Raman Phonon Modes Research Articles

A study on the vibrational frequencies, elastic properties and sound velocities of vanadium spinel oxides AV2O4 (A = Mn, Fe and Zn) short-range non-Coulomb potential theoretical model

Owing to the fact of the AB2O4 spinel oxide’s chemical and thermal stability, and other intriguing properties make them suitable candidate materials for many applications, including chemical looping and catalytic reactions. To do our investigations, a short-range non-Coulomb potential theoretical model is used to calculate the zone-centre, elastic constants, infrared phonon mode frequencies, Raman phonon mode frequencies, velocities of the sound wave along the highly symmetric three crystallographic-axes and Debye temperature of the vanadium spinel oxides AV2O4 (A = Mn, Fe and Zn). The preliminary results of our calculations show that the interaction in the second neighbour (V–O) is much stronger than the interaction of the first neighbour (A–O). Moreover, from the analysis of the obtained results of elastic constants, the nature of the studied vanadium spinels are found to be ductile.

Temperature-dependent Raman spectroscopy, domain morphology and photoluminescence studies in lead-free BCZT ceramic

Present work focuses on detailed temperature-dependent X-ray diffraction, Raman scattering, domain configuration, and photoluminescence (PL) studies in the (Ba0·85Ca0.15) (Zr0·10Ti0.90)O3 (BCZT) ceramics. The comprehensive Raman spectroscopy analysis in the present work not only validates the presence of the intermediate orthorhombic phase in BCZT, but also provides evidence of another transition: rhombohedral R3c phase to R3m at low temperature. Temperature behaviour of the lowest frequency transverse optical mode (soft E (TO) phonon) and hard modes was studied. Temperature dependence of peak positions, intensities, and linewidths of Raman phonon modes signalled the presence of phase transitions near −50 ± 5 °C, 0±5 °C, 35±5 °C and 110 ± 10 °C. Evolution of domain morphology occurring at phase transitions above room temperature was studied by piezoresponse force microscopy technique. Analysis of PL spectra revealed disorder/heterogeneity in the sample and indicated the existence of self-trapped excitons. PL spectra are composed of four distinct colour components (~2.55eV:blue, ~2.32eV:green, ~2.08eV:orange and ~1.78eV:red).

Conductivity relaxations and phase purity in strontium cobalt oxides prepared by numerous chemical routes

Strontium cobalt oxide (SrCoO3-δ) nanoparticles were successfully synthesized using; composite mediated hydrothermal (CMHM), without water and surfactants (WOWS) sol-gel and co-precipitation methods. The probable electrical conduction mechanism of synthesized strontium cobaltite was investigated via complex impedance analysis. Characterization techniques were employed to study the dependence of structure, homogeneity, physical parameters and electrical properties on synthesis procedures. After heat treatment, X-Ray Diffraction (XRD) confirmed the formation of phase pure SrCoO3-δ powders synthesized with CMHM, WOWS sol-gel and co-precipitation methods. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated the presence of fingerprint region of perovskite (ABO3-δ) structure. Raman spectroscopy revealed the internal motion of oxygen inside the CoO6 octahedra of SrCoO3-δ perovskite structure. A Raman phonon mode under 600 cm−1 position was identified which is commonly observed for such perovskite oxide. Scanning Electron Microscopy (SEM) images showed uniformly diffused, microporous and agglomerated sphere like morphology. Differential Thermal Analysis (DTA) and Thermogravimetry (TGA) verified formation of intermediate metal carbonates that decomposed to final product. Complex impedance spectroscopic plots (Nyquist plots) against frequency (20 Hz–3 MHz) discovered single semi-circular arcs in the low frequency region. These arcs showed that, grain boundary contribution is dominated over grain contribution to the total electrical conduction behavior. Modulus analysis disclosed non-Debye type conductivity relaxation in hydrothermally synthesized samples. The AC conductivity graphs followed Jonscher’s power law and hopping model. Hydrothermally synthesized samples exhibited minimum impedances and maximum AC conductivity, which makes them excellent candidate for cathode material in intermediate temperature range solid oxide fuel cells (IT-SOFCs) applications.

