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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Influence of heavier impurity deposition on surface morphology development and sputtering behavior explored in multiple linear plasma devices

Surface morphology development and sputtering behavior of Cr, as a test material, have been explored under He plasma exposure at a low incident ion energy of ~80 eV in multiple linear plasma devices: PISCES-A, PSI-2, and NAGDIS-II. From comparison of the experiments in these devices, deposition of a small amount of heavier impurities (Mo in NAGDIS-II and Ta in PISCES-A) onto Cr is found to result in the formation of cone structures on the Cr surface due to preferential sputtering, resulting in a significant reduction (up to ~10 times) in the sputtering yield of Cr due to line-of-sight redeposition onto the neighboring cones. The heavier impurities are thought to originate from a sample holding cap/cover, which can be sputtered by a trace amount of intrinsic impurities (C, O, etc) as well as by Cr ionized in the plasma. It can be concluded from the Cr experiments, as well as additional Be data collected in PISCES-B, that heavier impurity deposition plays a major role in the cone structure formation, while other mechanisms (e.g. surface irregularity and oxide) also exist.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Deposition pressure dependent structural and optoelectronic properties of ex-situ boron-doped poly-Si/SiO x passivating contacts based on sputtered silicon

Among common methods to form polycrystalline silicon (poly-Si) films for passivating-contact solar cells, physical vapor deposition, in particular sputtering, is the safest one as it does not require any toxic gaseous precursors. One of the critical parameters to control the properties of sputtered silicon films is their deposition pressure. In this work, structural and optoelectronic characteristics of ex-situ boron-doped poly-Si/SiO x passivating contacts, formed from sputtered intrinsic amorphous silicon (a-Si) deposited at different pressures on top of SiO x /c-Si substrates and subjected to a high-temperature boron diffusion step, are investigated. The deposition rate and density of the as-deposited a-Si films increase with reducing pressure. Low-temperature photoluminescence spectra captured from the as-deposited samples at different pressures do not show typical emissions from hydrogenated a-Si. Meanwhile, their Fourier-transform infrared absorption spectra all show Si–H stretching modes, indicating that hydrogen had been initially incorporated into the chemical SiO x layers and eventually hydrogenated the a-Si/SiO x interfaces during the sputtering process. After the high-temperature boron-diffusion step, all hydrogen-related peaks disappear. Lower pressure films (1.5 and 2.5 mTorr) show more consistent improved performance after hydrogen treatments, compared to higher pressure films (4 and 5 mTorr). Overall, the resultant passivating contacts at 2.5 mTorr achieve a low single-side recombination current density Jo of ~9 fA/cm 2 , whereas their contact resistivity is still low at 15 mO cm 2 .

14 SOLAR ENERGY↗
DOE OSTI2021

Sputter-deposited CdMgTe for rear contact to CdSeTe/CdTe solar cells

CdTe-based photovoltaic device performance improvement is predominantly limited by open-circuit voltage. This work approaches the voltage deficit challenge through the incorporation of a cadmium magnesium telluride (CdMgTe) electron reflector layer at the back of 1.5- μm CdSeTe/CdTe absorbers to reduce back-surface recombination through a conduction band offset. A sputtered CdMgTe electron reflector layer permitted low fabrication temperatures and circumvented the intolerance of CdMgTe to thermal processing present in traditional close-space sublimation (CSS)-deposited CdMgTe devices. Here, we demonstrate that sputtered CdMgTe simultaneously promotes the retention of chlorine passivation and magnesium which is not feasible with CSS fabrication. We also show the importance of the Cu and Te back contact order in CdMgTe devices. Through the optimization of the sputtered CdMgTe substrate temperature, doping, and back structure configuration, 1.5 μm CdSeTe/CdTe devices with a sputtered CdMgTe layer achieved an efficiency of 16.0%, significantly higher than with CSS CdMgTe, and demonstrated partial enactment of electron-reflector behavior.

