Laser Molecular Beam Epitaxy Research Articles

Rapid identification and quantitative analysis of malachite green in fish via SERS and 1D convolutional neural network

Rapid and quantitative detection of malachite green (MG) in aquaculture products is very important for safety assurance in food supply. Here, we develop a point-of-care testing (POCT) platform that combines a flexible and transparent surface-enhanced Raman scattering (SERS) substrate with deep learning network for achieving rapid and quantitative detection of MG in fish. The flexible and transparent SERS substrate was prepared by depositing silver (Ag) film on the polydimethylsiloxane (PDMS) film using laser molecular beam epitaxy (LMBE) technique. The wrinkled Ag NPs@PDMS film exhibits high SERS activity, excellent reproducibility and good mechanical stability. Additionally, the fast in situ detection of MG residues onfishscales was achieved by using the wrinkled Ag NPs/PDMS film and a portable Raman spectrometer, with a minimum detectable concentration of 10-6 M. Subsequently, a one-dimensional convolutional neural network (1D CNN) model was constructed for rapid quantification of MG concentration. The results demonstrated that the 1D CNN quantitative analysis model possessed superior predictive performance, with a coefficient of determination (R2) of 0.9947 and a mean squared error (MSE) of 0.0104. The proposed POCT platform, integrating a transparent flexible SERS substrate, a portable Raman spectrometer and a 1D CNN model, provides an efficient strategy for rapid identification and quantitative analysis of MG in fish.

Composition-dependent optical, dielectric and d-orbital electron characteristic of high-throughput horizontal composition gradient Li1-xMgxTi2O4 combinatorial film

The unique physical properties of LiTi2O4 and MgTi2O4 attracted extensive research interest in various fields, including new type batteries and high-temperature superconductors. However, the intricate mechanism governing the d-orbital electron within this system still awaits further excavation. Herein, we employed the combinatorial laser molecular beam epitaxy technique to fabricate a high-quality composition-spread Li1-xMgxTi2O4 film and evaluated its structure, composition, surface morphology and phonon modes by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and Raman scattering spectroscopy. The optical constants and dielectric properties of diverse microregions with varying Li/Mg content over a wide spectral range (189–1658 nm) were measured nondestructively using spectroscopic ellipsometry, revealing the composition-dependent optical properties of Li1-xMgxTi2O4. By fitting the second derivative spectra (d2ε/dE2) using the standard critical point model, five transitions within the detected spectral range were observed. Combining previous analyses and first-principles calculation, we attribute the critical points to crystal field (CF) transition 4A2 →4T1 originating from the spin state of tetrahedral Li/Mg ions, the binding of Ti-related pairs and electron transitions between O-2p to Ti-3d orbits. This exploration of the precise structure of the d-metal band provides a positive reference for the regulation and application of relevant devices.

Role of Surface Chemistry of Ta Metal Foil on the Growth of GaN Nanorods by Laser Molecular Beam Epitaxy and Their Field Emission Characteristics.

This study investigates the influence of surface nitridation of Ta metal foil substrates on the growth of GaN nanorods using the laser molecular beam epitaxy (LMBE) technique and the field emission characteristics of the grown GaN nanorod ensemble. Surface morphology examinations underscore the pivotal role of Ta foil nitridation in shaping the dimensions and densities of GaN nanorods. Bare Ta foil fosters the formation of high-density, vertically self-aligned GaN nanorods at a growth temperature of 700 °C. Furthermore, the density of these nanorods is directly related to the duration of Ta foil nitridation, with increased duration leading to a reduced nanorod density. X-ray Photoelectron Spectroscopy (XPS) studies reveal that the transition of the Ta foil surface from tantalum oxide to tantalum nitride during nitridation emerges as a crucial factor influencing GaN nanorod growth. Photoluminescence (PL) spectroscopy at ambient temperature reveals a strong near-band-edge (NBE) emission peak with negligible defect-related peaks, displaying the high optical quality of the GaN nanorods. The highly dense vertically aligned GaN nanorod ensemble growth without Ta prenitridation exhibits the most favorable field emission performance, featuring a turn-on field of 2.1 V/μm, a field enhancement factor of 2480, and a stable long-term operation at the emission current density of 2.26 mA/cm2. This study advances the understanding of the role of the surface chemistry of metal foil in determining GaN nanorod growth and opens up exciting possibilities for tailoring advanced optoelectronic devices for specific application requirements.

