Study of carrier concentration profiles in Al‐implanted Ge by micro‐Raman spectroscopy under different excitation wavelengths

The distribution profile of Al implanted in crystalline Ge has been investigated by micro‐Raman spectroscopy. Using different excitation laser lines, corresponding to different optical penetration depths, the Al concentration at different depths beneath the sample surface has been studied. We have found a strong correlation between the intensity of the Al–Ge Raman peak at ~370 cm⁻¹, which is due to the local vibrational mode of substitutional Al atoms, and the carrier concentration profile, obtained by the spreading resistance profiling analysis. A similar connection has been also observed for both shape and position of the Ge–Ge Raman peak at ~300 cm⁻¹. According to these experimental findings, we propose here a fast and nondestructive method, based on micro‐Raman spectroscopy under different excitation wavelengths, to estimate the carrier concentration profiles in Al‐implanted Ge. Copyright © 2013 John Wiley & Sons, Ltd.     

A non‐destructive approach for doping profiles characterization by micro‐Raman spectroscopy: the case of B‐implanted Ge

B‐implanted Ge samples have been investigated by micro‐Raman spectroscopy under different excitation wavelengths, with the aim of gaining insights about the B distribution at different depths beneath the sample surface. The intensities, observed under the different excitation wavelengths, of the B–Ge Raman peak at about 545 cm⁻¹, which is due to the local vibrational mode of the substitutional B atoms in the Ge matrix, have been used to calibrate the optical absorption lengths in B‐implanted Ge. Then, by using these calibrated values, a very sharp correlation between the spectral features of the Ge–Ge Raman peak at ~300 cm⁻¹ and the content of substitutional B atoms has been derived. Accordingly, a non‐destructive approach, based on micro‐Raman spectroscopy under different excitation wavelengths, is presented to estimate, at least at the lowest depths, the carrier concentration profiles from the spectral features of the Ge–Ge Raman peak. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of Ge-Sn at high pressure and high temperature in a laser-heated diamond anvil cell

Ge–Sn compound is predicted to be a direct band gap semiconductor with a tunable band gap. However, the bulk synthesis of this material by conventional methods at ambient pressure is unsuccessful due to the poor solubility of Sn in Ge. We report the successful synthesis of Ge–Sn in a laser-heated diamond anvil cell (LHDAC) at ~7.6 GPa &; ~2000 K. In situ Raman spectroscopy of the sample showed, apart from the characteristic Raman modes of Ge TO (Г) and β-Sn TO (Г), two additional Raman modes at ~225 cm^?1 (named Ge–Sn₁) and ~133 cm^?1 (named Ge–Sn₂). When the sample was quenched, the Ge–Sn₁ mode remained stable at ~215 cm^?1, whereas the Ge–Sn₂ mode had diminished in intensity. Comparing the Ge–Sn Raman mode at ~225 cm^?1 with the one observed in thin film studies, we interpret that the observed phonon mode may be formed due to Sn-rich Ge–Sn system. The additional Raman mode seen at ~133 cm^?1 suggested the formation of low symmetry phase under high P–T conditions. The results are compared with Ge–Si binary system.     

Micro‐Raman depth profiling of silicon amorphization induced by high‐energy ion channeling implantation

In this work, we study the silicon amorphization dependence on the crystal depth induced by 6‐MeV Al²⁺ ions implanted in the <110> and randomly oriented silicon crystal channels, which was not directly experimentally accessible in the previous similar high‐energy ion–crystal implantation cases. Accordingly, the micro‐Raman spectroscopy scanning measurements along the crystal transversal cross section of the ion implanted region were performed. The ion fluence was 10¹⁷ particles/cm². The scanning steps were 0.2 and 0.3 µm, for the channeling and random ion implantations, respectively. The obtained results are compared with the corresponding Rutherford backscattering spectra of 1.2‐MeV protons in the random and channeling orientations measured during the channeling implantation. Additionally, scanning electron microscope picture was taken on the transversal cross section of the implanted region in the channeling implantation case. We show here that the obtained silicon amorphization maxima are in excellent agreement with the corresponding estimated maxima of the aluminum concentration in silicon. This clearly indicates that the used specific micro‐Raman spectroscopy scanning technique can be successfully applied for the depth profiling of the crystal amorphization induced by high‐energy ion implantation. Copyright © 2013 John Wiley & Sons, Ltd.     

