Flat Surface Morphology Research Articles

Effects of Li concentration in the precursor solution on NiO thin films deposited using electrostatic spray deposition

Abstract Undoped and Li-added NiO thin films were deposited using electrostatic spray deposition (ESD) techniques. Initially, the NiO thin films displayed minimal contamination, predominantly C and H. The NiO thin films exhibited a flat surface morphology comprising grains of uniform size, approximately 20–30 nm in diameter, and reliable crystal growth, with a full width at half maximum of approximately 0.30 in X-ray diffraction analysis. Moreover, the NiO/ZnO diode demonstrated superior properties when a 5 at. % Li concentration solution was incorporated. The rectification ratio reached approximately 2.3 × 10³ at ± 1.0 V, with an ideality factor of 1.9. Additionally, the NiO/ZnO diodes exhibited remarkable photovoltaic properties even without detailed optimization. These findings underscore the potential of ESD in advancing semiconductor thin-film technology, thereby paving the way for more cost-effective and scalable production methods.

Amorphous In–Al–Sn–O Thin Film Transistors and Their Application in Optoelectronic Artificial Synapses

AbstractIn‐Al‐Sn‐O (IATO) is a very promising novel amorphous oxide as the active layer of thin film transistors (TFTs). Herein, IATO TFTs are first fabricated with the effects of annealing on IATO films and TFTs being studied. The IATO films possessed amorphous structure, flat surface morphology, high visible light transmittance, and wide optical bandgap ≈4.20 eV before and after annealing even at 400 °C. The minimal surface roughness and internal defects are obtained for the 300 °C annealed IATO film. Correspondingly, the 300 °C annealed TFTs demonstrated the best overall performance including high saturation mobility (8.55 ± 0.62 cm2 V−1 s−1), low subthreshold swing (0.40 ± 0.07 V dec−1), ideal on/off current ratio (1.25 ± 0.09 × 108), and negligible hysteresis (0.23 ± 0.03 V) values. The 300 °C annealed TFTs are then applied in optoelectronic artificial synapses and exhibit typical synaptic properties, including excitatory postsynaptic current, paired‐pulse facilitation, and short‐term plasticity to long‐term plasticity conversion in response to light stimulation. The international Morse code and repetitive learning‐forgetting behavior of the human brain are also successfully simulated. In particular, an emotion‐memory efficiency model is proposed and the emotion effect on human memory efficiency is successfully imitated via the regulation of gate voltage.

Investigation of low temperature amorphous (InxGa1−x)2O3 films modulated by indium content for optimization in solar-blind photodetector

In this study, bandgap engineering of amorphous (InxGa1-x)2O3 alloy films fabricated at room temperature using pulsed laser deposition and alloy targets with different indium contents from 0 % to 50 % have been investigated. The effect of indium content on the characteristics of (InxGa1-x)2O3 films and the performance of metal–semiconductor-metal solar-blind photodetectors have been explored in detail. The moderate number of indium atoms introduced into Ga2O3 can obtain a flat surface morphology and adjusted bandgap to enhance the performance of solar-blind photodetector. When the excessive indium atoms were incorporated into the film, the obviously In enriched (InxGa1-x)2O3 alloy nano-clusters are observed on the film surface despite of the low growth temperature. It can be attributed to the segregation phenomenon because of the solid solubility limitation for indium in Ga2O3. Both of dark current and photocurrent of (InxGa1-x)2O3 photodetector increase with the incremental indium content mainly attributed to enhanced oxygen deficiency. As a result, the solar-blind photodetector can achieve an optimal performance using a balanced indium content of 20 % with an extremely low dark current of 4.4 × 10-12 A, a responsivity of 10.8 mA/W, a substantial on/off current ratio of 1.5 × 104 and a short rise/decay time of 0.33 s/0.54 s.

