Table of contents

The symposium, `Low Friction Coatings on Glass and Ceramics', was held in Baltimore, MD, in April 2005. This was part of the American Ceramic Society's annual meeting. The symposium was co-organized by Jacqueline A Johnson and Osman L Eryilmaz of Argonne National Laboratory (ANL). They would like to thank all the speakers who participated so enthusiastically in the symposium and the sponsors who kindly contributed to its success: NSF (National Science Foundation) and NIH (National Institutes of Health).

Novel barium aluminate (BaAl₂O₄) and barium alumino-titanate (BaAl₂TiO₆) glasses have been produced by aerodynamic levitation and laser heating. BaAl₂O₄ forms a clear and colourless glass under containerless and rapid quenching conditions. Under similar rapid quenching conditions BaAl₂TiO₆ forms an opaque and black glass, while under slower and controlled quenching conditions it is possible to form a clear and colourless glass. The formation of the opaque or clear glass is reversible and purely dependent on the quench rate used. By slowing the quench rate further, it is possible to produce a milky glass suggestive of liquid–liquid phase separation in the liquid before glassification. High-energy x-ray diffraction experiments confirm the glassy state of these materials and show coordination structures and bond distances similar to their crystalline analogues.

In multi-component lipid membranes, phase separation can lead to the formation of domains. The morphology of fluid-like domains has been rationalized in terms of membrane elasticity and line tension. We show that the morphology of solid-like domains is governed by different physics, and instead reflects the molecular ordering of the lipids. An understanding of this link opens new possibilities for the rational design of patterned membranes.

It is well known that lamellar structure, hexagonal structure of cylinder domains, gyroid and body-centred cubic structure of spherical domains all exist as equilibrium structures in AB-type diblock copolymers. We shall show in the present letter that, in addition to the above four phases, there is another equilibrium phase, the so-called Fddd structure which is an interconnected but uniaxial structure. We confirm this conclusion by two different methods. One is the mode-expansion including a substantial number of modes. The other is direct simulations of the time-evolution equation in three dimensions.

I review single-molecule experiments (SMEs) in biological physics. Recent technological developments have provided the tools to design and build scientific instruments of high enough sensitivity and precision to manipulate and visualize individual molecules and measure microscopic forces. Using SMEs it is possible to manipulate molecules one at a time and measure distributions describing molecular properties, characterize the kinetics of biomolecular reactions and detect molecular intermediates. SMEs provide additional information about thermodynamics and kinetics of biomolecular processes. This complements information obtained in traditional bulk assays. In SMEs it is also possible to measure small energies and detect large Brownian deviations in biomolecular reactions, thereby offering new methods and systems to scrutinize the basic foundations of statistical mechanics. This review is written at a very introductory level, emphasizing the importance of SMEs to scientists interested in knowing the common playground of ideas and the interdisciplinary topics accessible by these techniques.

The review discusses SMEs from an experimental perspective, first exposing the most common experimental methodologies and later presenting various molecular systems where such techniques have been applied. I briefly discuss experimental techniques such as atomic-force microscopy (AFM), laser optical tweezers (LOTs), magnetic tweezers (MTs), biomembrane force probes (BFPs) and single-molecule fluorescence (SMF). I then present several applications of SME to the study of nucleic acids (DNA, RNA and DNA condensation) and proteins (protein–protein interactions, protein folding and molecular motors). Finally, I discuss applications of SMEs to the study of the nonequilibrium thermodynamics of small systems and the experimental verification of fluctuation theorems. I conclude with a discussion of open questions and future perspectives.

In order to determine the influence of the thermal history (fictive temperature) and OH content on the elastic properties of silica glass, we have investigated high resolution in situ Brillouin experiments on SiO₂ glass from room temperature to the supercooled liquid at 1773 K across the glass transition. The well known anomalous increase of elastic modulus in the glassy state and in the supercooled liquid regime is observed. No change in the slope of the elastic moduli of silica appears as a characteristic of the glass transition, in contrast to what happens in various other glasses. We show that thermal history has a weak effect on elastic moduli in the glass transition regime for silica glass. The effect of the water content in silica glass is greater than the fictive temperature effect and gives larger changes in the amplitude of the elastic modulus for the same thermal dependence. A singular decrease above 1223 K is also observed in the shear moduli for hydrated samples. Different models explaining the temperature dependence of the elastic properties in relationship with frozen-in density fluctuations or with the structure are discussed.

