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Planned cryogenic gravitational-wave detectors will require improved coatings with a strain thermal noise reduced by a factor of 25 compared to Advanced LIGO. We present investigations of HfO_{2} doped with SiO_{2} as a new coating material for future detectors. Our measurements show an extinction coefficient of k=6×10^{-6} and a mechanical loss of ϕ=3.8×10^{-4} at 10 K, which is a factor of 2 below that of SiO_{2}, the currently used low refractive-index coating material. These properties make HfO_{2} doped with SiO_{2} ideally suited as a low-index partner material for use with a-Si in the lower part of a multimaterial coating. Based on these results, we present a multimaterial coating design which, for the first time, can simultaneously meet the strict requirements on optical absorption and thermal noise of the cryogenic Einstein Telescope.

Low mechanical loss at low temperatures and a high index of refraction should make silicon optimally suited for thermal noise reduction in highly reflective mirror coatings for gravitational wave detectors. However, due to high optical absorption, amorphous silicon (aSi) is unsuitable for being used as a direct high-index coating material to replace tantala. A possible solution is a multimaterial design, which enables exploitation of the excellent mechanical properties of aSi in the lower coating layers. The possible number of aSi layers increases with absorption reduction. In this work, the optimum heat treatment temperature of aSi deposited via ion-beam sputtering was investigated and found to be $450\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. For this temperature, the absorption after deposition of a single layer of aSi at 1064 nm and 1550 nm was reduced by more than 80%.

In a typical single molecule experiment, dynamics of an unfolded proteins is studied by determining the reconfiguration time using long-range Forster resonance energy transfer where the reconfiguration time is the characteristic decay time of the position correlation between two residues of the protein. In this paper we theoretically calculate the reconfiguration time for a single flexible polymer in presence of active noise. The study suggests that though the MSD grows faster, the chain reconfiguration is always slower in presence of long-lived active noise with exponential temporal correlation. Similar behavior is observed for a worm like semi-flexible chain and a Zimm chain. However it is primarily the characteristic correlation time of the active noise and not the strength that controls the increase in the reconfiguration time. In a nutshell, such active noise makes the polymer to move faster but the correlation loss between the monomers becomes slower., Comment: 18 pages, 8 figures

Au60Ag30Cu10(in at%) gold alloy exhibits a mechanical loss spectrum composed of a Zener peak due to Cu atoms in the solid solution and of a second relaxation peak at higher temperature or lower frequency. It is shown that this second peak is related to the presence of grain boundaries as it is absent in the spectrum of a single crystal. This mechanical loss peak, which is stable and reproducible in heating and cooling cycles, is thermally activated with an activation enthalpy of 2.35 eV and an apparent limit relaxation time of 9.6·10-17s. As it is hard to imagine that a whole grain should slip at once along a touching grain, the relaxation peak is interpreted by a dislocation model, which may account not only for the activation parameters but also for the stress amplitude dependency of the peak.

Metal matrix composites, made of Mg or Mg-2wt.%Si matrices reinforced with C or SiC long fibres, were processed by gas-pressure infiltration. Such composites are an advantageous solution for developing light metallic materials, which exhibit simultaneously good mechanical properties and a high damping capacity. For instance C/Mg-Si composites have a specific Young's modulus more than 4 times and a damping capacity 10-100 times higher than steels or aluminium alloys. The thermal behaviour of these materials was investigated by mechanical spectroscopy. Thermal stress relaxation at interfaces gives rise to transient damping, which is interpreted as being due to hysteretic dislocation motion. Hysteretic dislocation motion is also responsible for the mechanical loss background. As this mechanism is not thermally activated, high damping is maintained in a wide frequency and temperature range.

In metal matrix composites (MMCs) thermal stress relaxation can be achieved either by interface debonding, crack propagation or by dislocation motion. The present paper shows that in the case of magnesium matrix, interface thermal stresses are relaxed by dislocation motion. Moreover the results obtained by mechanical spectroscopy prove that this dislocation motion is controlled by a solid friction mechanism, which is not thermally activated. This point is very interesting for the development of MMCs, which exhibit a high damping capacity over a wide frequency range. Dislocation hysteretic motion in the magnesium matrix is evidenced by the dependence of the mechanical loss on the stress amplitude. The obtained relationship obeys perfectly to the Granato-Lucke model for dislocation breakaway. (C) 2009 Elsevier Ltd. All rights reserved.

