Cm-1 Line Research Articles

Structural, morphological, and EMI shielding evaluations of Sm-Mn co-doped Sr-based M-type hexaferrite for Ku band applications

High-performance, thin, and lightweight EMI (Electromagnetic interference) materials with outstanding shielding effectiveness were explored over the last years to solve the problems in electronic devices. Magnetic absorbing materials have extensive bandwidth, good impedance matching, and excellent absorption features. In the present study, Sm-Mn Sr-doped M hexaferrites with Sr1-xSmxFe12-yMnyO19 whereas (x= 0.00, 0.025, 0.05, 0.075, y = 0.00, 0.25, 0.5, 0.75) were prepared by the chemical route. XRD, FESEM, HRTEM, FTIR, VSM, and VNA are used to evaluate the properties of the Sm-Mn doped Sr-based M-type hexagonal ferrite. The XRD (X-ray diffraction) results revealed the presence of a hexagonal phase in the prepared samples. Rietveld refinement also confirmed the phase purity for the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FESEM (Field emission scanning electron microscopy) and HRTEM (High-resolution transmission electron microscopy) images revealed the hexagon-type shapes of the particles in the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FTIR (Fourier transform infrared spectroscopy) spectra showed the 446–620 cm-1 lines, confirming the presence of the tetrahedral and octahedral phases of hexagonal ferrites. Dielectric and electromagnetic shielding effectiveness (SE) parameters are evaluated for Sm-Mn doped Sr-based M-type hexagonal ferrite. The electromagnetic parameters, such as complex refractive index, absorption and impedance, are also investigated for the Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having epoxy resin with 20 wt%, 30 wt% and 50 wt% samples, respectively. SE parameters are higher at more extensive filler loading. The green shielding index was found higher for Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having 20 wt% epoxy resin and decreased with filler loading. It is found the epoxy/Sm-Mn doped Sr-based M-type hexagonal ferrites-based composites are excellent absorbers in the Ku band. The investigated absorbers could be the best candidates for next-generation EMI green shielding absorbing devices and applications.

Spectroscopy and Theoretical Modeling of Tetracene Anion Resonances.

The positions and widths of the optically allowed electronic states of the tetracene radical anion located above the detachment threshold energy (i.e anion resonances) are mapped out using total photodetachment yield spectroscopy of cryogenically cooled ions. The presence of these states is detected via the sharp increase in the photodetachment yield compared to that of the monotonic nonresonant direct photodetachment background. The resolution of the resulting spectrum is limited by the ∼5 cm-1 line width of the tunable laser and thus provides a stringent benchmark for computations of the energies and autodetachment lifetimes of these resonance states. The experimental results are compared to high-level electronic structure computations and line width modeling using the orbital stabilization method. These theoretical results are found to be in near quantitative agreement with the experimental data, highlighting their capability to accurately describe the energies and lifetimes of anion resonances for relatively large molecules.

Crystallographic Insights into the Crystal Structure and Intrinsic Properties of Ca12Al14O33-Type Rb3LiZn2(MoO4)4 Single Crystals.

Molybdate oxide materials have attracted considerable academic interest owing to their multifunctional optoelectronic properties and applications. However, to date, studies on the intrinsic properties of multiple molybdates have rarely been implemented. Herein, a prospective triple molybdate crystal, Rb3LiZn2(MoO4)4, with high crystalline quality was successfully grown using top-seeded solution growth (TSSG) approaches. Intriguingly, it affords a cage-like structure with the I4̅3d space group, analogous to that of Ca12Al14O33 (C12A7). The Rb3LiZn2(MoO4)4 crystal exhibits excellent thermal stability up to 603 °C, accompanied by a congruent melting nature. Simultaneously, it preserves the optical merits of a large band gap of 4.10 eV and a wide transmission window of 0.29-5.4 μm, which are superior to those of most molybdate crystals. More importantly, Raman spectroscopic measurements demonstrated that the title compound possesses an intense Raman shift located at 925 cm-1 and narrow line width, facilitating a stimulated Raman laser. In addition, first-principles calculations were also implemented to elucidate the structure-property relationships of Rb3LiZn2(MoO4)4. These observations provide an empirical platform for intuitively comprehending the underlying properties of multiple molybdates and pave the way for exploiting Raman crystals.