14 SOLAR ENERGY↗
DOE OSTI2023

Influence of oxygen on the optical and electrical properties of magnetron-sputtered indium tin oxide thin films at ambient temperature

Indium Tin Oxide (ITO) thin films are commonly used as transparent conductive layers in the production of solar cells. ITO films are typically heat-treated at temperatures exceeding 200 °C after magnetron sputtering to optimize the physical, optical, and electrical characteristics for photovoltaic devices. Here, this high temperature heating procedure greatly limits the use of potential substrates, particularly those comprised of low-temperature-rated polymers. Herein, we examine the physical, optical, and electrical transport effects of oxygen:argon plasmas during radio frequency magnetron sputtering of ITO on glass and flexible polymer surfaces without subsequent heat treatment. ITO thin films were characterized via sheet resistance testing, UV-Vis spectroscopy, X-ray diffraction, and scanning electron microscopy imaging. Sheet resistance measurements revealed an increase in surface resistance with increasing oxygen concentration during sputtering. UV-Vis optical transmittance measurements demonstrated an improvement in optical transmittance with an increase in oxygen concentration reaching a maximum transmittance at an oxygen concentration of 1-2 %. Most importantly, it was discovered that producing bilayers of ITO with pure argon sputtered plasmas followed by oxygen:argon plasmas produced ITO thin films with suitable resistance and transmittance without the need for high temperature post annealing. These results highlight a methodology for the deposition of ITO thin films on temperature sensitive substrates for flexible photovoltaics and low-cost module production.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Carbon Electrode with Sputtered Au Coating for Efficient and Stable Perovskite Solar Cells

Halide perovskite solar cells (PSCs) represent a low-cost and high-efficiency solar technology. However, most of the highly efficient PSCs need a noble electrode, such as Au, through thermal evaporation. Here it is reported that a sputtered Au electrode on a PSC could damage the organic hole transport layer (HTL) and the perovskite layer. Here, we report a simple, yet effective sputtered gold nanoparticle decorated carbon electrode to fabricate efficient and stable planar PSCs. The sputtered Au layer on the doctor-bladed coated carbon electrode can be directly applied to the perovskite semicells by mechanical stacking. By optimizing the gold thickness, a power conversion efficiency (PCE) of 16.87% was obtained for the composite electrode-based PSC, while the reference device recorded a PCE of 12.38%. The composite electrode-based device demonstrated 96% performance retention after being stored under humid conditions (50-60%) without encapsulation for ~100 h. This demonstrates a promising pathway toward the commercialization of large-scale manufacturable sputtered electrodes for the PSC solar module.

14 SOLAR ENERGY↗
DOE OSTI2018

Combinatorial Nitrogen Gradients in Sputtered Thin Films

High-throughput synthesis and characterization methods can significantly accelerate the rate of experimental research. For physical vapor deposition (PVD), these methods include combinatorial sputtering with intentional gradients of metal/metalloid composition, temperature, and thickness across the substrate. However, many other synthesis parameters still remain out of reach for combinatorial methods. Here, we extend combinatorial sputtering parameters to include gradients of gaseous elements in thin films. Specifically, a nitrogen gradient was generated in a thin film sample library by placing two MnTe sputtering sources with different gas flows (Ar and Ar/N 2 ) opposite of one another during the synthesis. The nitrogen content gradient was measured along the sample surface, correlating with the distance from the nitrogen source. The phase, composition, and optoelectronic properties of the resulting thin films change as a function of the nitrogen content. Furthermore, this work shows that gradients of gaseous elements can be generated in thin films synthesized by sputtering, expanding the boundaries of combinatorial science.

14 SOLAR ENERGY↗
DOE OSTI2022

Co-sputtering of lithium vanadium oxide thin films with variable lithium content to enable advanced solid-state batteries

Advanced solid-state batteries most likely will entail aggressive structures or architectures with constraints that typically limit processing temperatures. Considering this, we have identified the importance of providing lithiated electrode materials at a modest processing temperature. Here we describe a pathway to meet this by the development of a co-sputtering process using lithium oxide and vanadium oxide targets which enables the growth of lithiated vanadium oxide (LVO) thin films for application in solid-state batteries. Analysis of the structure and film composition of samples deposited with different co-sputtering rate ratios and post-annealing shows that multiple phases of Li x V 2 O 5 likely coexist (i.e. α-, ε-, δ-, and γ-V 2 O 5 ), and that this is unchanged after electrochemical cycling. The co-sputtering process can tune the lithium content up to a highly lithiated state of at least Li 2 V 2 O 5 . Electrochemical half-cells showed a significant amount of lithium available on the first charge (delithiation of LVO). LVO samples post-annealed at 300 °C showed typical redox peaks for Li x V 2 O 5 for both one and two lithium insertion reactions, which were highly reversible in most cases. A thin-film solid-state battery prototype using LVO as a cathode had 20% of the expected capacity, although the coulombic efficiency is near 100% at a fast rate (22C). As a result, this co-sputtering technique represents an opportunity for low temperature synthesis of pre-lithiated cathodes for thin film batteries, and introduces a broader methodology of depositing metal oxides with different alkali metal contents.

