Showing papers in "Surface and Interface Analysis in 1999"

Structure and physicochemistry of anodic oxide films on titanium and TA6V alloy

Abstract: Anodization of titanium and its alloys is an important surface treatment, especially for adhesion applications, but is not as well studied as for aluminium alloys. This paper deals with the morphological, structural and physicochemical characterization of anodic oxide films grown on titanium and Ti–6Al–4V (TA6V) in chromic acid solution without (CA) or with (CA/HF) hydrofluoric acid addition. Several investigations methods are used: high-resolution scanning electron microscopy (HR-SEM), reflection high-energy electron diffraction (RHEED), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), nuclear reaction analysis (NRA) and wetting angle measurements. The occurrence and morphology of the nanoporous structure for CA/HF anodization are described. The compact films grown in CA solution are amorphous and the porous films grown in the CA/HF solution are partially crystalline. The thickness and morphology of the films are described and discussed as a function of the anodizing conditions and of the composition of the underlying substrate. The composition of the film appears to be TiO2+Al2O3 (with Ti/Al atomic ratio ∽5), with incorporation of fluorine from the solution in the porous films and of small quantities of vanadium in the films that are grown. The specific role played by the Cr(VI) and F species on the film growth-and-dissolution formation process is discussed and a growth mechanism is proposed. Copyright © 1999 John Wiley & Sons, Ltd.

XPS of sulphide mineral surfaces: metal‐deficient, polysulphides, defects and elemental sulphur

Abstract: This paper reviews evidence for the assignments of components of the S 2p XPS spectra from sulphide mineral surfaces under different conditions of preparation, oxidation and reaction. Evidence from other techniques confirming assignment of high-binding-energy S 2p components to metal-deficient sulphide surfaces, polysulphides, elemental sulphur and electronic defect structures is considered for specific cases. Reliable assignment of S 2p 3/2 components at 163.6-164.0 eV to elemental sulphur S n 0 can be confirmed by evaporative loss at 295 K and/or observation of S-S bonding by x-ray absorption fine structure (XAFS), x-ray diffraction or vibrational spectroscopy. Assignment to polysulphides S n 2- at 162.0-163.6 eV requires confirmation of S-S bonding by XAFS or vibrational spectroscopy. Metal-deficient lattices can be represented as electronic defects (e.g. vacancies) or restructured surface phases confirmed by diffraction or XAFS evidence. High-binding-energy S 2p 3/2 components can also result from Cu(I) substitution into ZnS with associated oxidation of sulphur as electronic defect sites without S-S bonding, metal deficiency or restructuring. This assignment is confirmed by XAFS evidence.

Pulsed force mode: a new method for the investigation of surface properties

Abstract: Scanning force microscopy is extended by the pulsed force mode from simple imaging of topography to measuring elastic, electrostatic and adhesive sample properties. Lateral forces are virtually eliminated so that mapping of delicate samples with high resolution in air and fluids is easily possible. Scanning speed is comparable to that in contact mode. The new opportunities for scanning force microscopy given by the pulsed force mode is demonstrated in selected applications.

Quantitative material characterization by ultrasonic AFM

Abstract: In an atomic force microscope equipped with a micromachined cantilever tip, the cantilever vibration spectra in contact with the sample were found to be strongly dependent on the excitation power. However, if the excitation power is small enough, the resonance peak width decreases and the peak frequency increases to a certain limiting value. In this condition the tip-sample contact is kept linear, and satisfactory agreement between the measured and calculated frequency is obtained, assuming a constant contact stiffness; the agreement is further improved by taking into account the lateral stiffness. More quantitative information on the elasticity of the sample is obtained from the contact load dependence of the frequency, where contact stiffness of a non-spherical tip shape is derived from the Sneddon-Maugis formulation, and the tip shape index is estimated by an inverse analysis of the load-frequency relation. A further advantage of evaluating not only the vertical but also the lateral stiffness is demonstrated on a ground silicon wafer by simultaneous measurement of deflection and torsional vibration.

