Search

We present the design and vacuum performance of a compact room-temperature trapped ion system for quantum computing, consisting of a ultra-high vacuum (UHV) package, a micro-fabricated surface trap and a small form-factor ion pump. The system is designed to maximize mechanical stability and robustness by minimizing the system size and weight. The internal volume of the UHV package is only 2 cm$^3$, a significant reduction in comparison with conventional vacuum chambers used in trapped ion experiments. We demonstrate trapping of $^{174}$Yb$^+$ ions in this system and characterize the vacuum level in the UHV package by monitoring both the rates of ion hopping in a double-well potential and ion chain reordering events. The calculated pressure in this vacuum package is about 1.5e-11 Torr, which is sufficient for the majority of current trapped ion experiments.

Recently, layered materials have been extensively studied and attracted unprecedented attention. Layered oxides with superior properties have potential applications for nanoscale devices. Here, we report variable supercells in layered bismuth manganite controlled by oxygen pressure and reveal the strong piezoelectric responses from the layered supercells with tunable physical properties, including an approximately three-times difference in the magnetization range and 10% difference in the optical transmittance. The tunability of the sublattice from Bi3O3 to Bi2O2 in supercells is realized by a precise oxygen pressure control of 10 mTorr and 100 mTorr, respectively. The results presented here show a tantalizing opportunity to discover emerging multifunctional oxides for future nanoelectronics.

Gallium nitride (GaN) is a wide-bandgap semiconductor that is useful for optoelectronics and high speed and high power electronics. Fabrication of GaN devices requires etching for many processing steps. Gas phase thermal atomic-layer-controlled etching is desirable for damage-free isotropic etching. In this letter, the thermal atomic layer etching (ALE) of crystalline GaN was demonstrated using sequential exposures of XeF2 and BCl3. GaN ALE was achieved with an etch rate of 0.55 A/cycle at 195 °C using XeF2 exposures for 20 s at 40 mTorr and BCl3 exposures for 0.5 s at 50 mTorr. At the same reactant exposures, GaN etch rates varied with temperature from 0.18 A/cycle at 170 °C to 0.72 A/cycle at 300 °C. The GaN etch rates increased slowly with increasing XeF2 exposure. In addition, the GaN etch rate was self-limiting with respect to both increasing BCl3 pressures and BCl3 exposure times. This self-limiting behavior for BCl3 is consistent with a ligand-exchange mechanism for GaN ALE. Alternative fluorination reactants were also investigated including HF, SF4, and NF3 plasma. Sequential exposures of NF3 plasma and BCl3 yielded GaN etch rates of 2.5–2.9 A/cycle at 250 °C. In contrast, the HF and SF4 fluorination reactants could not etch crystalline GaN.

Absolute atomic hydrogen and methyl radical production resulting from direct electron impact dissociative excitation of CH4 has been measured in pulsed discharge by two-photon allowed laser induced fluorescence. For 20 Torr pure methane discharge with 480 ns pulse duration, 4–6 kV voltage applied, and 6–11.5 mJ input electrical energy yield of 10–22×1015 cm−3 hydrogen atoms, i.e., up to 4.5% dissociation of CH4 is achieved by direct electron impact with 50% energy conversion efficiency.

We report on the pulsed-laser ablation of aluminum in ambient pressure of nitrogen varying from 0.01 to 70 Torr using images of the expanding plasma plume. At pressures ⩾1 Torr plasma–gas interface showed severe distortion in the front of the expanding plume. The plasma expansion velocity showed oscillatory behavior with delay time beyond 260 ns and is attributed to Rayleigh–Taylor instability. The effect of background gas on inducing polarization in the ablated plasma is also reported. At low pressure of 0.1 Torr the degree of polarization of Al III transition 4s 2S1/2–4p 2P3/20 at 569.6 nm increased with delay time. At pressures ⩾1 Torr it showed an oscillatory behavior. The observed steep pressure gradient at the plasma–gas interface may result in strong self-generated magnetic field due to Rayleigh–Taylor instability.

