Quantitative measurement of chromium's ability to promote adhesion

Using atomic force spectroscopy, we investigated the adhesion-promoting ability of chromium. An intermediate layer of chromium can overcome the low adhesion between metal films and silicon dioxide. For the first time, we quantitatively studied this experimentally well known fact. We compared the adhesion between chromium and different substrates such as gold, silver, mica, and silicon dioxide and, beyond that, the adhesion between silicon dioxide and the same substrates. To avoid additional effects due to water, we chose ethanol as a nonpolar solvent. Taking the interfacial energies of the surfaces with the liquid into account eliminates the direct influence of the fluid medium on the adhesion of the solid material. The results we obtained corroborate the experimental fact of higher adhesion of chromium with the chosen substrates, as well as substantiate the value of chromium as an adhesion promoter. The adhesion of chromium-coated probes on gold, silicon dioxide, and mica is higher than the adhesion of silicon dioxide probes on the same substrates.     

Optical visualization of ultrathin mica flakes on semitransparent gold substrates

We show that optical visualization of ultrathin mica flakes on metallic substrates is viable using semitransparent gold as substrates. This enables to easily localize mica flakes and rapidly estimate their thickness directly on gold substrates by conventional optical reflection microscopy. We experimentally demonstrate it by comparing optical images with atomic force microscopy images of mica flakes on semitransparent gold. Present results open the possibility for simple and rapid characterization of thin mica flakes as well as other thin sheets directly on metallic substrates.     

Mapping of adhesion forces on soil minerals in air and water by atomic force spectroscopy (AFS)

The adhesion force between an atomic force microscope (AFM) tip and sample surfaces, mica and quartz substrates, was measured in air and water. The force curves show that the adhesion has a strong dependence on both the surface roughness and the environmental conditions surrounding the sample. The variability of the adhesion force was examined in a series of measurements taken at the same point, as well as at different places on the sample surface. The adhesion maps obtained from the distribution of the measured forces indicated regions contaminated by either organic compounds or adsorbed water. Using simple mathematical expressions we could quantitatively predict the adhesion force behavior in both air and water. The experimental results are in good agreement with theoretical calculations, where the adhesion forces in air and water were mostly associated with capillary and van der Waals forces, respectively. A small long-range repulsive force is also observed in water due to the overlapping electrical double-layers formed on both the tip and sample surfaces.     

A study of the initial stages of diamond deposition on ferrous substrates coated by a nitrided chromium interlayer and on nitrided polycrystalline chromium substrates

The use of a nitrided chromium interlayer has been found to improve the interfacial properties of diamond films deposited on ferrous substrates. This is achieved by hindering diffusion process of carbon and iron, good adhesion of the interlayer to the steel substrate, and very stable mechanical and chemical bonding between the interlayer and the diamond film. In the present study the initial stages of diamond deposition on steel substrates coated by a nitrided chromium interlayer and on nitrided polycrystalline chromium substrates are reported. Nitridation of chromium films deposited by electrochemical methods and polycrystalline chromium substrates resulted in the formation of two chromium nitrides phases, CrN and Cr₂N, and a rough surface morphology. The initial stages of diamond deposition were found to be accompanied by carburization of the substrates surface resulting in chromium carbide formation. The incubation time, diamond particle density and growth rate at the very initial stages of the deposition process were found to differ for these two substrates. It is suggested that these differences originate from different carburization rates of the two substrates. Phase transformation, recrystallization and diffusion processes in the near surface regions of both substrates resulted in very stable chemical bonding and good adhesion of the diamond film to the substrates. Raman spectra of the deposited films, on both substrates, show shift of the diamond peak position to higher wave numbers and split of the peak. These effects are associated with compressive stresses in the diamond film. Residual stresses in the deposited films were calculated from the shift of the diamond Raman peak. The residual stresses, as calculated from the Raman spectra, were found to increase with deposition time reaching values of 8.4 and 6.9 GPa for continuous diamond films on steel substrate coated with the nitrided chromium film and on nitrided chromium substrates, respectively. Based on a simple model it was estimated that thermal stress, arising from mismatch between the thermal expansion coefficient of diamond and the underlying substrates, is the major component of the compressive stress in the diamond films.     

