Showing papers in "Journal of Vacuum Science and Technology in 2010"

Optical emission spectroscopy as a tool for studying, optimizing, and monitoring plasma-assisted atomic layer deposition processes

Abstract: In this note it is demonstrated that optical emission spectroscopy (OES) is an easy-to-implement and valuable tool to study, optimize, and monitor thin film growth by plasma-assisted atomic layer deposition (ALD). The species in the plasma can be identified through the analysis of the light emitted by the plasma. OES provides therefore information on the reactant species delivered to the surface by the plasma but it also yields unique insight into the surface reaction products and, as a consequence, on the reaction mechanisms of the deposition process. Time-resolved measurements reveal information about the amount of precursor dosing and length of plasma exposure needed to saturate the self-limiting half reactions, which is useful for the optimization of the ALD process. Furthermore, time-resolved OES can also be used as an easy-to-implement process monitoring tool for plasma-assisted ALD processes on production equipment; for example, to monitor reactor wall conditions or to detect process faults in real time.

Deposition rates of high power impulse magnetron sputtering: Physics and economics

Abstract: Deposition by high power impulse magnetron sputtering (HIPIMS) is considered by some as the new paradigm of advanced sputtering technology, yet this is met with skepticism by others for the reported lower deposition rates, if compared to rates of more conventional sputtering of equal average power. In this contribution, the underlying physical reasons for the rate changes are discussed, including (i) ion return to the target and self-sputtering, (ii) the less-than-linear increase in the sputtering yield with increasing ion energy, (iii) yield changes due to the shift of species responsible for sputtering, (iv) changes due to greater film density, limited sticking, and self-sputtering on the substrate, (v) noticeable power losses in the switch module, (vi) changes in the magnetic balance and particle confinement of the magnetron due to self-fields at high current, and (vii) superposition of sputtering and sublimation/evaporation for selected materials. The situation is even more complicated for reactive systems where the target surface chemistry is a function of the reactive gas partial pressure and discharge conditions. While most of these factors imply a reduction in the normalized deposition rate, increased rates have been reported for certain conditions using hot targets and less poisoned targets. Finally, some points of economics and HIPIMS benefits are considered.

Comparison of the sputter rates of oxide films relative to the sputter rate of SiO2

Abstract: There is a growing interest in knowing the sputter rates for a wide variety of oxides because of their increasing technological importance in many different applications. To support the needs of users of the Environmental Molecular Sciences Laboratory, a national scientific user facility, as well as our research programs, the authors made a series of measurements of the sputter rates from oxide films that have been grown by oxygen plasma-assisted molecular beam epitaxy, pulsed laser deposition, atomic layer deposition, electrochemical oxidation, or sputter deposition. The sputter rates for these oxide films were determined in comparison with those from thermally grown SiO2, a common reference material for sputter rate determination. The film thicknesses and densities for most of these oxide films were measured using x-ray reflectivity. These oxide films were mounted in an x-ray photoelectron or Auger electron spectrometer for sputter rate measurements using argon ion sputtering. Although the primary objec...

Atmospheric oxygen plasma activation of silicon (100) surfaces

Abstract: Silicon (100) surfaces were converted to a hydrophilic state with a water contact angle of <5° by treatment with a radio frequency, atmospheric pressure helium, and oxygen plasma. A 2 in. wide plasma beam, operating at 250 W, 1.0 l/min O2, 30 l/min He, and a source-to-sample distance of 3±0.1 mm, was scanned over the sample at 100±2 mm/s. Plasma oxidation of HF-etched silicon caused the dispersive component of the surface energy to decrease from 55.1 to 25.8 dyn/cm, whereas the polar component of the surface energy increased from 0.3 to 42.1 dyn/cm. X-ray photoelectron spectroscopy revealed that the treatment generated a monolayer of covalently bonded oxygen on the Si(100) surface 0.15±0.10 nm thick. The surface oxidation kinetics have been measured by monitoring the change in water contact angle with treatment time, and are consistent with a process that is limited by the mass transfer of ground-state oxygen atoms to the silicon surface.

