Effects of thermal treatment on the tribological characteristics of thermoplastic polymer film

Friction tests were carried out using a microtribometer to investigate the effect of thermal treatment on microscale friction and wear between poly(methyl methacrylate) (PMMA) film and a fused silica lens. Two films were examined: one that was baked at 413 K for 2 min and one that was baked at 433 K for 24 h. The friction forces on the PMMA films were measured under atmospheric conditions as the temperature of the films was increased from 300 K to 443 K. The contact area between the films and the lens was also examined. As the temperature increased, the friction force increased for both films. The slope of the friction force with temperature and the contact area varied, depending on the state of the film surface; glassy, rubbery, and viscous flow states. The baking conditions also affected the slope, contact area, and wear generation. For temperatures at which the samples were in a glassy state, wear particles were not generated on the sample baked for 24 h. The results demonstrate that the tribological characteristics can be altered by the thermal treatment of the PMMA film as well as the temperature. When the film contains some residual solvent, the residual solvent in the PMMA film can diffuse to the PMMA surface due to heating and thus decrease the friction force under room-temperature conditions.     

Indium oxide thin film based ammonia gas and ethanol vapour sensor

A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a miniature heater. For the fabrication of miniature heater indium tin oxide thin film was grown on special high temperature corning glass substrate by flash evaporation method. Gold was deposited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an hour. The thermocouple attached on sensing surface measures the appropriate operating temperature. The thin film gas sensor for ammonia was operated at different concentrations in the temperature range 323–493 K. At 473 K the sensitivity of the sensor was found to be saturate. The detrimental effect of humidity on ammonia sensing is removed by intermittent periodic heating of the sensor at the two temperatures 323K and 448 K, respectively. The indium oxide ethanol vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293–393 K. Above 373 K, the sensor conductance was found to be saturate. With various thicknesses from 150–300 nm of indium oxide sensor there was no variation in the sensitivity measurements of ethanol vapour. The block diagram of circuits for detecting the ammonia gas and ethanol vapour has been included in this paper.     

Electrical transport behaviour of silver–PMMA nanocomposite films at low temperature

In this study, the silver nanoparticles, capped with oleylamine, were embedded in polymethylmethacrylate (PMMA) using sonication to fabricate Ag–PMMA nanocomposites. The well-dispersed nanocomposite samples are analysed using UV-Vis absorption spectroscopy, atomic force microscopy and small angle X-ray scattering. The interfacial interaction of Ag nanoparticles and PMMA polymer is investigated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. It is concluded that a ligand-exchange process occurs when capped silver nanoparticles are incorporated in PMMA polymer. Electrical resistivity of nanocomposite samples was measured by a four-probe technique in the 70–300?K range. The nanocomposites showed a transition with onsets at ～230 and ～160?K. They exhibited a semiconductor-like conductivity at higher temperatures, a rapid metallic conductivity at middle range and nearly temperature independent conductivity at lower temperatures.     

Photophysical properties and photoisomerization processes of Methyl Red embedded in rigid polymer

The photophysical properties of Methyl Red molecules embedded in a poly(methyl methacrylate) (PMMA) matrix were investigated with photoinduced absorption, absorption kinetics, steady-state, and time-resolved luminescence spectroscopy. The excited singlet (S(1)) state lifetimes for trans and cis isomers of Methyl Red in PMMA at room temperature have been measured as 35 and 420 ps, respectively. The excited triplet (T(1)) state energy level and its lifetime at 77 K were also obtained. A slow trans-cis isomerization process having a time constant of a few hundred seconds was observed for the illuminated Methyl Red in rigid polymer. Based on measured photophysical properties and dynamic processes, an energy-level diagram for Methyl Red molecules in rigid polymer is introduced to explain these observations.     

