Photothermal Deflection Technique Research Articles

Rapid standoff spectroscopic characterization of plastic waste using quartz tuning fork

Standoff molecular identification of chemicals finds immense applications in homeland security, forensic investigation and plastic recycling industries. Although, standoff detection using mid-infrared radiation offers excellent molecular selectivity, sensitive detection of mid-IR radiation using inexpensive detectors is a challenge. In the present work, we show commercially available inexpensive Quartz Tuning Fork (QTF) can be effectively used for rapid standoff detection of solid samples using mid-IR radiation. In this method, a plastic sample placed 40 cm away was excited with tunable infrared (IR) radiation pulsed at the resonance frequency of the QTF. The IR radiation scattered off the plastic sample was used for exciting the QTF into resonance. Plotting the QTF resonant amplitude as a function of irradiating IR wavelength represents the unique IR spectrum of the plastic sample under study. The resolution of spectra recorded using QTF was found to be superior to those collected with ATR-FTIR and the technique based on QTF was 103 times faster than microcantilever-based photothermal deflection techniques. By combining simple machine learning algorithms with QTF standoff resonance IR spectra, various plastic samples can be effectively classified with 100% accuracy. Also, this technique was found to be capable of identifying black plastics without any further sample preparation requirements.

Uses of 3D photothermal deflection technique for the investigation of nickel-graphene foam sheets

The aim of this work is to investigate the influence of pores density on the thermal properties of Nickel-graphene foam sheets. The study demonstrates a detailed theoretical and experimental treatment of the three-dimensional photothermal deflection (PTD) technique, under laser excitation of nickel foam of various porosity density coated graphene thin film of 200 nm thickness. Green's function and integral transformations are used in the theoretical treatment. The effect of certain parameters on the sensitivity of the PTD technique with respect to the variation in the specimens' pore density was studied via using analytical and numerical developments. The thermal properties showed that the thermal conductivity and thermal diffusivity were 4.12 W m−1. K −1 and 0.147 cm2. s−1. The numerical results show that decreasing the modulation frequency of the laser causes a decrease in the sensitivity of the thermal signal. Photothermal deflection techniques have shown a good efficiency in determining the thermal properties of porous materials.

Effect of Al0.1Ga0.9As thickness on the structural, optical, thermal, and electrical properties of (Al0.1 Ga 0.9As)/GaAs heterojunctions

Al0.1Ga0.9As nano-films of various thicknesses were deposited on GaAs substrate and examined using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), UV–Visible spectrophotometry, Photoluminescence (PL), Electrochemical Impedance Spectroscopy (EIS), and Photothermal Deflection (PTD). The PTD technique is used to analyze the effect of Al0.1Ga0.9As thickness on thermal properties and showed its sensitivity to weak structural changes. By increasing the Al0.1Ga0.9As thickness, the crystallinity was degraded, an infrared emission centered at 997.4 nm whose intensity is the highest for 50 nm was observed. A pn junction was formed for thicknesses higher than 400 nm, the band gap was increased from 1.59 to 1.68 eV. The thermal conductivity increased from 35.3 to 37.3 W m− 1 K−1 and the thermal diffusivity increased from 0.195 to 0.22 cm2 s−1. As a result of this investigation, the Al0.1Ga0.9As/GaAs can be considered for potential applications in photoelectric and thermoelectric devices.

Structural, Dielectric, Electrical, and Thermal Properties of the Ce-Doped Ba2TiMoO6 Double Perovskite

Abstract Ce-doped Ba2TiMoO6 with different Ce percentage was synthesized by solid state reaction and investigated. Electrical and thermal properties were examined by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and photothermal deflection (PTD) technique. The electrical investigation shows that the increase of Ce doping percentage favors the electrical confinement which leads to a decrease in the electrical capacitance from 2.6 nF to 1.6 nF, an increase in the grain boundaries resistance from 5.88 × 107 to 6.50 × 108 Ω, a decrease in the current density from 60 nA to 3 nA, and a decrease of thermal conductivity from 1.8 W m−1 K−1 to 0.12 W m−1 K−1. These results introduce the Ce-doped Ba2TiMoO6 perovskite as a potential candidate for a new generation of thermal barrier coatings (TBCs).

