermetal dielectric application
Authors: Cheng Yi-Lung , Wang Ying-Lang , Lan Jin-Kun , Wu Sze-Au , Chang Shih-Chieh , Lo Kuang-Yao , Feng Ming-Shiann
Published: August 2004

Integration issues of metal line delamination from fluorinated silica glass (FSG) in deep submicron intermetal dielectric applications were investigated in this study. A metal line peeled off after a nonoptimized in situ deposition of undoped-silicon-glass (USG; SiO2) capping layer followed the post-FSG-chemical mechanical polishing N2 treatment. It was found that higher bias power and longer process time of N2 treatment led to more active fluorine species diffusing from the FSG films to the USG surface, which might react with subsequent Ti/TiN/W metal layer and result in metal delamination. Using plasma-enhanced N2 treatment and ex situ USG capping with lower initial deposition temperature by extra cooling step, the stability of the FSG films was improved and resulted in a robust structure without metal peeling.
Single step electron-beam lithography for asymmetric recess and gamma gate in high electron mobility transistor fabrication
Authors: Lin Cheng Kuo , Wang Wen-Kai , Hwu Ming-Jyh , Chan Yi-Jen
Published: August 2004

We have developed an asymmetric recess etch in conjunction with a gamma metal gate process for the fabrication of high electron mobility transistors (HEMTs). This process is based on direct electron-beam lithography with a single exposure of a three stack poly(dimethylglutarimide) and poly(methylmethacrylate) photoresists. It can modify the voltage drop over a wider region fabricated by the so called wide-recess technique as compared with the conventional approach, while maintaining a low source resistance, to reduce the electric field intensity at the gate edge, and therefore enhance the breakdown voltage. This gate engineering process for the 0.2 μm InAlAs/InGaAs metamorphic HEMTs achieved a 45% off-state breakdown voltage improvement as compared with the traditional bilayer T-gate device.
Topographic and kinetic effects of the SF6/O2 rate during a cryogenic etching process of silicon
Authors: Marcos G. , Rhallabi A. , Ranson P.
Published: August 2004

In order to fabricate the structures with high aspect ratio (depth/width), it is necessary to develop plasma etching processes with a very accurate feature control and improvements in etching rates. We have developed an etching simulator which takes into account the main plasma–surface interactions in a SF6/O2 plasma etching on silicon substrate process. In this article, the role of oxygen on final trench topography and etching rate evolution is discussed. The presented results show that the notion of balance between the passivation regime and the etching processes has great consequences in topographic and kinetic trench characteristics. In particular, a good correlation has been established between the roughness on the trench sidewalls and zones of underpassivation.
Si diffusion in p-GaN
Authors: Pan C. J. , Chi G. C. , Pong B. J. , Sheu J. K. , Chen J. Y.
Published: August 2004

The characteristics of p-type Mg-doped GaN films diffused with Si are studied. N-type conductivity is achieved, and the carrier mobility of diffused GaN is 90–150 cm2 V−1 s−1, higher than that of p-GaN but less than that of epitaxially grown n-GaN. The Mg acceptor states could become deep compensating defects, and the compensation ratio NA/ND is 0.3, 0.45, 0.6, and 0.75 for 800, 900, 1000, and 1100 °C diffused GaN, respectively. The carrier transport may be dominated by electron hopping through these deep compensating centers or through diffusion. The results of temperature-dependent carrier concentration indicate that thermal annealing may induce defects at the surface, leading to an additional activation energy Ed∼10 meV in the 200–500 K region in diffused GaN.
Etch rate and surface morphology control in photoelectrochemical etching of GaN
Authors: Yang Bo , Fay Patrick
Published: August 2004