25 ENERGY STORAGE↗
DOE OSTI2013

Measuring the energy flux at the substrate position during magnetron sputter deposition processes

In this work, the energetic conditions at the substrate were investigated in dc magnetron sputtering (DCMS), pulsed dc magnetron sputtering (pDCMS), and high power impulse magnetron sputtering (HiPIMS) discharges by means of an energy flux diagnostic based on a thermopile sensor, the probe being set at the substrate position. Measurements were performed in front of a titanium target for a highly unbalanced magnetic field configuration. The average power was always kept to 400 W and the probe was at the floating potential. Variation of the energy flux against the pulse peak power in HiPIMS was first investigated. It was demonstrated that the energy per deposited titanium atom is the highest for short pulses (5 {mu}s) high pulse peak power (39 kW), as in this case, the ion production is efficient and the deposition rate is reduced by self-sputtering. As the argon pressure is increased, the energy deposition is reduced as the probability of scattering in the gas phase is increased. In the case of the HiPIMS discharge run at moderate peak power density (10 kW), the energy per deposited atom was found to be lower than the one measured for DCMS and pDCMS discharges. In these conditions, the HiPIMS discharge could be characterized as soft and close to a pulsed DCMS discharge run at very low duty cycle. For the sake of comparison, measurements were also carried out in DCMS mode with a balanced magnetron cathode, in the same working conditions of pressure and power. The energy flux at the substrate is significantly increased as the discharge is generated in an unbalanced field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

In situ analyses on negative ions in the indium-gallium-zinc oxide sputtering process

The origin of negative ions in the dc magnetron sputtering process using a ceramic indium-gallium-zinc oxide target has been investigated by in situ analyses. The observed negative ions are mainly O{sup -} with energies corresponding to the target voltage, which originates from the target and barely from the reactive gas (O{sub 2}). Dissociation of ZnO{sup -}, GaO{sup -}, ZnO{sub 2}{sup -}, and GaO{sub 2}{sup -} radicals also contributes to the total negative ion flux. Furthermore, we find that some sputtering parameters, such as the type of sputtering gas (Ar or Kr), sputtering power, total gas pressure, and magnetic field strength at the target surface, can be used to control the energy distribution of the O{sup -} ion flux.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Near sputter-threshold GaSb nanopatterning

Nanopatterning at sputter-threshold energies with Ar irradiation of GaSb (100) surfaces is presented. Comparison with high-energy irradiations up to 1000 eV is conducted measuring in-situ the composition evolution over irradiation time at early stages (e.g., <10{sup 17} cm{sup −2}) and up to nanostructure saturation (e.g., ∼10{sup 18} cm{sup −2}). Low-energy irradiation is conducted for energies between 15–100 eV and a low-aspect ratio nanostructured dot formation is found. Furthermore, the role of oxide on GaSb is found to delay nanostructure formation and this is predominant at energies below 100 eV. In-situ quartz crystal microbalance measurements collect sputtered particles yielding the sputter rate at threshold energies indicating a correlation between erosion and surface composition consistent with recent theoretical models. Ion-induced segregation is also found and indicated by both compositional measurements of both the surface and the sputtered plume.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

An innovative experimental setup for the measurement of sputtering yield induced by keV energy ions

An innovative experimental equipment allowing to study the sputtering induced by ion beam irradiation is presented. The sputtered particles are collected on a catcher which is analyzed in situ by Auger electron spectroscopy without breaking the ultra high vacuum (less than 10{sup −9} mbar), avoiding thus any problem linked to possible contamination. This method allows to measure the angular distribution of sputtering yield. It is now possible to study the sputtering of many elements such as carbon based materials. Preliminary results are presented in the case of highly oriented pyrolytic graphite and tungsten irradiated by an Ar{sup +} beam at 2.8 keV and 7 keV, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Highly oriented polycrystalline Cu{sub 2}O film formation using RF magnetron sputtering deposition for solar cells