Micro- and Nano-scale Measurement of the Thermophysical Properties of Polymeric Materials Using Atomic Force Microscopy

To realize the benefits and optimize the performance of micro- and nano-structured materials and thin films, designers need to understand and thus be able to characterize their thermal, thermophysical, and thermomechanical properties on appropriate length scales. This paper describes the determination of glass-transition temperatures of polymers on the micro-scale, obtained from contact force–distance curves for poly(methyl methacrylate) and poly(vinyl acetate) measured using an atomic force microscope (AFM). Measurements were made using a standard AFM tip where thin films were heated using a temperature controlled hot stage and by using a scanning thermal microscopy (SThM) probe. The latter was used either with the hot stage or with the SThM probe providing a localized heating source via Joule heating. Differences in the glass-transition temperature measured using the hot stage and Joule heating were apparent and considered to be due to heat transfer effects between the probe, specimen, and surroundings. Gradients of force–distance curves, pull-off and snap-in forces, and adhesion energy were obtained. The results suggest that the onset of changes in the material’s mechanical properties at the glass transition was found to be dependent on the mechanical property measured, with pull-off force values changing at lower temperatures than the snap-in force and adhesion energy.     

Electrical properties of thin V-A1 alloy films

The electrical properties of V-Al alloy films of various thicknesses and compositions were studied. The V-Al films were evaporated using an electron gun in vacuum (pressure p ≈ 10^-5 Pa) onto quartz substrates at room temperature. The film resistivity vs. temperature was measured in situ in a vacuum of 10^-8-10^-6 Pa at temperatures ranging from 300 to 850 K. A saturation effect was observed in the resistivity. The above findings were analysed in terms of the shunt resistance model.     

Structural changes of evaporated tantalum during film growth

According to the Sondheimer approximation the resistivity of an infinitely thick film with the same structure as a thin film can be determined from the graph of ?d versus d (where ? is the resistivity and d the film thickness). Since the resistivity is highly sensitive to film structure it is possible to observe structural changes by making in situ measurements during film growth. From these measurements it can be established that tantalum films condense under ultrahigh vacuum at room temperature onto oxide substrates (e.g. Corning 7059 glass, sapphire or BeO) as the β phase. It can be demonstrated that the transition temperature from β-Ta to α-Ta decreases with increasing film thickness. Increasing the substrate temperature (e.g. to 300 °C) causes the tantalum films to nucleate first as the β phase and to be converted into α-Ta during film growth. This effect is influenced by the substrate. The thickness dependence of the structure of tantalum was confirmed by ultrahigh vacuum in situ annealing experiments and electron optical investigations.     

Thermally assisted semiconductor-like to insulator transition in gold-poly(methyl methacrylate) nanocomposites

Gold-polymethylmethacrylate (PMMA) nanocomposites were fabricated by mixing gold nanoparticles capped with oleylamine in polymethylmethacrylate. The samples were analysed using UV-vis absorption spectroscopy, transmission electron microscopy, small angle x-ray scattering, Fourier transform infrared spectrometry (FTIR) and x-ray photoelectron spectroscopy (XPS). Electrical resistivity of nanocomposite samples was measured by a four-probe technique in the 70-300?K range. The nanocomposites showed a transition with an onset at ～160-165?K. They exhibited a semiconductor-like conductivity at higher temperatures and nearly temperature independent conductivity at lower temperatures. The interfacial interaction of Au nanoparticles and PMMA polymer is investigated using FTIR and XPS. A ligand-exchange process occurs when capped gold nanoparticles are incorporated in PMMA polymer.     

Stress Evolution With Temperature in Titanium‐Rich NiTi Shape Memory Alloy Films

Abstract: The effect of deposition temperature on residual stress evolution with temperature in Ti‐rich NiTi films deposited on silicon substrates was studied. Ti‐rich NiTi films were deposited on 3″ Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 °C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 °C and the lowest for the film deposited and annealed at 300 °C. All the three films were found to be amorphous in the as‐deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 °C) was similar for all three films although the spike in tensile stress, which occurs at ～330 °C, was significantly higher in the film deposited and annealed at 300 °C. All the films were also found to undergo partial crystallisation on heating up to 450 °C and this resulted in decrease in the stress values around 55–60 °C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 °C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.     