Polycrystalline zirconia (3Y-TZP grade) specimens unreinforced and reinforced with multiwalled carbon nanotubes (MWCNTs) or silicon carbide whiskers (SiCws) were processed by powder metallurgy and studied by mechanical spectroscopy. The high-temperature mechanical-loss spectrum of pure 3Y-TZP presents mainly an exponential background. Doping 3Y-TZP with nano-sized reinforcements such as MWCNT or SiCw results in a decrease in the high-temperature background with respect to pure zirconia. It has been shown that these spectrum modifications by doping are associated with a better resistance to creep. (C) 2009 Elsevier B.V. All rights reserved.

Mechanical-loss measurements were performed in three grades of martensitic high-carbon tool steels. These steels were treated under carburizing gas before quenching, in order to vary the concentration of interstitial carbon in the martensite, as assessed by thermoelectric-power measurements. The mechanical-loss spectra present a relaxation peak due to interaction between dislocations and carbon interstitials, similar to the Snoek-Koster peak found in ferrite. The amplitude of the Snoek-Koster peak is expected to be independent of the concentration of interstitials. However, the amplitude of the corresponding peak in martensite is found to increase with the concentration of interstitial carbon. This effect is attributed to an increase of the dislocation density with the carbon content. (C) 2009 Elsevier B.V. All rights reserved.

We consider dislocations as vortices in elastic strain field and show that an ordered system of partial dislocations in faulted martensites is analogous to a system of flux lines (supercurrent vortices) in type-II superconductors. The network of interacting partial dislocations can form vortex matter, whose dynamics is controlled by applied stress amplitude and by a degree of quenched and thermal disorder. Experimental results on elasticity and ultrasonic anelasticity of ternary faulted martensites from Cu-Al, Cu-Zn families and from binary Cu-Al system, obtained for temperatures between 6 and 300 K, point to the existence of glassy and liquid states of vortex matter in martensites. We show that the liquid and glassy dynamics of vortex matter and reversible transitions between these states account for a large number of unusual low-temperature anelastic effects in faulted martensites. (C) 2007 Elsevier B.V. All rights reserved.

The results of precision measurements of creep in Co-based metallic glass are presented. It is shown that, in spite of generally accepted concepts, plastic flow at low stresses under intense structural relaxation conditions is of a non-Newtonian type. Consequences of this fact are considered. (C) 2000 MAIK "Nauka/Interperiodica".

The mechanical loss and dynamic modulus temperature spectra of two 18-carat white gold alloys, Au58%Cu24%Pd18% without (grade A) and with alloying additions (grade B), were measured in the 400-1000 K temperature range. A peak interpreted as a Zener relaxation peak is found at about 630 K in both alloys. In the as-quenched state the peak shifts to lower temperatures due to excess vacancies, creating a transient peak at 520 K visible only upon the first heating. In grade A, a relaxation peak is observed at 750 K and is attributed to grain boundary relaxation, since it is absent in monocrystalline sample. in the same temperature region, the grade B features a peak with a large hysteresis between heating and cooling. A sharp peak observed in heating at 830 K is accompanied by a strong modulus decrease. In cooling, we observe a peak at 750 K, below which the mechanical loss abruptly decreases, accompanied by a modulus recovery. The peak hysteresis is interpreted as being due to dissolution or precipitation, respectively. The internal friction spectrum is correlated with the alloy's mechanical properties, namely the hardening of the grade B upon tempering at a temperature below the dissolution peak. (C) 2009 Elsevier B.V. All rights reserved.

The effects of heating-induced crystallization on the structural and mechanical properties of Mg-Ni-Fe amorphous ribbons were studied by anelastic spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction. DSC results show that the crystallization occurs through several non-reversible steps, which correspond to significant changes in the Young's modulus and concomitant irreversible elastic energy loss peaks. Moreover, an anelastic peak is found at 215 K, which for the first time indicates the presence of some dynamical process related to the simultaneous presence of different phases. The formation of a metastable Mg6Ni phase is detected, which transforms into Mg and Mg2Ni stable phases. A quantitative analysis of the different phases present at the different steps was also carried out. (C) 2007 Elsevier B.V. All rights reserved.

The author investigates quantitatively the influence of random surface roughness on the quality factor Q of nanoresonators due to noise by impinging gas molecules. The roughness is characterized by the amplitude w, the correlation length xi, and the roughness exponent H that describes fine roughness details at short wavelengths. Surface roughening (decreasing H and increasing ratio w/xi) leads to lower Q, which translates to lower sensitivity to external perturbations, and a higher limit to mass sensitivity. The influence of the exponent H is shown to be important as that of w/xi, indicating the necessity for precise control of the surface morphology. (c) 2007 American Institute of Physics.