Room temperature sputtering deposition and re-crystallization of the deposited thin films by rapid thermal annealing have been evaluating in detail as a formation method of Cu{sub 2}O active layer for solar cells, which minimize thermal budget in fabrication processes. Single phase polycrystalline Cu{sub 2}O films were obtained by a magnetron rf sputtering deposition and its crystallinity and electrical characteristics were controlled by the annealing. Hall mobility was improved up to 17 cm{sup 2}V{sup −1}s{sup −1} by the annealing at 600°C for 30s. Since this value was smaller than 47 cm{sup 2}V{sup −1}s{sup −1} of the film deposited under thermal equilibrium state using pulsed laser deposition at 600°C, some contrivances were necessary to compensate the deficiency. It was understood that the sputter-deposited Cu{sub 2}O films on (111)-oriented Pt films were strongly oriented to (111) face also by the self-assembly and the crystallinity was improved by the annealing preserving its orientation. The sputter-deposited film quality was expected to become equivalent to the pulsed laser deposition film from the results of X-ray diffractometry and photoluminescence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Controlling ion fluxes during reactive sputter-deposition of SnO{sub 2}:F

Magnetron sputtering of fluorine-doped tin oxide (FTO) is a scalable deposition method for large-area transparent conducting films used in fenestration, photovoltaics, and other applications. The electrical conductivity of sputtered FTO is, however, lower than that of spray-pyrolized FTO because of the ion damage induced by high energy ions leading to a reduction of the crystal quality in sputtered FTO films. In this study, various ion species present during the reactive sputtering of a metallic tin target in a mixed Ar/O{sub 2}/CF{sub 4} atmosphere are systematically characterized by energy and mass spectrometry, and possible ways of controlling the ion fluxes are explored. Ion energy distribution functions (IEDFs) of the negative ions F{sup −} and O{sup −} exhibit large peaks at an energy corresponding to the full target voltage. Although the applied partial pressure of CF{sub 4} is about 1/30 than that of O{sub 2}, the obtained IEDFs of F{sup −} and O{sup −} have comparable peak height, which can be attributed to a higher electronegativity of F. The IEDFs of positively charged O{sup +}, O{sub 2}{sup +}, Ar{sup +}, and Sn{sup +} species have their peaks around 2–8 eV. To control ion fluxes a solenoid or permanent magnets were placed between the target and the mass spectrometer. The flux of positive ions could be varied by several orders of magnitude as a function of the applied current through the solenoid, whereas the high-energy (>100 eV) negative F{sup −} and O{sup −} ions were not notably deflected. By using permanent magnets with the B-field orthogonal to the ion trajectory, the flux of O{sup −} ions could be decreased by two orders and the exposure to the high-energy F{sup −} ions was completely suppressed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Limits of carrier mobility in Sb-doped SnO{sub 2} conducting films deposited by reactive sputtering

Electron transport in Sb-doped SnO{sub 2} (ATO) films is studied to unveil the limited carrier mobility observed in sputtered films as compared to other deposition methods. Transparent and conductive ATO layers are deposited from metallic tin targets alloyed with antimony in oxygen atmosphere optimized for reactive sputtering. The carrier mobility decreases from 24 cm{sup 2} V{sup −1} s{sup −1} to 6 cm{sup 2} V{sup −1} s{sup −1} when increasing the doping level from 0 to 7 at. %, and the lowest resistivity of 1.8 × 10{sup −3} Ω cm corresponding to the mobility of 12 cm{sup 2} V{sup −1} s{sup −1} which is obtained for the 3 at. % Sb-doped ATO. Temperature-dependent Hall effect measurements and near-infrared reflectance measurements reveal that the carrier mobility in sputtered ATO is limited by ingrain scattering. In contrast, the mobility of unintentionally doped SnO{sub 2} films is determined mostly by the grain boundary scattering. Both limitations should arise from the sputtering process itself, which suffers from the high-energy-ion bombardment and yields polycrystalline films with small grain size.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Visible-light active thin-film WO{sub 3} photocatalyst with controlled high-rate deposition by low-damage reactive-gas-flow sputtering

A process based on reactive gas flow sputtering (GFS) for depositing visible-light active photocatalytic WO{sub 3} films at high deposition rates and with high film quality was successfully demonstrated. The deposition rate for this process was over 10 times higher than that achieved by the conventional sputtering process and the process was highly stable. Furthermore, Pt nanoparticle-loaded WO{sub 3} films deposited by the GFS process exhibited much higher photocatalytic activity than those deposited by conventional sputtering, where the photocatalytic activity was evaluated by the extent of decomposition of CH{sub 3}CHO under visible light irradiation. The decomposition time for 60 ppm of CH{sub 3}CHO was 7.5 times more rapid on the films deposited by the GFS process than on the films deposited by the conventional process. During GFS deposition, there are no high-energy particles bombarding the growing film surface, whereas the bombardment of the surface with high-energy particles is a key feature of conventional sputtering. Hence, the WO{sub 3} films deposited by GFS should be of higher quality, with fewer structural defects, which would lead to a decrease in the number of centers for electron-hole recombination and to the efficient use of photogenerated holes for the decomposition of CH{sub 3}CHO.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A hybrid electron cyclotron resonance metal ion source with integrated sputter magnetron for the production of an intense Al{sup +} ion beam

