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Tetsuo Ikari - One of the best experts on this subject based on the ideXlab platform.

  • Photoacoustic Spectra for porous silicon using piezoelectric transducer and microphone
    Japanese Journal of Applied Physics, 2001
    Co-Authors: Toshio Kawahara, Kenji Yoshino, Masaki Okamoto, Jun Morimoto, Akitsugu Kimura, Toru Miyakawa, Kenichiro Tahira, Tetsuo Ikari
    Abstract:

    Photoacoustic (PA) Spectra are measured for porous Si (PS) using piezoelectric detectors (PPT) and compared with the microphone PA (MPA) Spectra to examine the nonradiative properties of PS that has complicated nanostructures. Three peaks (peaks 1 and 2, and a small peak at 600 nm) are observed in samples 2 and 3 with porosities p=60 and 70%, respectively, while only a single peak (peak 1) is observed in sample 1 with p=30%. Peak 2 is related to the band gap of the Si substrate. In contrast, peak 1 seems to be due to the absorption change at the band gap unique to the PS. This band gap shifts to higher energy for PS samples with higher porosity. We propose that this band gap is defined by the largest size nanocrystals, where PS has nanocrystallite size distribution. The small peak at 600 nm is related to the PL peak and it is observed only in PPT Spectra. These results suggest that different mechanisms are operating in PPT Spectra and MPA ones for the enhancement of the PA Spectra.

  • piezoelectric Photoacoustic Spectra of zn doped ingaalp light emitting diodes
    Materials Science in Semiconductor Processing, 2001
    Co-Authors: Atsuhiko Fukuyama, Hiroaki Nagatomo, Yoshito Akashi, Tetsuo Ikari
    Abstract:

    Abstract Zn atoms diffused from the Zn-doped p-InAlP cladding to the active layer in InGaAlP visible-light-emitting diodes may cause a degeneration of light output efficiency. A doping effect of the Zn atoms was investigated using a piezoelectric Photoacoustic measurement from a nonradiative transition point of view. The results indicate that the Zn-doping induces a decrease of the nonradiative component of the electron transitions above the bandgap of the active layer.

  • Photoluminescence and Photoacoustic Spectra of ZnSe bulk crystals and epitaxial layers
    Journal of Luminescence, 2000
    Co-Authors: Kenji Yoshino, Minoru Yoneta, H Mikami, Tetsuo Ikari
    Abstract:

    Temperature dependence of the piezoelectric Photoacoustic (PPA) and photoluminescence (PL) Spectra are clearly observed between liquid helium and room temperatures for nondoped ZnSe bulk crystals and epitaxial layers. In both samples, the PPA signals are clearly observed at room temperature. However, any PL emissions are not observed at room temperature. Two kinds of recombination processes, i.e., both radiative and nonradiative processes are observed at 80 K in the bulk crystals.

  • temperature dependence of Photoacoustic Spectra in cuinse2 thin films grown by molecular beam epitaxy
    Solar Energy Materials and Solar Cells, 1998
    Co-Authors: Kenji Yoshino, Atsuhiko Fukuyama, T Shimizu, Koji Maeda, Paul Fons, Akimasa Yamada, Shigeru Niki, Tetsuo Ikari
    Abstract:

    Abstract CuInSe2 (CIS) thin films, the thickness of about 1.0 μm and composition of Cu In ratio (γ = 1.79), were grown on (0 0 1)-oriented GaAs substrate by molecular beam epitaxy (MBE) at substrate temperature of Ts, = 450°C. The samples have been characterized by means of piezoelectric Photoacoustic (PPA) measurements between liquid helium (4.2 K) and room temperature (300 K). Two distinct PPA signals due to band gap of CIS and GaAs are observed in the whole temperature range from 4.2 to 300 K and the PPA signals of CIS decrease curvilinearly at the temperature range. Since the PPA signals of CIS thin films can be obtained up to room temperature, the PPA measurements are quite effective to obtain the optical characterizations, especially for the nonradiative recombination processes.

  • Photoacoustic Spectra of si wafers at liquid helium temperature
    Japanese Journal of Applied Physics, 1995
    Co-Authors: Hiroyuki Matsuyama, Tetsuo Ikari, Hirosumi Yokoyama, Koji Futagami
    Abstract:

    Photoacoustic (PA) measurements of p- and n-type Si single crystals are carried out at liquid helium temperature (4.2 K). Two small peaks around 1.2 eV are observed in both samples. The energy of the higher-energy peak at 1.21 eV agrees with the thresholds of free exciton absorption with the emission of TO momentum-conserving phonons. The lower-energy peak shifts to the higher energy side with the decrease of the excitation light intensity. The possibility of the formation of an electron-hole drop for the lower energy peak will be discussed to explain the experimental results.