Structure, Optical and Electrical Properties of the High Doped ZnO Thin Films Deposited By RF Magnetron Sputtering of Powder Target in Methane Ambient

The ZnO thin films were deposited by RF-magnetron sputtering of ZnO powder target using pure argon, argon with hydrogen and argon with methane as reactive gas. Surface morphology and crystalline structure of the films were studied by SEM, XRD and XRR techniques. Chemical composition and optical properties were investigated by SIMS, Raman scattering spectroscopy (RSS), PL spectroscopy and spectral ellipsometry. Electrical measurements were performed on the ZnO films deposited on SiO2-Si and silicon wafers n- and p-type with Ni contacts by TLM, IV, CV characteristics, admittance spectroscopy, Van der Pauw and Hall methods. It was found that growth morphology, crystalline structure, optical and electrical properties of the films are strongly affected by adding methane to argon during the deposition process. Adding of methane resulted in a destruction of hexagonal phase texture and considerable increase a size of ZnO nanocrystallites (from 50 nm for argon to 200 nm for argon/methane working gas). SIMS measurements demonstrated that methane promoted hydrogen incorporation into the ZnO film that was more than an order of magnitude larger in comparison with adding molecular hydrogen in the gas mixture at the same concentration. Adding of methane resulted in a high energy shift of near band edge ultraviolet photoluminescence band, quenching of deep level emission in the visible spectral range and increase of optical band gap from 3.24 to 3.45 eV. The strongest effect of methane has been found for electrical resistivity that reduced by 3 orders of magnitude in comparison with films deposited in pure argon. Additionally, electrical conductance of the ZnO film deposited at high methane concentration does not depend on measurement temperature. Hall method with combination with Van der Pauw resistivity measurements shows: strong n-type doping of the film; donor concentration more than 1020 cm-3 slightly depending on methane concentration; maximum electron mobility about 7 cm2/V s. The direct comparison of resistivity and donor concentration of the films deposited using methane and molecular hydrogen as doping precursors has demonstrated that doping efficiency of methane is about an order of magnitude larger than that of molecular hydrogen under similar deposition conditions. On the other hand, methane addition in working gas resulted in an intensity decrease of the E2L (100 cm-1) and E2H (438 cm-1) lines in the RSS that can be associated with some disturbance of the ZnO structure. Additionally a peak at 71 cm-1 was observed in some films that can be related to the metallic Zn. The possible mechanisms of the ZnO film formation, nature of the doping and electron transport mechanisms will be discussed.

Оптоэлектронные и наноразмерные особенности наноструктурированного пористого кремния

This paper considers the optoelectronic properties of porous nanostructured silicon obtained by electrochemical etching method. It was noted that the electrolyte concentration affects the depth of porosity, while the anodizing current density affects the density and size of crystallites, as well as the photoluminescence spectra. The results of the Raman measurement showed a low-frequency shift of the wavenumber on the 504 cm-1 line, which changes the frequency difference Δω to 16 cm-1 wavenumber units, while the cross-sectional diameter of the nanocrystallites is distributed from 2.3 nm to 4.3 nm.

