Function Of Growth Temperature Research Articles

Influence of growth temperature on the magnetization dynamics of sputtered CoFeB thin films on various substrates and their microwave device functionality

In the present investigation, sputtering growth of 100 nm thick Co40Fe40B20 (CoFeB) film has been investigated in a low temperature range from room temperature (RT) to 400 ℃ on silicon (Si), silicon dioxide (Si/SiO2), and sapphire (Al2O3) substrates. The film surface morphology, static and dynamic magnetization were measured as a function of growth temperature and substrate. The grown films were further tested as a potential material for microwave device functionality in terms of filter and phase shifter. Surface roughness was lowest for the film grown on Si/SiO2 substrate at 200 ℃ (0.39 nm) measured from atomic force microscopy. Static magnetic properties measured by tracing magnetic hysteresis loop suggest a soft magnetic behaviour with in-plane magnetic anisotropy. Film saturation magnetization increases with the increase in growth temperature up to 200 ℃ and then decreases from 200 ℃ to 400 ℃. This suggest that the sputtering growth from room temperature to 200 ℃ offer a moderate to low interfacial stress resulting in low defects density. Gilbert damping constant (αeff) of the thin film is obtained from the ferromagnetic resonance measurements in a broad band of microwave frequencies. Damping was lowest (5.4×10−3) in the film grown at 200 ℃ on the Si/SiO2 substrate which correlates with the roughness and magnetization data. A low value of αeff is desirable for a material to be used in energy efficient spintronics and magnonic applications. The CoFeB films were also utilized in prototype microwave band-stop filter and phase shifter device applications. The filter has been tested in the frequency range from 6GHz to 25GHz with an applied magnetic bias up to 4.0 kOe. The frequency tunability with respect to the applied magnetic bias measured to be around 3.64 GHz/kOe. The maximum attenuation of −4dB was observed for the film grown on Si/SiO2 substrate at 200 ℃. Whereas, phase shifter fabricated on Si/SiO2/CoFeB film grown at 200 ℃ shows a differential phase shift up to 75°/cm. These results indicates that the CoFeB film deposited at low growth temperature can be a potential material in spintronics and CMOS applications where low temperatures are required for device fabrications.

A systematical investigation of layer growth rate, impurity level and morphology evolution in TiO2 thin films grown by ALD between 100 and 300 °C

TiO2 thin films prepared by atomic layer deposition (ALD) have attracted great attention due to the widespread application of the oxide as a promising charge storage material for lithium or proton batteries. In this work, we study TiO2 film grown on Si substrates by atomic layer deposition with tetrakis (dimethylamino) titanium as metal precursor (TDMAT) and water vapour as an oxidant. The chemical composition and impurity content of the film as a function of growth temperature is studied by Ion Beam Analysis (IBA). D2O (99.8%) was used as oxidant to study the film growth to distinguish between hydrogen atoms originating from the water oxidant or the metal precursor. Combining ellipsometry with Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA) reveals film density as a function of growth temperature. Atomic force microscopy (AFM) was used to characterize the film surface structure. By investigating the structural and compositional range of ALD TiO2 films will open the new opportunities of application.

Adatom controlled emergence of high hardness in biocompatible beta-Ti3Au intermetallic thin film surfaces