Jun Morimoto - One of the best experts on this subject based on the ideXlab platform.

  • Photoacoustic Spectra and thermoelectric properties of amorphous si au ge au superlattice
    Japanese Journal of Applied Physics, 2008
    Co-Authors: Hiroaki Takiguchi, Yoichi Okamoto, Hisashi Miyazaki, Jun Morimoto
    Abstract:

    The amorphous Si–Ge–Au superlattice shows highly superior thermoelectric properties. In this paper, we describe the Photoacoustic Spectra and thermoelectric properties of these materials with various Au concentrations and discuss the mechanism responsible for high thermoelectric properties. Amorphous Si/Au/Ge/Au superlattice was prepared by alternate deposition of Si, Ge and Au. The Au concentration dependence of electric and optical properties was measured. We investigated the band structure of amorphous Si–Ge–Au over a wide energy range by combining the electrical and optical measurements. The energy range was from 0.01 (the impurity level of the Au dopant) to 2 eV (band edge). We found that the Au atoms in amorphous Si–Ge not only produce strong potential fluctuations but also act as acceptor impurities.

  • Photoacoustic Spectra on mn doped zinc silicate powders by evacuated sealed silica tube method
    Journal of Materials Science, 2008
    Co-Authors: Yoshihiro Inoue, Taro Toyoda, Jun Morimoto
    Abstract:

    The non-radiative transition processes on non-doped Zn2SiO4 and Zn2SiO4:Mn powders with various Mn concentrations were studied by Photoacoustic (PA) spectroscopy. Zn2SiO4:Mn x powders were prepared by dry reaction within an evacuated silica glass tube. As the result of photoluminescence (PL) measurement, the increase of PL intensity for green emission on samples doped with Mn between 1% and 6% and the concentration quenching for luminescence on samples doped with Mn between 7% and 12% were confirmed. For the green luminescence on zinc silicate doped with Mn phosphor, the PL decay behavior is assumed to be due to tunneling directly from excited states of electron traps to the excited states of Mn-ion. The Mn content dependence of PL intensity for green emission is well interpreted by tunneling theory and the results of PA Spectra, that is, the green emission is assisted by tunneling from non-radiative levels of Mn-ion to luminescencet level as 4T1(4G).

  • Photoacoustic Spectra on pr doped zno powders
    Journal of Alloys and Compounds, 2006
    Co-Authors: Yoshihiro Inoue, Masaki Okamoto, T Kawahara, Jun Morimoto
    Abstract:

    Abstract Photoacoustic (PA) spectroscopy is a powerful tool for examining optical properties as non-radiative recombination in powdered samples that are difficult to measure by the conventional reflection or transmission spectroscopy because of the light scattering. We applied the PA spectroscopy to evaluate the non-radiative transition of the Pr 3+ in ZnO powders with various Pr concentrations and sintering temperatures. The PA Spectra seems to depend on the inner state of the Pr 3+ in ZnO matrix, where the Pr can easily segregate to the ZnO grain boundaries and form intergranular phase based Pr 2 O 3 .

  • nonradiative transition processes observed from Photoacoustic Spectra of zno thin films fabricated by pulsed laser deposition
    Japanese Journal of Applied Physics, 2005
    Co-Authors: Yoshihiro Inoue, Masaki Okamoto, Toshio Kawahara, Jun Morimoto
    Abstract:

    Photoacoustic (PA) spectroscopy is a powerful tool for evaluating nonradiative transition processes in semiconductors. By this technique, we evaluated the nonradiative transition process (NRTP) in ZnO thin films that were fabricated by pulsed laser deposition on R-sapphire and C-sapphire substrates in vacuum and in oxygen ambient. The samples each exhibited a specific PA spectrum reflecting the characteristics based on different crystalline orientations and qualities. The relationships between a NRTP and a radiative transition process (RTP) were studied using photoluminescence and PA spectroscopy to investigate the effect of oxygen vacancy (VO) compensation in films. (1120) ZnO/R-sapphire indicated that the NRTP in the UV region and the RTP in the green-yellow region dominate strongly over transition processes. On the other hand, (0001) ZnO/C-sapphire had opposite domination relationships in the RTP and the NRTP to those of (1120) ZnO/R-sapphire. We concluded that the decrease of the NRTP that originated from the compensation of VO strongly affected the RTP in (0001) ZnO/C-sapphire and the NRTP in (1120) ZnO/R-sapphire.