(Invited) Raman Thermography of β-Ga2­O3 Nanomembrane FETs on Diamond

Despite the extremely low thermal conductivity of Ga2O3, remarkable progress in device technology has been achieved in a very short time since commercial HVPE epilayers were first introduced by Novel Crystal Technology, Japan. For example, Schottky barrier diodes with a forward current of 2 A were recently demonstrated, and thicker, low-doped epi has pushed breakdown voltage beyond 2 kV [1, 2]. Recent demonstrations of Raman thermography in Ga2O3 transistors, however, have proven that a heat spreading solution must be developed in order to realize the potential of Ga2O3 for high power operation [3]. As all devices eventually become thermally limited, effective heat dissipation will also assist in improving reliability and eventual commercialization of Ga2O3 devices. A number of approaches have been devised for GaN HEMTs in the past, where heat generated by the 2DEG under high electric field near the gate can push device temperatures above GaN reliability limits [4, 5]. In this work, we show for the first time that a reasonable operating temperature can be achieved in a Ga2O3 device at a practical power density. While wafer-scale thermal management solutions for Ga2O3 are still being developed, we have exploited the natural (100) cleave plane of Ga2O3 to mechanically exfoliate a highly-doped Ga2O3 membrane onto an insulating single-crystalline CVD diamond substrate and subsequently fabricate a Ga2O3-channel FET using standard electron-beam lithography techniques. Thermal characterization in the transistor channel was performed using a Raman thermography setup by first calibrating the Raman shift of the 169 cm-1 line as a function of temperature on a thermal chuck. This phonon line was chosen as its temperature dependent shift is relatively linear [6]. Independent measurements of the Au contact temperature using thermoreflectance imaging and modeling of the device produced a good agreement with the data [7, 8]. The combination of a thin, highly Sn-doped (2.7x1018 cm-3) Ga2O3 channel, high quality ALD Al2O3 gate dielectric, high thermal conductivity diamond substrate, and a very high critical field for both the channel and substrate (8 MV/cm for Ga2O3, 10 MV/cm for diamond) allowed for a high current density to be maintained under high drain bias. As a result, a maximum DC power density of about 60 W/mm and channel temperature of about 160 °C were simultaneously obtained before destructive failure occurred in the Ga2O3 FET channel. To the authors’ best knowledge, this is the highest power density demonstrated by any semiconductor device. [1] J. Yang et al., IEEE Trans. Electr. Dev., vol. 65, no. 7, pp. 2790, 2018. [2] J. Yang et al., ECS Jour. Solid State Sci. and Technol., vol. 7, no. 5, pp. Q92-Q96, 2018. [3] J.W. Pomeroy et al., IEEE Electr. Dev. Lett., 2018. DOI: 10.1109/LED.2018.2887278. [4] M.J. Tadjer et al., IEEE Electron Dev. Lett., vol. 33, no. 1, pp. 23-25, 2012. [5] K.D. Chabak et al., IEEE Electr. Dev. Lett., vol. 31, no. 2, pp. 99-101, 2010. [6] D. Dohy, G. Lucazeau, A. Revcolevschi, J. Solid State Chem. 45, 180-192 (1982). [7] J. Noh et al., Proc. Dev. Res. Conf., 2018. DOI: 10.1109/DRC.2018.8442276. [8] J. Noh et al., “High Performance β-Ga2O3 Nano-membrane Field Effect Transistors on a High Thermal Conductivity Diamond Substrate,” IEEE Jour. Electr. Dev. Soc., under review.

ICL-based mid-infrared carbon dioxide sensor system for deep-sea natural gas hydrate exploration.

For deep-sea natural gas hydrate exploration, highly sensitive detection of the dissolved gas in seawater near the seabed is significant because it requires the sensor system to be small in size, low in power consumption, and high in sensitivity. A mid-infrared sensor system was developed to detect dissolved carbon dioxide (CO2) in sea-water, while employing a 4319 nm continuous-wave interband cascade laser (ICL) and a multi-pass gas cell (MPGC) with a 29.8 m optical path length. A compact rectilinear optical structure was proposed by using the free-space-emitting ICL and tunable laser absorption spectroscopy (TLAS). This leads to a minimized sensor size and a simple optical alignment for deep-sea operation. A strong CO2 absorption line, located at 2315.19 cm-1 and a weak 2315.28 cm-1 line and at a low pressure of 40 Torr, was targeted for low- and high-concentration CO2 detection within a concentration range of 0-1000 parts per billion by volume (ppbv) and 0-40 parts per million by volume (ppmv), respectively. The limit of detection (LoD) was assessed to be 0.72 ppbv at an averaging time of 2 s, and the response time was measured to be ~30 s at a flow rate of ~180 standard cubic centimeters per minute (sccm). Deployment of the CO2 sensor combined with a gas-liquid separator was carried out for the CO2 detection in the gas extracted from water, which validated the reported sensor system's potential application for deep-sea natural gas hydrate exploration.

