bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-based trace gas detection of ethane as a result of photo-oxidative damage in chilled cucumber leaves (invited)
Authors: Santosa I. E. , Laarhoven L. J. J. , Harbinson J. , Driscoll S. , Harren F. J. M.
Published: January 2003

At low temperatures, high light intensity induces strong photooxidative lipid peroxidation in chilling sensitive cucumber leaves. A sensitive laser-based photoacoustic detector was employed to monitor on-line the evolution of ethane, one of the end products of lipid peroxidation. The Δv=2 CO laser operated in the 2.62–4.06 μm infrared wavelength region with a maximum intracavity power of 11 W. In combination with an intracavity placed photoacoustic cell the laser was able to detect ethane down to 0.5 part per billion. Cucumber leaf disks chilled in the light produce ethane; the rate of ethane production depends on the applied temperature, light intensity, and period of chilling.
Ultratraces of carotenes in tomato purées: HPLC-TLS study
Authors: Luterotti S. , Marković K. , Franko M. , Bicanic D. , Vahc̆ić N. , Doka O.
Published: January 2003

The present study was designed to provide information about (i) the profile of carotene pigments and (ii) trace quantities of lycopene and β-carotene left in tomato purées. The ultrasensitive method comprising HPLC and thermal lens spectrometric (TLS) detection enabled us to detect as low as 0.3 and 1.1 ng ml−1 lycopene and β-carotene in purée extracts, respectively. Total concentration of β-carotene and lycopene (varying from 3 to 170 ng g−1) in the examined tomato purées may serve as an indicator of the carotene-specific antioxidative capacity of these products. Although conventional spectrophotometry can be used to rapidly assess the quality of products derived from tomatoes, a highly sensitive and selective method such as HPLC-TLS is needed for reliable analyses of samples such as, for example, those subjected to inappropriate storage and/or handling.
Rapid, accurate, and direct determination of total lycopene content in tomato paste
Authors: Bicanic D. , Anese M. , Luterotti S. , Dadarlat D. , Gibkes J. , Lubbers M.
Published: January 2003

Lycopene that imparts red color to the tomato fruit is the most potent antioxidant among carotenes, an important nutrient and also used as a color ingredient in many food formulations. Since cooked and processed foods derived from tomatoes were shown to provide optimal lycopene boost, products such as paste, puree, juice, etc. are nowadays gaining popularity as dietary sources. The analysis of lycopene in tomato paste (partially dehydrated product prepared by vacuum concentrating tomato juice) is carried out using either high pressure liquid chromatography (HPLC), spectrophotometry, or by evaluating the color. The instability of lycopene during processes of extraction, etc., handling, and disposal of organic solvents makes the preparation of a sample for the analysis a delicate task. Despite a recognized need for accurate and rapid assessment of lycopene in tomato products no such method is available at present. The study described here focuses on a direct determination of a total lycopene content in different tomato pastes by means of the laser optothermal window (LOW) method at 502 nm. The concentration of lycopene in tomato paste ranged between 25 and 150 mg per 100 g product; the results are in excellent agreement with those obtained by spectrophotometry. The time needed to complete LOW analysis is very short, so that decomposition of pigment and the formation of artifacts are minimized. Preliminary results indicate a good degree of reproducibility making the LOW method suitable for routine assays of lycopene content in tomato paste.
Detection of ethanol and acetaldehyde released from cabbage seeds of different quality: Laser photoacoustic spectroscopy versus FTIR and headspace gas chromatography
Authors: Bicanic D. , Persijn S. , Taylor A. , Cozijnsen J. , van Veldhuyzen B. , Lenssen G. , Wegh H.
Published: January 2003

Detecting early ageing stages of seeds in storage is of great concern to vegetable seed companies. Despite their reliability conventional germination tests are destructive and time consuming. One alternative towards assessing the quality of seed is to monitor the concentration of certain volatiles (acting as biological markers) evolved from the seeds; examples are ethanol (EtOH), acetaldehyde, ethane, methanol, etc. Most of the presently used methods have only moderate insensitivity and are therefore not suitable for the on-line measurements. In this work CO laser photoacoustic spectroscopy (LPAS) was used to investigate the on-line evolution of EtOH and acetaldehyde from the imbibed nonaged and aged seeds of cabbage. The overall performance of LPAS was superior to that of Fourier transform infrared and of gas chromatography.
Time resolved thermal lens in edible oils
Authors: Albuquerque T. A. S. , Pedreira P. R. B. , Medina A. N. , Pereira J. R. D. , Bento A. C. , Baesso M. L.
Published: January 2003

In this work time resolved thermal lens spectrometry is applied to investigate the optical properties of the following edible oils: soya, sunflower, canola, and corn oils. The experiments were performed at room temperature using the mode mismatched thermal lens configuration. The results showed that when the time resolved procedure is adopted the technique can be applied to investigate the photosensitivity of edible oils. Soya oil presented a stronger photochemical reaction as compared to the other investigated samples. This observation may be relevant for future studies evaluating edible oils storage conditions and also may contribute to a better understanding of the physical and chemical properties of this important foodstuff.
Contrast enhancement of modulated optical reflectance microscopy of semiconductor devices
Authors: Dietzel D. , Roecken H. , Bein B. K. , Pelzl J.
Published: January 2003