Heat Transfer Enhancement of n-Type Organic Semiconductors by an Insulator Blend Approach.

The transfer of heat energy in organic semiconductors (OSCs) plays an important role in advancing the applications of organic electronics, especially for lifetime issues. However, compared with crystalline inorganic semiconductors, the thermal transport of OSCs is less efficient and a relevant understanding is very limited. In this contribution, we show that the heat conduction of OSCs can be enhanced by blending with a “commodity” insulator (both thermal and electrical). PC71BM, a well-known electron transporter but poor thermal conductor, was selected as the host OSC material. The blending of a small amount of polystyrene (PS), a commonly used insulating polymer, can facilitate the heat transfer of PC71BM films, as substantiated by the scanning photothermal deflection technique and an infrared thermal camera. The phase thermodynamics of PC71BM/PS blends indicates that the efficient heat transfer preferably occurs in the OSC/insulator blends with better intimate mixing, where isolated PC71BM domains can be effectively bridged by PS that thread through the regions. The applicability of this approach can be observed in blends with another host material—ITIC. This work provides a facile strategy for designing thermally durable organic electronic devices.

Effect of porosity on structural, optical, thermal, and electrical properties of nickel-foam coated graphene sheets

Nickel foam of various pore-size coated graphene thin film of 200 nm thickness was investigated as a function of the pore size. The structural properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The optical properties were analyzed through the UV–Visible reflectance and Photoluminescence spectra. Hall Effect and Electrochemical impedance spectroscopy techniques were used to study the electrical and dielectric properties. The thermal properties were measured through the photothermal deflection technique. By decreasing the pore size, the electrical conductivity was increased from 9.42 × 107 to 33.26 × 107 S m−1, volume and surface carrier densities were decreased from −8.66 × 1021 to −2.05 × 1021 cm−3 and from −1.13 × 1014 cm−2 to −0.41 × 1014 cm−2; respectively, the specific capacitance was increased from 15.52 × 106 F to 19.65 × 106 F and the dielectric permittivity of value in the order of 1.5 × 103 F m−1 was decreased with the frequency. It was developed the photothermal deflection technique and discussed its sensitivity to the determination of thermal properties which show that the thermal conductivity decreased from 4.12 to 3.58 W m−1 K−1 and the thermal diffusivity decreased from 0.146 to 0.109 cm2 s−1. It was established semi-empirical relationships which allow to deduce the thermal properties and optical band gap without needing to measure them. These results introduce the graphene coated on Nickel foam sheets as good candidate for potential use in photoelectric and thermoelectric devices.

Thermal annealing effects on microstructural and thermo-optical properties of V/V2O5 alternating layers structure

In this work, the effect of annealing time on structural, optical, and thermal properties of VxOy used as functional material in microbolometer applications is studied. A suitable thermal annealing to three samples composed of eleven alternating layers of vanadium pentoxide (V2O5) and vanadium (V) grown by a sputtering method is applied. These samples were annealed for 30, 40, and 50 min at 300 °C in O2 atmosphere. Raman spectroscopy, Photothermal Deflection Technique “PDT” and Photothermal Deflection Spectroscopy “PDS“ have been employed respectively for microstructure, thermal and optical characterization for VxOy samples. The thermal annealing induces formation of multiphase identified as VO2, V2O5, and V6O13. Also, the studied films showed that the thermal conductivity increases with increasing annealing duration however the gap energy decreases. As important results compared to our previous work, an investigation of thermal and optical properties of vanadium oxide V2O5/V thin films having high (TCR) and low resistivity is presented.

