Clean Aluminum Surface Research Articles

First-Principles Study of Chlorine Adsorption on Clean Aluminum Surface

Using density functional theory (DFT) we investigated the adsorption of chlorine atom on aluminum surface in the orientations, (100), (110), and (111). The structural and thermodynamic properties of chlorine atoms adsorbed on the Al (100), Al (110), and Al (111) surface for chlorine coverages of 1/9, 1/4, 1/3, 1/2, 3/4, and 1 monolayer (ML) are calculated. The largest bond strength is observed for a top, fcc, and hcp mixed structure at 3/4 ML coverage on Al (111). Adsorption free energy analysis reveals that the chlorine coverage of 3/4 ML of Al (111) is the most thermodynamically stable over the widest range of chlorine chemical potential and 1 ML of Al (111) is thermodynamically unstable, whereas various chlorine coverages of Al (100) and Al (110) take stable phase for a range of chlorine chemical potential.

Dioxygen molecule adsorption and oxygen atom diffusion on clean and defective aluminum(111) surface using first principles calculations

First principles calculations are conducted to investigate kinetic behavior of oxygen species at the surface of clean and defective Al(111) substrate. Oxygen island, aluminum vacancy, aluminum sub-vacancy, aluminum ad-atom and aluminum terraces defects are addressed. Adsorption of oxygen molecule is first performed on all these systems resulting in dissociated oxygen atoms in main cases. The obtained adsorbed configurations are then picked to study the behavior of atomic oxygen specie and get a detailed understanding on the effect of the local environment on the ability of the oxygen atom to diffuse on the surface. We pointed out that local environment impacts energetics of oxygen atom diffusion. Close packed oxygen island, sub-vacancy and ad-atoms favor oxygen atom stability and decrease mobility of oxygen atom on the surface, to be seen as surface area for further nucleation of oxygen island.

Atmospheric pressure plasma treatment of flat aluminum surface

The atmospheric pressure ambient air and oxygen plasma treatment of flat aluminum sheets using the so-called Diffuse Coplanar Surface Barrier Discharge (DCSBD) were investigated. The main objective of this study is to show the possibility of using DCSBD plasma source to activate and clean aluminum surface. Surface free energy measurements, X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDX) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) were used for the characterization of the aluminum surface chemistry and changes induced by plasma treatment. Short plasma exposure times (several seconds) led to a significant increase in the surface free energy due to changes of its polar components. Various ageing effects, depending on the storage conditions were observed and discussed. Effects of air and oxygen plasmas on the removal of varying degrees of artificial hydrocarbon contamination of aluminum surfaces were investigated by the means of EDX, ATR-FTIR and XPS methods. A significant decrease in the carbon surface content after the plasma treatment indicates a strong plasma cleaning effect, which together with high energy efficiency of the DCSBD plasma source points to potential benefits of DCSBD application in processing of the flat aluminum surfaces.

The characterisation of the interfacial chemistry of adhesion of rigid polyurethane foam to aluminium

The interfacial interactions between a rigid polyurethane foam (RPUF) and aluminium have been studied to understand the mechanisms of adhesion. Three different blowing systems are used in the production of the foam: chemical blowing, physical blowing and a mix of chemical and physical blowing systems. In addition an unfoamed system has been examined for comparison of the catalysts behaviour with and without blowing agents and the surfactant. Peeled failure surfaces have been examined by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF–SIMS). To examine the intact interfacial regions of the RPUFs cured against aluminium, samples have been sectioned by microtomy. The failure surfaces of the aluminium sides exhibit relatively clean aluminium surfaces with RPUF residues observed for all three foamed systems; such thin RPUF layers (ca. 1 nm) indicate good adhesion (and a cohesive failure) between foam and substrate and that the interfacial adhesion is higher than the cohesive strength of the foam. The unfoamed system behaves in a similar manner but has a higher peel strength. A fragment indicative of covalent bond formation between isocyanate and aluminium (nominal mass at 102 u: AlCHNO3 −) is observed on the failure surface of aluminium side, where RPUF/aluminium interface region is present, for all foams. The catalyst used in these formulations, pentamethyldiethylenetriamine (PMDETA), is concentrated at the interface area. Whilst examination of the sectioned specimens shows that the silicone surfactant is concentrated within the cell area fulfilling its role on cell formation and stabilisation, and is not segregated at the RPUF/aluminium interface.