Photothermal microscopy based on combined optical and electrical excitation has been applied to insulating lines prepared by focused ion beam implentation on oxygen implanted mesas. The double excitation technique permits to image electrical properties of the implanted structures which are complementary to simple defect tracing when a single excitation is applied. In addition, the contrast of imaging of implanted structures can be increased considerably. Apart from combining modulated optical excitation with electrical direct current voltages, double modulation configurations can improve the contrast further, by detecting either on a higher harmonic of the single excitation frequency or on the sum or difference of two different excitation frequencies. The influence of different parameters characterizing the experimental configuration gives information on the physical processes of the signal generation, indicating that the observed contrast enhancement is mainly of thermal origin related to the photoinduced currents.
Geometry of crossing null shells
Authors: Jezierski Jacek
Published: January 2003

New geometric objects on null thin layers are introduced and their importance for crossing null-like shells are discussed. The Barrabès–Israel equations are represented in a new geometric form and they split into a decoupled system of equations for two different geometric objects: tensor density Gba and vector field I. Continuity properties of these objects through a crossing sphere are proved. In the case of spherical symmetry Dray–t’Hooft–Redmount formula results from continuity property of the corresponding object.
Analysis of the photopyroelectric signal for investigating thermal parameters of pyroelectric materials
Authors: Sahraoui A. Hadj , Longuemart S. , Dadarlat D. , Delenclos S. , Kolinsky C. , Buisine J. M.
Published: January 2003

The photopyroelectric signal is analyzed in order to simultaneously obtain the thermal diffusivity and effusivity of pyroelectric materials. Two different experimental configurations are described and compared in terms of accuracy and sensitivity. The information is obtained via a frequency scan of the amplitude or the phase of the pyroelectric signal. The methods have been used for the measurement of thermophysical properties of a lead–titanate–zirconate ceramic sample.
Reconstruction of thermal properties of inhomogeneous materials from one dimension to two dimensions
Authors: Zhang Shu-yi , Zhou Qing-biao , Lu Yue-kai
Published: January 2003

Based on one-dimensional theory of thermal wave reconstruction, a two-dimensional theory of thermal conductivity profile reconstruction is developed. The important developments in the two-dimensional (2D) inverse problem are that a line source is used instead of the source with a large cross section in one dimension, and a finite difference method is adopted for the numerical solution of the 2D heat equation. Numerical simulations demonstrate that this approach is effective and stable even with 5% random noise disturbance in the signal.
Acoustic waves at interfaces studied by laser ultrasonics (invited)
Authors: Glorieux C. , Van de Rostyne K. , Beers J. D. , Gao W. , Petillion S. , Van Riet N. , Nelson K. A. , Allard J. F. , Gusev V. E. , Lauriks W. , Thoen J.
Published: January 2003

When energy is deposited at the interface between two materials, then acoustic waves that are confined in the interface region and traveling in the plane of the interface may arise. In this article, we illustrate the feasibility and versatility of interface wave laser ultrasonics by presenting a selection of recently developed laser ultrasonic configurations for detecting acoustic waves at the free surface of a solid and at a liquid–solid interface in a variety of applications, such as nonlinear wave propagation, characterization of coatings, porous materials and substrates, and acoustic wave imaging.
Laser generation of acoustic waves in an anisotropic medium; parametric analysis for application to material characterization
Authors: Rossignol C. , Meri H. , Audoin B.
Published: January 2003

A noncontact laser-ultrasonic technique is described that allows determination of materials anisotropic properties. Plane waves are synthesized by scanning the surface with a laser line source at judiciously chosen intervals. The identification of the stiffness-tensor components is based on the inversion of the phase velocities of these transmitted plane waves. The procedure developed is presented and applied to both simulated and experimental signals. The influence of the spatial extent of the laser source in the identification of the stiffness-tensor components is also discussed; the effect of the spot size is analyzed in the ablation regime for which the acoustic source is localized at the surface, whereas the influence of the optical penetration depth is quantified in the thermoelastic regime.
Precursors in the optical excitation of giant surface acoustic wave pulses in solids
Authors: Kolomenskii Al. A. , Jerebtsov S. N. , Schuessler H. A.
Published: January 2003

The surface perturbations related to sound bulk waves are excited in a solid simultaneously with surface acoustic waves and propagate away from the source. These waves arrive before the arrival of the surface wave that gives the main contribution to the observed signal and therefore are referred to as precursors. In the wave zone the precursors can be registered at the surface as separate signals providing information on the elastic moduli of the material. We have observed the precursors for fused silica and stainless steel at relatively large distances due to extremely high pressure amplitudes created in the generation region. The parameters of the precursors were also calculated using a model of a normal force acting on a free solid surface. Relatively higher amplitudes observed in the experiments as compared to theoretical predictions are attributed to the effect of liquid loading during the generation process.
Microstructure effects on the thermal properties of vacuum sintered AISI 316L stainless steel
Authors: Lima W. M. , Weinand W. R. , Biondo V. , Nogueira E. S. , Medina A. N. , Baesso M. L. , Bento A. C.
Published: January 2003