Tribological and mechanical properties of nanocrystalline-TiC/a-C nanocomposite thin films

Abstract: This article reports on interrelationships between x-ray structure, mechanical properties, coefficient of friction μ, and wear coefficient k of ∼3000 m thick nc-TiC/a-C nanocomposite films sputtered using unbalanced magnetron from a composed C/Ti target (∅=100 mm); here nc and a denotes the nanocrystalline and amorphous phase, respectively. It is shown that (1) μ and k of the nc-TiC/a-C nanocomposite film strongly depend not only on its hardness H but also on its effective Young’s modulus E∗=E/(1−ν2); here ν is the Poisson s ratio, (2) the nc-TiC/a-C nanocomposite films with C/Ti>1.5 and the ratio H3/E∗2 (characterizing the resistance of film to plastic deformation) ranging from ∼0.2 to ∼0.3 exhibit the lowest values of μ and k, and (3) μ increases with increasing load L of the testing ball. The main result of this investigation is the finding that the achievement of the lowest value E∗ at a given value of H is of key importance in the formation of films with the lowest values of coefficient of friction μ...

β-Ga2O3 growth by plasma-assisted molecular beam epitaxya)

Abstract: The authors demonstrate the heteroepitaxial and homoepitaxial growth of single crystalline β-Ga2O3 by plasma-assisted molecular beam epitaxy. Phase-pure (2¯01) and (100) β-Ga2O3 thin films were grown on c-plane sapphire and (100) β-Ga2O3 substrates, respectively. Based on the homoepitaxial results, detailed information is reported on the dependence between the β-Ga2O3 film quality and various growth parameters. At an optimized growth temperature of 700 °C, a growth relationship between growth rates and increasing gallium fluxes was established at a fixed oxygen pressure. A three-dimensional columnar growth with a relatively high growth rate was measured at a low gallium flux while a terrace surface morphology with a reduced growth rate was observed as the gallium flux increased. The gallium flux played an important role on both surface morphology and growth rate. We associated the decreasing growth rate with increasing gallium flux with the formation of gallium suboxides monitored by quadrupole mass spect...

Coating growth behavior during the plasma electrolytic oxidation process

Abstract: In this study, aluminum oxide was deposited on an Al alloy substrate to produce hard ceramic coatings using a plasma electrolytic oxidation (PEO) process working at atmospheric pressure. The process utilizes dc and unipolar pulsed dc in the frequency range 0.2–20 kHz. Optical emission spectroscopy was employed to study the species and electron temperature of the plasma. The morphology and microstructure of the coatings were investigated using scanning electron microscopy. It was found that in the first 12 min of the PEO process, the plasma electron temperature increased with the applied voltage during the experiments, the plasma electron temperature was found to be in the range 4000–9000 K, and the applied voltage to the electrodes ranged up to 550–600 V for the different current modes. The plasma temperature profile exhibits a wider peak temperature spike for the dc power mode than for the pulsed dc mode, indicating that the dc plasma discharges would provide longer sintering time. The pulsed dc mode inc...

Reactive magnetron cosputtering of hard and conductive ternary nitride thin films: Ti–Zr–N and Ti–Ta–N

Abstract: Ternary transition metal nitride thin films, with thickness up to 300 nm, were deposited by dc reactive magnetron cosputtering in Ar–N2 plasma discharges at 300 °C on Si substrates Two systems were comparatively studied, Ti–Zr–N and Ti–Ta–N, as representative of isostructural and nonisostructural prototypes, with the aim of characterizing their structural, mechanical, and electrical properties While phase-separated TiN–ZrN and TiN–TaN are the bulk equilibrium states, Ti1−xZrxN and Ti1−yTayN solid solutions with the Na–Cl (B1-type) structure could be stabilized in a large compositional range (up to x=1 and y=075, respectively) Substituting Ti atoms by either Zr or Ta atoms led to significant changes in film texture, microstructure, grain size, and surface morphology, as evidenced by x-ray diffraction, x-ray reflectivity, and scanning electron and atomic force microscopies The ternary Ti1−yTayN films exhibited superior mechanical properties to Ti1−xZrxN films as well as binary compounds, with hardness

X-ray photoelectron spectroscopy study of polyimide thin films with Ar cluster ion depth profiling

Abstract: X-ray photoelectron spectroscopy depth profiling of polyimide thin films on silicon substrates using an Ar cluster ion beam results in an extremely low degradation of the polyimide chemistry. In the range from 2.5 to 20 kV, a lower cluster ion energy produces a lower sputter induced damage to the polymer and results in an improved polyimide to silicon interface width. The sputtering rates of the polyimide are found to increase exponentially with an increase in the Ar cluster ion energy.

