Time and space resolved Langmuir probe measurements of a pulsed vacuum arc plasma

The time and space evolution of pulsed vacuum arc plasma parameters have been measured using a single cylindrical Langmuir probe in a free expansion cup. Electron density n_e, effective electron temperature T_eff and electron energy distribution function (EEDF) are derived from the I-V curves using Druyvesteyn method. Results show that during the discharge time, the electron density n_e is between 0.27 and 1.82 × 10¹⁸ m⁻³ and the effective electron temperature T_eff is between 6.14 and 14.72 eV, both of which decrease as a function of the discharge time. The electron energy distribution function (EEDF) is no-Maxwellian since the high-energy electrons depart from the Maxwellian distribution. Due to the plasma expansion, the electron density n_e decreases as increase of the expansion distance, but the effective electron temperature T_eff is weakly dependent on the distance in the free expansion cup.     

Comparative study of erbium disilicide thin films grown in situ under ultrahigh vacuum or ex situ with a capping layer

Erbium disilicide (ErSi_2-x) thin films grown by two different techniques are compared using a variety of characterization techniques, both electrical and physical. The first technique involves Er deposition and annealing under ultrahigh vacuum and the second one focuses on Ti/Er/Si(100) stacks evaporated under high vacuum and heated ex situ by rapid thermal annealing. Crystalline phase identification by X-ray diffraction reveals the formation of ErSi_2-x for all the studied samples. Cross-sectional transmission electron microscopy shows that the Ti cap transforms into Ti-Si compounds. The efficient stripping of the capping layer is also demonstrated. Atomic force microscopy evidences the formation of inverted pyramidal defects in both cases, with some improvement for the Ti-capped samples. X-ray photoelectron spectroscopy depth profiles show that the ErSi_2-x films and the ErSi_2-x/Si interfaces are oxygen-free. The extracted Schottky barrier height of ErSi_2-x/n-Si contacts lies around 0.3 eV notwithstanding the annealing temperature or the growth technique. It thus demonstrates a route to form ErSi_2-x thin films that advantageously compares with reference ultrahigh vacuum samples with less stringent fabrication conditions.     

Method for measuring a vacuum in an environment at liquid helium temperatures

The experimental results of a new method to measure a vacuum in an environment at liquid helium temperatures are presented. The method uses a thin superconducting wire suspended in the vacuum vessel, the wire is heated by a current pulse > l_c. The cool down time, which depends on the heat transfer into the rest gas and on the axial heat conductance of the wire, is a measure of the vacuum and it is detected by the recovery of the wire to superconductivity. The results exhibit good resolution in the range of pressures from 5 × 10^?3 to 5 Pa (5 × 10^?5 to 5 × 10^?2 mbar).     

Structural and optical properties of Ti-doped ZnO thin films prepared by the cathodic vacuum arc technique with different annealing processes

Highly transparent Ti-doped ZnO thin films were prepared on glass substrates at a deposition rate of approximately 33 nm/min using the cathodic vacuum arc technique with a Zn target power of 550 W and a Ti target power of 750 W, respectively. X-ray diffraction measurements have shown that the Ti-doped ZnO thin film with a vacuum post-annealing condition is c-axis oriented but an amorphous phase at the other post-annealing atmosphere and as-deposited condition. Transmittance measurements show that the best optical quality of the Ti-doped ZnO thin films occurred at a post-annealing atmosphere of N₂/H₂ mixed gases. Additionally, the optical transmittance of all films has been found more than 85% in a range of 500-700 nm. The lowest electrical resistivity was 3.48 × 10⁻³ Ω cm, obtained on as-deposited films. However, the post-annealing condition greatly increased the resistivity.     

Influence of different annealing processes under various atmospheres on the oxidation behaviour of γ-TiAl

Abstract

A detailed study of the oxidation behaviour of bare γ-TiAl based alloy Ti–45Al–8Nb under various conditions, such as different atmospheres, pressures, temperatures (900°C, 1000°C) and times (100–200 h) is presented. Under high vacuum conditions (10^–6 mbar) a continuous zone of α-₂Ti₃Al was formed at the surface with an oxygen-enriched phase on top. No oxide scale formation was obvious. During thermal treatment under Ar-atmosphere at low vacuum pressure (approximately 50 mbar) mainly nitrides (TiN, Ti₂AlN) and Al₂O₃ particles were formed at the surface with an α-₂layer below. Annealing γ-TiAl in hydrogen atmosphere (about 1040 mbar) led to the formation of a thick reaction zone. A TiO₂ layer was formed on top, followed by a mixed oxide scale. Beneath that scale a thick region with alumina, σ–Nb₂Al and α-₂Ti₃Al was observed.

