Thickness Of Contamination Layer Research Articles

Numerical Modeling of Rigid and Flexible Footings Constructed on Natural and Contaminated Soil Strata

In this article, a numerical model has been developed in order to examine the effect of rigid and flexible footings vertically loaded on the behavior of oil-contaminated soil layers by black oil with respect of natural soil strata characteristics. The analyses have included modeling the spread rigid and flexible footings founded on natural soil have been collected from south of Iraq, and contaminated specimens of 10% by weight. The thickness of the contaminated layer (D) has been gradually increased from 1.0 m to 4.0 m from footing base. Three footing width (B), 1.0m, 2.0m and 3.0 m have been simulated in the study. The finite element package PLAXIS 3D has been adopted to simulate the oil contamination problem and to relate the performance of a spread footing supported on natural soil and contaminated soil with different footing width (B) and thickness of contamination layer (D). The outcomes have found out that the vertical ground movement can be reduced by minimum thickness of soil contamination layer. The vertical ground movement has been reduced because of soil contamination when the contamination depth (D) is less than or equal footing width (B) with respect to vertical ground movement of natural soil in case of two types of footing. The behavior of rigid footing has showed more lessening in vertical ground movement as contamination layer thickness (D) 1.0m for all the footing widths.

Electron emission properties of silver oxide and its impact on the secondary emission yield of air-exposed silver

Surface oxidation, contamination and adsorption are commonly considered as three leading factors of secondary electron yield (SEY) increase for metals exposed to various environments. Whereas, the influence of these three factors on SEY is different for diverse metal materials. To discover the SEY dependence on surface oxidation for silver, a group of silver oxide (Ag2O) and silver coatings are therefore prepared. Experimental results show the SEY of Ag2O is just about 0.1 higher than that of silver coating whether before or after ion cleaning, and SEY difference becomes smaller under oblique incidence, which indicates the surface oxidation may not be the major causes of SEY increase for air-exposed silver. To further verify the speculation, various surface conditions are achieved on silver surface. Microscopic analysis reveals the adsorptions and contaminations can be effectively removed by heating treatment, meanwhile, SEY is remarkably decreased. Furthermore, the treatment of ion cleaning eliminates all the surface additions and achieves a superlative cleanliness for silver sample, the SEY peak value of air-exposed silver decreases from 2.61 to 1.73 after ion cleaning for 10 min, and to 1.70 after ion cleaning for 30 min, which indicates the surface oxidation contributes little to the SEY raise of air-exposed silver. The SEY dependence on the thickness of contamination layer is also theoretically explained. This work does a systematic research on how the surface oxidation and modification influence SEY of silver, which makes significant sense for comprehending the SEE characteristics of silver with various surface conditions.

Laser decontamination microscopic process study on radioactive contaminations with Cs+ ion of 304 stainless steel surface

The decommissioning of contaminated metal equipment in nuclear facilities may produce a wide range of radioactive waste. For metallic equipment like the primary loop, the radioactivity is mainly located in the oxide surface. Laser decontamination was performed on 304 stainless steel specimens with a stable isotope Cs contamination layer. Laser melting was used to create oxide layer on the surface of polished specimen for enhancing the penetration of Cs+ ion. The interaction between laser and matter (contamination, oxide and substrate) was studied by the stratification theory considering the difference in the thickness of contamination layer. At higher pulse duration (τp = 5ns), laser decontamination is mainly caused by thermal effects. The metal near oxide layer melts and vaporizes to form a molten pool and crater. For short pulse duration (τp = 1ns), the removal of surface contaminations mainly depends on thermal effect and stress wave, CsCl particles were removed by vaporization; however, oxide layer was stripped from the substrate in the form of solid fragment. For ultra-short pulse duration (τp = 150ps), the oxide layer has been partially ablated. Most of the heat absorbed by γ (austenite) is used for heating and evaporation to form porous structure, while the great mass of heat absorbed by M (martensite) is used for thermal diffusion. Therefore, the M regions only form a dynamic molten pool on its surface without vaporization.