The photothermal technique open photoacoustic cell and the non-Adiabatic thermal relaxation calorimetric are applied to measure thermal properties of the sintered stainless steel AISI 316L as a function of the porosity. The results showed that thermal diffusivity and thermal conductivity values as a function of the applied uniaxial pressure presented a strong correlation with the surface area of contact of the particles, which constitute the porous medium. Besides, the study of the relationship between physical properties, such as mass density, porosity, and permeability and the microstructure shows that the greater the particle interaction the better the thermal properties correlation.
Photoacoustic monitoring of real time blood and hemolymph sedimentation
Authors: Landa A. , Alvarado-Gil J. J. , Gutı́errez-Juárez G. , Vargas-Luna M.
Published: January 2003

The dynamics of blood and hemolymph sedimentation is studied in real time using the photoacoustic technique. A modified configuration of a conventional photoacoustic cell is used, where the advantage of this methodology is that the sample is not illuminated directly and that the process can be monitored through the measurement of the thermal contact between a reference material and the blood. It is demonstrated that during the process the thermal effusivity decreases at the region of contact between the sample and the reference materials. The usefulness of these results in real time monitoring using photothermal techniques is discussed.
Determination of aminolevulinic-acid-induced protoporphyrin IX in mice skin
Authors: Stolik S. , Tomás S. A. , Ramón-Gallegos E. , Cruz-Orea A. , Sánchez-Sinencio F.
Published: January 2003

The kinetics of Protoporphyrin IX (PpIX) production in mice skin was studied by photoacoustic spectroscopy. PpIX was induced in mice by intraperitoneal administration of δ-aminolevulinic acid (δ-ALA) in doses of 10, 20, and 30 mg/kg. Mice were sacrificed at specific times within an 8 h interval following δ-ALA administration, and their abdominal skin was excised for the optical measurements. The PpIX content was determined from the photoacoustic amplitude at 410 nm, where PpIX presents its Soret band. For each dose, maximum PpIX was observed at two points. The first maximum occurred at around 15–45 min, depending on the ALA dose, and the second one took place approximately 2 h after δ-ALA administration. These peaks are associated with PpIX production in blood vessels and tissue, respectively. Fluorescence measurements of the PpIX content in plasma extracted intracardiacally confirmed the previous statement. Finally, phase resolved photoacoustic spectroscopy was applied to evaluate the mean depth at which PpIX is generated within the mice skin. This evaluation confirms that the ALA-induced porphyrins in skin are rather produced in the epidermis than in the dermis.
Apparent band-gap energies of mixed TiO2 nanocrystals with anatase and rutile structures characterized with photoacoustic spectroscopy
Authors: Toyoda Taro , Tsuboya Ikumi
Published: January 2003

Extreme small-sized titanium dioxide (TiO2) particles (nanocrystals) have been extensively used in the field of heterogeneous photo-oxidation catalysis for environmental cleanup. We have measured the optical absorption of mixed TiO2 nanocrystals with rutile and anatase structures (10–40 nm diameter) by photoacoustic (PA) spectroscopy. The values of apparent band-gap energies Eg of the TiO2 nanocrystals with different rutile contents were determined by the theory of interband transition. The value of Eg of a mixed TiO2 nanocrystal with rutile and anatase structures decreases continuously with the increase of rutile content. This indicates that Eg can be controlled by mixing the nanometer-sized TiO2 powders with rutile and anatase structures, hence, we can obtain TiO2 materials with an arbitrary apparent Eg between rutile and anatase structures. The PA spectrum of anatase-type TiO2 nanocrystals with a diameter of 15 nm shows a maximum around a photon energy of 3.9 eV, suggesting a quantum confinement effect with decreasing particle size. Applying the effective mass approximation to the PA spectrum, we can deduce the value of the hole effective mass in anatase-type TiO2 as 0.01 m0 (where m0 is electron rest mass).
Generation of surface acoustic waves in silicon with energetic femtosecond laser pulses
Authors: Kolomenskii Al. A. , Jerebtsov S. N. , Schuessler H. A.
Published: January 2003

The generation of surface acoustic wave (SAW) pulses in Si single crystal by femtosecond laser pulses with high energy of up to 30 mJ is studied. The generation is rather efficient even at a free silicon surface. In this case the shape of the observed SAW pulses corresponds to the thermoelastic mechanism despite the fact that a well developed ablation takes place. Excitation through a liquid layer is also studied and provides longer SAW pulses. SAW gratings are generated by focusing the laser beam through a mask and the changes in the spectrum of the pulse due to nonlinear interactions are observed.
Laser induced acoustic pulse propagation in submicron metallic thin films having variable sound velocities
Authors: Vollmann Jacqueline , Profunser Dieter M. , Dual Jürg
Published: January 2003