混凝土封闭底漆的研制

为了提高混凝土建筑物的使用寿命,必须使用封闭底漆对其进行封闭处理.本文合成了一种耐碱性和抗渗透性强的苯丙乳液;往其中加入硅溶胶、云母粉、二氧化钛和助剂等原料,制备了一种新的有机一无机复合型封闭底漆.研究了硅溶胶与苯丙乳液配比、pH、颜填料配比对漆膜性能的影响.结果表明,硅溶胶与乳胶的质量比为0.3:1～0.4:1,体系pH在8.5～10之间,采用8%二氧化钛,15%云母粉和5%滑石粉的颜填料配比,所形成的漆膜具有优良的耐水、耐碱和抗渗透性,附着力0级,与聚氨酯,丙烯酸,聚脲及乳液型面漆的配套性和重涂性好.该底漆适用于水利水电和港口钢筋混凝土建筑物的封闭涂装.     

Fabrication of a miniature twin-fuel-cell on silicon wafer

The fabrication and performance evaluation of a miniature twin-fuel-cell on silicon wafers are presented in this paper. The miniature twin-fuel-cell was fabricated in series using two membrane-electrode-assemblies sandwiched between two silicon substrates in which electric current, reactant, and product flow. The novel structure of the miniature twin-fuel-cell is that the electricity interconnect from the cathode of one cell to the anode of another cell is made on the same plane. The interconnect was fabricated by sputtering a layer of copper over a layer of gold on the top of the silicon wafer. Silicon dioxide was deposited on the silicon wafer adjacent to the copper layer to prevent short-circuiting between the twin cells. The feed holes and channels in the silicon wafers were prepared by anisotropic silicon etching from the back and front of the wafer with silicon dioxide acting as intrinsic etch-stop layer. Operating on dry H₂/O₂ at 25 °C and atmospheric pressure, the measured peak power density was 190.4 mW/cm² at 270 mA/cm² for the miniature twin-fuel-cell using a Nafion 112 membrane. Based on the polarization curves of the twin-fuel-cell and the two single cells, the interconnect resistance between the twin cells was calculated to be in the range from 0.0113 Ω (at 10 mA/cm²) to 0.0150 Ω (at 300 mA/cm²), which is relatively low.     

Growth and Adhesion Enhancement of Diamond Films Deposited on Steel Substrates by a Cr–N Interlayer

Diamond film deposition onto iron-based substrates by chemical vapor deposition methods is complicated by the formation of black carbon or graphitic soot on the substrate surface prior to diamond nucleation and growth, by fast diffusion of carbon into the iron substrate, and by poor adhesion of the deposited film. These complications suggested the use of a buffer layer between the deposited diamond film and the iron-based substrate. We review different methods used to improve the adhesion of diamond film to steel substrates. In particular we describe in detail our own studies which involve the use of a Cr-N interlayer. The use of a chromium nitride interlayer has been found to improve significantly the adhesion of diamond films deposited on ferrous substrates. This is achieved by hindering diffusion processes of carbon and iron, very stable mechanical and chemical bonding between the interlayer and the diamond film, and good adhesion of the interlayer to the steel substrate. We also report on our studies related to residual stress present in the films, as well as a correlation between the interlayer properties and adhesion strength of deposited films.     