Heat transfer in binary and ternary bulk heterojunction solar cells

Ternary strategy is one of the most commonly used methods to boost the performance of organic solar cells (OSCs) from a binary blend of donor and acceptor. Fullerene derivatives are popular choices for the ternary component as they could benefit the electrical property. However, the ternary component could also affect other physical properties of the bulk-heterojunction (BHJ). Among these properties, heat transfer has rarely been reported, despite its relevance for thermal durability of OSCs. Here, we employ scanning photothermal deflection technique to study thermal diffusion properties of binary PM6:Y7 and ternary PM6:Y7:X BHJs, where X = PC71BM, ICBA, and N2200. It is found that fullerene derivatives deteriorate the thermal diffusivity (D) of blend films and the device thermal durability, despite enhancing the electrical and device performance. In contrast, when an n-type conjugated polymer N2200 is used as the ternary component, both the electrical and thermal properties are enhanced, with improved power conversion efficiency and prolonged device thermal durability. These results offer a perspective on how to choose a favorable third component. Fullerene derivatives are not necessarily the optimal choice for ternary component for BHJ cells because of the inferior thermal properties.

Characterization of Chirality in Diffractive Metasurfaces by Photothermal Deflection Technique

Chirality, a lack of mirror symmetry, is present in nature at all scales; at the nanoscale, it governs the biochemical reactions of many molecules, influencing their pharmacology and toxicity. Chiral substances interact with left and right circularly polarized light differently, but this difference is very minor in natural materials. Specially engineered, nanostructured, periodic materials can enhance the chiro-optical effects if the symmetry in their interactions with circular polarization is broken. In the diffraction range of such metasurfaces, the intensity of diffracted orders depends on the chirality of the input beam. In this work, we combine a photothermal deflection experiment with a novel theoretical framework to reconstruct both the thermal and optical behavior of chiro-optical behavior in diffracted beams.

Diffracted Beams from Metasurfaces: High Chiral Detectivity by Photothermal Deflection Technique

AbstractMeasurements of difference in optical interactions between circularly polarized excitations of opposite handedness (circular dichroism) are highly important for both natural and artificial chiral structures. Here the photothermal deflection technique is proposed as a method to detect the optical chirality of a metasurface, analyzing the diffracted beams by the metasurface itself. Two metasurfaces are investigated, based on Au and Ag. The samples are fabricated by nanosphere lithography, with a tilted deposition of thin metal layer, which produces symmetry‐breaking. The unit cell periodicity of these metasurfaces allows for multiple order diffraction in the 450–520 nm range, which encompasses the emission lines of an Ar laser. The metasurfaces are placed on a mirror and excited by an Ar pump beam at different orientations, laser wavelengths, and circular polarization degree; the probe beam scans the absorption of the diffraction orders back‐reflected from the underlying mirror. In this way, the chiral investigation is simplified by placing the scanning of absorption‐induced thermal effect into the metasurface plane, thus avoiding the transmission/reflection measurements of a specific order, which are done by angular placement of detector. Theoretical and numerical approaches are further developed to reconstruct both thermal and optical behavior of the chirality at the nanoscale.

Thermal diffusivity downscaling of molybdenum oxide thin film through annealing temperature-induced nano-lamelle formation: a photothermal beam deflection study

The present work proposes a method of downscaling the thermal diffusivity (α) of MoO3 thin films through annealing temperature-induced nano-lamelle formation. The thermal diffusivity modification of the MoO3 films, prepared by the doctor blade method, is investigated by the sensitive transverse photothermal beam deflection technique. The X-ray diffraction analysis confirms the structural phase transformation from monoclinic to orthorhombic in the films annealed from 300 to 450 °C. The thermal induced anisotropy of the film is evident from the variation of the morphology index and texture coefficient. The field emission scanning electron microscopic analysis unveils the morphology modifications from blocks to the nano-lamelle structure with layers of average thickness ~ 77 nm. The thermal diffusivity measurement reveals a 53% reduction upon annealing the film to 450 °C. The drastic reduction is achieved through the annealing temperature-induced nano-lamelle formation and the phase transformation from monoclinic to orthorhombic in the MoO3 films.

