Lower Wavenumber Side Research Articles

Infrared spectra study of the Moslavacka Gora (Croatia) tourmalines O-H stretching region: Inference of fluid involvement in the Late Cretaceous igneous evolution of a complex Adria-Europe convergence zone

Infrared spectra (IR) in the O-H stretching region were recorded for natural tourmalines from the magmatic and magmatic-hydrothermal systems of Moslavacka Gora (Croatia). Samples of disseminated tourmaline (schorl) representing magmatic products were collected from leucogranite. Nodular tourmaline (intermediate members of the schorl-dravite series) from twomica granite represents a magmatic-hydrothermal mineral related to the final stage of granite crystallization. IR spectra of the typically disseminated tourmaline show four sharp O-H stretching bands: 3643, 3633, 3550, and 3484 cm?1, while typical nodular tourmaline shows spectra with asymmetric and relatively broad O-H stretching bands on 3635 and 3554 cm?1 with shoulders at the higher and lower wavenumber side. The broadening in the lower wavenumber region of nodular tourmaline compared to disseminated tourmaline indicates a higher water content in the nodular type. At the same time, the observed shifts between the corresponding bands can be explained by the shortening of the O-H1 and O-H3 distances, which can be attributed to different genetic and/or evolutionary processes. According to the models applicable to the Moslavacka Gora, disseminated tourmaline from the leucogranite can be considered a typical magmatic (pegmatitic) product and a standard accessory phase of the leucogranite. The origin of nodular tourmaline, which was the last mineral to crystallize in the evolved Late Cretaceous granitic system of Moslavacka Gora, is attributed to the interaction of a fluid phase from the residual granitic melt with the fluid originating from the wall-rock in the low-pressure crustal setting, which was accompanied by relatively rapid cooling. This interaction resulted in an increased dravite content of the nodular tourmaline and is reflected in the observed IR spectral features.

Complex Er-doped selenium-based chalcogenides in the far-infrared region: a structural bonding arrangement study

Selenium-based chalcogenide glasses show tremendous infrared transmission in the 2–15 μm region, and these amorphous glasses could be easily formed into optical devices i.e. optical fibers and lenses, owing to their good thermo-mechanical properties. Even though the phonon energy for tellurium-based glasses is on the lower side, still, selenium-based glasses are worthwhile for mid to long-wavelength infrared emissions. Here, we have developed Er-doped selenium-based, Ge 17 Sb 8 Se 75−x Er x where x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, chalcogenides by conventional melting and quenching technique for possible mid to far-infrared applications. Far-infrared transmission spectra of the synthesized chalcogenides are obtained at room temperature in the spectral range of 35–450 cm−1. The bonding arrangements in the synthesized chalcogenides are investigated as a function of composition. It has been found that with the addition of Er content, the far-infrared transmission spectra shift toward the lower wavenumber side. The experimental results are correlated with the theoretically calculated parameters such as relative probability, bond energy, wave number, force constant etc. The obtained results provide insight into understanding the synthesized chalcogenides’ optical behavior, which is dynamic for designing the optical components operated in mid-infrared to far-infrared regions.

Key role of Tb3+ doping on structural and photoluminescence properties of Gd2Ti2O7 pyrochlore oxide