Binding and Competition of Be2+ and Ca2+ with Model Phospholipid Membranes

Membrane surfaces, carrying multiple electronegative groups, attract metal ions and provide a rich environment for multiple ion-mediated signaling events. Be2+, a small divalent ion known for its toxicity and ability to activate abnormal immune responses is recognized as a strong ligand for anionic lipids. Be2+'s tight binding to the surface of phosphatidylserine-containing (PS) membranes was recently shown to diminish the recognition of phosphatidylserine by macrophages. The major hypothesis for the mechanism of this process is that Be2+ is able to outcompete and partially displace Ca2+ from its binding sites. This displacement may be due to a very different 4-fold coordination of Be2+ by oxygens, and the inability of small Be2+ to substitute for six-coordinated Ca2+ in physiological reactions. FTIR is a highly informative technique in studies of ligand binding and ion coordination at membrane interfaces. Despite ITC studies showing that Be2+ has the capacity to compete with Ca2+ on the surface of PS liposomes, there have been no spectroscopic studies of Be2+ interactions with phospholipids. In this work, we apply the ATR-FTIR technique and present the spectral ‘signature’ of Be2+ binding to PS manifested as a dominant 1095 cm-1 line apparently arising from ion binding to phosphate oxygens. Be2+ produces no visible alteration of carbonyl bands and appears to partially suppress carboxyl vibrational bands. Dialysis experiments show that FTIR can be used to watch the ionic equilibria and determine binding constants for specific atomic groups in the phospholipids. We show that Be2+ tightly binds not only to anionic PS, but also to zwitterionic PC. We also observe Be2+ readily displacing more abundant Ca2+ from phosphate head groups.

Measurement of Low Concentration Nitrogen in Czochralski Silicon by Infrared Absorption Spectroscopy

Nitrogen in Czochralski silicon mainly forms pair with oxygen at low concentration, in contrast to forming NN pair at high concentration. To measure nitrogen concentration in NO pair form, local vibration modes of NO family such as NO, NOO and NOO2 were examined. By removing LVMs by NN family and oxygen complexes from the spectra, weak absorption lines hidden by them were successfully delineated. To identify them, their dependence on the N concentration, and annealing temperature and time was examined and compared to the annealing behavior of NN family and far infrared absorption of shallow thermal donor family composed of NO family. The LVM candidates were identified, 769 and 945 cm-1 lines for NO, 736 and 1022 cm-1 lines for NOO, 973 and 1002 cm-1 lines for NOO2 and 855 and 1064 cm-1 lines for ONO configurations. Nitrogen concentration in the NO family was obtained from the sum of the absorbance of these lines

Measurement of Low Concentration Nitrogen in Czochralski Silicon by Infrared Absorption Spectroscopy