Moreover, the oxidation behaviour of several thermally pre-treated samples was tested by cyclic oxidation at 900°C in air. The microstructure of the oxide scale formed after testing can be compared with that of non pre-treated material. γ-TiAl annealed under high vacuum conditions exhibits the lowest oxidation rate, while the mass gain of specimens pre-treated under Ar-atmosphere increased rapidly in the first cycles. All pre-treated specimens exceeded a lifetime of 600 cycles at minimum. The reference material failed after 520 cycles.     

Vacuum effects on fatigue crack growth in submicrometre‐thick freestanding copper films

To clarify vacuum effects on fatigue crack growth in freestanding metallic thin films, experiments were conducted on approximately 500‐nm‐thick copper films inside a field emission scanning electron microscope. Fatigue crack growth accompanied by intrusion/extrusion formation occurred in vacuum, and da/dN was smaller than in air in the middle‐ΔK region (ΔK ≈ 1.7‐3.1 MPam^1/2). Conversely, in the low‐ΔK region (ΔK ? 1.7 MPam^1/2), da/dN was larger in vacuum than in air. Further, fatigue crack growth in vacuum occurred below the fatigue threshold in air (ΔK_th,air). A nonpropagating crack after reaching ΔK_th,air continued to propagate in vacuum when the environment changed from air to vacuum. This indicates that fatigue crack growth resistance is smaller in vacuum than in air under the same effective driving force. The fatigue damage area near the crack paths in vacuum in the low‐ΔK region became wider, suggesting that the nucleation of fatigue damage was enhanced in vacuum.     

Optical and dielectric properties of thin SiOx films of variable composition

The effect of the composition of amorphous SiO_x films produced by the vacuum evaporation of SiO, on their optical and dielectric properties was investigated. The variation in the composition of the films was achieved by changing the deposition rate and the pressure of the residual gases.The optical band gap was observed to increase from 2.2 to 3.1 eV as the deposition rate was decreased from 50 to 5 Å s^-1 and simultaneously the refractive index, the permittiviity and the dielectric loss factor were found to decrease. The composition and structure of the films were determined from the optical absorption and IR spectroscopy.The experimental results revealed that SiO_x films produced by vacuum evaporation do not comprise a simple mixture of silicon and SiO₂ phases but they have a single-phase structure.     

Electron microscopic studies of vacuum-evaporated (Pb1 −x Sn x )1 −y Te y thin films

Thin films of (Pb_{1 −x} Sn _x )_{1 −y} Te _y have been deposited by vacuum evaporation onto glass, mica, CaF₂ and NaCl substrates heated to various temperatures at low deposition rates. Transmission HEED, TEM and SEM studies have been carried out for as-grown films. HEED photographs show that (i) the degree of crystallinity of the films improves at higher substrate temperatures and (ii) the crystallites have smaller dimensions on CaF₂ than on NaCl, mica and even glass, under identical conditions of deposition. SEM studies reveal that with increasingT _sub, grains tend to form clusters through mobility coalescence. Needleshaped grains are formed when the deposition rate exceeds a certain critical value. Formation of needle-like grains has been attributed to the excess Te atoms possessing trigonal structure so that such grains can be observed only inp-type PbSnTe films.     

A model for distribution of aluminum in silicon refined by vacuum directional solidification

We propose a simple numerical model for distribution of Aluminum (Al) in silicon ingot during vacuum directional solidification, including segregation from silicon crystal to silicon melt as well as evaporation from silicon melt to vacuum atmosphere. According to the model, the effective segregation K_eff and the total evaporation coefficient k_T(Al)of Al under the experimental conditions are 0.0137 and 2.6755 × 10⁻⁶ m·s⁻¹, respectively. In comparison with experimental results, the segregation of Al is dominated at the beginning of solidification, whereas at the last stage of solidification the removal of Al is mainly depended on the evaporation. It is also found that the critical influences on aluminum removal during vacuum directional solidification are temperature and solidification rate.     

Crystallization of amorphous antimony films deposited onto glass substrates in ultrahigh vacuum

The crystallization of amorphous antimony (a-Sb) films deposited onto glass substrates in an ultrahigh vacuum of 10^?6?10^?7 Pa is investigated through in situ observation with an optical microscope camera. In comparison with the results for deposition in a conventional vacuum of 10^?4?10^?5 Pa, a marked reduction is observed in the critical thickness d_c for crystallization. For thicknesses less than the previous d_c value of about 250 Å, the dependence of the crystallization rate on the thickness is found to weaken drastically and the activation energy of the atoms for crystallization to increase. The antimony crystallites which nucleate in such thin a-Sb films do not take a simple spherical form.     