Analytical Modeling of Participation Reduction in Superconducting Coplanar Resonator and Qubit Designs Through Substrate Trenching

A strategy aimed at decreasing dielectric loss in coplanar waveguides (CPW) and qubits involves the creation of trenches in the underlying substrate within the gaps of the overlying metallization. Participation of contamination layers residing on surfaces and interfaces in these designs can be reduced due to the change in the effective dielectric properties between the groundplane and conductor metallization. Although finite element method approaches have been previously applied to quantify this decrease, an analytical method is presented that can uniquely address geometries possessing small to intermediate substrate trench depths. Conformal mapping techniques produce transformed CPW and qubit geometries without substrate trenching but a non-uniform contamination layer thickness. By parametrizing this variation, one can calculate surface participation through the use of a two-dimensional, analytical approximation that properly captures singularities in the electric field intensity near the metallization corners and edges. Examples demonstrate two regimes with respect to substrate trench depth that capture an initial increase in substrate-to-air surface participation due to the trench sidewalls and an overall decrease in surface participation due to the reduction in the effective dielectric constant, and are compared to experimental measurements to extract loss tangents on this surface.

Thickness of natural contaminant layers on metal surfaces and its effects on laser-driven ion acceleration

In the laser-driven ion acceleration studies, the naturally deposited contaminant layer on the target surface is thought to be a source of energetic ions and protons. Using ellipsometric measurements, we found that the thickness of the surface natural contaminant layer, which cannot be modified without external surface treatment, is on the order of a few nanometers. A conceptual approach is developed where “thick” and “thin” contaminant layer regimes of acceleration are identified and parameterized by the normalized thickness of the contaminant layer. These studies may also help in developing an ion acceleration concept using multilayered targets or through modifications of the target surface.

On the use of AES data analysis to determine local enrichments of conversion coating elements at intermetallic particles on rolled Al

In this paper, the behaviour of the industrial applied Ti/Zr conversion coating (CC) pretreatment on rolled automotive aluminium samples (AA5182) is analysed. Due to its nanometre lateral and depth resolution, Auger electron spectroscopy (AES) is used to analyse the CC distribution at surface cathodic intermetallic particles. As a result of its high surface sensitivity, the AES technique is very susceptible to differences in the top contamination layer thickness. It is demonstrated that AES point measurements performed on aluminium model samples coated with 1.5 and 3 nm of Ti (oxide) layer cannot differentiate the two‐layer thicknesses if a difference in the top contamination thickness is not taken into account. A data analysis methodology is introduced, based on the ratio of normalized peak areas (enrichment ratios), to eliminate the effect of the contamination layer thickness. The experimental validation of the methodology is performed on the model samples, demonstrating errors of 2% on the enrichment ratios on similar samples with different contamination layer thicknesses, while the conventional spectra quantification results in errors of 49%. The methodology is also theoretically substantiated within certain constraints. By the use of the AES methodology, an enriched Ti and Zr deposition is confirmed at the cathodic intermetallic particles at the surface of the industrial no‐rinse CC sprayed automotive aluminium sheet samples.

Numerical Simulation Studies on the Influence of Metallurgical Contamination on the Electric Field of RTV Coating

The metallurgical industry in China has developed rapidly, which has caused an increasing amount of exhausted gas emission. After a long period of operation, a layer of metallurgical contamination is deposited on the surface of insulators near the metal work, which may have an effect on the distribution of electric field on the surface of insulator. The chemical test indicates that the metallurgical contamination layer contains particles of Fe3O4 with strong conductivity, which may become suspended potential conductor. In this paper, the influence of thickness of contamination layer and diameter, arrangement of conductive particles on the electric field are discussed by the simulation model.