The dependence of the etch rate and etch morphology on photoelectrochemical (PEC) process conditions is reported. Considerable control over the etch rate and surface roughness can be exerted through selection of the electrolyte concentration, illumination intensity, as well as through the use of bias voltage applied during the PEC etch process. The etch rate for n-type GaN was dramatically enhanced from 10 to 32 nm/min by the application of +2 V bias during PEC etching. In addition, the surface morphology can be controlled by applying a bias voltage; smooth etched surfaces with root-mean-square (rms) roughness of 0.5 nm have been obtained with bias of +0.65 V, comparable to as-grown surfaces, compared to a rms roughness of 8 nm when no bias is applied. The use of reverse bias voltages was found to suppress PEC etching and produce rough surfaces. The etch rate and morphology have been found to depend on the n-type GaN doping density, with highly doped material resulting in slower etch rates and rougher surfaces than for lightly doped material under the same etch conditions.
Laser annealing of silicon nanocrystal films prepared by pulsed-laser deposition
Authors: Chen X. Y. , Lu Y. F. , Wu Y. H. , Cho B. J. , Yang B. J. , Liew T. Y. F.
Published: August 2004

We studied the laser annealing effects on the structures and properties of silicon (Si) nanocrystal films fabricated by pulsed-laser deposition in inert argon gas. The as-deposited samples show large particles (i.e., droplets) with size ranging from ∼100 nm to several μm on a uniform background film. The strong photoluminescence (PL) was from the background film rather than from the crystalline droplets. The consistency of the PL and crystal size from the background film supports the quantum confinement effect theory. After KrF excimer laser annealing, nanoparticles (NPs) with sizes of 10–50 nm were formed in the as-deposited films. In the vicinity of the droplets, the NPs were aligned together to form incident-light-angle-dependent cylindrical ripples which were caused by the interference of the incident light and the surface-scattered waves. The threshold fluence of surface melting was also reduced due to the interference. The intensity enhancement and blueshift of PL, the correlation between the indirect transition in optical absorption, and the bonding information in infrared spectra, further reveal the oxidation and ablation during the laser annealing process.
In situ nanoscale observation and control of electron-beam-induced cluster formation
Authors: Adelung R. , Ernst F. , Zheng N. , Landau U.
Published: August 2004

We have developed a method for controlled generation and in situ observation of nanoscopic metal clusters (Cu) on solid substrates: high-energy electron irradiation of weakly bonded salts (CuCl2). Employing the primary electron beam of a scanning electron microscope as a metal-generating probe, we can initiate, observe, and control the nucleation and further evolution of Cu clusters on a substrate covered with a layer of solid CuCl2. Agglomerates of metal clusters with lateral dimensions below 10 nm can be “written” by this method, e.g., to carry out diffusion experiments. Using this method, we have found strong evidence for the existence of a growth mechanism of metal particles that has not been described before in the literature: incorporation of metal atoms at the metal–substrate interface.
Carbon nanotube networks: Nanomaterial for macroelectronic applications
Authors: Snow E. S. , Novak J. P. , Lay M. D. , Houser E. H. , Perkins F. K. , Campbell P. M.
Published: August 2004

We describe the properties and potential applications of an electronic material that consists of an interconnected random network of single-walled carbon nanotubes. This material possesses useful electronic properties, and it can be patterned into devices with high yield using conventional microfabrication technology. One unique aspect of this material is that every atom is a surface atom. For this reason nanotube networks form an ideal electronic material to utilize interface phenomena to engineer its properties for specific applications. We discuss two such applications: chemical sensing and macroelectronics.
Characterization of metalorganic chemical vapor deposition growth of cubic GaN by in situ x-ray diffraction
Authors: Schmidegg Klaus , Kharchenko Alexander , Bonanni Alberta , Sitter Helmut , Bethke Johannes , Lischka Klaus
Published: August 2004

X-ray diffraction is used for the in situ characterization of the growth of cubic GaN by metalorganic chemical vapor deposition. Our setup permits the simultaneous measurement of a wide angular range and requires neither goniometer nor exact sample positioning. Time-resolved measurements during growth give access to film thickness and growth rate as well as information on the chemical composition of ternary compounds. Additionally, the relaxation of the crystal lattice during heteroepitaxial growth of GaN on AlGaN can be measured directly.
Atomic resolution scanning tunneling microscope study of single-walled carbon nanotubes on GaAs(110)
Authors: Ruppalt L. B. , Albrecht P. M. , Lyding J. W.
Published: August 2004