低温与真空条件下1Cr18Ni9Ti钢的疲劳行为

分别在室温大气、室温真空及低温真空几种环境条件下,对1Cr18Ni9Ti钢进行对称载荷拉-压疲劳试验,利用TEM观察疲劳断口附近的显微组织,研究了环境因素对疲劳性能的影响,并对影响的原因进行了分析和讨论.研究表明:1Cr18Ni9Ti钢在低温真空条件下疲劳性能显著提高;疲劳断口附近出现大量板条马氏体;真空与低温显著提高1Cr18Ni9Ti钢疲劳性能的原因与真空对裂纹表面的净化效应,以及低温促进疲劳裂纹前沿形成板条马氏体有关.     

Electrical properties of vacuum annealed CdS films

Cadmium sulphide (CdS) films were evaporated in vacuum on glass substrates maintained at room temperature. These films were later annealed in vacuum at temperatures in the range 30 to 300° C. The variation of d.c. electrical conductivity was studied in the temperature range 100 to 300 K. While the conductivity data in the range 100 to 150 K were observed to follow Mott's variable range hopping process, the conductivity in the high-temperature region (150 to 300 K) could be explained by Seto's model.     

Effect of vacuum and H2S annealing on the electrical properties of CdS thin films

Polycrystalline CdS films were grown on to glass substrates kept at room temperature using a resistive heating technique. Films grown from the same batch were annealed in vacuum and H₂S vapour at 300 and 400° C for various periods up to 2 h. D.C. conductivity studies were made on these films in the temperature range 77 to 300 K. It was found that the d.c. conductivity decreases with vacuum and H₂S annealing; however, decrease is more significant in the latter films. X-ray diffraction studies were also carried out on these films.     

Effect of heating rate on the hysteresis in the phase transition in silver telluride thin films

The electrical resistance of vacuum deposited silver telluride thin films was measured in the temperature range from 300 to 430 K at different heating rates. It is found that silver telluride films undergo a structural phase transition, with a hysteresis. The phase transition occurs over a wide temperature range of about 30 K and the transition temperature as well as the hysteresis width are found to be influenced by the heating rate. The effect of heating rate on the phase transition temperature and the hysteresis are discussed.     

Temperature dependence of the energy dissipation in dynamic force microscopy

The dissipation of energy in dynamic force microscopy is usually described in terms of an adhesion hysteresis mechanism. This mechanism should become less efficient with increasing temperature. To verify this prediction we have measured topography and dissipation data with dynamic force microscopy in the temperature range from 100?K up to 300?K. We used 3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) grown on KBr(001), both materials exhibiting a strong dissipation signal at large frequency shifts. At room temperature, the energy dissipated into the sample (or tip) is 1.9?eV/cycle for PTCDA and 2.7?eV/cycle for KBr, respectively, and is in good agreement with an adhesion hysteresis mechanism. The energy dissipation over the PTCDA surface decreases with increasing temperature, yielding a negative temperature coefficient. For the KBr substrate, we find the opposite behaviour: an increase of dissipated energy with increasing temperature. While the negative temperature coefficient in the case of PTCDA agrees rather well with the adhesion hysteresis model, the positive slope found for KBr points to a hitherto unknown dissipation mechanism.     

Preparation and properties of antiperovskite Mn3NiN thin film

The magnetic and electronic transport properties of the antiperovskite Mn₃NiN thin film deposited on quartz substrate using magnetron sputtering were investigated. The film shows a (100) preferred orientation. It is worthwhile noting that a positive magnetoresistance (MR) effect was found in the whole measured temperature region and the maximum MR value by 31% was obtained at about 300 K under 2 T. On the other hand, when cooling from room temperature, a spin-glass behavior was also observed in the Mn₃NiN film and the Tb shifted to lower temperature with increasing external magnetic field. In contrast to the bulk counterpart, the temperature dependent resistivity of the film shows a semiconductor-like behavior.     