Ready‐to‐eat mussel meat processed in retort pouches for the retail and export market

A processing method has been developed to prepare ready‐to‐eat mussel meat, retaining its natural texture and succulence. The product was vacuum‐packed in an indigenously developed retortable pouch and processed in a still over‐pressure retort. Time and temperature data was collected during heat processing using an Ellab data recorder cum F₀ and cook value integrator. The heat penetration characteristics were determined using a formula method. The total process time was 35 min with a F₀ value of 9.8 and a cook value of 90.3 min. These vacuum‐packed retort‐processed samples were rated excellent by the taste panel and remained in good condition even after storage for 1 year at room temperature. Copyright © 2004 John Wiley & Sons, Ltd.     

Wear resistant and anti-corrosive treatment for TI-6AL-4V using metal vapor vacuum arc source in comparison with plasma immersion ion implantation

This study utilizes two ion-implantation methods, plasma immersion ion implantation (PIII) and metal vapor vacuum arc (MeVVA), to prepare Ti-N phases on the surface of Ti-6Al-4V. By the nitrogen PIII method, both nitrogen and minor oxygen species are simultaneously attracted by the negatively charged substrate. The penetration of N and O interstitial elements to an extensible depth is possible owing to the effect from the negatively charged target. The nitrogen PIII treatment does not produce a novel Ti-N phase. As a result, the modified surface does not behave anticorrosive. The H_n and the E determined by nanoindentation also remain unchanged. It is still potential to apply this non-directional treatment by increasing bias voltage of the target, coating pure titanium on Ti-6Al-4V, and adjusting the regeneration process of nitrogen ions. The MeVVA treatment creates a novel αTiN_0.3 (011) phase on Ti-6Al-4V in present study. It signifies that the interactions between kinetic Ti ions of varied energies and minor nitrogen molecules, with minor participation of oxygen, are highly feasible. The novel ion-implanted Ti-N phase is corrosion resistant, which is capable to reduce passivation current density by forming a passive film. Moreover, the MeVVA-treated surface is surface-hardened; the E is simultaneously increased. The increase of nano mechanical properties can be visualized by 3D images using Nano Vision and determined by analyzing the tip/surface impact structure on the indentation site.     

Optical functions and time-resolved luminescence of lithium hydride single crystals upon far-ultraviolet excitation

Low-temperature reflection spectra of lithium hydride (LiH) single crystals cleaved in ultrahigh vacuum (3 × 10⁻¹⁰ Torr, T = 10 K), were recorded using synchrotron radiation in vacuum ultraviolet spectral region. Based on the obtained experimental data, the optical functions of LiH in the energy range from 3.7 to 35 eV were analyzed using the Kramers–Krönig relations. Time-resolved photoluminescence excitation spectra were studied in detail for the near edge free exciton-phonon luminescence at 4.67 eV and photoluminescence at 2.4 eV due to the Bi³⁺ impurity centers. The effect of multiplication of electronic excitations due to inelastic scattering of hot photoelectrons and hot photoholes was revealed at photon energies above 15 eV (more than 3E_g). It was found that the radiative lifetime for free excitons in LiH at 4.67 eV is less than 1 ns as low temperatures as at 10 K. The interpretation of the electronic band structure of lithium hydride in the ultraviolet and vacuum ultraviolet spectral regions were carried out on the basis of the present experimental results with the involvement of the available band structure calculations.     

Powder disperser for the continuous aerosolizing of dry powdered nanoparticles

A new method has been developed for the continuous aerosolization of dry powdered nanoparticles using a commercially available and cost-effective vacuum generator. A commercial doser was used to supply nanoparticles continuously and precisely. A novel device (called a pressure equilibrium unit) was designed to connect the doser and the vacuum generator to make sure both parts avoid suffering from pressure shock. This system is denoted as a continuous vacuum generator disperser (CVGD). The dosing rate of the CVGD for different particle materials tends to a constant value. All the aerosolized engineered nanoparticles (ENPs) of varying materials and primary diameter obtained through the CVGD distribute identically log-normally as a whole. It is more difficult to separate the nanoparticles of smaller primary diameter using the CVGD, due to the stronger van der Waals attractive force between them. The total particle concentration can be adjusted easily by changing the motor speed of the doser (Dr), which was directly proportional to the dosing rate. As Dr increased, the PSDs shifted to a larger diameter to some extent. For sufficient large dosing rates, the CVGD performance could be improved significantly by increasing the inlet pressure of the vacuum generator (P_j).     

Vacuum Technology Considerations For Mass Metrology

Vacuum weighing of mass artifacts eliminates the necessity of air buoyancy correction and its contribution to the measurement uncertainty. Vacuum weighing is also an important process in the experiments currently underway for the redefinition of the SI mass unit, the kilogram. Creating the optimum vacuum environment for mass metrology requires careful design and selection of construction materials, plumbing components, pumping, and pressure gauging technologies. We review the vacuum technology¹ required for mass metrology and suggest procedures and hardware for successful and reproducible operation.     

