Longitudinal Optical Modes Research Articles

Fabrication and Characterization of Aluminum Nitride Nanoparticles by RF Magnetron Sputtering and Inert Gas Condensation Technique

Aluminum nitride nanoparticles (AlN-NPs) were fabricated by a RF magnetron sputtering and inert gas condensation technique. By keeping the source parameters and sputtering time of 4 h fixed, it was possible to produce AlN-NPs with a size in the range of 2–3 nm. Atomic force microscopy (AFM), Raman spectroscopy, X-ray diffraction (XRD), and UV-visible absorption were used to characterize the obtained AlN-NPs. AFM topography images showed quazi-sphere nanoparticles with a size ranging from 2 to 3 nm. The XRD measurements confirmed the hexagonal wurtzite structure of AlN nanoparticles. Furthermore, the optical band gap was determined by the UV-visible absorption spectroscopy. The Raman spectroscopy results showed vibration transverse-optical modes A1(TO), E1(TO), as well as longitudinal-optical modes E1(LO), A1(LO).

Polar vibrational and dielectric properties of monolayer transition metal dichalcogenides from macroscopic equations

Long wavelength polar vibrations in monolayer (ML) transition metal dichalcogenides (TMDs) are systematically studied for in-plane and out-of-plane motions, using two pairs of macroscopic equations deduced from a microscopic dipole lattice model accounting for local field effects (LFEs) and electronic polarization (EP). Longitudinal and transverse optical modes and out-of-plane modes are derived, and the analytical expressions describe previous first-principles calculations very well. Owing to the LFEs, the in-plane dielectric susceptibilities of ML TMDs are one order of magnitude greater than the out-of-plane susceptibilities. Furthermore, the effects of the dielectric environment on the polar vibrations are studied. Both EP and LFEs should be accounted for obtaining an accurate evaluation of dielectric susceptibility and key lattice-dynamical properties such as Born charge and phonon dispersion. A two-dimensional (2D) Lyddane–Sachs–Teller relation and a frequency–susceptibility relation are derived for in-plane and out-of-plane motions, relating the 2D dielectric functions or susceptibilities to the polar phonon frequencies. The results are also compared in detail with those of ML hexagonal boron nitride.

Infrared-active phonon modes in single-crystal thorium dioxide and uranium dioxide

The infrared-active phonon modes, in single-crystal samples of thorium dioxide (ThO2) and uranium dioxide (UO2), were investigated using spectroscopic ellipsometry and compared with density functional theory. Both ThO2 and UO2 are found to have one infrared-active phonon mode pair [consisting of one transverse optic (TO) and one associated longitudinal optic (LO) mode], which is responsible for the dominant features in the ellipsometric data. At room temperature, our results for the mode pair’s resonant frequencies and broadening parameters are comparable with previous reflectance spectroscopy characterizations and density functional theory predictions. For ThO2, our ellipsometry and density function theory results both show that the LO mode broadening parameter is larger than the TO mode broadening. This signifies mode anharmonicity, which can be attributed to the intrinsic phonon–phonon interaction. In addition to the main mode pair, a broad low-amplitude impurity-like vibrational mode pair is detected within the reststrahlen band for both ThO2 and UO2. Elevated temperature measurements were performed for ThO2 in order to study the mechanisms by which the phonon parameters evolve with increased heat. The observed change in the TO resonant frequency is in excellent agreement with previous density functional calculations, which only consider volume expansion of the crystal lattice. This suggests that the temperature-dependent change in the TO frequency is primarily due to volume expansion. The change in the main mode pair’s broadening parameters is nearly linear within the temperature range of this study, which indicates the intrinsic anharmonic scattering (via cubic anharmonicities) as the main decay mechanism.

