N. S. McIntyre

An AES and XPS study of the initial oxidation of polycrystalline magnesium with water vapour at room temperature

Abstract The initial oxide formation on polycrystalline magnesium surfaces at room temperature has been quantitatively followed from the earliest stage using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Clean surfaces were prepared by sputtering with a minimum dose of argon ions to avoid the creation of heavily disordered crystal planes. Crystallographic orientations of various grain faces were determined using the electron back scattering diffraction technique in order to allow AES measurements to be made on grains of known orientation. By using calibrated doses of deuterated water vapour, three stages of early oxide growth were recognised: (1) a chemisorption stage during doses up to approximately 0.7 langmuir (L) ( 1 L = 1.3 × 10 −4 Pa · s); (2) a rapid oxide nucleation and island growth stage which is complete by about 5 L at an average island height of four monolayers and (3) a slow, diffusion-controlled growth stage after coalescence of the islands. Modelling results suggest that the rate of initial oxygen uptake is faster on grain faces that have more open-packed, high index orientations, particularly in the second (island nucleation and growth) stage. In addition, the slow growth stage has been adequately described by a logarithmic type growth law for exposures up to 1 × 10 6 L, suggesting a limiting oxide thickness in water vapour of approximately 11 monolayers of MgO. The slow growth process was found to be controlled by the movement of metal cations through the oxide film from the metal/oxide interface to the oxide/gas interface. Finally, the role of hydrogen in the oxide film was studied using XPS and nuclear reaction analysis (NRA). The results indicated that hydrogen was present in the film only in small relative amounts, likely as hydroxyl groups trapped at the metal/oxide interface. Detailed XPS spectra showed two distinct types of oxygen: one of these is assigned to be oxygen in a normal MgO lattice position; the other is ascribed to oxygen in a “defective” chemical environment.

Atomic force microscopy study of polypropylene surfaces treated by UV and ozone exposure: modification of morphology and adhesion force

Exposing polypropylene (PP) to ozone in the presence of UV light is a simple and effective way of modifying its surface to improve its wettability and adhesion. Atomic force microscopy (AFM) showed a dramatic change in the morphology and a clear increase in the adhesion force resulting from the modification of a PP film by UV/ozone exposure. A relationship has been demonstrated between a change in surface energy (measured by wetting contact angle) and the adhesion force (measured by AFM).

Deconvolution of pyrite, marcasite and arsenopyrite XPS spectra using the maximum entropy method

Abstract The maximum entropy method (MEM) is a new procedure for deconvoluting exciting line width and instrument resolution contributions from XPS spectra. MEM has been used to obtain additional detail from XPS 2p spectra collected from pyrite, marcasite and arsenopyrite surfaces which have been exposed by fracturing under UHV conditions. The resultant spectra have line widths that are nearly 50% narrower than the original spectra. Deconvoluted S 2p and Fe 2 p 3 2 spectra are shown to contain contributions from species located in disrupted lattice sites near the fracture surface as well as species on the outermost fracture surface. Iron 2p spectra are also found to exhibit fine structure which is attributed to multiplet splitting.

Effects of argon ion bombardment on basal plane and polycrystalline MoS2

Abstract Argon ion bombardment effects have been studied for two molybdenum disulphide samples with differing surface crystal orientations. High resolution X-ray photoelectron spectroscopy was used to monitor detailed changes in the core and valence levels. The specimens were dosed using a 2 kV argon ion beam, 45° to the surface at fluences ranging from 1 × 1014 to 1.2 × 10 16 ions cm 2 . A basal 〈0001〉 plane of MoS2 dosed to 1 × 10 14 ions cm 4 exhibited a Fermi level shift of −0.55 eV; this is interpreted as a of the level further away from the conduction band minimum as a result of defects introduced by the beam. Pinning at a similar point occurs naturally for the other specimen studied — a polycrystalline thin film of MoS2. Increasingly higher fluences of Ar+ on the basal plane MoS2 resulted in the gradual conversion of MoS2 to one prominent surface product — a molybdenum species with a Mo (3d 5 2 ) binding energy of 228.1 eV: evidence suggests that this molybdenum species is still associated with the Mo-S lattice framework. Similar doses of Ar+ on a polycrystalline surface results in substantially greater sulphur depletion and a number of different molybdenum-sulphur and molybdenum-oxide species.

