Film Contamination Research Articles

Sub-micro organic light emitting diode arrays defined by tip-induced resist hollow structures

Fabrication of micro-nanoscaled organic light-emitting diodes (OLEDs) with uniformity and scalability has emerged as a promising technology in next-generation displays and light sources. Patterning polymer resist into well-defined structures is a crucial step in the fabrication of optoelectronic device arrays, especially for cost-effectively fabricating lithographical sub-micro resist structures. Atomic force microscopy (AFM) ploughing is promising for patterning high-resolution polymer resist structures owing to nanoscaled resolution, high controllability, with relatively low cost under flexible working conditions. However, the defects of structures resulting from polymer debris contamination or spin-coated film exfoliation in ploughing procedure limit their further application in fabrication of device arrays. Herein, lithographical poly(methyl methacrylate) (PMMA) resist patterns in micro-nanoscale with excellent reproducibility and uniformity are achieved via AFM mechanical ploughing at the optimized lithography conditions. Taking use of the isolated PMMA cavities as current channels, we fabricate prototype OLED arrays with pixels of 500 nm and 1 μm. This work paves the way for developing a tip-based mechanical lithography approach to fabricate micro-nanoscaled optoelectronic devices in a simple and low-cost way.

Space Environment Effects on the Electron Yields of Thermal Control Coatings

Space-environment-induced degradation of white thermal control coatings from the Long Duration Exposure Facility (LDEF) was investigated. Much of the exterior of the LDEF was painted with a white thermal control coating, Aeroglaze A276; and most of the interior was coated with a black thermal control coating, Aeroglaze Z306. Outgassing from these coatings and other LDEF materials interacted with the white surface when exposed to sunlight after volatile materials condensed on the LDEF surfaces. Surface morphology was characterized by optical and scanning electron microscopies. Fourier-transform infrared spectroscopy and energy-dispersive x-ray spectroscopy were used to identify the chemical compounds and elements present in the contamination film. Many material properties were modified due to the prolonged approximately six year low-Earth-orbit exposure, but electron yield (EY) was the focus of this study due to its dominance in spacecraft charging. Measurements showed an increase in maximum EY with increased contamination, with the maximum EY more than doubling in some cases. The NASA Charging Analyzer Program simulations for simplified models of the LDEF showed the impact of the degradation on spacecraft charging under different environmental conditions; equilibrium surface potentials varied by more than 100% in some cases.

Surface Cleaning and Modification of Oxide Films by Atomic Hydrogen Annealing

To suppress degradation of the electrical property of field-effect transistors, the removal of C contamination without damaging oxide films is important in the semiconductor industry. In addition, to reduce bonding failure, it is necessary to remove native oxide films from metal films. To achieve this, atomic hydrogen was generated by the decomposition of H2 gas on a heated tungsten mesh. This surface treatment is referred to as atomic hydrogen annealing (AHA). The reaction of atomic hydrogen with various oxide films, such as AlOx, TiOx, CrOx, NiOx, CuOx, and SiOx, was investigated. The O concentrations in Al, Ti, and Cr slightly decreased by AHA. The thermal oxide films prepared at 400 ℃ were not changed by AHA, except for CuOx. The reduction in the reactivity of the oxide film due to atomic hydrogen depends on the metal–oxygen bond strength. In addition, although the thermal oxide film of the Si substrate prepared at 1000 ℃ was not etched, AHA resulted in the etching of the Si-rich SiOx. These findings are useful for the removal of C contamination and native oxide films and for controlling the surface properties of oxide films.

New Self-Clinching Fasteners for Electric Conductive Connections

This paper presents new rotational and longitudinal symmetric self-clinching fasteners to fabricate reliable connections in busbars with low electrical resistance for energy distribution systems. Connections consist of form-closed joints that are hidden inside regions where two busbars overlap. The investigation into the fabrication and performance of the new self-clinched joints involved finite element modelling and experimentation to determine the required forces and to evaluate the electric current flow and the electrical resistance at different service temperatures. The original design of the joints that was proposed in a previous work was modified to account for busbar strips of copper and/or aluminum with similar or dissimilar thicknesses, connected by means of self-clinching fasteners made from the same materials of the busbars, instead of steel. The effectiveness of the new self-clinched joints was compared to that of conventional bolted joints that are included in the paper for reference purposes. The results show that rotational symmetric self-clinching fasteners yield lighter fabrication and more compact joints with a similar electrical resistance to that of bolted joints. They also show that longitudinal symmetric self-clinching fasteners aimed at replicating the resistance-seam-welding contact conditions yield a reduction in electrical resistance to values close to that of ideal joints, consisting of two strips in perfect contact and without contaminant or oxide films along their overlapped surfaces.

