Thermal Wave Microscopy Research Articles

Nanoscale Imaging and Measurements of Grain Boundary Thermal Resistance in Ceramics with Scanning Thermal Wave Microscopy.

Material thermal conductivity is a key factor in various applications, from thermal management to energy harvesting. With microstructure engineering being a widely used method for customizing material properties, including thermal properties, understanding and controlling the role of extended phonon-scattering defects, like grain boundaries, is crucial for efficient material design. However, systematic studies are still lacking primarily due to limited tools. In this study, we demonstrate an approach for measuring grain boundary thermal resistance by probing the propagation of thermal waves across grain boundaries with a temperature-sensitive scanning probe. The method, implemented with a spatial resolution of about 100 nm on finely grained Nb-substituted SrTiO3 ceramics, achieves a detectability of about 2 × 10-8 K m2 W-1, suitable for chalcogenide-based thermoelectrics. The measurements indicated that the thermal resistance of the majority of grain boundaries in the STiO3 ceramics is below this value. While there are challenges in improving sensitivity, considering spatial resolution and the amount of material involved in the detection, the sensitivity of the scanning probe method is comparable to that of optical thermoreflectance techniques, and the method opens up an avenue to characterize thermal resistance at the level of single grain boundaries and domain walls in a spectrum of microstructured materials.

Measurement of thermal conductivity of Bi2Te3 nanowire using high-vacuum scanning thermal wave microscopy

With the increasing application of nanomaterials in the development of high-efficiency thermoelectric energy conversion materials and electronic devices, the measurement of the intrinsic thermal conductivity of nanomaterials in the form of nanowires and nanofilms has become very important. However, the current widely used methods for measuring thermal conductivity have difficulties in eliminating the influence of interfacial thermal resistance (ITR) during the measurement. In this study, by using high-vacuum scanning thermal wave microscopy (HV-STWM), we propose a quantitative method for measuring the thermal conductivity of nanomaterials. By measuring the local phase lag of high-frequency (>10 kHz) thermal waves passing through a nanomaterial in a high-vacuum environment, HV-STWM eliminates the measurement errors due to ITR and the distortion due to heat transfer through air. By using HV-STWM, we measure the thermal conductivity of a Bi2Te3 nanowire. Because HV-STWM is quantitatively accurate and its specimen preparation is easier than in the thermal bridge method, we believe that HV-STWM will be widely used for measuring the thermal properties of various types of nanomaterials.

Measurement of thermal transport using time-resolved thermal wave microscopy

A theoretical and experimental analysis of a time resolved thermal wave microscopy (TRTWM) technique used for thermal transport measurements is presented. TRTWM utilizes elements of frequency and time domain laser based thermoreflectance techniques and is well suited to measure both lateral and cross plane thermal transport. A primary advantage of this method is that the pump and probe spot sizes do not have to be known accurately. Implementation of TRTWM to measure thermal transport in oxide substrates coated with thin metal films is demonstrated.

Measurement of the Kapitza resistance across a bicrystal interface

The Kapitza resistance across a Si bicrystal interface was measured using a pump probe optical technique. This approach, termed time resolved thermal wave microscopy (TRTWM), uses ultrafast laser pulses to image lateral thermal transport in bare semiconductors. The sample geometry is that of a Si bicrystal with the vertically oriented boundary intersecting the sample surface. High resolution transmission electron microscopy of the boundary region revealed a thin SiO2 layer at the interface. By comparing experimental results with a continuum thermal transport model the Kapitza resistance between the Si and SiO2 was estimated to be 2.3 × 10−9 m2K/W.

Lateral Looking Time-Resolved Thermal Wave Microscopy

Time-resolved thermal wave microscopy was used to measure lateral thermal transport in a thin metallic film on an insulating substrate. The basis of this approach is to decompose the reflectivity signal into a component that varies with delay time and a steady state component that varies with pump modulation frequency. The transient component is a summation of thermal waves at integral multiples of the pulse repetition frequency (76 MHz). The steady state component depends only on thermal waves at the pump chopping frequency (10-100 kHz). It is shown that for long delays, the steady state component is dominant and can be used to measure the thermal diffusivity.