Raman spectroscopy study of structural disorder degree of ZnO ceramics

A detailed study of Raman line-shape of low and high dense ZnO ceramics was carried out using a Raman microprobe system with a solid-state laser source of 532 nm wavelength and 100 mW power at room temperature. The Raman activated bands for the ZnO wurtzite structure were observed in both samples. The line-width, asymmetry parameter, and Raman shift were determined by fitting the Raman spectra to Breit-Wagner-Fano (BWF) function and the degree of lattice disorder in the wurtzite structure were investigated by phonon confinement physical models (PCM). The correlation length (L) and defect concentration (N) could be estimated based on the spatial correlation model, being 3.01 nm and 3.15 nm (E2low mode) and 2.70 nm and 2.83 nm (E2high mode) and 8.84×1018cm−3 and 7.64×1018cm−3 (E2low mode) and 1.21×1019cm−31.05×1019cm−3 (E2high mode) for ZnO-LD and ZnO-HD samples, respectively. Since the E2low and E2high Raman phonon modes are sensitive to vibration in Zn sub-lattice and oxygen vacancy, respectively, the results indicated that low dense samples have a higher level of both defects.

High performance UV photodetector based on MoS2 layers grown by pulsed laser deposition technique

Highly efficient ultraviolet (UV) photodetector based on Molybdenum Disulfide (MoS 2 ) layers has been fabricated using pulsed laser deposition (PLD) technique. Systematic layer dependent photoresponse studies have been performed from single layer to 10 layers of MoS 2 by varying the laser pulses to see the effect of the number of layers on the photoelectrical measurements. Raman and Photoluminescence studies have been carried out to ensure the growth of high-quality MoS 2 layers. Layers of MoS 2 grown at 100 pulses were found to exhibit the characteristic Raman phonon modes i.e. E 1 2g and A 1g at 383.8 cm −1 and 405.1 cm −1 respectively and Photoluminescence (PL) spectra show B exciton peak for MoS 2 at around 625 nm suggesting the growth of high-quality MoS 2 layers. Atomic force microscopy (AFM) thickness profiling and cross sectional-high resolution transmission electron microscopy (HRTEM) analysis gives the thickness of grown MoS 2 to be 2.074 nm and 1.94 nm, respectively, confirming the growth of trilayers of MoS 2 . X-ray photoelectron spectroscopy (XPS) spectra of the grown trilayer sample show characteristic peaks corresponding to Molybdenum and Sulphur doublet (Mo 4+ 3d 5/2,3/2 and S 2p 3/2 , 1/2 ) confirming the chemical state of pure MoS 2 phase without the presence of any Molybdenum oxide state. Dynamic photoelectrical studies with Indium Tin Oxide (ITO) as contact electrode upon UV laser illumination show superior responsivity of 3 × 10 4 A/W at 24 μW optical power of the incident laser (λ = 365 nm) and very high detectivity of 1.81 × 10 14 Jones at a low applied bias of 2 V. The obtained results are highly encouraging for the realization of low power consumption and highly efficient UV photodetectors based on MoS 2 layers. • Optimization of high-quality large area MoS2 layers utilizing the PLD technique. • Demonstration of low power operated UV photodetector on optimized MoS2 layers. • Explained the Physics of the UV photodetector using energy band diagrams. • Work justifies the development of efficient photodetectors using PLD technique.

Ultrafast Control of Excitonic Rashba Fine Structure by Phonon Coherence in the Metal Halide Perovskite CH_{3}NH_{3}PbI_{3}.