Contaminant film thickness affects walkway friction measurements.

Walkway tribometers are used to measure available friction for evaluating walkway safety and pedestrian slip risk. Numerous variables can affect tribometer measurements, including the type and distribution of contaminants on the surface. Here, we quantified the effect of application method on contaminant film thickness, and the effect of film thickness on tribometer measurements on the four reference walkway surfaces used in ASTM F2508-16e. Distilled water, 0.05% sodium lauryl sulfate (SLS) solution, and 0.04% Triton X-100 solution were poured, squirted, and sprayed onto the surfaces to quantify their naturally occurring film thicknesses. These application methods had a significant effect on the resulting film thickness (p < 0.038), with the pour method consistently generating the thickest films and the spray method generating the thinnest films. We then quantified the effect of film thickness for the three contaminants (thickness range 0.3–3.3 mm) on the friction measurements of three common tribometers (Mark IIIB, English XL, and BOT 3000E) on each reference surface. A separate ANOVA was used for each of the 3 × 4 × 3 = 36 combinations of tribometer, surface, and contaminant. Friction measured with the Mark IIIB decreased with increasing film thickness on one surface across all three contaminants and on a second surface with the SLS contaminant. Friction measured with the BOT 3000E was sensitive to film thickness on two surfaces with water and one surface with Triton. The XL was unaffected by contaminant film thickness. Overall, despite significant differences in film thickness with contaminant application method, friction measurements were either insensitive to film thickness or varied only a small amount in all cases except for the Mark IIIB on the roughest surface. Film thickness did not alter the relative slip resistance of the four ASTM F2508 reference surfaces.

CONTROL OF THE OPTICAL SURFACE PURITY OF THE ELEMENTS BY THE ELLIPSOMETRIC METHOD

The possibility of controlling the chemical purity of the surface of optical elements by the ellipsometric method has been analyzed. The rationale of the possibility of measuring the parameters of contaminating films on the optical surface of elements by the ellipsometric method has been given simplification has been&#x0D; shown of the process of determining the thickness of the contaminating film while expanding the possibility of its measurement on an optical element made of different materials. Ellipsometric studies of freshly polished and used metal mirrors made of copper and copper alloy (zirconium bronze), aluminum and its alloys AMG-6, AL-9, AL-24 have been carried out. Research has also been conducted on elements made of K-8 and&#x0D; K-108 (State Standard 3514-94) optical glasses, which are the most typical materials used for manufacture of optical parts for laser technique of visible and near IR-range, from single crystals of NaCl, BaF2 and sapphire (Al2O3). Parameters of contaminating films on the surface of these elements have been measured.&#x0D; It has been concluded that it is advisable to use the ellipsometry method during the input (before carrying out physicochemical cleaning) and during the output (after cleaning) control of the optical element to assess the contamination of the optical surface and also for the quantitative analysis of the concentration of contaminants on the optical surface of the elements while working off the technology of their physicochemical cleaning.

Intermittent failure mechanism and stabilization of microscale electrical contact

The stability and lifetime of electrical contact pose a major challenge to the performance of microelectro-mechanical systems (MEMS), such as MEMS switches. The microscopic failure mechanism of electrical contact still remains largely unclear. Here conductive atomic force microscopy with hot switching mode was adopted to simulate the asperity-level contact condition in a MEMS switch. Strong variation and fluctuation of current and adhesion force were observed during 10,000 repetitive cycles, exhibiting an “intermittent failure” characteristic. This fluctuation of electrical contact properties was attributed to insulative carbonaceous contaminants repetitively formed and removed at the contact spot, corresponding to degradation and reestablishment of electrical contact. When contaminant film was formed, the contact interface became “metal/carbonaceous adsorbates/metal” instead of direct metal/metal contact, leading to degradation of the electrical contact state. Furthermore, a system of iridium/graphene on ruthenium (Ir/GrRu) was proposed to avoid direct metal/metal contact, which stabilized the current fluctuation and decreased interfacial adhesion significantly. The existence of graphene enabled less adsorption of carbonaceous contaminants in ambient air and enhanced mechanical protection against the repetitive hot switching actions. This work opens an avenue for design and fabrication of microscale electrical contact system, especially by utilizing two-dimensional materials.