A study of thin film Au–Al alloy oxidation in ambient air by X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and secondary ion mass spectrometry (SIMS)

Abstract The oxidation behavior of Al2Au and Au2Al alloys during a 3-month laboratory air exposure has been investigated using SIMS, XPS and XANES. The oxide growth on both alloys and Al metal were found to be remarkably similar in the whole exposure range. XPS studies showed a rapid initial growth of oxide over the first 10 days. The oxidation of the aluminum component caused phase transitions at the near-surface to alloys which were more Au-rich. SIMS depth profiling showed that the oxide thickness was considerably greater than that estimated by XPS using a simple overlayer model. Both alloy structures were shown to be epitaxically grown homologues to the base aluminum grain structures; by contrast, oxide structures showed no preferred growth on particular alloy grains. Oxidation of the Au2Al results in a major depletion in the aluminum in the immediately below the oxide. Al L2,3-edge XANES was used to probe the nature of the oxide formed on the alloys as compared to that on pure Al. The chemical characteristics of the oxide was found to be affected by the presence of the gold. This difference in oxide structure is detected at the interface and not through the oxide generally.

Unstable amplitude and noisy image induced by tip contamination in dynamic force mode atomic force microscopy

Liquid 1-decanethiol was confined on an atomic force microscope (AFM) tip apex and the effect was investigated by measuring amplitude-distance curves in dynamic force mode. Within the working distance in the dynamic force mode AFM, the thiol showed strong interactions bridging between a gold-coated probe tip and a gold-coated Si substrate, resulting in unstable amplitude and noisy AFM images. We show that under such a situation, the amplitude change is dominated by the extra forces induced by the active material loaded on the tip apex, overwhelming the amplitude change caused by the geometry of the sample surface, thus resulting in noise in the image the tip collects. We also show that such a contaminant may be removed from the apex by pushing the tip into a material soft enough to avoid damage to the tip.

Application of lateral force imaging to enhance topographic features of polypropylene film and photo-cured polymers

Abstract It is well known that topographic features can give rise to edge effects when making lateral force measurements in contact mode atomic force microscopy (AFM). Using a `smooth polypropylene film, which was also imaged by non-contact mode AFM, we showed that the edge effect can be used to reveal topographic features clearly through an enhancement of their outlines. Using photo-cured polymers we demonstrated that lateral force imaging is especially useful in revealing topographic features on surfaces which have large height differences.

Analysis of three-dimensional SIMS images using image cross-correlation spectroscopy

Three-dimensional (3D) SIMS images of secondary ion distributions in a solid volume can be produced from a stack of individual images acquired sequentially at different depths during depth profiling of the solid. While it is often possible to obtain visual correlations of large-scale features that occur in several images in the stack, the correlation of less-obvious features requires a more mathematical approach. We present here two cases where image cross-correlatiob spectroscopy (ICCS) can be used to clarify the presence or absence of organized structure in a 3D depth profile. In one example, the images of deuterium distribution in a zirconium oxide thin film were confirmed to exhibit order over a series of images, thereby suggesting the existence of continuous pores in the material. In a second example, the apparent clustering of gold distributions in a 3D profile of an arsenopyrite mineral was shown to be uncorrelated and likely an artefact of data collection.

Quantitative SIMS analysis of trace Au in pyrite using the infinite velocity (IV) method

Abstract The quantitative analysis of trace concentrations of Au in pyrite using a new procedure of SIMS quantification is investigated. Analysis of an Au implanted pyrite standard demonstrates the infinite velocity (IV) method as a viable procedure for evaluation of trace concentrations of Au in pyrite. Comparison of naturally occurring trace concentrations of Au in pyrite using standard-derived relative sensitivity factor (RSF) and IV quantification methods is shown as a means of evaluating the chemical environments in which Au is found in pyrite.

Nanolithography of a full-coverage octadecylphosphonic acid monolayer spin coated on a Si substrate

The authors describe a lithographic method based on a scanning probe technique to selectively remove octadecylphosphonic acid (OPA) molecules from their self-assembled monolayers (SAMs) spin coated on a Si substrate. This lithographic technique involves the use of a positively biased probe tip to scan an OPA SAM having a thickness of ∼2nm and provides an opportunity for developing a scanning probe based lithography that accommodates the need for ever-decreasing size of semiconductor devices.