There is growing international interest in hard biocompatible thin film surface coatings to extend the lifetime of medical implants. Parameters of the physical vapour deposition technique can be utilized to fine tune the microstructure and resulting properties of the growing thin film surface by modifying the adatom mobility of the incoming species. This work investigates the evolution of high hardness and biocompatibility of sputter deposited beta-Ti3Au intermetallic thin film surfaces as a function of growth temperature and pressure. Titanium and gold are sputtered in an optimised 3:1 ratio over glass and Ti6Al4V substrates at varying pressures of 0.3 to 1.2 Pa and temperatures of 25 to 450°C. The microstructure and crystallinity of the deposited films improved with reduction in pressure from 1.2 to 0.3 Pa but development of the β-Ti3Au intermetallic compound occurred at temperatures above 350˚C. The density of the films also increased with reducing pressure, whereas improvement in their columnar structure was observed with increasing substrate temperature. These microstructural changes caused by adatom mobility variation, led to the emergence of superior mechanical surface hardness, reaching a peak value of 12.5 GPa for films grown at 0.3 Pa and 450°C. All thin film surfaces were highly biocompatible with ion leaching levels below 1 ppm, and films deposited at lower pressure exhibited much safer cytotoxic profiles against L929 mouse fibroblasts. This work demonstrates the emergence of high hardness and biocompatibility in Ti3Au thin film surfaces with potential as next generation medical implant coating materials.

Simultaneous Quantification of Trehalose and Trehalose 6-Phosphate by Hydrophilic Interaction Chromatography/Electrospray Accurate Mass Spectrometry with Application in Non-Targeted Metabolomics.

High-resolution mass spectrometry (HRMS) was coupled with ultra-high-performance liquid chromatography (UHPLC) to simultaneously quantify trehalose and trehalose 6-phosphate without derivatization or sample preparation. The use of full scan mode and exact mass analysis also makes it possible to carry out metabolomic analyses as well as semi-quantification. In addition, the use of different clusters in negative mode makes it possible to compensate for deficiencies in linearity and inerrant saturation at time-of-flight detectors. The method has been approved and validated for different matrices, yeasts, and bacteria, and has shown differentiation between bacteria as a function of growth temperatures.

Why and how In composition fluctuations appear in InGaN?

We modeled by kinetic Monte Carlo simulations the growth of InGaN alloys on perfectly oriented and misoriented GaN surfaces. As the growth temperature increases, we show that two phenomena occur: composition pulling along the growth direction and lateral indium rich cluster formation. We show that both phenomena have the same origin, strain, and that temperature enables these phenomena to manifest themselves in measurable quantities. Indeed, there is a continuous transition as a function of growth temperature between statistical alloys, described by a binomial distribution law, and heterogeneous layers with indium rich clusters occurring at higher growth temperatures. We quantify this transition by introducing a cluster index based on the In and Ga atom spatial distribution. We show that this cluster index increases above a given temperature, while at low temperature and, in thin layers, it is determined by surface roughness and the associated In fluctuations. Composition pulling can be observed on a larger temperature range. Composition fluctuations are thus caused by strain, and permitted by In mobility at the surface during growth at sufficiently high temperature.

Tailoring interface epitaxy and magnetism in La1−xSrxMnO3/SrTiO3 heterostructures via temperature-driven defect engineering

Defect engineering of La1−xSrxMnO3 (LSMO)—a strongly correlated oxide displaying half metallicity and ferromagnetism above room temperature—has been the focus of a long-standing quest aimed at the exploitation of this material as a functional building block for memory storage and spintronic applications. Here, we discuss the correlation between structural defects and magnetism in La0.74Sr0.26MnO3/SrTiO3 (LSMO/STO) epitaxial heterostructures as a function of growth temperature and post-deposition annealing. Upon increasing the growth temperature from 500 to 700 °C at a fixed oxygen partial pressure of 0.007 mbar, the sputter-deposited epitaxial LSMO films experience a progressive increase in Curie temperature Tc from 110 to 270 K and saturation magnetization Ms from 1.4 to 3.3 μB/u.c. owing to a reduction in oxygen deficiencies. Concurrently, however, growth temperatures above 600 °C trigger the formation of off-stoichiometric, dendritic-like SrMoOx islands at the film/substrate interface as a possible aftermath of temperature-driven diffusion of impurities from the STO substrate. Notably, although the interfacial spurious islands cause an increase in sample surface roughness, the heterostructure still preserves high-quality epitaxy. In general, the best compromise in terms of both structural and magnetic properties, comprising high-quality epitaxy, atomically flat surface, and robust ferromagnetism above room temperature, is obtained for LSMO films grown at a relatively low temperature of about 500–540 °C followed by a post-deposition annealing treatment at 900 °C for 1 h in air. Our study compares effective routes based on temperature-controlled defect engineering to finely tailor the complex interplay between microstructure and magnetism in LSMO thin films.