Adsorbate-enhanced transport of metals on metal surfaces: Oxygen and sulfur on coinage metals

Abstract: Coarsening (i.e., ripening) of single-atom-high, metal homoepitaxial islands provides a useful window on the mechanism and kinetics of mass transport at metal surfaces. This article focuses on this type of coarsening on the surfaces of coinage metals (Cu, Ag, Au), both clean and with an adsorbed chalcogen (O, S) present. For the clean surfaces, three aspects are summarized: (1) the balance between the two major mechanisms—Ostwald ripening (the most commonly anticipated mechanism) and Smoluchowski ripening—and how that balance depends on island size; (2) the nature of the mass transport agents, which are metal adatoms in almost all known cases; and (3) the dependence of the ripening kinetics on surface crystallography. Ripening rates are in the order (110)>(111)>(100), a feature that can be rationalized in terms of the energetics of key processes. This discussion of behavior on the clean surfaces establishes a background for understanding why coarsening can be accelerated by adsorbates. Evidence that O and...

Deep GaN etching by inductively coupled plasma and induced surface defects

Abstract: GaN etching was studied in Cl2/Ar plasmas as a function of process parameters. In addition, for a better understanding of the etching mechanisms, Langmuir probe measurements and optical emission spectroscopy were carried out. Etch rate was found to depend strongly on bias power. After optimization, an etch rate greater than 1000 nm/min was achieved. A second part of this work is dedicated to the etched surface defects. An original method to estimate GaN dislocation density and to localize nanopipes in the material is presented. Columnar defects could also appear with impurities in the etching reactor. The authors also present a possible formation mechanism of those columnar defects.

Microplasma-assisted growth of colloidal Ag nanoparticles for point-of-use surface-enhanced Raman scattering applications

Abstract: The authors present a facile, rapid, one-step process to synthesize Ag nanoparticle for surface-enhanced Raman scattering (SERS) applications. Aqueous metal ions are electrochemically reduced by a microplasma to nucleate nanoparticles at ambient conditions (room temperature and atmospheric pressure) without any chemical reducing agents or stabilizer molecules. The nanoparticles are characterized by UV-visible absorbance and transmission electron microscopy, and found to be spherical, crystalline, and uniform with an average diameter of approximately 10 nm. Preparing nanoparticles with only a target analyte molecule present in solution allows intimate interaction between the metal particle surface and the analyte. Raman analysis shows that the scattered signal from a test molecule, crystal violet, is dependent on the process time and maximized after nanoparticles are grown for 20 min. This optimal SERS signal is large and permits detection of an analyte down to 10−10M concentrations.

Comparison of compressive and tensile relaxed composition-graded GaAsP and (Al)InGaP substrates

Abstract: The authors present a comparison of metal organic chemical vapor deposition grown compositionally graded metamorphic buffers, which enable virtual substrates with very high quality crystal lattices with lattice constants from 5.45 to 5.65 A (threading dislocation density, ρt, around 104 cm−2). The structures, grown on GaP or GaAs, consist of graded In-fraction InGaP and AlInGaP or graded P-fraction GaAsP. They show that surface roughness and locally strained regions of phase separation (branch defects) limit misfit dislocation glide velocity and escalate threading dislocation density. High surface roughness and branch defects in (Al)InGaP lead to the lowest quality virtual substrates we observed, with ρt of around 3×106 cm−2. In contrast, graded mixed-anion films of GaAsP avoid branch defects and minimize surface roughness, giving superior defect densities, as low as 104 cm−2 at useful lattice constants halfway between that of Si and Ge. Tensile graded GaAs1−zPz layers yield the smoothest films (0.78 nm r...