A correlation between thermal, optical and morphological properties of self-sustained films formed from blends of poly(3-hexylthiophene) (P3HT) and thermoplastic polyurethane (TPU), with 1, 10 and 20 wt% of P3HT in TPU, is established. Images of scanning electron microscopy (SEM) show the formation of domains of P3HT into the TPU matrix, characterizing the blend material as heterogeneous. The heat capacity (C_p) dependence on P3HT contents was investigated in a large temperature interval. In the region of the TPU glass transition, the difference between the experimental and predicted ΔC_p values is more pronounced for the 1 wt% case, which strongly suggests that in this case there is a higher influence of the P3HT chains on the TPU matrix. The SEM images for the 1 wt% blended film present the formation of the smallest P3HT domains in the TPU matrix. The relatively high reduction of the PL intensity of the pure electronic transition peak in the 1 wt% blended film, in comparison to the other blended films and also to a pure P3HT film, favours the assumption that the smallest P3HT domains are at the origin of a more structural disordered character. This fact is in agreement with the results obtained by Raman spectroscopy and also by photoluminescence resolved by polarization in stretched self-sustained films, showing an ample correlation between morphological, thermal and optical properties of these blended materials. In addition, the thermoplastic properties of the polyurethane configure very good conditions for tensile drawing of P3HT and other conjugated polymer molecules.

Actual polymer chains cannot cross themselves and each other. However, the popular Rouse model for unentangled polymers considers the chains as being like 'phantoms'. It is shown that excluded volume effects on single-chain statics may be introduced by analytic corrections to the Rouse results. The final expressions do not depend on free parameters. They exhibit excellent agreement with the molecular-dynamics simulations of polymer melts with chain lengths in the range 3≤M≤30. Preliminary results for entangled polymer melts are presented.

Molecular dynamics simulations have been carried out of the radial distribution function of the hard sphere fluid for a range of densities in the equilibrium fluid and just into the metastable region. The first derivative of the hard-sphere radial distribution function at contact was computed and its density dependence fitted to a simple analytic form. Comparisons were made with semi-empirical formulae from the literature, and of these the formula proposed by Tao et al (1992 Phys. Rev. A 46 8007) was found to be in best agreement with the simulation data, although it slightly underestimates the derivative at the higher packing fractions in excess of about 0.45. Close to contact, within a few per cent of the particle diameter, the radial distribution function can be represented well by a second order polynomial. An exponential function, which has some useful analytic features, can also be applied in this region.

Using molecular dynamics simulation with the embedded atom method, the structural properties of liquid NiAl in a pressure range of 0–20 GPa are investigated with a quenching rate of 2 K ps⁻¹. Not only is vitrification of liquid at low temperature detected, but also crystallization by change of average atomic volume as a function of temperature. Convincing evidence is presented that the applied pressure strongly affects the vitrification and crystallization of metallic liquid. The simulated glass transition temperature T_g increases with pressure by 38.4 K GPa⁻¹ within the range 0–10 GPa, while external pressure induces crystallization of metallic liquid within the pressure range 10–20 GPa, and the crystallization temperature T_c increases with a slope of 6.4 K GPa⁻¹. Therefore, the critical pressure for the formation of metallic glass at this cooling rate is estimated to be 10 GPa. The competition between the densification and the suppression of atomic diffusion in the liquid by pressure is able to explain the vitrification and crystallization behaviours of the liquid. Our present work provides a possible guidance for an experiment to study the pressure effect on the glass transition and crystallization process in metallic liquid.

We present a modified version of a thermodynamically self-consistent Ornstein–Zernike approximation (SCOZA) for a fluid of spherical particles with a pair potential given by a hard core repulsion and a Yukawa tail . We take advantage of the known analytical properties of the solution of the Ornstein–Zernike equation for the case in which the direct correlation function outside the repulsive core is given by the multi-screened Coulomb plus power series (multi-SCPPS) tails and the radial distribution function g(r) satisfies the exact core condition g(r) = 0 for r<1. The SCOZA is known to provide very good overall thermodynamics and a remarkably accurate critical point and coexistence curve. However, the SCOZA presented so far for continuum fluids has the deficiency that the solution behaves singularly at a density ρ where the screening length z₁(ρ) of the hard sphere fluid nearly coincides with the Yukawa-tail screening length z₂ (>3.8). This is by no means a rare case in the studies of real fluids and colloidal suspensions. We show that the deficiency is resolved in the modified version of the SCOZA with multi-SCPPS tails. As a demonstration, we present some numerical results for z₂ = 8.0.