Phase contrast and surface energy hysteresis in tapping mode scanning force microsopy

Abstract: Phase imaging is one of the most attractive features of tapping mode scanning force microscopy operation. In this paper we analyse the relationship between phase contrast imaging and the energy loss due to tip-sample interaction forces. An analytical relationship is obtained between the phase shift and the energy loss. Experiments performed on graphite are in agreement with the analytical expression.

Effect of plasma shielding on laser ablation rate of pure metals at reduced pressure

Abstract: The ablation rate expressed as the amount of removed material per laser shot was calculated for pure metal samples under different experimental conditions: laser fluence (1.3‐16.7 J cm 2 ), buffer gas (air, He and Ar) and gas pressure (10 3 ‐10 5 mbar). Fluence values covered the range between the plasma threshold (~1‐2 J cm 2 for most elements) and 16.7 J cm 2 . The 581 nm output of an excimer-pumped dye laser was used. Results pointed out a strong dependence of ablation rate on experimental parameters. At high fluence, the ablated material efficiently attenuates the incoming laser radiation (plasma shielding) and reduces the ablation rate. The extent of this shielding effect depend also on the experimental variables (buffer gas, pressure) and sample nature. These studies are useful to determine the amount of ablated material as a function of experimental parameters, to understand the extension of the shielding process and to establish the conditions under which it may be avoided. Copyright ” 1999 John Wiley & Sons, Ltd.

Carbon Nanotubes as AFM Tips: Measuring DNA Molecules at the Liquid/Solid Interface

Abstract: High-resolution imaging of soft and weakly adsorbed biomolecules on surfaces within buffer solutions presents a big challenge in research. Here we demonstrate that a single carbon nanotube could be used as a tip for probing biomolecules in solution using atomic force microscopy (AFM). Combining the unique properties of carbon nanotube tips with the newly developed magnetically driven oscillating AFM technique, we were able to obtain molecular-level, high-resolution images of DNA molecules adsorbed on the mica surface in solution. The length and the buckling force of the single nanotube tip can be derived directly from the force-distance curve. These measurements indicate that the nanotube tip is quite resilient, and it can quickly recover to its full length after repeatedly being crashed on the surface with excess force. The well-defined tip geometry provides extraordinary resolution in AFM imaging. The application of carbon nanotubes as AFM tips could lead to breakthroughs in biological studies.

From depth resolution to depth resolution function: refinement of the concept for delta layers, single layers and multilayers

Abstract: At present, the definition of the depth resolution, Δz, recommended by the International Union of Pure and Applied Chemistry (IUPAC) and by committee E 42 of the American Society of Testing and Materials (ASTM-E42), is given by the distance over which the change between 16% and 84% of the intensity of the profile at a sharp interface is measured. This definition has a precise physical meaning only for a Gaussian shape of the depth resolution function. With the advances in high-resolution depth profiling during the past decade and the increasing demand for profile reconstruction with monolayer accuracy, the often strongly asymmetric depth resolution functions cannot be represented by Δz with sufficient accuracy. Using the mixing-roughness-information depth (MRI) model for the calculation of sputter depth profiles, it is shown that, for the same Δz, different resolution functions can be obtained with different full width at half-maximum (FWHM) values. The consequences for profiles of delta layers, single layers and multilayers are outlined. Although an exact characterization of the depth resolution in general needs three parameters, characterization with one parameter superior to Δz is the inverse maximum slope of an interface profile or the FWHM of the according depth resolution function.

Measuring and modifying the electric surface potential distribution on a nanometre scale : a powerful tool in science and technology

Abstract: The combination of atomic force microscopy (AFM) and Kelvin probe technology is a powerful tool to obtain high-resolution maps of the electric surface potential distribution on conducting and non-conducting samples. We show that potential maps of composite metal films and semiconductors show a clear chemical contrast and can be used to differentiate between different materials with a lateral resolution of a few 10 nm. Because AFM tips are not point-like structures, we establish a simple model to correlate the measured quantities with the true surface potential distribution, and compare numerical simulations of the three-dimensional tip-specimen model with experimental data from test structures. For the first time, we combine the electrostatic surface potential and the topography data to derive the local electrostatic field strength on active transistors. Using suitable substrates, trapped surface charges can be generated by applying short voltage pulses between the tip and the sample surface. These surface charges can be detected in the electric surface potential image and might be used as bits in new data storage systems or as target sites in self-assembly processes.

