The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals

This paper presents results of the photoacoustic (PA) spectral studies of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. This is the first attempt of the quantitative evaluation of the surface quality of the samples from the photoacoustic experimental spectra.     

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals with the use of the optimization methods

This paper shows results of the photoacoustic (PA) spectral studies, with the microphone detection, of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. The procedure of computations of the volume and surface absorption spectra with the use of the optimization method is presented in the paper too.     

Numerical analysis of the photoacoustic spectra of silicon samples with differently treated surfaces

This paper presents results of the photoacoustic (PA) spectral studies of a series of silicon samples with differently prepared surfaces. The PA amplitude and phase spectra of the samples indicated existence of the damaged surface layers. In the paper the two layer mathematical model of a sample with a damaged surface layer, that was used for numerical interpretation of the amplitude and phase PA spectra of the investigated samples, is presented and discussed. This model comprises the Urbach edge contribution to the optical absorption coefficient spectrum and it enabled observation of its influence on the PA amplitude spectra of silicon samples.     

Photoacoustic spectroscopy analysis of thin semiconductor samples

This paper is an analysis of determination possibility of the optical absorption coefficient spectra of thin semiconductor layers from their normalized photoacoustic amplitude spectra. Influence of multiple reflections of light in thin layers on their photoacoustic and optical absorption coefficient spectra is presented and discussed in detail. Practical formulae for the optical absorption coefficient spectrum as a function of the normalized photoacoustic amplitude spectrum are derived and presented. Next, they were applied for computations of the optical absorption coefficient spectra of thin In₂S₃ thin layers deposited on a glass substrate. This method was experimentally verified with the optical transmission method.     

Numerical analysis of absorption and transmission photoacoustic spectra of silicon samples with differently treated surfaces

This paper presents results of the photoacoustic (PA) spectral studies, of a series of silicon samples with differently prepared surfaces, in two PA experimental configurations, so-called, absorption and transmission ones. The PA amplitude spectra of the samples indicated existence of the damaged surface layers. In the paper, the two layer mathematical models of a sample with a damaged surface layer that were used for numerical interpretation of the amplitude PA spectra of the investigated samples, are presented and discussed.     

Piezoelectric photoacoustic spectroscopy of surface states of Zn0.81Be0.04Mg0.15Se mixed crystals

This paper presents basics of the space selective piezoelectric photothermal spectroscopy method. This method is illustrated with the experimental piezoelectric amplitude and phase spectra of ZnBeMgSe(4%Be, and 15%Mg) samples and with the corresponding optical transmission spectra. The fitting of theoretical curves computed in the piezoelectric space sensitive spectroscopy method to experimental data indicated the presence of surface states located on both surfaces of the sample. From the fitting procedure the optical absorption coefficient spectra connected with the surface absorption on both sides of the sample were determined.     

Transmission and absorption based photoacoustic methods of determination of the optical absorption spectra of Si samples — Comparison

This paper is a comparison of two photoacoustic methods of determination of the optical absorption coefficient spectra of semiconductors illustrated with results obtained from Si samples. It presents experimental transmission and absorption photoacoustic spectra of Si samples as also the appropriate models leading to the determination of optical absorption coefficient spectra. The idea and the experimental set-up of the analyzed methods are presented in the paper too. From the fitting procedure of theoretical characteristics to experimental transmission and absorption photoacoustic spectra and after computations of the optical absorption coefficient spectra three components of the optical absorption coefficient spectra of Si samples were identified i.e. band to band transitions, Urbach tail and free carrier absorption. Their parameters are given and discussed in the paper. At the end the advantages and disadvantages of both methods are discussed. To the best of our knowledge, no such proof of the correctness of the PA method of determination of optical absorption spectra has been done.     

Optical properties of xenon implanted CuInSe2 by photoacoustic spectroscopy

A theoretical relation is derived for the normalized photoacoustic amplitude signal of a gas-coupled cell for the case of double-layer solid samples with particular application given to ion implanted semiconductors. Numerical estimates for a solar cell of the type CdS/CuInSe₂ based on experimental measured data of these compounds are given to illustrate the photoacoustic effect originating from double-layer samples. In application to ion implanted semiconductors, we show that the absorption coefficient of the implanted layer can be very easily extracted by photoacoustic spectroscopy if the absorption coefficient of the untreated substrate is known. We also present the optical properties results obtained from the analysis of the effect of xenon implantation into CuInSe₂ single crystals with the energy of 40 keV and a dose of 5×10¹⁶ ions/cm².     