Free surfaces as well as interfaces between two neighboring materials are often subjected to diffusion processes like oxidation or migration of atoms. Such processes smooth out the difference of the acoustic impedances leading to microstructures having gradually varying mechanical properties like density and Young’s modulus. In the one-dimensional case of a metallic thin-film multilayer, the speed of sound becomes a function of the spatial thickness variable. Depending on the ratio between the acoustic wave length and the thickness of the diffusion zone, bulk waves reaching the zone are either dominantly transmitted or dominantly reflected. Thus a continuum having a variable sound velocity can be considered as an acoustic filter. The partial differential wave equation is solved numerically for an assumed velocity-versus-propagation direction function and the results are discussed. A series of experimental results obtained by a pump–probe–laser-acoustic technique is presented. Mechanical waves are excited and detected using laser pulses of 70 fs duration at a wavelength of 810 nm. An improved pump–probe setup is developed in order to detect the acoustic echoes of very thin layers. Simulations and experimental results are compared and potential engineering applications are proposed.
Quantum confinement effects in variable band-gap GaNxAs1−x thin films studied by photoacoustic spectroscopy
Authors: Cardona-Bedoya J. A. , Cruz-Orea A. , Tomas-Velazquez S. A. , Zelaya-Angel O. , Mendoza-Alvarez J. G.
Published: January 2003

By using the magnetron radio frequency (rf) sputtering deposition technique we have grown a new family of III–V nitride semiconductors: GaNxAs1−x thin films with nanocrystalline grain sizes and different N concentrations obtained by controlling the rf power used in the growth process. We have used the photoacoustic spectroscopy to measure the absorption edge behavior for the series of GaNAs films grown with different stoichiometries. The absorption spectra show a clear shift to higher energies as the N concentration increases; also, very remarkable shoulders in these spectra are clear evidence of the presence of optical transitions between energy levels produced by the quantum confinement effects that takes place because the average grain sizes (16 Å) are comparable to the exciton Bohr radius for GaN (28 Å). We discuss the quantum confinement regime for this case, and how information concerning the hole effective mass can be obtained by comparing a theoretical model to the experimentally observed transitions between the quantized electronic levels.
Fluorescence quantum efficiency measurements using the thermal lens technique
Authors: Andrade A. A. , Lima S. M. , Pilla V. , Sampaio J. A. , Catunda T. , Baesso M. L.
Published: January 2003

The single wavelength thermal lens (TL) method jointly with the multiwavelength TL method are used to determine the fluorescence quantum efficiency η of Nd3+-doped glasses and crystals. The concentration quenching and the upconversion parameter for Nd3+-doped solids is also described in this article. In addition, the TL method is used to study the temperature behavior of η for Cr3+-doped fluoride crystal.
Photothermal induced variations in the optical transmission of a photonic band gap structure
Authors: Larciprete M. C. , Sibilia C. , Paoloni S. , Leahu G. , Li Voti R. , Bertolotti M. , Panajotov K.
Published: January 2003

We consider an application of the photothermal effect for the realization of an optical limiter with a photonic band gap (PBG) structure. By means of a pump–probe setup, we investigate the optical transmission of 12 periods of a ZnSe/MgF2 PBG structure under different heating conditions. The investigated spectral range (600–700 nm) corresponds to a band edge in the transmission spectrum. The induced temperature increase is responsible for both thermal expansion of the layers and refractive index changes, thus redshifting the transmission curve by several nanometers. The initial transmission of the probe beam is restored after pump laser removal, thus indicating the reversible nature of the observed changes. The maximum transmission variation we obtained is 40% of signal at 660 nm. A theoretical reconstruction of the transmission spectra was calculated for different temperatures in order to evaluate the temperature increase ΔT corresponding to the observed shift. In order to have a confirmation, ΔT has also been measured by means of an interferometric technique. The obtained value has been found to be consistent with the theoretical predictions.
Novel approach for the analysis of infrared photothermal microscopy data
Authors: Paoloni S. , Fournier D.
Published: January 2003

We consider a photothermal microscope based on spatially resolved infrared (IR) radiometric measurement to perform thermal diffusivity measurements. The nonlinearity in the IR emission due the continuous temperature distribution and the finite resolution of the collecting optics makes the radiometric scan distorted with respect to the thermal wave distribution at the sample surface. These distortions, which are responsible for raising the phase signal profile and hence for a thermal diffusivity overestimate, are further enhanced in the case of a reduced spectral bandwidth (≈2–5 μm) as compared to the typical range 2–12 μm typically offered by common HgCdTe detectors. An approach to estimate thermal diffusivity for distorted data is presented here. The fundamental idea is constituted by the possibility of evaluating the quantities necessary for signal deconvolution directly from the experimental data obtained for properly selected conditions. The method is applied to measure the thermal diffusivity of transparent samples like BK7 glass by using a CO2 laser as pump beam.
Thermal wave and acoustic investigation of thyristor structures
Authors: Suszyński Z. , Arsoba R. , Majchrzak P. , Napieralski A. , Tylman W.
Published: January 2003

In this article the photoacoustic method and a method that consists of dynamic induction heating and infrared detection of the thermal field were used to investigate a high-power thyristor structure. The results of thermal wave investigations were compared with acoustic images. A novel approach for determination of the thermal properties of the structure is presented. The thermal profiling is based on a genetic algorithm using temperature contrast characteristics in the frequency domain.
Development of the laser absorption radiation thermometry technique to measure thermal diffusivity in addition to temperature
Authors: Levick Andrew , Lobato Killian , Edwards Gordon
Published: January 2003