Mechanisms of Quasi van der Waals Epitaxy of Three-Dimensional Metallic Nanoislands on Suspended Two-Dimensional Materials.

Understanding structure at the interface between two-dimensional (2D) materials and 3D metals is crucial for designing novel 2D/3D heterostructures and improving the performance of many 2D material devices. Here, we quantify and discuss the 2D/3D interface structure and the 3D morphology in several materials systems. We first deposit faceted Au nanoislands on graphene and transition metal dichalcogenides, using measurements of the equilibrium island shape to determine values for the 2D/Au interface energy and examining the role of surface reconstructions, chemical identity, and defects on the grown structures. We then deposit the technologically relevant metals Ti and Nb under conditions where kinetic rather than thermodynamic factors govern growth. We describe a transition from dendritic to faceted islands as a function of growth temperature and discuss the factors determining island shape in these materials systems. Finally, we show that suspended 2D materials enable the fabrication of a novel type of 3D/2D/3D heterostructure and discuss the growth mechanism. We suggest that emerging nanodevices will utilize versatile fabrication of 2D/3D heterostructures with well-characterized interfaces and morphologies.

Application of machine learning to reflection high-energy electron diffraction images for automated structural phase mapping

We have developed a phase mapping method based on machine learning analysis of reflection high-energy electron diffraction (RHEED) images. RHEED produces diffraction patterns containing a wealth of static and dynamic information and is commonly used to determine the growth rate, the growth mode, and the surface morphology of epitaxial thin films. However, the ability to extract quantitative structural information from the RHEED patterns that appear during film growth is limited by the lack of versatile and automated analysis techniques. We have created a deep learning-based analysis method for automating the identification of different RHEED pattern types that occur during the growth of a material. Our approach combines several supervised and unsupervised machine learning techniques and permits the extraction of quantitative phase composition information. We applied this method to the mapping of the structural phase diagram of ${\mathrm{Fe}}_{\mathrm{x}}{\mathrm{O}}_{\mathrm{y}}$ thin films grown by pulsed laser deposition as a function of growth temperature and oxygen pressure close to the hematite-magnetite phase boundary. The in situ RHEED-based mapping method produces results that are qualitatively similar to postsynthesis x-ray diffraction analysis.

Magnetic transition behavior in epitaxial Fe47Rh47Pd6 films

The properties of Fe–Rh–Pd epitaxial thin films grown on MgO(001) were studied as a function of growth temperature. Films grown above 400°C exhibit a first-order antiferromagnetic to ferromagnetic magnetic phase transition with a transition temperature that decreases as the growth temperature is increased. The chemical order parameter computed from the ratio of intensities of the (001) and (002) diffraction peaks is nearly independent of the growth temperature, while the lattice constants change slightly. A comparison of our structural, magnetic, and electrical transport results with first-principle-based calculations as well as literature results indicates that the transition temperature of Fe–Rh-based alloy films depends sensitively on the lattice parameters and is of electronic origin. The transition temperature and its width can be tuned over a wide range by controlling the crystal structure via growth conditions or postdeposition annealing.