Secondary electron emission spectra from clean and cesiated Al surfaces: the role ofplasmon decay and data analysis for applications

We report measurements of energy spectra of secondary electrons emitted from clean andcesiated aluminum surfaces under the impact of 130 eV electrons. Measurements show thatthe decay of bulk and surface plasmons dominates the electron emission. In contrast withtheoretical calculations, our experiments indicate that the electron collision cascade insidethe solid produced by electrons excited by plasmon decay do not contribute significantly toelectron emission.A simple analysis of electron energy distributions measured as a function of Cs surfacecoverage allows separation of rediffused incident electrons from the continuumbackground of true secondary electrons. The result shows that yields of rediffusedelectrons used in several applications may have been significantly overestimated.

Abstractive dissociation of oxygen over Al(111): a nonadiabatic quantum model.

The dissociation of oxygen on a clean aluminum surface is studied theoretically. A nonadiabatic quantum dynamical model is used, based on four electronically distinct potential energy surfaces characterized by the extent of charge transfer from the metal to the adsorbate. A flat surface approximation is used to reduce the computation complexity. The conservation of the helicopter angular momentum allows Boltzmann averaging of the outcome of the propagation of a three degrees of freedom wave function. The dissociation event is simulated by solving the time-dependent Schrödinger equation for a period of 30 femtoseconds. As a function of incident kinetic energy, the dissociation yield follows the experimental trend. An attempt at simulation employing only the lowest adiabatic surface failed, qualitatively disagreeing with both experiment and nonadiabatic calculations. The final products, adsorptive dissociation and abstractive dissociation, are obtained by carrying out a semiclassical molecular dynamics simulation with surface hopping which describes the back charge transfer from an oxygen atom negative ion to the surface. The final adsorbed oxygen pair distribution compares well with experiment. By running the dynamical events backward in time, a correlation is established between the products and the initial conditions which lead to their production. Qualitative agreement is thus obtained with recent experiments that show suppression of abstraction by rotational excitation.

Ab initio calculations of field emission from ultrathin Si(100) films

We have analyzed field emission from ultrathin Si(100) films on a metal substrate by using ab initio density functional calculations incorporating scattering states. We have shown that the clean Si(100) film can screen an external electric field sufficiently due to metallic states of surface dangling bonds, and thus field emission from the clean silicon film is attributed to that from surface states. We have also analyzed effects of metal adsorption on field emission from Si(100) films. We have obtained a much larger emission current from the Si(100)2×2-Al surface at 0.5 monolayer coverage than that from clean silicon and aluminum surfaces. The minimum local barrier height clearly explains the difference between the Si(100)2×2-Al surface and the clean Al(100) surface, which cannot be explained from the small difference in the work function between the two surfaces. We have also found that the emission current further increases with a change in the atomic position of adsorbed aluminum addimers which causes both a decrease in the minimum local barrier height and an increase in the local density of states at a surface around the Fermi level.

Probing inelastic interactions of ions moving in solids by electron spectroscopy

We have measured energy distributions of electrons emitted from clean aluminum surfaces by 20 keV/amu H+, He+ and He0 projectiles. Ratios of energy distributions obtained from two types of projectiles carry information on differences in the electron excitation collisions. We discuss these differences in terms of screening of the projectile by valence electrons, Auger capture and projectile ionization, with the aid of linear response theory. We find the shapes of secondary electron energy spectra are dominated by the energy dependence of the electron escape depth and of the binary ion–electron interaction. The latter must be determined by considering the screened potential of the projectile and its changing charge state as it penetrates the solid.

The Effect of Surface Contamination on Adhesive Forces as Measured by Contact Mechanics

ABSTRACTThe contact adhesive forces between two surfaces, one being a soft hemisphere and the other being a hard plate, can readily be determined by applying an external compressive load to mate the two surfaces and subsequently applying a tensile load to peel the surfaces apart. The contact region is assumed the superposition of elastic Hertzian pressure and of the attractive surface forces that act only over the contact area. What are the effects of the degree of surface contamination on adhesive forces? Clean aluminum surfaces were coated with hexadecane as a controlled contaminant. The force required to pull an elastomeric hemisphere from a surface was determined by contact mechanics, via the JKR model, using a model siloxane network for the elastomeric contact sphere. Due to the dispersive nature of the elastomer surface, larger forces were required to pull the sphere from a contaminated surface than a clean aluminum oxide surface.