Incorporating multiwall carbon nanotubes (CNTs) directly into the cylindrical cathode of Ni screen/BN/Ni microplasma devices significantly improves all device performance parameters—operating and ignition voltages, as well as radiative efficiency. Having a cathode diameter of 200 μm, these devices exhibit operating voltages as much as 30 V (∼22%) lower than those required for an identical structure without CNTs. For Ne pressures of 100–300 Torr, ignition voltages are reduced by 14%–18% with the introduction of CNTs. In contrast, radiative efficiencies in the 300–800 nm spectral region are increased with CNTs by 6%–9% over the entire pressure range studied (200–600 Torr Ne). Voltage–current characteristics for two device configurations suggest that electrons generated within the cathode microcavity by CNT field emission are most effective in impacting device performance.

The thermal stability of electrically conducting SrRuO3 thin films grown by pulsed-laser deposition on (001) SrTiO3 substrates has been investigated by atomic force microscopy and reflection high-energy electron diffraction (RHEED) under reducing conditions (25–800 °C in 10−7–10−2 Torr O2). The as-grown SrRuO3 epitaxial films exhibit atomically flat surfaces with single unit-cell steps, even after exposure to air at room temperature. The films remain stable at temperatures as high as 720 °C in moderate oxygen ambients (>1 mTorr), but higher temperature anneals at lower pressures result in the formation of islands and pits due to the decomposition of SrRuO3. Using in situ RHEED, a temperature and oxygen pressure stability map was determined, consistent with a thermally activated decomposition process having an activation energy of 88 kJ/mol. The results can be used to determine the proper conditions for growth of additional epitaxial oxide layers on high quality electrically conducting SrRuO3.

The power-coupling mode was changed from a capacitively coupled (E-mode) to an inductively coupled (H-mode) with an increase of rf input power in an immersed-coil-type inductively coupled Ar discharge at 1 mTorr. It was identified that the bimodal-shaped ion energy distribution (IED) of the capacitively coupled discharge was dominant below 100 W (E-mode), while the single peak due to the inductively coupled discharge became dominant above 250 W (H-mode). In addition, it was possible to quantitatively determine the relative amounts of capacitively and inductively coupled components at both modes, making the analysis of IED one of most effective methods to investigate the power-coupling mode transition in an inductively coupled plasma system.

Thin films of Ba(Zr0.15Ti0.85)O3 were crystallized in situ at several different oxygen background pressures and temperatures. The optimal temperature and pressure for obtaining films with smooth surface morphology and good electrical properties was found to be 675 °C and 300 mTorr, respectively. Films grown at this temperature were found to have a Pr of 3.31 μC/cm2 and an Ec of 93.5 kV/cm. Low field dielectric measurements and C-V measurements were performed in order to study the dielectric behavior of the films. A tunability of ∼45% was recorded on the films.

Polycrystalline silicon carbide (poly-SiC) thin films were grown in a large-volume, low pressure chemical vapor deposition furnace using dichlorosilane and acetylene precursors. The deposition temperature was fixed at 900 °C and the pressure was varied between 0.46 and 5 Torr. The residual stress of as-deposited SiC films ranged from highly tensile to moderately compressive as the deposition pressure was increased from 0.46 to 5 Torr, with tensile stress below 50 MPa in films deposited at around 2.5 Torr. Cantilever beams with no vertical deformation were fabricated from the low tensile stress films, and they indicated that the stress gradient was also very low in these films. X-ray diffraction analysis indicated that all the films were highly textured polycrystalline (111) 3C-SiC regardless of the residual stress. Transmission electron microscopy indicated that both the tensile and compressive films were columnar in microstructure, with slight differences in the axial alignment of the grains with respect...

Argon propellant is introduced from the upstream and downstream sides of a high power helicon plasma thruster. The plasma density profile and the imparted thrust are measured for various upstream and downstream argon flow rates, where the total gas flow rate of 70 sccm and the resultant vacuum chamber pressure of 0.2 mTorr are maintained. It is observed that the imparted thrust increases with an increase in the downstream gas flow rate; simultaneously an upstream-peaking profile of the plasma density observed for the upstream gas injection becomes uniform for the downstream gas injection. The difference in the thrust between the upstream and downstream gas injections is enhanced by increasing the rf power. The observed density profiles are qualitatively consistent with theoretical predictions taking a neutral depletion effect into account.

Ferroelectric BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/Si substrates in various oxygen pressures of 0.001–0.1 Torr at a temperature as low as 450 °C by pulsed-laser deposition. The crystallinity of the films was studied by x-ray diffraction. X-ray photoelectron spectroscopy showed that the films have a single phase of perovskite BiFeO3. The BiFeO3 thin films deposited at 0.01–0.1 Torr show good current-density–applied-voltage characteristics. It is obtained from polarization–electric-field characterization that 2Pr is about 71.3 μC/cm2 and 2Ec is 125 kV/cm. Stable current density and saturated ferroelectric hysteresis loop have been observed in BiFeO3 thin films.