Pyrochlore structured compounds form a special class of ceramics as host matrices in phosphors with better luminescent properties. In the present work, the optical properties of pyrochlore oxide Gd2-xTbxTi2O7 (0 ≤ x ≤ 0.16) were investigated and linked with structural properties via examination of structural distortion produced with the doping of rare-earth element. These oxide compositions were produced through standard solid-state reaction method. The investigations using advanced characterization techniques; X-ray diffraction and Raman spectroscopy give a signature of single phasic pyrochlore structure in the synthesized samples optimized through multiple heating protocol. The diffraction patterns and Raman spectra, both were continuously being shifted towards lower 2θ value and lower wave-number side, respectively with the doping concentration which can be interpreted by the production of defects in cationic lattice. A similar decreasing trend in particle size has been observed from W–H plot (728 Å to 616 Å) and Scanning electron micrographs (0.82 μm–0.78 μm) with the introduction of Tb3+ ion. The band-gap for the host matrix Gd2Ti2O7 through UV absorption pattern came out to be 2.26 eV. From photoluminescence excitation (λem = 545 nm), a broad excitation band was observed in the wavelength range 305 nm–380 nm due to the f→d transition of 4f shell of Tb ion. Furthermore, emission spectra (λex = 375 nm) consist of bands at 489 nm, 545 nm, 585 nm and 623 nm due to the transitions at 5D4 → 7F6,5,4, and 3, respectively with doping. For an optimum doping concentration with x = 0.12, a high intensity green emission line at 545 nm came out as 5D4 → 7F5 dominating transition of terbium ion. Hence, the results explore the application of Gd2Ti2O7 composition as Tb-fluorescence with the optimum doping concentration of 6%.

Effect of annealing and swift heavy ions irradiation on vanadium oxide thin films

In this work, thin films (∼200 nm) of vanadium oxide were deposited on Si (100) substrate by e-beam evaporation method with low-cost V2O5 powder. Some of the as-deposited samples were annealed in the argon atmosphere at 500°C for 1 h and cooled at a natural rate in the argon atmosphere. The as-deposited samples were also irradiated with 100 MeV Ag ions beam at different fluences. Grazing incidence X-ray diffraction (GIXRD) and Raman spectroscopy revealed that as-deposited films were composed of the V6O13 phase (mixed valance state). This V6O13 phase was transformed into polycrystalline V2O5 phase after post-annealing. Raman spectra of irradiated films had a new peak of the V6O13 phase, and no change was observed at higher fluence, and in the FTIR spectra, bands shifted toward lower wavenumber side at higher fluence. This band shifting toward the lower wavenumber side may be due to the weakening of vanadium oxygen bonds, which create oxygen vacancies in the film. The creation of defects in films was due to the pressure applied by the molten zone, which is formed by the passage of SHIs in the material.

Evaluation of Strain-Shift Coefficients for SiSn by Raman Spectroscopy

1. Introduction Silicon tin (SiSn) is a new promising candidate material for next-generation optical devices since its energy band-gap is theoretically expected to a direct band-gap as Sn fraction increases [1, 2]. The lattice constant difference (strain states) between the substrate and the SiSn thin film directly affects a band-gap, a carrier mobility, and device design. Therefore, it is important to evaluate strain states in SiSn thin film and accurate strain evaluation techniques are indispensable.Raman spectroscopy is one of the powerful strain evaluation techniques because it is a high spatial resolution and nondestructive measurement. However, the strain shift coefficient of SiSn has not been experimentally investigated in contrast to silicon germanium, germanium tin, and highly accurate strain measurement cannot be performed by Raman spectroscopy. In this study, Raman measurement was performed to extract the strain-shift coefficient of SiSn thin films, accurately. 2. Experimental method SiSn thin films (Sn fraction: 0.50, 0.90, 1.8, 2.0, and 6.0%) were grown on (001)-Si substrate by molecular beam epitaxy. Their thickness was set to 50 nm. Sn fraction and in-plane biaxial strain were confirmed by X-ray diffraction (XRD).The Si1-x Sn x thin films were evaluated by Raman spectroscopy. Excitation source of ultraviolet laser (λ = 355 nm) was used and focal length of the Raman spectrometer was 2,000 mm. Wavenumber resolution is approximately 0.1 cm-1. The Raman spectra of the Si1-x Sn x thin films for Si-Si vibration mode were measured to determine the strain-shift coefficient. 3. Results and Discussion Figure 1 shows Raman spectra of Si1-x Sn x with x of 0.06 and bulk Si (Si-Si mode) for comparison. As a result, asymmetrical broadening on the low-wavenumber side with slight peak shift in the Raman spectrum for the SiSn thin film were observed. In the Raman scattering, this broadening is often explained using the so-called spatial correlation model, which reproduces the relaxation of momentum conservation due to random atom positions.Figure 2 shows the relationship between Raman peak shift of SiSn for Si-Si mode (Δω LO) and in-plane strain estimated by reciprocal space mapping using XRD. In this study, D’Costa model (see below equation) was used to obtain strain-free Raman shift for Si-Si mode [3]: ω 0 = 520 – 141.8x. (1)It was revealed that the relationship between Raman peak shift of SiSn for Si-Si mode and in-plane strain has clear linear dependence. From the slope of the straight line which calculated by linear approximation as shown in Fig. 2, the value of the strain-shift coefficient b was found to be -732 cm-1. This value shows good agreement with that of strained Si [4] and SiGe [5]. On the basis of the result, it is suggested that the strain-shift coefficient b is not affected by random atom positions (alloy state), and the value of b may not change by composition and strain state.In conclusion, these insights play an important role in the strain evaluation for the next-generation SiSn device by Raman spectroscopy and in the understanding the relationship between phonon behavior and strain. Acknowledgements This work was supported partly the Japan Society for the Promotion of Science (JSPS) (19K21971 and 17J08240).