Study of dielectric polarization and electrical transport in Bi1·2Sb0·8Te0·4Se2.6 nanofilms

Studying the dielectric response of topological insulators (TIs) can unveil their unique physical mechanisms such as charge transport and spin-orbit coupling effects. However, due to the manifestation of material's topological nature and band structure primarily in nanofilm, such thickness poses challenges for dielectric testing. To date, research on TI dielectric aspects remains relatively unexplored. Therefore, this paper successfully synthesizes nanofilm of quaternary topological insulator Bi1·2Sb0·8Te0·4Se2.6 (BSTS) using laser molecular beam epitaxy (LMBE) technique. Utilizing a wide-frequency dielectric spectrometer and a comprehensive physical properties measurement system (PPMS), we measured and thoroughly analyzed the dielectric polarization and charge transport characteristics of BSTS. We observed various polarization responses in the frequency range of 101–103 Hz, with the dipole orientation gradually failing to keep pace with the frequency increase in the range of 103–105 Hz, and the relaxation polarization unable to establish itself in the range of 105–107 Hz, with polarization primarily contributed by displacement polarization. Subsequently, we further analyzed the dependence of BSTS dielectric polarization response on temperature and film thickness, which will help reveal the influence of external factors on TI dielectric response, providing crucial insights for controlling TI materials' dielectric response. This not only deepens our understanding of the fundamental physical properties of this novel material but also offers important scientific basis and technological support for its applications in quantum computing, photonics, spintronics, and other fields.

Enhanced photoresponsivity in Bi2Se3 decorated GaN nanowall network-based photodetectors

Recently, highly responsive photodetectors which are capable of photodetection in a wide range of wavelength spectra are in great demand. To fulfil this, photodetectors formed using heterojunctions of multiple semiconducting materials gain a lot of interest as they cover a broad range of photodetection, and the built-in electric field developed at their interface helps to enhance photoresponse. Here, we have demonstrated a fascinating broadband metal-semiconductor-metal type photodetector (PD) by integrating sputtered Bi2Se3 with the laser molecular beam epitaxy (LMBE) grown GaN film and porous nanowall network on sapphire (0001) substrates. The fabricated photodetectors using a hybrid Bi2Se3/LMBE-GaN nanowall structure exhibit broadband characteristics with a high responsivity of 51.4 and 1.46 A/W when illuminating with the laser of wavelength 355 nm (UV) and 1064 nm (NIR), respectively. The enhanced UV responsivity and good response in the NIR region using Bi2Se3/GaN heterojunction nanostructures suggest futuristic application in dual-wavelength detector devices.

(Energy Technology Division Supramaniam Srinivasan Young Investigator Award) Fundamental Insights into the Oxygen Evolution Reaction from Epitaxial Oxide Thin Films

The intermittent nature of renewable energy sources requires a clean, scalable means of converting and storing energy. One Earth-abundant storage option is water electrolysis: storing energy in the bonds of O2 and H2, and later extracting electricity by the electrochemical reaction of gasses in a fuel cell. The efficiency of this process is primarily limited by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode, resulting in extensive use of precious metal electrocatalysts in current devices. We have worked to build mechanistic understanding of the OER on benchmark catalysts rutile IrO2 and RuO2, and have investigated competition with the chlorine evolution reaction (CER) in saline feeds, where breaking scaling relations between oxidative processes can broaden the range of acceptable water sources for electrolysis. We have also investigated earth-abundant oxide materials as alternatives, especially nickel-based perovskites, focusing on fundamental understanding of the electrode/electrolyte interface and its relation to catalyst electronic structure.I will present studies of model oxide electrodes grown by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) that display a known crystallographic orientation, strain, surface area, and path for charge transport. Such measurements can establish the intrinsic activity of oxide catalysts in a way that cannot be realized with polydisperse nanoparticle systems, and we use these findings to rationally design composition and structure to maximize activity.