Infrared active phonons in monoclinic lutetium oxyorthosilicate

A combined generalized spectroscopic ellipsometry measurement and density functional theory calculation analysis is performed to obtain the complete set of infrared active phonon modes in Lu2SiO5 with a monoclinic crystal structure. Two different crystals, each cut perpendicular to a different crystal axis, are investigated. Ellipsometry measurements from 40to1200cm−1 are used to determine the frequency dependent dielectric function tensor elements. The eigendielectric displacement vector summation approach and the eigendielectric displacement loss vector summation approach, both augmented with anharmonic lattice broadening parameters proposed recently for low-symmetry crystal structures [Mock et al., Phys. Rev. B 95, 165202 (2017)], are applied for our ellipsometry data analysis. All measured and model calculated dielectric function tensor and inverse dielectric function tensor elements match excellently. 23 Au symmetry and 22 Bu symmetry infrared active transverse and longitudinal optical modes are found. We also determine the directional limiting modes and the order of the phonon modes within the monoclinic plane. Results from density functional theory and ellipsometry measurements are compared and nearly perfect agreement is observed. We further compare our results to those obtained recently for the monoclinic crystal Y2SiO5, which is isostructural to Lu2SiO5 [Mock et al., Phys. Rev. B 97, 165203 (2018)]. We find that the lattice mode behavior of monoclinic Lu2SiO5 is qualitatively identical with Y2SiO5 and differs only quantitatively. We anticipate that members of the isostructural group of monoclinic symmetry oxyorthosilicates such as Dy2SiO5 or Yb2SiO5 will likely behave very similar in their phonon mode properties as reported here for Lu2SiO5.

Evaluation of carrier density and mobility in Mn ion-implanted GaAs:Zn nanowires by Raman spectroscopy

The fabrication of complex nanoscale electronics with reduced dimensions poses challenges on novel techniques to accurately determine fundamental electronic parameters. In this article, we present a universal contactless method based on Raman scattering for measuring the mobility and hole concentration independently in GaAs:Zn and Mn ion-implanted GaAs:Zn nanowires, potentially of great interest for spintronics applications. Clear coupled longitudinal optical phonon-plasmon modes were recorded and fitted with a dielectric function, based on the Drude model, which includes contributions from both plasmons and phonons. From the fitting, we extract accurate values of the plasma frequency and plasma damping constant from which we directly calculate the hole density and mobility, respectively. The extracted mobilities were also used as input data for analysis of complementary four-probe transport measurements, where the corresponding hole concentrations could be calculated and found to be in good agreement with those extracted directly from the Raman data. We also investigated the influence of annealing of the GaAs:Zn nanowires on the hole concentration and mobility and found strong indications of thermally activated defects related to a formed crystalline As/oxide shell around the nanowires. The method proposed here is extremely powerful for the characterization of nanoelectronics in general, and nanospintronics in particular for which Hall measurements are difficult to pursue due to problems related to contact formation, as well as to inherent magnetic properties of the devices.

Depth Profiling of Ion-Implanted 4H–SiC Using Confocal Raman Spectroscopy

For silicon carbide (SiC) processed by ion-implantation, dedicated test structure fabrication or destructive sample processing on test wafers are usually required to obtain depth profiles of electrical characteristics such as carrier concentration. In this study, a rapid and non-destructive approach for depth profiling is presented that uses confocal Raman microscopy. As an example, a 4H–SiC substrate with an epitaxial layer of several micrometers thick and top layer in nanoscale that was modified by ion-implantation was characterized. From the Raman depth profiling, longitudinal optical (LO) mode from the epitaxial layer and longitudinal optical phonon-plasmon coupled (LOPC) mode from the substrate layer can be sensitively distinguished at the interface. The position profile of the LOPC peak intensity in the depth direction was found to be effective in estimating the thickness of the epitaxial layer. For three kinds of epitaxial layer with thicknesses of 5.3 μm, 6 μm, and 7.5 μm, the average deviations of the Raman depth analysis were −1.7 μm, −1.2 μm, and −1.4 μm, respectively. Moreover, when moving the focal plane from the heavily doped sample (~1018 cm−3) to the epitaxial layer (~1016 cm−3), the LOPC peak showed a blue shift. The twice travel of the photon (excitation and collection) through the ion-implanted layer with doping concentrations higher than 1 × 1018 cm−3 led to a difference in the LOPC peak position for samples with the same epitaxial layer and substrate layer. Furthermore, the influences of the setup in terms of pinhole size and numerical aperture of objective lens on the depth profiling results were studied. Different from other research on Raman depth profiling, the 50× long working distance objective lens (50L× lens) was found more suitable than the 100× lens for the depth analysis 4H–SiC with a multi-layer structure.