Rietveld analysis, magnetic, transport, and optical properties of (1 − x)BiFeO3–(x)Pb(Zr0.52Ti0.48)O3 ceramics prepared by sol–gel route

Pb(Zr0.52Ti0.48)O3 (PZT)-modified samples of BiFeO3 (BFO) were synthesized by a sol–gel method in composition range 0.0 ≤ x ≤ 0.15 to see the effect of PZT on structural, optical, dielectric, and magnetic properties of BFO ceramics. It is demonstrated that the PZT-modified BFO can expressively improve the dielectric and magnetic properties. Structural analysis was carried out with the Rietveld FullProf program, revealed that changes in lattice parameters and stability of rhombohedral structure with R3c symmetry up to x = 0.15 dilution of PZT. Structural distortion and strain were calculated by the Williamson–Hall approach. Moreover, a significant improvement in magnetization at room temperature was achieved for PZT-modified samples ascribed to the disturbance in the spin cycloid arrangement of Fe ions. PZT-modified BFO samples are showing better dielectric properties than undoped BFO attributed to suppression of Bi and oxygen vacancies. Our results demonstrate that the significant role of PZT can be seen in conductivity vs. 1000/T plots and the appearance of dissimilar kinds of conduction mechanisms in the different linear regions. Optical studies were performed in the 1 eV–4.5 eV spectral range and the calculated optical bandgap was found to decrease with PZT doping. The results of infrared spectroscopy show shifts of IR phonon modes in the lower wavenumber side.

Observations of phonon anharmonicity and microstructure changes by the laser power dependent Raman spectra in Co doped SnO2 nanoparticles

SnO2 nanoparticles are of critical importance owing to their necessity for fundamental studies and highly attractive applications in optoelectronic devices and photocatalytic activities. In this study Raman spectroscopy was rigorously employed to investigate the effect of low concentrations of cobalt doping in rutile SnO2 nanoparticles. The effect of annealing temperature and laser power dependent molecular vibrations was used to directly realize the localized microstructural changes and phonons interaction within the lattice. A large broadening and shifting towards the lower wavenumber side in the Raman spectra for A1g and B2g modes of vibration were observed. This was mainly attributed to microstructural changes, maximum possible quasiharmonic shift and a large proportion from pure anharmonic shifts as a function of increasing laser power. Two approaches were adopted to calculate the localized temperature that has increased due to laser heating during the Raman measurements in the samples. In a more feasible and reliable approach the full with at half maxima (FWHM) broadening and frequency shifting as a function of laser power were directly compared with the previously reported experimental results. In another approach the well-known Klement model based on the kinematics of three-phonon processes was also used to determine the localized temperature.