Dry Lubricant Films for Aluminum Forming

During metal forming, lubricants are necessary to prevent direct contact, adhesion, transfer, and scuffing of workpiece materials and tools. Boric acid films, which can be firmly adhered to clean aluminum surfaces by spraying their methanol solutions, provide extremely low friction coefficients (≈0.04). The adhesion strengths of the bonded films vary with the type of aluminum alloy (6061, 6111, and 5754). Sheet metal forming tests indicate that boric acid films and combined films of boric acid and mineral oil can enable larger strains than commercial liquid and solid lubricants, showing that their lubricities are excellent for aluminum forming. Scanning electron microscopy analyses indicate that the dry boric acid films effectively separate the workpiece and die materials and, thus, prevent direct contact and preserve the surface qualities. Because boric acid is nontoxic and easily removed by water, the authors can expect these films to be environmentally friendly, cost-effective, and very efficient lubricants for sheet aluminum cold forming. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999

Application of parallel factor analysis and X-ray photoelectron spectroscopy to the initial stages in oxidation of aluminium

The three-way parallel factor analysis (PARAFAC) has been used to decompose a set of XPS (X-ray photoelectron spectroscopy) spectra which result during the oxidation of aluminium surfaces by water vapour. Al(2p) and O(1s) core-level photoelectron lines have been used to follow oxide film growth on clean aluminium surfaces as a function of exposure time and pressure of water vapour. The PARAFAC solution provides new information on elemental processes in the very initial stages of oxidation kinetics, showing new components in the XPS spectrum, as well as their evolution through the range of time and pressure variables. Reaction of H 2O vapour with aluminium results in attenuation of the metallic peak, binding energy (BE) at 72.87±0.05 eV, and increase of the oxidic peak, BE at 75.80±0.05 eV. An additional factor is identified, which suggests the formation of an interface metal hydride, with BE at 72.4(4) eV, as well as a concomitant oxide peak at 75.4(3) eV. At pressures above 1.3×10 −5 Pa this factor is diminished; this is presumably due to the increase in recombination of atomic hydrogen.

Application of parallel factor analysis and x-ray photoelectron spectroscopy to the initial stages in oxidation of aluminium. I. The Al 2p photoelectron line

Three-way parallel factor analysis (PARAFAC) has been used to decompose a set of x-ray photoelectron spectroscopy (XPS) spectra that result during the oxidation of aluminium surfaces. The Al 2p core-level photoelectron lines have been used to follow oxide film growth on clean aluminium surfaces as a function of exposure time and pressure of water vapour. In this paper, a fine peak structure of the XPS Al 2p spectrum has been extracted using PARAFAC. The PARAFAC solution provides new information on elemental processes in the very initial stages of oxidation kinetics, showing new components in the XPS spectrum as well as their evolution through a range of time and pressure variables. As expected, the reaction of water vapour with aluminium results in attenuation of the metallic peak at binding energy (BE) 72.87±0.05 eV and an increase of the oxidic peak at BE 75.80±0.05 eV. However, an additional factor is also identified, which suggests the formation of an interfacial metal hydride at BE 72.4(4) eV, as well as a concomitant oxide peak at 75.4(3) eV. Both are ascribed to products of the hydrolysis of adsorbed water molecules at the aluminium interface. At pressures above and below 1.3×10−5 Pa this factor is diminished; in the case of higher pressure, this is ascribed to an increase of the recombination of atomic hydrogen. Copyright © 1999 John Wiley & Sons, Ltd.