Comparative studies of CdS thin films by chemical bath deposition techniques as a buffer layer for solar cell applications

Cadmium sulfide (CdS) buffer layer that decouples the absorber layer and window layer in thin-film solar cells was synthesized by two different chemical bath deposition (CBD) techniques with varying deposition parameters. X-ray diffraction (XRD) revealed that the CdS thin film crystallizes in a stable hexagonal wurtzite structure having a preferential orientation along (002) reflection plane with a crystallite size varying from 20 to 40 nm. First longitudinal optical phonon mode was identified at Raman shift of 305 cm−1. Uniform, granular, continuous, and smooth surface with an average grain sizes (< 100 nm) as well as small roughness (< 9 nm) was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The symmetric composition of cadmium and sulfur along with larger grains (20 nm) was observed at higher deposition temperatures and times. The optical band gap of CdS samples obtained from process one was in the range of 2.3–2.35 eV, while the band gap by the second CBD process lay in between 2.49 and 2.65 eV, showing the most stable compound of CdS. The presence of a green emission band in photoluminescence spectra (PL) demonstrated that the CdS material has better crystallinity with minimum defect density. Hall effect studies revealed the n-type conductivity of CdS thin films with a carrier concentration values in the order of 1016 cm−3. Furthermore, CdS thin films fabricated by CBD process exposed better quality that might be more suitable material as a buffer layer for thin-film solar cells.

Dual-doped CdSe:Cu:O films grown by sputtering using CdSe–CuO composite targets

The effects of the simultaneous incorporation of Cu and O in CdSe films grown by sputtering are presented. The Cu and O contents varied between 1 and 5 at.% in films deposited at 150, 200, 250 and 300 °C. Concentrations of 2, 3, 4 and 5 at.% of CuO in the target promoted the formation of copper selenide clusters immersed within the CdSe:Cu:O host. Energy considerations (enthalpy of formation and bond dissociation energy) were used to discuss the absence of copper oxide and the formation of copper selenide aggregates, as well as the film thickness dependence on the concentration of CuO in the target. The band gap of the films ranged from 1.21 to 2.07 eV, depending upon growth conditions. Significant below-band-gap absorption was observed which was ascribed to the copper selenide micro and nano clusters. Good crystalline quality of the films, for high substrate temperatures, was evidenced through the appearance of overtones of the vibrational longitudinal optic modes detected by Raman micro spectroscopy. It was determined that the electronic properties, optical transmission and electrical conductivity depended on the chemical composition and crystalline structure. This characteristic is relevant because through copper and oxygen co-doping is possible to control these technologically important physical properties of CdSe in a simple and reliable manner.

Superior stiffness and vibrational spectroscopic signature of two-dimensional diamond-like carbon nitrides