Heat transfer in photovoltaic polymers and bulk‐heterojunctions investigated by scanning photothermal deflection technique

AbstractOrganic semiconductors in electronic devices usually have poor thermal conduction which could trap considerable amount of heat, inducing operational instability and reducing device lifetime, limiting commercialization potential. Despite the technological essence to understand and enhance device heat‐dissipation, related studies on organic semiconductors are very limited. In this study, the authors show that the scanning photothermal deflection technique can be employed to study the thermal transport in thin films of organic photovoltaic (OPV) polymers and bulk‐heterojunctions (BHJs), with a simple empirical correction for the extrinsic experimental configuration. Phonons are identified to dominate the thermal transport due to the low carrier mobility. For OPV semiconductors, the positive correlation between the thermal diffusivity and the molecular planarity, – stacking and crystallinity is demonstrated. High‐performance 2D polymers such as PM6 can possess values comparable to alloys like stainless steel. In BHJs, using a polymeric acceptor can retain high thermal diffusivities compared to fullerene and ITIC acceptors, attributed to the efficient heat transfer within the polymer chains. The results offer not only a simple, highly customizable but sensitive experimental method for thermal transport in OPV systems, but also insights into the phonon dynamics and clinical investigations for thermal stability, pushing forward strategic material design.

SSD detection on LIDT tested coated Fused Silica samples

Material changes and Sub-Surface Damage (SSD) under Laser Induced Damage Threshold (LIDT) testing sites were investigated on 3 diverse single layer coated transparent fused silica samples to obtain additional information on damage precursors on these samples. As a detection method, photothermal deflection technique utilizing a resonant UV laser beam was used. The local variations in UV absorption and probe beam transmittance due to previous exposure to high fluence laser pulses were strongly dependent on the coating itself and on the laser energy used during the LIDT testing. Also the obtained LIDT values differ from coating to coating. Detected effects on the coatings and substrate surface beneath ranged from small surface dislocations to complete coating damage with material transformations. Additional absorbing damage precursors were found close to the damaged sites.

A note on the history of photoacoustic, thermal lensing, and photothermal deflection techniques

We review the history of photoacoustic, thermal lensing, and photothermal deflection techniques from early experiments to the current time. The paper also describes the main fields of application in chronological order, showing the primary advantages and listing initial technological developments.

Improvement of carriers diffusion length and mobility in annealed GaAsPN materials for intermediate band solar cells

In this paper, we investigate the effect of thermal annealing on nonradiative recombination parameters of GaAsPN materials used for intermediate band solar cells. This study is performed thanks to photothermal deflection technique PTD. Indeed, nonradiative lifetime, electronics diffusivity, surface and interface recombination, are extracted through a good fit between theoretical and experimental amplitude and phase of PTD signal. Then, the effects of annealing temperature on charge transport were analyzed and discussed. As an important result for solar cells improvement, we have found that hole diffusion length and mobility increases respectively from 13.8 to 19 (±2.5%) μm and from 112 (±4.9%) to 153 (±3.5%) cm2/V·s for GaAsPN as grown to that annealed at 800 °C.

Mid-IR photothermal beam deflection technique for fast measurement of thermal diffusivity and highly sensitive subsurface imaging

The resonances of phonon and plasmon modes make the absorbance coefficient of materials tremendously high in the mid-infrared spectral range, which allows for a mid-infrared excitation laser to heat the surface layers of these materials with high efficiency. Furthermore, phonon scattering by defects and defect-induced localized vibrational modes affect the local infrared dielectric function and, hence, the local infrared absorption coefficient. In this paper, we present a mid-infrared photothermal beam deflection technique that takes advantage of the strong interaction between infrared optical excitations and vibrational modes to measure the thermal diffusivity of materials without any sample preparation and takes advantage of the strong dependence of the infrared complex dielectric function on defects to detect subsurface defects with high sensitivity. We demonstrate the importance of the developed technique by measuring the thermal properties of highly transparent and reflective samples and detecting defects undetectable with any of the existing optical methods. Namely, using the developed technique, we find that the thermal diffusivities of high-quality Si, crystalline AlN, and crystalline α-SiO2 substrates are 1.00 ± 0.05, 0.67 ± 0.02, and 0.09 ± 0.01, respectively, and we record highly resolved images of structural subsurface defects as well as defects produced by ion-implantations at a depth of 62 μm under the surfaces of 4H-SiC substrates.

