Transfer Layer Thickness Research Articles

Effects of He+ and H+ Co-Implantation with High Energy on Blisters and Craters of Si and SiO2-On-Si Wafers

In this paper, effects of He+ and H+ co-implantation with high implantation energy on surface blisters and craters at different annealing conditions are systematically investigated. Surface morphology as well as defect microstructure are observed and analyzed by various approaches, such as scanning electron microscopy (SEM), optical microscopy (OM), atomic force microscopy (AFM), and Raman spectroscopy. It is found that after 500 °C annealing and above for 1 h, surface blisters and exfoliation are observed for Si and SiO2-on-Si wafers except for the samples implanted with only He+ ions. AFM images reveal that the heights of blisters in Si and SiO2-on-Si wafers are 432 nm and 397 nm respectively and the thickness of transfer layer is at the depth of about 1.4 μm, which is consistent with the projected range of He+ and H+ ions. Raman spectroscopy demonstrates that higher annealing temperature can lead to a stronger intensity of the VH2 peak. Under the same implantation parameters, surface morphology of Si and SiO2-on-Si wafers is different after annealing process. This phenomenon is discussed in detail.

Effect of Self-Generated Transfer Layer on the Tribological Properties of PTFE Composites Sliding against Steel

Coatings are normally employed to meet some functional requirements. There is a kind of self-generated coating during use, such as the transfer layer during sliding, which may greatly affect the tribological behavior. Although the transfer layer has aroused much attention recently, the formation of the transfer layer closely depends on the service conditions, which need to be further studied. In this paper, the effects of sliding speed, normal load, and duration of wear test on the transfer layer thickness during friction of Ni/PTFE (Polytetrafluoroethylene) composites were experimentally investigated. The formation mechanism of transfer layer and the relationships between tribological properties and transfer layer thickness were analyzed in detail. It was found that the transfer layer thickness increased with increases of sliding speed and normal load; and after a period of wear test, the transfer layer thickness remained stable. The transfer layer thickness correlates linearly with the friction coefficient and wear volume of the PTFE composites. With the increase of the transfer layer thickness, the friction coefficient decreased, while the wear volume increased, which means that a uniform, thin, and stable transfer layer is beneficial for the reduction of friction and wear of the polymeric composites.

Revisiting polymer tribology for heavy duty application

Polymers are frequently considered as a candidate material for heavy duty tribological applications. Standard tribological testing for such applications may result in unrealistic tribological properties in terms of wear mechanism, transfer film formation and friction coefficient etc. Thus the present research aims to explore the tribological behaviour of currently available neat polymers under heavy duty loading condition. In this background, nine different polymers (PAI, PEI, PC, PPSU, PA6, PET, PPS, PVDF, and UHMWPE) of amorphous and semi-crystalline groups were chosen from engineering and high performance grades. Large scale reciprocating sliding wear tests with 50×50mm contact area were used. Considering heavy duty loading condition, the operational parameter were idealised at 10kN normal force and 50mm/s sliding speed. From the test results the polymers are classified into three groups based on the wear mechanisms and the transfer layer characteristics observed from the counterface. Group 1 did not persist any transfer layer (PC and PEI), whereas Group 2 materials (PET, PPS, PPSU and PAI) has lumpy discontinuous transfer layer and finally Group 3 materials evidenced uniform thin transfer layer. Clear signs of three body abrasion were evidenced in Group 1 material which is due to the absence of transfer layer and also from the large loose debris. Poor adhesion of inhomogeneous lumpy transfer layer in Group 2 showed an intermediate wear rate. Based on the wear and friction performance, the Group 3 materials (PVDF, UHMWPE and PA6) are proposed as the candidate materials for heavy duty tribological application. In regards to the transfer layer thickness and wear mechanisms at large scale testing, the present observations showed incomparable results with the literature. This research concludes that the revisit to polymer tribology at high load condition has indicated the difference in wear mechanism and the corresponding tribological characteristics in large scale testing. As a future work multi-scale testing is an absolute must for the complete understanding of tribological characteristics w.r.t a specific material.

2-Mercaptobenzimidazole as a copper corrosion inhibitor: Part I. Long-term immersion, 3D-profilometry, and electrochemistry

The high corrosion inhibition effectiveness of 2-mercaptobenzimidazole (MBIH) in 3wt.% aqueous NaCl solution is reported using long term immersion tests, 3D-profilometry, electrochemical impedance spectroscopy, and potentiodynamic curve measurements. The high corrosion inhibition performance was proven after 180days of immersion. The impedance spectra were characterized by two time constants relating to charge transfer and finite layer thickness or semi-infinite diffusion of copper ions through the surface layer, therefore Cu corrosion in solution containing MBIH follows kinetic-controlled and diffusion-controlled processes. Moreover, it is shown that MBIH is a mixed-type inhibitor.

Effect of Transfer Layer on Ultra Low Friction of CNx Coating under Blowing Dry Ar

In order to clarify the ultra low friction mechanism of Carbon Nitride (CNx) coatings under blowing dry Ar, thickness and area of transfer layers on mating surface were in-situ observed with an optical microscope during sliding against a sapphire hemisphere under blowing dry Ar. During sliding, thickness of transfer layer from CNx coating to a sapphire hemisphere increased and leaded to ultra low friction. When thickness and area of transfer layer was thick and small respectively, ultra low friction was observed. The result showed that the coefficient of friction decreased from 0.18 to 0.003 and remained constant throughout the friction test. It was confirmed the formation of a graphite-like transfer layer with Raman analysis and Auger Electron Spectroscopy (AES).