Abstract Carbon nitride materials are promising for applications in electronics, clean energy production, and heat dissipation. Two-dimensional (2D) diamond-like carbon nitrides α -C 2 N 2 , β -C 2 N 2 , and γ -C 4 N 4 rise as beyond graphene semiconductors. Here, we apply first-principles calculations and group theory to study their structure, mechanical properties, and vibrational signature. The α -C 2 N 2 is the strongest among them, with a 2D Young’s modulus E 2D equal to 616(6) N/m, followed by the γ -C 4 N 4 with an E 2D equal to 632(6) N/m and 581(7) N/m along its zigzag and armchair directions, respectively, and the β -C 2 N 2 with an E 2D equal to 582(9) N/m. These materials are about 2 times stiffer than graphene, and are the stiffest among 2D networks of carbon and nitrogen atoms. The zigzag direction of 2D γ -C 4 N 4 is approximately 8% stronger than its armchair direction, unusual for in-plane anisotropic 2D materials, where the armchair direction is considerably weaker than the zigzag direction. These findings from stress–strain analysis are consistent with the high sound speed and elastic constants values we found by using 2D density-functional perturbation theory framework, suggesting them for mechanical reinforcement. We report the phonon wavenumber, atomic vibrational pattern, and Raman and infrared spectra for all polytypes. The longitudinal and transverse optical modes of the in-plane isotropic polytypes display the breakdown of LO–TO splitting, characteristic of 2D polar crystals. We found that the difference between their phonon wavenumbers can be probed in their unpolarized Raman and infrared spectra. The simulated angular dependency of the Raman intensity under backscattering parallel and cross polarizations show how to assign the A 1 ′ and E ′ modes of the α -C 2 N 2 , the A 1 g and E g modes of the β -C 2 N 2 , and of the A g and B 1 g modes of the γ -C 4 N 4 , being key for polytype identification. These results provide comprehensive information on the emerging 2D diamond-like carbon nitrides, necessary for further developments on their synthesis, characterization, and future device fabrication.

Indium Composition Dependence of Raman Spectroscopy and Photocurrent of InxGa1−xAs Strained Layers Grown by Using MOCVD

The photocurrent and Raman were studied for the InxGa1−xAs strained layers grown on GaAs (001) substrates by using metalorganic chemical vapor deposition (MOCVD) with different indium compositions. The indium composition in the InxGa1−xAs strained layers was determined by using high-resolution X-ray diffraction (HR-XRD) and Vegard’s rule. The in-plane lattice constants and tensile strains of the InxGa1−xAs strained layers were evaluated as functions of the indium composition. The tensile strain of the InxGa1−xAs strained layers increases as the indium composition increases. The Raman spectra are observed to be dominated by the GaAs longitudinal optical (LO) phonon mode as the strongest peaks show up around 287∼292 cm−1. Moreover, the weak and broad spectral features in the range of 265∼270 cm−1 originate from the peaks associated with the GaAs transverse optical (TO) phonon mode. The Raman peak also shifts toward lower wave number with increasing indium compositions, which indicates the presence of tensile strain in the InxGa1−xAs layers. As the indium composition increases, the band-gap shift decreases for temperatures ranging from 30 to 300 K.

Longitudinal optical Raman mode A1 to calculate the indium molar fraction of epitaxial InGaN layers grown by LP-MOCVD on polar and non-polar planes

This work discusses the frequency shift of Raman mode A1(LO) for InGaN epitaxial layers grown on polar (0002) and non-polar (11–20) planes concerning strain state, indium composition, and the probe excitation energy. Furthermore, it proposes MOCVD growth conditions to grow fully relaxed polar and non-polar InGaN layers, without indium droplets formation. Then, using the probe excitation energies of 2.33 eV and 2.68 eV, Raman measurements exhibited phonon mode A1(LO) frequency shift in polar and non-polar InGaN. Besides, theoretical calculations showed that for x < 0.20, and changing the excitation energy from 2.33 to 2.68 eV, the expected frequency shift is less or equal to 15 cm−1. Also, the XRD spectra exhibited two different indium compositions for non-polar a-plane InGaN and one composition for polar c-plane InGaN. According to XRD, for non-polar a-plane InGaN, the frequency shift measured corresponds to an indium composition gradient along the growth direction and the probe excitation energy change. On the other hand, for polar c-plane InGaN, the frequency shift measured is attributed to the probe excitation energy change. Also, AFM showed that there is an excellent island coalescence in GaN and InGaN epitaxial growth. The average surface roughness for polar InGaN was 75.678 nm and was 61.216 nm for non-polar InGaN. Moreover, these values are ten times smaller than their peak-to-peak distance, and the growth follows the Stranski–Krastanov model. FWHM for all samples corresponds to a total dislocations density of ~ 109/cm2 near the surface.

