Chromium-doped diamond-like carbon films deposited by dual-pulsed laser deposition

Diamond-like carbon (DLC) and Cr-doped diamond-like carbon layers were studied. DLC and Cr-DLC were deposited on silicon and titanium substrates (Ti-6Al-4V) by dual-pulsed laser ablation using two KrF excimer lasers and two targets (graphite and chromium). The composition was analyzed using wavelength-dependent X-ray spectroscopy. The Cr content increased from 2.2 to 17.9 at%. The topology and surface properties as roughness of layers were studied using scanning electron microscopy and atomic force microscopy. With the chromium concentration increased the roughness and the number of droplets. Carbon and chromium bonds were determined by Raman spectroscopy. With an increase in chromium content the I _D/I _G ratio increased. Mechanical properties of DLC films with various chromium content were evaluated. Hardness (reduced Young’s modulus) was determined by nanoindentation and reached of 51 GPa (309 GPa). Films adhesion was studied using scratch test and with concentration of chromium increased up to 20 N.     

Defects in silicon: the role of vibrational entropy

Vibrational free energies are calculated from first-principles in the same Si periodic supercells routinely used to perform defect calculations. The specific heat, vibrational entropy, and zero-point energy obtained in defect-free cells are very close to the measured values. The importance of the vibrational part of the free energy is studied in the case of two defect problems: the relative energies of the H₂ and H₂^∗ dimers and the binding energy of a copper pair. In both cases, the vibrational entropy term causes total energy differences to change by about 0.2 eV between 0 and 800 K. We also comment on the rotational entropy in the case of H₂ and the configurational entropy in the case of the Cu pair. These examples illustrate the importance of extending first-principles calculations of defects in semiconductors to include free energy contributions.     

Protecting convex sets

A point-setS is protecting a collection F =T ₁,T ₂,..., _n ofn mutually disjoint compact sets if each one of the setsT _i is visible from at least one point inS; thus, for every setT _i ∈F there are points xS andy T _i such that the line segment joining x to y does not intersect any element inF other thanT _i . In this paper we prove that [2(n-2)/3] points are always sufficient and occasionally necessary to protect any family F ofn mutually disjoint compact convex sets. For an isothetic family F, consisting ofn mutually disjoint rectangles, [n/2] points are always sufficient and [n/2] points are sometimes necessary to protect it. IfF is a family of triangles, [4n/7] points are always sufficient. To protect families ofn homothetic triangles, [n/2] points are always sufficient and [n/2] points are sometimes necessary.     

X-Ray Emission from Thin Films on a Substrate – Calculation and Experiments

 Monte Carlo simulation of electron transport in solids is widely used in electron microscopy, spectroscopy and microanalysis. The reliability of physical models incorporated in a Monte Carlo code is usually checked by comparing with experimental results. Elastic or inelastic collisions are usually considered as the basic interactions of electrons with atoms. In our Monte Carlo code the single scattering model is employed for simulation of X-ray emission from thin films of Au on the Si substrate. The electron beam energy was in the range 10–30 keV, the take-off-angle was 40°. The simulated values of X-ray production were calculated in our Monte Carlo code using several models of ionisation cross-sections. For the emitted intensities the depths of inelastic collision and X-ray absorption were taken into account, then the k-ratios were calculated. These data were compared with experimental values of k-ratios calculated from X-ray intensities of Au M and Au L characteristic lines. We followed mainly the dependence of the k-ratios of the film element on film thickness. The film thickness was in the range 0.05–1 μm. Reasonably good agreement was found for dependences of X-ray intensity on film thickness in the whole energy range and for both lines, especially for Powell’s model of the ionisation cross-section.     

Domain wall motion in magnetically soft metallic glasses

The magnetic domains on the surface of amorphous alloys of the composition Fe₄₀Ni₄₀B₂₀ and Fe₅₀Ni₃₀B₂₀ were observed by means of the scanning electron microscope. The details of the experimental arrangement are described that enhance the s.c. type II magnetic contrast and enable us to apply a static magnetic field in the plane of the sample. The displacement of the domain walls under the influence of the applied field were measured and are discussed.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.One of the authors (K. Z.) is grateful to Dr. S. Krupika who initiated him in the field of magnetization processes and never lost patience with him in numerous discussions in the course of several decades. We also benefited from the discussions with Dr. I. Tomá after the presentation of our preliminary results at the Second Czechoslovak-Soviet Symposium on the Physics of Magnetic Domains in May 1986.     

Nitrodestannylation. A new synthesis of conjugated nitro cyclo olefins

A new process for the conversion of cyclic ketones to 1-nitro olefins, as outlined below, is described.     

Single-Ion Magnetic Behaviour in an Iron(III) Porphyrin Complex: A Dichotomy Between High Spin and 5/2–3/2 Spin Admixture

A mononuclear iron(III) porphyrin compound exhibiting unexpectedly slow magnetic relaxation, which is a characteristic of single-ion magnet behaviour, is reported. This behaviour originates from the close proximity (≈550 cm⁻¹) of the intermediate-spin S=3/2 excited states to the high-spin S=5/2 ground state. More quantitatively, although the ground state is mostly S=5/2, a spin-admixture model evidences a sizable contribution (≈15 %) of S=3/2 to the ground state, which as a consequence experiences large and positive axial anisotropy (D=+19.2 cm⁻¹). Frequency-domain EPR spectroscopy allowed the m_S= |±1/2⟩→|±3/2⟩ transitions to be directly accessed, and thus the very large zero-field splitting in this 3d⁵ system to be unambiguously measured. Other experimental results including magnetisation, Mössbauer, and field-domain EPR studies are consistent with this model, which is also supported by theoretical calculations.     

The random integral representation conjecture: a quarter of a century later

In [Z.J. Jurek, Relations between the s-selfdecomposable and selfdecomposable measures, Ann. Probab., 13(2):592–608, 1985] and [Z.J. Jurek, Random integral representation for classes of limit distributions similar to Lévy class L ₀, Probab. Theory Relat. Fields, 78:473–490, 1988] the random integral representation conjecture was stated. It claims that (some) limit laws can be written as the probability distributions of random integrals of the form ò_{( a,b ]}h(t)\textdY_v( r(t) ) \int {_{\left( {a,b} \right]}h(t){\text{d}}{Y_v}\left( {r(t)} \right)} for some deterministic functions h, r, and a Lévy process Y_v(t),  t \geqslant 0 {Y_v}(t),\;t \geqslant 0 . Here we review situations where such a claim holds. Each theorem is followed by a remark that gives references to other related papers, results, and historical comments. Moreover, some open questions are stated.