Structural and Reactivity Analyses of Nitrofurantoin–4-dimethylaminopyridine Salt Using Spectroscopic and Density Functional Theory Calculations

Pharmaceutical salt, nitrofurantoin–4-dimethylaminopyridine (NF-DMAP), along with its native components NF and DMAP are scrutinized by FT-IR and FT-Raman spectroscopy along with density functional theory so that an insight into the H-bond patterns in the respective crystalline lattices can be gained. Two different functionals, B3LYP and wB97X-D, have been used to compare the theoretical results. The FT-IR spectra obtained for NF-DMAP and NF clearly validate the presence of C33–H34⋅⋅⋅O4 and N23–H24⋅⋅⋅N9 hydrogen bonds by shifting in the stretching vibration of –NH and –CH group of DMAP+ towards the lower wavenumber side. To explore the significance of hydrogen bonding, quantum theory of atoms in molecules (QTAIM) has been employed, and the findings suggest that the N23–H24⋅⋅⋅N9 bond is a strong intermolecular hydrogen bond. The decrement in the HOMO-LUMO gap, which is calculated from NF → NF-DMAP, reveals that the active pharmaceutical ingredient is chemically less reactive compared to the salt. The electrophilicity index (ω) profiles for NF and DMAP confirms that NF is acting as electron acceptor while DMAP acts as electron donor. The reactive sites of the salt are plotted by molecular electrostatic potential (MEP) surface and calculated using local reactivity descriptors.

Synthesis and Chraracterization of Tin Sulfide Nanoparticles

In my present paper, Tin sulfide nanoparticles were successfully synthesized using wet chemical process and studied their structural properties. The prepared nanoparticles were characterized by X-Ray diffraction (XRD) and Raman spectroscopy. The XRD confirms the Tin Sulfide nanoparticles possessing orthorhombic structure having particle size is approx. 12.72 nm. The Raman spectrum shows the frequency of the phonon in these nanoparticles and the Raman modes of Tin Sulfide nanoparticles were found to shifts towards lower wave number side.

Influence of alloy engineering on structural and photo detection properties of SbXSn1-XSe2 ternary alloys

In order to exploit effect of Sb incorporation on properties of SnSe2, alloy engineering is performed in SbxSn1-xSe2 (x = 0, 0.1, 0.2, 0.3) ternary compounds. The single crystals are grown by direct vapour transport technique. The elemental composition and purity of as-grown compounds are characterized by EDAX. The optical microscopy and scanning electron microscopy show characteristic morphological features like helical spiral, layered structure, clean surface, etc. on surface of grown crystals. The powder X-ray diffraction shows that the pristine and Sb incorporated samples possess 2H-Hexahonal lattice structure. However, lattice parameters and unitcell volume are changed on incorporation of Sb in SnSe2 structure due to increase in microstrain. The Raman spectroscopy reveals SnSe2-type A1g vibrational mode and the corresponding peak is shifted on lower wavenumber side on increasing Sb content. The results confirm substitution of Sb(+5) on Sn(+4) lattice site in host network. The influence of alloy engineering on photo response is studied. The highest photocurrent of 1.88 μA, responsivity of 43.45 mAW−1, detectivity of 18.25 × 1011 Jones and EQE (%) of 47.28% are observed for X = 0.1 sample.