Dependence of WAL effect and enhancement of spin-orbit coupling effect in Bi1.2Sb0.8Te0.4Se2.6 low-temperature magnetic transport

The strong spin-orbit coupling and time-reversal symmetry in topological insulators (TIs) produce a new quantum state known as the topological surface state (TSS). The study of low-temperature magnetic transport in the TSS provides opportunities to explore exotic physical phenomena such as the spin Hall effect and the topological phase transition. An important goal in obtaining intrinsic TI systems is to eliminate internal defects and thereby reduce the contributions of metallic states in transport measurements. In this work, we are committed to overcoming this difficulty by elemental alloying. This paper reports the successful preparation of high-quality and stoichiometrically stable Bi1.2Sb0.8Te0.4Se2.6 (BSTS) thin films by innovatively combining the hybrid target structure with the laser molecular beam epitaxy (LMBE) system and low-temperature magnetic transport tests conducted on BSTS thin films of different thicknesses. Due to stronger spin-orbit coupling, we observed a weak anti-localization (WAL) effect, and the strength of the effect was affected by the film thickness and temperature in the low-temperature magnetic transport study. The dependence of the WAL effect provides a way to regulate the TSS.

Structural, Magnetic, and Magneto-Optical Properties of Thin Films of BaM Hexaferrite Grown by Laser Molecular Beam Epitaxy.

Thin films of BaM hexaferrite (BaFe12O19) were grown on α-Al2O3(0001) substrates by laser molecular beam epitaxy. Structural, magnetic, and magneto-optical properties were studied using medium-energy ion scattering, energy dispersive X-ray spectroscopy, atomic force microscopy, X-ray diffraction, magneto-optical spectroscopy, and magnetometric techniques, and the dynamics of magnetization by ferromagnetic resonance method. It was shown that even a short time annealing drastically changes the structural and magnetic properties of films. Only annealed films demonstrate magnetic hysteresis loops in PMOKE and VSM experiments. The shape of hysteresis loops depends on thickness of films showing practically rectangular loops and high value of remnant magnetization (Mr/Ms~99%) for thin films (50 nm) and much broader and sloped loops in thick (350-500 nm) films. The magnitude of magnetization 4πMs ≈ 4.3 kG in thin films corresponds to that in bulk BaM hexaferrite. Photon energy and sign of bands in magneto-optical spectra of thin films correspond to ones observed earlier in bulk samples and films of BaM hexaferrite. FMR spectra of 50 nm films at 50 GHz consist of a number of narrow lines. The width of main line ΔH~20 Oe is lower than has been reported up to now.

Heteroepitaxial growth of anatase (0 0 1) films on SrTiO3 (0 0 1) by PLD and MBE

The epitaxial growth of anatase (001) films deposited by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) on SrTiO3 (001) (STO) single crystals has been studied using X-ray diffraction and surface sensitivity UHV techniques. The evolution of the strain represented by the microstrain and the change of the in-plane and out-of-plane lattice parameters with film growth temperature, the effect of the annealing temperature and the influence of the oxygen content of the film have been investigated.The out-of-plane lattice strain shows a compressive (−0.2 %) or expansive (+0.3 %) behavior, in the range 600–900 °C, for temperatures below or above 700 °C, respectively. The in-plane lattice parameters, as well as the cell volume of the film, remain under compression over the entire temperature range explored.PLD films grow into square islands that align with the surface lattice directions of the STO substrate. The maximum size of these islands is reached at growth temperatures close to 875–925 °C. Film annealing at temperatures of 800 °C or higher melts the islands into flat terraces. Larger terraces are reached at high annealing temperatures of 925 °C for extended periods of 12 h. This procedure allows flat surface terrace sizes of up to 650 nm to be achieved.The crystalline quality achieved in anatase films prepared by PLD or MBE growth methods is similar. The two-step anatase growth process used during the synthesis of the films with both methods: film growth and post-annealing treatment in oxygen or air at ambient pressure, using temperature and time as key parameters, allows to control the surface terrace size and stoichiometry of the films, as well as the anatase/rutile intermixing rates at sufficiently high temperatures. This growth process could allow the substitution of their equivalent single crystals. The range of applicability of these films would include their use as structural and electronic model systems, or in harsh experimental conditions due to their low production cost.