Layered phase composition and microstructure of κ-Ga2O3-dominant heteroepitaxial films grown via MOCVD

Phase and microstructural evolution of gallium oxide (Ga2O3) films grown on vicinal (0001) sapphire substrates was investigated using a suite of analytical tools. High-resolution transmission electron microscopy and scanning transmission electron microscopy of a film grown at 530 °C revealed the initial pseudomorphic growth of three to four monolayers of α-Ga2O3, a 20–60 nm transition layer that contained both β- and γ-Ga2O3, and a top ∼700 nm-thick layer of phase-pure κ-Ga2O3. Explanations for the occurrence of these phases and their sequence of formation are presented. Additional growths of Ga2O3 films in tandem with x-ray diffraction and scanning electron microscopy investigations revealed that the top layer varied in phase composition between ∼100% κ-Ga2O3 and ∼100% β-Ga2O3; the surface microstructure ranged from poorly coalesced to completely coalesced grains as a function of growth temperature, growth rate, or diluent gas flow rate. In general, it was found that the κ-phase is favored at lower growth temperatures and higher triethylgallium flow rates (low VI/III ratios). The growth of nominally single-phase κ-Ga2O3 within the top layer was observed in a temperature range between 500 and 530 °C. Below 470 °C, only amorphous Ga2O3 was obtained; above 570 °C, only the β-phase was deposited.

A versatile Fe(II) diketonate diamine adduct: Preparation, characterization and validation in the chemical vapor deposition of iron oxide nanomaterials

Iron(III) oxide nanomaterials are extremely promising for the development of magnetic devices, gas sensors, photocatalysts, and photoelectrodes for solar water splitting. The fabrication of such systems by chemical vapor deposition (CVD) relies on the use of molecular sources joining shelf-stability, high volatility, and clean decomposition. Herein, we report for the first time on a versatile iron(II) precursor, namely Fe(tfa)2TMEDA (tfa = 1,1,1-trifluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine), combining the above features with a simple molecular concept. A theoretical-experimental characterization confirmed the compound spectroscopic purity and monomeric nature, and enabled to elucidate its structural, vibrational and electronic properties, along with its fragmentation pathway and thermal behavior. The ideal Fe(tfa)2TMEDA characteristics for CVD applications were finally validated through the fabrication of high purity iron oxide nanomaterials. The latter, comprising the sole metastable β-Fe2O3 polymorph rather than the most stable rust (α-Fe2O3), were characterized by the occurrence of oxygen defects and a nano-organization tunable as a function of growth temperature and reaction atmosphere.

A growth diagram for chemical beam epitaxy of GaP1−xNx alloys on nominally (001)-oriented GaP-on-Si substrates

The compound GaP1−xNx is highly attractive to pseudomorphically integrate red-light emitting devices and photovoltaic cells with the standard Si technology because it is lattice matched to Si with a direct bandgap energy of ≈1.96 eV for x = 0.021. Here, we report on the chemical beam epitaxy of GaP1−xNx alloys on nominally (001)-oriented GaP-on-Si substrates. The incorporation of N into GaP1−xNx was systematically investigated as a function of growth temperature and the fluxes of the N and P precursors, 1,1-dimethylhydrazine (DMHy) and tertiarybutylphosphine (TBP), respectively. We found that the N mole fraction exhibits an Arrhenius behavior characterized by an activation energy of (0.79 ± 0.05) eV. With respect to the fluxes, we determined that the N mole fraction is linearly proportional to the flux of DMHy and inversely proportional to the one of TBP. All results are summarized in a universal equation that describes the dependence of x on the growth temperature and the fluxes of the group-V precursors. The results are further illustrated in a growth diagram that visualizes the variation of x as the growth temperature and the flux of DMHy are varied. This diagram also shows how to obtain single-phase and flat GaP1−xNx layers, as certain growth conditions result in chemically phase-separated layers with rough surface morphologies. Finally, our results demonstrate the feasibility of chemical beam epitaxy to obtain single-phase and flat GaP1−xNx layers with x up to about 0.04, a value well above the one required for the lattice-matched integration of GaP1−xNx-based devices on Si.