Quantitative detection of plasticizer migration in starch/polyvinyl alcohol film with UV-Vis and GC-MS/MS

In this work, the migration of urea and/or formamide plasticizers in crosslinked starch/polyvinyl alcohol (PVA) films under UV irradiation has been accurately quantified by using a combination of GC-MS/MS and UV–Vis analysis. The crosslinked starch/PVA films, prepared with different amide plasticizers (urea, formamide, urea-formamide), were characterized via scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and X-ray photoelectron spectroscopy (XPS). After 7 days of UV irradiation, the starch/PVA film plasticized with urea-formamide (A7-SPF-UF) exhibited a flat surface morphology, high crystal stability, and highest thermal stability. The migration ratio of urea and formamide for A7-SPF-UF was also quantified to be 3.2 % and 4.5 %, respectively, using GC-MS/MS and UV–Vis analysis, indicating optimal migration resistance. The synergistic effect of urea and formamide as plasticizers built the dense network structure of An-SPF-UF and improved the UV aging resistance, toughness and durability of the film. On one hand, this enhances the market competitiveness of the products; on the other hand, it promotes the development of environmentally friendly materials, aligning with sustainability requirements.

UV/Ozone-Treated and Sol-Gel-Processed Y2O3 Insulators Prepared Using Gelation-Delaying Precursors.

In this study, a Y2O3 insulator was fabricated via the sol-gel process and the effect of precursors and annealing processes on its electrical performance was studied. Yttrium(III) acetate hydrate, yttrium(III) nitrate tetrahydrate, yttrium isopropoxide oxide, and yttrium(III) tris (isopropoxide) were used as precursors, and UV/ozone treatment and high-temperature annealing were performed to obtain Y2O3 films from the precursors. The structure and surface morphologies of the films were characterized via grazing-incidence X-ray diffraction and scanning probe microscopy. Chemical component analysis was performed via X-ray spectroscopy. Electrical insulator characteristics were analyzed based on current density versus electrical field data and frequency-dependent dielectric constants. The Y2O3 films fabricated using the acetate precursor and subjected to the UV/ozone treatment showed a uniform and flat surface morphology with the lowest number of oxygen vacancy defects and unwanted byproducts. The corresponding fabricated capacitors showed the lowest current density (Jg) value of 10-8 A/cm2 at 1 MV/cm and a stable dielectric constant in a frequency range of 20 Hz-100 KHz. At 20 Hz, the dielectric constant was 12.28, which decreased to 10.5 at 105 Hz. The results indicate that high-quality, high-k insulators can be fabricated for flexible electronics using suitable precursors and the suggested low-temperature fabrication methods.

Decreased Accumulation of SnO2 Particles Results from Sodium Citrate Dispersant Assisted Chemical Bath Deposition for High Quality Perovskite Solar Cells

Electron transport layer (ETL) is a crucial part for perovskite solar cells (PSCs). However, leakage current and oxygen vacancies result from little pores grown from sol‐gel method would inevitably deteriorate the performance of ETL. In contrast, thin films prepared by chemical bath deposition (CBD) could significantly restrain the little cracks. Here, SnO2 ETL are prepared by optimized CBD process, sodium citrate (SC) is explored as an auxiliary reagent to disperse ETL, thus enhances the smoothness and conductivity of the ETL, resulting in a pore‐free flat surface morphology and decreased oxygen vacancy, which is favorable for electron transport and deposition of perovskite (PVK). The PVK film fabricated on the oxygen vacancy free substrate demonstrates high quality and decreased defect density, thus effectively prevents the non‐radiative recombination of carriers. As a result, the short‐circuit current (JSC) and open circuit voltage (Voc) of the PSC devices have been obviously improved, leading to increased photoelectric conversion efficiency from 21.03% to 22.04%. Meanwhile, the long‐term and moisture stability have been promoted simultaneously.

