On some measurements of the propagation properties of thermal waves in the Nb-H and Ta-H systems

Summary By means of an experimental technique based on a nonsteady-state method,i.e. on the propagation of thermal waves, we have measured at room temperature for oscillation frequencies between 6 and 30 mHz the thermal diffusivity, the lateral thermal-loss coefficient and the ?fractional heat loss? in Nb and Ta wires as a function of hydrogen doping. The appearance of hydride formation and precipitation notably changes the behaviour of these quantities. From these measurements it was also possible to calculate the propagation velocity and attenuation coefficient of thermal waves. It was found that the increase of the hydrogen concentration in the solid solution produces a gradual decrease in the velocity and increase in the attenuation coefficient until the solubility limit is reached. For larger hydrogen concentrations, the velocity showed a tendency to increase towards the value of the pure metal, while the attenuation coefficient decreased below the value of the pure metal. These results as a whole appear quite promising for studying the properties of hydrogenated systems. This work was supported by the Gruppo Nazionale di Struttura della Materia of the Consiglio Nazionale delle Ricerche and by the Centro Interuniversitario di Struttura della Materia of the M.P.I., Roma (Italia).     

Longitudinally detected electron spin resonance: Recent developments

Multiple-quantum spectroscopies are reviewed in the frame of electron paramagnetic resonance. Some properties of different nonlinear techniques are discussed for both transverse and longitudinal detection. The connections of effects recently presented with the procedure of longitudinal detection of electron paramagnetic resonance (LODESR) in presence of double transverse irradiation are stressed. Peculiarities of LODESR spectroscopy and its capabilities in facing problems related to relaxations in presence of very slow dynamic processes are evidentiated. Recent results show the vitality of the LODESR technique, that in the future could be applied to new fields, owing to experimental updating.     

New method for determining the optical constants by the angular modulation of reflectance

A new method is proposed here for measuring the optical constants of solids. The method is based on measuring the change of the derivative of reflectance with the angle of incidence Θ of p-polarized light for different Θ around the pseudo-Brewster angle. The accuracy of the method has been checked by determining the optical constants of some transparent and opaque materials. The method seems very sensitive to the presence of thin oxide layers and it is also expected to be useful in determining oxide thicknesses.     

On some measurements of thermal diffusivity by means of thermal-wave propagation in wires

Summary By means of a new experimental technique based on a non-steady-state method,i.e. on the propagation properties of thermal waves, we have measured the thermal diffusivityD of a copper wire by changing properly its boundary conditions in order to ascertain whether the values ofD were independent of the surface heat losses. Temperature oscillations at the fixed frequency of 0.0121 Hz were excited at one end of the specimen which was in nitrogen atmosphere at different pressures ranging from ∼10⁻² mTorr to 220 mTorr. The temperatures of the far end of the specimen and the walls of the container had the same constant value of 0°C, while the temperature gradient between the average value of the oscillating temperatures and this constant temperature was changed from 2°C to 12°C for each pressure by adjusting the heater power. By operating in this way it was possible to change either the heat losses due to conduction and convection or those due to radiation. The major cause of error came from the uncertainty in the measurements of the phase shift between the thermal oscillations detected at the two fixed points of the specimen which introduces in the evaluation ofD an error of about 2%. The experimental values obtained for the thermal diffusivity in these different boundary conditions were in any case comprised within this uncertainty sinceD=(1.17±0.02) cm²s⁻¹, in good agreement with the literature. The results so far obtained show that the experimental method has the great advantage of giving the thermal diffusivity and, therefore, the thermal conductivity of a solid without the necessity of taking particular care in insulating the specimen.

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Riassunto Utilizzando una tecnica sperimentale che consente di determinare in fili metallici sia la diffusività termicaD sia il coefficienteμ di perdita superficiale mediante la misura diretta del ritardo di fase e dell'attenuazione di un'onda termica tra due punti fissi del campione, ci si è proposti di analizzare alcuni risultati ottenuti recentemente in un campione di rame, variando opportuamente le condizioni al contorno. In particolare, ci si è voluti assicurare che la diffusività termica non risultasse dipendente dal valore del coefficiente di perdita superficiale. Le misure sono state eseguite alla frequenza fissa di 0.0121 Hz in atmosfera di azoto, a pressioni diverse comprese tra ∼10⁻² mTorr e 220 mTorr. L'estremità lontana del campione e le pareti del contenitore erano tenuti costantemente alla stessa temperatura (0°C), mentre il gradiente termico era sistematicamente variato tra 2°C e 12°C, in corrispondenza di ciascuna pressione. Operando in questo modo, si potevano variare opportunamente sia la conduzione sia l'irraggiamento del calore dalla superficie laterale del campione nel mezzo circostante. In queste misure, la causa predominante di errore viene dalla misura dello sfasamento delle due onde, che introduce nella valutazione diD un'incertezza del 2%. I valori sperimentali ottenuti nelle diverse condizioni prima ricordate risultano, in ogni caso, compresi entro i limiti di questa incertezza, poichéD=(1.17±0.02) cm²/s, in ottimo accordo con i dati della letteratura. Questo risultato dimostra pertanto che la diffusività termica, determinata con questo metodo dinamico, risulta effettivamente indipendente dalla quantità di calore transmesso dal campione nel mezzo circostante, consentendo pertanto piú agevoli determinazioni della conducibilità termica dei solidi, noti la densità ed il calore specifico.