Introduction Nitrogen plays an important role in suppressing the grown-in defects in single crystalline silicon. Nitrogen in silicon mainly forms interstitial Ni-Ni pairs. In low concentration CZ silicon, for example in the 1013 cm-3 range, however, nitrogen mainly forms Ni-Oi pair. The concentration of nitrogen in silicon ([N]) is measured by infrared absorption spectroscopy (IR) of local vibration modes of NN pair [1]. Therefore IR measurement of [N] in the 1013 cm-3 range is impossible and far infrared electronic transition absorption of shallow thermal donors due to NO is used [2]. To solve this problem, we have been looking for the IR absorption of NO pairs [3]. Here we show the new absorption we found, tentative identification and trial to measure [N] using these absorption lines. Experimental Samples were cut from the nitrogen doped CZ (NCZ) silicon crystals. They were polished on both sides for IR measurement. Samples were annealed at 450-1100 oC for 2 hours [4]. IR measurement was done at room temperature with wavenumber resolution of 2 cm-1. The differential absorption spectra using the nitrogen-free sample as the reference were obtained. New absorption and its thermal behavior As we have already reported, there were many new absorption lines in the annealed samples. They were located at 714, 720, 736, 855, 945, 973, 989, 1002, 1045, 1065 cm-1 and so on [3]. The annealing temperature dependence of their intensity was examined in detail and compared to that of the NN group. The thermal behavior of NN, NNO and NNO2 had been interpreted as the quasi-equilibrium reaction of the oxygen attaching and detaching among these complexes [4]. Absorption lines located at 855, 973, 1002, 1065 cm-1 showed maxima at 600 oC and weak above that, similar to NNO2 behavior. This suggested that similar quasi-equilibrium reaction occurred in NO group also at the same temperature. The 973 and 1002 cm-1 lines saturated for high [N], similar to STD, in contrast to NNO2 increased linearly with [N] [6]. Thus the 1002 cm-1 line was assigned as NOO2i [6]. Absorption lines located at 720 and 736 cm-1 showed maxima at 650 oC and were gradually weakened above that, similar to NNO behavior. Absorption lines located at 945 and 989 cm-1 showed minima at 600 oC and strong around 700-800 oC, similar to NN behavior. Therefore it is likely that lines at 720 and 736 cm-1 correspond to NOO and lines at 945 and 989 cm-1 to NO. Concentration measurement of NO group In the high concentration range, nitrogen has three configurations. Nitrogen concentration is obtained as the sum of [NN], [NNO] and [NNO2]. The dipole moments of the three configurations are not equal. They were determined both theoretically and experimentally. As a result, nitrogen concentration is obtained as the weighted sum of absorption coefficients of three NN based configurations, multiplied by the conversion coefficient from absorption coefficient α to concentration, k; k(αNN+1.5×αNNO+0.5×αNNO2) [1]. The weight is reciprocal ratio of the dipole moment. As the quasi equilibrium holds, the sum of [NN] [NNO] and [NNO2] should be constant and was already confirmed in many cases. Fig. 1 shows that in this case, the sum was nearly constant under 800 oC and confirms that [N] can be obtained in this way. In case of NO group, the same procedure is thought to be possible. Dipole moment of NO group was calculated to be about 1/2 of that of NN group [6], because there is only one N in NO group. The weighted sum of absorbance of NO, NOO and NOO2 candidates using the same weight as those of NN group is shown also in the figure. It suggested the similar tendency, though difficulty in determining the weak and overlapping absorption was observed. Conversion coefficient for NO group may also be 1/2 of that for NN group. Roughly speaking, the absorbance of NO group in this sample is about 1/10 of NN group. Therefore [N] in NO group is about 1/20 of that in NN group. It depends on the sample. [1] N. Inoue, K. Shingu and K. Masumoto, Semiconductor Silicon 2002, 875 (2002). [2] H. Ono and M. Horikawa, Jpn. J. Appl. Phys. 42, L261 (2003). [3] N. Inoue, M. Nakatsu and H. Ono, Physica B, 376-377, 101 (2006). [4] K. Tanahashi and H. Yamada-Kaneta, Jpn. J. Appl. Phys. 42, L223 (2003). [5] H. Ch. Alt and H. E. Wagner, J. Appl. Phys., 106, 103511 (2009). [6] N. Inoue, M. Nakatsu, H. Ono and Y. Inoue, Materials Sci. Eng., B, 134, 202 (2006). Figure 1

Design and Performance Evaluation of MB-MIMO-UWB for Different Transmission Techniques

This work represents a design of multiple input multiple output multi band ultra wide band (MIMO-MB-UWB) system by using four antennas at the transmitter and eight antennas at the receiver with the combination of orthogonal space time block code encoders and minimum mean square (MMSE) equalizes. The proposed system used for a short range wireless communication and is one of the most promising technologies for generating a high data-rate. It will likewise take on a very important role in next generation wireless communication system where everyone will be plugged in at anywhere, anytime, hence use of 4 * 8 antennas enables to increase capacity and data-speed of the system by four times and also supplies an efficient wireless link as the receiver has multiple choice to commit the best data by comparing the quality of meeting data. The functioning and efficiency of the system are valued along the basis of bit-error-rate (BER, transmitted–received signal, constellation plot and MMSE performance plot for binary phase shift keying, quadrature phase shift keying (QPSK), 16-quadrature amplitude modulation (QAM), 64-QAM, 256-QAM modulation schemes under CM1 line of sight (LOS) channel and CM2 non-line of sight (N-LOS) channel condition of the range between 0 and 4 m. Outcomes show that with use of MMSE equalizer, inter symbol interference is reduced, especially for a high order modulation system which further raises the operation of the proposed scheme. On the basis of BER It is also noted, that QPSK is the best modulation scheme for LOS condition and 16-QAM is the best for N-LOS condition. Additionally, proposed work will also be helpful in academics and for the different researchers and technologists who are operating in the UWB system, because a complete illustration of simulation will be exemplified and explained.

