Dispersive infrared photothermal beam deflection spectroscopy

A single-beam dispersive photothermal beam deflection (PBD) spectrometer system usable in the IR range is described. A Nernst glower along with a severely modified Perkin-Elmer Model 421 monochromator were used to illuminate a solid sample with modulated monochromatic IR radiation. The resulting photothermal effect generated at the sample's surface caused modulated changes in the refractive index of the air over the sample, causing a probe laser beam grazing the surface to be deflected. The deflections were measured with a bi-cell silicon photodetector. Experiments and analysis of the deflection system showed that lenses used to focus the probe beam at the sample were not needed, and that an improvement in the PBD signal could be obtained by increasing the sample-to-detector distance, but only until a certain sample-detector separation was attained. The dispersive PBD instrument is less sensitive than one based on an interferometer but can be profitably used for studies requiring control of the modulation frequency. Useful spectra of solids were recorded over the 4000-550 cm⁻¹ region using IR excitation in the approximately 5 × 10⁻⁶−5 × 10⁻⁷W range.     

Sagnac interferometer for photothermal deflection spectroscopy

Photothermal deflection spectroscopy is combined with a Sagnac interferometer to enhance the sensitivity of the absorption measurement by converting the photothermal beam deflection effect into the light intensity change by the interference effect. Because of stable light interference due to the common path, the signal intensity can be amplified without increasing the noise by extending the optical path length between a sample and a photodetector. The sensitivity is further improved by the use of focusing optics and double-pass geometry. This makes photothermal deflection spectroscopy applicable to any kind of material in the whole visible region with a xenon lamp for excitation and water or air as a deflection medium.     

Hydrogen chemisorption on a-Si:H

Work function measurements, Auger-electron spectroscopy, and electron energy-loss spectroscopy were used to study the adsorption of atomic hydrogen on sputter-cleaned H-depleted surfaces of a-Si:H. Chemisorption proceeds by the formation of surface monohydride and dihydride, to be distinguished by energy-losses of 9 eV and 7 eV, resp., and by energy shifts of the L₁L₂₃V Coster-Kronig transitions. Surface hydrogeneration is also achieved by effusion of hydrogen during heat treatments at T ? 200° C. For H exposures exceeding some Langmuirs the surfaces are decomposed due to the formation of SiH₃ or SiH₄.     

Characterization of photovoltaic cells using the photothermal deflection spectroscopy

The equilibrium segregation coefficientK ₀ of the following impurities has been measured in high-purity tellurium: Ag, Al, As, Cr, Cu, Fe, In, Mn, Ni, Pb, Pd, Ti, V, and their diffusion coefficient in liquid tellurium determined at 550 °C.     

New calibration method for UV-VIS photothermal deflection spectroscopy set-up

Photothermal deflection spectroscopy has emerged as a useful technique for the determination of the absorption of materials with a small absorption coefficient. The technique offers relative values of the material absorptivity and, therefore, requires a calibration procedure in order to determine the absolute values. In this work, we present a new calibration method for a photothermal deflection spectroscopy set-up working in the UV-VIS, spectral range. The method is based on the use of reference samples with different levels of absorption. The samples, consisting of single thin films of amorphous carbon on transparent substrates, are optically characterized by means of spectrophotometric measurements. The accurate characterization of the samples enables the computation of their corresponding optical absorptivity in the PDS set-up. The calibration method is cross-checked by comparison of the measurements for the different reference samples and is finally applied to the study of the absorption of dielectric films in the UV.     

Continuous-wave photothermal deflection spectroscopy with fundamental and harmonic responses

A diffraction theory of continuous-wave photothermal deflection (PD) spectroscopy with fundamental and harmonic responses is presented. The displacement of the probe beam centroid is found to be a rigorous measurement of PD effect, which leads to a set of analytical solutions to the fundamental and the second-order harmonics. Harmonics are caused by the diffraction of the probe beam in the mirage region, which could not be handled by geometric-optics theory. This theory can be used to study bulk materials, thin films, and layered-structure samples. Experimental results are in good agreement with the theory.     

Hydrogen bonding in methanol studied by infrared spectroscopy

Infrared spectra in the region of the OH stretching band of supercritical methanol (T_c = 239.4 °C, P_c = 8.08 MPa) have been recorded over the 100–400 °C temperature range and 30–100 MPa pressure range. The spectra were obtained using an FT-IR spectrometer equipped with a special high-pressure, high-temperature IR cell and a specially developed measuring technique that utilizes the C–H stretching vibrations as an internal standard. The experimental results show that both pressure and temperature affect the OH stretching band of supercritical methanol. Isobaric heating leads to a strong decrease in the peak intensity and a shift to higher frequencies. Isothermal compression leads to a slight increase in peak intensity and shifts to lower frequencies. These studies are consistent with previous studies conducted at lower pressures and with qualitative models of the extent of hydrogen bonding in liquid and supercritical methanol.     

Effect of He+ and H+ ion irradiation on polystyrene films probed by NIR photothermal deflection spectroscopy

+ and H⁺ ions. Photothermal deflection spectroscopy (PDS) technique was used to record the absorption spectrum in the wavelength range 1.20 μm to 2.0 μm. The evolution of the various overtone and combination bands occurring in this range has been related to the changes taking place in the polystyrene structure. Received: 1 September 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999     

双层材料光热偏转光谱的定量研究

从三线传热方程出发,给出了双层材料的光热偏转光谱的理论模型,讨论了光热偏转信号的特征及其在扫描成象应用中的意义.     

Hyperfine interaction between hydrogens and dangling bonds in a-Si:H studied by endor

In order to investigate the corelation between dangling bonds and hydrogens in a-Si:H, electron-nuclear double resonance (ENDOR) experiment has been employed on undoped a-Si:H films before and after isochronal annealings. It has been demonstrated through the analyses of ENDOR as well as ESR and NMR that in high ESR spin-density sample the dangling bonds are coupled mainly with hydrogens corresponding to the broad component of NMR, while those are with the narrow component in low ESR spin-density sample.     

An investigation of the photothermal deflection spectroscopy technique for temperature measurements in a flame

The technique of photothermal deflection spectroscopy (PTDS) is investigated for temperature measurements in a flame. The spatial distribution of temperature is measured in two different types of burners operating with methane and oxygen, and methane and air. The spatial distributions of the temperature are in qualitative agreement with our expectations. At two points, the temperatures measured by PTDS have been compared with those measured by Boltzmann distributions. The measurements agree within their uncertainties. All the effects that affect the reliability of this technique are investigated and discussed. Finally, the pros and cons of the PTDS technique for temperature measurement are discussed. Received: 31 January 2002 / Published online: 8 August 2002     

Nonlinear absorption in ionic crystals determined by pulsed photothermal deflection

Intensity-induced nonlinear absorption in several ionic crystals have been investigated at 308 nm by pulsed phototermal deflection in the prebreakdown region. The main mechanism of energy deposition is two or three photon absorption.     

Simultaneous measurement of absolute OH concentration,temperature and flow velocity in a flame by photothermal deflection spectroscopy

We demonstrate the use of photothermal deflection spectroscopy for a simultaneous measurement of absolute minority-species concentration, temperature and flow velocity in a flame from the analysis of a single data trace. The ability to make absolute concentration measurements, as well as the ability to measure three important combustion parameters simultaneously, may make this technique quite useful in many circumstances. Received: 27 August 2002 / Revised version: 26 September 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +1-479/575-4580, E-mail: rgupta@uark.edu