Conformational and structural studies of n‐propylamine from temperature dependent Raman and far infrared spectra of xenon solutions and ab initio calculations

The Raman and infrared spectra (4000 to 50 cm^–1) of the gas, liquid or solution, and solid have been recorded of n‐propylamine, CH₃CH₂CH₂NH₂. Variable temperature (−60 to −100 °C) studies of the Raman (1175 to 625 cm^–1) and far infrared (600 to 10 cm^–1) spectra dissolved in liquid xenon were carried out. From these data, the five possible conformers were identified and their relative stabilities obtained with enthalpy difference relative to trans–trans (Tt) for trans–gauche (Tg) of 79 ± 9 cm^–1 (0.9 ± 0.1 kJ/mol); for Gg of 91 ± 26 cm^–1 (1.08 ± 0.3 kJ/mol); for Gg′ of 135 ± 21 cm^–1 (1.61 ± 0.2 kJ/mol); for Gt of 143 ± 11 cm^–1 (1.71 ± 0.1 kJ/mol). The percentage of the five conformers is estimated to be 18% for the Tt, 24 ± 1% for Tg, 23 ± 3% for Gg, 18 ± 1% for Gg′ and 18 ± 1% for Gt at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug‐cc‐pVTZ from both second‐order Møller–Plesset (MP2, full) and density functional theory calculations by the Becke, three‐parameter, Lee–Yang–Parr method. Vibrational assignments were provided for the observed bands for all five conformers, which are supported by MP2(full)/6‐31G(d) ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. Estimated r₀ structural parameters were obtained from adjusted MP2(full)/6‐311+G(d,p) calculations. The results are discussed and compared with the corresponding properties of some related molecules. Copyright © 2012 John Wiley & Sons, Ltd.     

Application of mechanical scanning to ion implantation

Abstract

Atomic depth profiles from Be-implanted Si have been examined as a function of implant fluence and annealing, and the results have been correlated with theoretically calculated implantation induced damage profiles. The Be atomic depth profiles were obtained by secondary ion mass spectrometry (SIMS) techniques from samples implanted at 300 keV to fluences ranging from 2 × 10¹² to 10¹⁵ cm^?2. Subsequent to annealing at 600°C for 30 min, the Be SIMS profiles exhibited anomalous redistribution effects. The Be profiles obtained from the annealed samples had the same general features as the depth distribution of implant energy deposited into damage, based on Brice's¹ calculations. The correlation of the SIMS atomic profiles and the theoretical damage profiles indicated that Be “decorates” the implantation induced damage regions while redistributing during the annealing process.     

Spectroscopic analysis of a dye–mineral composite–a Raman and FT‐IR study

In this investigation, we address the question of how organic thioindigo binds to inorganic palygorskite to form a pigment similar to Maya Blue. We also address how such binding, if it occurs, might be affected by varying the proportion of dye relative to that of the mineral, and by varying the length of heating time used in preparation of the pigment. In addition to samples of palygorskite and thioindigo both alone, four synthetic pigment samples were prepared; two samples of 8 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h, and two samples of 16 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h. All samples were examined using Fourier transform‐infrared (FT‐IR) and FT‐Raman spectroscopy. For the pigment samples, FT‐IR peaks at 1627 cm⁻¹ are attributed to a downshifted CO stretching mode of thioindigo due to dye–clay interaction. This interpretation is corroborated by FT‐Raman CO peaks with 14 cm⁻¹ shifts to lower wavenumber for the pigment relative to thioindigo alone. Additional Raman scattering between 550 cm⁻¹ and 650 cm⁻¹ also suggests dye–clay interaction through metal–oxygen bonding. We are thus led to the possibility of mostly hydrogen bonding between silanol and carbonyl at lower dye concentration, with a predominance of metal–oxygen bonding at higher dye concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Germanium – the superior dopant in n‐type GaN

We present an experimental study about the influence of Si and Ge doping in GaN with focus on the occurring strain levels and overall crystalline quality. Extremely high quality samples were examined by means of Raman spectroscopy, demonstrating effective, n‐type doping concentrations up to the 5 × 10¹⁹ cm^–3 regime. By studying the full width at half maximum (FWHM) of the E₂(high) Raman mode with rising doping concentration, Ge is approved as the by far superior dopant if compared to Si. Even elevated nominal Ge concentrations yield corresponding FWHM values of just 3 cm^–1, a most competitive value even for bare bulk GaN samples. At the same time, the biaxial, compressive stress that is introduced by such high Ge doping amounts to just 0.2 GPa, in clear contrast to the particular case of silicon. Here, even moderate doping levels lead to tensile stress up to 1 GPa and consequently to a serious degeneration of the overall crystal quality as approved by our Raman analysis. Additionally, the examined high doping concentrations enable the observation of longitudinal optical phonon plasmon (LPP) modes in the Raman spectra, which serve as a direct tool for the determination of the effective doping concentration. A careful analysis of the LPP coupling at cryogenic and room temperature yields within the error interval identical free carrier concentrations in all germanium doped samples, pointing towards an energetically shallow nature of the dopant. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Raman spectroscopy of CaM2+Ge2O6 (M2+ = Mg,Mn, Fe,Co, Ni,Zn) clinopyroxenes