Correlation of optically stimulated electron emission with failure mode of adhesively bonded epoxy composites

Carbon fiber reinforced polymers (CFRP) reduce weight in aerospace and automotive applications while maintaining or improving structural performance. Additional performance gains can be realized with composites if adhesive bonding is used in place of mechanical fasteners for structural assemblies. Surface preparation for adhesive bonding plays a critical role in the assembly process. Effective techniques for monitoring the pre-bonding surface conditions are crucial to obtain surfaces free from bond-degrading contaminants, e.g. mold release agents, which are widely used in CFRP manufacturing. In this work, optically stimulated electron emission (OSEE) was used prior to and after laser ablation to measure deposited levels of polydimethylsiloxane (PDMS) on CFRP (Torayca P2302-19). OSEE was also used to model the contamination layer thickness. After the specimens were adhesively bonded with a modified epoxy film adhesive (Loctite EA 9696 Aero), they were subjected to double cantilever beam (DCB) tests to investigate the hypothesis that surface contamination species and levels affect the fracture characteristics of adhesively bonded joints. This study relates OSEE photocurrent and the classification of the bond failure modes to their PDMS surface contamination levels prior to adhesive bonding. DCB test results show that (1) the region under the traces within the load and unloading boundaries consistently correlates with the bond strength and the probability of different failure modes, and (2) bond performance at fracture depends on the surface PDMS film thickness coating prior to laser surface treatment. The decrement in bond performance in this study correlates to the OSEE readings of contaminant levels on the adherent surfaces.

Influence of surface contamination on the wettability of heat transfer surfaces

The wettability of heat transfer surfaces plays an important role in liquid–vapor phase change phenomena, including boiling incipience, the critical heat flux, the Leidenfrost transition, and condensation. The influence of adsorbed surface contamination at the nanoscale, though seldom considered, can have a profound impact on wetting behavior. This study quantitatively investigates the impact of contaminant layer thickness on wettability. Various cleaning treatments are explored on zirconium and 6061 aluminum to determine the effect on contaminant and oxide layer thickness. Angle-resolved X-ray photoelectron spectroscopy can be used to measure the thickness of oxide and contaminant layers, which is then correlated to wettability by measuring the equilibrium contact angle. Results indicate that even after solvent cleaning, the contact angle of water on practical heat transfer surfaces is dominated by a hydrocarbon contaminant overlayer around five nanometers thick.

Development of Tool for Contamination Layer Thickness Measurement Using High Power Extreme Ultraviolet Light and in Situ Ellipsometer

Extreme ultraviolet (EUV) lithographic exposure is performed in a vacuum environment. The Mo/Si multilayers used as imaging optics and a mask can be contaminated by carbon, which is originally an outgassing species of the hydrocarbons that decompose from the resist materials during EUV exposure. This carbon contamination reduces the total reflectivity of the imaging optics and mask, and affects the lithographic performance, including the throughput and resist pattern replication resolution. This contamination should be reduced to maintain the lithographic performance; thus, the relationship between the carbon contamination and the outgassing species should be clarified. We therefore developed a novel tool for in situ contamination layer thickness evaluation. The distinctive features of this tool are as follows: 1) exposure using a total power of in-band EUV light (267 mW/cm2) that is as high as that required for high-volume manufacturing (>100 mW/cm2), 2) the visible light beam of the in situ spectroscopic ellipsometry is focused on the Mo/Si multilayer witness sample to obtain the detection limit for measured thickness and that the limit was found to be 0.03 nm, and 3) the witness and 8-in. resist wafer sample stages have extremely low outgassing characteristics. Using this tool, a starting adhesion point was observed and the carbon contamination layer thickness was evaluated during the resist exposure. For 90 min resist exposure, no contamination adhered onto the Mo/Si witness sample until the exposure time reached 25 min, and after which, the contamination started to adhere to the witness sample.