Lateral force microscopy using acoustic friction force microscopy

Abstract: Conventional friction force microscopy (FFM) is widely used for tribological studies of engineering surfaces. It is, however, difficult to separate friction forces resulting from interactions dependent upon interfacial material properties from surface topography-induced lateral forces. We have developed and employed a technique to operate acoustic friction force microscopy (AFFM) by oscillating the sample laterally at megahertz frequencies. The in-plane vibrations perpendicular to the longitudinal axis of the cantilever are generated because of lateral forces between the probe tip and the sample. Torsional cantilever vibrations were detected at frequencies of up to 2 MHz. A mean cantilever lift-off was observed that can be explained by elastohydrodynamic lubrication. The high-frequency torsional vibration amplitude provides information about the lateral forces that can be used to calculate the friction and viscosity of thin surface films. The AFFM images of metal-particle magnetic tapes were produced, revealing a resolution apparently better than FFM images. Unlike FFM images, AFFM images are independent of the scanning direction, indicating that AFFM images are less sensitive to topography-induced lateral forces. Also, AFFM, allows friction measurements at relative velocities of the order of 1 mm s −1 which is much larger than that obtained in conventional FFM (several μm s−1). Copyright © 1999 John Wiley & Sons, Ltd.

Charge compensation and binding energy referencing in XPS analysis

Abstract: Throughout the evolution of XPS, the ability to compensate for surface charging and accurately calibrate the binding energy scale, particularly with electrically inhomogeneous samples, has remained one of the most intractable problems. The last decade, however, has seen some quite significant advances in this area. Best exemplified perhaps by the Kratos (UK) 'in the lens' electrostatic mirror/electron source coupled with a magnetic immersion lens, a number of concepts have been advanced that take a quite different conceptual approach to charge compensation. They differ in a number of fundamental ways from the electron flood-type compensators, which are widely used and historically are absolutely essential with instruments based on monochromatized sources. Even more recent has been the use of combined ion and electron flood systems. Thus, modern approaches to compensation represent a more sophisticated understanding both of how charging arises and how it may be mitigated to improve the accuracy and utility of XPS spectra.

TEM, XPS and FTIR characterization of sputtered carbon nitride films

Abstract: Carbon nitride films were grown on Si(100) substrates using d.c. magnetron sputtering with r.f. bias. Reactive deposition was achieved using a graphite target in an argon/nitrogen plasma. These films were characterized by transmission electron microscopy (TEM), XPS and Fourier transform infrared spectroscopy (FTIR) spectroscopy. Relatively large carbon nitride crystal grains in polycrystalline structures were observed with TEM. According to calculations from electron diffraction patterns, these crystalline structures were hexagonal β-C 3 N 4 . From XPS data, N/C ratios in the films were calculated to be in the range of 0.18-0.5. The XPS spectra of the films typically showed three peaks in the C Is core-level spectrum (centred at 284.6, 285.9 and 287.2 eV) and two peaks in the N Is core-level spectrum (centered at 398.7 and 400.2 eV). This indicates that there are two types of C-N bonds; N is bonded to sp 2 - or sp 3 -coordinated C atoms in the as-deposited films. The FTIR spectra showed three absorption bands in the range 1000-3000 cm -1 . The absorption band at -2367 cm -1 can be attributed to the C≡N nitrile bond. The absorption bands at -1559 cm -1 and 1201 cm -1 demonstrate the existence of C=N (sp 2 ) and C-N (sp 3 ) bonds. Moreover, the relative absorption intensity of C-N bonds seems to increase with increasing nitrogen content. Both XPS and FTIR measurements showed the presence of fourfold-coordinated β-C 3 N 4 crystals in the films, which is in good agreement with TEM and electron diffraction results.