  • Photoacoustic Spectra of heavily co doped zno powders
    Japanese Journal of Applied Physics, 2005
    Co-Authors: Masaki Okamoto, Yoshihiro Inoue, Toshio Kawahara, Jun Morimoto
    Abstract:

    Photoacoustic (PA) Spectra were measured for heavily Co-doped ZnO powders using a microphone at room temperature. In PA Spectra, the PA signal peaks of Co2+ and Co3+ can be observed with the ZnO band-gap signals. The two PA peaks related to Co ions show the Co valency change induced by the sintering, and depend on the sintering temperature and the Co concentration. For the heavily Co-doped samples, the Co valency conversion occurred at a low sintering temperature. PA spectroscopy has potential for estimating the inner ion state change during the sintering process.

Xueding Wang - One of the best experts on this subject based on the ideXlab platform.

  • frequency domain analysis of Photoacoustic imaging data from prostate adenocarcinoma tumors in a murine model
    Ultrasound in Medicine and Biology, 2011
    Co-Authors: Ronald E Kumon, Cheri X Deng, Xueding Wang
    Abstract:

    Photoacoustic imaging is an emerging technique for anatomical and functional sub-surface imaging but previous studies have predominantly focused on time-domain analysis. In this study, frequency-domain analysis of the radio-frequency signals from Photoacoustic imaging was performed to generate quantitative parameters for tissue characterization. To account for the response of the imaging system, the Photoacoustic Spectra were calibrated by dividing the Photoacoustic Spectra (radio-frequency ultrasound Spectra resulting from laser excitation) from tissue by the Photoacoustic spectrum of a point absorber excited under the same conditions. The resulting quasi-linear Photoacoustic Spectra were fit by linear regression and midband fit, slope and intercept were computed from the best-fit line. These Photoacoustic Spectral parameters were compared between the region-of-interests (ROIs) representing prostate adenocarcinoma tumors and adjacent normal flank tissue in a murine model. The mean midband fit and intercept in the ROIs showed significant differences between cancerous and noncancerous regions. These initial results suggest that such frequency-domain analysis can provide a quantitative method for tumor tissue characterization using Photoacoustic imaging in vivo.

  • frequency domain analysis of Photoacoustic imaging data from prostate adenocarcinoma tumors in a murine model
    Ultrasound in Medicine and Biology, 2011
    Co-Authors: Ronald E Kumon, Cheri X Deng, Xueding Wang
    Abstract:

    Abstract Photoacoustic imaging is an emerging technique for anatomical and functional sub-surface imaging but previous studies have predominantly focused on time-domain analysis. In this study, frequency-domain analysis of the radio-frequency signals from Photoacoustic imaging was performed to generate quantitative parameters for tissue characterization. To account for the response of the imaging system, the Photoacoustic Spectra were calibrated by dividing the Photoacoustic Spectra (radio-frequency ultrasound Spectra resulting from laser excitation) from tissue by the Photoacoustic spectrum of a point absorber excited under the same conditions. The resulting quasi-linear Photoacoustic Spectra were fit by linear regression and midband fit, slope and intercept were computed from the best-fit line. These Photoacoustic Spectral parameters were compared between the region-of-interests (ROIs) representing prostate adenocarcinoma tumors and adjacent normal flank tissue in a murine model. The mean midband fit and intercept in the ROIs showed significant differences between cancerous and noncancerous regions. These initial results suggest that such frequency-domain analysis can provide a quantitative method for tumor tissue characterization using Photoacoustic imaging in vivo . (E-mail: cxdeng@umich.edu and xdwang@umich.edu )

Leszek Bychto - One of the best experts on this subject based on the ideXlab platform.

  • determination of the optical absorption Spectra of thin layers from their Photoacoustic Spectra
    Optical Materials, 2018
    Co-Authors: Leszek Bychto, M Malinski, A Patryn, M S Tivanov, V F Gremenok
    Abstract:

    Abstract This paper presents a new method for computations of the optical absorption coefficient Spectra from the normalized Photoacoustic amplitude Spectra of thin semiconductor samples deposited on the optically transparent and thermally thick substrates. This method was tested on CuIn(Te0.7Se0.3)2 thin films. From the normalized Photoacoustic amplitude Spectra, the optical absorption coefficient Spectra were computed with the new formula as also with the numerical iterative method. From these Spectra, the value of the energy gap of the thin film material and the type of the optical transitions were determined. From the experimental optical transmission Spectra, the optical absorption coefficient Spectra were computed too, and compared with the optical absorption coefficient Spectra obtained from Photoacoustic Spectra.