Improvements to the analysis of x-ray photoelectron spectra using a maximum entropy method for deconvolution

X-ray photoelectron spectra are typically broadened by the inclusion of contributions from the exciting X radiation, as well as the spectrometer itself. A procedure for removal of much of this broadening using a version of the maximum entropy method is described. This method uses a nonlinear functional (the spectral “entropy” or information content) to stabilize the noise amplification problem inherent to deconvolution of real data. A less ambiguous solution is therefore obtained compared to previous approaches which use linear estimates. This algorithm avoids the subjective nature of many previous deconvolution methods by assuming that the informational uncertainty is always maximized within the constraint of the data provided. This large scale, nonlinear optimization problem can be solved on a fast personal computer using a sequential quadratic programming algorithm. For spectra with adequately high signal/noise, the linewidths produced approach the limiting core hole lifetime values. The method is applied to study the extended growth of an oxide layer on clean polycrystalline aluminum surfaces following exposure to water vapor. For the early growth stages, the spectral detail is comparable to recent synchrotron-based studies where one or more precursor phases are detected at the interface prior to the nucleation of the extended oxide film. In a related study of the oxidation of gold–aluminum alloy surface films, the evolution of the gold–aluminum near-surface phase could be followed through changes in the Au(4f ) and the Al(2p) spectra. From the latter, the surface oxides grown on the alloy surface are seen to differ distinctly from those on pure aluminum.

An atomic force microscopy study of the corrosion and filming behaviour of aluminium

Corrosion and filming behaviour of aluminium have been investigated by atomic force microscopy (AFM). Preliminary examination of the aluminium surfaces prepared by conventional surface pre-treatment procedures, e.g. electropolishing, mechanical polishing, etc., has shown that microscopically smooth aluminium surfaces suitable for AFM study cannot be obtained readily by existing procedures. Thus, a new and novel technique has been developed for the preparation of clean and microscopically smooth aluminium surfaces for AFM study. The technique is based on cutting small strips of aluminium specimens, encapsulated in an epoxy resin, by a diamond knife using an ultramicrotome. With this technique, clean aluminium surfaces, which are microscopically smooth to within 1 nm over a scanned area of 1 μm × 1 μm or, perhaps, even greater, are readily prepared. Aluminium specimens with such microscopically smooth surfaces were given various treatments and examined by AFM. It was found that AFM, despite its unprecedented high resolution, does not allow one to one correspondence to be made between local film character and microscopic inhomogeneities of the aluminium surfaces associated with fine features such as grain boundaries or cellular boundaries which are known to play a crucial role in the development of chromate chemical conversion coatings or nucleation of pits. Fortunately, however, microscopical information can be obtained by transmission electron microscopy of ultramicrotomed sections. Thus, the potential of AFM is realized fully if it is combined with transmission electron microscopy of ultramicrotomed sections. Otherwise and for aluminium in particular, AFM is merely an approach to image surfaces in situ or ex situ at resolutions considerably higher than those attained by high resolution scanning electron microscopy.

Microscopic Estimates for Electromigration Velocities of Intragranular Voids in Thin Aluminum Lines

AbstractWe explore the effect of faceting on possible mechanisms for mass transport around electromigration voids in aluminum interconnects. Motivated by linear response estimates which suggest that particle flux would be much higher along steps than across terraces on a clean aluminum surface, we study step nucleation in the presence of a small driving force along a surface. We find that step nucleation, even on a nearly defect-free void surface, would be slow if the step energy is equal to that calculated for a clean aluminum surface. In the presence of a uniform electromigration force, the creation of new steps between existing ones should not occur unless the free energy cost of a step is much less than thermal energies. We conclude that voids cannot move intragranularly at μm/hr rates without help from other factors such as local heating and impurities.

Roll bite conditions controlling formation of wear debris during cold rolling of aluminum

The cleanliness of rolled aluminum sheet is important for the cosmetic properties of the metal and its downstream performance in forming operations. The surfaces of rolled sheet are covered by residual rolling oil and inorganic debris produced during rolling. This wear debris is often labelled as smut or smudge. In this paper we examine effects on smut formation of various tribological parameters associated with high-speed cold rolling. Experimental variables include metal entry temperature, roll roughness, and lubricant properties such as chemistry and viscosity. Surface attributes of the metal; cleanliness, topography and residual oil were measured before and after rolling. Mill data such as currents, rolling loads, forward slip, tensions and speeds are monitored to allow calculations of rolling friction. Metal cleanliness is found to deteriorate under conditions where hydrodynamic lubrication dominates. Low smut levels were correlated with relatively high metal entry temperatures. Further analysis of sheet topography and rolling friction data suggests that this temperature effect is related to the oil film thickness in the roll bite. Smut decreases with decreasing oil film thickness and therefore increases with decreasing friction. Changes in lubricant composition, with the exception of using methyl esters with weak load bearing properties, and roll roughness have a relatively small effect on cleanliness. In practical terms, a clean aluminum surface can be produced under conditions that minimize surface break-up. Thus for cold rolling, a relatively small hydrodynamic component of lubrication is favoured. This necessitates rolling at relatively high temperatures with thin lubricant films of large load bearing capacity.

