- Andreas Mandelis is a Full Professor of Mechanical and IndustrialEngineeringedit
Non-conventional (anomalous) current–voltage characteristics are reported with increasing frequency for colloidal quantum dot-based (CQD) solar cells.
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Active infrared thermography has gained increasing popularity for nondestructive testing and evaluation in various industrial fields, especially for composite structures. In this regard, thermal wave radar (TWR) imaging is recognized as... more
Active infrared thermography has gained increasing popularity for nondestructive testing and evaluation in various industrial fields, especially for composite structures. In this regard, thermal wave radar (TWR) imaging is recognized as the next-generation active thermography technology to obtain great resolution and depth range over the inspected objects. A critical aspect concerns the optimal test parameter selection to guarantee reliable quality assurance required for industrial products. In this work, single- and multiple-frequency TWR was investigated in a quantitative manner with the goal of optimizing the detection parameters in terms of probing range and lateral and depth resolution. The effects of test parameters, including sampling frequency, modulation frequency, chirp duration, chirp bandwidth, etc, were investigated in detail through experiments on a glass fiber reinforced polymer specimen with multi-scale diameter-to-depth ratio defects. This paper aims to help yield a...
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The extension of an earlier monolithic photopyroelectric spectroscopic model [A. Mandelis et al., Phys. Rev. B 48, 6808 (1993)] to include surface and bulk optical absorptions and the subsequent optical-to-thermal (nonradiative) energy... more
The extension of an earlier monolithic photopyroelectric spectroscopic model [A. Mandelis et al., Phys. Rev. B 48, 6808 (1993)] to include surface and bulk optical absorptions and the subsequent optical-to-thermal (nonradiative) energy conversion efficiencies associated with these sites has allowed the self-consistent determination of visible spectra of these quantities, using a very sensitive noncontact experimental configuration to obtain in-phase and quadrature photopyroelectric spectra of Ti:sapphire crystals of two thicknesses and figures of merit.
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The spectroscopic information related to the optical-absorption coefficients of solids and liquids, which is contained in the signal-magnitude and time-delay channels of cross-correlation photoacoustic spectroscopy (CPAS), has been... more
The spectroscopic information related to the optical-absorption coefficients of solids and liquids, which is contained in the signal-magnitude and time-delay channels of cross-correlation photoacoustic spectroscopy (CPAS), has been investigated. Powders of holmium oxide and aqueous solutions of black India ink of variable concentrations were used as solid and liquid samples, respectively. The experimental results were found to be in general agreement with a one-dimensional theoretical model of the CPAS-signal generation.
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A theoretical model of pulsed photothermal radiometry based on conduction-radiation theory is introduced for a two-layered medium with a first layer having optical and thermal properties different from those of the semi-infinite... more
A theoretical model of pulsed photothermal radiometry based on conduction-radiation theory is introduced for a two-layered medium with a first layer having optical and thermal properties different from those of the semi-infinite substrate. This geometry closely represents the optical and thermal properties of biotissues, a major intended application. The theory derives the spatial distribution of the frequency spectrum of the pulsed photothermal signal from the composite two-layer boundary-value problem and matches the spectral frequency domain results to the measured photothermal transients through an efficient inverse Fourier transformation algorithm, which involves the optical, thermal, and geometric parameters of the experimental system. This approach avoids the complicated and computationally expensive analytical Laplace transform approach usually adopted in similar studies and yields a complete conduction–radiation description of photothermal signals without simplifying, yet r...
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Publisher Summary Over the years, photothermal and photoacoustic-based spectroscopic techniques have proliferated as primary methodologies for measuring the optical absorption coefficient, α, in broad ranges of solids, which are not... more
Publisher Summary Over the years, photothermal and photoacoustic-based spectroscopic techniques have proliferated as primary methodologies for measuring the optical absorption coefficient, α, in broad ranges of solids, which are not easily measurable by other more conventional spectroscopic techniques. It is noted that these techniques are now widely used to measure directly the optical absorption coefficient α (λ) from a dynamic measurement of the heat released via the spatial rate of optical-to-thermal energy conversion in a material, rather than the extinction coefficient, k (λ). The major α-measuring methodologies in this field include gas-cell and piezoelectric photoacoustic spectroscopy and various photothermal spectroscopies —such as photothermal beam-deflection spectroscopy, Fourier-transform infrared photoacoustic spectroscopies, and photopyroelectric spectroscopy. This chapter illustrates description of the techniques, their instrumental implementation, and finally applications to optical-property measurements of semiconductors, specifically at a single wavelength or within a spectral range.