A comparative technique based on photothermal radiometry has been developed to measure thermal diffusivity of semi-infinite targets with arbitrary geometry. The technique exploits the principle that the frequency response of the temperature modulation induced by a periodic modulated heating source (in this case a laser spot) scales with thermal diffusivity. To demonstrate this technique, a photothermal radiometer has been developed, which detects modulated thermal radiance at a wavelength of 2 μm due to a small temperature modulation induced on the target surface by a modulated erbium fiber laser of power 1 W. Two frequency responses were measured for platinum and oxidized Inconel 600 targets (the frequency response is a scan of the amplitude of the modulated thermal radiance over laser modulation frequency). Scaling the two responses with respect to frequency gives a ratio of thermal diffusivities Dplatinum/DInconel of 4.45(33) which compares with a literature value of 4.46(50). The aim is to combine this technique with laser absorption radiation thermometry to produce multithermal property instrument for measuring “industrial” targets.
The photoelastic effect evaluation by means of photothermal deflection technique
Authors: Paoloni S. , Bertolotti M.
Published: January 2003

The collinear configuration of the photothermal deflection technique is applied here to evaluate the influence of the photoelastic effect in the refractive index variation. The measurement procedure is based on analysis of the phase signal linear decay as a function of the distance between the beams. By comparing lateral scans obtained for different polarization states of the probe beam, it is possible to derive the relative influence of the two mechanisms (opto-thermal and photoelastic) responsible for deflecting the probe. Experimental results obtained for a glass sample which validate the proposed method are also shown.
Investigation of the annealing effect on the nonradiative carrier recombination in AlGaAs/GaAs utilizing the piezoelectric photothermal technique
Authors: Fukuyama A. , Ohno R. , Akashi Y. , Ikari T.
Published: January 2003

The electron nonradiative recombination process of photoexcited carriers in as-grown and annealed n=Al0.2Ga0.8As/GaAs heterostructure samples is investigated by using piezoelectric photothermal (PPT) spectroscopy. The PPT signal above the band-gap energy of GaAs substrate decreased when the sample was annealed at 815 °C. In the frequency dependent measurements, the deviations from the 1/f linear function are clearly observed in the AlGaAs/GaAs samples. This critical deviation frequency was found to shift to the lower frequency region by annealing. Our experimental results are explained by assuming that the sample annealing generates an unknown deep level in the AlGaAs epitaxial layer region and this level effectively traps the photoexcited carriers nonradiatively.
Study of low energy implants for ultrashallow junctions using thermal wave and optical techniques
Authors: Nicolaides Lena , Salnick Alex , Opsal Jon
Published: January 2003

A combination of the thermal wave and optical technologies was found to be advantageous in characterization of implants for ultrashallow junctions. Two sets of Si wafers implanted with boron and arsenic ions at low energies (0.5–5.0 keV) and high dose (5×1014 cm−2) were studied after implantation and prior to annealing. Signals obtained by using the thermal wave and optical methods exhibit a linear dependence on implantation energy below 2 keV for both implants. Results of the thermal wave and optical studies were also correlated to conventional TRIM calculations of crystalline damage and implanted ion concentration.
Nondestructive analysis of ultrashallow junctions using thermal wave technology
Authors: Nicolaides Lena , Salnick Alex , Opsal Jon
Published: January 2003

It is shown that the thermal wave (TW) nondestructive technology widely used in semiconductor industry for ion-implant monitoring can also be used for characterization of ultrashallow junctions created as a result of thermal annealing of ion implanted wafers. A set of Si wafers implanted with boron at energies 0.2–0.5 keV and implantation doses in the range of 1014–1015 cm−2 thermally annealed at different temperatures (950–1100 °C) has been studied. For all samples, the TW signal is found to vary linearly with junction depth and is shown to exhibit a very good correlation with secondary ion mass spectrometry data. A special processing of experimental data using both the TW quadrature and in-phase signal components allowing for resolution of effects introduced by different implantation doses, energies, and annealing temperatures is discussed.
A contribution of carrier transport processes to the photoacoustic effects in doped narrow gap semiconductors
Authors: Radulović K. T. , Nikolić P. M. , Vasiljević-Radović D. , Todorović D. M. , Vujatović S. S. , Bojic̆ić A. I. , Blagojević V. , Uros̆ević D.
Published: January 2003

The contribution of free carrier transport processes to the photoacoustic effect in doped AIVBVI compounds was investigated using the photoacoustic (PA) frequency modulated transmission technique as a valuable tool in the study of thermal and carrier transport processes in semiconductors. The PA signals were measured and analyzed as a function of the modulation frequency in a specially constructed PA cell. The multiparametric fitting procedure was used to obtain some thermal and electronic transport parameters of doped and pure AIVBVI compounds.
Multilayer models in the piezo-PAS analysis of AII–BVI compounds
Authors: Maliński M. , Zakrzewski J.
Published: January 2003