Large-quantity (grams) one-dimensional ZnO nanowires of different sizes have been synthesized by a simple thermal evaporation of ZnO powder in a tube furnace at a temperature controlled to 1000–1200 °C and pressure to 1–2 Torr air. A mixture of ZnO and graphite powder was used as the source. Fine graphite flakes were used to promote the growth. The graphite flakes are the key for large-quantity yield and were easily removed by oxidation in flowing O2 at about 700 °C for 1–3 h. The scanning- and transmission-electron-microscopic studies show that the diameter and length of the nanowires vary from 20 to 100 nm and 0.5 to 10 μm, respectively. Room temperature photoluminescence studies found that the luminescent intensity depends on the processing conditions. A reduced band edge ultraviolet (380 nm) and deep-band green (520 nm) emission have been observed for these nanowires. Most importantly, the method can be extended to any other oxide nanowires that will be the building block of future nanoscale devices.

The effect of excitation frequency in the 13.56–60 MHz range on the electron energy distribution function (EDF) of capacitively coupled plasma is investigated. Under a fixed rf voltage (50–130 V peak-to-peak) and argon pressure (100 mTorr), a remarkable change in the EDF is observed: a Druyvesteyn type at low frequencies (≃13.56 MHz) evolves into a bi-Maxwellian type in a very high frequency (VHF) above 30 MHz. The transition frequency decreases with increasing the rf voltage. The observed frequency effect on the EDF is tentatively explained in terms of the transition of electron heating mode from the collisional ohmic heating at low frequencies into the plasma surface heating in the VHF range.

Natural-superlattice-structured ferroelectric thin films, Bi3TiNbO9–Bi4Ti3O12 (BTN–BIT), have been grown on Pt/TiO2/SiO2/Si and SrTiO3(001) single-crystal substrates by pulsed-laser deposition (PLD) using BTN–BIT (1 mol:1 mol) targets. BTN–BIT films show natural-superlattice peaks below 2θ=16° in x-ray diffraction patterns only when using an oxygen pressure of 0.05–0.07 Torr in the deposition. The c-axis lattice constant (8.300 nm) of BTN–BIT films suggests a natural superlattice structure consisting of iteration of two unit cells of Bi3TiNbO9 and one unit cell of Bi4Ti3O12. This 2–1 superlattice structure is different from that of BTN–BIT ceramics (2.909 nm), which is 1–1 superlattice. Natural-superlattice-structured BTN–BIT thin films having the 2–1 superlattice prepared at 550 °C exhibit superior ferroelectricity reflected by the value of 2Pr, which is 50 μC/cm2.

Strong nonuniformities of plasma production are expected in capacitive discharges if the excitation wavelength becomes comparable to the reactor size (standing-wave effect) and/or if the plasma skin depth becomes comparable to the plate separation (skin effect) [M. A. Lieberman et al., Plasma Sources Sci. Technol. 11, 283 (2002)]. Ion flux uniformity measurements were carried out in a large-area square (40 cm×40 cm) capacitive discharge driven at frequencies between 13.56 MHz and 81.36 MHz in argon gas at 150 mTorr. At 13.56 MHz, the ion flux was uniform to ±5%. At 60 MHz (and above) and at low rf power, the standing-wave effect was seen (maximum of the ion flux at the center), in good quantitative agreement with theory. At higher rf power, maxima of the ion flux were observed at the edges, due either to the skin effect or to other edge effects.

Friction and wear are major concerns in the performance and reliability of microelectromechanical systems (MEMS) devices employing sliding contacts. While many tribological coating materials are available, most traditional surface coating processes are unable to apply conformal coatings to the high aspect ratio (height/width) structures typical of MEMS devices. We demonstrate that thin, conformal, wear-resistant coatings can be applied to Si surface-micromachined structures by atomic-layer deposition (ALD). For this demonstration, we apply 10-nm-thick films of Al2O3 using a binary reaction sequence with precursors of trimethyl aluminum and water. Deposition is carried out in a viscous flow reactor at 1 Torr and 168 °C, with N2 as a carrier gas. Cross-section transmission electron microscopy analysis shows that films are uniform to within 5% on MEMS device structures with aspect ratio ranging from 0 to >100. Films are stoichiometric Al2O3, with no evidence of contamination from other species, and are amorp...