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Photothermal deflection spectroscopy (PDS), like the other thermal-wave methods, can be used to obtain the absorption spectra of materials. Several groups have obtained PDS spectra of semiconductor electrodes in photoelectrochemical (PEC)... more
Photothermal deflection spectroscopy (PDS), like the other thermal-wave methods, can be used to obtain the absorption spectra of materials. Several groups have obtained PDS spectra of semiconductor electrodes in photoelectrochemical (PEC) cells [1–3]. Subsequent to our original work [1], we have carried out an extensive study involving the measurement of both PDS and photoaction spectra for several different n-CdS electrodes in polysulfide electrolytes. The information obtained by the two combined spectroscopic techniques can be qualitatively compared taking into account both the magnitude and phase variations of the spectra. The phase information is especially useful in helping one to decide whether the weak subbandgap signals are due to bulk absorptions, surface absorptions, or a combination of both.
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Non-conventional (anomalous) current–voltage characteristics are reported with increasing frequency for colloidal quantum dot-based (CQD) solar cells.
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Osteoporosis is a skeletal disorder characterized by a compromised bone strength predisposing a person to an increased risk of fracture. The early detection of osteoporosis is important to a successful treatment. Current prominent bone... more
Osteoporosis is a skeletal disorder characterized by a compromised bone strength predisposing a person to an increased risk of fracture. The early detection of osteoporosis is important to a successful treatment. Current prominent bone densitometry techniques include, among others, Dual Energy X-Ray Absorptiometry (DEXA) and Mechanical Response Tissue Analysis (MRTA). However, DEXA uses ionizing radiation and MRTA results are often
Research Interests: Engineering, Materials Science, Optics, Laser, Optoelectronics, and 14 moreOrganic Semiconductor Laser, Low Power, Radiometry, Early Detection, Photothermal Therapy, Bone Loss, Ionizing Radiation, Thermal Properties, Experimental Data, Theoretical Model, IR Detector, Bone Strength, Mercury cadmium telluride, and DXA: Dual Energy X-Ray Absorptiometry
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A comparison between the conventional photothermal frequency scan method and the recently developed photothermal lock‐in rate window technique for thermal diffusivity measurements of materials, is presented. In this comparison, a... more
A comparison between the conventional photothermal frequency scan method and the recently developed photothermal lock‐in rate window technique for thermal diffusivity measurements of materials, is presented. In this comparison, a completely noncontact experimental configuration has been utilized based on infrared photothermal radiometry. This work shows that for thick materials with long thermal transport times across the sample where low‐frequency measurements are required, the frequency scan method may be more appropriate due to its simplicity. The rate window method, however, gives superior signal‐to‐noise ratio (SNR) for materials with very short thermal transport times such as metal foils, which otherwise require high frequency, low SNR measurements. A further advantage of the pulse duration‐scanned rate‐window mode is that it does not require knowledge of the instrumental transfer function as an input.
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A formalism involving the ac photocurrent and photothermal reflectance (PTR) spectroscopic response of a semiconducting p‐n junction device is presented. The differential equations for the photovoltaic and PTR signals are solved... more
A formalism involving the ac photocurrent and photothermal reflectance (PTR) spectroscopic response of a semiconducting p‐n junction device is presented. The differential equations for the photovoltaic and PTR signals are solved explicitly and special limits of use in experimental applications [J. Appl. Phys. 66, ⧠ ⧠ ⧠ ⧠ (1989), part II] are considered. The dependence of the photocurrent and PTR signal modulation frequency response on electronic transport parameters is identified and the suitability of ac PTR as a noncontact diagnostic technique is assessed in comparison with the more conventional ac photocurrent method.