Preparation, comparison and performance of hydrophobic AFM tips

Abstract: Hydrophobic coatings for atomic force microscopy (AFM) tips generated through sputter coating with gold, chemical vapour deposition from a hexafluoropropene plasma or silanization with octadecyltrichlorosilane are compared with respect to their macroscopic hydropobicity, influence on tip radius, abrasion behaviour during imaging and complexity of the coating procedure. The performance of the coated tips is assessed by measuring their adhesion from force curves at different humidities. From these tests, the hexafluoropropene plasma-treated tips turned out to exhibit the best overall quality and so are used to image the hexagonally packed intermediate surface (HPI) layer of the eubacterium Deinococcus radiodurans, a natural two-dimensional protein crystal, to demonstrate the capability of these tips to image fragile, hydrophilic samples at high humidities with reduced tip-sample adhesion.

Dynamic force microscopy in fluid

Abstract: Low-amplitude dynamic force microscopy can operate in a non-contact mode, sensing changes in liquid properties near a surface. Operation of the microscope in water at the higher amplitudes often required for stable imaging has been investigated. When driven by direct application of a force to the tip, the microscope is stable over a wide range of operating frequencies. At low frequency, the interfacial stiffness extracted from approach curves is found to be of the order of 1 N m -1 on first contact, which is indicative of imaging via a compressed liquid layer. Measurements of the spectral response of the cantilever and numerical simulations confirm this and show that viscous damping at the surface also plays a role.

Conservative and dissipative interactions in dynamic force microscopy

Abstract: Dynamic force microscopy has proved to be a powerful imaging tool. Here, the tip of an atomic force microscope is vibrated at a high frequency, typically the resonance frequency of the lever sensor, and at a large vibration amplitude, typically of the order of 10 nm. Imaging contrast is obtained from measuring shifts of the resonance frequency, which provides information on conservative interactions, and of the Q-factor, which is sensitive to dissipative interactions. Problems associated with interaction sensing are discussed from a theoretical and an experimental point of view. Copyright © 1999 John Wiley & Sons, Ltd.

Angle-resolved x-ray photoelectron spectroscopy studies of the evolution of plasma-treated surfaces with time

Abstract: Coupons of polished aluminium, glass and polystyrene were exposed to radiofrequency (r.f.) plasmas containing helium, nitrogen and oxygen. Angle-resolved XPS measurements of the treated surfaces were made immediately, after a few days and after about 9 months. The data were interpreted in terms of a simplified substrate–overlayer model with allowance for fractional coverage. The results are consistent with surface cleaning followed by hydrocarbon re-contamination for aluminium and glass, and with the diffusion of adatoms towards the bulk in the case of polystyrene. Copyright © 1999 John Wiley & Sons, Ltd.

Corrosion resistance of single TiN layers, Ti/TiN bilayers and Ti/TiN/Ti/TiN multilayers on iron under a salt fog spray (phohesion) test: an evaluation by XPS

Abstract: The corrosion resistance of three different TiN coatings on iron (single TiN layer, Ti/TiN bilayer and Ti/TiN/Ti/TiN multilayer) subjected to a salt (ammonium sulphate and sodium chloride) fog spray (Prohesion) test has been investigated by means of x-ray pbotoelectron spectroscopy (XPS). The relative intensities of the Fe 2p and 0 1s signals in the XPS spectra of the corroded samples increase with their extent of degradation. The results show that the corrosion resistance of these coatings decrease in the order bilayer > multilayer > single layer.

Aspects of dynamic force microscopy on NaCl/Cu(111): resolution, tip–sample interactions and cantilever oscillation characteristics

Abstract: Ultrathin films of NaCl on Cu(111) have been studied using a dynamic force microscope. We present images with atomic resolution at step sites on the NaCl films, Force spectroscopy measurements of the tip-sample interaction on NaCl-covered areas and the Cu substrate are analysed with respect to electrostatic, van der Waals and short-range contributions, The interaction contrast between NaCl and Cu is shown to be reflected in the oscillation characteristics of the cantilever, First results of a resonance analysis with the help of a novel digital oscillation control system are presented.