We have studied single-walled carbon nanotubes (SWNTs) on the cleaved GaAs(110) surface using an ultrahigh vacuum (UHV) scanning tunneling microscope (STM). SWNTs were deposited via an in situ UHV dry contact transfer (DCT) procedure and subsequent STM images provide simultaneous resolution of the nanotube chirality and substrate lattice. Room temperature scanning tunneling spectroscopy measurements reveal semiconducting nanotube features within the substrate band gap indicative of a transport mechanism other than direct tip to substrate tunneling. Nanotube gaps scale appropriately and are found to be in reasonable agreement with theoretical values. SWNTs were transferred to the GaAs surface with minimal additional contamination and no indication of damage to either nanotube or substrate, recommending the DCT technique as a general deposition procedure for a variety of systems incompatible with ambient processing.
Power loss measurements in quasi-1D and quasi-2D systems in an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterostructure
Authors: Prasad C. , Ferry D. K. , Wieder H. H.
Published: August 2004

We have carried out Joule heating measurements on three etched quantum wires (QWRs) of various widths and 2D electron gases (2DEGs) over temperatures ranging from 0.035 K to 20 K. The devices are fabricated in an InAlAs/InGaAs/InAlAs heterostructure with a 25 nm wide In0.53Ga0.47As quantum well region, grown on a lattice matched InP substrate. Comparison of the Shubnikov–de Haas oscillations (SdHO) in the wires and 2DEGs and the phase-breaking time (from conductance fluctuations) in the narrowest wire are used to extract the temperature dependence of the power loss per electron.
Treatment of interface roughness in SOI-MESFETs
Authors: Khan T. , Vasileska D. , Thornton T. J.
Published: August 2004

We have investigated the effect of interface roughness on the operation of n-channel SOI MESFET device structure. Due to the presence of a rough interface between the buried oxide and the silicon layer, interface roughness scattering limits the velocity of the carriers at high transverse fields. Following Fischetti and Laux, we model interface roughness as a real space scattering event, separated into specular and diffusive (isotropic) type of reflection from an ideal interface. This model gives rise to low field silicon electron mobility in agreement with available experimental values. To examine the performance improvement of SOI devices, we have simulated analogous SOI MESFET and MOSFET device structures. The results of these investigations suggest that the mobility of the MOSFET device follows the experimental values and the mobility of the MESFET is five to ten times higher than that of the MOSFET in the subthreshold and the on-state regime.
Interface recombination velocity measurement by a contactless microwave technique
Authors: Ahrenkiel R. K. , Dashdorj J.
Published: August 2004

The interface or surface recombination velocity (SRV) is a critical and important parameter in many applications. In this work, we have developed and applied a contactless microwave technique, which in combination with a continuously tunable pulsed light source, is able to probe the excess carrier lifetime in the surface and bulk regions of a semiconductor wafer. The technique is called resonant coupled photoconductive decay and has been described by the authors in the literature. For strongly absorbed light, the initial (t=0) decay time is a strong function of the absorption coefficient α, as well as the bulk lifetime. The effective bulk lifetime is measured by using very weakly absorbed light, or by measuring the asymptotic decay rate of strongly absorbed light. For asymmetric surfaces (such as a wafer polished on one surface only), the measurement with strongly absorbed light is made at both wafer surfaces. We have developed a method to measure SRV independently of bulk lifetime by plotting the surface lifetime data versus the absorption coefficient of the incident light pulse. A number of measurements of silicon wafers, with a variety of surface conditions, will be described.
Experimental determination of valence band maxima for SrTiO3, TiO2, and SrO and the associated valence band offsets with Si(001)
Authors: Chambers S. A. , Droubay T. , Kaspar T. C. , Gutowski M.
Published: August 2004