The Wear Behavior of Cross-Linked UHMWPE under Dry and Bovine Calf Serum–Lubricated Conditions

The present study was performed to investigate the effects of gamma radiation on the wear behavior of unirradiated and irradiated ultra-high-molecular-weight polyethylene (UHMWPE) against Ti-6Al-4V under dry and lubricated conditions at different applied loads. The UHMWPE specimens were exposed directly to nominal doses of 0, 25, 40, 50, and 100 kGy. Scanning electron microscope (SEM) analysis of the worn surface of UHMWPE and Ti-6Al-4V was performed to understand the mechanism of wear involved between the contact surfaces during wear testing. From the wear test results, there were significant differences between the wear of unirradiated UHMWPE and UHMWPE irradiated at 25, 40, and 50 kGy under dry and lubricated conditions. SEM results for the worn surface of unirradiated and irradiated UHMWPE samples showed that dry and lubricated conditions affected the wear behavior of irradiated UHMWPE. Examination of the Ti-6Al-4V alloy counterface tested under dry conditions revealed that the maximum transfer layer thickness was as high as 22.79 μm. In addition, the UHMWPE irradiated at 100 kGy resulted in a more continuous and adherent transfer film on the Ti-6Al-4V surface compared to the unirradiated sample under dry conditions. Under serum-lubricated conditions, the transfer film layer on the Ti-6Al-4V alloy surface was thinner compared to under dry conditions.

The Role of Transfer Layers on Friction Characteristics in the Sliding Interface between Friction Materials against Gray Iron Brake Disks

The effect of transfer layer formation on friction performance was studied using a brake friction material containing 15 ingredients. Based on a base formulation, 13 friction material specimens containing different relative amounts of ingredients were produced and they were tested on gray iron disks using a small-scale friction tester. A non-destructive four-point probe technique to measure electrical resistance of the thin film was used to estimate the transfer layer thickness. Results showed that the transfer layer formation was highly dependent on the relative amount of ingredients in the friction material and temperature. Among various ingredients, solid lubricants and iron powders increased the transfer layer thickness but no apparent correlation between transfer layer thickness and the coefficient of friction was found. Strong influence from individual ingredients was observed, dominating the friction characteristics during sliding. On the other hand, the thick transfer layers on the disk surface tended to reduce the friction material wear and the amplitude of the friction coefficient oscillation during sliding.

Effect of mass transfer and catalyst layer thickness on photocatalytic reaction

AbstractSemiconductor photocatalytic processes have been studied for nearly 20 years due to their intriguing advantages in environmental remediation. A rational approach in determining the effect of mass transfer and catalyst layer thickness during photocatalytic reactions is proposed. The reaction occurs at the liquid–catalyst interface, and therefore when the catalyst is immobilized, both external and internal mass transfer plays significant roles in overall photocatalytic processes. Several model parameters—external mass‐transfer coefficient, dynamic adsorption equilibrium constant, adsorption rate constant, internal mass‐transfer coefficient, and effective diffusivity—were determined either experimentally or by fitting realistic models to experimental results using benzoic acid as a model component. Even though all these parameters are critical to the design and development of photocatalytic processes, they are not available in the literature. The effect of the internal mass transfer on the photocatalytic degradation rate over different catalyst layer thicknesses under two different operating configurations was analyzed theoretically and experimentally verified. It was observed that an optimal catalyst layer thickness exists for substrate‐to‐catalyst illumination.

Valence band offset in AlAs/GaAs heterojunctions and the empirical relation for band alignment

The valence band offset in AlAs/GaAs heterojunctions is found to be 0.45±0.05 eV from analysis of charge transfer versus undoped spacer layer thickness. This result and several recent experiments on AlxGa1−xAs/GaAs heterojunctions indicate that the valence band offset is approximately linear in AlAs fraction x over the entire alloy composition range and more than twice the previously accepted value. The relation between heterojunction band offsets and Fermi level pinning for metals on semiconductors is discussed.

"Erratum: Laminar, Transitional, and Turbulent Flow with Adverse Pressure Gradient on a Cone-Flare at Mach 10"

Abstract : An experimental investigation of the boundary layer on a cone-flare body at Mach 10 is presented. Measurements of pressure, heat transfer and boundary layer thickness are made in regions of zero and adverse pressure gradient. Several noses are fitted to the cone to produce blunted cone-flares, which are used to study separation. The experimental results are compared to some recent analytical investigations. The results showed a small amount of blunting can lower the Reynolds number sufficiently to produce separation. The experiment results also showed that a small amount of crossflow (produced by placing the model at small angles of attack) was capable of eliminating separation.

Applications of similar solutions for calculation of laminar boundary-layer characteristics in the presence of a pressure gradient.

Similar calculation of hypersonic laminar boundary layer characteristics in presence of pressure gradient, specifically heat transfer, skin friction and boundary layer thickness