Anomalous Arrhenius and Berthelot behavior of temperature dependent photoluminescence of Mn-doped ZnS nanostructures

We studied charge carrier relaxation in ZnS:Mn nanostructures synthesized by vapor-liquid-solid (VLS) technique for increasing thickness (tc = 0.5, 1 and 3 nm) of thermal deposited Mn catalyst. The dominant phase of the synthesized ZnS:Mn nanostructures was hexagonal Wurtzite, and no trace of secondary phase was observed. The longitudinal optical (LO) and transverse optical (TO) Raman modes in these structures were found at 269 and 348 cm−1, respectively, which were typical of Wurtzite ZnS. Temperature-dependent photoluminescence (PL) spectroscopy showed violet band-to-band transition (~380 nm) along with defect related blue and green bands (~420 and 510 nm), while Mn:d→d band peak was observed at ~ 570 nm. In addition, red band (~670 nm) showed strong appearance at low temperature (10 K) and disappeared at high temperatures was attributed to the formation of possible MnS clusters present in the ZnS:Mn nanostructures. The PL integrated intensities of various bands demonstrated mixed anomalous Berthelot and Arrhenius behavior with increase in temperature. All the emission bands obtained from ZnS:Mn (tc = 3 nm) nanostructures showed a Berthelot-type behavior, where the carrier escape (activation) energies were found to be 29 ± 2 (2.3 ± 0.3), 21 ± 1 (2.6 ± 0.5), 11 ± 1 (1.8 ± 0.4) meV and 51 ± 3 meV (1.5 ± 0.1 meV) for the 390 nm, 470 nm, 520 nm and 670 nm bands, respectively. The green and red band of ZnS:Mn (tc = 0.5 nm) nanostructures showed a normal Arrhenius behavior whereas, the violet band exhibited the abnormal Berthelot behavior. Increasing Mn thickness also exhibited large modulation of color perception, which is critical to realize single active-layer white light-emitting diodes.

Hot Phonon and Auger Heating Mediated Slow Intraband Carrier Relaxation in Mixed Halide Perovskite

A clear understanding of excited carrier relaxation to their equilibrium state via carrier-phonon, carrier-carrier interaction etc. is always required for the advancement of perovskite based device performance. Organic/inorganic lead halide perovskite have shown remarkable slow hot carrier cooling properties. Herein, we investigate the effect of hot phonon and Auger heating on hot carrier relaxation dynamics in Methyl-ammonium lead iodide-chloride (CH3NH3PbI3-XClX or mixed halide) perovskite using transient absorption spectroscopy. The reduced energy-loss rate on sub-picosecond time scale clearly shows the non-equilibrium build-up of longitudinal optical and acoustic phonon modes (carrier-phonon interaction) at low pump excitation (1018 cm-3). However at high pump excitation (1019 cm-3), dominating Auger heating process (carrier-carrier interaction) further reduces the energy-loss rate by more than two order of magnitude and delays the carrier relaxation process to tens of picoseconds which makes perovskite as a promising candidates in hot carrier photovoltaic.

Fabrication and characterization of GaAs nanoparticles achieved using femtosecond laser ablation

GaAs Nanoparticles (NPs) were produced using femtosecond pulsed laser (∼50 fs, 1 kHz repetition rate, 800 nm) ablation of bulk GaAs in distilled water. Effect of different laser energies such as 100 μJ, 200 μJ, and 500 μJ on the produced NPs was investigated. The produced NPs possessed size distribution in the range of 10–200 nm, most of the particles having an average particle size around 57 nm. In addition, nanoflake like structures having amorphous nature were also observed. With an increase in laser energy it was observed that there was a slight increase in the NPs size. For ablation performed at an energy of 500 μJ, a clear colour change (yellowish) of solution was observed due the increase in the efficiency of ablation, which could be due to a higher concentration of the NPs. Optical properties of these nanoparticles depict the absorption in the range of 264–274 nm and emission in the range of 410–440 nm. The longitudinal optical phonon-plasmon coupled (LOPC) and longitudinal optic (LO) modes observed near 266 cm−1 and 288 cm−1 in the Raman spectrum confirmed the presence of GaAs. The small shift observed in the Raman modes of GaAs NPs may be due the stress formed during the ablation. The X-ray diffraction studies revealed that the produced nanoparticles possessed cubic zinc blende structure of the GaAs.