We address the issue of accurate determination of the valence band maximum (VBM) for SrTiO3(001) single crystals and epitaxial films, as well as TiO2(001) anatase and SrO epitaxial films. These measurements are of critical importance in determining valence band offsets in heterojunctions of these oxides with Si. Three different methods are analyzed: (1) fitting a Gaussian broadened theoretical density of states to the x-ray photoelectron valence band spectrum; (2) finding the intersection of a regression line that spans the linear portion of the x-ray photoelectron valence band leading edge with the background between the valence band maximum and the Fermi level; and (3) determining the energy at which high-resolution ultraviolet photoemission intensity at the leading edge goes to zero. We find that method 1 yields physically unreasonable results when used in conjunction with density functional theory because the latter does not predict the detailed shape of the valence bands in these oxides with sufficient accuracy. In contrast, methods 2 and 3 give physically reasonable results that are in good mutual agreement. The difference in VBM between method 1 and methods 2 and 3 is 0.4–0.6 eV, depending on the oxide. Methods 2 and 3 yield the most reliable VBM, provided the experiments are carried out with adequate energy resolution.
Roles of nitrogen incorporation in HfAlOx(N) gate dielectrics for suppression of boron penetration
Authors: Nabatame Toshihide , Iwamoto Kunihiko , Yamamoto Katsuhiko , Tominaga Koji , Hisamatsu Hirokazu , Ohno Morifumi , Akiyama Koji , Ikeda Minoru , Nishimura Tomoaki , Ota Hiroyuki , Horikawa Tsuyoshi , Toriumi Akira
Published: August 2004

We have investigated impacts of nitrogen incorporation into HfAlOx films on the gate leakage currents and the flat band voltage VFB shifts. Also, a role of O–Hf–N bonding states in HfAlOx(N) in suppression of boron penetration is discussed. The nitrogen concentration CN in HfAlOx(N) was controlled by changing the NH3 annealing temperature at the step of the layer-by-layer deposition and annealing process as well as the O2 annealing temperature of post-deposition annealing. The CN over 10 at. % in HfAlOx(N) films effectively suppressed boron penetration as revealed by very slow diffusion in Hf3N4 films and the formation of boron-nitrogen remote complex in HfOx(N), preserved the amorphous structure and reduced the VFB shift compared to the case of HfAlOx without nitrogen incorporation, while CN exceeding 13 at. % led to a significant increase of the gate leakage current. This suggests the excess O–Hf–N bond formation enhanced the leakage current.
Structural and magnetic properties of epitaxial Fe3Si/GaAs(001) hybrid structures
Authors: Herfort J. , Schönherr H.-P. , Friedland K.-J. , Ploog K. H.
Published: August 2004

The structural, electrical, and magnetic properties of Fe3Si/GaAs(001) hybrid structures with high crystalline and interfacial perfection are studied. The Fe3Si/GaAs(001) hybrid structures are fabricated by molecular beam epitaxy at 200 °C. The composition of the films, which can be regarded as a Heusler alloy, is tuned over a wide range of Si content. The high crystalline and interfacial perfection is correlated with the stable Fe3Si phase. The resistivity of the films shows a strong minimum at almost exact stoichiometry which can be explained by the perfection of the ordering of the Si atoms within the Fe3Si phase. The layers are ferromagnetic at room temperature with saturation magnetization values close to bulk Fe3Si. The layers show very small coercive fields which again is correlated with high crystalline and interfacial perfection of the layers within the Fe3Si phase.
Initial oxide/SiC interface formation on C-terminated β-SiC(100) c(2×2) and graphitic C-rich β-SiC(100) 1×1 surfaces
Authors: Silly M. G. , Roy J. , Enriquez H. , Soukiassian P. , Crotti C. , Fontana S. , Perfetti P.
Published: August 2004

We investigate the initial interface formation of oxide/C-terminated β-SiC(100) c(2×2) and oxide/C-rich β-SiC(100) 1×1 surfaces by Si 2p and C 1s core level photoemission spectroscopy using synchrotron radiation. Contrary to the Si-rich SiC surfaces, the C-terminated and C-rich surfaces are much less reactive to oxygen, with much higher exposures and temperatures required to grow a significant amount of oxides. This leads to nonabrupt oxide/SiC interface formation including predominantly mixed oxide products containing carbon species, with marginal amounts of SiO2 only. The lack of dangling bonds on the surface together with the C plane and/or graphitic species limiting oxygen insertion into the SiC lattice are likely at the origin of this very different behavior when compared to Si-rich SiC surfaces.
Nanoscale two-dimensional patterning on Si(001) by large-area interferometric lithography and anisotropic wet etching
Authors: Lee S. C. , Brueck S. R. J.
Published: August 2004