Residual stress stability in fiber textured stoichiometric AlN film grown using rf magnetron sputtering

Abstract: The authors report on the stability of mechanical stress with aging and thermal cycling for columnar structured stoichiometric and homogeneous aluminum nitride thin films grown using radio frequency magnetron sputtering technique. The set of deposition parameters were optimized for the best possible orientation of crystallites in the c axis of compositionally stoichiometric films. The as-grown stress in the slightly nitrogen-rich film does not change when exposed to the atmosphere following deposition, while that in the nitrogen-deficient film, it changes due to oxidation. Additionally, the magnitude of as-grown stress has been found to depend on the substrate material in addition to the deposition parameters. The stress in the film grown on a Si(001) substrate was more tensile than in the film grown on a semi-insulating (si) GaAs(001) substrate for a given set of deposition parameters. Furthermore, the stress in the film grown on Si decreased with temperature, while that on si GaAs increased, indicating ...

Surface loss rates of H and Cl radicals in an inductively coupled plasma etcher derived from time-resolved electron density and optical emission measurements

Abstract: A study is undertaken of the loss kinetics of H and Cl atoms in an inductively coupled plasma (ICP) reactor used for the etching of III-V semiconductor materials. A time-resolved optical emission spectroscopy technique, also referred to as pulsed induced fluorescence (PIF), has been combined with time-resolved microwave hairpin probe measurements of the electron density in a pulsed Cl2/H2-based discharge for this purpose. The surface loss rate of H, kwH, was measured in H2 plasma and was found to lie in the 125–500 s−1 range (γH surface recombination coefficient of ∼0.006–0.023), depending on the reactor walls conditioning. The PIF technique was then evaluated for the derivation of kwCl, and γCl in Cl2-based plasmas. In contrast to H2 plasma, significant variations in the electron density may occur over the millisecond time scale corresponding to Cl2 dissociation at the rising edge of the plasma pulse. By comparing the temporal evolution of the electron density and the Ar-line intensity curves with 10% of Ar added in the discharge, the authors show that a time-resolved actinometry procedure using Ar as an actinometer is valid at low to moderate ICP powers to estimate the Cl loss rate. They measured a Cl loss rate of ∼125–200 s−1 (0.03≤γCl≤0.06) at 150 W ICP power for a reactor state close to etching conditions. The Cl surface loss rate was also estimated for high ICP power (800 W) following the same procedure, giving a value of ∼130–150 s−1 (γCl∼0.04), which is close to that measured at 150 W ICP power.

Etching studies of silica glasses in SF6/Ar inductively coupled plasmas: Implications for microfluidic devices fabrication

Abstract: To fabricate microlaboratories, commercially available silica glasses represent a good alternative to the expensive quartz or fused silica substrates. Therefore, the authors have here investigated the behavior of four of them—Vycor, Pyrex, D263, and AF45—in SF6 and SF6/Ar inductively coupled plasmas. Using Vycor, a material close to pure SiO2, as a reference, they demonstrated that the etch rate negatively correlates with the global content in metallic oxides. However, no such clear trend was found for the surface roughness and they hypothesize that the large asperities (>500 nm) sometimes observed might be due to local variation in the glass surface composition. Furthermore, investigations on the influence of the plasma conditions (i.e., source power, dc self-bias, gas mixture, and pressure) on the etch rate, surface chemistry, and surface morphology, as well as positive ion current and fluorine concentration measurements, enable them to unravel an ion enhanced chemical etching mechanism, where stronger ...

Highly piezoelectric AlN thin films grown on amorphous, insulating substrates

Abstract: AlN thin films were grown by reactive sputtering on amorphous SiO2 thin films. Film texture, x-ray rocking curve width, mechanical stress, and the clamped piezoelectric constant d33,f were studied as a function of rf bias power and substrate roughness. A high d33,f of 5.0 pm/V was achieved at low substrate roughness and low mechanical AlN film stress. Increasing substrate roughness and stress leads to a deterioration of d33,f, which is correlated with a higher density of opposite polarity grains detected by piezoresponse force microscopy. Extrapolating to 100% uniform polarity, a d33,f of 6.1 pm/V is derived as highest possible value, probably corresponding to the d33,f=e33/c33E of perfect single crystalline material. Growth mechanisms are proposed and underlined by high resolution transmission electron microscopy to explain the observed phenomena.