Sputter-grown two-dimensional α-MoO3 thin films: Microstructure dependence on growth conditions

Van der Waals epitaxy is an emerging technology for transferring freestanding films grown at high temperatures onto arbitrary substrates using two-dimensional epitaxial layers. This study investigates the microstructure and growth of α-MoO3 thin films prepared via sputtering. Under a narrow deposition temperature range, epitaxial α-MoO3 thin films were successfully grown on SrTiO3 substrates. The films were characterized by a flat surface morphology, corresponding to (0k0) planes, without undergoing reaction with the substrates. To examine the growth behavior and surface morphological variation of the α-MoO3 thin films under various process parameters, we modified the Ar:O2 ratio, working pressure, sputtering power, and crystal structure of the substrates. Transmittance electron microscopy confirmed the epitaxial growth of the α-MoO3 thin films on (001)-oriented SrTiO3 substrates with a two-dimensional layer structure. Finally, we demonstrate the morphological evolution of the α-MoO3 thin films etched in heated water as a function of soaking time. The etching results suggest that the α-MoO3 thin films are promising sacrificial layers for the transfer of large-scale epitaxial thin films onto flexible substrates. External control of the strain states of transferred freestanding thin films by bending or stretching provides new perspectives for the design of flexible or wearable electronic devices.

Homoepitaxial growth of (100) Si-doped β-Ga2O3 films via MOCVD

Homoepitaxial growth of Si-doped β-Ga2O3 films on semi-insulating (100) β-Ga2O3 substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga2O3 films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga2O3 film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 1015 – 1.74 × 1020 cm−3. Hall measurements demonstrate a high electron mobility value of 51 cm2/(V·s), corresponding to a carrier concentration of 7.19 × 1018 cm−3 and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10-4 Ω·cm2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 1019 cm−3, confirming the effective Si doing in the MOCVD epitaxy.

Tensile strength and wear resistance of glass-reinforced PA1212 fabricated by selective laser sintering

ABSTRACT Glass fibre (GF) and glass bead (GB)–reinforced polyamide1212 (PA1212) was additively manufactured by selective laser sintering. The effects of laser power and GF content on the tensile and tribological properties of the printed specimens with a base GB weight fraction of 40 wt.% were investigated. The strengthening mechanism of GFs/GBs was illustrated by analyzing the interfacial adhesion between the fillers and the PA1212 matrix. The specimens with 40 wt.% GBs and 10 wt.% GFs fabricated at a laser power of 30 W exhibited a strength of 52 MPa, a friction coefficient of 0.23, and a wear rate of 0.0011 mm3/N·m. The selected optimal laser power and GF addition contributed to the strong interfacial adhesion, which realised flat surface morphology and an adequate encapsulation of fillers in the specimen. The reinforcement of GBs/GFs in PA1212 can serve as a reference for a deeper understanding of the strengthening mechanisms for other additively manufactured engineering plastics.

Magnetic anisotropy modulation of co-sputtered Fe–SrTiO3 nanocomposite thin films

Nanocomposite thin films that exhibit magnetic anisotropy, in which the direction of the easy axis is perpendicular, are highly desirable for emerging spin-based devices. In this study, the growth behavior and magnetic properties of single-layer Fe thin films sputtered at different temperatures were investigated. The surface morphologies of Fe films dramatically changed when the deposition temperature was varied, and the iron oxide phase was detected in a high-temperature-sputtered film, resulting in the degradation of magnetization and magnetic anisotropy. Then, the microstructures and magnetic properties of the co-sputtered Fe-SrTiO3 nanocomposite thin films were examined. The low-temperate-grown thin films exhibited a flat surface morphology with isotropic magnetic loops at a low power supplied to the Fe target, whereas spherical grains with a strong magnetic anisotropy with in-plane easy axis appeared in a film grown at high power. However, the nanocomposite thin films grown at a high temperature with a higher power for Fe showed perpendicular magnetic anisotropy owing to the vertically aligned Fe rod surrounded by SrTiO3. The modulation of magnetic anisotropy by tuning the geometry and composition of metal–metal-oxide nanocomposites offers a promising approach for the design of future multifunctional devices.