YBa2Cu3O x superconducting thin films prepared by low temperature vacuum codeposition

Y-Ba-Cu-O films were prepared by low temperature codeposition of three components. The Y and Cu contents were evaporated from metallic sources, while Ba was vacuum-evaporated from Ba, BaO and BaF₂ sources in separate codeposition experiments. The lowest temperature at which superconducting YBa₂Cu₃O _x thin films (about 0.5μm thick) preparedin situ was near 500°C. This process enables preparation of superconducting films on various substrates (SrTiO₃, MgO, Al₂O₃, Si) without a buffer layer. Zero-resistance critical temperature was as high as 88 K and the critical current density was 10⁴ A/cm² at 4.2 K. The morphology of the films was granular with disordered grain orientation, the average grain size being typically 0.5μm.     

Apatite formation from simulated body fluid on various phases of TiO2 thin films prepared by filtered cathodic vacuum arc deposition

Hydroxyl (OH⁻)-free TiO₂ thin films with amorphous and crystalline phases were deposited onto (100) silicon substrates using filtered cathodic vacuum arc deposition in order to investigate the in vitro apatite formation in simulated body fluid (SBF). The surface morphology, composition and structure of the TiO₂ thin films were characterized. The X-ray photoelectron spectroscopy results confirmed the presence of calcium and phosphorus on all TiO₂ thin film surfaces after immersion in SBF at 37 °C. Fourier transform infra red results showed the presence of carbonated apatite on the surface of these films. Amorphous structured TiO₂ thin film showed poor ability to form apatite on its surface in SBF. Apatite formation was more pronounced on the surfaces of the anatase films in comparison to those of rutile. The carbonated apatite deposition rate increased significantly when the TiO₂ film was illuminated with UV light prior to immersing in the SBF. In particular, the UV-treated anatase and rutile films showed increased rates of carbonated apatite formation on their surfaces in comparison to samples not treated with radiation. The increase in hydrophilicity due to UV treatment appears beneficial for the apatite growth on these surfaces.     

Engineering of Superconducting Ba1?x K x BiO3 Thin Films: Novel Electrochemical Route

A novel electrochemical processing technique was used to prepare thin films of Ba_1?x K _x BiO_3??? . The course of action consists of co-deposition of Ba, K, and Bi metals from single electrolytic bath at ?2.1?V_SCE followed by annealing at 175?°C in vacuum and air to control the quantity of K in the film. The desired metal stoichiometries were obtained by adjusting the electrolytic bath composition empirically. The nucleation and growth mechanism of the electro-deposit is found to be of progressive type. Well-connected and compact grain growth was observed after annealing. The crystallinity and purity of phase in the film annealed in vacuum is found be better than sample annealed in air. The superconductivity in the sample processed in vacuum and air is seen at 26?K with the width of 1.3?K and at 18.4?K with width 6?K. Electrodeposited thin films processed in vacuum exhibit current densities of the order to 6.1×10⁴?A?cm^?2 at 5?K.     

Regulate the content of magnesium in MgxZn1−xO films by vacuum anneal

Mg_xZn_1−xO thin films were grown on c-sapphire substrates by metal-organic chemical vapor deposition (MOCVD), followed by annealing in vacuum at different temperatures for 1 h. The UV emission peak was blue shifted in the photoluminescence (PL) spectra and a dramatic shift of (0 0 2) diffraction peak to higher angle was observed in X-ray diffraction (XRD) pattern with increasing anneal temperature. This suggested the band gap and the lattice parameter of Mg_xZn_1−xO had been affected by annealing in vacuum. Furthermore, the structure of the film became sparser due to annealing in vacuum. From the X-ray photoelectron spectroscopy (XPS) and ICP of the Mg_xZn_1−xO film, we can find that the anneal temperature have an effect on the content of each element in Mg_xZn_1−xO quantitatively. In addition, the value of x in Mg_xZn_1−xO varied slightly as the annealing temperature increased. The above phenomena indicated that annealing in vacuum could slightly adjust the percentage of Mg indirectly in Mg_xZn_1−xO film and offer a good idea in Mg_xZn_1−xO devices facture.     

Enhancing epitaxial SixC1 − x deposition by adding Ge

In this work, a possible way to enhance the epitaxial growth of metastable, tensile strained Si_xC_1 − x layers by the addition of germanium is demonstrated. During ultra-high vacuum chemical vapor deposition growth, the co-mixing of germane to the Si_xC_1 − x precursors was found to enhance the growth rate by a factor of ~ 3 compared to the growth of pure Si_xC_1 − x. Furthermore, an increase of the amount of substitutional incorporated carbon has been observed. Selective Si_xGe_yC_{1 − x − y} deposition processes utilizing a cyclic deposition were developed to integrate epitaxial tensile strained layers into source and drain areas of n-channel transistors.