Interfacial Degradation Mechanism of Au/Al and Alloy/Al Bonds Under High Temperature Storage Test: Contamination, Epoxy Molding Compound, Wire and Bonding Strength

In this paper, the effects of Al pad contamination, epoxy molding compound [biphenyl (BP) and ortho-cresol novolac (OCN)] and wire (Au and alloy) on the propensity for the interfacial degradation of wire bond in a quad flap package under high temperature storage (HTS) tests at 125degC, 150degC, and 170degC are meticulously investigated. The interfacial degradation intends to be explicated in regards to change in surface morphology of Au-Al and alloy-Al intermetallic compound (IMC) and bonding strength as a function of HTS test. The combination of atomic force microscope and Auger electron spectrometry reveals that initial bonding strengths from wire pull and ball shear test decrease with increasing the thickness of contamination layer on Al pad, carbon and oxygen, and subsequent surface roughness. Indeed, the plasma exposure on Al pad prior to wire bonding enhances both mechanical bonding strengths up to 10% and 15%. It is found that the failure behaviors at 125degC are dissimilar to 150degC and 170degC. We first report that Sb diffused from the OCN exists at the intermetallics of Au-Al bonds, leading to rapidly deteriorate mechanical integrity. Furthermore, inductively coupled plasma mass spectrometry affirms that the OCN is a resource of Br. Above 150degC, the interdiffusion of Br and Sb from the OCN significantly impacts the integrity of Au-Al bonds. In turn, such physical degradation mechanism governed by Sb and Br can be linearly accelerated. It is also found that in the case of Au-Al bonds, the life time with the BP is much longer than that with the OCN under the given HTS tests due to less content of halogen ions. In contrast, neither Sb nor Br was found from the intermetallic layers of alloy-Al bond encapsulated with the OCN and BP. Thus, alloy-Al bonding strengths are intact even after longer stressing. With an alloy wire having Pd as an impurity, the growth kinetics of IMC fueled by Br and Sb seems to be sluggish, providing better reliability than Au wire. Obviously, lower flame retardants and higher are critical intrinsic material properties that should be taken into account when a new epoxy molding compound is introduced to pursue cost effectiveness without loosing reliability. Finally, upon painstaking work over a wide range of analyses herein, a quality affordable guideline for the selection of wire type associated with epoxy molding compound that can ensure the long-term reliability is presented in order to secure reliable supplyline management as well as package assembler.

Determination of ZnO(0001) surface termination by x‐ray photoelectron spectroscopy at photoemission angles of 0° and 70°

AbstractWe present an XPS method to determine the termination of the ZnO(0001) surface. By measuring O 1s and Zn 2p3/2 core‐level x‐ray photoelectron spectra at photoemission angles of 0° and 70° and comparing the intensity ratio (IO1s/IZn2p3)θ=0/(IO1s/IZn2p3)θ=70, the Zn and O termination can be distinguished. Calculations show that these two terminations have intensity ratios differing by ∼17%. This difference is not affected by a contamination layer provided that the contamination layer thickness is the same for these two differently terminated surfaces. Although this determination method prefers a clean ZnO(0001) surface (in situ measurement), it seems also feasible for surfaces with known contamination layer thickness (ex situ measurement). We have measured ex situ ZnO(0001)‐Zn, ZnO(000&1macr;)‐O single crystals and an epitaxial ZnO film deposited on Al2O3(0001). The measured intensity ratios of the first two samples agree with the calculated values for a 0.2 and 0.26 nm contamination layer, respectively. The intensity ratio and the O 1s contamination component intensity of the epitaxial ZnO film are close to those of the ZnO(0001)‐Zn single crystal thus pointing at Zn termination of the film. Copyright © 2004 John Wiley & Sons, Ltd.