This article presents the results of computations of the photoacoustic piezoelectric spectra, both amplitude and phase, of a series of AII–BVI compounds and their comparison with experimental results. For the interpretation of experimental spectra several multilayer models were developed and applied. Computer analysis showed that it was not possible to interpret the experimental results in the model of a single layer in the case of real samples. In this article three multilayer models are presented and illustrated by experimental results and numerical characteristics.
Photothermal microscopy of silicon epitaxial layer on silicon substrate with depletion region at the interface
Authors: Ikari T. , Roger J. P. , Fournier D.
Published: January 2003

Photothermal microscopy has been used for investigating semiconductor materials to evaluate carrier diffusivity, lifetime, and surface recombination velocity. The effects of the depletion region between epitaxial and substrate Si with different conduction types are studied. Although the observed curves are well explained by the theoretical predictions for surface reflectivity, no drastic change is observed for the different structures. This may be due to the fact that the thickness of the epitaxial layer is too large to reveal clearly the effect of the depletion region at the PN junction. However, the result for low-frequency modulation at 10 kHz may indicate this effect.
Boundary conditions in theory of photothermal processes in solids
Authors: Gurevich Yuri , Logvinov Georgi , Lashkevich Igor
Published: January 2003

In this work general boundary conditions are obtained for the linear nonstationary heat diffusion equation. It is shown that both surface heat conduction and surface heat accumulation must be taken into account for the validity of energy balance at the surface. The latter process is important at fast temperature variation in time.
Investigation of nonradiative transition processes in p- and n-type silicon single crystals by piezoelectric photothermal spectroscopy
Authors: Memon Aftab A. , Fukuyama Atsuhiko , Sato Syoichiro , Ikari Tetsuo
Published: January 2003

The piezoelectric photothermal spectroscopy (PPTS) technique was used to study the nonradiative excitation/deexcitation process in p- and n-type single crystal silicon. The effectiveness of PPTS to investigate surface states and bulk properties of single crystal silicon has been demonstrated. PPTS measurements were conducted on p- and n-type, 〈100〉 orientation, single crystal silicon samples. A broad peaked signal around 1.18±0.01 eV at room temperature showed the characteristics of slow surface states present on a silicon surface. One more signal bearing a peak around 1.07±0.005 eV was due to bulk effect. The PPTS measurements conducted at various temperatures revealed band-to-band and valence band-to-excitons states’ transition with phonon assistance. The measurements at 4.2 and 110 K resolved four types of phonon participation. A good agreement between theoretical expressions and experimental data substantiates our findings that our proposed technique is useful to investigate phonon contribution in the absorption edge for rather thin semiconductor samples.
Piezoelectric and pyroelectric study of Zn1-x-yBexMnySe mixed crystals
Authors: Zakrzewski J. , Firszt F. , Legowski S. , Meczynska H. , Pawlak M. , Marasek A.
Published: January 2003

This paper deals with investigations of thermal properties of Zn1-x-yBexMnySe bulk crystals by the photoacoustic (PA) method. Piezoelectric and pyroelectric transducers were used for investigation of continuous wave photoacoustic spectra. The values of thermal diffusivity were estimated using the dependence of amplitude and phase of the PA signal on the light modulation frequency.
Dependence of thermal conductivity of porous silicon on porosity characterized by photoacoustic technique
Authors: Shen Qing , Toyoda Taro
Published: January 2003

We have applied a photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching with greatly different porosities (20%–60%). From the dependence of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration, the effective thermal diffusivities for the two-layer PS on Si samples were determined. Using a two-layer model, the thermal conductivity of the PS films was evaluated and found to decrease greatly as the porosity is larger than 30%, which was two or three orders of magnitude lower than that reported for monocrystalline silicon. The results demonstrate that the thermal conductivity of PS films depends strongly on its structure.
Effect of sensitization by quantum-sized CdS on photoacoustic and photoelectrochemical current spectra of porous TiO2 electrodes
Authors: Toyoda Taro , Sato Jun , Shen Q.
Published: January 2003

We report the optical absorption characteristics of highly porous, polycrystalline TiO2 electrodes, on which CdS nanocrystal particles are adsorbed, measured by the photoacoustic (PA) method together with the photoelectrochemical (PEC) current characteristics. The PA spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase in the number of CdS coating layers to 20 and becomes almost constant at more than 20 layers, indicating the possibility of the growth of CdS coated layers. The increase in PEC current intensity and a clear shift of spectra to the lower photon energy region are observed with the increased number of CdS coated layers, indicating the possibility of the transfer of photoexcited electrons of the CdS nanocrystals to the TiO2 conduction band. The PEC current spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase of in the number of CdS coating layers to 20 and decreases with a further increase in the number of layers coated to 40. Thus, nanocrystals of low-band-gap semiconductors are suitable for the sensitization of TiO2 PEC solar cells as well as dye sensitization.
The effects of eluent’s optothermal parameters on TLS detection in gradient HPLC
Authors: Kožar Logar J. , Franko M.
Published: January 2003