Intrinsic (Trap-Free) Transistors Based on Epitaxial Single-Crystal Perovskites.

The first experimental realization of the intrinsic (not dominated by defects) charge conduction regime in lead-halide perovskite field-effect transistors (FETs) is reported. The advance is enabled by: i) a new vapor-phase epitaxy technique that results in large-area single-crystalline cesium lead bromide (CsPbBr3 ) films with excellent structural and surface properties, including atomically flat surface morphology, essentially free from defects and traps at the level relevant to device operation; ii) an extensive materials analysis of these films using a variety of thin-film and surface probes certifying the chemical and structural quality of the material; and iii) the fabrication of nearly ideal (trap-free) FETs with characteristics superior to any reported to date. These devices allow the investigation of the intrinsic FET and (gated) Hall-effect carrier mobilities as functions of temperature. The intrinsic mobility is found to increase on cooling from ≈30 cm2 V-1 s-1 at room temperature to ≈250 cm2 V-1 s-1 at 50 K, revealing a band transport limited by phonon scattering. Establishing the intrinsic (phonon-limited) mobility provides a solid test for theoretical descriptions of carrier transport in perovskites, reveals basic limits to the technology, and points to a path for future high-performance perovskite electronic devices.

Surface Morphology and Structure in ZnO films doped with Ga and In impurities

The ZnO:Ga:In nanocrystal (NC) films co-doped with Ga and In donor type impurities have been investigated The films were produced by spray pyrolysis ultrasonic on Si substrates kept at 400°C. The group of samples was grown with permanent In content of 1at% in the films, and with various Ga contents of 0.5 at% up to 2.5 at% Ga. All samples for better crystallization have been further annealed in a nitrogen flow (5 L/min) at 400°C during 4h.The non-monotonous varying the surface morphology has been detected in ZnO:Ga:In NC films. With a small Ga content (≤1.0 at%) and a high Ga content (≥2.0 at%), the grains have the form of small sheets distributed randomly on the surface. The sheet like shape changes to nanorod with hexagonal cross sections of the size 50-100 nm in films with 1.5 at% Ga. With all Ga concentrations the ZnO films studied demonstrated the crystal structures of wurtzite. However, the XRD peak positions and ZnO lattice parameters change non monotonically versus Ga contents. The factors that favor the non-monotonic change of the parameters of the ZnO crystal lattice have been analysed. The Ga/In doping concentrations necessary to obtain ZnO films with low roughness and flat surface morphology have been estimated.

Chemical Substitution‐Grown Lithium‐Magnesium Alloy as Ion Redistributor and Surface Protector for Highly Stable Lithium‐Metal Anode

AbstractAddressing lithium‐dendrite problem caused by uneven lithium (Li) plating/stripping is crucial for improving cycle‐life and safety of Li‐metal batteries. Here we describe a simple chemical substitution method of 2Li+Mg(PF6)2=Mg+2LiPF6 to construct a highly stable Li−Mg alloy on Li metal anode. The self‐grown Li−Mg alloy exhibits homogeneous β‐phase bulk structure with flat and dense surface morphology. Systematic studies reveal that the obtained Li−Mg film acts as ion redistributor and surface stabilizer to protect Li metal anode by its low strain, fast conductivity, superior lithophilicity and excellent stability. Compared to the bare Li metal, symmetric cells assembled using Li−Mg‐protected Li exhibit better cycling performance with lower charge‐discharge overpotential. Notably, this Li−Mg film demonstrates great potential for Li‐metal batteries, it can effectively suppress Li‐dendrite growth and work effectively in LiFePO4//Li and LiNi0.8Co0.1Mn0.1O2//Li cells. This work provides a simple and effective strategy to construct Li‐ion redistributor and surface protector to guard Li anodes operating in high‐energy Li batteries.