Arrays of cylindrical microdischarge devices, ∼200 μm in diameter, have been fabricated with internally recessed annular electrodes in multilayer ceramic structures and operated both continuously and with pulsed excitation in the rare gases at pressures up to 800 Torr of Ne and 300 Torr of Xe. The overall thickness of the ceramic structure is ∼1.6 mm and each microdischarge is individually ballasted by a ∼225 kΩ resistor, produced and integrated into the structure by a thick film process. Arrays as large as 13×13 pixels have been tested to date. Spatially uniform glow discharges are generated in the pixels for all of the pressures investigated and strong emission from excited states of the singly charged Xe ion, lying ∼26–27 eV above the neutral (…5p6 1S0) ground state, is observed. For a 169 element array drawing a total current of 30 mA, the output power of the array in the 300–1000 nm spectral region falls to ∼55% of its initial value in ∼8.3 h of continuous operation with a static gas fill.

A strong, current-free, electric double-layer with eΦ/kTe∼3 and a thickness of less than 50 debye lengths has been experimentally observed in an expanding, high-density helicon sustained rf (13.56-MHz) discharge. The rapid potential decrease is associated with the “neck” of the vacuum vessel, where the glass source tube joins the aluminum diffusion chamber, and is only observed when the argon gas pressure is less than about 0.5 mTorr. The upstream electron temperature Te appears 25% greater than the downstream Te, and there is a density hole on the downstream edge. This experiment differs from others in that the potentials are self-consistently generated by the plasma itself, and there is no current flowing through an external circuit. The plasma electrons are heated by the rf fields in the source, provide the power to maintain the double-layer, and hence accelerate ions created in the source out into the diffusion chamber.

We report on a localized high-density electron beam in large-area microwave discharges in argon. The beam is observed only for certain antenna configurations at gas pressures of about 50 mTorr, and it strongly modifies the radial plasma density profiles. The beam current near the quartz plate is estimated to be ≈140 mA/cm2.

Atomic N and excited N2 (N2*) play important roles in plasma-assisted synthesis of nitride materials, such as GaN. Absolute densities of N and N2* were measured at the substrate plane in an inductively coupled N2 plasma in the pressure range of 10 to 200 mTorr using modulated-beam line-of-sight threshold ionization mass spectrometry. The density of N increased with increasing pressure from 2.9×1018 to 1.8×1019 m−3, while the density of N2* was in the range of 9.7×1017 to 2.4×1018 m−3, with a maximum at 50 mTorr. Based on the appearance potential of N2* at ∼12 eV, we identify this excited molecule as long-lived N2 (A3Σu+) metastable.

Cylindrical microdischarge devices having cavity diameters as small as 13 μm and volumes as low as several nanoliters have been fabricated in metal/polymer structures with and without screen electrodes. These devices produce stable glow discharges in Ne, Xe, air, Xe/O 2 , and Ne/air mixtures at total pressures up to the maximum investigated, 1200 Torr. Neon discharges in 30 μm diameter devices are well behaved for p Ne above 700 Torr (pd>2.1 Torr cm) and generate strong emission in the UV from singly charged Ne-ion transitions at above-atmospheric pressures. Fluorescence in the visible from Xe + and Xe 2+ as well as molecular features in the green (∼530 nm) and blue (∼484 nm) that appear to be attributable to the neutral dimer are also observed from Xe in the 650–1100 Torr range. Discharges in air (100–740 Torr) and Ne/air mixtures produce strong N 2 (C→B) and N 2 + (B→X) emission in the near-UV and violet. The lowest observed operating voltage for Ne discharges in 30 μm devices is 87 V (p Ne =1200 Torr). Discharges in microcavities of dimensions below 50 μm represent a unique spectroscopic tool.

Suppression of silicidation in ZrO2/SiO2/Si structure by high-temperature helium (He) gas annealing was demonstrated. Comparison of ultrahigh vacuum, 1 Torr N2 and He annealing with controlled oxygen partial pressure (PO2) at 920 °C revealed that the optimal PO2 range in He at which the thermal stability of the layered structure can be achieved is over one order wider than that in N2. This result suggests that He gas physically obstructs SiO removal through the quenching of atomic vibration and the occupation of SiO diffusion path in the ZrO2/SiO2 layer, thus impeding the contact of ZrO2, SiO, and Si effectively, which is the trigger of silicidation. Moreover, rapid thermal He annealing is found to be the most effective means of suppressing transition of interface structure.