Temperature dependence on dielectric properties of CdTe and ZnTe using first-principles method and experimental data

The dielectric properties of ZnTe and CdTe at high temperature are studied by both of vibrational frequencies and experiment damping constants. We perform systematic calculations to investigate the vibrational properties of perfect crystalline ZnTe and CdTe for a wide range of temperature ranging from 0K to 1400K by combining the first-principles methods and quasi-harmonic approximation (QHA). Then, this method is performed to estimate the temperature dependence of dielectric properties of ZnTe and CdTe with the transverse-optical (TO) and longitudinal-optical (LO) mode frequencies and the damping coefficient obtained from experimental data under lower temperature. Furthermore, we extended the estimations of dielectric properties of ZnTe and CdTe to higher temperatures.

Yoğunluk Fonksiyoneli Teorisi ile LiAlSi’un Basınç Altında Elektronik ve Titreşim Özellikleri

Li containing materials have an important place in the development of technology. Therefore, knowledge of the structural and dynamic properties of electronic Li-containing crystals is important. The structural, electronic and lattice dynamic properties of LiAlSi crystal was performed by an ab-initio pseudopotential method and a linear response with the General Gradient Approximation. LiAlSi crystal is in Zincblende structure and the space group is . The lattice parameter of LiAlSi crystal was 6.0306 A. The computed lattice parameter, bulk modulus and first-order pressure derivative of the bulk modulus agree well with the experimental and other theoretical calculations. The electronic band structure and phonon dispersion curve were analyzed by using the Quantum Espresso program. Phonon dispersion curve and phonon density of states were calculated by a density functional perturbation theory. Since the phonon frequency values are positive values, the LiAlSi crystal is stable. Then, electronic band structure and phonon distribution curve under P= 8.892 GPa pressure were examined. LiAlSi crystal showed semiconductor properties at P = 0.0 GPa pressure, whereas P = 8.892 GPa pressure showed semi-metal properties. At this pressure, the phonon frequency values are also positive. In addition, transverse, longitudinal acoustic and transverse, longitudinal optical mode values at high symmetry points Γ, X and L under two different pressures (P = 0.0 GPa and P = 8.892 GPa) are listed. It is thought that the results of this study will contribute to the literature.

Exciton–phonon properties in cylindrical quantum dot with parabolic confinement potential under electric field

Abstract The mixed confinement potential effect on exciton in cylindrical quantum dot (QD) is calculated in the presence of an electric field with and without confined longitudinal optical (LO) phonon mode contribution. The variational approach within the effective mass approximation is used to describe the exciton–phonon interaction with three variational parameters of the trial wave function. The ground state binding energy of exciton has been calculated numerically for the parabolic (axial direction) and square (lateral direction) finite confinement potentials under the electric field applied along the growth direction of the QD. The system both with and without LO-phonon contribution is investigated. The combined effects of applied electric field and parabolic confinement on the ground state binding energy, the polaronic correction and the Stark shift are examined in detail. The findings indicate that the electric field strongly reduces the binding energy in both ignoring and considering LO-phonon interaction especially for wider thickness of QD. We have shown that the contribution of LO-phonon leads to an increase in the binding energy and to decrease in the Stark shift energy. Furthermore, our numerical results illustrate a strong dependence of Stark shift on the QD height, electric field strength and LO-phonon contribution.