Surface analysis and bioreactions of Ti‐ and V‐containing a‐C : H

Abstract: Amorphous hydrogenated carbon films (a-C : H) containing different amounts of Ti or V were produced by combined plasma-activated chemical vapour deposition and d.c. magnetron sputtering. New bioactive materials resulted from the combination of the excellent tribological and biological properties of the a-C : H matrix with the biological response to the incorporated metals. By adding Ti to the a-C : H matrix, an enhanced differentiation of osteoblast- and reduced osteoclast-like cell activity was achieved, leading to a coating that is valuable for bone implants: enhancing bone ingrowth through increased osteoblast activity and reducing bone resorption through osteoclast-like cell inhibition. The a-C : H/V films reduced lysosomal activity as well as neutral red uptake in bone marrow cell cultures, thus being an interesting coating for short-term implants where reduced cell attachment is required. Prior to cell culture tests, the surfaces of the metal-containing a-C : H films were investigated by x-ray photoelectron spectroscopy. The relation between chemical surface composition and cellular response is discussed.

XPS determination of the forms of nitrogen in coal pyrolysis chars

Abstract: The N Is spectra from four pulverized Australian coals and their chars produced by pyrolysis for 2 s at 1100°C and 1300°C in a pressurized furnace are evaluated, with particular reference to the binding energy region above 402 eV. The spectra for the feed coals were broadly similar to those reported previously for bituminous coals, in that pyrrolic nitrogen was the dominant functional form in each case. A minor component between 403 and 404.5 eV was assigned to ammonium nitrogen in liberated mineral matter. The N Is spectra for the chars were also broadly similar to those expected for pyrolysis under intermediate residence time conditions, in that the proportion of pyrrolic nitrogen was no more than half that for the feed coal. Intensity in the 402-404.5 eV region was more consistent with N-O species formed post-pyrolysis than similar species formed as intermediates during pyrolysis.

Probing linear and non-linear tip–sample interaction forces by atomic force acoustic microscopy

Abstract: The cantilever–sample system of an atomic force acoustic microscope is excited in the frequency range from 10 kHz to 3 MHz. By analysing the cantilever vibration in the frequency domain, one obtains information about the stiffness and the damping of the whole mechanical system, consisting of the flexural beam clamped at one end and the sensor tip at the other end in force interaction with the sample surface. Variation of the cantilever–sample distance or of the excitation amplitude changes the range of the tip–sample distance covered during the vibration cycles and consequently the section of the non-linear force interaction curve that is probed. Starting from high static loads and small excitation amplitudes, the contact resonance frequencies shift to lower values when the excitation amplitude is increased or when the static cantilever force is decreased. A further increase of the excitation amplitude leads to asymmetric resonance peaks, showing hysteresis when the direction of the frequency scan is changed. We present experimental spectra in the linear and non-linear regime and compare them to theoretical results. Copyright © 1999 John Wiley & Sons, Ltd.

XPS characterisation of carbon‐coated alumina support

Abstract: Hybrid carbon-alumina supports, synthesised by pyrolysis of grafted 4,4'-methylenebis-(phenylisocyanate) moiety on the alumina surface, were characterised by X-ray photoelectron spectroscopy. The recorded Al 2p and C 1s envelopes showed asymmetry that decreased with an increase in carbon loading. In all experimental Al 2p envelopes, the high-energy individual components at 75.3-75.9 eV were present along with the low-energy component at 74.0 eV typical for Al 2 O 3 . In the case of the C Is envelope, the component around 284.3-284.4 eV and three high-energy individual components at 285.9-286.0, 288.0-288.3 and 290.1-290.6 eV were observed. The presence of the high-energy Al 2p components can be explained considering the occurrence of a steady-state charging of the different parts of insulating alumina supports. The component around 284.3-284.4 eV in C Is envelopes can be attributed to carbon, which constitutes the coating and, hence, ensures surface conductivity. The component around 285.9-286.0 eV is connected with carbon in carbonaceous surface species, which do not form the conducting layer on the alumina support. Carbonaceous surface species associated with C-O, C=O and O=C-O groups in carbon coating can be also identified due to the presence of corresponding components in XPS spectra at 285.9-286.0, 288.0-288.3 and 290.1-290.6 eV.