Calculation of overlayer thickness on curved surfaces based on XPS intensities

AbstractAccurate determination of overlayer thickness on samples with curved surfaces is of growing importance, especially in connection with nanometric materials systems. In this work two simple geometries are treated; closely packed spheres, well representing powder samples, and close‐packed cylinders, modelling fibrous samples. In the case of the powder samples (the arrangement is similar to the structure of the closest packed spheres) in addition to the intensity originating from curved layers of the top row of the spheres, the contribution of the partially visible spheres of the second and third rows below the top row are also considered, enhancing the accuracy of the calculations. As is shown, the method of calculation for spheres and cylinders is similar but the values of the geometry correction factors are different. The applicability of the derived geometry correction factors, based on pure geometrical considerations, is supported with experimental data obtained in two material systems: the thickness of oxide and carbonaceous contaminant layers on Si3N4 powder and Al foil were determined.These types of calculations were conveniently performed by the XPS MultiQuant program providing not only the geometry correction factors but also other parameters, such as cross‐sections, asymmetry parameters, etc. Copyright © 2004 John Wiley & Sons, Ltd.

Changes in surface composition of GaN by impurity doping

Changes in the surface composition of GaN films by p- and n-type doping were studied using both Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It was found that the surface composition of the GaN films was affected by impurity doping, i.e. the surface of the p-type GaN film was enriched with gallium and that of the n-type GaN film with nitrogen, compared with that of the undoped GaN film. The surface composition of the GaN films by AES agrees with that by XPS after taking the contamination layer thickness into account. The experimental results thus obtained were discussed by taking account of the formation energies of native defects in p- and n-type GaN.

Electrical performance of non-ceramic insulators in artificial contamination tests. Role of resting time

The paper presents the results of an investigation on the electrical performance of artificially contaminated non-ceramic insulators as a function of resting time. Resting time is defined as the time interval between the application of contamination and start of testing. New (unaged), full scale, 69 kV non-ceramic insulators using different types of silicone rubber and ethylene propylene diene monomer (EPDM) rubber as weathersheds were studied. Their electrical performance was assessed using the clean fog technique. The applied voltage was kept constant throughout the test, while contamination severity and resting time were varied as parameters. The transfer of hydrophobicity through the contamination layer was demonstrated by flashover tests. This was also visually depicted by analyzing samples in a scanning electron microscope. The results show that resting time exerts little influence on the electrical performance of EPDM insulators. However, for silicone rubber insulators, resting time is shown to drastically improve its electrical performance. Experimental evidence indicates that the transfer or recovery process of hydrophobicity in silicone rubber insulators occurs as a progressive superposition of silicone oil layers with time. Thus, the net effect of resting such insulators before tests can be thought of as a gradual reduction of the effective contamination layer thickness. Such a reduction alters the way in which the contaminant layer interacts with external stressing agents, which could impact the insulator's electrical performance in service. In this work, an attempt has been made to identify and quantify the electrically significant changes introduced by a reduction in the effective contamination thickness. It is in the light of this reduced effective contamination layer that we explain how a seemingly wettable silicone rubber insulator is still able to hold the applied voltage without flashover.

Influence of the surface chemistry on the wettability of stainless steel

AbstractDegreasing with solvents, chemical etching, polishing, oxygen and argon plasma treatment and heating and drying produce stainless‐steel surfaces with different amounts of organic contamination and ‘bonded water’. The hydroxide/oxide layer of the passive film formed on stainless‐steel foils is also affected by surface pretreatment. Electron spectroscopy for chemical analysis (ESCA) has been used to analyze the composition of the surface film formed after different cleaning procedures. Organic contamination on 304 stainless‐steel foils can be reduced by a factor of five using various cleaning treatments. Wettability or surface energy measurements have been performed on the treated surfaces and it was found that the surface energy of the metal decays with the inverse of the contamination layer thickness. As these cleaning treatments lead to different oxide layers, it is concluded that the nature of the oxide layer is not the main parameter that determines the surface free energy of metals.