Suppression of cluster formation in GaN growth by tri-halide vapor phase epitaxy with external GaCl3 gas supply system

One critical issue hindering high-quality, high-speed growth of GaN is cluster formation in the gas phase. We investigated cluster formation in tri-halide vapor phase epitaxial growth of GaN. The growth system is equipped with an external GaCl3 gas supply system. We observed cluster formation under certain growth conditions experimentally. A simulation was also carried out to reveal the critical conditions for cluster formation. We propose that increasing the gas temperature is an effective way to suppress cluster formation, and thus achieve a higher growth rate with a flat surface morphology.

Structural and electrical properties of thick κ-Ga2O3 grown on GaN/sapphire templates

Thick (23 µm) films of κ-Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on GaN/sapphire templates at 630 °C. X-ray analysis confirmed the formation of single-phase κ-Ga2O3 with half-widths of the high-resolution x-ray diffraction (004), (006), and (008) symmetric reflections of 4.5 arc min and asymmetric (027) reflection of 14 arc min. Orthorhombic κ-Ga2O3 polymorph formation was confirmed from analysis of the Kikuchi diffraction pattern in electron backscattering diffraction. Secondary electron imaging indicated a reasonably flat surface morphology with a few (area density ∼103 cm−2) approximately circular (diameter ∼50–100 µm) uncoalesced regions, containing κ-Ga2O3 columns with in-plane dimensions and a height of about 10 µm. Micro-cathodoluminescence (MCL) spectra showed a wide 2–3.5 eV band that could be deconvoluted into narrower bands peaked at 2.59, 2.66, 2.86, and 3.12 eV. Ni Schottky diodes prepared on the films showed good rectification but a high series resistance. The films had a thin near-surface region dominated by Ec − 0.7 eV deep centers and a deeper region (∼2 µm from the surface) dominated by shallow donors with concentrations of ≤1016 cm−3. Photocurrent and photocapacitance spectra showed the presence of deep compensating acceptors with optical ionization energies of ∼1.35 and 2.3 eV, the latter being close to the energy of one of the MCL bands. Deep level transient spectroscopy revealed deep traps with energies near 0.3, 0.6, 0.7, 0.8, and 1 eV from the conduction band edge. The results show the potential of HVPE to grow very thick κ-Ga2O3 on GaN/sapphire templates.

Van der Waals Epitaxial Growth of ZnO Films on Mica Substrates in Low-Temperature Aqueous Solution

In this article, we demonstrate the van der Waals (vdW) epitaxial growth of ZnO layers on mica substrates through a low-temperature hydrothermal process. The thermal pretreatment of mica substrates prior to the hydrothermal growth of ZnO is essential for growing ZnO crystals in epitaxy with the mica substrates. The addition of sodium citrate into the growth solution significantly promotes the growth of ZnO crystallites in a lateral direction to achieve fully coalesced, continuous ZnO epitaxial layers. As confirmed through transmission electron microscopy, the epitaxial paradigm of the ZnO layer on the mica substrate was regarded as an incommensurate van der Waals epitaxy. Furthermore, through the association of the Mist-CVD process, the high-density and uniform distribution of ZnO seeds preferentially occurred on mica substrates, leading to greatly improving the epitaxial qualities of the hydrothermally grown ZnO layers and obtaining flat surface morphologies. The electrical and optoelectrical properties of the vdW epitaxial ZnO layer grown on mica substrates were comparable with those grown on sapphire substrates through conventional solution-based epitaxy techniques.

Dependence of the structure of Bi-2212 superconducting thin film prepared by sol-gel method on different complexing agents