Quantitative manipulation of DNA and viruses with the nanomanipulator scanning force microscope

Abstract: The nanoManipulator, a modified scanning force microscope with a direct manipulation interface that allows natural and controlled manipulation of nanometer-sized samples, was used to investigate DNA and adenoviruses. During a manipulation, the scanning tip is coupled to a hand-held stylus via a force-feedback loop. Accordingly, the tip follows the movement of the user's hand; moreover, the user is able to feel the topography of the sample. For imaging fragile biological samples, a magnetically driven intermittent contact (MDIC) mode in fluid was implemented and added to the microscope. In this mode, a cantilever with a magnetic particle glued onto its back is driven by an external, oscillating magnetic field. In contrast to regular intermittent contact (tapping) mode imaging in liquids, where the whole liquid cell is excited (resulting in many resonance peaks in the spectrum), in this mode the cantilever is driven directly and the spectrum usually displays a single, easily identifiable resonance peak. Using this set-up, adenoviruses were manipulated in liquids and 1100 bp DNA molecules were manipulated in ambient conditions while recording lateral force data. In these experiments, the rupture force of DNA was measured directly for the first time. In an effort to measure the interaction force between a virus and a substrate, adenoviruses were pushed over a silicon substrate. A force of ∽25 nN was measured to move the virus on this surface. Copyright © 1999 John Wiley & Sons, Ltd.

Glow discharge optical emission spectrometry (GDOES) depth profiling analysis of anodic alumina films—a depth resolution study

Abstract: Anodic alumina films with precisely known distributions of incorporated species have been used as standards for glow discharge optical emission spectrometry (GDOES) depth profiling analysis to quantify depth resolution. It is evident that the depth resolution of GDOES is excellent and is comparable with, or better than, secondary ion mass spectrometry depth profiling of similar films. Further, the sensitivity for detection of elements is also high, given the amounts of impurity species detected successfully. Thus, GDOES, with its further ability of routine and rapid analysis of films (organic, inorganic or metallic) of thicknesses up to several hundreds of microns, has significant potential in studies of the corrosion and filming behaviour of materials. © 1999 John Wiley & Sons, Ltd.

Elastic mapping of heterogeneous nanostructures with ultrasonic force microscopy (UFM)

Abstract: Ultrasonic force microscopy (UFM) is an atomic force microscopy (AFM)-related technique originally introduced to study the surface elastic properties of stiff materials. We report elastic images of heterogeneous nanostructures with a lateral resolution of the order of a few nanometres. One of the main intentions of this paper is not only to show the capability of UFM to allow one to image surface elastic properties of stiff materials but also to show that UFM can be applied to relatively soft materials with reproducible and interpretable results. The samples presented were chosen over a wide range of stiffness values (with Young's modulus E = 0.1-400 GPa): very stiff silicon carbide fibres embedded in a mullite matrix, less stiff carbon fibres embedded in an epoxy matrix and relatively compliant rubber inclusions in a polymethylmethacrylate matrix. A discussion of the conditions required to obtain unambiguous data is also provided. Results obtained using the more traditional force modulation mode are also presented and compared with the UFM images of the same samples.

Combined ToF-SIMS/XPS study of plasma modification and metallization of polyimide

Abstract: The combination of time-of-flight secondary mass spectrometry (ToF-SIMS) and monochromatized x-ray photoelectron spectroscopy (XPS) has proved to be a valuable tool for the analysis of chemically modified polymer surfaces. By applying these techniques in situ, together with a plasma modification chamber and a Knudsen cell, we have investigated the plasma modification of polyimide in an oxygen plasma and the first steps of copper deposition on the untreated and the plasma-modified polyimide substrate. Characterization of the initial stages of copper deposition by XPS and comparison with the untreated and the plasma-modified substrate indicate that, in the case of the untreated substrate, copper binds to the carbonyl group of the repeat unit, whereas after plasma modification a great number of C–O and C–N functionalities are available as binding sites for the metal overlayer. The molecular ion species identified by ToF-SIMS allow the identification of specific plasma-induced fragmentation mechanisms and confirm the interface reaction mechanisms deduced from the XPS results. The nature and amount of copper–substrate bonds are directly correlated to the adhesion strength of the copper/polyimide interface as measured by the force applied in a standard industrial peel test. Copyright © 1999 John Wiley & Sons, Ltd.