Optical properties study of high-throughput horizontal composition gradient FeSe1-xTex thin film based on ellipsometry

The high-throughput superconductivity research model can effectively accelerate the material synthesis and physical characterization process. It can rapidly form a database of materials and reveal the hidden key physical laws, which provides significant assistance to the research of superconducting materials, especially the exploration of superconductivity mechanism. In this work, FeSe1-xTex thin film with spread composition was grown by combined laser molecular beam epitaxy, the third generation combined thin film preparation technique. The film thickness and surface morphology were obtained by atomic force microscopy, which showed that the sample surface was relatively smooth. In addition, we measured the distribution of critical elements and c-axis lattice constants within the different microzones along the direction of composition variation on the surface of the film, by X-ray photoelectron spectroscopy and X-ray diffraction, respectively, which verified that the film was prepared in accordance with a continuous composition gradient. Based on this, nine microzones of the film were tested using the ellipsometer equipped with a focused light spot. The dispersion model of the FeSe1-xTex layer was established using the Drude-Lorentz oscillator, and the optical constants of the film with horizontal composition gradient were obtained by inversion and fitting of the data within each microzone. The results indicate that the FeSe1-xTex thin film shows an obvious composition-dependent optical property. Our work reports the optical constants of FeSe1-xTex composition-spread thin film by using a nondestructive and accurate method, spectroscopic ellipsometry, which enriches the database of this material. This work may provide a reference for establishing the correlation between the optical and superconducting properties of FeSe-based superconductors.

Sputter-grown c-axis-oriented PdCoO2 thin films

Metallic delafossites, ABO2 (A = Pd or Pt), are layered oxides that are as conductive as elemental metals. The high conductivity and surface polarity make metallic delafossites fascinating electrode materials for heterostructure devices. Here, we report the successful growth of c-axis-oriented PdCoO2 thin films on Al2O3 (001) substrates by magnetron sputtering that is widely used in industries. The observation of the PdCoO2 thin films through scanning transmission electron microscopy revealed layered crystal structures. A sharp interface exhibiting a layer stacking sequence of Pd/CoO2/Al2O3 was observed clearly, similar to the interfaces obtained with other growth methods such as pulsed laser deposition and molecular beam epitaxy. This layer stacking is particularly interesting because it can induce a high work function at the interface. The in-plane resistivity of the as-grown PdCoO2 thin film was 73 μΩ cm at room temperature, which decreased to 11 μΩ cm after post-annealing. The residual resistivity ratio of the annealed thin films was approximately 2.9. The impurity phases of PdOx were observed using x-ray diffraction and scanning transmission electron microscopy. The sputtering deposition of c-axis-oriented thin films could lead to the practical application of the polar surface of PdCoO2 in semiconductor devices.

Fabrication of GaN-based MSM droplet triboelectric nanogenerator by the conjunction of photovoltaic and triboelectric effect

The present work focuses on the fabrication of Gallium Nitride based triboelectric nanogenerators for energy harvesting from moving NaCl droplets of various concentrations between 0.1 M and 1.0 M. Fabricated Droplet-Based (DB)-TENG is found to generate a voltage of ∼18.3 V, current of 0.9 µA and power of 64 µW at a load resistance of 150 MΩ by drop casting the NaCl droplet over GaN thin film. The direct growth of GaN on Aluminium Nitride over different substrate including Si(n + +), Si (100), Sapphire, and Si (111) is achieved using the Laser Molecular Beam Epitaxy technique, for the improved device performance, a substrate-dependent comparison analysis is also conducted. The effect of ultraviolet (UV) light of wavelength 325 nm on the DB-TENG has also been studied to enhance the induced signal and the maximum output voltage of ∼ 42 V, current of 8.8 µA and maximum output power of 824 µW were measured with 150 MΩ load resistance. The results indicate an enhancement in the generated voltage by 3 times and the current by one order upon UV illumination. This work is used for energy harvesting in the form of mechanical energy and photon energy by coupling the photovoltaic and triboelectric effects.