Atomic structures of amorphous Al₈₉La₆Ni₅, prepared by single-roller melt spinning, and pre-annealed at 493 and 588 K for 1 h, were characterized by differential scanning calorimetry, x-ray diffraction with a large wavevector transfer value, La L₃-edge and Ni K-edge x-ray absorption fine structure and the reverse Monte Carlo technique. In the as-prepared amorphous alloy, our study reveals that the Ni–Al distance is 2.38 ± 0.02 Å coupled with a coordination number as low as 6.2. The Al–Al distance was found to be ∼4.5% shorter than the nominal atomic diameter of aluminium and the coordination number to be ∼39% less than expected from the dense random packing model. Crystallization of the Al₈₉La₆Ni₅ glassy alloy at high temperatures can be described as follows: [amorphous alloy] [fcc-Al] + [bcc-(AlLa)] + residual amorphous [fcc-Al] + [o-Al₃Ni ] + [o-La₃Al₁₁ ].

Time-resolved two-dimensional infrared (2D IR) spectroscopy has been applied to analyse an electro-optic switching ferroelectric liquid crystal (FLC) mixture. The 2D IR correlation technique clearly shows that the Goldstone mode in the SmC* phase is suppressed by an applied electric field. The field-induced reorientation process initiates from intramolecular motions in about 10 µs. The intramolecular motions then propagate from the molecular segments attached to the same molecule to those fragments on other surrounding molecules. During the field-induced switching, the IR dipoles undergo a collective reorientation but with hindered rotation about the molecular long axis.

Small air-bubble deformations, caused by electro-acoustic signals generated in electrolytic solutions have been detected by angle-modulation of a refracted He–Ne laser beam. The observed electromechanical resonance at low frequency, below 100 Hz, has proved to be directly related to the oscillations of characteristic ion-doped water structures when driven by an external electric field. The presence of structure-breaking or structure-making ions modifies the water structure, which varies the mechanical losses of the oscillating system and can be registered as changes in the width of the observed resonance curves.

The single-crystal non-stoichiometric magnetic shape memory alloy Ni_1−x−yMn_xGa_y with x = 0.2817, y = 0.2136 is studied using magnetic resonance spectroscopy: ferromagnetic resonance (FMR) and conduction electron spin resonance (CESR). The temperature dependence of the integral intensity, the resonance field and the line-width are measured across the wide temperature interval from 4.2 to 570 K. Three phase transformations are found in this alloy: with a Curie temperature of 360 K, austenite-to-martensite (direct with T_ms = 312 K and reverse with T_as = 313 K), and a transformation at T = 45 K, suggestive of the spin-glass state. The angular dependence of the FMR signals is measured in the martensitic and austenitic states before and after the martensite-to-austenite transition. The experimental data are used for determination of the magnetization M_m and anisotropy parameters K₁ and K₂ in the martensitic state. The obtained coefficient K₂ is determined to be not small and, moreover, it is comparable with K₁. The temperature dependence of the resonance signals is also investigated at temperatures significantly higher than T_C, where FMR was transformed to CESR. In the paramagnetic austenitic state (above T_C) the alloy reveals an extremely intensive signal of CESR, which suggests a high concentration of conduction electrons and correlates with the large value of the magnetic-field-induced strain observed in the alloys of such composition. The temperature dependence of the skin layer depth is found from the sharp decay of the CESR signal with temperature, which is related to the disappearing large magnetic resistance after transformation to the paramagnetic state.

The magnetocaloric effect (MCE) in fine grained perovskite manganites of the type La_1−xK_xMnO₃ (0<x<0.15) prepared by a pyrophoric method has been investigated. Potassium addition in lanthanum manganite enhances the Curie temperature (T_C) of the system from 260.4 K (x = 0.05) to 309.7 K (x = 0.15). A large magnetic entropy change associated with the ferromagnetic–paramagnetic transition has been observed. The maximum entropy change |ΔS_M^Max| in an applied field of 1 T shows an enhancement by ∼10% with increase in K content up to x = 0.15. La_0.85K_0.15MnO₃ exhibits the largest |ΔS_M^Max| value of 3.00 J kg⁻¹ K⁻¹ at 310 K amongst the compounds investigated. Moreover, the maximum magnetic entropy change exhibits a linear dependence with applied magnetic field. The estimated adiabatic temperature change at T_C and at 1 T field also increases with K doping, being a maximum of 2.1 K for the La_0.85K_0.15MnO₃ compound. The relative cooling power (RCP) of La_1−xK_xMnO₃ compounds is estimated to be about one-third of that of the prototype magnetic refrigerant material (pure Gd). However, La_1−xK_xMnO₃ compounds possess an MCE around room temperature, which is comparable to that of Gd. Further, tailoring of their T_C, higher chemical stability, lower eddy current heating and lower cost of synthesis are some of the attractive features of K doped lanthanum manganites that are advantageous for a magnetic refrigerant. The temperature dependence of the magnetic entropy change (ΔS_M) measured under various magnetic fields is explained fairly well using the Landau theory of phase transitions. Contributions of magnetoelastic and electron interaction are found to have a strong influence in the magnetocaloric effect of manganites.