The Raman spectra of Ge‐clinopyroxenes CaM²⁺Ge₂O₆ (M²⁺ = Mg, Mn, Fe, Co, Ni, Zn), general formula M2M1T₂O₆, are reported for the first time. Their spectral features are discussed in comparison with corresponding Si‐pyroxenes. The vibrational wavenumbers of germanates may be roughly obtained by a scale factor of about ~0.8 by those of the corresponding silicates, due to the Ge‐Si mass difference. The main peaks in the germanate Raman spectra at ~850 and ~540 cm⁻¹ may be related to Ge‐O tetrahedral stretching and chain bending, respectively; minor peaks between 200 and 400 cm⁻¹ are ascribed to bending and stretching of the non‐tetrahedral cations. Within Ge‐pyroxenes, possible correlations between crystallographic parameters and the vibrational wavenumbers are investigated. The main stretching mode at ~850 cm⁻¹ shows wavenumber changes with M²⁺ substitutions, but no simple correlation can be found with M²⁺ cation mass or size. On the other hand, the chain bending wavenumber linearly decreases with increasing ionic radius of the M²⁺ cation: the expansion of the M1 polyhedron reduces the chain kinking angle and the Ge‐Ge distances correspondingly increase. Copyright © 2015 John Wiley & Sons, Ltd.     

Spectroscopic study of phase transitions in dolomite mineral

The process and the formation of new minerals upon heating carbonate rocks containing clay minerals together with dolomite are determined by thermal analysis, X‐ray diffraction (XRD), infrared and Raman spectroscopy. The dolomite–calcite–calcium oxide phase transition sequences were followed up to 947 °C in a naturally occurring dolomite sample. The spectral variations of the internal modes of the carbonate trigonal (ν₁, ν₂, ν₃ and ν₄) were used to probe the structural phase transitions. A new Raman mode emerged at 1090 cm⁻¹ in the ν₁ mode region, and infrared modes emerged at 713, 874, and 1420 cm⁻¹ in the ν₄, ν₂ and ν₃ regions at 750 °C, indicating the onset of the dolomite phase. The calcium oxide phase, (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 °C, was also characterized by the appearance of the infrared mode around 450 cm⁻¹. The minerals, which were formed upon heating the dolomite, were calcite, calcium oxide and diopside. Copyright © 2007 John Wiley & Sons, Ltd.     

Far infrared absorption of amorphous GaAs and Ge

Far infrared reflection spectra of amorphous GaAs and Ge have been obtained in the frequency region from 30–600 cm^?1. For each material, curves of ω?₂ vs frequency have been obtained whose corresponding reflectivity curves give a best fit to the data. The peak value of the abdorption coefficient is about 4000 cm^?1 for GaAs and 160 cm^?1 for Ge. The results are compared with Raman spectra and with theoretical calculations.     

Raman‐induced Kerr effect spectroscopy of single‐wall carbon nanotubes aqueous suspensions in the range 0.1–10 and 100–250 cm−1

Here, we study a low (less than 0.1 µg/ml) concentration aqueous suspension of single‐wall carbon nanotubes (SWNTs) by Raman‐induced Kerr effect spectroscopy (RIKES) in the spectral bands 0.1–10 and 100–250 cm⁻¹. This method is capable of carrying out direct investigation of SWNT hydration layers. A comparison of RIKES spectra of SWNT aqueous suspension and that of milli‐Q water shows a considerable growth in the intensity of low wavenumber Raman modes. These modes in the 0.1–10 cm⁻¹ range are attributed to the rotational transitions of H₂O₂ and H₂O molecules. We explain the observed intensity increase as due to the production of hydrogen peroxide and the formation of a low‐density depletion layer on the water–nanotube interface. A few SWNT radial breathing modes (RBM)are observed (ω_RBM = 118.5, 164.7 and 233.5 cm⁻¹) in aqueous suspension, which allows us to estimate the SWNT diameters (∼2.0, 1.5, and 1 nm, respectively). Copyright © 2011 John Wiley & Sons, Ltd.     