Investigation of solvation of ammonium salts: A Raman spectroscopy and ab initio study

AbstractThe effect of dissolved salts on the hydrogen bonded network in water is extremely important to be understood, as it plays an important role in many aspects of structure and dynamics in aqueous solutions. We have undertaken a study of this phenomenon, using NH4Cl (AC) and (NH4)2SO4 (AS), as the salts for influencing the hydrogen bonded network in water. The effects of varying the temperature and concentration in these aqueous solutions of both the salts, on the Raman spectra were studied, over the wavenumber range 50–4000 cm−1. It was found that at 25 °C, with increasing AS concentration, a monotonic increase in intensity of spectral features on the low wavenumber side (~3200 cm−1 region) of the O–H stretching band was observed, whereas AC showed the opposite effect. A parameter (χstruct) is defined from the spectral data, which indicates that more hydrogen bonded network forms in presence of AS salt compared with AC salt, in aqueous solution. Temperature variation study also reveals that, presence of AC induces a more disordered network in aqueous solutions, than AS. To support these conclusions, we have performed ab initio calculation for the salt⋯nW species, where n = 1−8, using the MP2/6–31+G(d,p) level of theory. Solvent separated ion pair formation has been reported for NH4+ and Cl− ions, whereas NH4+ and SO42− ions remain as contact ion pair up to AS⋯8W cluster. This study helps understand the effect of salt water interaction at the molecular level and may have huge implications in atmospheric physics, geophysics, and ice crystallization.

Micro-Raman Characterization of Cluster Carbon Implanted Si before and after Rapid Thermal Annealing

To meet various physical property requirements of materials for advanced high performance devices, combinations of Si1-xGex and Si:C have been introduced for strain control in PMOS and NMOS regions of devices. Two types of carbon (C) doping techniques have been explored for tensile stress generation in the NMOS device region. Carbon-doped Si epitaxial growth with C doping and C-implantation into Si are two major approaches. Carbon implanted Si requires annealing for recrystallization, damage recovery and tensile strain control. Strain characterization, monitoring and control are as important as material preparation. Non-contact, non-destructive strain and crystallinity characterization techniques with high spatial resolution and virtual depth profiling capability are strongly desired for in-line monitoring. In this study, we report the micro-Raman characterization results on cluster C-implanted Si for tensile strain generation before and after various rapid thermal annealing (RTA) techniques and conditions. Phosphorous ion clusters (P4) (8 keV, 4x1015 cm-2) were implanted with carbon ion clusters (C7) targeting 1.3% and 1.5% flat C profile (~50 nm from the surface). Various excitation wavelength laser beams were used in Raman characterization for virtual strain depth profiling. Flash anneal (fRTP) at 1200oC and impulse spike anneal (iRTP) at 1000oC and 1050oC were used as annealing conditions. As-implanted Si wafers showed almost no Raman signal due to the crystalline lattice damage from high dose cluster ion beam implantation. After RTA of implanted Si wafers under different techniques and conditions, significant broadening and shift of Raman peaks towards the lower wavenumber side was measured, indicating the presence of tensile strain and crystallinity alterations. X-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS) depth profiling and transmission electron microscopy (TEM) analysis results will be reported along with multiwavelength micro-Raman characterization results. Figure 1 shows 363.8nm excited micro-Raman spectra from reference Si and cluster C implanted Si wafers before and after rapid thermal annealing (RTA). Figure 1

Micro-Raman Characterization of Cluster Carbon Implanted Si before and after Rapid Thermal Annealing

Phosphorous ion clusters (P4 +) (8 keV, 4x1015 cm-2) were implanted with carbon ion clusters (C7) targeting 1.30 at.% and 1.50 at. % flat C profile (~50 nm from the surface) for NMOS device performance enhancement by tensile strain generation. Flash anneal (fRTP) at 1200oC and impulse spike anneal (iRTP) at 1000oC and 1050oC were used as annealing conditions. Micro-Raman characterization of cluster C-implanted Si was done before and after various rapid thermal annealing (RTA) techniques and conditions under various excitation wavelengths for virtual depth profiling of Si stress. As-implanted Si wafers showed almost no Raman signal due to the crystalline lattice damage from high dose cluster ion beam implantation. After RTA of the implanted Si wafers under different techniques and conditions, significant broadening and shift of Raman peaks, towards the lower wavenumber side, was measured, indicating the presence of tensile strain and crystallinity alterations. High resolution X-ray diffraction (HRXRD), secondary ion mass spectroscopy (SIMS) depth profiling and sheet resistance measurement results were compared with multiwavelength micro-Raman characterization results.