Single crystals of TiO₂ rutile doped with Cr, Mn, Fe, Co, Ni, and Cu were grown with the flux method in a Na₂B₄O₇ melt. The samples, checked in their structural and phase homogeneity by x-ray diffraction and micro-Raman spectroscopy, were single-phase needle-shaped crystals several millimetres long. Paramagnetic and ferromagnetic behaviours at room temperature were observed and they are discussed also in connection with the magnetic properties of undoped TiO₂ crystals.

Time differential perturbed angular correlation measurements using the ¹⁸¹Ta probe in La_0.7Sr_0.3Mn_0.995Hf_0.005O₃ reveal the presence of two distinct hyperfine components, identified with probe atoms occupying Mn sites which are rich and deficient in hole concentration. The Mn⁴⁺ rich zones exhibit ferromagnetic ordering at all temperatures below 360 K, the bulk Curie temperature. In the case of Mn⁴⁺ deficient zones, the paramagnetic order is seen to evolve into a canted antiferromagnetic ordering below 360 K, that becomes ferromagnetic below 250 K. Concomitantly, there is a change in the fractions below 250 K. The implications of these results are discussed in terms of electronic phase separation.

The piezoelectric properties of a Pb[(Mg_1/3Nb_2/3)_0.68]Ti_0.32O₃ binary system single crystal poled along the [001] direction in the rhombohedral phase were investigated under pressures up to 400 MPa at 25 °C. For the transverse electromechanical property, the difference Δf between the resonance f_r and antiresonance frequencies f_a, the Δf/f_r and the electromechanical coupling coefficient k₃₁ value in the k₃₁ mode with hydrostatic pressure (p) became smaller because of the increase in f_r and the almost constant f_a with p. The k₃₁ value decreased by 16% at 400 MPa. On the other hand, for the longitudinal electromechanical property, the Δf, the Δf/f_r and the k₃₃ value in the k₃₃ mode with p remained almost constant because of the almost constant f_r and f_a with p. The changes in the values of the elastic compliances s₁₁^E and s₃₃^E with p were found to be large from the changes in f_r and f_a with p. s₁₁^E and s₃₃^E at 400 MPa were estimated to be 35.4 and 75.1 × 10⁻¹² m² N⁻¹, respectively. A mechanical quality factor Q almost constant with p in the k₃₃ mode in contrast to the large decrease in Q in the k₃₁ mode with p in the pressure range up to 200 MPa was observed. A k₃₃ value almost constant with p is considered, on the basis of the engineered domain concept, to be due to the stable domain configuration responsible for the longitudinal k₃₃ mode. Furthermore, the superior piezoelectric properties of the rhombohedral [001] single crystal in the vicinity of the morphotropic phase boundary composition were recently pointed out to come from the large shear piezoelectric constant d₁₅ of their single domain property. The hydrostatic pressure cannot influence the piezoelectric properties from the viewpoint of the contribution of the large shear mode d₁₅, since the uniform pressure introduces no shearing stresses. Consequently, the k₃₃ value measured for the k₃₃ mode remained almost constant with p in the measured pressure range.

We give an analytical formula in term of continued fraction expansions for the spectral function of a tunnelling electron, coupled to a local lattice oscillation, in a two-site cluster at non-zero temperature. We also study the spectral function of the polaron, a better defined quasi-particle in the anti-adiabatic regime and at sufficiently low temperature. The exact results obtained allow us to look into a wide range of temperature and coupling. Asymptotic results can be obtained directly from the continued fraction expansions in both adiabatic and anti-adiabatic regimes. In the intermediate/strong anti-adiabatic case, in contrast to the usual Lang–Firsov approximation scheme, we found that there is no shrinking of the polaron band as temperature increases. Polaron bandwidth gets broader by temperature effects.