The complexed sol-gel method has unique advantages in the preparation of multi-component functional thin films. In this paper, Bi2212 superconducting thin films were prepared by sol-gel method on SrTiO3(100) single crystal substrates. Glycine and glycolic acid were used as complexing agents. The thermal decomposition processes of the two sols were analyzed by contrasting thermal-thermogravimetric curves. The heat treatment processes of the different complexing agent systems were optimized to obtain films with flatter surface morphology. The phase composition of the intermediate products during the precursor heat treatment was changed by adjusting the conditions of the complexing agent and the acidity of the sol, which expanded the pure phase temperature interval of the final product. The pure phase temperature interval, morphology, surface roughness, and electrical transport properties of Bi2212 superconducting films prepared with different complexing agent sol-gel systems were investigated. When glycolic acid was used as the complexing agent, the Bi-2212 superconducting films showed the widest phase formation temperature zones of 25 K. They also had a smaller surface roughness of 10–15 nm. Other than that, all samples had good epitaxial properties, and electrical transport properties. This work provides a new idea for expanding the phase-forming temperature region of multicomponent functional ceramics. It also shows the promising potential of sol-gel method for preparing multicomponent functional films with high quality surfaces.

Self-assembled growth and magnetic properties of Fe and FeTiO3 core–Sr(Ti,Fe)O3 shell nanocomposites

In this study, a promising method for the modulation of the microstructure, composition, and magnetic properties of thin films fabricated by co-sputtering metallic Fe and oxide SrTiO3 targets is proposed. The proposed method can potentially be applied in multifunctional electronics. The flat surface morphology was observed in the thin film sputtered under a low power for the Fe target, whereas micro-height rods were fabricated on an uneven layer at a higher power. Strong magnetic anisotropy was not observed in the co-sputtered thin films because of the randomly oriented growth of the magnetic rods. Detailed microstructural and compositional studies using high-resolution transmission electron microscopy and scanning transmission electron microscopy revealed that self-assembled nanocomposites with three components were grown with a core–shell structure, in which Fe and FeTiO3 phases grew in the Sr(Ti,Fe)O3 matrix. This report provides an insight into designing multifunctional metal–metal oxide nanocomposites with single-step co-sputtering, which is capable of adjusting the composition and geometry of the nanocomposites.

Thermally induced metastability of InGaAs single-layer for highly strained superlattices by metal-organic chemical vapor deposition

In this study, the metastability of In0.68Ga0.32As layers on InP substrates was investigated at various growth temperatures. The thickness of each metastable In0.68Ga0.32As layer was 40 nm, which is four times the critical thickness of the stable lattice with a stress of approximately 1%. The surface morphologies and roughness of the metastable In0.68Ga0.32As layers were highly sensitive to the growth conditions. Cross-hatches were observed on their surfaces when they were grown at various growth temperatures, and over this range, the surface roughness varied from 0.11 nm to 0.16 nm. The lowest surface roughness of 0.11 nm was achieved at 770 °C, and the metastable In0.68Ga0.32As layer showed a flat surface morphology with terraces parallel to the step edges. These results corresponded to those of the strain relaxation analysis of the metastable In0.68Ga0.32As layers using X-ray diffraction spectra. The In0.68Ga0.32As layer grown at 770 °C was almost fully strained, whereas those grown at other growth temperatures were relieved by approximately 10%. The flat surface morphologies and almost fully strained lattices suggested that the growth conditions were suitable for preparing high-quality superlattices with well-defined interfaces. The intuitive results of the metastable In0.68Ga0.32As single layers were utilized to grow high-quality In0.67Ga0.33As/Al0.64In0.36As superlattices with a reduction in the misfit dislocation by 41.8%. The results obtained herein suggest that the growth conditions for superlattices can be easily and efficiently optimized using the metastability of the materials.

Hydrogen etching of the SiC(0001) surface at moderate temperature

Hydrogen etching of a 4H-SiC(0001) surface at a moderate temperature of 1200 °C with molecular hydrogen gas was investigated to obtain enough flat and clean surface for large-scale high-quality epitaxial graphene synthesis. We found after a prolonged hydrogen etching that micro scratches, large depressions, and contaminations produced on the wafer in the manufacturing process disappeared and that a periodic array of atomic steps appeared, maintaining initial flat surface morphology. One hour of etching with a flow of 1.0 l/min was the optimum condition to obtain a flat and clean SiC surface in the present study. Using such surfaces, we were able to synthesize the so-called zero layer graphene by thermal annealing in ultrahigh vacuum.