Ion implantation damage and crystalline-amorphous transition in Ge

Experimental studies on the damage produced in (100) Ge substrates by implantation of Ge⁺ ions at different energies (from 25 to 600 keV), fluences (from 2×10¹³ to 4×10¹⁴ cm⁻²) and temperature (room temperature, RT, or liquid-nitrogen temperature, LN₂T) have been performed by using the Rutherford backscattering spectrometry technique. We demonstrated that the higher damage rate of Ge with respect to Si is due to both the high stopping power of germanium atoms and the low mobility of point defects within the collision cascades. The amorphization of Ge has been modeled by employing the critical damage energy density model in a large range of implantation energies and fluences both at RT and LN₂T. The experimental results for implantation at LN₂T were fitted using a critical damage energy density of ∼1 eV/atom. A fictitious value of ∼5 eV/atom was obtained for the samples implanted at RT, essentially because at RT the damage annihilation plays a non-negligible role against the crystalline–amorphous transition phase. The critical damage energy density model was found to stand also for other ions implanted in crystalline Ge (Ar⁺ and Ga⁺).     

Analysis of cold denaturation mechanism of β‐lactoglobulin and comparison with thermal denaturation from Raman spectroscopy investigations

Cold‐ and heat‐induced β‐lactoglobulin (BLG) transformations have been analyzed in the presence of 4 M urea, from Raman spectroscopy investigations carried out simultaneously in the low wavenumber range (10–400 cm⁻¹) and in the amide I region (1500–1800 cm⁻¹). These investigations show common features between the denaturation processes at low and high temperatures. The denatured states are reached via an intermediate state characterized by a soft tertiary structure without detectable conformational changes. This intermediate is intimately connected with a tetrahedral hydrogen‐bond structure of water which extends over a limited range. It is shown that the disruption of the hydrogen‐bond network of D₂O has an important consequence on the solvent dynamics, which controls protein dynamics and is characterized by an anharmonic behavior. By monitoring the amide I mode, conformational changes are detected at low temperature (below 5 °C) and determined to be similar to those detected at high temperature in the presence of urea near 65 °C, and in the absence of urea near 80 °C. The conformational changes are described as a loss of α‐helix structures and a concomitant formation of β‐sheets. The temperature dependence of the amide I wavenumber in BLG dissolved in the 4 M urea aqueous solution was interpreted on the basis of a two‐state model, leading to the protein stability curve related to its molecular conformation. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermo‐Raman spectroscopy of synthetic nesquehonite — implication for the geosequestration of greenhouse gases

Pure nesquehonite (MgCO₃·3H₂O)/Mg(HCO₃)(OH)·2H₂O was synthesised and characterised by a combination of thermo‐Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo‐Raman spectroscopy shows an intense band at 1098 cm⁻¹, which shifts to 1105 cm⁻¹ at 450 °C, assigned to the ν₁CO₃²⁻ symmetric stretching mode. Two bands at 1419 and 1509 cm⁻¹ assigned to the ν₃ antisymmetric stretching mode shift to 1434 and 1504 cm⁻¹ at 175 °C. Two new peaks at 1385 and 1405 cm⁻¹ observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO₃)⁻ units. Throughout all the thermo‐Raman spectra, a band at 3550 cm⁻¹ is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm⁻¹ are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo‐Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO₃)·2H₂O. Copyright © 2008 John Wiley & Sons, Ltd.     

Sub‐picosecond Raman spectrometer for time‐resolved studies of structural dynamics in heme proteins

We describe a pump–probe Raman spectrometer based on a femtosecond Ti:sapphire laser, an optical parametric generator and two optical parametric amplifiers for time‐resolved studies, with emphasis on the structural dynamics in heme proteins. The system provides a 100‐fs pump pulse tunable in the range 500–600 nm and a transform‐limited sub‐picosecond probe pulse tunable in the range 390–450 nm. The spectrometer has spectral (25 cm⁻¹) and temporal (∼0.7 ps) resolutions which constitute an effective compromise for identifying transient heme protein species and for following their structural evolution by spontaneous Raman scattering in the time range 0.5 ps to 2 ns. This apparatus was applied to time‐resolved studies of a broad range of heme proteins, monitoring the primary dynamics of photoinduced heme coordination state and structural changes, its interaction with protein side‐chains and diatomic gaseous ligands, as well as heme vibrational cooling. The treatment of transient Raman spectra is described in detail, and the advantages and shortcomings of spontaneous resonance Raman spectroscopy for ultrafast heme proteins studies are discussed. We demonstrate the efficiency of the constructed spectrometer by measuring Raman spectra in the sub‐picosecond and picosecond time ranges for the oxygen‐storage heme protein myoglobin and for the oxygen‐sensor heme protein FixLH in interaction with the diatomic gaseous ligands CO, NO, and O₂. Copyright © 2010 John Wiley & Sons, Ltd.     