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Tooth decay, or dental caries, is a widespread and costly disease that is reversible when detected early in its formation. Current dental caries diagnostic methods including X-ray imaging and intraoral examination lack the sensitivity and... more
Tooth decay, or dental caries, is a widespread and costly disease that is reversible when detected early in its formation. Current dental caries diagnostic methods including X-ray imaging and intraoral examination lack the sensitivity and specificity required to routinely detect caries early in its formation. Thermophotonic imaging presents itself as a highly sensitive and non-ionizing solution, making it suitable for the frequent monitoring of caries progression. Here, we utilized a treatment protocol to produce bacteria-induced caries lesions. The lesions were imaged using two related three-dimensional photothermal imaging modalities: truncated correlation photothermal coherence tomography (TC-PCT) and its enhanced modification eTC-PCT. In addition, micro-computed tomography (μ-CT) and visual inspection by a clinical dentist were used to validate and quantify the severities of the lesions. The observational findings demonstrate the high sensitivity and depth profiling capabilities...
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Development of accurate and sensitive dental imaging technologies is a top priority in the pursuit of high-quality dental care. However, while early dental caries detection and routine monitoring of treatment progress are crucial for... more
Development of accurate and sensitive dental imaging technologies is a top priority in the pursuit of high-quality dental care. However, while early dental caries detection and routine monitoring of treatment progress are crucial for effective long-term results, current radiographic technologies fall short of this objective due to low sensitivity for small lesions and use of ionizing radiation which is unsuitable for frequent monitoring. Here we demonstrate the first application of enhanced Truncated Correlation-Photothermal Coherence Tomography (eTC-PCT) to dental imaging. eTC-PCT is non-invasive and non-ionizing, operates well below the maximum permissible exposure (MPE) limit, and features 3D subsurface imaging capability with operator controlled axial resolution. We explore the potential of this method for dental applications and demonstrate its capability for depth-resolved tomographic 3D reconstructions of the details and subsurface extent of a variety of dental defects. To th...
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A detailed photothermal electrostatic consideration of the Pd-pyroelectric junction H 2 sensor is presented. Experimental evidence is in agreement with the fundamental features of the theory, which supports two possible mechanisms of... more
A detailed photothermal electrostatic consideration of the Pd-pyroelectric junction H 2 sensor is presented. Experimental evidence is in agreement with the fundamental features of the theory, which supports two possible mechanisms of ac-mode device operation: pyroelectric coefficient dependence on the hydrogenic dipole-induced charge density at the Pd-insulator (polyvinylidene fluoride, PVDF) interface; upon H 2 adsorption, absorption and diffusion into the Pd matrix, and Pd work-function shift due to hydrogen absorption. The dominant operating mechanism is found to depend on the experimental conditions. The concept of image dipole thermostatistical vibration and libration in the pyroelectric matrix is further successfully used to explain the temperature dependence of the photopyroelectric signal in support of the former above-mentioned mechanism.
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Research Interests: Physics, Optics, Medicine, Oscillations, Physical, and 4 moreElectric Field, Fourier Series, Amplitude, and Excitation
Green-function-based thermal-wave fields were compared in the case of 2- and 3-dimensional geometries, with the intention of resolving the boundary value problems through the effects of the assumed boundary conditions for a given... more
Green-function-based thermal-wave fields were compared in the case of 2- and 3-dimensional geometries, with the intention of resolving the boundary value problems through the effects of the assumed boundary conditions for a given geometry. It was found that in a number of conventional photothermal configurations it is important to identify the proper boundary conditions in order to correctly formulate the problem and perform accurate thermophysical measurements.