A strong basis for friction as the origin of size effect in cutting of metals

A study has been made of the phenomenon of size effect in cutting of metals, namely increase in the specific energy with decreasing chip thickness, in the absence of edge radius effects and under ideal two-dimensional cutting conditions. Freshly cleaved glass knives are used to achieve cutting edges that are sharp on an atomic level. An instrumented ultramicrotomy apparatus is described in which it is possible to achieve two-dimensional orthogonal cutting at small cutting depths in the range of 100 nm to 3 micrometers. Based on observations with three metals (aluminum, copper and zinc), new evidence is presented in support of tool-chip friction as the primary source of the size effect. It is shown that size effect arises as a result of non-proportional decrease of the friction component with the underlying length scale. Calculation of the shear flow stress during cutting showed that this was approximately constant for a given material, independent of the depth of cut. Size dependence of tool-chip friction and contact size is interpreted in terms of the junction growth and adhesion models. Cutting experiments are also carried out with tools covered with solid and liquid contaminants. These results show that contaminant films effectively diminish adhesion and lead to a drastic reduction in the size effect, suggesting practical benefits for industrial manufacturing processes.

Twin-CQCM and Twin-TQCM Sensors With Wide Operating Temperature Range for Outgassing and Atomic Oxygen Measurement

In this paper, we propose a new Quartz Crystal Microbalance (QCM) sensor with temperature control, which can assess outgassing properties during spacecraft development. It will be referred to as the “Twin-QCM sensor”. There are two types. The Twin-Cryogenic QCM (Twin-CQCM) sensor is warmed by a built-in heater with an operating temperature of -190 to +125°C, and the Twin-ThermoelectricQCM (Twin-TQCM) sensor is warmed and cooled by a built-in Peltier module that can control the temperature within -80 to +125°C. Using a temperature compensation technique, the temperature-dependent drift of the frequency was found to be less than ±10 ppm over all operating temperatures. An RTD temperature sensor was mounted on the quartz crystal to improve the accuracy of temperature measurement. To confirm the accuracy, an additional temperature sensor installed at the center of the crystal. The sensor output temperature value was compared to that of the additional sensor, with the difference between both temperature sensors being +0.4 to +2.6°C in the temperature range from -130 to +100°C. Through the measurement of the sensor's dynamic range, it was found that the deposited contaminant film in a vacuum increasingly changed such physical properties as viscoelasticity as the temperature increases.

Rubber Adhesion and Friction: Role of Surface Energy and Contamination Films

We study the influence of the surface energy and contamination films on rubber adhesion and sliding friction. We find that there is a transfer of molecules from the rubber to the substrate which reduces the work of adhesion and makes the rubber friction insensitive to the substrate surface energy. We show that there is no simple relation between adhesion and friction: adhesion is due to (vertical) detachment processes at the edge of the contact regions (opening crack propagation), while friction in many cases is determined mainly by (tangential) stick-slip instabilities of nanosized regions, within the whole sliding contact. Thus while the pull-off force in fluids may be strongly reduced (due to a reduction of the work of adhesion), the sliding friction may be only slightly affected as the area of real contact may be dry, and the frictional shear stress in the contact area nearly unaffected by the fluid.