A completely automated vibrating-reed apparatus for measurements of the mechanical quality factor and dynamic elasticity moduli has been developed. The apparatus is equipped with heating and cooling stages allowing continuous temperature ramps and isothermal measurements in the range 90-1400 K. Measurements in a magnetic field up to 8 x 10(4) A/m can also be performed. The data acquisition is computer-controlled through a software specifically developed allowing, with a high acquisition rate, automatic measurements and control of all the apparatus components and real-time data analysis. Some results are reported to illustrate the capabilities. These refer to bulk submicro-grained alloys obtained by severe plastic deformation, nanocrystalline metal hydrides for hydrogen storage and metal foams. The results are briefly discussed to emphasize the utility of employing mechanical spectroscopy in synergy with other techniques for a structural and functional characterization of various materials for industrial applications. (c) 2006 Elsevier B.V. All rights reserved.

The results of precision measurements of creep in Co-based metallic glass are presented. It is shown that, in spite of generally accepted concepts, plastic flow at low stresses under intense structural relaxation conditions is of a non-Newtonian type. Consequences of this fact are considered. (C) 2000 MAIK "Nauka/Interperiodica".

In this work we investigate the influence of adsorption-desorption noise on nanoresonators with random rough surfaces. Indeed, surface roughening leads to an increased number of adsorption sites and thus to an increased limit to mass sensitivity and decreased dynamic range leading to increased nonlinear behavior. Extensive analysis of the surface morphology is necessary because it is not only the roughness amplitude w that contributes to adsorption-desorption noise but also the lateral roughness correlation length xi, and the roughness exponent H that characterizes short wavelength roughness (

Phase transitions and related anelastic effects are examined in Fe-xGa alloys (x =19 and 27 at.%) by means of in situ neutron diffraction, vibrating sample magnetometry, dilatometry, and three different mechanical spectroscopy techniques: torsion forced pendulum, vibrating reed, and commercial DMA Q800. Anelastic transient effects due to ordering-disordering (D0(3) A(2)) in Fe-19Ga, and first order phase transitions (D0(3) -> L1(2) -> D0(19) -> B2) in Fe-27Ga compositions, are discussed with respect to phase and magnetic transitions. (C) 2019 Elsevier B.V. All rights reserved.

Nitrogen-rich Ca-alpha-SiAlON ceramics made with different starting powder compositions have been studied by high-temperature mechanical spectroscopy in parallel with compressive deformation in a spark plasma sintering equipment. The mechanical loss spectra measured upon heating show a relaxation peak at about 1150 K and a high-temperature exponential background at higher temperatures (> 1400 K), which are attributed to the alpha-relaxation in the glassy phase and to grain-boundary sliding, respectively. A theoretical interpretation of the results shows that the peak position is mainly a function of glass viscosity. The amplitude of the peak is not only affected by the glassy phase quantity but also depends on the restoring force due to grain elasticity. Therefore, despite a higher amount of glassy phase specimens containing elongated grains may show a lower peak. The amplitude of the internal friction peak corresponding to alpha-relaxation can be used to predict the compression creep of silicon-nitride-based ceramics.

Tempering effects have been studied in three martensitic carbon steels by mechanical spectroscopy. The mechanical-loss spectra present a relaxation peak similar to the Snoek-Koster peak in ferrite. The peak amplitude decreases upon tempering, indicating a decrease of the dislocation density. Transition carbides start to precipitate at 380 K in all the three grades. This tends to decrease the mechanical loss and to increase the modulus. Retained austenite decomposes around 520 K in two of the grades. In the third grade, the presence of Si delays this decomposition to 670 K. The decomposition of retained austenite leads to a sudden decrease of amplitude of the relaxation peak and a modulus anomaly. Both these effects can be attributed to a decrease of the dislocation density in martensite, probably associated with the depletion of carbon atoms in the dislocation core. At low frequency, a mechanical-loss peak associated with the decomposition of retained austenite is visible.

The temperature dependence of the Young modulus along the crystallographic axes b and c (E(b) and E(c)), and the internal friction of a terbium single crystal have been measured. At 4.2 K, E(b) and E(c) are equal to 38 and 84.5 GPa, respectively. The lattice part of the Young modulus and the Debye temperature has been calculated. The origin of the Young modulus anomalies arising at the transition to the magnetically ordered state is discussed.

Mechanical loss measurements were performed at high temperature in fine-grained ceramics, such as zirconia and alumina. At high temperature, the mechanical loss increases exponentially with temperature, which accounts for material creep. The results are analyzed with a model of grain-boundary sliding lubricated by an intergranular glassy phase. When the amount of the intergranular glassy phase is higher, the mechanical loss level is globally higher and so is the creep rate. On the other hand, doping fine-grained ceramics with nano-sized reinforcements such as multiwall carbon nanotubes results in a decrease in the high-temperature mechanical loss. In this case grain-boundary sliding is more difficult and as a consequence better creep resistance is observed.