The Ångström method is a promising thermal diffusivity measurement method for microfibers. Based on the heat-loss Ångström method and micro-Ångström method, the FFT (Fast Fourier Transform) Ångström method can be used to shorten the testing time and enhance the testing robustness of thermal conductivity. The FFT Ångström uses multi-frequency superimposed input signals and then uses the FFT for frequency division analysis. Since different frequencies are input at the same time, the measuring time is greatly reduced. Moreover, because different frequencies are input in the same environment, the random and environmental perturbations of the frequencies are the same, enhancing the fitting robustness. In contrast, the single feeding strategy is relatively time-consuming, and its measurement homogeneity for different frequencies cannot be guaranteed. By comparing the measurement results from a multi-frequency input and separated single-frequency input, the FFT shows good feasibility and robustness. It may also have great potential in other types of thermal wave measurements.

Damage and annealing recovery of boron-implanted ultra-shallow junction: The correlation between beam current and surface configuration

This paper explored the results of experimental investigation on carbon fiber reinforced polymer (CFRP) composite sample with thermal wave technique. The thermal wave technique combines the advantages of both conventional thermal wave measurement and thermography using a commercial Infrared camera. The sample comprises the artificial inclusions of foreign material to simulate defects of different shape and size at different depths. Lock-in thermography is employed for the detection of defects. The temperature field of the front surface of sample was observed and analysed at several excitation frequencies ranging from 0.562 ㎐ down to 0.032 ㎐. Four-point methodology was applied to extract the amplitude and phase of thermal wave’s harmonic component. The phase images are analyzed to find qualitative and quantitative information about the defects.

The influence of nitrogen and oxygen additions on the thermal characteristics of aluminium-based thin films

Multifunctional coatings consisting of transition metal oxycarbides and oxynitrides deposited by physical vapour deposition techniques on tool steel are analysed in this work by means of modulated IR radiometry (MIRR), a non-contact non-destructive thermal wave measurement technique, with respect to the thermal transport properties relevant for time-dependent surface heating processes of coating–substrate systems. In order to interpret the measured data quantitatively, an inverse solution of the two-layer thermal wave problem is applied, which relies on the thermal wave phase lag data measured as a function of modulation frequency of the periodically modulated laser beam heating intensity. Based on these measurements and their quantitative interpretation, correlations between the thermal transport properties of the coatings and their deposition conditions have been found, which can be used to monitor deposition processes. For a second objective of this work, namely to determine the film thickness by means of MIRR, different sets of thin films of approximately constant thermal transport properties, but differing film thickness, have been measured. To discuss the limitations and error limits of these non-contact non-destructive measurements of the coating thickness, the results obtained by MIRR are compared with the coating thickness determined by destructive measurements.

Analysis of influence of Yb concentration on thermal, elastic, optical and lattice parameters in YAG single crystal

A short review of thermal wave measuring methods is presented in the paper. Based on fundamental laws of heat transport, experimental methods for determination of thermal properties of solids are divided into two groups – steady flux techniques and variable flux ones. Special attention is paid to the wave methods belonging to the second group and methods used by the author in his experiments. The idea of Angstrom's method for determination of the thermal diffusivity of metals is reminded. Then different modifications of this classical technique using in investigations of bulk materials and thin films are described. Examples of a few thermal wave measurements are also presented.

Thermal wave phase measurements are reported on the drying of wet paint films on aluminium substrates. Measurements of the change in thickness as the paint dries have also been obtained using a differential focussing technique on an optical microscope. By including the optical microscope measurements of the drying paint film thickness together with estimates for the density and thermal properties of the drying and cured paint, predictions have been made of the thermal phase/thickness relationships for the wet, dry, curing and cured paints. It is concluded that a phase measurement on the wet paints could be used to predict a final cured paint thickness with an accuracy of approximately ±2 μm. Errors in predicting cured film thickness from a wet film thermal phase measurement arises principally from uncertainty over the solvent content of the wet paint film, the state of cure, and the consequent uncertainty over the paint density and thermal properties.

In this paper, a method of determination of thermal properties of multilayer structures using thermal wave measurements and artificial neural networks (ANN) is described. The copper-corundum bondings were examined. The presented method is based on analysis of amplitude and phase characteristics of the photoacoustic signal and usage of ANN for determination of thermal parameters.