Correlation of preparation conditions of SrRuO<sub>3</sub> ultrathin films with topological Hall effect

As one of the magnetic transition metal oxides, SrRuO<sub>3</sub> (SRO) has received much attention in recent years, which is mainly due to its unique itinerate ferromagnetism and the unusual electrical transport properties–behaving as Fermi liquid at low temperature and bad metal at high temperature. In the growth of SRO thin films, there are many factors that can affect the quality of thin films. In this work, we study various factors affecting the growth and quality of SRO thin films by using laser molecular beam epitaxy (laser MBE), including laser energy density, substrate temperature and target surface conditions, and explore their influences on the topological Hall effect (THE) in SRO. For thin films grown at high laser energy density and high temperature, we found that there are large trenches at the edge of steps, which deteriorate the transport properties of the thin films. When using low laser energy density, extra SrO may exist in the films, which also suppresses the conductivity. Films grown at low temperature tend to have poor crystallinity while films grown at high temperature exhibit island structures. The ablation degree of the target surface increases the decomposition of SRO to SrO, Ru and volatile RuO<sub>4</sub>, resulting in Ru defects in the grown thin film. The SRO thin film grown under the optimal conditions (1.75 J·cm<sup>–2</sup>, 670 ℃, fresh target surface) exhibits the optimal conductivity and the strongest THE. For non-optimal growth conditions that favors thickness inhomogeneity or Ru defects in the film, THE becomes weaker or even disappears. Therefore, we believe that the THE is due to the Dzyaloshinskii-Moriya interaction (DMI) resulting from the interfacial inversion asymmetry and the associated chiral spin structures.

Atomic Magnetic Heating Effect Enhanced Hydrogen Evolution Reaction of Gd@MoS2 Single-Atom Catalysts.

Atomic heating on single atoms (SAs) to maximize the catalytic efficiency of each active site would be a fascinating solution to break the bottleneck for the performance improvement of single-atom catalysts (SACs) but highly challenging task. Here, based on the Gd@MoS2 SACs synthesized by a facile laser molecular beam epitaxy method, high-frequency alternating magnetic field (AMF) technology is employed to induce atomic magnetic heating on Gd SAs that is meanwhile demonstrated to be the catalytic active center. Significant improvement in catalytic kinetics under AMF excitation (3.9 mT) is achieved, yielding a remarkable enhancement of hydrogen evolution reaction magnetothermal-current by ≈924%. Through theoretical calculations and spin-related electrochemical experiments, such promotion in catalyst activity can be attributed to spin flip (or canting) in Gd SAs leading to the atomic magnetic heating effect on catalytic active center. Together with the embodied high stability, the implement of AMF to the SAs field is demonstrated in this work, and the precisely atomic magnetic heating on specific SAs offers unprecedented thinking for further improvement of SACs performance in the future.

Correlation of crystalline and optical properties with UV photodetector characteristics of GaN grown by laser molecular beam epitaxy on a-sapphire

Correlation of crystalline and optical properties with UV photodetector characteristics of GaN grown by laser molecular beam epitaxy on a-sapphire

Optical and electrical properties of BaSnO3 and In2O3 mixed transparent conductive films deposited by filtered cathodic vacuum arc technique at room temperature