We discover hidden Rashba fine structure in CH_{3}NH_{3}PbI_{3} and demonstrate its quantum control by vibrational coherence through symmetry-selective vibronic (electron-phonon) coupling. Above a critical threshold of a single-cycle terahertz pump field, a Raman phonon mode distinctly modulates the middle excitonic states with persistent coherence for more than ten times longer than the ones on two sides that predominately couple to infrared phonons. These vibronic quantum beats, together with first-principles modeling of phonon periodically modulated Rashba parameters, identify a threefold excitonic fine structure splitting, i.e., optically forbidden, degenerate dark states in between two bright ones with a narrow, ∼3 nm splitting. Harnessing of vibronic quantum coherence and symmetry inspires light-perovskite quantum control and sub-THz-cycle "Rashba engineering" of spin-split bands for ultimate multifunction device.

Raman scattering measurements of phonon anharmonicity in the delafossite CuGa1‐xCrxO2 (0 ≤ x ≤ 1) films

AbstractRaman spectra of the delafossite CuGa1‐xCrxO2 (0 ≤ x ≤ 1) solid solution films have been measured in the temperature range from 80 to 823 K. Raman phonon modes are observed at 224 (Ag), 328 (A2u), 396 (Eg), and 757 (A1g) cm−1 for the CuGaO2 film, and phonon modes of the CuCrO2 film are around 211 (Ag), 324 (A2u), 458 (Eg), and 712 (A1g) cm−1, respectively. The A1g phonon mode has a distinct redshift with increasing Cr composition, which indicates that the interatomic potential becomes weaker between Cu and O atoms. Except Raman modes at the Brillouin zone center, the additional phonon modes in the spectral range of 500−670 cm−1 were observed due to Raman selection rules being relaxed by the crystal defects. With increasing temperature, the A1g phonon mode undergoes a larger phonon softening but a smaller line broadening relative to that of the Eg phonon mode, which indicated the anisotropic behavior for the delafossite CuGa1‐xCrxO2 films. The nonlinear temperature dependence of the phonon frequency and linewidth is an indication of nonharmonic lattice dynamics. The Raman shift and the linewidth of the Eg and A1g optical modes as a function of temperature were studied as an experimental evidence of the combined effect of lattice expansion and anharmonic phonon–phonon interaction. And the three‐phonon anharmonic coupling plays the dominant role in the anharmonicity behavior. The phonon anharmonicity behavior of the CuGaO2 and CuCrO2 films is slightly different. The larger Γ0 is intrinsic for the A1g mode of the CuGa0.8Cr0.2O2 film due to the broadening by the crystalline defects, which perturb the translation symmetry of the harmonic crystal, making the momentum conservation rule for phonon scattering partially relaxed.

Magnetodielectricity induced by coexisting incommensurate conical magnetic structure and cluster glass-like states in polycrystalline BaFe10In2O19

Indium doped barium hexaferrite BaFe10In2O19 is shown to exhibit complex magnetic behaviour below 110 K wherein there is a coexistence of a long-range conical magnetic order along with a cluster spin-glass-like state. Temperature dependent dc magnetization measurements reveal that the system exhibits an anomaly around 110 K. Temperature dependent neutron diffraction (ND) measurements measured in the Q-range 0.28–7.35 Å−1 characterize this anomaly as a transition to a longitudinal conical magnetic state from the ferrimagnetic state at room temperature. Ac susceptibility and thermoremanent magnetization relaxation measurements also reveal the existence of cluster spin-glass like behavior below 110 K, indicating coexistence with conical magnetic order. The lattice parameters determined from the analysis of ND data show a sharp change at ∼110 K which is also reflected in the anomalous changes seen in the temperature dependent Raman phonon modes around this temperature. This gives a clear indication of spin lattice coupling in the system. Finally, temperature and magnetic field dependent dielectric constant measurements reveal the occurrence of large magnetodielectric effect (MDE) near 110 K. This intriguing intrinsic magnetodielectric feature can be explained in terms of spin lattice coupling.