The characteristic features of polarization and spontaneous depolarization kinetics in non-uniform telluric acid ammonium phosphate (TAAP) crystals are investigated by observation of the domain structure using a nematic liquid crystal method. We present experimental results showing the correlation between the internal bias field, responsible for the offset of the hysteresis loop and the backswitching process. The internal field caused by structural disorder accounts for a broad spectrum of energy barriers for domain nucleation. The switching kinetics was analysed in the framework of the nucleation and growth model based on Avrami statistical theory, using the modified Kolmogorov–Avrami–Ishibashi (KAI) model. It has been found that the switching kinetics in TAAP crystals can be approximated by averaging the KAI model over a broad distribution of characteristic domain growth times. The spectra of the distribution of the characteristic domain growth times are derived from the experimental data.

We present the electrical spin injection from room-temperature ferromagnetic (Ga, Mn)N in nitride-based spin-polarized light-emitting diodes. The electroluminescence spectra from the spin LED indicate the existence of the spin polarization via optical polarization of emitted light up to room temperature. This demonstrates that the spin injection from the (Ga, Mn)N layer into (In, Ga)N quantum wells was achieved persisting up to room temperature by comparing it with the magnetic field dependence of the Hall resistance, which is proportional to the out-of-plane magnetization. These results support that (Ga, Mn)N is an appropriate material for a spin injection source in room-temperature operating semiconductor spintronic devices.

Hydrogenated amorphous silicon (a-Si:H) films were prepared by sputtering a Si target in an atmosphere of Ar+H₂. The Er (and Er+Yb) doping of the films was achieved by partially covering the Si target with small pieces of Er (Er+Yb) metal. After deposition the films were annealed up to 700 °C in an inert atmosphere. Ion beam analyses, Raman spectroscopy, optical transmission and photoluminescence measurements were employed for characterization purposes. According to the experimental results, thermal treatments up to ∼300 °C do not significantly alter the composition, atomic structure or optical bandgap of the present a-Si:H films. On the contrary, the Er-related photoluminescence intensity at 1540 nm increases and reaches its maximum at about 400 °C. Treatments at temperatures higher than ∼400 °C reduce both the Er-related light emission and the optical bandgap of the films due to the out-diffusion of hydrogen atoms. Furthermore, the relatively small optical bandgap and the presence of tail states prevent any optical activity of Yb³⁺ ions in the measured a-Si:H films. At the present doping levels and sample characteristics, ytterbium only increases the incidence of non-radiative processes.

The effects of tetragonal strain on the electronic and magnetic properties of strontium-doped lanthanum manganite, La_2/3Sr_1/3MnO₃ (LSMO), are investigated by means of density-functional methods. As far as the structural properties are concerned, the comparison between theory and experiments for LSMO strained on the most commonly used substrates shows an overall good agreement: the slight overestimate (at most of 1–1.5%) for the equilibrium out-of-plane lattice constants points to possible defects in real samples. The inclusion of a Hubbard-like contribution on the Mn d states, according to the so-called 'LSDA+U' approach, is rather ineffective from the structural point of view, but much more important from the electronic and magnetic point of view. In particular, full half-metallicity, which is missed within a bare density-functional approach, is recovered within LSDA+U, in agreement with experiments. Moreover, the half-metallic behaviour, particularly relevant for spin-injection purposes, is independent of the chosen substrate and is achieved for all the considered in-plane lattice constants. More generally, strain effects are not seen to crucially affect the electronic structure: within the considered tetragonalization range, the minority gap is only slightly (i.e. by about 0.1–0.2 eV) affected by a tensile or compressive strain. Nevertheless, we show that the growth on a smaller in-plane lattice constant can stabilize the out-of-plane versus in-plane e_g orbital and significantly change their relative occupancy. Since e_g orbitals are key quantities for the double-exchange mechanism, strain effects are confirmed to be crucial for the resulting magnetic coupling.

We found various GePt/FePt microstructures at different post-annealing temperatures. The Ge₂Pt₃ compound was formed when the annealing temperature was 800 °C and the particle-like structure was able to relax the growth stress between Ge₂Pt₃ and quartz. After deposition of FePt film, a discontinuous L1₀ FePt layer was formed when it was post-annealed at 400 °C. However, isolated L1₀ FePt particles were observed at 800 °C post-annealing temperature, and each particle contains many grains. Furthermore, the magnetic viscosity was measured to investigate the different GePt/FePt morphology effects on thermal activation behaviour. When the applied field was less than the coercivity field H_c, we found smaller activation volume (V_a = 0.5 × 10⁻¹⁸ cm³) for a film with 400 °C post-annealing. This is because smaller FePt grains are in between GePt islands and the moments in these grains are hard to reverse. In contrast, a larger V_a (= 1.9 × 10⁻¹⁸ cm³) was found in samples post-annealed at 600–800 °C. This is because the GePt islands agglomerate to become particle-like at high temperature and larger FePt grains were distributed on each GePt particle.