For the crystalline temperature of BaSnO3 (BTO) was above 650 °C, the transparent conductive BTO-based films were always deposited above this temperature on epitaxy substrates by pulsed laser deposition or molecular beam epitaxy till now which limited there application in low temperature device process. In the article, the microstructure, optical and electrical of BTO and In2O3 mixed transparent conductive BaInSnO x (BITO) film deposited by filtered cathodic vacuum arc technique (FCVA) on glass substrate at room temperature were firstly reported. The BITO film with thickness of 300 nm had mainly In2O3 polycrystalline phase, and minor polycrystalline BTO phase with (001), (011), (111), (002), (222) crystal faces which were first deposited at room temperature on amorphous glass. The transmittance was 70%–80% in the visible light region with linear refractive index of 1.94 and extinction coefficient of 0.004 at 550-nm wavelength. The basic optical properties included the real and imaginary parts, high frequency dielectric constants, the absorption coefficient, the Urbach energy, the indirect and direct band gaps, the oscillator and dispersion energies, the static refractive index and dielectric constant, the average oscillator wavelength, oscillator length strength, the linear and the third-order nonlinear optical susceptibilities, and the nonlinear refractive index were all calculated. The film was the n-type conductor with sheet resistance of 704.7 Ω/□, resistivity of 0.02 Ω ⋅cm, mobility of 18.9 cm2/V⋅s, and carrier electron concentration of 1.6 × 1019 cm−3 at room temperature. The results suggested that the BITO film deposited by FCVA had potential application in transparent conductive films-based low temperature device process.

Low temperature epitaxial technology for GaN-based materials

<p indent="0mm">The band gap of GaN-based semiconductor materials covers the entire visible light band and has excellent physical and chemical properties, which makes it widely used in the fabrication of optoelectronic devices, power electronic devices, and radio frequency and microwave devices. Traditional GaN-based materials are usually epitaxially grown on high-temperature-resistant single-crystalline substrates such as sapphire, silicon, or silicon carbide using metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). These epitaxial techniques usually use high temperature to crack the precursors involved in the reaction. With the deepening of informatization and intelligentization, the common demands for low-cost and flexibility of opto(electronic) devices have emerged. On one hand, the display technology is a key link to realize information exchange and intelligence. Moving towards an intelligent society requires further reduction of the display cost per unit area. At the same time, the wearable and portable flexible display technology also has broad application prospects. In addition, solid-state lighting has gradually penetrated into every corner of human life with the improvement of device performance. The application scenarios are rich and colorful. Judging from this, low-cost surface light sources will be a strong competitor for the next generation of lighting technology routes. On the other hand, reducing the fabrication cost of electronic devices per unit area also needs more attention in the future. For example, flexible electronic skin has broad and huge application prospects in artificial limbs, robotics, medical detection and diagnosis, etc., which has also spawned the demand for low-cost flexible sensors. It can be seen that the common requirements of the above applications for core components are low cost and flexibility, which is also one of the main development directions of the next generation of (opto)electronic devices. Amorphous substrates (such as glass, plastic, metal, polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), etc.) that are cheap and easy to fabricate are ideal choices, but a significant disadvantage is that amorphous substrates cannot withstand high growth temperatures. Therefore, the need for low-temperature epitaxy of GaN-based materials has arisen, that is, a kind of epitaxy equipment that can use external electric field energy to crack the reaction precursor at low temperatures. So far, a variety of low-temperature epitaxial technologies have been developed based on the physical vapor deposition (PVD) and the chemical vapor deposition (CVD), and preliminary research results have been obtained. The PVD techniques include reactive magnetron sputtering, plasma-assisted MBE (PA-MBE), pulsed laser deposition (PLD), pulsed sputtering deposition (PSD), laser MBE (LMBE), etc. The CVD techniques include remote plasma CVD (RPCVD), migration enhanced afterglow CVD (MEA-CVD), remote plasma-enhanced MOCVD (RPEMOCVD), radical-enhanced MOCVD (REMOCVD), electron cyclotron resonance plasma-enhanced MOCVD (ECR-PEMOCVD), inductive coupled plasma MOCVD (ICP-MOCVD), etc. In this paper, the two types of low-temperature epitaxial technologies are introduced in detail, including the device structure, working conditions and related epitaxial growth results, and the characteristics of each type of technology are summarized. Finally, the development prospect of low temperature epitaxial technologies is prospected, and the focus of future research is pointed out. We hope this work can provide a useful reference for the low temperature epitaxy research of GaN-based materials.