Abstract In this paper, a thermal wave in the bath of superfluid helium II is measured by a new type of superconductor temperature sensor under different heat fluxes and bath temperatures, and at the same time, a thermal shock wave is also studied experimentally and theoretically. © 2001 Scripta Technica, Heat Trans Asian Res, 30(5): 419–425, 2001

Surface damage induced by reactive ion etching (RIE) was investigated in terms of its depth, distribution, and correlation with dislocation generation due to subsequent oxidation. Damage structure was evaluated using transmission electron microscopy, reflection high energy electron diffraction (RHEED), Auger electron spectroscopy, and thermal wave measurement technique. A chemical dry etching and surface analyze technique of RHEED and TW were utilized to profile the damage distribution. It is identified that the surface damaged layer consists of two parts; the upper part from the surface to about 4 nm is a heavily damaged amorphous structure containing carbon and the lower part, between 5 and 30 nm, is a single crystal Si with a lot of lattice defects. It is found that RIE damage may form film edge dislocations by the interaction of subsequent selective oxidation even though damage was minimized to suppress oxidation induced stacking faults generation. High leakage current occurs when n+–p junctions are fabricated on this RIE and selective oxidation because of these film edge dislocations. It seems that generation of film edge dislocations has correlated with this carbon contained amorphous layer.

The feasibility of an ultrasonic technique using normal-incident compressional waves and a thermal wave measurement technique was evaluated for their sensitivity to surface and subsurface damage in ceramics. Well-defined damage in the form of surface and subsurface cracks was introduced by Vickers indentation in soda-lime glass and silicon nitride. The indentation impressions were first examined by optical microscopy to identify the types of cracks and to measure the size of the indents and cracks. As expected, indentation produced median/radial cracks emanating from the indent corners and subsurface lateral cracks. The ultrasonic technique was successful in detecting the subsurface lateral cracks in both materials. The signals obtained by focusing the transducer into the material (i.e., defocusing) was used to estimate the depth of subsurface cracks. The lateral cracks and the median/radial cracks were detected by the thermal wave measurement technique using the optical beam deflection method. The lateral cracks and the median/radial cracks were identified separately by using two deflection components of the probe beam. The transverse deflection component of the probe beam was used for the detection of the median/radial cracks, whereas the normal deflection component was used for the detection of the lateral cracks. The results are discussed in terms of the applicability of these two techniques as nondestructive methods for the detection of machining-induced damage in ceramics.

This work investigates and compares three laser-based ac heating methods for measuring thermal diffusivity of free-standing thin-film structures. These methods employ a modulated laser beam as the heating source and a miniature thermocouple as the temperature sensor. Three laser beam configurations including uniform illumination, a line, and a point are utilized as the heating sources. Different models and systems are developed for these beam configurations. Samples studied include a GaAs/AlGaAs two-layer thin-film structure, a periodic GaAs/AlAs thin-film structure, and a silicon film. Both the phase and amplitude signals of the ac temperature rise of samples are used to derive their thermal diffusivities. It is found that the uniform illumination method is more susceptible to error than the other two configurations due to two-dimensional effects. Both the line and the point source configurations yield satisfactory results.

The effect of grain size on the grinding response, i. e., grinding forces, surface roughness, and grinding‐induced subsurface damage, is investigated in a series of alumina ceramics with the average grain size ranging from 3 to 35 μm. The grinding forces are measured as a function of depth of cut in surface grinding. It is found that the grinding forces decrease as the grain size is increased from 3 to 9 μm. But at larger grain sizes, the grinding forces are independent of the grain size. Subsurface damage in grinding is observed using a bonded‐interface sectioning technique. The subsurface damage is found to consist of intragrain twin/slip bands and intergranular microcracks. The density of grinding‐induced subsurface microcracks increases with the grain size. In addition to using optical microscopy on the sections of the ground specimens, a nondestructive thermal wave measurement technique is used directly on the ground surfaces for the detection of grinding‐induced subsurface microcracks. The grain size dependence of the microcrack density estimated from the thermal images is found to agree with the results obtained using the bonded‐interface technique.

The relationship between grinding forces and the material's resistance to microfracture is investigated in abrasive machining of silicon nitride ceramics. Surface grinding is performed on two forms of silicon nitride with different microstructures, and the grinding forces are measured. In addition, single-point scratching is performed on polished surfaces to amplify the damage associated with the action of an individual abrasive particle in grinding. A thermal wave measurement technique is then used on the cross sections to characterize the density of subsurface microcracks associated with scratching. Compared to a fine-grain silicon nitride, the density of microcracks in a course-grain silicon nitride is significantly larger, while the grinding force is smaller. The smaller grinding force for the coarse-grain silicon nitride is attributed to the ease of local intergranular microfracture and grain dislodgement during grinding.