Photoacoustic method of determination of quantum efficiency of luminescence in Mn<Superscript>2+</Superscript> ions in Zn<Subscript>1−x−y</Subscript>Be<Subscript>x</Subscript>Mn<Subscript>y</Subscript>Se crystals

This paper presents step by step the procedure of determination of the quantum efficiency of luminescence of Mn²⁺ ions in the Zn_1−x−yBe_xMn_ySe crystals. The method is based on the photoacoustic spectroscopy approach. In the paper, the experimental spectra of absorbance, transmission, absorption and photoacoustic spectra of the samples are presented and analyzed from the point of view of the possibility of determination of the quantum efficiency of Mn²⁺ ion luminescence at room temperature. It was determined experimentally that in the investigated crystals the quantum efficiency of luminescence in the Mn²⁺ ions is about 35%, 40%, 32% for the absorption peaks at 430 nm, 470 nm, and 510 nm, respectively, for Zn_0.75Be_0.2Mn_0.05Se crystal.     

Photoacoustic spectra of Zn<Subscript>1-x</Subscript>Be<Subscript>x</Subscript>Te near the energy gap

The results of experimental studies of optical and structural properties in bulk crystals of Zn_1-xBe_xTe (x = 0.02, 0.06 and 0.12) were presented. The amplitude and phase photoacoustic (PA) spectra were measured and analyzed in dependence on the wavelength of the excitation optical beam, at different frequencies of modulation, using the PA microphone (PAmic) and PA piezoelectric (PApze) spectroscopy methods. The differences in PA spectra of as grown and annealed in zinc vapor samples were observed.     

An Overview of The Photoacoustic Phase Spectra of Rare Earth Complexes

Abstract

The photoacoustic(PA) amplitude and phase spectra of several kinds of rare earth (RE) complexes are reported and summarized briefly. It is observed that both the amplitude and phase spectra well characterize the different energy levels of the RE complexes. The phase angle of the RE complexes is associated with the relaxation time τ and the optical absorption coefficient β concerning with the π-π? transition and the f-f transitions, respectively. After individual detailed discussion of the phase spectra, a reasonable theoretical consideration is given to interpret the results.     

Photoacoustic phase shift as a chemically selective spectroscopic parameter

The phase information obtained in photoacoustic experiments can be used to separate the signals originating from chemical species with overlapping absorption spectra. This approach was applied to quantify parts per million CO levels in propylene using quartz-enhanced photoacoustic spectroscopy and a quantum cascade laser as an excitation source. The experimental data were used to evaluate V–T relaxation rates of CO and N₂O in propylene. PACS 42.62.Fi; 43.35.Sx     

Infrared-laser photoacoustic spectroscopy

This paper reviews the applications of IR-laser photoacoustics to trace-gas monitoring as well as to spectroscopic studies on absorbing liquids.In the first part we present a stationary, dual-beam CO-laser and a mobile CO₂-laser photoacoustic system which have both been applied to the monitoring of various gaseous pollutants. Emphasis is put on selectivity, sensitivity and on temporal resolution. Novel cell designs and experimental techniques and an iterative procedure for the analysis of photoacoustic spectra of multicomponent mixtures are introduced. New results are presented for measurements on car and industrial exhausts as well as on ambient air.The second part is devoted to theoretical and experimental photoacoustic studies on strongly absorbing liquids, in particular on the investigation of different boundary conditions. A characteristic enhancement of the photoacoustic signal in the liquid is obtained if a liquid or solid surface layer is present. This new phenomenon permits the analysis of surface films with a thickness of ⩾ 1 μm. Furthermore, the photoacoustic in-situ monitoring of the polymerization process on a liquid surface is presented for the first time.     

The photoacoustic absorption spectrum of V ions in α cristobalite SiO2

The photoacoustic absorption spectra of pure and vanadium-doped α cristobalite SiO₂ samples have been observed at room temperature. The results suggest a new assignment to the peaks in the spectrum of vanadium-doped samples.     