Theoretical and experimental study of (Ga1-xFex)2O3 ternary alloys

Thin films of Ga2O3 and its alloys open the possibility of ultrawide bandgap heterostructure device designs that includes HEMT, quantum well UV optoelectronics, wide bandgap spintronics, high resistive buffer layers for FET and electrocatalytic applications. In this paper, (Ga1-xFex)2O3 (for x = 0.0–0.50) thin film alloys as a function of growth temperatures (450–750 °C) and partial oxygen pressures (10-1 −10-6 torr) grown using pulsed laser deposition are reported. The results suggest that, with the increase of Fe content at a fixed growth temperature and pressure, the bandgap decreases (4.93 to 3.43 eV and 4.39 to 2.25 eV for direct and indirect, respectively) due to a change in the Fe oxidation states as the Fe composition is increased from 0 to 50%. Density functional theory calculations also show a reduction in the bandgap of the alloy as the Fe content increases with the formation of a localized band of states close to the conduction band. Fe content, ≥ 40% in the alloy leads a phase change in the crystal structure with the formation of a gamma phase, also corroborated by theoretical calculations. Finally, room temperature ferromagnetic property was observed in thin films with the introduction of Fe into the Ga2O3 lattice.

The carbon and hydrogen contents in ALD-grown ZnO films define a narrow ALD temperature window

Zinc oxide thin films grown by atomic layer deposition have been subject to great attention over the past few years. In this work, we study ZnO films grown on Si substrates by atomic layer deposition with di-ethyl zinc (DEZ) as metal precursor and H2O or D2O water vapour as oxidant. Film composition as a function of growth temperature is studied by Ion Beam Analysis (IBA) using Rutherford Backscattering Spectrometry (RBS) to determine Zn areal density; Nuclear Reaction Analysis (NRA) for C and O areal density, and Elastic Recoil Detection Analysis (ERDA) for hydrogen areal density. The Zn/O ratio is close to 1 within a broad ALD window consistent with previous studies, however the carbon content varies substantially within this window and is minimum only within a much narrower temperature range.

Very thin (111) NiO epitaxial films grown on c-sapphire substrates by pulsed laser deposition technique

(111) NiO epitaxial layers are grown on c-sapphire substrates by pulsed laser deposition technique. Structural and morphological properties of the films are studied using in-plane as well as out-of-plane high resolution x-ray diffraction and atomic force microscopy techniques as functions of growth temperature, oxygen pressure and the pulses count of the laser. The study shows that continuous epitaxial films of thickness as low as 3 nm with high crystalline quality, smooth surface and interface morphology can be grown by this technique. The study also reveals the co-existence of 60°-rotated (111) triangular domains of NiO in the film. The study also evidences the presence of a very low density of 60° dislocations in these films. Density of screw and edge dislocations are also estimated to be quite low. It has been found that growth-temperature, oxygen partial pressure and the film thickness can influence differently the density of various dislocation types. These parameters are also found to affect significantly the strain developed in the films.

Role of high nitrogen flux in InAlN growth by plasma-assisted molecular beam epitaxy

We study the impact of increased active nitrogen flux (N-flux) on the indium content and structural properties of InAlN layers grown by plasma-assisted molecular beam epitaxy. It is shown that high N-flux can stabilize In-N bonds, so that In0.18Al0.82N is grown at 605 °C, which is the highest reported temperature so far for the composition lattice-matched (LM) to GaN. Adiagram of InAlN indium content is shown as a function of growth temperature and N-flux. The InAlN layers grown using low and high N-flux had grainy surface morphology typical for N-rich conditions. Inhomogeneity in indium distribution on nanometer scale, i.e. typical honeycomb microstructure, is found for InAlN layers grown using both: low and high N-flux. An increase of average cell size is observed for LM-InAlN when the N-flux and growth temperature are increased.

Effect of Growth Temperature and Postgrowth Annealing on Magnetic Properties of Mn1 + xSb Nanoparticles Embedded in GaSb Thin Films

Magnetic properties of two-phase granular semiconductor–ferromagnet GaSb–MnSb films obtained by pulsed laser deposition as a function of growth temperature and postgrowth annealing were stu-died.