Possible lattice and charge order in CuxBi2Te2Se

Metal intercalation into layered topological insulator materials such as the binary chalcogenide Bi2X3 (X = Te or Se) has yielded novel two-dimensional (2D) electron-gas physics, phase transitions to superconductivity, as well as interesting magnetic ground states. Of recent interest is the intercalation-driven interplay between lattice distortions, density wave ordering, and the emergence of new phenomena in the vicinity of instabilities induced by intercalation. Here, we examine the effects of Cu-intercalation on the ternary chalcogenide Bi2Te2Se. We report the discovery, in Cu0.3Bi2Te2Se, of a periodic lattice distortion (PLD) at room temperature, together with a charge density wave (CDW) transition around Td = 220 K. We also report, for the first time, a complete study of the CuxBi2Te2Se system, and the effect of Cu-intercalation on crystal structure, phonon structure, and electronic properties for 0.0 ≤ x ≤ 0.5. Our electron diffraction studies reveal strong Bragg spots at reciprocal lattice positions forbidden by ABC stacking, possibly resulting from stacking faults, or a superlattice. The c-axis lattice parameter varies monotonically with x for 0 < x < 0.2, but drops precipitously for higher x. Similarly, Raman phonon modes and soften monotonically for 0 < x < 0.2 but harden sharply for x > 0.2. This indicates that Cu likely intercalates up to x ∼ 0.2, followed by partial site-substitutions at higher values. The resulting strain makes the 0.2 ≤ x ≤ 0.3 region susceptible to instabilities and distortions. Our results point toward the presence of an incommensurate CDW above Td = 220 K. This work strengthens prevalent thought that intercalation contributes significantly to instabilities in the lattice and charge degrees of freedom in layered chalcogenides. Further work is required to uncover additional density wave transitions, and possible ground states such as superconductivity.

Spin phonon coupling in Mn doped HoFeO3 compounds exhibiting spin reorientation behaviour

An investigation has been carried out on the spin phonon coupling in a series of isostructural polycrystalline orthorhombic (Space group Pnma) compounds HoFe1−XMnXO3 (x ⩽ 0.6) exhibiting spin reorientation below Néel temperature (TN), using magnetization, neutron diffraction, and Raman scattering techniques. Mn doping leads to an anomalous increase in the spin reorientation temperature (TSR), shifting it close to room temperature from TSR ~ 60 K for x = 0 sample, and concomitant lowering of TN. The TSR is absent in samples for x ⩾ 0.5. The magnetic structure undergoes a transition at TSR from Γ4 → Γ1 in the Mn doped compounds as against Γ4 → Γ2 observed in HoFeO3 sample. In the region T < TN an anomalous softening of Raman phonon modes viz., B2g(5) and B3g(3), identified with the stretching motion and breathing mode, respectively, of Fe/Mn–O6 octahedra, is observed in compounds exhibiting spin-reorientation behaviour, indicating a spin-phonon coupling in these compounds. A quadratic correlation between the deviation of phonon frequency and variation of antiferromagnetic moment (Δω M2) is observed in these compounds. The temperature evolution of the M2+ mode obtained from the analysis of neutron diffraction data based on symmetry adapted mode decomposition of the Pnma structure further corroborates the mode softening observation.

First-principles study on the mechanical, vibrational and thermodynamic characteristics of intermetallic compound Ni2Ta

The mechanical, vibrational and thermodynamic characteristics of Ni2Ta were systematically investigated by means of density functional theory. The fully relaxed structure parameters were agreed well with the available experimental measured datas and published theoretical results. The single crystal elastic constants， polycrystalline modulus, Possion's ratio σ and Vickers hardness Hv were obtained. The anisotropic characters were studied by plotting the 3D surface contour of shear modulus and Young's modulus. Using the finite displacement method, the phonon dispersion curves and the phonon density of states were reported for the first time. The infrared-active and Raman phonon modes at the Г point were assigned and discussed. Finally, the thermodynamic characteristics such as isochoric specific heat capacities Cv and Debye temperature θD were predicted by the phonon density of states. Based on these exceptional properties, it was expected that Ni2Ta could be a promising intermetallic compound with high temperature and corrosion resistant performance.