Determination of the low absorption coefficients of thick semi-conductor samples using rear side photoacoustic spectroscopy detection

Based on the Rosencwaig and Gersho theory, we have theoretically derived the photoacoustic signal in the gaz behind the unilluminated surface of thick samples and presented a simple analytical procedure for determining the low optical absorption spectra of these samples.The rear side photoacoustic spectroscopy (PAS) detection has been employed on thick samples of GaP (0,2-1mm) and optical absorption coefficients in the region between 15 to 200 cm^?1 were measured.Our results are discussed in comparison with those obtained by usual front side PAS detection and spectroscopic ellipsometry.     

Energy efficiency of near infrared cobalt luminscence in ZnSe:Co determined by a photoacoustic method

The paper presents results of computations of the energy efficiency of the cobalt luminescence in ZnSe:Co determined by the photoacoustic method. The transmission spectra, photoacoustic experimental and theoretical spectra, and the frequency dependence on the photoacoustic amplitude characteristics are presented. From them, the energy efficiency of Co²⁺ the near infrared luminescence (3200 nm) was computed in the frame of new proposed photoacoustic model of computations of the luminescence energy efficiency.     

Piezoelectric spectroscopic studies of Zn<Subscript>1-x-y</Subscript>Be<Subscript>x</Subscript>Mn<Subscript>y</Subscript>mixed crystals

This paper presents results of experimental and theoretical piezoelectric studies of a group of mixed crystals of the type Zn_{1 - x - y}Be_xMn_ySe. The fittings of theoretical to experimental amplitude and phase piezoelectric spectra were performed in a modified Jackson and Amer model. The influence of the surface treatment such as grinding, polishing and etching on the PZE spectra is analysed in the model of surface defects applied for the interpretation of the spectra for energies of photons below the energy gap of the crystal.     

Photoacoustic and reflectance spectra of zirconium-silicate pigments

Photoacoustic spectra and diffusion reflectance spectra of powdered zirconium-silicate ceramic pigments (Zr_0·97V_0.03Si₄, Zr_0·98Pr_0·02SiO₄ and ZrSiO₄ 0·05 -Fe₂O₃) have been measured and found to be closely correlated. The signal saturation problem connected with both spectral techniques is extensively discussed with respect to a particle size of powdered samples. The photoacoustic technique enables one to establish the bulk optical absorption coefficients of the powdered samples and thermal parameters, knowing the particle size diameters.     

Stimulated Raman rotational photoacoustic spectroscopy using a quartz tuning fork and femtosecond excitation

Molecular alignment of linear molecules (O₂, N₂, CO₂ and CO) is measured photoacoustically in the gas phase. The rotational excitation is accomplished using a simple femtosecond stimulated Raman excitation scheme, employing two femtosecond pulses with variable delay between the pulses. Molecular alignment is determined directly by measuring the energy dumped into the gas by quartz-enhanced photoacoustic spectroscopy (QEPAS), utilizing a quartz tuning fork as a sensitive photoacoustic transducer. The experimental results demonstrate for the first time the use of a tuning fork for resonant photoacoustic detection of Raman spectra excited by femtosecond double pulses and match both simulation and literature values.     

Photoacoustic spectroscopy of diamond powders and polycrystalline films

Photoacoustic spectroscopy is used to study optical absorption in diamond powders and polycrystalline films. The photoacoustic spectra of diamond powders with crystallite sizes in the range from ∼100 μm to 4 nm and diamond films grown by chemical vapor deposition (CVD) had a number of general characteristic features corresponding to the fundamental absorption edge for light with photon energies exceeding the width of the diamond band gap (∼5.4 eV) and to absorption in the visible and infrared by crystal-structure defects and the presence of non-diamond carbon. For samples of thin (∼10 μm) diamond films on silicon, the photoacoustic spectra revealed peculiarities associated with absorption in the silicon substrate of light transmitted by the diamond film. The shape of the spectral dependence of the amplitude of the photoacoustic signal in the ultraviolet indicates considerable scattering of light specularly reflected from the randomly distributed faces of the diamond crystallites both in the polycrystalline films and in the powders. The dependence of the shape of the photoacoustic spectra on the light modulation frequency allows one to estimate the thermal conductivity of the diamond films, which turns out to be significantly lower than the thermal conductivity of single-crystal diamond. Fiz. Tverd. Tela (St. Petersburg) 39, 1787–1791 (October 1997)