Origin of additional broad peaks in Raman spectra from thin germanium-rich silicon–germanium films

Additional broad peaks in Raman spectra from thin Ge-rich SiGe films were examined in detail. The broad peak on the low-wavenumber side of first-order optical phonon was also present for pure Ge, which indicates that the localized mode is not the reason for the broad peaks. Furthermore, other factors, e.g., strain, defect, phonon confinement effect, Fano effect, and fluorescence from oil, were excluded from the origin of the broad peaks. We assigned the broad peaks to surface optical phonon modes. The dependence of this surface mode on Ge concentration in Ge-rich SiGe was also investigated and the behavior was discussed.

Evaluation of Anisotropic Biaxial Stress in Si1-X Ge x /Ge Mesa-Structure by Oil-Immersion Raman Spectroscopy

Introduction Silicon Germanium (Si1-x Ge x ) is recognized as a material for the next-generation transistor device [1]. In particular, Si1-x Ge x is attractive as a channel material that has higher carrier mobility than Si. Furthermore, strain engineering is also valid for Si1-x Ge x similar to the Si to improve transistor performance. Nowadays, complicated nanostructures, such as FinFET, has used in the devices. Thus, the strain (stress) states in Si1-x Ge x nanostructures should be complicated because of hetero junction and nanoscalling processes [2]. In the nanostructure devices, accurate evaluation of anisotropic biaxial stress states is indispensable. In our previous report, we demonstrated the evaluation of the anisotropic biaxial stress states in various nanostructures including strained Si1-x Ge x with low Ge concentration on the Si substrate by oil-immersion Raman spectroscopy [3,4]. In this study, we investigated the biaxial stress states in Si1-x Ge x mesa structure with high Ge concentration on Ge substrates depending on nanostructure size by oil-immersion Raman spectroscopy. Experiments Si1-x Ge x films were epitaxially grown on the Ge substrate (Si1-x Ge x /Ge) whose Ge concentration were approximately x = 0.76, 0.85, and 0.92. The film thicknesses of the samples were 50, 76, and 35 nm, respectively. Furthermore, the various size mesa structures were fabricated by electron beam lithography and reactive ion etching. Figure 1(a) and (b) show the schematic of the Si1-x Ge x mesa structure and cross-sectional TEM image (x = 0.76). The sample widths (Ws) were 1.0, 0.5, 0.2, 0.1, and 0.05 μm, while the length (L) was fixed at 3.0 μm. In the oil-immersion Raman measurements, the anisotropic biaxial stresses in the strained Si1-x Ge x were evaluated. The numerical aperture was 1.4 and the refraction index in the atmosphere was 1.5. The excitation light source wavelength and the spectroscope focal length were 532 nm and 2,000 mm, respectively. Results and Discussion Figure 2 shows Raman spectra from the Si1-x Ge x mesa structures with various Ge concentration, where the width of W = 1.0 μm. These spectra were calibrated by the Ge substrate peak at 300 cm-1. From the result, the peaks of Si1-x Ge x with lower Ge concentration were observed at lower wavenumber side. The peak shift was caused by the combination of decreasing Ge concentration and increasing tensile stress. Figure 3 shows the biaxial stresses σ xx and σ yy in the Si1-x Ge x with x = 0.76. Here, the variation of σ xx and σ yy were clearly observed. The stress variation was depending on the width of mesa structure (W). As a result, σ yy was more relaxed than σ xx with decreasing of the width. Furthermore, σ yy was dramatically decreased at less than W = 0.2 μm, while σ xx remains almost constant through W = 1.0, 0.5, 0.2 μm. This result demonstrates that the biaxial stress state was clearly depend on the Si1-x Ge x mesa structure W width. We believe that it is important to evaluate anisotropic biaxial stress states. Therefore, oil-immersion Raman spectroscopy is useful for the stress engineering. Acknowledgement This study was partially supported by the Japan Society for the promotion of Science through a Grant-in-Aid for Scientific Research B (No. 24360125) and Funding program for World-Leading innovative R&D on Science and Technology.