The refractive index in the wavelength range 350–2500 nm of solar absorbing and anti-reflecting thin films was determined from reflectance and transmittance measurements. Knowing the refractive indices of such films was important when designing an optimized spectrally selective surface for solar thermal usage. The absorbing thin films were made of nickel–alumina composites with a nickel content varying from 20 to 80%. The anti-reflecting films were made of silica, hybrid-silica, alumina and silica–titania composites.

We present an overview of two leading methods of determining probability distributions from Mössbauer spectra, using the model amorphous magnet Fe₈₀B₂₀. A comparison is made between the maximum-entropy method, which permits analysis using truly arbitrary parameter probability distributions, and a Voigtian-based analysis, which uses a sum of Gaussian components to create parameter distributions of pseudo-arbitrary shape. Our results indicate that, in Fe₈₀B₂₀, a Gaussian distribution of magnetic hyperfine fields is a very good approximation, although small deviations from a Gaussian shape are evident. We find that the apparent existence of correlations between the isomer shift and magnetic hyperfine field parameters, as found using Voigt-based analyses, may be an artefact of imposing a Gaussian shape on the parameter distributions. We conclude that maximum entropy and Voigtian analyses together provide a very powerful means of characterizing magnetic materials with Mössbauer spectroscopy.

This work reports a detailed infrared reflectivity investigation of the phase transitions in single crystals of sodium ammonium sulfate dihydrate (SASD). The polarized reflectivity spectra allow us to follow the temperature dependence of the polar vibrational modes and detect the critical behaviour of the vibrational parameters through the two low temperature structural phase transitions observed in the compound. The results obtained show that the mechanism of the transitions in SASD is complex, involving a strong coupling between pseudo-spins and phonons. In the paraelectric phase, the driving mechanism of the first phase transition (T_c1 = 95 K) appears to be related to a relaxation with a characteristic frequency that is much lower than the phonon frequencies. In the temperature range corresponding to the first ferroelectric phase (T_c1>T>T_c2 = 79 K), the dynamics of the lattice change considerably and the parameters characterizing several vibrational modes display anomalous temperature dependences. The second phase transition occurring at T_c2 is marked by an important and discontinuous change of the spectral shape, indicating that a considerable lattice distortion is involved.

Polarized Raman spectra of the strontium vanadium oxide bronze β-Sr_0.33V₂O₅ are measured in the temperature range between 300 and 77 K. The charge ordering phase transition at about 165 K is characterized by the appearance of new Raman-active modes in the spectra, as well as through an abrupt change of the phonon frequencies and dampings. The Raman scattering spectra of β-Sr_0.33V₂O₅ in the charge disordered phase are in apparent resemblance with those of α'-NaV₂O₅, which suggests that there is a similar charge-phonon dynamics in both compounds. We also suggest that the electrons are delocalized into V₁–O₅–V₃ orbitals in the mixed valence state of β-Sr_0.33V₂O₅.

When a rubber block is sliding on a hard rough substrate, the substrate asperities will exert time-dependent deformations of the rubber surface resulting in viscoelastic energy dissipation in the rubber, which gives a contribution to the sliding friction. Most surfaces of solids have roughness on many different length scales, and when calculating the friction force it is necessary to include the viscoelastic deformations on all length scales. The energy dissipation will result in local heating of the rubber. Since the viscoelastic properties of rubber-like materials are extremely strongly temperature dependent, it is necessary to include the local temperature increase in the analysis. At very low sliding velocity the temperature increase is negligible because of heat diffusion, but already for velocities of order 10⁻² m s⁻¹ the local heating may be very important. Here I study the influence of the local heating on the rubber friction, and I show that in a typical case the temperature increase results in a decrease in rubber friction with increasing sliding velocity for v>0.01 m s⁻¹. This may result in stick–slip instabilities, and is of crucial importance in many practical applications, e.g. for tyre–road friction and in particular for ABS braking systems.

A succinonitrile (SCN)–3.6 wt% acetone (ACE) alloy was unidirectionally solidified with a constant temperature gradient G = 5.7 K mm⁻¹ in the growth rate ranges V = 6.5–113 µm s⁻¹ and a constant growth rate V = 6.5 µm s⁻¹ in the temperature gradient ranges G = 3.5–5.7 K mm⁻¹. The primary dendrite arm spacings, secondary dendrite arm spacings, dendrite tip radius and mushy zone depth were measured as a function of growth rate and temperature gradient. Theoretical models for the dendrite arm spacing and tip radius have been compared with the experimental observations, and a comparison of our results with the current theoretical models and previous experimental results has also been made. The stability constant (σ) for this alloy system was measured and this result was compared with various similar organic transparent alloys.