Joint Estimation of TOA and PPM Symbols Using Sub-Nyquist Sampled IR-UWB Signal

Impulse radio ultra wideband (UWB) signals are used in various applications which require joint localization and communication. Due to the large bandwidth of the UWB signal, the estimation of time of arrival (TOA) and data symbols requires high sampling rates. This letter describes a sub-Nyquist rate receiver, which can jointly estimate TOA and data symbols. We first represent the received UWB signal in a new domain in which it is sparse. Then, we design physical layer waveforms and estimation algorithms to exploit this sparsity for joint estimation of TOA and pulse position modulation data symbols. The performance of the receiver is compared against the maximum likelihood (ML)-based receiver using an IEEE 802.15.4a CM1 line of sight UWB channel model. The proposed algorithm yields performance similar to the ML-based algorithms with only a fraction of sampling rate at high SNRs (> 25 dB).

Stimulated Raman scattering in liquid water in a low-frequency region

Stimulated Raman scattering is studied in liquid water using pulse laser at a wavelength of 532 nm. At a lower excitation energy, Stokes line and anti-Stokes line 3426 cm-1 can be observed in the forward Raman scattering. When excitation intensity is increased to 140 mJ, the low frequency 313 cm-1 line in the forward Raman scattering can be observed, and the 3389 cm-1 Stokes line and 3268 cm-1 Stokes line in the backward Raman scattering can also be observed. The experimental results demonstrate that the structure of water under the action of the intense excitation energy is similar to that of ice Ⅷ.

CELLA MEDIA DISTANCE IN HUMAN BRAIN IN RELATION TO AGE AND GENDER

To determine whether simple linear measurements can be used as an accurate and reproducible replacement of the volumetric ones. We measured the cella media distance (CM1) and the distance between the right and left human brain surfaces (CM2)--measured along the CM1 line--in the groups of women (F) and men (M) who were divided according to diagnoses into three subgroups (F1-3 and M1-3). Examinations were carried out under standardized conditions: axial serial CT (Computed Tomography) images, in 4 mm layers (333 patients). Measured values were detected by Osiris Software. Recorded values were statistically analysed. We found very highly significant (subgroups M1, M3), and significant (subgroups F1, F2, F3, M2) associations between the cella media distance and the decade of age. There were only non-significant differences in CM1 distances between men and women and between the diagnoses groups as well. Correlation between cella media distance and volume of lateral ventricles was greater in men in both, subgroup M1 (r = 0.659, P < 0.0001) and in a mixed group where all the three male subgroups M1-3 were combined into one group (r = 0.675, P < 0.0001). Among women the correlation was lower, however still significant (r = 0.357, P < 0.0001 for F1 and r = 0.465, P < 0.0001 for F1-3). The cella media distance is much better predictor of brain lateral ventricular volume in men than in women.

High spectral resolution analysis of tunable narrowband resonant grating waveguide structures

A high spectral resolution analysis of narrowband reflection filters based on resonant grating waveguide structures is presented. A tunable high-performance dye laser with ∼ 0.15 cm-1 line width and a beam analyzing system consisting of three simultaneously controlled CCD cameras were used to investigate grating waveguide resonances at wavelengths in the 694 nm and 633 nm ranges. A reflectivity of ∼ 91% and a line width of ∼ 0.55 nm were measured and theoretically modeled for a resonant reflection filter specifically designed for the ruby laser wavelength 694.2 nm. For a second grating waveguide structure, designed for the helium-neon laser emission wavelength 632.8 nm, we observed a thermal shift of its spectral resonance position of several nanometers, when increasing the sample temperature by some degrees. An inverse thermal shift was observed when the structure was subsequently cooled down to room temperature. Our results suggest implementation of grating waveguide devices combining a narrow line width with a tunability of the resonant response into innovative concepts for reflection filter and sensor applications.

Spectral Properties of Americiuin(III) in Silicate Matrices-Concentration-dependent Up-conversion Emission.