Hall effect in chromium-copper alloy films

Chromium-copper alloy was deposited in thin film form by vapor deposition at room temperature onto well cleaned glass substrates at a pressure of 10⁻⁵ Pa. The polycrystalline alloy thus formed was vacuum annealed up to a temperature of 525 K. Hall coefficient R_H and Hall mobility μ have been measured for annealed polycrystalline chromium-copper alloy films at 300 K. Below 50 nm, a film thickness dependence (size effect) was observed. Data on polycrystalline alloy film agree well with Sondheimer theory for perfect diffuse scattering so that the best fit mean free path value can be calculated. The calculated mean free path value (37 nm) agrees fairly well with the mean free path value reported from electrical resistivity data (37.6 nm) and temperature coefficient of resistivity data (36.3 nm) for perfect diffuse scattering. The decline of the Hall mobility is expected theoretically. The bulk Hall coefficient and bulk mobility of the alloy can be predicted from the experimental data and comes out to be −5.2 × 10⁻⁵ cm³/coulomb and 13.57 cm²/v-sec respectively. The results are discussed.     

Investigation of distribution and state of rare-earth elements in pure aluminium by method of internal friction

The dislocation internal friction at room temperature for 99.99% pure Al with different rare-earth (RE) contents (0–3 wt %) was measured with Ke's torsion pendulum in a vacuum. A new method is presented for accurately determining the parameters of Granato-Lück plot and processing the experiment data. It was found that at room temperature the unpinning stress of dislocations and the slope of the G-L plot increase with RE content and tend to change little when RE ? 0.1 %. The binding energy between RE atom and dislocation, and the lattice solubility of RE in Al at room temperature were obtained according to the dependence of unpinning strain on temperature, which are about 0.19 eV and 0.0003 wt%, respectively. The existence of solid solution RE in dislocations and the lattice was confirmed and some behaviour of RE in the interior of the Al grain mentioned in part I was also proved.     

Intercalation of iridium atoms into a graphene layer on a metal

The intercalation of iridium atoms into a graphene (two-dimensional graphite) layer on a metal substrate (iridium (111) crystal face) has been studied. It is established that a thin film of iridium deposited at room temperature onto the graphene surface in a vacuum is completely destroyed on heating to 1000–1200 K and iridium atoms pass to an intercalated state between the graphene layer and the substrate. Vacuum deposition of iridium directly onto a heated sample of graphene/Ir(111) at 1000–1500 K leads to the accumulation of Ir atoms only in the intercalated state, while the outer surface of graphene remains free of the adsorbate.     

Suction component in adhesion of mushroom-shaped microstructure

To shed light on the role of suction in adhesion of microstructure with mushroom-shaped terminal elements, we compared pull-off forces measured at different retraction velocities on structured and smooth surfaces under different pressure conditions. The results obtained allow us to suggest that suction may contribute up to 10 per cent of the pull-off force measured on the structured surfaces at high velocities. We therefore conclude that the attachment ability of this biomimetic adhesive must not be solely based on van der Waals forces. Our experiments also suggest a change in visco-elastic properties of the structured surfaces compared with the bulk material. Based on the results obtained, it is assumed that this adhesive may be suitable in dynamic pick-and-drop processes even under vacuum conditions at which sufficiently high adhesive capability is maintained.     

Synthesis,characterization and temperature studies on the conductivity of AlCl<Superscript>−</Superscript><Subscript>4</Subscript> ion doped polypyrrole

Synthesis of free standing conducting polypyrrole film using room temperature melt as the electrolyte is reported. We also report variation in the contribution of ionic conductance with temperature of the polymer film by four probe method and electrochemical properties like diffusion coefficient and ionic mobility of AlCl⁻₄ doped polypyrrole film. An attempt has been made to arrive at the stability of charge carrier concentration over a temperature range of 295 to 350 K under vacuum. The film was characterized by optical techniques and scanning electron micrography.