Mathematical description of automobile headlight contamination when driving on a wet road

The article describes the process of contamination of automobile headlights in order to calculate contamination speed using a mathematical model. The authors published results of the study aimed at solving the problem of negative application of the CAIM (chemical anti-icing materials) on winter roads. In particular, it was found that when driving vehicles on winter roads covered with CAIM, the headlights become contaminated. The headlight contamination with dirty droplets from under the wheels of a vehicle ahead was analyzed. The detachment of droplets from the moving wheel and the path of droplets from the wheel to the headlights of the vehicle behind were analyzed and described. Process is studied of contaminant film formation which decreases light transmission was carried out. Road experiments were carried out. Along with the physicomathematical description of the process under consideration, they give new knowledge about headlight contamination depending on the vehicle speed. The mathematical model supplemented by the experimental study allows us to predict the rate of headlight contamination by the wheels of vehicles ahead when moving along roads covered with chemical anti-icing reagents depending on the speed and the distance between the vehicles.

Blind to Chemistry: Molecular Contaminant Films We Could Be Missing During Visual Inspections and the Potential Impact to System Performance

Abstract Throughout the assembly, integration, and test process, molecular contamination levels of space mission hardware are monitored to meet system performance requirements. Qualitatively, reflective surfaces and witness mirrors are continuously inspected for the visible presence of molecular contaminant films. Quantitatively, periodic reflectance measurements of witness mirrors indicate changes of mirror reflectivity over time due to the accumulation of molecular contaminant films. However, both methods only consider the presence of a contaminant film and not the molecular composition. Additionally, there is a risk that hardware may appear to be “visibly clean” even with a molecular contaminant film present on critical surfaces. To address these issues, experiments were performed to quantify the maximum molecular contaminant film that could be missed in visual inspections on witness mirrors with five different contaminants present. The corresponding changes in mirror reflectivity were modeled using the program STACK to determine the impact to space mission hardware performance. The results of this study not only show the criticality in considering the chemical make-up of molecular contaminant films on system performance, but also the need to recognize and understand the limitations of traditional visual inspection techniques on detecting molecular contaminant films.

Electrodeposition of Gadolinium Metal from Organic Solvents

Neutron phase contrast imaging (NPCI) is a non-destructive analysis tool currently in use with thermal neutrons. It relies on neutron transmission gratings to detect the phase signal. These gratings are typically fabricated from gadolinium (Gd), as this element has the highest neutron absorption cross section at 250,000 barns. There is a wealth of literature documenting the fabrication process of these gratings, including depositing Gd via sputter coating, evaporation and particle settling techniques at dimensions appropriate to absorb thermal neutrons. However tighter packing density, less contamination and thicker Gd films are necessary for neutrons at higher energy levels ( >0.025 eV). With these requirements in mind, we investigated the electrodeposition of Gd on Si substrate gratings for use with higher energy neutrons.Electrodeposition of Gd alloys is well documented in literature. With a very cathodic reduction potential of -2.28 V (acidic solution), depositing pure Gd metal is a tricky endeavor. In addition to excessive hydrogen evolution during plating, Gd undergoes rapid oxidation when exposed to air. This phenomenon is exacerbated with thin films due to their high surface area and can lead to pyrophoric events and brittle films that sluff off the substrate over time. We investigated aqueous solutions and with the use of many oxygen scavengers, we successfully plated gadolinium oxide (Gd2O3) thin films. However, this technique was not viable due to poor adhesion and rapid oxidation. Hoping for less oxygen contamination, we moved to two polar, aprotic organic solvents with promising potential windows: dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The solubility of gadolinium(III) salts was investigated in the two solvents. At elevated temperatures, gadolinium(III) fluoride and gadolinium(III) chloride were soluble compounds, as well as gadolinium toluenesulfonic acid (GdTsOH). To increase conductivity, potassium chloride (KCl) and tetrabutylammonium tetrafluoroborate (TBATFB) were used as conducting salts. Pulsed plating techniques led to repeatable thin film deposition and EDS confirmed the presence of gadolinium uniformly spread over the surface. However, these films also suffered from poor adhesion, likely due to water contamination in the bath.The limitations outlined above led to electroplating Gd in dimethyl sulfone (DMSO2). DMSO2 is used in industry as a high-temperature solvent; its large dielectric constant reflects its high polarity, indicating strong intermolecular interactions in liquid phase. A melting temperature of 109 °C eliminates the concern of water contamination in the bath. Solubility tests are being repeated in this new polar solvent and linear sweeps and EIS continue to indicate favorable plating conditions. Parameters, such as Gd metal loading and substrate pretreatments are being optimized for thick films with good adhesion. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2020-5179 A