The effects of changing solvent composition on the limits of detection (LOD) of thermal lens spectroscopy (TLS) detection in gradient elution HPLC have been studied from the perspective of solvent’s thermooptical properties. The refractive index and the temperature dependence of refractive index were measured and are reported for the first time for the methanol-acetone and methanol-ammonium acetate solutions used in this work, and some other methanol based chromatographic eluents. The TLS signal noise during a gradient HPLC protocol is increasing and its value reaches the maximum with a considerable time delay (up to 3 min) compared to the end point of the gradient protocol. The length of the chromatographic column was found to be an important parameter in reduction of signal noise resulting from incomplete solvent mixing. For some carotenoids the LOD values on the order of 50–100 pg/mL can be obtained on a 25 cm column with solvents that yield an increase in TLS enhancement factor up to 1.6 times during the gradient HPLC analysis.
Buffer-gas pressure influence on multiphoton absorption in SF6–N2 mixtures
Authors: Markushev D. D. , Terzić M. , Jovanović-Kurepa J.
Published: January 2003

In this article the results of pulsed IR photoacoustic spectroscopy measurements of multiphoton absorption and relaxation processes in SF6–N2 mixtures are presented. The total average number of absorbed photons per one absorbing molecule (basic physical quantity which characterized multiphoton processes) during the laser pulse 〈n〉total is used and analyzed with a generalized coupled two-level model. This type of analysis is based on buffer-gas pressure (pbuff) functional behavior of 〈n〉total and calculation of its partial values depending on collisions, 〈n〉coll, and laser fluence, 〈n〉Φ, influence. Using different methods of photoacoustic spectroscopy, collisionaly induced rotational and vibrational to translational relaxation process parameters (τrot and τV-T, respectively) are quantitatively obtained and used to determine partial values of 〈n〉coll, 〈n〉rot, and 〈n〉V-T. It will be shown that a method based on ∂〈n〉total/∂p functional dependence on pbuff and laser fluence Φ can be used to confirm or predict the existence of some processes during the laser pulse, such as dissociation or strong vibrational to vibrational energy transfer, which can contribute to the total amount of energy absorbed into the investigated sample. This could allow one to apply this method and control laser field–molecule interaction in different gas mixtures, and help one to understand multiphoton absorption processes in detail.
Determination of physical parameters of conducting polymers by photothermal spectroscopies
Authors: de Albuquerque J. E. , Melo W. L. B. , Faria R. M.
Published: January 2003

Photothermal spectroscopies, photopyroelectric and photoacoustic, were used to obtain physical parameters of polyaniline–emeraldine base (PANI-EB) and poly(o-methoxyaniline)–emeraldine base (POMA-EB), such as thermic parameters like thermal diffusivity, thermal conductivity, and specific heat. These studies were done for PANI-EB and POMA-EB films in the 400<λ<900 nm wavelength range. The photopyroelectric intensity Vn(f ) and the phase Fn(f ) (f being the chopping frequency) for a given λ of the saturation part of the PPES spectrum signal were independently measured, as well as the intensity Vn(λ) and its phase Fn(λ). Equations of both the intensity and the phase of the PPES signal, taking into account the thermal and the optical characteristics of the PANI and POMA films and the pyroelectric detector, were used to fit the experimental results. It was observed that, in contrast with the strong doping dependence of the electrical conductivity, the thermal parameters of PANI films remained practically unchanged under doping. This apparent discrepancy is explained by the granular metal model of doped PANI.
Photoacoustic spectral studies on lanthanide amino acid complexes
Authors: Yang Yue-tao , Zhao Gui-wen , Zhang Shu-yi
Published: January 2003

Several kinds of lanthanide complexes with glycine, alanine, phenylalanine, and tryptophan were synthesized and their photoacoustic (PA) spectra were measured. For the complexes of weakly fluorescent lanthanide ions with amino acids, the PA spectra reflect the influences of the ligands on the energy levels of lanthanide ions, whereas for the complexes of fluorescent lanthanide ions with amino acids, the PA spectra can be used to study the energy transfer from aromatic amino acids to lanthanide ions. At last, separating the overlapping peaks of lanthanide complex with tryptophan using the PA phase resolved method is introduced.
Nonradiative processes in transition ions in crystals
Authors: Grinberg M. , Śliwiński A. , Sikorska A.
Published: January 2003

We present a model describing a photoacoustic signal in the presence of spatial energy migration from the luminescence center to the surface. The model has been used for describing the relation between photoacoustic and absorption spectra in the YAG:Cr3+ crystal. Considering the frequency dependence of photoacoustic spectra signals and absorption under 348 and 605 nm excitation, we have estimated the radius of the excitation energy diffusion length.
Acoustic mode suppression in an off-axially coupled resonant cell for laser photoacoustic spectroscopy
Authors: Nukihara K. , Izuhara I. , Sokabe N.
Published: January 2003