Diffused magnetic transitions in NiFe2O4/SrTiO3(0 0 1) epitaxial heterostructures

Magnetization reversal in as-grown and annealed NiFe2O4 / SrTiO3(001) epitaxial heterostructures, prepared by laser molecular beam epitaxy (LMBE), was studied using magneto-optical technique in geometry of polar (PMOKE) and longitidual (LMOKE) Kerr effect. It was found that the hysteresis loops of polarization plane rotation and ellipticity measured in LMOKE geometry are combinations of symmetric (even in magnetic field) SPart and antisymmetric (odd in magnetic field) AsPart parts, caused by quadratic (QMOKE ∼ MiMj) and linear (LMOKE ∼ Mi) in magnetization M contributions, correspondingly. The angular dependences of SPart demonstrate in-plane biaxial magnetic anisotropy (BMA) and show that magnetization reversal in as-grown structures occurs by one jump (1j) process, in contrast to the annealed structures, in which two jumps (2j) process takes place when the deviation of magnetic field from the hard axis is less than ∼20°. Analysis within the framework of the Stoner-Wohlfarth (SW) model with account of domain mechanism of magnetization jumps shows that the first jump occurs due to formation and movement of domain walls. Second jump is remarkably diffused, that is associated with the dispersion of the biaxial anisotropy field Ha and misorientations of the magnetic easy axes in different regions of the film. Narrow and strong FMR lines are observed in the most perfect structures in which the diffusion of the second jump is small. The degree of second jump diffusion can be used to assess the structural perfection of the films.

Interface magnetization in Y3Fe5O12 / Nd3Ga5O12 epitaxial heterostructures caused by Fe3+ - Nd3+ exchange coupling

The spectral and magnetic field dependences of the polar magneto-optical Kerr effect (PMOKE) were studied in heterostructures formed by 10 - 40 nm Y3Fe5O12 (YIG) layer grown by laser molecular beam epitaxy on Nd3Ga5O12 (NdGG) and Gd3Ga5O12 (GGG) substrates. The PMOKE spectra can be decomposed into two components, one of which, caused by the Faraday effect in the substrate, is linear in magnetic field H, and the second is saturated at H ∼ 0,04 – 0,056 MA/m. In YIG / NdGG, the spectral dependence of the substrate-caused PMOKE clearly reveals a series of narrow bands corresponding to electronic transitions (absorption bands) in the Nd3+ ion. The saturable component of PMOKE, which reflects the behavior of the magnetization of the YIG film, is similar to that observed in YIG / GGG, but at the same time clearly reveals anomalies at the photon energies, corresponding to electronic transitions in the Nd3+ ion. This indicates the presence of magnetization of Nd3+ ions in the interface region of the YIG / NdGG structure, induced by the exchange interaction Nd3+ - Fe3+. The signs of the PMOKE anomalies and possible influence of NdGG substrate complex refractive index on PMOKE caused by YIG film are discussed.

Optical properties of LMBE grown c-axis oriented GaN thin films using Surface Plasmon Resonance technique

Present work reports the growth and optimisation of thin films of Gallium nitride (GaN) with preferred c-axis (0002) orientation on Si (111) substrate using the Laser Molecular Beam Epitaxy technique. For the development of optically efficient GaN thin film, the nitrogen gas flow during film deposition has been optimised and film properties are measured using the highly sensitive Surface Plasmon Resonance (SPR) technique in OTTO configuration. Structural, morphological and optical properties of the GaN thin films were studied using XRD, AFM, PL and FTIR spectroscopy. Varying the deposition gas flow from 1.3 sccm to 4 sccm led to a decrease in refractive index values from 2.77 to 2.21. By using the SPR technique, the refractive index (n) dispersion of GaN thin films was also analysed with the incident radiated wavelength.