Photoluminescence quenching of WS2 nanoflakes upon Ga ion irradiation

Modification of the electronic structure by defect engineering is crucial towards controlling the semiconductor band gap. In this report, the WS2 nanoflakes produced by self-sustaining high temperature synthesis are irradiated by Ga ion beam. Intensities of the Raman phonon modes and the photoluminescence (PL) are decreased upon increasing dose of Ga ion beam irradiation from 2·1013 to 1016 cm−2. This leads to the defect generation in the nanoflakes and their thinning. The maximum irradiation dose at 1016 cm−2 results in the degradation of the WS2 nanoflakes, thus to total quenching of the PL signals.

Au incorporation into various ZnO crystallographic cuts realised by ion implantation – ZnO damage characterization

Non-polar surfaces, such as a-plane (11–20) and m-plane (10-10), for ZnO have become more attractive as numerous efforts have recently been made to grow non-polar ZnO facets for applications in nanoscale photonic devices. Noble-metal incorporation into transparent semiconductors such as ZnO has been investigated because of the non-linear optical response of such structures. This paper presents a study of defect evolution in various ZnO crystallographic cuts caused by Au implantation. The investigation has focused on ZnO structure characterisation, Au distribution and the interior morphology of the a-, m- and c-planes ZnO single crystals implanted with 400 keV Au+ ions at the ion fluences of 5 × 1014 and 1 × 1015 cm−2 and subsequently annealed at 600 °C in O2. The structure modification was studied using Rutherford backscattering spectrometry (RBS) in the channelling mode (RBS/C) and Raman spectroscopy. After the ion-implantation process, low surface damage was observed in all ZnO orientations unlike deep structural damage. Deep structural damage grew with increased Au-ion fluence and Au did not exhibit strong out-diffusion from the depth to the surface during the post-implantation annealing. Small but noticeable differences were observed between different ZnO orientations. RBS measurements during ion implantation revealed more progressive deep-damage formation in the c- and m-planes than in the a-plane ZnO. Simultaneously, the smallest Zn sub-lattice disorder deduced from RBS/C measurements was observed in the a-plane ZnO. During post-implantation annealing, a slight structure recovery (about 4%) was observed in all orientations. Raman spectroscopy confirmed the increasing structure disorder with the enhanced ion fluence for all as-implanted ZnO orientations and a partial reconstruction of the ZnO structure during annealing, when the intensity of E2 phonons was increased and that of longitudinal optical (LO) phonons was suppressed because of the disorder recovery. E2 (high) and E1(LO) Raman phonon modes connected with oxygen sub-lattice ordering/disordering have been investigated in detail – they show a significant modification mainly in the m-plane. The cause of the different behaviour of ZnO planes as well as the differences in the incorporation and movement of Au and Er atoms in the ZnO structure are discussed in the work.

Phonon invisibility driven by strong magneto-elastic coupling in AlFeO3 thin film

Thin films of a lead-free magnetoelectric compound AlFeO3 have been deposited using a pulsed laser deposition technique. X-ray diffraction, X-ray absorption spectroscopy, and reflectivity measurements established the orthorhombic structure and a material density of 4.5 g/cm3, which is comparable to the bulk AlFeO3. The polycrystalline AlFeO3 film showed a strong magnetoelastic coupling. The Raman study carried out at variable temperatures and under an applied magnetic field at room temperature showed spectacular results. One of the Raman modes corresponding to AlFeO3 was found to vanish completely when the magnetic field of 0.08 T was applied at room temperature. The mode was also found to vanish between the temperature window of 280 K–236 K in temperature dependent studies. The observation was further supported by the detailed analysis of magnetization studies, which showed a change in the magnetic order in the same temperature interval. The invisibility of the Raman phonon mode has been attributed to the lattice deformation caused by the magnetoelastic effect. Additionally, the phonon frequencies showed renormalization below 200 K demonstrating a strong spin-lattice coupling.