Initial metal fluoride formation at metal/fluorocarbon interfaces

The interaction of several perfluoroalkyl ethers [CF3OCF3, CF2OCF2OCF2 , and CF3OCF2OCF3] and an acyl fluoride [CF3OCF(CF3)CFO] with iron and aluminum surfaces has been studied with x-ray photoelectron spectroscopy. The perfluoroalkyl ethers were found to not interact with either the clean iron surface or the clean aluminum surface. In contrast, the acyl fluoride compound was observed to readily decompose when in contact with the clean aluminum surface. The same molecule formed a surface carboxylate structure when in contact the clean iron surface. Interactions were also observed on native oxides of aluminum and iron exposed to acyl fluoride. For the aluminum surface, the degradation of the acyl fluoride molecule is not limited to the carbonyl group as it is for the iron surface. Rather, the entire molecule dissociates on the surface.

Study of the Degradation by Friction of an Aluminum Foil Rolling System in a Testing Machine

An experimental system at laboratory scale, capable of simulating the main mechanisms, i.e., friction and clean aluminum surface generation, during the rolling process of aluminum foil has been designed, built, and adjusted. The equipment is capable of rapidly aging the lubricant system with n-tetradecane (NT) as the base oil, and dodecanoic acid (DA) and butyl palmitate (BP) as additives. The main contribution of the present work is obtaining significant amounts of aluminum soaps by mechanical means, due to the generation in the reaction medium of highly reactive, non-oxidized, aluminum surfaces. These soaps are similar to those obtained in the industrial foil rolling process. An infrared study of the filters shows a significant evolution of the 3740, 3500, 1760, and 985 cm-1 absorption bands, probably due to the change in the molecular structure of the soaps. The forming of aluminum dilaurate seemed to be favored under the conditions studied, allowing its separation by filtration due to the high amounts...

Surface chemistry of dimethylaluminum hydride and trimethylaluminum on polycrystalline aluminum

The surface chemistry of both dimethylaluminum hydride (DMAH)and trimethylaluminum (TMA) on a polycrystalline aluminum surface has been investigated with temperature-programmed desorption (TPD), secondary ion mass spectrometery (SIMS), and Auger electron spectroscopy (AES). Under the authors experimental conditions, DMAH adsorbs on the aluminum surface in its trimeric form and TMA adsorbs primarily in a dimeric form. DMAH desorbs from the atomically clean aluminum surface at 235 K, and TMA desorbs at 200 K. Both DMAH and TMA dissociate readily on the aluminum surface, and analysis by SIMS shows that this decomposition leaves a partially methylated aluminum surface at temperatures up to 500 K. DMAH desorbs from the carbon-contaminated aluminum surface at about 200 K. Both TMA and DMAH are found to produce methane product during the TPD experiments. The TPD experiments also suggest that the surface reactions of DMAH produce TMA as a reaction product. However, the reactions that form methane and TMA product occur in minor yield under their experimental conditions. By AES the surface is comprised of both aluminum and carbon after either DMAH-TPD or TMA-TPD.

A Microscopic theory of electron energy loss spectroscopy for a simple metal

We present a quantum-mechanical theory for the inelastic scattering of slow electrons by a simple metal surface, due to the coupling to electron-hole pair excitations. The solid surface is described within the self-consistent jellium model, and the self-energy of the beam electrons is modeled by a local step-like optical potential, whose strength is related to the experimental values of the electron mean free path. The calculated reflection electron energy loss spectra show a broadening of the surface-plasmon peak which is in good agreement with measurements at clean aluminum surfaces.