Electrical and optical properties of Nb-doped TiO2 films deposited by dc magnetron sputtering using slightly reduced Nb-doped TiO2−x ceramic targets

Abstract: Nb-doped anatase TiO2 films were deposited on unheated glass by dc magnetron sputtering using slightly reduced Nb-doped TiO2−x targets (Nb concentration: 3.7 and 9.5 at. %) with various hydrogen or oxygen flow ratios. After postannealing in a vacuum (6×10−4 Pa) at 500 °C for 1 h, both films were crystallized into the polycrystalline anatase TiO2 structure. The resistivity decreased from 1.6×10−3 to 6.3×10−4 Ω cm with increasing Nb concentration from 2.8 to 8.0 at. %, where the carrier density increased from 5.4×1020 to 2.0×1021 cm−3 and the Hall mobility was almost constant at 5–7 cm2 V−1 s−1. The films exhibited a high transparency of over 60%–80% in the visible region.

In situ analyses on negative ions in the sputtering process to deposit Al-doped ZnO films

Abstract: The origin of high energy negative ions during deposition of aluminum doped zinc oxide (AZO) films by dc magnetron sputtering of an AZO (Al2O3: 2.0 wt %) target was investigated by in situ analyses using the quadrupole mass spectrometer combined with the electrostatic energy analyzer. High energy negative oxygen (O−) ions which possessed the kinetic energy corresponding to the cathode sheath voltage were detected. The maximum flux of the O− ions was clearly observed at the location opposite to the erosion track area on the target. The flux of the O− ions changed hardly with increasing O2 flow ratio [O2/(Ar+O2)] from 0% to 5%. The kinetic energy of the O− ions decreased with decreasing cathode sheath voltage from 403 to 337 V due to the enhancement of the vertical maximum magnetic field strength at the cathode surface from 0.025 to 0.100 T. The AZO films deposited with the lower O− bombardment energy showed the higher crystallinity and improved the electrical conductivity.

Structural and optical properties of yttrium oxide thin films for planar waveguiding applications

Abstract: Thin films of Yttrium Oxide, Y2O3 were deposited by reactive sputtering and reactive evaporation to determine their suitability as a host for a rare earth doped planar waveguide upconversion laser. The optical properties, structure and crystalline phase of the films were found to be dependent on the deposition method and process parameters. X-ray diffraction (XRD) analysis on the 'as-deposited' thin films revealed that the films vary from amorphous to highly crystalline with a strong peak along the plane of Y2O3. The samples with the polycrystalline structure had a stoichometry close to bulk cubic Y2O3. SEM imaging revealed a regular column structure confirming their crystalline nature. The thin film layers which allowed guiding in both the visible and infra-red region had lower refractive indices, higher oxygen content and had a more amorphous structure. Higher oxygen pressures during the deposition leads to a more amorphous layer.

Flexible indium zinc oxide/Ag/indium zinc oxide multilayer electrode grown on polyethersulfone substrate by cost-efficient roll-to-roll sputtering for flexible organic photovoltaics

Abstract: The authors describe the preparation and characteristics of flexible indium zinc oxide (IZO)-Ag-IZO multilayer electrodes grown on flexible polyethersulfone (PES) substrates using a roll-to-roll sputtering system for use in flexible organic photovoltaics. By the continuous roll-to-roll sputtering of the bottom IZO, Ag, and top IZO layers at room temperature, they were able to fabricate a high quality IZO-Ag-IZO multilayer electrode with a sheet resistance of 6.15e/square, optical transmittance of 87.4%, and figure of merit value of 42.03×10−3Ω−1 on the PES substrate. In addition, the IZO-Ag-IZO multilayer electrode exhibited superior flexibility to the roll-to-roll sputter grown single ITO electrode due to the existence of a ductile Ag layer between the IZO layers and stable amorphous structure of the IZO film. Furthermore, the flexible organic solar cells (OSCs) fabricated on the roll-to-roll sputter grown IZO-Ag-IZO electrode showed higher power efficiency (3.51%) than the OSCs fabricated on the roll-to...