Transition of chromium oxyhydroxide nanomaterials to chromium oxide: a hot‐stage Raman spectroscopic study

The transition of disc‐like chromium hydroxide nanomaterials to chromium oxide nanomaterials has been studied by hot‐stage Raman spectroscopy. The structure and morphology of α‐CrO(OH) synthesised using hydrothermal treatment were confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The Raman spectrum of α‐CrO(OH) is characterised by two intense bands at 823 and 630 cm⁻¹ attributed to ν₁ Cr^III O symmetric stretching mode and the band at 1179 cm⁻¹ attributed to Cr^III OH δ deformation modes. No bands are observed above 3000 cm⁻¹. The absence of characteristic OH stretching vibrations may be due to short hydrogen bonds in the α‐CrO(OH) structure. Upon thermal treatment of α‐CrO(OH), new Raman bands are observed at 599, 542, 513, 396, 344 and 304 cm⁻¹, which are attributed to Cr₂O₃. This hot‐stage Raman study shows that the transition of α‐CrO(OH) to Cr₂O₃ occurs before 350 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

FT‐Raman,FT‐IR spectra and DFT calculations on monomeric and dimeric structures of 5‐fluoro‐ and 5‐chloro‐salicylic acid

The experimental and theoretical study on the structures and vibrations of 5‐fluoro‐salicylic acid and 5‐chloro‐salicylic acid (5‐FSA and 5‐ClSA, C₇H₅FO₃ and C₇H₅ClO₃) is presented. The Fourier transform infrared spectra (4000–400 cm⁻¹) and the Fourier transform Raman spectra (4000–50 cm⁻¹) of the title molecules in the solid phase were recorded. The molecular structures, vibrational wavenumbers, infrared intensities, Raman intensities and Raman scattering activities were calculated for a pair of molecules linked by the intermolecular O H···O hydrogen bond. The geometrical parameters and energies of 5‐FSA and 5ClSA were obtained for all eight conformers/isomers from density functional theory (DFT) (B3LYP) with 6‐311++G(d,p) basis set calculations. The computational results identified the most stable conformer of 5‐FSA and 5‐ClSA as the C1 form. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The spectroscopic and theoretical results were compared with the corresponding properties for 5‐FSA and 5‐ClSA monomers and dimer of C1 conformer. The optimized bond lengths, bond angles and calculated wavenumbers showed the best agreement with the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

Temperature dependence of the Raman spectra of Bi2Te3 and Bi0.5Sb1.5Te3 thermoelectric films

The temperature dependence of the Raman spectra of Bi₂Te₃ and Bi_0.5Sb_1.5Te₃ thermoelectric films was investigated. The temperature coefficients of the E_g(2) peak positions were determined as –0.0137 cm^–1/°C and –0.0156 cm^–1/°C, respectively. The thermal expansion of the crystal caused a linear shift of the Raman peak induced by the temperature change. Based on the linear relation, a reliable and noninvasive micro‐Raman scattering method was shown to measure the thermal conductivity of the thermoelectric films. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raman study of datolite CaBSiO4(OH) at simultaneously high pressure and high temperature

Using an in situ method of Raman spectroscopy and resistance‐heated diamond anvil cell, the system datolite CaBSiO₄(OH) – water has been investigated at simultaneously high pressure and temperature (up to Р ~5 GPa and Т ~250 °С). Two polymorphic transitions have been observed: (1) pressure‐induced phase transition or the feature in pressure dependence of Raman band wavenumbers at P = 2 GPа and constant T = 22 °С and (2) heating‐induced phase transition at T ~90 °С and P ~5 GPа. The number of Raman bands is retained at the first transition but changed at the second transition. The first transition is mainly distinguished by the changes in the slopes of pressure dependence of Raman peaks at 2 GPa. The second transition is characterized by several strong changes: the wavenumber jumps of major bands, the merging of strong doublets at 378 and 391 cm⁻¹ (values for ambient conditions), the splitting of the intermediate‐intensity band at 292 cm⁻¹, and the transformation of some low‐wavenumber bands at 160–190 cm⁻¹. No spectral and visual signs of overhydration and amorphization have been observed. No noticeable dissolution of datolite in the water medium occurred at 5 GPa and 250 °С after 3 h, which corresponds to typical conditions of the ‘cold’ zones of slab subduction. Copyright © 2014 John Wiley & Sons, Ltd.