Microstructural and band gap exploration on Ni-doped SnO2 nanoparticles co-doped with Cu

Sn0.97−xNi0.03CuxO2 (x = 0, 0.01, 0.02) nanoparticles have been successfully synthesized by employing a simple co-precipitation method. Tetragonal rutile structure of the samples was confirmed by X-ray diffraction technique. The change in crystallite size and optical properties such as absorption, transmittance and band gap were discussed based on Cu concentration and density of defect states. Morphologies and composition of products were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Lower optical absorption and higher transmittance of Sn0.96Ni0.03Cu0.01O2 nanoparticles described that it is one of the suitable materials for opto-electronic device applications. The shift of band position towards lower wave number side and the decrease in the intensity of Fourier transform infrared spectra peaks confirmed the presence of Cu in Sn–Ni–O lattice.

Optical properties of germanium nanoparticles synthesized by pulsed laser ablation in acetone

Germanium (Ge) nanoparticles (NPs) are synthesized by means of pulsed laser ablation of bulk germanium target immersed in acetone with ns laser pulses at different pulse energies. The fabricated NPs are characterized by employing different techniques such as UV-visible absorption spectroscopy, photoluminescence, micro-Raman spectroscopy, transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The mean size of the Ge NPs is found to vary from few nm to 40 nm with the increase in laser pulse energy. Shift in the position of the absorption spectra is observed and also the photoluminescence peak shift is observed due to quantum confinement effects. High resolution TEM combined with micro-Raman spectroscopy confirms the crystalline nature of the generated germanium nanoparticles. The formation of various sizes of germanium NPs at different laser pulse energies is evident from the asymmetry in the Raman spectra and the shift in its peak position towards the lower wavenumber side. The FESEM micrographs confirm the formation of germanium micro/nanostructures at the laser ablated position of the bulk germanium. In particular, the measured NP sizes from the micro-Raman phonon quantum confinement model are found in good agreement with TEM measurements of Ge NPs.

Evaluation of Anisotropic Biaxial Stress in Thin Strained-SiGe Layer Using Surface Enhanced Raman Spectroscopy