Analysis of structural and vibrational properties of ZnSe nanostructures: A DFT/TDDFT study

The structural and vibrational properties of ZnnSen (n=1,3,7,13) nanostructures have been investigated using the Gaussian 09 program, density functional theory and time-dependent density functional theory at the B3LYP level with 6–311G basis functions. The structural properties showed that the rebuilding in surface atoms deviated many bonds from their ideal length, the Zn-Se bond length decreased with the increase in the size of nanostructures and converged to the experimental value. Quantum confinement effect diminution was observed with the growing size of the nanostructures; hence, the energy gap converged to the experimental value of 2.7 eV. Moreover, the binding energy increased with the increase of the structure size, such that wurtziod2c (Zn13Se13) is more stable than smaller structures. The vibrational properties results indicated that the experimental longitudinal optical mode (LO mode) is situated between bare and hydrogen passivated LO modes and very near to the bare case, this gave a good agreement with experimental findings. The presence of hydrogen atoms at the surface caused a several times decrease in vibrational force constant in comparison to the bare case. The IR spectrum for wurtzoid and HP wurtzoid were investigated. The optical edge in UV-Vis spectra of wurtzoid reduced from 4.5 eV to 4.2 eV of wurtzoid2c due to the increase in the size of the nanostructure, while the maximum peak for wurtzoid at 2.88 eV increased to 3.06 eV for wurtzoid2c showing a clear blue shift. These results leads to wide applications in fields such as photoelectronic devices, lasers, sensors, and LEDs.

Electronic structure and photocatalytic activity of samarium doped cerium oxide nanoparticles for hazardous rose bengal dye degradation

Sm doped CeO2 (Sm = 0%, 2%, 4%, 6% and 8%) nanoparticles have been synthesized by sol-gel method for spintronics and photodegradation applications. Structural properties were studied using X-ray diffraction that showed single-phase crystalline nature with some structural distortions. Raman spectroscopy was employed to study the defects where longitudinal optical mode confirmed the presence of defects in the form of oxygen vacancies. Magnetic studies infer that saturation magnetization (MS) increased with Sm doping from 0.36 × 10−3 emu/g for pure CeO2 to 15.8 × 10−3 emu/g for Sm 6% and then, decreased for Sm 8%. Reported results also demonstrated the excellent photodegradation of UV-irradiated rose bengal dye. X-ray photoelectron spectroscopy (XPS) was used to illustrate the electronic structure, including the contribution of each ionic state, i.e. Ce3+ and Ce4+. Oxygen vacancies and formation of new networks led to the origin of room temperature ferromagnetic behaviour and excellent photocatalytic degradation of harmful rose bengal dye.

Structural and optical study of alternating layers of In and GaAs prepared by magnetron sputtering

Currently, the obtention of nano-structures based on III-V materials is expensive. This calls for novel and inexpensive nanostructure manufacturing approaches. In this work we report on the manufacture of a nanostructures consisting of alternating layers of In and GaAs on a silicon substrate by magnetron sputtering. Furthermore, we characterized the produced nanostructures using secondary ion mass spectroscopy (SIMS), X-ray diffraction analysis, and Raman spectroscopy. SIMS revealed variation in the concentration of In atoms across In/GaAs/In interphases, and X-ray diffraction revealed planes corresponding to phases associated with GaAs and InAs due to In interfacial diffusion across GaAs layers. Finally, in order to study the composition and crystalquality of the manufactured nanostaructures, Raman spectra were taken using laser excitation lines of 452 nm, 532 nm, and 562 nm at different points across the nanostructures.This allowed to determine the transverse and longitudinal optical modes of GaAs and InAs,characteristic of a two-mode behavior. An acoustic longitudinal vibrational mode LA(Γ) of GaAs and an acoustic longitudinal mode activated by disorder (DALA) were observed. These resulted from the substitution of Ga atoms for In atoms in high concentrations due to the generation of Ga(VGa) and/or Arsenic(VAs) vacancies.This set of analyses show that magnetron sputtering can be aviable and relatively low-cost technique to obtain this type of semiconductors.