Influence of different initiators on the adhesion properties of photopolymerized epoxides on gold and silicon

Photocuring of epoxides proceeds by a cationic mechanism. The required photoinitiators are iodonium or sulfonium salts with non-nucleophilic anions. The influence of different photoinitiators on the adhesion properties of both a rigid and a soft epoxide is examined. Depending on the substrates to be joined, different decomposition products of the initiators are concentrated in the interphase. This accumulation of decomposition products in the interphase leads to a decreased adhesion. On gold surfaces the sulfur of sulfonium salts is concentrated as expected. But surprisingly the iodine of the iodonium salts is also concentrated on gold. It could be shown by immobilization experiments that organic iodine compounds with the iodine in any oxidation state reacted with gold surfaces. Due to this reaction iodide anions are formed. On silicon surfaces the fluorine of the anions PF₆ ^- and SbF₆ ^- is concentrated due to the high affinity of silicon for fluorine. The iodonium salt with [B(C₆F₅)₄]anion contains no fluorine able to react with the silicon. Therefore, the fluorine cannot be concentrated in the interphase and the joints prepared with the soft epoxide containing this initiator have a higher shear strength compared to adhesives with conventional anions.     

Improved adhesion and tribological properties of fast-deposited hard graphite-like hydrogenated amorphous carbon films

Graphite-like hard hydrogenated amorphous carbon (a-C:H) was deposited using an Ar-C₂H₂ expanding thermal plasma chemical vapour deposition (ETP-CVD) process. The relatively high hardness of the fast deposited a-C:H material leads to high compressive stress resulting in poor adhesion between the carbon films and common substrates like silicon, glass and steel. A widespread solution to this problem is the use of an adhesion interlayer. Here we report on the changes in adhesion between the graphite-like a-C:H films and M2 steel substrates when different types of interlayers are used. Insignificant to very small improvements in adhesion were observed when using amorphous silicon oxide (a-SiO_x), amorphous organosilicon (a-SiC_xO_y:H_z) and amorphous hydrogenated silicon carbide (a-SiC_x:H_y) as adhesion layers. However, when sputtered Ti was used as an interlayer, the adhesion increased significantly. The dependence of the adhesive properties on the deposition temperature and interlayer thickness, as well as on the thickness of the a-C:H layer is presented and discussed. The low wear rates measured for the a-C:H/Ti/M2 stack suggest that these films are ideal for tribological applications.     

The interactions of amphiphilic latexes with surfaces: the effect of surface modifications and ionic strength

The effect of surface modifications brought about by a polymeric stabilizer on the interactions between polymer colloid particles and various substrates in aqueous media are directly measured using atomic force microscopy. The interactions of polystyrene particles with grafted hydrophilic ‘hairs’ of hydroxypropyl cellulose (denoted HPC/PS), of molecular weight ∼10⁵, with mica, silica and graphite substrates are measured. HPC/PS is found to be compatibilized so that it will interact with both hydrophobic and hydrophilic substrates. The observed jump-to contact between HPC/PS and silica is characteristic of polymer solutions and is the result of the grafted hairy layer. Further direct evidence of HPC-substrate interaction is seen in a secondary adhesion with mica. The adhesion of the particles was found to follow the order silica>graphite>mica. The magnitudes of these interactions are rationalized in terms of the interactions of each of the substrate, core polymer and surface modification. It is concluded that the combined effects of surface roughness and hairy layer collapse due to compression give rise to the observed trend.     

Effects of Nanoparticle Coating on the Adhesion of Emulsion Aggregation Toner Particles

Toner is a key material for the xerographic printing and copying industry. Compared to conventional pulverized toner particles, emulsion aggregation (EA) toner particles could adhere more strongly to substrates and their property distributions are narrower because of their near-perfect spherical shape and higher surface free energy. However, in general, uncoated EA toner is more difficult to transfer and clean during printing/copying processes for the same reasons. Nanoparticle additives could be used as control agents to reduce the toner particle–substrate adhesion. In order to optimize their adhesion and handling performances, an accurate adhesion characterization of the toner particles coated with different levels of additives is required. In current study, two non-contact adhesion characterization techniques based on acoustic air-coupled excitation and ultrasonic base excitation are presented. Their use for the adhesion characterization of individual bare toner particles with an average diameter of 6.0 μm on silicon substrates, and their silica nanoparticle coated variants with a surface area coverage (SAC) of 50% is demonstrated. The techniques are based on the detection of the resonance frequencies of rocking motion of micro-spheres. The out-of-plane transient displacement responses of the rocking particles are captured by a laser interferometer, and the natural frequencies of particle rocking motion obtained from transient displacements at the top of particles and the substrate are related to the strength of the adhesion bond. It is reported that the work of adhesion values of the 50% SAC-coated toner on silicon substrates are almost an order of magnitude lower than those for the bare ones.     