A fabrication technique for nanoscale two-dimensional (2D) patterning by large-area interferometric lithography (IL) and anisotropic wet etching (AWE) is reported. On a Si(001) substrate corrugated by one-dimensional (1D) periodic V-grooves in a first IL/AWE step, an additional 1D IL/AWE patterning perpendicular to the groove direction is performed. In this process, {111} facets—the sidewalls of a V-groove having an extremely low etch rate in AWE—are utilized as an etch barrier to confine AWE to a nanoscale-wide (001) stripe facet between V-grooves. IL on the corrugated Si surface results in an array of photoresist (PR) lines localized on each (001) stripe. The subsequent AWE with a Cr etch mask fabricated from this unusual PR pattern thus begins from the inner side of (001) stripe but slows down as it reaches the (001)-{111} facet intersection of the V-groove. The {111} planes at each facet intersection play the important role of an etch barrier laterally confining the etch area within each (001) stripe. The direction along the stripe is also confined with the formation of 2D {111} inverted pyramids. A 355 nm period, 2D array of Si mesas having a rectangular top (001) facet of area ∼150 nm×110 nm and surrounded by various (111) facets in a unit period is fabricated on a Si(001) substrate.
Nanoimprint lithography in the cyclic olefin copolymer, Topas®, a highly ultraviolet-transparent and chemically resistant thermoplast
Authors: Nielsen T. , Nilsson D. , Bundgaard F. , Shi P. , Szabo P. , Geschke O. , Kristensen A.
Published: August 2004

Thermal nanoimprint lithography (NIL) of the cyclic olefin copolymeric thermoplast Topas® is demonstrated. Topas® is highly UV-transparent, has low water absorption, and is chemically resistant to hydrolysis, acids and organic polar solvents which makes it suitable for lab-on-a-chip applications. In particular, Topas® is suitable for micro systems made for optical bio-detection since waveguides for UV-light can be made directly in Topas®. In this article full process sequences for spin coating Topas® onto 4 in. silicon wafers, NIL silicon stamp fabrication with micro and nanometer sized features, and the NIL process parameters are presented. The rheological properties of Topas® are measured and the zero shear rate viscosity is found to be 2.16×104 Pa s at 170 °C and 3.6×103 Pa s at 200 °C while the dominant relaxation time is found to be 4.4 s and 0.9 s, respectively. The etch resistance of Topas® to two different reactive ion etch processes, an oxygen plasma, and an anisotropic silicon etch, is found to be 12.6 nm/s and 0.7 nm/s, respectively. The etch rates are compared to the similar etch rates of 950 k PMMA, cross-linked SU-8, and standard AZ5214E photoresist. Finally, UV-lithography (UVL) followed by metal deposition and lift-off on top of a Topas® film patterned by NIL is demonstrated. This exploits the chemical resistance of Topas® to sodium hydroxide and acetone. The demonstrated UVL and lift-off on top of an imprinted Topas® film opens new possibilities for post-NIL processing.
Real-time characterization of GaSb homo- and heteroepitaxy
Authors: Kim S. , Flock K. L. , Asar M. , Kim I. K. , Aspnes D. E.
Published: August 2004

We examine the homo- and heteroepitaxial growth of moderately thick (∼700 nm) layers of GaSb with the objectives of optimizing growth conditions and determining the initial phase of heteroepitaxy on (001)GaAs. Real-time spectroscopic ellipsometry (RTSE) data show that the (001)GaSb surface degrades immediately in excess trimethylgallium (TMG), but both (001)GaSb and As-terminated (001)GaAs surfaces are stable in trimethylantimony (TMSb). The surface-dimer contribution to the optical-anisotropy (OA) signal of (001)GaSb is small and generally masked by structural (roughness) effects, hence it is not useful for determining surface stoichometry. However, we show that laser light scattering (LLS) data do allow the V/III ratio to be fine-tuned during growth to minimize macroscopic roughness. TEM micrographs show that our GaSb/GaAs heterointerface is relatively defect-free except for the necessary local accommodation of lattice mismatch. The initial phase of heteroepitaxy on (001)GaAs occurs here as a coexistence of separate regions of GaAs and GaSb.
X-ray absorption spectra for transition metal high-κ dielectrics: Final state differences for intra- and inter-atomic transitions
Authors: Lucovsky G. , Hong J. G. , Fulton C. C. , Zou Y. , Nemanich R. J. , Ade H.
Published: August 2004