Dynamical phenomena of moving vortices and voltage noise spectra are studied in disordered Josephson junction arrays (JJAs). The plastic motion of vortices, smectic flow, and moving Bragg glass phases are separated by two dynamic melting transitions driven by current. From the voltage noise spectra of moving vortices, it is found that the driving current plays an important role in the melting of pinning vortices glass and ordering of moving vortices. The features of noise spectra obtained in the disordered JJA model have been observed recently in the high-temperature superconductor Bi₂Sr₂CaCu₂O_y near the first-order melting transition, indicating that both of them are related to each other.

This paper reports on a systematic investigation of the optical properties of Ta_1−xZr_xN single-phase and ZrN–Ag multi-phase films fabricated by unbalanced magnetron sputtering using vacuum ultraviolet spectroscopic ellipsometry (VUV-SE). VUV-SE is a newly developed technique that was used to evaluate the strength and energy of the interband electronic excitations/transitions in these films. The energy of the interband transition was found to be altered by any changes in the elemental composition for single-phase materials. For example, it was found to increase with the increase in the covalent character of the bond as more Zr atoms are substituted for by Ta atoms in the ZrN rock-salt structure. In contrast, the peak positions did not vary in the multi-phase structures because the constituent phases were immiscible and retained their electronic structure. However, the strength and width of the interband transition were found to change to reflect changes in phase composition and microstructure. The optical and electronic properties of these materials were simulated using density functional theory (DFT) within the generalized gradient approximation. The calculated refractive indices and density of states were in good agreement with the VUV-SE data.

Coatings of CrN, TiN, ZrN, TaN and NbN were deposited using an unbalanced magnetron sputtering system with two different degrees of unbalancing to investigate the effect of the degree of unbalancing on both plasma characteristics and film properties. The degree of unbalancing was determined by an extensive characterization of the magnetic field fluxes in the X–Z plane perpendicular to the target. Then, the plasma parameters, such as electron temperature, plasma potential, plasma density and ion current density, were obtained for each target and as a function of the unbalance coefficient. The film microstructure, hardness, corrosion and wear resistant were measured to determine the effect of the degree of unbalancing on these properties. The results suggested that the degree of unbalancing, through the variations induced in the ion bombardment and plasma ionization, had a strong influence on the film hardness, microstructure and preferred orientation.

Water adsorption on hydrogenated carbon film surfaces can drastically affect friction behaviour. In this work, we investigate water adsorption and desorption properties of sulfur-doped hydrogenated films, which we have observed to retain ultra-low friction properties of hydrogenated carbon films in humid air. Water adsorption studies using a quartz crystal microbalance show that there is an almost threefold reduction in equilibrium water coverage at room temperature on hydrogenated carbon films doped with 5 at.% sulfur. Thermal desorption studies indicate that sulfur doping weakens the binding of water molecules on hydrogenated carbon film surfaces.

This study was performed with the aim of evaluating the relative tribological behaviour at high temperature of (Ti_1−xAl_x)N coatings commercially deposited on WC inserts. The (Ti_1−xAl_x)N multilayered, nanostructured and single-layer coatings, which contained different Ti/Al atomic ratios varying from 7/3 to 2/3 respectively, were deposited by employing a commercial PVD cathodic arc process. The absolute hardness value for each coating is also reported and has been calculated from the Vickers microhardness measurements by using one of the models published in the literature. Standard ball-on-disc testing was conducted in order to determine friction coefficients and wear rates for these systems against a 6 mm alumina ball. These tests have been carried out in conditions that are not common in industrial use, e.g. metal cutting tools inasmuch as alumina is not a representative workpiece material. The sliding tests were performed out at 25, 500 and 700 °C with 5 N normal loads. At 25 °C, a wear volume, V, of approximately 10⁻² mm³ was obtained for all the tested coatings. When the test temperature increased to 500 °C, the single-layered coatings showed a wear volume of the same order of magnitude as those tested at room temperature. The multilayered coated samples decreased their wear volume by one order of magnitude, whereas the nanostructured samples showed almost no wear. At 700 °C, the wear volume values reported for all samples were similar and of the same order of magnitude as those tested at room temperature. The wear mechanism is discussed together with the morphological and compositional characteristics, determined by SEM coupled with EDX analysis.