SERS substrates formed by gold nanorods deposited on colloidal silica films

We describe a new approach to the fabrication of surface-enhanced Raman scattering (SERS) substrates using gold nanorod (GNR) nanopowders to prepare concentrated GNR sols, followed by their deposition on an opal-like photonic crystal (OPC) film formed on a silicon wafer. For comparative experiments, we also prepared GNR assemblies on plain silicon wafers. GNR-OPC substrates combine the increased specific surface, owing to the multilayer silicon nanosphere structure, and various spatial GNR configurations, including those with possible plasmonic hot spots. We demonstrate here the existence of the optimal OPC thickness and GNR deposition density for the maximal SERS effect. All other things being equal, the analytical integral SERS enhancement of the GNR-OPC substrates is higher than that of the thick, randomly oriented GNR assemblies on plain silicon wafers. Several ways to further optimize the strategy suggested are discussed.     

Investigation of mask selectivities and diamond etching using microwave plasma-assisted etching

Diamond etching is characterized using a microwave ECR plasma reactor with regard to etch rate selectivity, surface morphology, and feature size. Etching is performed on diamond substrates using a variety of etch mask materials including aluminum, titanium, gold, silicon dioxide and silicon nitride. The etch feed gases are combinations of oxygen, sulfur hexafluoride and argon. Aluminum masks provided the highest selectivity ratio of diamond etch rate to mask etch rate, both with and without SF₆ in the oxygen/argon feedgas. Selectivity was not found to be dependent on mask feature size. Gold masks produced the least degree of micromasking.     

Use of high temperature and high humidity to test the adhesion of sputtered copper to a polyimide surface modified by an AC nitrogen glow discharge

We have used an extreme environmental stress test to study the adhesion of a thin sputtered copper film (0.5 μm) to flexible polyimide (PI) substrates between 25 and 125 μm thick. The polyimide types include Kapton (PMDA-ODA) and Upilex (BPDA-PDA). When there was no surface modification on the PI, the adhesion of the film to Upilex type S was better than the adhesion to Upilex type R or Kapton type HN. When the polymer surface was treated with a simple AC nitrogen glow discharge (NGD), there was an improvement in the adhesion of the film to each of these polyimides. This improvement in adhesion became apparent after the film/substrate combination was subjected to either boiling water or steam for 30 min or more; the difference became quite clear after 2 h. A simple tape test was used to quickly estimate a relative adhesion strength. In order to compare the effect of our AC NGD treatment with other substrate surface modification methods, we used it to improve the coupling of a thick (> 10 μm) layer of copper (via a thin intermediate chromium layer) to a rigid PI substrate, formed from spin coating its precursor onto a silicon wafer. Peel test results were within a factor of 2-3 of the corresponding results obtained with a radio frequency (RF) plasma and ion beam treatments.     

Thermochemical Nitridation of Microporous Silica Films in Ammonia

Microporous silicon dioxide thin Films were deposited on silicon substrates from a solution of tetraethoxysilane, ethanol, and water. These were converted to dense oxynitrides through a high-temperature reaction with ammonia. The ammonia treatments yielded amorphous, compositionally homogeneous films with overall nitrogen contents ranging up to 40 mol%. For ammonia treatments below 800°C, nitrogen was incorporated into the films as an amine species, whereas higher temperature treatments produced a nitride material.     