We have been pursuing the spectroscopic properties of actinide ions in silicate matrices. One facet of these studies involves the behavior of Stokes and anti-Stokes emissions exhibited by Am3+ in these hosts. Several attributes have been found to influence the spectral profile, which include excitation wavelength, laser power, and dopant-concentration. Excitation with the 514.5 nm (19435 cm-1) line of argon laser provides anti-Stokes emissions at 21100 and ~19920 em-1 in the boro-silicate matrices. This up-conversion was found to proceed through a multi-photon scheme, and the efficiency increases with increased dopant concentration. Based on our concentration-dependent studies, the up-conversion is suggested to involve a cross-relaxation process [(5D1', 7F0') (7F6, 7F2')] between neighboring americium ions.

Collision-Free Infrared Multiphoton Dissociation of Silane

We have measured an upper limit of 17 J/cm2 for the threshold fluence for collision-free CO2 laser IRMPD of silane by detecting the SiH2 product in its electronic and vibrational ground state. The threshold drops to ∼4 J/cm2 when silane molecules are irradiated by all lines from a pulsed NH3 laser. This value further drops to less than 2 J/cm2 when the molecules are pre-excited to the first Si−H stretch overtone. Using the NH3 laser on the 868 cm-1 line, the dissociation yield of pre-excited SiH4 reaches saturation at a laser fluence of 6 J/cm2. The substantial difference in the fluence threshold and optimal dissociation frequency of the ground and excited molecules allows us to perform highly selective dissociation of pre-excited silane in the presence of a large excess of ground-state molecules.

Metalation of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin in silver colloids studied via time dependence of surface-enhanced resonance Raman spectra

In SERS-active systems, when a free base porphyrin is adsorbed at a roughened metal surface, the metal ion may be incorporated into the porphyrin core. We have investigated the metalation kinetics of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP), reflected in the time evolution of its SERRS spectra. To establish proper metalation Raman markers, resonance Raman spectra of the free base and chemically Ag metalated TMPyP forms were measured under different conditions. The increase in intensity of the 395 cm-1 line, the decrease in intensity of the 329 cm-1 line, the reduction of the 1337+1360 cm-1 doublet to one strong line at 1340 cm-1 and the vanishing of the 1140 cm-1 medium line (the last exceptionally for 514.5 nm excitation) were found to be suitable markers for quantitative analysis. All other spectral changes related to metalation may coincide with effects caused by other variations of the porphyrin state. Time evolution of the porphyrin metalation was studied in various Ag colloid systems, with or without phosphate anions, citrate and/or Triton X-100. Time-dependent SERRS spectra of TMPyP were recorded within periods from minutes to several hours. Factor analysis of the SERRS spectra proved that the spectral changes were induced by only one phenomenon (metalation). The SERRS spectra were decomposed into the spectrum of the free base TMPyP and that of its Ag metalated form, and the metalation kinetics were determined by means of the time dependence of the metalated form portion in the SERRS spectrum. The results show a remarkable reliance on the state of the metal surface. © 1998 John Wiley & Sons, Ltd.

The 1280 Cm−1 Absorption Line in Amorphous Hydrogenated Boron Carbide

AbstractWe report infrared absorption measurements that provide evidence for the presence of boron carbide icosahedra in amorphous hydrogenated boron carbide thin films. The infrared absorption spectra is dominated by an intense line at 1280 cm-1 with a FWHM of ≃320 cm-1. Similar lines have been previously reported in polycrystalline boron carbide, where boron carbide icosahedra make up the unit cell. In both systems, the linewidth narrows and the peak position shifts to higher energy with increasing carbon concentrations. From annealing studies of amorphous hydrogenated boron carbide, hydrogen plays a very small role in the 1280 cm-1 line. Finally, the integrated intensity of the 1280 cm-1 line is a sublinear function of the boron concentration, providing further evidence that the carbon concentration in these icosahedra increases as the carbon concentration of the film increases.

ION RADIATION DAMAGE OF C60 FILMS

The C60 films have been implanted with 120—360 keV H,N, Ar and Mo ions by using a 200 keV heavy ion accelerator. The samples were investigated by Raman spectra. The results showed an exponential decrease of intensity for 1469 cm-1 line depending on the kind of ions and dose. There appeared a structural transformation of C60 to amorphous carbon at certain doses, which is correlated to the nuclear energy transfer. H ions implantation resulted in an asymmetrical broadening of 1469 cm-1 line, which is due to the electronic energy transfer.