Impact of growth conditions and strain on indium incorporation in non-polar m-plane (101¯) InGaN grown by plasma-assisted molecular beam epitaxy

We establish the relationships between growth conditions, strain state, optical and structural properties of nonpolar m-plane (101¯0) InGaN with indium composition up to 39% grown by plasma-assisted molecular beam epitaxy. We find that indium mole fraction as a function of growth temperature can be explained by an Arrhenius dependence of InN decomposition only for high temperature and low indium composition InGaN films. For the samples following the Arrhenius behavior, we estimate the effective activation energy for InN thermal decomposition in m-plane InGaN to be about 1 eV. This value is approximately a factor of two smaller than that reported for c-plane InGaN films. At low growth temperatures, InGaN layers show less efficient indium incorporation than predicted by Arrhenius behavior. We attribute the lower than expected indium composition at low temperatures to the strain-induced compositional pulling effect. We demonstrate that at 540 °C, the increase in the InGaN layer thickness leads to a preferential strain relaxation along the a-direction and an increase in the indium composition. For the indium mole fraction up to x ∼ 0.16, 30-nm-thick m-plane InGaN layers can be coherently grown on GaN with smooth morphology and pronounced low-temperature photoluminescence indicating that the material quality is suitable for device applications.

Scalable synthesis of multilayer h-BN on AlN by metalorganic vapor phase epitaxy: nucleation and growth mechanism

We studied the nucleation and growth of hexagonal BN (h-BN) on AlN template on c-plane sapphire by metalorganic vapor phase epitaxy as functions of growth temperature, deposition time, and triethylboron (TEB) partial pressure. A lateral growth rate of about 25 nm min−1 for h-BN nuclei was obtained by atomic force microscopy and a nucleation activation energy of 2.1 eV was extracted from the temperature dependence of the nucleation density. A large TEB flow rate strongly enhances the formation of h-BN nuclei. At a reduced TEB flow rate, we observed a significantly decreased nuclei density and a delay in nucleation due to TEB desorption. By fine tuning the growth parameters, single-crystalline multilayer h-BN was successfully formed on AlN surface, as confirmed by x-ray diffraction and transmission electron microscopy (TEM). The epitaxial relationship between h-BN and AlN was [0 0 0 1]h-BN || [0 0 0 1]AlN and [1 0 −1 0]h-BN || [1 1 −2 0]AlN from TEM and electron backscatter diffraction measurements. In addition, TEM showed that the initial h-BN layers are not parallel and tend to form half-domes. On those half-domes (cap-shaped-like) a 2D lateral growth sets on, resulting in a well-oriented 2D multilayer observed in TEM. Thus, the surface topography further develops to form a relatively flat surface without wrinkles and finally a typical hexagon-like wrinkled surface at thicker h-BN layers. Particularly, the small h-BN nuclei have dangling bonds at their periphery that can interact with the substrate, forming actual bonds with AlN. Hence the choice on the substrate is important, despite the basal planes of multilayer h-BN are bonded by a weak van der Waals force.

Optoelectronic properties of hybrid diodes based on vanadyl- phthalocyanine and zinc oxide nanorods thin films

Herein, we report the optoelectronic properties of hybrid diodes fabricated using vanadyl phthalocyanine (VOPc) and zinc oxide nanorods (ZNR) with the configuration: ITO/ZNR/VOPc/MoO3/Al. Vertically aligned ZnO nanorods were grown using a simple aqueous solution (AS) method as a function of growth temperature. The correlation between the morphology of ZNR films and the optoelectronic properties of the ZNR/VOPc hybrid devices was investigated. The results show that the hybrid diodes with ZNR films grown at 120 °C offer the best optoelectronic properties. The higher photocurrent responsivity, Rph, (16.28 A/W) was achieved for devices with ZNR films grown at 120 °C. This value is 25 times higher than the Rph value obtained for the devices made with ZnO nanoparticle films that were reported earlier.