Quantitative XPS. Part II: Comparison between different quantitative approaches for two different spectrometers—determination of the contamination‐reduced thickness, application of the determined transmission functions and accuracy achieved

AbstractThe first principles model (FPM) has been compared with other quantitative approaches by using many standard samples. As a first step, the applicability of the theoretical dependence of IC 1s/ICKVV on the reduced thickness (x) of a hydrocarbon surface contamination layer was checked and shown to be approximately correct only in the middle range of x. A semi‐empirical relation between IC 1s/ICKVV and x has been developed. The advantage of this relation over that previously developed in the literature is that the transmission function of our spectrometer is well characterized. The reduced thickness calculated using this semi‐empirical relation has been shown to be close to the real value. The comparison of atomic ratios calculated using these quantitative approaches has shown that the best approach is the FPM. For the samples investigated in this work, the introduction of the anisotropy parameter L is not necessary: in most cases, the influence of L is smaller than the observed errors; and in certain cases where the difference of L values is large, more consistent results are obtained when L is ignored. The FPM approach provides consistent results not only when an inter‐comparison is made between different spectrometers but also when, within a given machine, the analysis conditions are varied. The accuracy of this approach is relatively good (with errors <15%) and holds true even when comparing peaks separated by more than 1000 eV. Finally, the comparison of results obtained with different previously determined transmission functions has allowed us to test the applicability of the methods used for the determination of these transmission functions (see Part I).

Composition and thickness of surface layer on molybdenum tips for scanning tunnelling microscopy (STM) studied by SEM/AES/(AR)XPS

AbstractA combination of SEM, AES and angle‐resolved XPS (ARXPS) has been applied to analyse the distribution of chemical compounds in the surface region of electrochemically etched molybdenum tips and to determine the contamination layer thickness. Carbon monoxide, graphite, molybdenum carbide and molybdenum oxide were found to be the main surface contaminants on molybdenum tips. Auger line profiling revealed a significant enrichment of carbon and oxygen upon the tip. The thickness of the oxygen–carbon contamination layer on the tip was estimated to be 13.5 ± 1.0 nm as measured by AES. The thickness of the contamination layer on a molybdenum sheet was found to be 8.0 ± 1.5 and 6.8 nm using AES and ARXPS respectively. Quantitative analysis of the surface concentrations of carbon, oxygen and molybdenum has been performed.

Removal of Fluorocarbon Residues on CF 4 / H 2 Reactive‐Ion‐Etched Silicon Surfaces Using a Hydrogen Plasma

A cleaning procedure based on a hydrogen plasma is described which removes most of the fluorocarbon passivation layer remaining on silicon surfaces exposed to reactive ion etching (RIE). Real time in situ ellipsometry performed during hydrogen plasma exposure of a reactive‐ion‐etched silicon surface showed removal of the bulk of this residue. The contamination layer thickness was reduced from 50Å to less than 10Å. X‐ray photoelectron spectroscopy of hydrogen‐plasma‐cleaned silicon showed an 80% reduction in carbon contamination and a 95% reduction in fluorine without appreciable oxidation of the surface. The contamination left after cleaning is a 10Å carbon film. Secondary ion mass spectrometry showed that hydrogen implantation into the silicon substrate during cleaning was negligible relative to the amount implanted during RIE. Continued exposure of the surface to the cleaning plasma resulted in a redeposition of contamination, the source of which is sputtered residue from the reactor walls that was deposited during RIE. Surface oxidation by residual water and oxygen desorbing from chamber surfaces may also take place during prolonged plasma cleaning.

A contamination reducing method by ion beam bombardment of the specimen in high resolution electron microscopy

The theory of contamination and a contamination reducing method are discussed on the basis of time dependent micrograph series and their tilted images for determining contamination. For a high current density of an electron probe in the field emission scanning electron microscope, it is observed that contaminated cones are formed in proportion to the exposure time of an electron beam. From the measurement of the contamination layer thickness and its area, the contamination rate and time dependent shape are formulated, mainly depending on the cross-section and current density together with the average lifetime of adsorption molecules. It is found that the contamination rate and stray contamination of outgassing molecules forming part of the specimen are effectively reduced by a pre-bombardment of argon ions on the surfaces of specimens. The contamination rate is reduced to a small extent (5%) using the present method.