We report a resonant photoacoustic cell of off-axis coupling type for laser photoacoustic spectroscopy of molecular species at low pressures. Using a waveguide CO2 laser operating on a 9 μm R (10) line and 4% C2H4/N2 standard gas, the time development of the photoacoustic signal from cylindrical resonant horns of different diameters is studied. Fast Fourier transform analysis of the observed photoacoustic signal revealed that (a) the resonant frequency depends strongly on pressure under low pressures, (b) the quality factor increases with pressure as well as with horn radius, (c) the number of excited modes and their relative intensities depend strongly on pressure as well as on horn radius, (d) an increase in horn radius results in multimode excitation and in interference of the modes, and (e) the mode interference tends to spoil the quality factor. An off-axially coupled resonant horn of medium volume is demonstrated to operate essentially on the fundamental axial mode with the quality factor being improved by a factor of 1.5.
Energy and volume changes induced by photoinitiated proton releasing reaction with apomyoglobin
Authors: Choi Jungkwon , Terazima Masahide
Published: January 2003

The photodissociation reaction of o-nitrobenzaldehyde (NBA) aqueous solution and of the NBA solution with a protein, apomyoglobin (ApoMb), were studied by the time-resolved transient grating (TG) technique. The amount of released thermal energy and the volume change accompanied with this reaction were determined by the TG and photoacoustic method. Without the protein, the photoproduct of NBA releases a proton in the solution (pH jump reaction). The time profile of the grating signal of NBA and ApoMb shows two diffusing species with diffusion coefficients of 1.39±0.15 and 0.14±0.02×10−9 m2 s−1, respectively. From the diffusion coefficients, we suggest that the photoproduct of NBA induces a molecular recombination reaction between ApoMb and another small molecule or ion in the solution.
Study of thermal parameter temperature dependence of pyroelectric materials
Authors: Longuemart S. , Sahraoui A. Hadj , Dadarlat D. , Delenclos S. , Kolinsky C. , Buisine J. M.
Published: January 2003

A simplified photopyroelectric configuration that allows the determination of the temperature-dependent thermal parameters of pyroelectric materials is described. The procedure is based on a combination of phase and amplitude signal data obtained at a single frequency. Experimental results obtained on the thermal parameters of LiTaO3 single crystal are presented.
Depth profilometric case studies in caries diagnostics of human teeth using modulated laser radiometry and luminescence
Authors: Jeon Raymond J. , Mandelis Andreas , Abrams Stephen H.
Published: January 2003

Simultaneous measurements from human teeth of photothermal radiometric (PTR) and luminescence (LM) signals induced by an intensity modulated laser have been performed to assess the feasibility of detecting deep lesions and near-surface cracks, to examine the effects of varying enamel thicknesses, the presence of fillings, and stains on the surface of teeth. A commercial dc luminescence monitoring instrument (DIAGNOdent by KaVo) was also used to examine a set of teeth for comparison purposes with PTR and LM. PTR amplitude signals from carious regions and from thin enamel were higher than those from healthy regions and thicker enamel. A crack produces a peak in the PTR amplitude scan, as well as a sudden change in the luminescence amplitude at the corresponding point. At low frequencies (5 Hz), the PTR amplitude showed high sensitivity to a deep (about 2 mm) lesion, while at high frequencies (700 Hz) it was more sensitive to surface cracks. It was concluded that by selecting proper modulation frequencies of the laser, measurements of PTR and LM signals could be used as a dental diagnostic technique with a small, inexpensive, low-power (<30 mW) semiconductor laser as a light source emitting in the optical window range of hard tissue (650–1000 nm).
Spectroscopic photothermal radiometry as a deep subsurface depth profilometric technique in semiconductors
Authors: Shaughnessy D. , Mandelis A.
Published: January 2003

The theoretical and experimental aspects of spectroscopic photothermal radiometry (PTR) of semiconductors are presented and the potential of the technique for depth profilometry is established. A three-dimensional model of the PTR signal from a semiconductor excited by light of arbitrary optical penetration depth is presented. Numerical simulations of the PTR response to the electronic transport parameters and the optical penetration depth of the excitation source are presented. Intensity-modulated frequency scans and two-dimensional surface scans at fixed frequencies have been performed at several different absorption depths on a Si wafer with various degrees of mechanical damage introduced to either the front or the back surface. The electronic transport parameters obtained from fitting the frequency scans to the theoretical model and analysis of the experimental curves show that while the surface recombination velocities extracted from the fits do not vary significantly with excitation wavelength, the carrier recombination lifetime and the overall sensitivity of the photothermal radiometric signal to spatially localized damage is strongly influenced by the proximity of the injected excess carrier density centroid to the defect location. This correlation between the sensitivity of the PTR signal to a localized defect and the proximity of the injected carriers to the defect demonstrates the potential for spectroscopic PTR as a depth profilometric technique for semiconductors.
Practical analysis of polymers with depth varying compositions using Fourier transform infrared photoacoustic spectroscopy (plenary)
Authors: McClelland John F. , Jones Roger W. , Luo Siquan
Published: January 2003

Fourier transform infrared photoacoustic spectroscopy can be used as a nondestructive method to probe the molecular composition of materials as a function of depth into the sample. This is done by varying the thickness of the surface layer being analyzed, which can be as great as some tens of micrometers, depending on optical and thermal properties. Computational methods are described to process photoacoustic amplitude and phase spectra for both semiquantitative and quantitative depth analyses. These methods are demonstrated on layered and gradient samples.