Removal of hydrocarbon contamination and oxide films from atom probe specimens

Many materials science phenomena require joint structural and chemical characterization at the nanometer scale to be understood. This can be achieved by correlating electron microscopy (EM) and atom probe tomography (APT) subsequently on the same specimen. For this approach, specimen yield during APT is of particular importance, as significantly more instrument time per specimen is invested as compared to conventional APT measurements. However, electron microscopy causes hydrocarbon contamination on the surface of atom probe specimens. Also, oxide layers grow during specimen transport between instruments and storage. Both effects lower the chances for long and smooth runs in the ensuing APT experiment. This represents a crucial bottleneck of the method correlative EM/APT. Here, we present a simple and reliable method based on argon ion polishing that is able to remove hydrocarbon contamination and oxide layers, thereby significantly improving APT specimen yield, particularly after EM.

The hybrid action tool for operations of cleaning of turbine units cavities

The paper deals with the hybrid action tool for cleaning of cavities and elements of turbine units whose operation is based on a combination of action of a water-ice flow with mechanical shock influence of the small concentrated masses mounted on elastic suspensions. Receiving energy from the flow, the masses, performing self-oscillating motion, come into contact with the treated surface having a layer of strong contamination, and create a multipoint shock-cyclic loading of the surface, which results in active development of initial defects of the contamination film, due to which the following action of the water-ice stream produces better and more productive cleaning. It is shown that the generated local stresses, determined on the basis of Hertz contact problems, reach 15-20 MPa, do not have a significant effect on the surface of the base, which is a thin curves shell, do not change the state of its surface in the plane of adhesion, but result in defects in surface film in the form of cracks and delaminations . In this case the film is eliminated by water-ice flow more dynamically. The use of water-ice jet, formed by the original tubeless device, enables the formation of a wide flow (with the top angle of p/12… p/6) and the work of its ice particles is spent on grinding the surface film. The jet stream cleans the surface and removes the products of destruction beyond the impact.The use of a hybrid tool has increased the productivity of treatment with the wetting angles of the jet flow, different from p/2, by more than 30%, while the consumption of cryogenic liquid (liquid nitrogen) is reduced by 20-25%.The process modeling is performed, the conditions of the destruction of the adhesive bond of the contaminant film with the surface are estimated, the conditions of its rational execution are determined.

Surface State Variation during Scanning in a Low-Voltage SEM and Its Effect on of Relief Structure Sizes

The variation of low-energy slow secondary electron emission from the surface of relief structures (bumps) during their prolonged scanning in a low-voltage scanning electron microscope is estimated. The variation nature depends on the bump region profile, which is especially complex near relief structure angles. As a result, corresponding curve portions of the bump video signal, which results in an increase or even a decrease in geometrical sizes of these portions. The emission variation is explained by local charge induction in the natural oxide layer on the silicon surface. The portion size also changes due to contamination film bump deposition on the surface. Presumably, its deposition depends on charges induced on the bump surface and, hence, is poorly reproducible. The case of the absence of contamination broadening of a bump due to its prolonged scanning is fixed.

Вариация состояния поверхности в ходе сканирования в низковольтном РЭМ и ее влияние на размеры рельефной структуры

The emission variation of SSE from surface fragments of protrusions in a silicon plate is evaluated during prolonged scanning in low energy SEM. Emission dynamic variation that is especially complex near the edges of protrusion upper bases and slopes is discovered that affects the sizes of all protrusion fragments. Emission variation is explained with changes of unevenly localized charge state at different surface fragments of protrusions in a natural silica and a contamination film. Contamination is occurred in vacuum and depends on a surface charge state so it is not uniform along protrusion surface. The total absence of contamination on some protrusions is fixed so its initial linewidth size is occurred a constant during a scanning. The limiting uprising of a linewidth size to 4.5 at a one case and the limiting decrease to -0.8 at another case are fixed. Yu. V. Larionov, Senior Researcher, A.M. Prokhorov General Physics Institute, RAS, Moscow, 119991, Russian Federation, E-mail: luv@kapella.gpi.ru, Yu. V. Ozerin, Leading Engineer, yozerin@mikron.ru Mikron Co., Zelenograd, Russia

Investigation of a Contamination Film Formed by the Electron Beam Irradiation

In the study of materials on electron probe devices in the field of action of the electron beam, a contaminating hydrocarbon film is formed, which affects the experimental results. In this paper, we have studied the influence of a contamination film on carbon-film-coated dielectrics on the intensity of cathodoluminescence and characteristic X-ray lines. The absorption coefficient of the contamination film in the visible and UV ranges has been determined. Filming mechanisms at different parameters of the electron beam have been discussed.