Influence of substrate temperature on glancing angle deposited Ag nanorods

Abstract: When Ag sculptured thin films were grown with glancing angle deposition by ion beam sputtering at either room temperature or elevated substrate temperatures TS, a large morphological difference was observed. The incident particle flux reached the silicon substrate at a glancing angle β≥80° as measured to the substrate normal. A slit aperture was used in order to reduce the particle beam divergence. At room temperature, columnar structures were formed, irrespective of the presence of the slit aperture. At elevated temperatures (573 and 623 K) and collimated particle flux in the presence of the slit aperture, however, enhanced surface diffusion causes the growth of crystalline nanorod- and nanowirelike structures. In the absence of the slit aperture, the flux beam divergence is higher, resulting in island- and mountainlike crystalline structures. The density of the nanorods and nanowires was observed to be higher on the planar Si substrates in comparison to honeycomblike prepatterned substrates with differe...

Tungsten oxide (WO3) thin films for application in advanced energy systems

Abstract: Inherent processes in coal gasification plants produce hazardous hydrogen sulfide (H2S), which must be continuously and efficiently detected and removed before the fuel is used for power generation. An attempt has been made in this work to fabricate tungsten oxide (WO3) thin films by radio-frequency reactive magnetron-sputter deposition. The impetus being the use of WO3 films for H2S sensors in coal gasification plants. The effect of growth temperature, which is varied in the range of 30–500 °C, on the growth and microstructure of WO3 thin films is investigated. Characterizations made using scanning electron microscopy (SEM) and x-ray diffraction (XRD) indicate that the effect of temperature is significant on the microstructure of WO3 films. XRD and SEM results indicate that the WO3 films grown at room temperature are amorphous, whereas films grown at higher temperatures are nanocrystalline. The average grain-size increases with increasing temperature. WO3 films exhibit smooth morphology at growth tempera...

Effective atomic layer deposition procedure for Al-dopant distribution in ZnO thin films

Abstract: A zinc-metal dopant-oxygen precursor exposure cycle is demonstrated as a modified deposition procedure for better distribution of Al-dopants in ZnO films by atomic layer deposition with the aim to reduce the formation of nanolaminate thin films that might form with the typically used alternating ZnO and metal oxide deposition procedure. The distribution and chemical bonding states of Al-dopants were studied with various dopant deposition intervals of Zn–Al–O precursor and Zn–O cycles at 1::4, 1::9, 1::14, and 1::19 ratios. The smallest resistivity of Al-doped ZnO film without degradation of transparency was obtained at 250 °C with 5.37×10−4 Ω cm.

Microstructure and chemical wet etching characteristics of AlN films deposited by ac reactive magnetron sputtering

Abstract: The influence of the surface morphology of a molybdenum underlayer on the crystallinity and etchability of reactively sputtered c-axis oriented aluminum nitride thin films was investigated. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, high resolution x-ray diffraction, and defect selective chemical etching were used to characterize the microstructure of the Mo and AlN films. 1000nm thick films of AlN with a full width at half maximum (FWHM) of the x-ray rocking curve ranging from 1.1° to 1.9° were deposited on 300nm thick Mo underlayers with a FWHM of around 1.5°. The Ar pressure during the Mo deposition had a critical effect on the Mo film surface morphology, affecting the structure of the subsequently deposited AlN films and, hence, their wet etching characteristics. AlN films deposited on Mo sputtered at a relatively high pressure could not be etched completely, while AlN films deposited on low pressure Mo etched more easily. Postdeposition etching of the Mo surface in Ar rf discharge prior to deposition of the AlN film was found to influence the formation of AlN residuals that were difficult to etch. Optimal rf plasma etching conditions were found, which minimized the formation of these residuals.