Introduction Silicon germanium (SiGe) is recognized as a high mobility channel material for the next-generation transistors in place of Si. Nowadays, various future devices using SiGe are being developed [1]. The accurate evaluation of strain (stress) is essential to realize future devices using SiGe. However, the evaluation of stress in thin SiGe layer is difficult because of poor signal embedded in those from huge amount of thick Si substrate [2]. We have previously reported that relatively weak TO phonon excitation in strained SiGe by oil-immersion Raman spectroscopy [3]. We also reported that the evaluation of anisotropic biaxial stress in strained Si on relaxed SiGe layer by exciting longitudinal optical (LO) and transversal optical (TO) phonons using surface enhanced Raman spectroscopy (SERS) [4]. In this study, the SERS measurements were performed to excite the TO phonon in strained SiGe layer more efficiently. Experiment The thin SiGe layer on Si substrate with approximately 30% Ge concentration was used as the sample. The thickness of the SiGe layer was approximately 38 nm. Undecane (C11H24) was used for the solvent of Ag nanoparticles. After spin-coating the Ag nanoparticles on the SiGe surface, the sample was sintered at 190 ›C for 5 min. The average diameter of Ag particles was approximately 30 nm (nominal value). Oil-immersion lens was used to enhance the SERS effect. The numerical aperture (NA) was 1.4 and the refraction index n was 1.5. On the other hand, in the conventional measurement, NA and n were 0.7 and 1.0, respectively. The wavelength of the excitation light source and the focal length of the spectroscope were 532 nm and 2,000 mm, respectively. Results and Discussion Fig. 1 shows the SEM image of the SiGe surface with the Ag nanoparticles. Fig. 2 shows Raman spectra from strained SiGe on the Si substrate coated (w/ SERS) and uncoated (w/o SERS) by the Ag nanoparticles. These spectra were normalized by the Si substrate peak at 520 cm-1. The relative intensity of the SiGe peak was dramatically enhanced and the peak position of SiGe shifted toward a lower wavenumber. Furthermore, the enhanced Raman spectrum was clearly attributed to not only the oil-immersion measurement but also the SERS effect. Fig. 3 shows the peak of strained SiGe obtained by the SERS measurement after the subtraction of the Si substrate peak from the raw data. Both TO and LO phonon components were clearly extracted in fig. 3. From these Raman shift values, the anisotropic biaxial stress can be calculated by the relationship between stress and Raman with the use of phonon deformation potentials (PDPs) and elastic compliances [4,5,6]. As a result, σxx = -2.13 and σyy= -2.21 GPa were obtained. From the results, it was confirmed that the TO phonon was able to be efficiently excited by the SERS. We concluded that the shift on the low wavenumber side was definitely attributed to the TO phonon excitation. The TO/LO phonon excitation allows us to evaluate anisotropic biaxial stress in thin strained-SiGe. Acknowledgement This study was partially supported by the Japan Society for the promotion of Science through a Grant-in-Aid for Scientific Research B (No. 24360125) and Funding program for World-Leading innovative R&D on Science and Technology.

150 MeV Au ion induced modification of Si nanoparticles prepared by laser ablation

We have investigated in detail the effects of 150MeV Au ions irradiation on Si nanoparticles (NPs) synthesized by picosecond laser ablation of single crystal Si wafers in acetone. The formation of Si NPs was confirmed by Raman spectroscopy, transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM) measurements. The size distribution of synthesized NPs was found to be in the range of few nm to 80nm. These samples were then irradiated with 150MeV Au ions at various fluences ranging from 1×1013 to 1×1014ions/cm2. The effects of ion irradiation on the size and shape of Si NPs were further investigated using TEM, FESEM and micro Raman spectroscopy. From TEM data, we have noticed the reduction in size of NPs with increasing ion irradiation fluence. Furthermore with the increasing fluence we also observed the nucleation of 6–9nm NPs in the vicinity of bigger NPs where there were no such NPs before ion irradiation. The increase in the FWHM of the Raman peak and its shift towards lower wave number side also suggests that the decrease in NP size is a result of increase in the fluence of irradiation.

Effect of Zr/Ti ratio on structural, vibrational, magnetic and dielectric properties of (0.95)PbZrxTi1−xO3–(0.05)BiFeO3 ceramics

We have investigated the structural, vibrational, ferroelectric, magnetic and dielectric properties of (0.95)PbZrxTi1−xO3–(0.05)BiFeO3 (x = 0.51, 0.53 and 0.55) ceramics, prepared by the sol–gel route. Rietveld refined X-ray powder diffraction patterns of these samples confirm the single phase formation with a tetragonal structure (P4mm) symmetry at room temperature. The Williamson–Hall analysis was used to study the contributions of crystallite size and lattice strain on the peak broadening in the different patterns. Reduction in c/a ratio with x indicates poor ferroelectric behaviour for x = 0.55. Infrared spectroscopy revealed the slight shift of phonon modes towards the lower wave number side and increase in the bond length with increasing x which is in good agreement with the Rietveld analysis. Room temperature dielectric measurements of these samples show dispersion in er which is associated with a peak in tanδ versus logf plots. M–H hysteresis loops exhibit weak ferromagnetism for x = 0.51 and almost anti-ferromagnetic behaviour for x = 0.55.