  • Investigations of the optical absorption Spectra of porous silicon layers on the Silicon backing by the nondestructive Photoacoustic method
    Thin Solid Films, 2010
    Co-Authors: Mirosław Maliński, Leszek Bychto, Ł. Chrobak, Tomasz Okupski
    Abstract:

    This paper presents a series of experimental Photoacoustic Spectra of porous silicon layers on the crystalline silicon and their numerical analysis performed in the proposed two layer model. The goal of the analysis was to calculate the optical absorption coefficient Spectra of porous silicon from the Photoacoustic Spectra of the porous silicon layer on the silicon backing. The character of the observed optical absorption band associated with the porous silicon was revealed.

  • Photoacoustic investigations of the optical absorption Spectra of porous silicon layers on a silicon backing
    Solid State Communications, 2009
    Co-Authors: Mirosław Maliński, Ł. Chrobak, Leszek Bychto
    Abstract:

    This paper presents a series of experimental Photoacoustic Spectra of porous silicon layers on crystalline silicon and their numerical analysis performed in the proposed two-layer model. The goal of the analysis was to calculate the optical absorption Spectra of porous silicon from the Photoacoustic Spectra of porous silicon layers on a silicon background. The experimental character of the observed absorption band associated with the porous silicon was revealed. This is the first attempt at a theoretical interpretation of the Photoacoustic Spectra of porous silicon on a silicon backing.

  • determination of a quantum efficiency of aii bvicompounds on the basis of Photoacoustic Spectra
    Journal De Physique Iv, 2005
    Co-Authors: M Malinski, Leszek Bychto, J Zakrzewski
    Abstract:

    The method of determination of the quantum efficiency η of irradiative relaxation processes in semiconductors is introduced and discussed. The correlation of the amplitude Photoacoustic Spectra in the high absorption region with the annealing process is used to estimate the values of η. The values of η, both for as grown and annealed crystals were determined and have been discussed. The results are presented for microphone and piezoelectric detection methods.

Ronald E Kumon - One of the best experts on this subject based on the ideXlab platform.

  • frequency domain analysis of Photoacoustic imaging data from prostate adenocarcinoma tumors in a murine model
    Ultrasound in Medicine and Biology, 2011
    Co-Authors: Ronald E Kumon, Cheri X Deng, Xueding Wang
    Abstract:

    Photoacoustic imaging is an emerging technique for anatomical and functional sub-surface imaging but previous studies have predominantly focused on time-domain analysis. In this study, frequency-domain analysis of the radio-frequency signals from Photoacoustic imaging was performed to generate quantitative parameters for tissue characterization. To account for the response of the imaging system, the Photoacoustic Spectra were calibrated by dividing the Photoacoustic Spectra (radio-frequency ultrasound Spectra resulting from laser excitation) from tissue by the Photoacoustic spectrum of a point absorber excited under the same conditions. The resulting quasi-linear Photoacoustic Spectra were fit by linear regression and midband fit, slope and intercept were computed from the best-fit line. These Photoacoustic Spectral parameters were compared between the region-of-interests (ROIs) representing prostate adenocarcinoma tumors and adjacent normal flank tissue in a murine model. The mean midband fit and intercept in the ROIs showed significant differences between cancerous and noncancerous regions. These initial results suggest that such frequency-domain analysis can provide a quantitative method for tumor tissue characterization using Photoacoustic imaging in vivo.

  • frequency domain analysis of Photoacoustic imaging data from prostate adenocarcinoma tumors in a murine model
    Ultrasound in Medicine and Biology, 2011
    Co-Authors: Ronald E Kumon, Cheri X Deng, Xueding Wang
    Abstract:

    Abstract Photoacoustic imaging is an emerging technique for anatomical and functional sub-surface imaging but previous studies have predominantly focused on time-domain analysis. In this study, frequency-domain analysis of the radio-frequency signals from Photoacoustic imaging was performed to generate quantitative parameters for tissue characterization. To account for the response of the imaging system, the Photoacoustic Spectra were calibrated by dividing the Photoacoustic Spectra (radio-frequency ultrasound Spectra resulting from laser excitation) from tissue by the Photoacoustic spectrum of a point absorber excited under the same conditions. The resulting quasi-linear Photoacoustic Spectra were fit by linear regression and midband fit, slope and intercept were computed from the best-fit line. These Photoacoustic Spectral parameters were compared between the region-of-interests (ROIs) representing prostate adenocarcinoma tumors and adjacent normal flank tissue in a murine model. The mean midband fit and intercept in the ROIs showed significant differences between cancerous and noncancerous regions. These initial results suggest that such frequency-domain analysis can provide a quantitative method for tumor tissue characterization using Photoacoustic imaging in vivo . (E-mail: cxdeng@umich.edu and xdwang@umich.edu )