The correlation between the vacuum ultraviolet (VUV) luminous efficiency and the plasma ion density has been investigated in terms of the xenon mole fraction in the neon filling gas for alternating current plasma display panels. The VUV luminous efficiency and plasma ion density are found to have strong correlation and to be saturated at xenon mole fractions greater than 7% and gas pressures of 400 Torr.

We measured electrical characteristics of transversely magnetized capacitively coupled plasma at low pressure (10 mTorr). From these measurements, we found that the power characteristics of the magnetized discharge were different from those of the unmagnetized discharge. As the magnetic field increases, a square dependence of power characteristic at high current changes to a linear dependence. This can be understood as a power dissipation mode transition by a magnetic field. A calculation from a simple sheath model agrees well with the experimental data.

Epitaxial GaN films of thickness ∼1 μm have been grown on sapphire(0001) and GaAs(001) substrates using the liquid-target pulsed-laser-deposition technique in a 5 Torr nitrogen atmosphere. Detailed x-ray diffraction and photoluminescence studies were carried out for both types of samples. Significantly enhanced low-temperature photoluminescence emissions at 3.368 eV (I3) and 3.310 eV (I4) were observed for the material deposited on a GaAs(001) substrate at ∼800 °C. We propose a model to explain the emission mechanism for both lines in which the electrons and holes are confined in cubic inclusions within the hexagonal material, analogously to a type-I quantum well.

Pulsed-laser deposition of Au thin films has been achieved by ablating a gold target with a KrF excimer Laser in various conditions of ambient Ar gas pressure (from 10−5 to 4 Torr) and target-to-substrate distance (from 1.0 to 11 cm). The dynamics of the plasma plume were measured in the same conditions. Highly oriented Au (111) thin films are obtained for pressure-distance deposition conditions such that the neutral Au species have a typical velocity larger than 2 km s−1, while a polycrystalline powder is obtained when the typical velocity is smaller than 0.8 km s−1.

A front-panel structure with a hollow channel between sustain electrodes for an alternating current plasma display panel is proposed to achieve a low breakdown voltage and short discharge time lag due to the strong electric field in the hollow channel. When compared with a conventional structure, the structure with a hollow channel produced a 15% firing voltage improvement, 8% minimum sustaining voltage improvement at a neon gas pressure of 150 Torr, and 8% discharge time lag improvement at a sustaining voltage of 270 V.

The performance of tunable microwave devices based on heteroepitaxial YBa2Cu3Ox/SrTiO3 films on (001) LaAlO3 substrates has been evaluated. It was ascertained that “out-of-plane” SrTiO3 lattice parameter is the relevant factor in determining both device agility and dielectric loss. After high temperature annealing (1100 °C, 1 atm O2), only SrTiO3 layers deposited under low oxygen pressure (∼10−5 Torr) show an appreciable reduction of the dielectric losses while maintaining high agility. Annealed samples exhibit voltage independent losses of ∼5×10−3 simultaneously with 55% dielectric agility at 6 GHz and 77 K.

Spin-dependent tunnel junctions with ZrAlOx barriers were formed by natural oxidation (5 min at 10 Torr) of 7-A-thick Zr–Al films. Resistance×area products of 6 Ω μm2 were achieved with a 15.3% tunnel magnetoresistance (TMR) signal. Bottom-pinned (MnIr) junctions were deposited on top of 600-A-thick, ion-beam-smoothed, low-resistance, Al electrodes. Effective average barrier height and thickness are 0.28 eV and 8.2 A, respectively, and breakdown voltage is 0.41 V for 1 μm2 junctions. The TMR signal decreases by half at a bias voltage of 210 mV. Junction TMR decreases for anneals above 250 °C. High-resolution transmission electron microscopy indicates that ZrAlOx forms an amorphous barrier that is smoother than pure crystalline ZrOx or pure amorphous AlOx barriers. These low-resistance tunnel junctions are attractive for read head applications above 100 Gbit/in.2 where competitive signal-to-noise ratios imply resistance×area products of few Ω μm2 and TMR signals near or above 20%.