Combined Electrical and Optical Heating in Thermal Wave Microscopy of Semiconductor Devices

Combined Electrical and Optical Heating in Thermal Wave Microscopy of Semiconductor Devices

Limitations of 1D thermal model in comparison with 2D model of high power thyristor structure in thermal wave microscopy

Thermal-wave methods are magnificent tool for visualisation and analysis of thermal non-uniformity in solids. Special case of thermal non-uniformity is lack of adhesion in multilayer structures. This very important parameter effects on efficiency of draining of the heat and the reliability of many of semiconductor devices. This paper presents possibility of detection of exfoliation in high-power thyristor structure with the help of photoacoustic microscope. Values of temperature contrasts were evaluated from thermal-wave images, which were registered in harmonic modulation and pulse modulation modes. Both methods are characterised by similar sensitiveness for lack of adhesion, however pulse modulation mode makes the time of investigation significantly shorter. Comparison of experimental data with 1-D modelling results shows differences between theoretical and experimental values of temperature contrast in range of low frequencies (harmonic modulation mode) and long times of registration (pulse modulation mode). These differences appear because the 1-D model does not take limited lateral dimensions of excitation and thermal non-uniformity into consideration. Therefore 2-D modelling process was performed in order to explain the influence of geometrical factors on temperature contrasts. On the other hand, analysis of results of 2-D modelling makes the estimation of real delamination more accurate.

Scanning Thermal Wave Microscopy (STWM)

This paper presents a technique, scanning thermal wave microscopy (STWM), which can image the phase lag and amplitude of thermal waves with sub-micrometer resolution by scanning a temperature-sensing nanoscale tip across a sample surface. Phase lag measurements during tip-sample contact showed enhancement of tip-sample heat transfer due to the presence of a liquid film. The measurement accuracy of STWM is proved by a benchmark experiment and comparison to theoretical prediction. The application of STWM for sub-surface imaging of buried structures is demonstrated by measuring the phase lag and amplitude distributions of an interconnect via sample. The measurement showed excellent agreement with a finite element analysis offering the promising prospects of three-dimensional thermal probing of micro and nanostructures. Finally, it was shown that the resolving power of thermal waves for subsurface structures improves as the wavelengths of the thermal waves become shorter at higher modulation frequencies.

New Developments in Thermal Wave Microscopy

New Developments in Thermal Wave Microscopy

Preliminary Experimental Study for Surface Plasmon Thermal Wave Microscopy

A Preliminary experiment for surface plasmon thermal wave microscopy (SPTWM) is reported. This is a new technique of nondestructive evaluation of thin films using thermal waves excited by energy conversion due to electron-phonon interaction with nonradiative surface plasmon.

Selected contactless optoelectronic measurements for electronic applications (invited)

The area of contactless characterization techniques for electronic applications is too wide a topic to be considered in full detail inside a single review article. On this line of argument, we considered only some contactless optoelectronic techniques paying particular attention to those optoelectronic techniques which can be easily employed for material diagnostics or to perform simple voltage or temperature measurements in electronic devices. In spite of their simplicity and reliability, some of these techniques are not well known by the electronic community. The considered techniques include: scanning electron, photoexcitation and force microscope, electro-optical sampling techniques, charge sensing probes, second harmonic generation, and photoacoustic and thermal wave microscopy. Applications to signal processing, detection and measurement of microcracks, temperature, lifetime, surface recombination velocity, diffusivity, and injection level are discussed. The article is, then, completed by a very rich bibliography and by three appendices describing some physical phenomena (electro-optic, plasma optic, and photoacoustic effect) instrumental for understanding most of the considered techniques. Most of the considered techniques can be mounted in almost each laboratory as they do not require particularly expensive and bulky instrumentation.

Scanning Electron-Acoustic Microscopy: Do You Know Its Capabilities?

Characterization of materials usually requires microscopy techniques. Some of the most useful are based on a scanning microscope and involve scanning the sample surface with a focused beam (e.g., photons, electrons, ions, etc.). For example, photoacoustic microscopy uses a laser beam, acoustic microscopy uses an ultrasound beam, and scanning electron microscopy uses an electron beam. The interaction between the material and the beam produces a signal that can be used to generate a two-dimensional image.In scanning photoacoustic microscopy (SPAM), an intensity-modulated light beam is used to produce oscillations in the surface temperature of the sample. These oscillations induce changes in the pressure of a fluid in the photoacoustic cell as a consequence of the periodic heat conduction from the surface to the cell fluid. Subsequently many material-characterization methods have employed the same philosophy as SPAM, using a modulated beam as an excitation probe. The breadth of such techniques is due to the large number of possible excitation sources and signal detectors that have been proposed to probe the specimen response. In particular, scanning electron-acoustic microscopy (SEAM), also referred to as thermal wave microscopy, is a technique based on the utilization of a scanning electron microscope developed in 1980 and applied in recent years to material characterization. It can be considered an additional mode of scanning electron microscopy (SEM), which uses the generation of acoustic waves in the sample. Most reviews have concentrated on the application of SEAM to metals and semiconductors. However many other possibilities exist.