Deuterium as a cleaning gas for ITER first mirrors: experimental study on beryllium deposits from laboratory and JET-ILW

Cleaning techniques for metallic first mirrors are needed in more than 20 optical diagnostic systems from ITER to avoid reflectivity losses. Plasma sputtering is considered as one of the most promising techniques to remove deposits coming from the main wall (mainly beryllium and tungsten). Previous plasma cleaning studies were conducted on mirrors contaminated with beryllium and tungsten where argon and/or helium were employed as process gas, demonstrating removal of contamination and recovery of optical properties. Still, both above-mentioned process gases have a non-negligible sputtering yield on mirrors. In this work, we explored the possibility to use a sputter gas having a small impact on mirrors while being efficient on Be deposits, e.g. deuterium. Two sputtering regimes were studied, on laboratory deposits as well as on mirrors exposed in JET-ILW, namely physical sputtering (220 eV ion energy) and chemically assisted physical sputtering (60 eV ion energy) using capacitively coupled plasma with radio frequency. The removal of Be and mixed Be/W contaminants, as well as the recovery of reflectivity, was achieved when deuterium was employed at 220 eV while cleaning at 60 eV was only fully efficient on laboratory beryllium deposits. On mirrors exposed in JET-ILW, the situation is more complex due to the presence of tungsten in the contaminant film, leading to the formation of a tungsten enriched surface that is not easily sputtered, especially at 60 eV.

Predicting radiation-induced carbon contamination of EUV optics

Predictions are made for the radiation-induced carbon contamination threat to ruthenium-coated extreme ultraviolet (EUV) optics for a range of incident EUV intensities, exposure pressures and types of hydrocarbon. A calculational philosophy is developed that acknowledges the ruthenium capping layer may have adsorbed oxygen on it and that the carbon contamination film is partially hydrogenated. The calculations incorporate the Nitta Multisite Adsorption framework, which accounts for the configurational adsorption difficulty encountered by the adsorption of large molecules on surfaces. Contributions from “out-of-band” radiation are included, both in the direct photon-induced dissociation of hydrocarbon molecules and in the out-of-band production of secondary electrons. For the hydrocarbon molecules, n-tetradecane, n-dodecane, n-decane, and benzene, for a range of EUV powers and hydrocarbon pressures, predictions are made for carbon thicknesses, the overall carbon deposition rates, and the relative amounts of contamination produced by primary photon excitation, secondary electrons, and out-of-band radiation. The comparison is made to relevant prior experiments. The model, with no adjustable parameters, provides a good account of prior experiments on n-tetradecane, n-decane, and benzene over the pressure ranges examined by the experiments (∼1 × 10−10 to ∼1 × 10−7 Torr) and over the EUV intensity range 0.001–100 mW/mm2. The level of agreement is within a factor of ∼4 or better, which is consistent with expectations based on the experimental uncertainties. Comparison with prior data for n-decane indicates that the carbon deposit produced by the EUV-induced dissociation of hydrocarbons is substantially hydrogenated. Out-of-band radiation accounts for ∼9%–12% of the overall optic contamination. Secondary electrons account for ∼2% of the overall optic contamination. The results show that the dominant mechanistic cause of the EUV carbon contamination is primary photon absorption by the adsorbed hydrocarbon molecule. The removal of carbon or hydrogen by electron stimulated desorption due to secondary electrons or photon stimulated desorption by primary EUV absorption can be safely ignored as negligible compared to the EUV-induced carbon deposition rate. The results allow comparison with past experiments, provide a framework for conducting future experiments, and predict contamination threats relevant for practical EUV lithography tool operation. The calculations also clarify the underlying physical phenomena at work in the EUV carbon contamination problem.