An array of cylindrical microdischarges has been demonstrated to significantly improve the ignition characteristics of a high-pressure arc discharge by preionizing the anode–cathode gap. Situated behind the cathode, the microdischarge array serves to reduce both the statistical and formative time delays by providing seed electrons in the critical early phases of the startup of a cold lamp. Experiments conducted in Ar and Ne/2% Xe mixtures at pressures ranging from 35 to 600 Torr with spacings between the tungsten electrodes of 1–3.5 cm show that a three element array of 400-μm-diam cylindrical microdischarges lowers the dc ignition voltage for the lamp by at least a factor of 2 when the Ar pressure is between 50 and 75 Torr. The required voltage is constant over a broad range in Ar pressure (35 to ∼90 Torr) and similar results are observed with 200-μm-diam microdischarges and for lamp ignition in Ne/2% Xe gas mixtures.

Spin-dependent tunnel junctions with AlOx barriers were fabricated by in situ natural oxidation of a 7 A thick Al film. Oxygen pressure was varied from 0.5 to 100 Torr, and oxidation time ranged from 5 min to 2 h. Junction resistances as low as 10 to 12 Ω μm2 were obtained with corresponding tunnelling magnetoresistance values (TMR) ranging from 14% to 17%, for the junctions oxidized at the lower pressure (0.5 Torr). Rutherford backscattering analysis (RBS) indicates an O/Al ratio of 1.29±0.34 denoting incomplete oxidation of the Al. Junctions oxidized at higher pressures (⩾10 Torr) can reach 25% to 30% TMR, with resistances ranging from 30 to 70 Ω μm2. RBS shows near-stoichiometric Al2O3 oxide composition (O/Al=1.51±0.43) in these barriers.

Large arrays (up to 30×30) of microdischarge devices having separately addressable subarrays have been fabricated in Si and operated continuously in Ne, Ne/Ar, and Ne/Xe gas mixtures at pressures up to 800 Torr. Eight 3×3 arrays fabricated on the same substrate operate simultaneously at voltages as low as 210 V in 400 Torr of Ne and exhibit lifetimes beyond 19 h, or approximately 1 order of magnitude larger than those for earlier arrays in which all devices have a common anode. Four 15×15 arrays have also been tested and, when operated in Ne/Ar or Ne/10% Xe gas mixtures, generate intense fluorescence in the green from a phosphor over an area of 16 mm2.

Microdischarges in flexible copper-polyimide structures with hole diameters of 200 µm have been used as stencil masks to pattern bare silicon in CF4/Ar chemistry. The discharges were operated at 20 Torr using the substrate as the cathode, achieving etch rates greater than 7 µm/min. Optical emission spectroscopy provides evidence of excited fluorine atoms. The etch profiles show a peculiar shape attributed to plasma expansion into the etched void. Forming discharges in multiple hole and line shapes permits direct pattern transfer in silicon and could be an alternative to ultrasonic milling and laser drilling.

O2(a 1Δg) was generated in a flowing discharge of a radio-frequency (rf) hollow electrode. The radio frequency was 99.9 MHz and the rf power was 200 W. The discharge was done in the gas mixture O2:N2:NO=200:20:10 sccm and then it was chilled reactively by the mixture Ar:NO2=200:10 sccm. The O2(a 1Δg) relative yield of 32% was achieved at the pressure of 0.43 Torr. Usage of the mixtures O2:NO=200:100 sccm and Ar:NO2=100:100 sccm resulted in the O2(a 1Δg) yield of 25% at the pressure of 0.6–0.9 Torr. The effluent was mixed with molecular iodine in a far afterglow region and it was tested in an oxygen–iodine laser. The iodine flow rate was 0.3 mmol/min. A strong enhancement of atomic iodine spontaneous emission at the wavelength of 1315 nm was observed in the optical resonator.

We demonstrate the synthesis of monodispersed, nonagglomerated silicon (Si) nanocrystallites, using an integrated process system composed of a unit for the formation of nanocrystallites by pulsed-laser ablation in an inert background gas, a unit for classification using a differential mobility analyzer (DMA), and a unit for deposition onto a substrate using a nozzle jet. The DMA has been designed to operate under pressures less than 5.0 Torr. We have synthesized nonagglomerated Si nanocrystallites of 3.8 nm mean diameter and 1.2 geometrical standard deviation on carbon thin films using this integrated process system.