The critical role of grain size in determining the nature of damage accumulation in silicon-nitride ceramics is evaluated using Hertzian contact testing. Single-cycle tests are conducted on materials of two grain sizes, 0.5 Μm (fine) and 2.0 Μm (coarse). Damage patterns for these two materials are compared and contrasted using a special bonded-interface specimen to investigate the subsurface regions. Optical and thermal wave-imaging techniques provide complementary pictures of the damage patterns: whereas the optical image maps elements of both deformation and fracture, the thermal wave image maps only the fracture. Taken together, these two imaging methods disclose a fundamental transition in the mechanical response in the two silicon nitrides, from cone-crack-dominated in the fine material to distributed-microcrack-dominated in the coarse material. Scanning electron microscopy (SEM) confirms the incidence of microfracture in the latter case. Thermal-wave measurements also allow a quantitative evaluation of the microfracture damage. Multiple-cycle tests on the coarse material show a build up of subsurface damage with increasing number of cycles, indicating mechanical fatigue. The results are discussed in terms of a shear-fault model, in which subsurface microcracks initiate from intrinsic planes of shear weakness in the microstructure. Implications concerning the microstructural design of silicon nitride ceramics for strength and wear applications are briefly considered, with reference to countervailing resisting and driving forces in the long-crack and short-crack toughness characteristics.

Si was etched with a plasma generated by an electron cyclotron resonance (ECR) source and the effects of etch‐induced damage were studied. Surface damage was evaluated by electrical characterization and surface analysis. Low ion energy and optimized reactive species concentration are necessary to minimize etch‐induced damage. The reactive species concentration is optimized when the etch conditions provide high concentration of reactive species and high etch rate. As RF power was increased from 20 to 250 W, the ideality factor for Schottky diode increased from 1.08 to 1.90 and the breakdown voltage decreased from 60 to 6 V. Using transmission electron microscopy, defect density increased from while the damage layer thickness decreased from 134 to 91 nm as RF power was increased from 50 to 500 W. The etch‐induced defects are mainly dislocation loops ranging from 1.2 to 2.4 nm. Higher RF power also caused an increase in thermal wave signal. At low self‐induced bias voltage (−50 V), leakage current and thermal wave signal increased with increasing microwave power. However, Schottky diode characteristics improved at higher microwave power when high self‐induced bias voltage (−150 V) was used. Addition of Ar degraded the Schottky diode performance and increased thermal wave signal. After removing 60 nm from the etched surface using low energy chlorine species, full recovery in the device performance is observed as indicated by the electrical and thermal wave measurements. A new damage model is proposed to relate the generation of defects to the etch conditions by comparing the increase in leakage current of the Schottky diodes after dry etching. The defect density is found to increase with self‐induced bias voltage and microwave power, but to decrease with etch rate and distance from the etched surface. Good agreement is obtained between the measured and the predicted Schottky diode characteristics.

Possible approaches to thermal wave measurement of thermal diffusivity were considered. The calculation of the transverse photodeflection signal in the framework of wave optics proves to be a more accurate approach compared to that of geometrical optics. The influence of the account of wave optics effects on the accuracy of the thermal diffusivity determination was theoretically analyzed under various conditions. It was shown that a difference between the thermal diffusivities calculated using both approaches is most apparent when the thermal diffusivity of a sample is smaller than that of the deflecting medium, at high modulation frequencies and/or at large probe beam radius.

The technique of thermal wave thermography combines advantages of both conventional thermal wave measurement and thermography using a commercial IR camera. This technique allows for shorter imaging time and depth profiling. Non-uniformity of heating area and optical surface structures can be suppressed in phase images. Several examples show the potential applications of thermal wave thermography in the field of non-destructive testing.

Abstract Recently a method for the evaluation of pyroelectric profiles from thermal wave measurements has been introduced, which is based on the construction of a scanning function from the measured pyroelectric spectra. This procedure is extended for the application to thermal pulse data. Well adapted to the propagation behaviour of thermal waves, the scanning function algorithm avoids problems with oscillations and instabilities and delivers an approximated polarization distribution in a very simple and direct way. An on-line analysis of thermal data is possible, giving access to a thermal recording of dynamic processes. The mathematical procedure and its physical basis are given together with numerical and experimental examples.