Nanomechanical characterizations of metals and thin films

Abstract: The local mechanical properties of different phases and grains in structural metallic alloys, composites and thin films determine their bulk properties and deformation behaviour. A nanoindenting atomic force microscope allows quantitative measurements of the local modulus of elasticity and the nanohardness with lateral resolutions of nearly 50 nm. Investigations on different nickel-base superalloys (Waspaloy, CMSX-6), NiAl, γ-TiAl and steels were performed, where their local mechanical properties could be determined separately on phases with lateral sizes down to 50 nm. With this measurement, the hardness of small γ'-precipitates and of the matrix in the superalloys was determined. Other examples are given, where the local mechanical properties around a crack tip and across a grain boundary were determined. The load-displacement curves obtained for these specimens often show pop-ins similar to yield point phenomena. The estimated maximum shear stress under the indenter at this load level is comparable to the theoretical shear strength of the materials. The investigations show that the appearance of pop-ins depends strongly on the surface preparation conditions and the existence of oxide layers. Investigations of thin gold films on glassy substrates of thickness 20-400 nm show an increasing hardness at lower indentation depths and higher hardness values of the thin films in comparison to bulk specimens.

Study of low energy high dose nitrogen implantation in aluminium, iron, copper and gold

Abstract: To advance the understanding of fundamental physical and chemical processes occurring in ion bombardment of metals, ion beam nitridation of aluminium, iron, copper and gold is studied in the energy range 2-5 keV, at current densities of 1 and 5 μA cm -2 , for each ion energy. The concentration profiles of nitrogen-ion-implanted metals were measured by x-ray photoelectron spectroscopy (XPS). The chemical composition and chemical structure of the implanted metals were also investigated.

Surface and bulk composition of lithium manganese oxides

Abstract: Lithium manganese oxides, and in particular the spinel-structured LiMn 2 O 4 , have been investigated as potential active cathode materials for lithium ion batteries. Recently both orthorhombic and monoclinic LiMnO 2 have attracted considerable attention. It has been reported that Al doping allows the preparation of monoclinic LiAl x Mn 1-x O 2 under suitable reaction conditions, and furthermore improves the capacity retention of both o-LiAl x Mn 1-x O 2 and m-LiAl x Mn 1-x O 2 . The aim of this study was to elucidate the structural effects of Al doping with particular attention to the surface properties of the material. X-ray diffraction data reveal that Al induces monoclinic stacking faults in orthorhombic LiAl x Mn 1-x O 2 and at Al contents of ∼5% the preferred cation ordering becomes that of monoclinic LiAl x Mn 1-x O 2 . X-ray photoelectron spectroscopy measurements show that the Al is homogeneously incorporated throughout the grains up to its solubility limit, and no surface enrichment of Al is observed. The XPS data indicate that Mn in the near-surface region of the material is predominantly present in its +3 oxidation state, even when annealed to temperatures of up to 250°C.

Dynamic friction force measurement with the scanning force microscope

Abstract: Scanning Force Microscopes excert lateral forces on the sample during measurement. The recording of the magnitude of these forces as a function of position gives friction maps. The possible scanning speeds of SFM, however, are far below the velocities of practical devices. The dynamic friction force measurement provides a solution to this problem. The sample is modulated laterally at frequencies up to several kilohertz and with amplitudes in the nanometer range. It is shown that the interaction with the sample is not only determined by friction, but also by the viscoelastic response of the sample. The combination of dynamic friction measurement with the intermittent contact measurement mode, the PulsedForceMode, gives full access to the relevant sample parameters: topography, lateral ‘friction’ forces, adhesion, sample stiffness and relaxations times.