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In this work, the optical and thermal properties of tissue-like materials are measured using frequency-domain infrared photothermal radiometry. This technique is better suited for quantitative multi-parameter optical measurements than the... more
In this work, the optical and thermal properties of tissue-like materials are measured using frequency-domain infrared photothermal radiometry. This technique is better suited for quantitative multi-parameter optical measurements than the widely used pulsed photothermal radiometry (PPTR), due to the availability of two independent signal channels, amplitude and phase, and the superior signal-to-noise ratio provided by synchronous lock-in detection. A rigorous three-dimensional thermal-wave formulation with a three-dimensional diffuse and coherent photon density-wave source is applied to data from model phantoms. The combined theoretical, experimental, and computational methodology shows good promise with regard to its analytical ability to measure optical properties of turbid media uniquely, as compared to PPTR, which exhibits uniqueness problems. From data sets obtained using calibrated test phantoms, the reduced optical scattering and absorption coefficients were found to be within 20% and 10%, respecti...
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An infrared photopyroelectric spectrometer with real‐time spectrum normalization capability measurements has been optimized and used for the spectroscopy of crystalline Ge, performed as a function of wavelength (1700–1960 nm) and... more
An infrared photopyroelectric spectrometer with real‐time spectrum normalization capability measurements has been optimized and used for the spectroscopy of crystalline Ge, performed as a function of wavelength (1700–1960 nm) and modulation frequency (0.5 to 400 Hz), to determine the optical absorption and nonradiative quantum efficiency spectra. High‐modulation‐frequency (thermally thick limit: f > 40 Hz) data yielded the optical absorption‐coefficient spectrum, while at low modulation frequency (thermally thin limit: f<15 Hz) the nonradiative quantum efficiency spectrum was obtained self‐consistently by substitution of the experimental optical absorption coefficient spectrum to the thermally thin limit photopyroelectric theory. The experimental results will be discussed in the light of an existing photopyroelectric model [A. Mandelis and M. M. Zver, J. Appl. Phys. 57, 4421 (1985)] and in terms of well‐established semiconductor germanium physics.
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The first-ever application of boxcar time-domain photothermal radiometry to the study of energy conversion processes in Ti: Saphire laser-quality rods is reported. The major result is the measurement of the polish-dependent surface... more
The first-ever application of boxcar time-domain photothermal radiometry to the study of energy conversion processes in Ti: Saphire laser-quality rods is reported. The major result is the measurement of the polish-dependent surface non-radiative energy generation rates.
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Photothermal, or thermal-wave, techniques for monitoring thermal and electronic properties of materials have recently been applied to high-Tc superconductors. Among the unique aspects of photothermal methods in these applications is their... more
Photothermal, or thermal-wave, techniques for monitoring thermal and electronic properties of materials have recently been applied to high-Tc superconductors. Among the unique aspects of photothermal methods in these applications is their ability for precise, noncontact, nondestructive evaluation. As such, there has been increasing use of these techniques in characterizing single-crystalline and thin-film superconductors, in addition to the polycrystalline and ceramic compounds. This review highlights the theoretical background for thermal-wave characterization, and examines various practical measurement methodologies and their associated instrumentation. Also discussed are specific photothermal techniques for the determination of the temperature-dependent specific heat, thermal conductivity, thermal diffusivity, the simultaneous monitoring of these thermal parameters, and scanned image thermal-wave microscopy of high-Tc superconductors. Applications include measurements on ceramic, polycrystalline and single-crystal YBa2Cu3O7-x, GdBa2Cu3O7-x, DyBa2Cu3O7-x and Bi2Sr2CaCu2Ox.
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InGaAs camera-based high-frequency heterodyne lock-in carrierographic (LIC) imaging of Si wafers and solar cells is introduced. The nonlinearity exponents of the photocarrier radiometric signals of the samples were measured by intensity... more
InGaAs camera-based high-frequency heterodyne lock-in carrierographic (LIC) imaging of Si wafers and solar cells is introduced. The nonlinearity exponents of the photocarrier radiometric signals of the samples were measured by intensity scan. Heterodyne LIC images in a wide frequency range (0.1 - 20 kHz) were obtained and the amplitude-frequency behavior was quantitatively analyzed. A contrast inversion phenomenon was observed in high frequency images which highlights image contrast from defective regions against a fading background. High frequency LIC imaging results in high-resolution and near-subsurface information, thus having excellent prospects for fundamental research and industrial in-line non-destructive testing of photovoltaic materials and devices.