The room-temperature epitaxial growth of CeO2 films on Si(111) substrates was examined in situ by combined use of a coaxial impact-collision ion scattering spectroscopy (CAICISS) and the laser molecular beam epitaxy (laser MBE). It was found that the crystal quality of CeO2 ultrathin films (∼3 nm thick) as-grown in UHV (∼10−9 Torr) could be improved remarkably by a few minutes of O2 gas exposure (∼10−5 Torr) at room temperature. A three-fold symmetry in the Ce signal intensity of azimuth rotational CAICISS spectra, which exhibited the type-B epitaxial growth ([110]CeO2‖[110]Si), was observed for the films thicker than about 1 nm.

Microdischarge devices having inverted, square pyramidal cathodes as small as 50 μm×50 μm at the base and 35 μm in depth, have been fabricated in silicon and operated at gas pressures up to 1200 Torr. For the polyimide dielectric incorporated into these devices (er=2.9), the discharges produced exhibit high differential resistance (∼2×108 Ω in Ne), ignition voltages for a single device of ∼260–290 V, and currents typically in the μA range. Arrays as large as 10×10 have been fabricated. For an 8 μm thick polyimide dielectric layer, operating voltages as low as 200 V for a 5×5 array have been measured for 700 Torr of Ne. Array lifetimes are presently limited to several hours by the thin (1200–2000 A) Ni anode.

High-purity and thick 4H–SiC(0001) epilayers have been grown by a horizontal hot-wall chemical vapor deposition (CVD) system, which was designed and built at the authors’ group. The background donor concentration has decreased by reducing pressure during CVD, and a low donor concentration of 1–3×1013 cm−3 was achieved by CVD growth at 80 Torr. The free exciton peaks dominated in low- and room-temperature photoluminescence spectra without titanium or point-defect related peaks. The electron mobility reaches 981 cm2/V s at room temperature and 46 200 cm2/V s at 42 K. The total trap concentration could be reduced to 4.7×1011 cm−3 by increasing the input C/Si ratio.

A localized hot-electron region was observed in low-pressure (

This letter investigates the role of postdeposition oxygen treatments upon their luminescent properties by synthesizing Eu:Y2O3 films by pulsed laser deposition under different conditions and subjecting them to various postdeposition oxygen treatments. Our results have shown that Eu:Y2O3 films grown in 300 mTorr oxygen ambient and cooled in vacuum (10−6 Torr) after the termination of growth exhibit better photoluminescent and cathodoluminescent brightness than those grown in (i) vacuum and cooled in vacuum and (ii) 300 mTorr oxygen and cooled in 2 Torr oxygen. Two possible mechanisms have been proposed to explain these results.

Surface contamination and cleaning processes of (BaxSr1−x)Ti1+yO3+z(BST) and Pt films were investigated using in situ, real-time mass spectroscopy of recoiled ions (MSRI). MSRI analysis revealed that BST film surfaces exposed to atmospheric ambient are contaminated with carbon and hydrogen containing species, which could be removed by thermal decomposition/desorption in an oxygen ambient. Cleaning of the BST surface was accomplished by annealing at 500 °C in ⩾1 mTorr O2, resulting in complete elimination of these species. Similar contamination on Pt film surfaces could be eliminated with only 200 °C annealing in 5×10−4 Torr of O2. Annealing of the BST film surface in oxygen prior to deposition of the top Pt electrode results in a clean top Pt/BST interface that yields BST capacitors with much lower and more symmetric leakage current characteristics, and lower dielectric losses compared to BST capacitors with contaminated top Pt electrode/BST interfaces.

Flexible microdischarge arrays have been fabricated in metal–polymer–metal structures having a total thickness of ∼30 μm (∼1.2 mils). Composed of individual cylindrical devices having a diameter of 150 μm, positive differential resistance (30–120 kΩ), and operating voltages as low as 114 V for a 5 μm thick dielectric layer, the arrays operate at pressures beyond 700 Torr of Ne and in 1 atm of air. For Ne pressures ⩽ 200 Torr, emission is produced from Ne ion excited states lying more than 55 eV above the neutral ground state (2p6). The structures reported here are inexpensive to fabricate and have lifetimes beyond 50 h. Arrays that have been sealed by conventional lamination have also been operated successfully.