Raman spectroscopic evidence of impurity‐induced structural distortion in SmB6

AbstractImpurity‐induced structural distortion in SmB6 is suggested by Raman spectroscopy study on impurity‐controlled samples. Significant differences in the Raman spectra of single crystals SmB6(6N), synthesized with 99.9999%‐pure boron, and SmB6(3N), synthesized with 99.9%‐pure boron, are detected. While no noticeable differences are detected in the X‐ray diffraction of SmB6(3N) and SmB6(6N), all the Raman phonon modes of the T2g, Eg, and A1g of SmB6(3N) are clearly broader and shift to higher wavenumbers than those of SmB6(6N), and the T2g and Eg modes of SmB6(3N) show doublet features. Based on the high‐pressure Raman measurements and phonon calculation in uniaxial compression model, we argue that small amount of impurities in SmB6(3N) is enough to induce anisotropic distortion in the B6 octahedra, leading to peculiar behaviors in Raman spectrum of SmB6(3N). Our results may present a clue for understanding the current puzzles about SmB6 of various origins with different impurities.

Study the contribution of surface defects on the structural, electronic structural, magnetic, and photocatalyst properties of Fe: CeO2 nanoparticles

In this work, the structural, ferromagnetic (FM) and photocatalytic properties of Ce1-xFexO2-δ (0≤ x ≤0.20) nanoparticles (NPs) synthesized through simple co-precipitation technique have been explored. X-ray diffraction (XRD) spectra revealed that all the samples possess single-phase fluorite structure. The crystallites size measured using XRD pattern found to decrease (8.9–6.5 nm) as the Fe content increased. The decrease in the crystallite size, further illustrated by TEM micrographs is also related to increase in the oxygen deficiency (δ) over the surfaces of Fe: CeO2-δ NPs. The Ov has been traced from the Raman spectra, in which the F2g Raman phonon mode at 462 cm−1 showed a broadening and red shift indicating that the Fe dopant further induces Ov. The NEXAFS spectral feature at Fe L3,2 edges signified that the Fe ions partially occupy the sites of Ce ions in the CeO2 matrix with Fe3+ and Fe2+ mixed valence state. Hence, the surface Ov is believed to activate the FM response based on bound magnetic polarons (BMP) mechanism, and the observed negative magnetic susceptibility at high applied magnetic field has been interpreted by simple approach dependent on coexistence of CeO2/Ce2O3 (core/shell) structures. The photo-catalyst activity of the samples were examined through decomposition of methylene blue (MB) dye under the sunlight. The catalyst efficiency and dissociation of adsorbed water molecules at the surfaces of NPs enhanced as the Fe doping content increased. This is related to Fe2+/Fe3+ redox cycles and creation of Ce3+/Fe2+ profound bands induced via Ov, which causes a suppression of the recombination of photo-generated electron–hole pairs.

Raman characterization of single-crystalline Ga0.96Mn0.04As:Zn nanowires realized by ion-implantation

Recent progress in the realization of magnetic GaAs nanowires (NWs) doped with Mn has attracted a lot of attention due to their potential application in spintronics. In this work, we present a detailed Raman investigation of the structural properties of Zn doped GaAs (GaAs:Zn) and Mn-implanted GaAs:Zn (Ga0.96Mn0.04As:Zn) NWs. A significant broadening and redshift of the optical TO and LO phonon modes are observed for these NWs compared to as-grown undoped wires, which is attributed to strain induced by the Zn/Mn doping and to the presence of implantation-related defects. Moreover, the LO phonon modes are strongly damped, which is interpreted in terms of a strong LO phonon-plasmon coupling, induced by the free hole concentration. Moreover, we report on two new interesting Raman phonon modes (191 and 252 cm−1) observed in Mn ion-implanted NWs, which we attribute to Eg (TO) and A1g (LO) vibrational modes in a sheet layer of crystalline arsenic present on the surface of the NWs. This conclusion is supported by fitting the observed Raman shifts for the SO phonon modes to a theoretical dispersion function for a GaAs NW capped with a dielectric shell.