Study of Ni2–Mn–Ga phase formation by magnetron sputtering film deposition at low temperature onto Si substrates and LaNiO3∕Pb(Ti,Zr)O3 buffer

Abstract: Film deposition of Ni2MnGa phaselike alloy by radio frequency (rf) magnetron sputtering was performed onto bare Si(100) substrates and LaNiO3∕Pb(Ti,Zr)O3 (LNO/PZT) ferroelectric buffer layer near room temperature. The prepared samples were characterized using conventional x-ray diffraction (XRD), superconducting quantum interference device, and electron dispersive x-ray spectroscopy from scanning electron microscope observations. The optimized films deposited under high rf power and low argon pressure present good surface quality and highly textured phase crystallization. The positioning distance between the substrate and the target-holder axis has some limited effect on the film’s composition due to the specific diffusion behavior of each element in the sputtering plasma. Extended four pole high resolution XRD analysis allowed one to discriminate the intended Ni–Mn–Ga tetragonal martensitic phase induced by the (100) LNO/PZT oriented buffer. This low temperature process appears to be very promising, allo...

Microstructure and tribological performance of nanocomposite Ti-Si-C-N coatings deposited using hexamethyldisilazane precursor

Abstract: Thick nanocomposite Ti–Si–C–N coatings (20–30 μm) were deposited on Ti–6Al–4V substrate by magnetron sputtering of Ti in a gas mixture of Ar, N2, and hexamethyldisilazane (HMDSN) under various deposition conditions. Microstructure and composition of the coatings were studied using scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy, while the mechanical and tribological properties of these coatings were studied using Rc indentation, and micro- and nanoindentations, solid particle erosion testing, and ball-on-disk wear testing. It has been observed that the Si concentration of these coatings is varied from 0% (TiN) to 15% (Ti–Si–C–N), while the structure of these coatings is similar to the nanocomposite Ti–Si–N coatings and consists of nanocrystalline B1 structured Ti(C,N) in an amorphous matrix of SiCxNy with the grain size of 5−>100 nm, depending on the coating preparation process. These coatings exhibit excellent adhesion when subjected to Rc indentation tests. The ...

Vacuum-calibration apparatus with pressure down to 10−10 Pa

Abstract: The vacuum-calibration apparatus is mainly composed of the extreme high-vacuum (XHV) system, ultrahigh vacuum system, and separated-flow system. The ultimate pressure of 7.9×10−10 Pa was obtained in the XHV calibration chamber by combining the magnetically levitated turbomolecular pump and nonevaporable getter pump (NEGP). The separated-flow method was used to extend the lower limit of vacuum-gauge calibration to 10−10 Pa. The uncertainty at lower limit was reduced when taking inert gases as test gases because NEGP has no pumping speed for inert gases. For this apparatus, the combined standard uncertainties were estimated to range from 1.5% at 10−4 Pa to 3.5% at 10−10 Pa.

Imaging characterization techniques applied to Cu(In,Ga)Se2 solar cells

Abstract: The authors present examples of imaging characterization on Cu(In,Ga)Se2 (CIGS) solar cell devices. These imaging techniques include photoluminescence imaging, electroluminescence imaging, illuminated lock-in thermography, and forward- and reverse-bias dark lock-in thermographies. Images were collected on CIGS devices deposited at the National Renewable Energy Laboratory with intentional spatial inhomogeneities of the material parameters. Photoluminescence imaging shows brightness variations, which correlate to the device open-circuit voltage. Photoluminescence and electroluminescence imaging on CIGS solar cells show dark spots that correspond to bright spots on images from illuminated and forward-bias lock-in thermography. These image-detected defect areas are weak diodes that conduct current under solar cell operating conditions. Shunt defects are imaged using reverse-bias lock-in thermography. The authors show how imaging can be used to detect structural defects detrimental to solar cell performance. T...

Comparison of Ti-Zr-V nonevaporable getter films deposited using alloy or twisted wire sputter-targets

Abstract: A comparison of the performance of nonevaporable getter (NEG) films deposited using two different types of targets has been made to find the one that has the best pumping properties. For the first time, the NEG coating was deposited using a preformed Ti-Zr-V alloy target. The NEG film characterization and pumping properties have been studied in comparison with a film deposited using the commonly used three-wire twisted target. It was demonstrated that the alloy target produces a NEG coating with uniform composition both laterally and in depth. The composition of the film was found to be the same as the target. Film topography and microstructure with 5 nm grain sizes were found to be the same for both targets. The main result is that the activation temperature of the NEG coating deposited using the Ti-Zr-V alloy target is 160 °C, which is 20 °C lower than for NEG coatings deposited using three twisted wires.