P. Schwaller

Nanostructural and mechanical properties of nanocomposite nc-TiC/a-C:H films deposited by reactive unbalanced magnetron sputtering

Thin films of nc-TiC/a-C:H nanocomposite have been deposited by reactive magnetron sputtering at substrate bias values of −240 and −91 V. The grain size and grain separation, which together define the nanostructure, are correlated to the amount of the amorphous phase. From the size of the TiC grains measured by x-ray diffraction and the amorphous hydrogenated carbon (a-C:H) phase content determined by x-ray photoelectron spectroscopy, the mean grain separation is estimated using a simple model for the nanostructure. Films deposited at −240 V show a hardness enhancement for a-C:H phase contents in the range 10% to 30% with TiC grain sizes around 5 nm. The mean grain separation for such films was estimated to be 0.3 nm. Films with higher a-C:H phase contents still have 5 nm small grains, but their mean grain separation is larger than 0.5 nm; their hardness is thus determined by the properties of the amorphous matrix. A less pronounced hardness enhancement is observed for films deposited at −91 V. They have ...

A new technique to determine the elastoplastic properties of thin metallic films using sharp indenters

In recent years, nanoindentation has established itself as one of the most convenient techniques to assess the mechanical properties of thin films by measuring the force–penetration (F–h) curve during loading and unloading. However, the mechanical understanding of the indentation process itself, which involves several non-linearities (inelastic material behaviour, large and non-homogeneous deformations), is very intricate and finite-element analysis is thus combined with experiments in order to develop methods allowing the determination of the flow stress. In this spirit, Dao et al. (Acta Materialia, 49, 2001, 3899) and Bucaille et al. (Acta Materialia, 51, 2003, 1663) conducted finite-element analysis using different sharp indenters and proposed functions relating F–h curves to elastoplastic parameters of metals. In the present work, these methods are applied on galvanically grown nickel films. Samples for both nanoindentation and microtensile tests were grown in the same batch and, therefore, allow their properties to be studied using two different techniques on identical materials. Nanoindentation tests were conducted with the Berkovich and cube corner pyramids at constant strain rate. Youngs modulus and stresses corresponding to representative strains, imposed by these indenters, of 3.3 and 12.6% were determined. These values are in good agreement with the stress–strain values measured in tension. We also showed the importance of taking into account the indentation size effect, the friction between the indenter and the material and the strain rate dependence of metal deformation behaviour. The application to thin metallic films is discussed.

A photoelectron spectrometer for k-space mapping above the Fermi level

The setup of an electron spectrometer for angle-resolved photoemission is described. A sample goniometer offers the opportunity for angle scanned photoemission over 2π solid angle above the surface. A monochromatized high flux He discharge photon source is exploited to measure thermally populated electronic states above the Fermi level EF. At energies greater than EF+5kBT the signal from a constant density of states declines below the photoelectron background caused by photons with higher energies than He Iα (21.2 eV). For He IIα (40.8 eV) the residual photoelectron background is lower and photoemission up to 6kBT above EF can be performed. Data showing two cuts through the Fermi surface of silver are presented. Furthermore the dispersion of the Shockley surface state on Ag (111) above the Fermi energy is quantified.

Wear protective coatings consisting of TiC–SiC–a-C:H deposited by magnetron sputtering

Hard coatings of the composition Ti Si C which consist of TiC, TiSi , a-SiC and a-C:H, have been deposited with the aim of xy z x depositing self-lubricating Ti SiC . The films were prepared by reactive unbalanced magnetron sputtering from elemental titanium 32 and silicon targets in the presence of argon and acetylene. The coatings are composed of nanocrystalline TiC and, depending on the composition, of titanium silicides, amorphous hydrogenated carbon and amorphous silicon carbide. Nanohardness values of up to 30 GPa could be obtained for coatings with friction values below 0.25 against steel in an unlubricated pin-on-disk setup. Low friction coefficients against steel were measured for higher concentrations of amorphous carbon at hardness values of approximately 15 GPa. In contrast to coatings composed of titanium, silicon and nitrogen, the hardness maximum is observed at TiC grains sizes of 25 nanometers. 2002 Elsevier Science B.V. All rights reserved.