The elastic constants of diamond between 100 and 1100 K have been calculated for the first time using molecular dynamics and the second-generation, reactive empirical bond-order potential (REBO). This version of the REBO potential was used because it was redesigned to be able to model the elastic properties of diamond and graphite at 0 K while maintaining its original capabilities. The independent elastic constants of diamond, C₁₁, C₁₂, and C₄₄, and the bulk modulus were all calculated as a function of temperature, and the results from the three different methods are in excellent agreement. By extrapolating the elastic constant data to 0 K, it is clear that the values obtained here agree with the previously calculated 0 K elastic constants. Because the second-generation REBO potential was fit to obtain better solid-state force constants for diamond and graphite, the agreement with the 0 K elastic constants is not surprising. In addition, the functional form of the second-generation REBO potential is able to qualitatively model the functional dependence of the elastic constants and bulk modulus of diamond at non-zero temperatures. In contrast, reactive potentials based on other functional forms do not reproduce the correct temperature dependence of the elastic constants. The second-generation REBO potential also correctly predicts that diamond has a negative Cauchy pressure in the temperature range examined.

As an element, carbon is rather unique and offers a range of rare opportunities for the design and fabrication of zero-, one-, two-, and three-dimensional nanostructured novel materials and coatings such as fullerenes, nanotubes, thin films, and free-standing nano-to-macroscale structures. Among these, carbon-based two-dimensional thin films (such as diamond and diamond-like carbon (DLC)) have attracted an overwhelming interest in recent years, mainly because of their exceptional physical, chemical, mechanical, electrical, and tribological properties. In particular, certain DLC films were found to provide extremely low friction and wear coefficients to sliding metallic and ceramic surfaces. Since the early 1990s, carbon has been used at Argonne National Laboratory to synthesize a class of novel DLC films that now provide friction and wear coefficients as low as 0.001 and 10⁻¹¹–10⁻¹⁰ mm³ N⁻¹ m⁻¹, respectively, when tested in inert or vacuum test environments. Over the years, we have optimized these films and applied them successfully to all kinds of metallic and ceramic substrates and evaluated their friction and wear properties under a wide range of sliding conditions. In this paper, we will provide details of our recent work on the deposition, characterization, and tribological applications of near-frictionless carbon films on glass and ceramic substrates. We will also provide chemical and structural information about these films and describe the fundamental tribological mechanisms that control their unusual friction and wear behaviour.

Carbide derived carbon (CDC) was produced on SiC by reaction with flowing Ar–3.5% Cl₂ gas at 900 and 1000 °C. The thickness of the CDC layer increased with time during high temperature exposure according to a parabolic rate equation represented by K_p = [2.48 × 10⁻⁶e^{−(165 000/RT)}] m² s⁻¹. Carbon loss due to the formation and spallation of graphitic powder was found to be negligible in these experiments. Residual chlorine contents in the CDC layer were measured, and a gradient in chlorine content increasing from the CDC/SiC interface to the CDC/gas interface was observed. This is consistent with diffusional transport of chlorine through the growing CDC layer as the rate controlling step in the CDC growth process. Because the value of the parabolic rate constant is high compared with solid state diffusion coefficients for carbon, transport by solid state diffusion is unlikely. Because the apparent activation energy of 165 000 J mol⁻¹ is high for a gas phase diffusion process, surface diffusion of adsorbed chlorine in the pores of the CDC is suggested as a transport mechanism for the growth of CDC under these conditions.

Hydrogen has long been known to be critical for the growth of high-quality microcrystalline diamond thin films as well as homoepitaxial single-crystal diamond. A hydrogen-poor growth process that results in ultra-nanocrystalline diamond thin films has also been developed, and it has been theorized that diamond growth with this gas chemistry can occur in the absence of hydrogen. This study investigates the role of hydrogen in the growth of ultra-nanocrystalline diamond thin films in two different regimes. First, we add hydrogen to the gas phase during growth, and observe that there seems to be a competitive growth process occurring between microcrystalline diamond and ultra-nanocrystalline diamond, rather than a simple increase in the grain size of ultra-nanocrystalline diamond. Second, we remove hydrogen from the plasma by changing the hydrocarbon precursor from methane to acetylene and observe that there does seem to be some sort of lower limit to the amount of hydrogen that can sustain ultra-nanocrystalline diamond growth. We speculate that this is due to the amount of hydrogen needed to stabilize the surface of the growing diamond nanocrystals.