A metal ion source prototype has been developed: a combination of magnetron sputter technology with 2.45 GHz electron cyclotron resonance (ECR) ion source technology—a so called magnetron ECR ion source (MECRIS). An integrated ring-shaped sputter magnetron with an Al target is acting as a powerful metal atom supply in order to produce an intense current of singly charged metal ions. Preliminary experiments show that an Al{sup +} ion current with a density of 167 μA/cm{sup 2} is extracted from the source at an acceleration voltage of 27 kV. Spatially resolved double Langmuir probe measurements and optical emission spectroscopy were used to study the plasma states of the ion source: sputter magnetron, ECR, and MECRIS plasma. Electron density and temperature as well as Al atom density were determined as a function of microwave and sputter magnetron power. The effect of ECR heating is strongly pronounced in the center of the source. There the electron density is increased by one order of magnitude from 6 × 10{sup 9} cm{sup −3} to 6 × 10{sup 10} cm{sup −3} and the electron temperature is enhanced from about 5 eV to 12 eV, when the ECR plasma is ignited to the magnetron plasma. Operating the magnetron at constant power, it was observed that its discharge current is raised from 1.8 A to 4.8 A, when the ECR discharge was superimposed with a microwave power of 2 kW. At the same time, the discharge voltage decreased from about 560 V to 210 V, clearly indicating a higher plasma density of the MECRIS mode. The optical emission spectrum of the MECRIS plasma is dominated by lines of excited Al atoms and shows a significant contribution of lines arising from singly ionized Al. Plasma emission photography with a CCD camera was used to prove probe measurements and to identify separated plasma emission zones originating from the ECR and magnetron discharge.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Elementary surface processes during reactive magnetron sputtering of chromium

The elementary surface processes occurring on chromium targets exposed to reactive plasmas have been mimicked in beam experiments by using quantified fluxes of Ar ions (400–800 eV) and oxygen atoms and molecules. For this, quartz crystal microbalances were previously coated with Cr thin films by means of high-power pulsed magnetron sputtering. The measured growth and etching rates were fitted by flux balance equations, which provided sputter yields of around 0.05 for the compound phase and a sticking coefficient of O{sub 2} of 0.38 on the bare Cr surface. Further fitted parameters were the oxygen implantation efficiency and the density of oxidation sites at the surface. The increase in site density with a factor 4 at early phases of reactive sputtering is identified as a relevant mechanism of Cr oxidation. This ion-enhanced oxygen uptake can be attributed to Cr surface roughening and knock-on implantation of oxygen atoms deeper into the target. This work, besides providing fundamental data to control oxidation state of Cr targets, shows that the extended Berg's model constitutes a robust set of rate equations suitable to describe reactive magnetron sputtering of metals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Study on re-sputtering during CN{sub x} film deposition through spectroscopic diagnostics of plasma

A nitrogen-carbon plasma was generated during the deposition of carbon nitride (CN{sub x}) thin films by pulsed laser ablation of a graphite target in a discharge nitrogen plasma, and the optical emission of the generated nitrogen-carbon plasma was measured for the diagnostics of the plasma and the characterization of the process of CN{sub x} film deposition. The nitrogen-carbon plasma was recognized to contain various species including nitrogen molecules and molecular ions excited in the ambient N{sub 2} gas, carbon atoms and atomic ions ablated from the graphite target and CN radicals. The temporal evolution and spatial distribution of the CN emission and their dependence on the substrate bias voltage show two groups of CN radicals flying in opposite directions. One represents the CN radicals formed as the products of the reactions occurring in the nitrogen-carbon plasma, revealing the reactive deposition of CN{sub x} film due to the reactive expansion of the ablation carbon plasma in the discharge nitrogen plasma and the effective formation of gaseous CN radicals as precursors for CN{sub x} film growth. The other one represents the CN radicals re-sputtered from the growing CN{sub x} film by energetic plasma species, evidencing the re-sputtering of the growing film accompanying film growth. And, the re-sputtering presents ion-induced sputtering features.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