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A novel hydrogen sensor made of thin, commercially available polyvinylidene difluoride (PVDF) pyroelectric film sputter-coated with palladium (Pd) is described. An infrared laser beam, produced by an infrared (ca. 800-nm) semiconductor... more
A novel hydrogen sensor made of thin, commercially available polyvinylidene difluoride (PVDF) pyroelectric film sputter-coated with palladium (Pd) is described. An infrared laser beam, produced by an infrared (ca. 800-nm) semiconductor laser, created alternating temperature gradients on the Pd-PVDF and on reference Ni-Al-PVDF films which, in turn, generated AC voltages due to the photopyroelectric effect. Exposure to hydrogen gas produces an increased differential signal between the Pd and reference electrodes; this is tentatively attributed to the adsorption and dissociation of hydrogen molecules on the Pd surface, which caused a shift on the Pd-PVDF pyroelectric coefficient, due to interactions at the Pd-PVDF interface. The differential signal has been found to follow a Langmuir isotherm in the range of 4 to 200 Pa. Other characteristics such as the response time, the reversibility, and the durability of the photopyroelectric sensor also are studied.<<ETX>>
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Abstract The photothermal origins and physical principles of the novel diagnostic technique of laser infrared photothermal radiometry of semiconductors are presented. Following super-bandgap optical excitation, it is shown that the signal... more
Abstract The photothermal origins and physical principles of the novel diagnostic technique of laser infrared photothermal radiometry of semiconductors are presented. Following super-bandgap optical excitation, it is shown that the signal consists of two contributions, one from the de-exciting carrier density (plasma wave) and another from direct absorption and heating of the lattice (thermal wave). The advantage of this technique over other photothermal methods in the field of diagnostics in solid-state electronics lies with the domination of the signal by the plasma wave component over a broad high-frequency range, quite accessible by today's electronic instrumentation. As a result, the primary photoinjected carrier parameters can be easily and reliably measured: lifetime, τ , electronic and thermal diffusivities, D and α , respectively, and surface recombination velocities, s j , on both semiconductor wafer surfaces. The theoretical section is complemented with key applications chosen from a rapidly increasing set of case studies, including Si wafer substrate transport property diagnostics, contamination control of chemically cleaned process wafers, MOS capacitor structures, carrier lifetime depth profiles in ion-implanted wafers, and bulk crystalline and thin-film photoconductors.
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Frequency‐modulation time‐delay spectrometry (FM‐TDS) has been implemented in photopyroelectric measurements of thermal diffusivity, on a series of well‐characterized samples. The strategy of FM‐TDS is sample excitation by a fast linear... more
Frequency‐modulation time‐delay spectrometry (FM‐TDS) has been implemented in photopyroelectric measurements of thermal diffusivity, on a series of well‐characterized samples. The strategy of FM‐TDS is sample excitation by a fast linear frequency sweep, whose autocorrelation function is mathematically equivalent to a Dirac delta function. The method permits the fast recovery of high‐quality frequency and impulse‐response information. Impulse responses recovered in the time‐delay domain showed good agreement with a Green’s function model of transient heat conduction. The present work demonstrates that the FM‐TDS measurement strategy yields photothermal information equivalent to that obtainable from a pulsed laser system, with much lower excitation power.
Research Interests: Engineering, Physics, Materials Science, Optics, Scientific Instruments, and 14 moreImpulse response, Thin Film, Physical sciences, THERMAL DIFFUSIVITY, Thermal Conductivity, CHEMICAL SCIENCES, Pyroelectricity, Transient Response, Time Domain, Signal to Noise Ratio, Detector, Frequency Response, Dirac Delta Function, and radiation detector
... be avoided because hydrogen when mixed with air in the ratio of 4.65-93.9 vol % isexplosive.4 For ... The role of palladium as a catalyst Catalytic effects play an important role in the field of gas detection. Solid-state gas sensors... more
... be avoided because hydrogen when mixed with air in the ratio of 4.65-93.9 vol % isexplosive.4 For ... The role of palladium as a catalyst Catalytic effects play an important role in the field of gas detection. Solid-state gas sensors are directly related to the phenomenon of catalysis. ...