Mikrothermographie als Werkzeug zur Prüfung von Klebeverbindungen

Thermal wave microscopy provides a reliable tool for non-contact, non-destructive testing of adhesive bonding of thin walled materials. The spatial distribution of the adhesive under a metal foil can be visualised during all stages of the curing process.

Damage analysis and engineering for ion implantation in ULSI process

To evaluate damaged silicon crystals, as implanted or after annealing in ULSI process, transmission electron microscopy (TEM), thermal wave, and scanning Raman microscopy techniques provide complementary methods for the detection of crystal lattice imperfections. Depth profile analysis using anodic oxidation-HF etching techniques, have also been developed for damage characterization. A new technique by combination of the anodic oxidation-HF etching and an atomic force microscopy (AFM) techniques is very suitable for the observation of the structure and distribution of the secondary defects. By using these damage characterization methods, clear understanding and effective prevention of the critical damage during ion implantation hold great promise for ULSI manufacturing.

Thermal-wave microscopy in corrosion studies

Thermal-wave microscopy in corrosion studies

Photodeflection signal formation in thermal wave spectroscopy and microscopy of solids within the framework of wave optics. “Mirage” effect geometry

A theoretical study of the photodeflection signal formation within the framework of wave optics is presented. It is shown that on this basis the correct quantitative interpretation of the data obtained in photodeflection experiments with solids is possible.

Determination of the Dislocation Network Density in GaAs Using Thermal Wave Microscopy

AbstractThe pattern and density of dislocations in GaAs is thought to affect the ultimate performance of finished devices. Previous studies of dislocation networks have usually involved molten KOK etching of GaAs wafers or X-ray topography. A relatively new technique, Thermal Wave Microscopy (TWM), offers an alternative method of analysis. High frequency blanking of the scanning electron beam in an SEM produces thermal waves that propagate approximately 1–2 wavelength through a sample, are then carried by thermoacoustic waves and detected by a piezoelectric transducer. Dislocations, microcracks, and voids will disturb this wave and the resulting image will show a change in contrast (bright or dark) at the defect site. Resolution is dependent on the thermal properties of the material being analyzed as well as on the accelerating voltage, beam current, beam blanking frequency and phase of the electron beam. TWMim ages of dislocation networks in as-received GaAs are very similar in appearance to the results of molten KOH etching. TWM is a relatively new technique for microanalysis. Its full range of applications are still being explored. For determination of dislocation networks it is a faster, less cumbersome method of analysis. TWM is a basically nondestructive technique involving none of the uncertainties of molten KOH etching (etch time, etch uniformity). For this reason TWM is recommended as an alternative analytical technique.

Thermal-wave microscopy: Allan Rosencwaig Solid St. Technol., 91 (March 1982)

Thermal-wave microscopy: Allan Rosencwaig Solid St. Technol., 91 (March 1982)

Thermal-wave microscopy and its application to imaging the microstructure and corrosion of cold-rolled steel

Thermal-wave microscopy (TWM), which employs heat flow to probe variations in the thermal properties of solid materials, can provide micron-level resolutions of subsurface features of opaque samples, this paper describes the principle of TWM, reviews its applications in material science, and presents the results of studies using this technique to imaging the microstructure and corrosion of cold-rolled steels. Preliminary results indicate that TWM can image the microstructure of cold-rolled steel with or without a corrosion layer. The results obtained also suggest that the technique can monitor and assess corrosion in its early stage of formation.

Detection of subsurface cracks and delaminations in polymeric materials by electron thermoelastic acoustic microscopy

Electron Thermoelastic Acoustic Microscopy (ETEAM), also termed Electron Acoustic Microscopy and Thermal Wave Microscopy, detects subsurface cracks, delaminations, and voids at depths up to at least 100 µm, as first reported by Cargill, The technique has previously been applied only to beam-insensitive materials, since high beam currents of about 1 µamp (1000 times greater than for routine SEM) are required to obtain adequate signal intensity. We present here a procedure for extending the technique to beam-sensitive polymeric materials.In the ETEAM technique, a periodic electron beam (frequency V = 10 kHz-10 MHz) generates an acoustic wave, leading to a periodic force on a transducer attached to the specimen. The ETEAM image is derived from the transducer voltage output as the electron beam is scanned over the sample in an SEM. The inability of an acoustic wave to travel through a delamination results in it being transmitted around the delamination as a transverse shear wave (Fig. 1).