This article applies x-ray absorption spectroscopy to a study of the electronic structure of the high-k gate dielectrics, TiO2, ZrO2, and HfO2. Qualitative and quantitative differences are identified between intra-atomic transitions such as the Zr 3p-state, M2,3 core state absorptions which terminate in TM 4d*- and 5s*-states, and inter-atomic transitions such as the Zr 1s- and O 1s-state K1 absorptions which terminate in Zr 4d*- and 5s*-states that are mixed with O atom 2p* states through nearest neighbor bonding interactions. Differences between the spectral peak energies of the lowest d*-features in the O K1 spectra are demonstrated to scale with optical band gap differences for TiO2, ZrO2, and HfO2, providing important information relevant to applications of TM oxides as high-κ gate dielectrics in advanced Si devices. This is demonstrated through additional scaling relationships between (i) conduction band offset energies between Si and the respective dielectrics, and the optical band gaps, and (ii) the conduction band offset energies, and the electron tunneling masses as well.
Planar InAs growth on GaAs(001) and subsequent quantum dot formation by a surface induced morphological instability
Authors: Eyink K. G. , Mahalingam K. , Pitz J. , Smith H. , Grazulis L.
Published: August 2004

InAs growth on GaAs has been studied extensively and most recently for the self-assembly of quantum dots on the surface. In this work, we have studied the growth conditions to form planar InAs, at an In beam-equivalent pressure of 3.1×10−8 Torr, under the metal rich (4×2) reconstruction and the subsequent formation of quantum dots (QDs) condensed from this layer by a rapid change in the As4 pressure. Atomic force microscopy (AFM) studied the surface morphology of InAs resulting from a nominal 12 ML growth with various As4 growth pressures while maintaining a metal rich condition. It was found that the surface roughness was dependent on the As4 pressure. At the higher As4 pressures studied, the growth was extremely rough and much smoother at the lower As4 pressures. For a beam-equivalent pressure of 1×10−7 Torr for As4 and 3.1×10−8 Torr for In, growth was seen to remain planar for a deposition thickness up to 3 ML. AFM analysis showed that a fingered morphology was formed with a roughness of ∼1 ML. When the As4 pressure incident on this surface was quickly changed, the reflection high-energy electron diffraction showed this surface roughened. Subsequent AFM analysis showed that QDs formed in long chains oriented down the [110]. We propose a model in which the fingered surface is segmented due to an underlying dislocation array in the formation of the chained QDs.
Indium nitride: Evidence of electron accumulation
Authors: Veal T. D. , Mahboob I. , Piper L. F. J. , McConville C. F. , Lu Hai , Schaff W. J.
Published: August 2004

The electronic properties of clean InN(0001) surfaces have been investigated by high-resolution electron-energy-loss spectroscopy of the conduction band electron plasmon excitations and valence band x-ray photoemission spectroscopy. An intrinsic surface electron accumulation layer is found to exist, with the associated downward band bending occurring to neutralize charged donor-type surface states. Semiclassical dielectric theory simulations of the energy-loss spectra and charge profile calculations indicate a surface state density of 2.5(±0.2)×1013 cm−2 and a surface Fermi level of 1.64±0.10 eV above the valence band maximum and 0.89±0.10 eV above the conduction band minimum. This location of the surface Fermi level is in agreement with the valence band photoemission spectra. These observations are compared with recent evidence of electron accumulation at InN surfaces provided by capacitance–voltage profiling, Hall measurements, and synchrotron-radiation photoemission spectroscopy.
Electron-beam evaporated cobalt films on molecular beam epitaxy prepared GaAs(001)
Authors: Ding Z. , Thibado P. M. , Awo-Affouda C. , LaBella V. P.
Published: August 2004

We have deposited Co films on the GaAs(001) surface by using an e-beam evaporation method. The thicknesses of the Co films are measured by using x-ray reflectivity and Rutherford backscattering. The magnetic properties of the films have been measured using superconducting quantum interference device. The magnetization of the films was found to decrease with increasing film thickness. The slight degradation of magnetic properties is attributed to increasing roughness on the Co surface or the Co/GaAs interface during the Co deposition.