Analysis of morphological, optical and thermal properties of porous p-type indium phosphide p-InP(100) prepared by the vapor etching method

In this paper we report for the first time, the effect of halogenic acids (HCl and HF) on the morphological, optical and thermal properties of porous p-InP layers (p-InP-Ls). The samples were elaborated by a vapor phase etching (VE) method with two halogenic acids (1M HF and 1M HCl). The recording of the porous surfaces' morphology was carried out by Scanning Electron Microscopy (SEM). The porous p-InP-Ls formed using 1M HCl steam was found to have a micro-porous structure in which the pores were distributed on the p-InP(100) substrate. The UV-Visible spectrum revealed that the porous p-InP-Ls formed by 1M HCl steam displayed a greater absorbance capacity in the visible range than the other layer which is formed using 1M HF steam. In addition, it was found that the band gap energy (Eg) of porous p-InP-Ls formed by 1M HCl steam was greater (1.254 eV) than the unetched p-InP substrate (1.228 eV), which was attributed to the quantum size effect. FTIR spectrum showed the presence of peaks related to P-Cl bonds. The thermal conductivity and thermal diffusivity of the porous p-InP-Ls were determined by the photo-thermal deflection technique, which studies the variation of the photothermal signal with the square root of the modulation frequency. The result showed that the vapor of halogenated acids (especially HCl steam) clearly affected the thermal properties.

Characterization of nonlinear optical crystal absorption

A simplified absolute calibration for the photothermal laser-induced deflection technique is introduced and applied to characterize different nonlinear optical crystals at common diode pumped solid state laser wavelengths. In particular, intensity-dependent absorption measurements at 355 nm are performed to investigate the nonlinear absorption in lithium triborate crystals. From the results, it is verified that at least to a certain extent the nonlinear absorption is related to impurities or defects, i.e., to sequential three-photon absorption in addition to a potential intrinsic three-photon absorption process.

Photothermal deflection technique investigation of thermal annealing effects of AlGaAsSb/GaSb laser structure: Non-radiative recombination parameters enhancement

Photothermal deflection technique (PTD) is used to investigate the effects of thermal annealing time on nonradiative recombination parameters i.e. nonradiative lifetime of minority carriers, electronic diffusion coefficient, and surface and interface recombination velocity of AlGaAsSb/GaSb laser structure. The extraction of the electronic parameters are performed by PTD technique through extensive modeling by fitting the experimental photothermal signal to the corresponding theoretical ones. We have found that nonradiative recombination parameters have been enhanced by annealing time. These results are very promising for improvement of active layer used for vertical-cavity surface-emitting lasers (VCSELs).

Configuration optimization of photothermal deflection for measurement sensitivity enhancement.

An accurate theoretical model based on thermoelasticity theory and Fresnel diffraction integral is developed to describe the photothermal deflection (PTD) signal with a continuous-wave modulated Gaussian beam excitation. A PTD experiment is performed to investigate the dependence of PTD amplitude on the experimental parameters, such as the radius, waist position, and wavelength of the probe beam, and the detection distance. Good agreement between the experimental and theoretical results is obtained. The results reveal that the optimal detection distance highly depends on the probe beam waist position and wavelength, and the PTD amplitude can be enhanced by optimizing the probe beam radius and waist position as well as the detection distance. Moreover, it is demonstrated experimentally that the PTD amplitude is inversely proportional to the probe beam wavelength by using three probe lasers with a wavelength of 375 nm, 543 nm, and 632.8 nm. Therefore, the measurement sensitivity of PTD technique could be enhanced by using a short-wavelength probe beam.