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Резюме С помощью новой экспериментальной техники, основанной на нестационарном методе, т.е. на свойствах распространения тепловых волн, мы измеряем коэффициент температуропроводностиD медного провода, посредством измения граничных условий, чтобы выяснить независимость величинD от поверхностных потерь тепла. Температурные осцилляции при фиксированной частоте 0.0121 Гц возбуждаются на одном конце образца, который помеЩен в атмосферу азота при различных давлениях в области от ∼10⁻² мтор до 220 мтор. Температуры другого конца образца и стенок контейнера являются постояннюми 0°C, тогда как градиент температуры между средним значением осциллирующей темпертурой и этой постоянной температурой изменяется от 2°C до 12°C для каждого значения давления, за счет регулировки мощности нагревателя. Этот метод позволяет изменять тепловые потери, обусловленные либо проводимостью и конвекцией, либо излучением. Основная причина ошибок проистекает из неопределенности в измерениях фазового сдвига между тепловыми осцилляциями, заререгистрированными в двух фиксированных точках образца. Ошибка при измерении составляет около 2%. Экспериментальные значения, полученные для коэффициента температуропроводности при различных граничных условиях,D=(1.17±0.02) см⁻²с⁻¹, хорошо согласуются с данными в литературе. Полученные результаты показывают, что предложенный экспериментальный метод обладает большим преимуществом при определении температуропроводности и, следовательно, теплопроводности твердых тел, не уделяя особого внимания изоляции образца.

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To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.

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This research was supported by the Consiglio Nazionale delle Ricerche, Rome (Italy).

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Some preliminary results were presented at the ?LXVII Congresso della Società Italiana di Fisica?, Pisa, October 1981.     

Modulation of hydrophobic effect by cosolutes

This work concerns a comparison of the hydration properties and self-association behavior in aqueous solution of three biologically relevant simple molecules: tert-butyl alcohol (TBA), trimethylamine-n-oxide (TMAO), and glycine betaine (GB). These molecules were used as a model to study hydrophobic behavior in water solutions. In particular, water perturbation induced by TBA, TMAO, and GB molecules was studied as a function of the solute molar fraction X(2) (0 < X(2) < 0.04) by Raman spectra of water in the fundamental OH-stretching region (3,800-2,800 cm(-1)). Furthermore, possible hydrophobic clustering of these molecules was investigated by studying the behavior of the alkyl CH stretching band in the 3,100-2,900 cm(-1) frequency region as a function of X(2). To establish the existence of a correlation between the effects of these three solutes on the micellization process and changes in the properties of the solvent, the behavior of the critical micelle concentration of sodium dodecyl sulfate was also investigated as a function of the added amount of TBA, TMAO, and GB. On the whole, these data show that there is no direct correlation between a solute's effect on the water structure and its effect on micelle or protein stability. Results indicate that, while TBA starts to self-aggregate at approximately X(2) = 0.025, both TMAO and GB do not exhibit any significant self-aggregation up to the highest concentration considered. In addition, nonadditive perturbations of the H-bonded networks of solvent water are observed in the case of TBA solutions, but are absent in both the TMAO and GB cases. The absence of these nonlinear effects in TMAO and GB water solutions allow for tracing the microscopical mechanism of the neutrality of these osmolytes toward hydrophobic effects. This confers the compatibility to these two osmolytes, which can be accumulated at high concentrations without interfering with biochemical processes in the cell.     

Influence of Si substrate preparation on surface chemistry and morphology of L-CVD SnO2 thin films studied by XPS and AFM

Results of experimental studies of the influence of substrate preparation on the surface chemistry and surface morphology of the laser-assisted chemical vapour deposition (L-CVD) SnO₂ thin films are presented in this paper. The native Si(1 0 0) substrate cleaned by UHV thermal annealing (TA) as well as thermally oxidized Si(1 0 0) substrate cleaned by ion bombardment (IBA) have been used as the substrates. X-ray photoemission spectroscopy (XPS) has been used for the control of surface chemistry of the substrates as well as of deposited films. Atomic force microscopy (AFM) has been used to control the surface morphology of the L-CVD SnO₂ thin films deposited on differently prepared substrates. Our XPS shows that the L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit the same stoichiometry, i.e. ratio [O]/[Sn] = 1.30 as that of the layers deposited on Si(1 0 0) substrate previously cleaned by UHV prolonged heating. AFM shows that L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit evidently increasing rough surface topography with respect to roughness, grain size range and maximum grain height as the L-CVD SnO₂ thin films deposited on atomically clean Si substrate at the same surface chemistry (nonstoichiometry) reflect the higher substrate roughness after cleaning with ion bombardment.     

Photoconductivity of multiwalled CNT deposited by CVD

Structural, optical and electrical properties of multiwalled carbon nanotubes deposited by chemical vapour deposition at 750 °C on sapphire substrate have been investigated. The main results concern the photoconductivity measurements. The photocurrent induced by white light illumination is a linear function of either the bias voltage or the optical power density in wide ranges. The photoresponse increases from the near infrared to the ultraviolet region with decreasing the wavelength of the monochromatic incident radiation in the 325–850 nm range. The photoresponse is strongly correlated to the optical absorbance. The optical and photoconductivity properties explored in multiwalled carbon nanotube samples with relatively large area appear very interesting for the development of light sensors.     

Structure of water-in-oil microemulsions of AOT by infrared spectroscopy

Summary The structure of water in water/AOT/n-heptane reverse micelles has been studied as a function of the [H₂O]/[AOT] ratio (W) by using the absorption IR due to O−H stretching modes in the 3800–3000 cm⁻¹ range. The results show that the IR spectra can be expressed as a sum of contributions from bound- and bulk-like water. The fraction of water in the two ?regions? within the water pool was evaluated as a function ofW. The ?bound? water region seems to hold 3.5 water molecules (corresponding to 7 O−H oscillators) per AOT molecule and its formation is nearly complete atW>6. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.