Effect of structural disorder on the electronic and phononic properties of Hf doped BaTiO3

The classical ferroelectric material BaTiO3 has been doped with large cation i.e., Hf at Ti site in order to understand the effect of structural disorder in electronic and phononic state. The Raman spectroscopy measurement on these samples indicates increase in the structural disorder with Hf doping. The detail analysis of the Raman spectroscopy data clearly suggests the appearance of new Raman mode at ~ 780 cm−1 and the presence of an asymmetry in almost all Raman modes. The appearance of new Raman mode has been attributed due to the structural disorder induced phonon modes; and this is further confirmed using laser irradiation studies. Additionally, it has been observed that the intensity of this new phonon mode increases systematically with Hf doping; indicating increase in the phononic disorder. It has been observed that the line shape Raman phonon modes show significant asymmetry and this asymmetry along with the full peak width at half maxima (FWHM) of Raman phonon mode shows systematic variation with Hf doping. The observed asymmetric Raman line profile has been analysed through Fano model of electron–phonon coupling which suggests an increase in the electron–phonon coupling with Hf doping. In order to get further insight on increase in the electron–phonon coupling near band edge optical absorption spectroscopy measurements has been carried out and value of electronic disorder in the form of Urbach energy has been estimated and the same is observed to scale with Hf doping. Thus, the systematic increase in the intensity of disorder phonon mode and that of electronic disorder has been observed. This suggests that structural disorder not only affects phonons but electronic state of the system as well. Thus, it appears that the increase in the width of electronic and phononic disorder may overlap in energy scale and may be responsible for the observed increase in the electron–phonon coupling parameter as estimated through Fano equation.

UV Photodetector Based on Mg-Doped GaN Thin Films Prepared by Sol-Gel Spin Coating

In this work, sol-gel spin coated of magnesium (Mg) doped gallium nitride (GaN) thin films grown on AlN sapphire substrate was reported. The structural, lattice vibrational, and electrical properties of the deposited films were investigated and compared. X-ray diffraction results show that the deposited films composed of wurtzite structure with preferred orientation of GaN(002). The Raman active phonon modes correspond to the E2(high) and A1(LO) at 568 cm-1 and 733 cm-1 phonon modes of the hexagonal GaN were observed, while a broad peak attributed to the Mg-related lattice vibrational mode was detected at 669 cm-1. The Raman phonon modes were detected by using Raman spectroscopy. Hall effects results show that the resistivity, carrier concentration, and hall mobility of the Mg-doped GaN film was 0.1397 Ω cm, 1.77 × 1018 cm3, and 6.04 cm2/Vs, respectively. Besides, the characteristics of the ultraviolet (UV) photoresponse of the fabricated detector were investigated. The current-voltage characteristics of the Mg-doped GaN UV photodetector exhibits Schottky behaviour. The current-voltage measurements were carried out at room temperature with a computer-controlled integrated Source Meter (Keithley 2400). Lastly, the ideality factor and Schottky barrier heights were calculated using thermionic emission theory.

Raman scattering study of magnetic layered MPS3 crystals (, Fe, Ni)**Project supported by the Ministry of Science and Technology of China (Grant Nos. 2016YFA0300504 and 2017YFA0302904), the National Natural Science Foundation of China (Grant Nos. 11474357 and 11774419), the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grant No. 14XNLQ03).

We report a comprehensive Raman scattering study on layered MPS3 (M=Mn, Fe, Ni), a two-dimensional magnetic compound with weak van der Waals interlayer coupling. The observed Raman phonon modes have been well assigned by the combination of first-principles calculations and the polarization-resolved spectra. Careful symmetry analysis on the angle-dependent spectra demonstrates that the crystal symmetry is strictly described by C2h but can be simplified to D3d with good accuracy. Interestingly, the three compounds share exactly the same lattice structure but show distinct magnetic structures. This provides us with a unique opportunity to study the effect of different magnetic orders on lattice dynamics in MPS3. Our results reveal that the in-plane Néel antiferromagnetic (AF) order in MnPS3 favors a spin–phonon coupling compared to the in-plane zig-zag AF in NiPS3 and FePS3. We have discussed the mechanism in terms of the folding of magnetic Brillouin zones. Our results provide insights into the relation between lattice dynamics and magnetism in the layered MPX3 (M=transition metal, X=S, Se) family and shed light on the magnetism of monolayer MPX3 materials.