A New Method to Evaluate Thin Film Adhesion

This paper discusses a new method of evaluating thin film adhesion both qualitatively and quantitatively via a combination of peeling and image processing techniques. The adhesion of thin film on the entire substrate can be quickly evaluated and quantified to a continuous response variable which is superior to a discrete response variable as described in the ASTM D3359-78 publication. Feasibility of this technique has been demonstrated through a gauge capability study which resulted in 2.7% P/T (precision to tolerance) ratio at six sigma standard deviation for a tolerance of 100. Experimental results using the proposed method to evaluate the process/property relationship of aluminum films as deposited onto various dielectric substrates such as polyimide, silicon dioxide, and silicon nitride have been obtained and have been shown to agree with conventional stud pull test results. The estimated cycle time to evaluate thin film adhesion is five minutes per 4-inch size wafer once the sample is prepared. This short process cycle time and proven reliability show that there is merit in implementing this technique both in the laboratory for process development and in the factory for statistical process control of products.     

Contents Lists and Abstracts from the Journal of the Adhesion Society of Japan

This paper discusses a new method of evaluating thin film adhesion both qualitatively and quantitatively via a combination of peeling and image processing techniques. The adhesion of thin film on the entire substrate can be quickly evaluated and quantified to a continuous response variable which is superior to a discrete response variable as described in the ASTM D3359-78 publication. Feasibility of this technique has been demonstrated through a gauge capability study which resulted in 2.7% P/T (precision to tolerance) ratio at six sigma standard deviation for a tolerance of 100. Experimental results using the proposed method to evaluate the process/property relationship of aluminum films as deposited onto various dielectric substrates such as polyimide, silicon dioxide, and silicon nitride have been obtained and have been shown to agree with conventional stud pull test results. The estimated cycle time to evaluate thin film adhesion is five minutes per 4-inch size wafer once the sample is prepared. This short process cycle time and proven reliability show that there is merit in implementing this technique both in the laboratory for process development and in the factory for statistical process control of products.     

Synthesis of alumina-bonded polycrystalline diamond by detonation

In this study, nanodiamond, aluminum isopropoxide, and hexogen (RDX) were used as starting materials to synthesize alumina-bonded polycrystalline diamond materials under high-temperature and high-pressure conditions generated by the detonation of the explosive. During detonation, the surface of the nanodiamond is coated with boron, silicon, and chromium through vacuum diffusion. Carbides of boron, silicon, and chromium referred as “bridges” are formed at the diamond/metal interface during the carbonization reaction. The "bridge" formed between diamond and nanoalumina considerably reduced the possibility of oxidation of nanodiamond as well as its graphitization during the detonation reaction. The phase, morphology, microstructure, and elemental composition of the detonation products were characterized by X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The results revealed that the explosion causes alumina and diamond to bond tightly to form alumina-bonded polycrystalline diamond composites. The thermal stabilities of the nanodiamond particles coated with boron, silicon, and chromium were found to be markedly higher, and the diamond phase remained intact even after heating at elevated temperatures. Thus, boron, silicon, and chromium reduced the wetting angle of diamond and alumina and improved the degree of bonding between them. Furthermore, boron facilitated the bonding between nanodiamond and alumina. In contrast, the bond was weaker in the case of silicon. Chromium also aided the bonding of the nanodiamond and alumina but introduced a large amount of oxygen into the composite.     

Atomic Force Microscope Techniques for Adhesion Measurements

The Atomic Force Microscope (AFM) has become a powerful apparatus for performing real-time, quantitative force measurements between materials. Recently the AFM has been used to measure adhesive interactions between probes placed on the AFM cantilever and sample surfaces. This article reviews progress in this area of adhesion measurement, and describes a new technique (Jump Mode) for obtaining adhesion maps of surfaces. Jump mode has the advantage of producing fast, quantitative adhesion maps with minimal memory usage.     

Atomic Force Microscope Techniques for Adhesion Measurements

The Atomic Force Microscope (AFM) has become a powerful apparatus for performing real-time, quantitative force measurements between materials. Recently the AFM has been used to measure adhesive interactions between probes placed on the AFM cantilever and sample surfaces. This article reviews progress in this area of adhesion measurement, and describes a new technique (Jump Mode) for obtaining adhesion maps of surfaces. Jump mode has the advantage of producing fast, quantitative adhesion maps with minimal memory usage.