We present an improvement in the procedure for fabricating YBa2Cu3O7−δ (YBCO) films by dc sputtering. An in situ anneal was used: (i) between as-deposition temperature Ts and 650 °C, 10 min annealing with oxygen pressure less than 20 Torr and (ii) cooling to room temperature in a pure argon atmosphere (oxygen free). This process has yielded stable, high-quality YBCO films with Tc of 92 K. Films were characterized using Rutherford backscattering spectrometry/channeling, elastic resonance reaction 16O(α,α)16O and x-ray diffraction techniques. They were found to have ideal 1-2-3 stoichiometry and oxygen content in addition to good crystalline quality. This new procedure can improve the epitaxial quality of in situ multilayered structure and is more favorable for device formation than the standard procedure.

Vacuum emission, breakdown, and current–voltage characteristics of a large surface area-to-volume ratio planar dc microdischarge have been measured for different He–Xe mixtures in the range of 10%–100% Xe and pressures in the range of 60–500 Torr. The electrical measurements show that the Paschen breakdown curves and the current–voltage characteristics are primarily controlled by the xenon concentration in the mixture. A study of the vacuum ultraviolet emission of xenon atoms at 147 nm and of xenon dimers at 150 nm normalized to the discharge power reveals the presence of local maxima in the emitted intensity as a function of discharge pressure and xenon concentration, indicative of complex excited-state atomic and excimer kinetic processes.

Electron temperature is controlled by varying the length of slits made in a grid immersed in a weakly ionized discharge plasma. The grid, which is kept at floating potential, has six slits in this experiment. With a decrease in the slit length from 6 to 0 cm, the electron temperature decreases from 2.1 to 0.09 eV, being accompanied by an electron-density increase from 0.32×109 to 1.53×109 cm−3 at argon gas pressure of 1.5 mTorr. This method of electron–temperature control is applicable to reactive plasmas in which grids are often covered by insulators.

A fused hollow cathode (FHC) plasma source is introduced. The system of radio-frequency (rf) generated hollow cathodes with flowing gas forms an integrated electrode source which operates in the pressure range from 1 Torr to atmospheric pressure. The diameter of the source is 3.5 cm. However, the construction perfectly enables further scaling up. The forward rf power to sustain the discharge at atmospheric pressure can be as low as 2 W. The discharge is stable, volume filling, silent, with no streamers. The FHC atmospheric plasma source is very promising for surface processing, specially on temperature sensitive substrates, and may substantially save costs by avoiding investments into the vacuum equipment.

The evolution of the electron energy distribution function (EEDF) over a pressure range of 5–100 mTorr is investigated in a planar inductive argon discharge. It is found that the EEDF, which appears to be a bi-Maxwellian distribution with a two-temperature structure at low pressures, evolves into a Druyvesteyn-like distribution as the pressure increases. The electron energy diffusion coefficient, which describes electron heating, is calculated under the same discharge conditions using discharge parameters and numerical results show that the heating of low-energy electrons is enhanced as the pressure increases resulting in a transition of the EEDF to a Druyvesteyn distribution.

By reducing the dimensions of the electrodes to the submillimeter range, it is possible to operate dc gas discharges at pressures up to 760 Torr (argon). A plane geometry for the cathode, different from the well-known microhollow cathode discharge, was used in these experiments. For anode hole diameters smaller than 0.6 mm and pD (D diameter of the anode hole) larger than 9 Torr cm, the differential resistivity in the I–V characteristics is similar to the hollow cathode one. The emission in the visible range is distributed more homogeneously over the entire cathode surface. By using a end-on coupled configuration of hollow and plane cathode geometries, the discharge can be stabilized over the entire (pD) range between 1 and 23 Torr cm. The discharge is stable, for both the hollow–plane and hollow–hollow cathode configurations in aligned geometries.

High-pressure subsonic mode operation of a chemical oxygen-iodine laser (COIL) was demonstrated. Singlet delta oxygen generated by a liquid-jet type singlet oxygen generator (SOG) was directly utilized in the laser cavity, without supersonic expansion. The operating pressure in the laser cavity was 0.80 kPa (6.0 Torr). Cooled nitrogen gas was added to the singlet oxygen flow to enhance the output power. An output power of 448 W was obtained for a chlorine input rate of 19.7 mmol/s. This is equivalent to a chemical efficiency of 25.0%, and it is comparable to the highest reported chemical efficiency of COIL using nitrogen as the buffer gas. The obtained value of specific energy of 3.5 J/liter, is more than fivefold higher than that for our supersonic COIL device.