Angle-scanned photoelectron diffraction

A brief survey is given on the current state-of-the-art of this surface structural technique based on photoelectron spectroscopy, with particular emphasis on the progress that has been made recently by routinely measuring full-hemispherical intensity distributions. We limit the discussion to the photoelectron forward focusing regime, which is attained at electron kinetic energies of a few hundred eV. Surface bond directions are directly revealed as pronounced maxima in the angular distributions from subsurface atoms, while characteristic interference features are observed for surface species. For both cases the dependence on the atomic type is weak enough so that these features provide a fingerprint of the local bonding geometry. For surface and near-surface species, this may then serve as a starting point for a structure refinement using single-scattering cluster calculations. Selected examples are given for illustrating these procedures.

In situ SEM indentation experiments: Instruments, methodology, and applications

The purpose of this article is to present the design and capabilities of two in situ scanning electron microscope (SEM) indentation instruments covering a large load range from μN to N. The capabilities and advantages of in situ SEM indentation are illustrated by two applications: indentation of a thin film and a nanowire. All the experiments were performed on electrodeposited cobalt, whose outstanding magnetic properties make it a candidate material for MEMS and NEMS devices. Microsc. Res. Tech., 2009.

Comparison of nanoindentation results obtained with Berkovich and cube-corner indenters

There is increasing interest in using sharp cube-corner indenters in nanoindentation experiments to study plastic properties. In combination with finite element methods, it is, for example, possible to extract stress–strain curves from load–displacement curves measured with differently shaped pyramidal indenters. Another example is the fracture toughness of coatings, which can be studied using cracks produced during indentation with cube-corner tips. We have carried out indentation experiments with Berkovich and cube-corner indenters on eight different materials with different mechanical properties. To gain information about the formation of pile-up and cracks, indentation experiments with cube-corner indenter were performed inside a scanning electron microscope (SEM) using a custom-built SEM-microindenter. The results show that reliable hardness and modulus values can be measured using cube-corner indenters. However, the fit range of the unloading curve has a much bigger influence on the results for the cube-corner than for the Berkovich tip. The unloading curves of a cube-corner measurement should, therefore, be carefully inspected to determine the region of smooth curvature, and the unloading fit range chosen warily. Comparison of the modulus results shows that there is no significant difference between cube-corner and Berkovich measurements. Also for hardness, no fundamental difference is observed for most of the investigated materials. Exceptions are materials, such as silicon nitride, cemented carbide or glassy carbon, where a clear difference to the hardness reference value has been observed although the modulus difference is not pronounced.

Experimental determination of the transmission factor for the Omicron EA125 electron analyzer

In this article a study of the transmission factor of the Omicron EA125 analyzer equipped with the universal lens is presented. The procedure is based on a model by Cross and Castle [J. Electron Spectrosc. Relat. Phenom. 22, 53 (1981)] and is applicable to every spectrometer which can be operated in the constant analyzer energy (CAE) and in the constant retarding ratio measuring mode. The advantage of the method is its independence on the sample and on the inelastic mean free path of the electrons. We find that the transmission factor for the CAE mode is proportional to Ekin−1 for most measuring setups. This dependence is predicted by theory for an ideal analyzer. Deviations from this behavior are observed if the retarding ratio for a given kinetic energy is too small. The limit value of the retarding ratio for ideal behavior, i.e., an Ekin−1 transmission factor, depends on the analyzer entrance slit aperture which has been selected.

Surface and friction characterization by thermoelectric measurements during ultrasonic friction processes

Even though friction is one of the oldest problems in physics many aspects of friction processes are not clear today. We present an experimental setup, which permits the study of tribological systems by measuring the dissipated heat at the interface of two surfaces during a friction process with a time resolution of 1 ms. The apparatus is based on a standard ultrasonic wire-bond machine used in semiconductor industries to connect the internal semiconductor die to the external leads, but the standard bond wire is replaced by a thermocouple. To demonstrate the ability of the apparatus it will be shown that bond substrates used in semiconductor industries can be unequivocally characterized.

Angle-resolved photoemission experiments on Bi2Sr2CaCu2O8+?(001): Effects of the incommensurate lattice modulation

Core-level X-ray photoelectron-diffraction patterns have been measured from cleaved Bi 2 Sr 2 CaCu 2 O 8+δ (001) surfaces for all elements present in this compound. The incommensurate modulation along b ([010]) leads to a strong inequivalence of a- and b-directions for Bi, Sr and Cu photoelectrons, while Ca and O emission show less effect. Ultraviolet-photoemission experiments recording the emission intensity at the Fermi energy over a large solid angle are also presented, providing a direct mapping of the Fermi surface. A c(2×2) superstructure is observed on the Fermi surface suggesting antiferromagnetic correlations within the Cu-O planes. The effects of the lattice modulation are clearly observable at the Fermi energy, and they are enhanced for binding energies higher than a few tens of meV