Crystalline Thin Films Research Articles

Influence of rapid annealing temperature on the mechanical properties of TiCN thin film as prepared by cathodic arc

In this study, titanium carbonitride (TiCN) thin films were deposited using cathodic arc deposition techniques. The as-deposited TiCN thin films were subsequently subjected to annealing treatment by rapid thermal annealing (RTA) technique at a temperature range from 400 to 600 °C. The effect of RTA temperature on the crystallinity, morphology, chemical composition, and mechanical properties of the TiCN thin films was investigated. The grazing incident X-ray diffraction (GIXRD) analysis confirmed the presence of a dominant face-centered cubic TiCN phase. Cross-sectional field-emission scanning electron microscopy (FE-SEM) images revealed a compact and homogeneous morphology, which became more pronounced with increasing RTA temperatures. The X-ray photoelectron spectroscopy (XPS) indicated the atomic concentration of the primary element (Ti, C, and N) remained relatively stable throughout the annealing process. Furthermore, the hardness of the TiCN thin films improved at 400 °C-RTA temperature. GRAPHICAL ABSTRACT HIGHLIGHTS Crystalline TiCN thin films were successfully deposited via cathodic arc deposition. RTA treatment improved the TiCN thin film, resulting in a highly compact morphology. The harness of TiCN showed enhancement at 400 oC-RTA temperature.

Enhanced perovskite solar cells performance with TiOx and SnOx thin films as electron transport layers

We report on the potential application of crystalline thin metal oxide films (TiOx, SnOx) with varying stoichiometries in perovskite solar cell devices. The oxides were deposited via reactive e-beam evaporation, involving the sublimation of pure metals under different pressures of pure oxygen, followed by thermal annealing at 200 °C. Variable angle spectroscopic ellipsometry, X-ray diffraction (XRD), contact angle measurements, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the films. XRD findings confirmed the crystalline phases of SnOx thin films treated at 200 °C for the most oxygen-rich films (deposited at 2e-4 Torr), while TiOx layers exhibited an amorphous phase. FESEM results confirmed that uniform and dense films were generated across the entire substrate surface. Using the measured refractive indices in a computational model, it was demonstrated that optimizing the device design with these films could result in power conversion efficiencies surpassing 25%.

Lead selenide thin films: From first principles to in situ crystalline thin film growth by thermal evaporation

Lead selenide thin films: From first principles to in situ crystalline thin film growth by thermal evaporation

Amorphous Silica Interlayer Unlocks Direct Epitaxial Growth of CsPbBr3 on Silicon via Slip-and-Stick Mechanism.

In this study, we investigate the "Slip and Stick" mechanism governing the epitaxial growth of CsPbBr3 on amorphous silica surfaces and its implications for silicon/perovskite tandem solar cell applications. The unique, low-energy diffusion behavior of cesium lead bromide on amorphous silica enables molecular species to traverse the surface efficiently without bond-breaking, thereby preserving structural integrity. Consequently, the chemically inert nature of amorphous silica facilitates the formation of crystalline CsPbBr3 thin films on silicon substrates, which is essential for tandem solar cell architectures. In contrast, the reactive silicon (111) surface, that induces fragment decomposition and Br doping of Si, poses challenges to device stability due to potential disruptions in structural and electronic continuity. Our findings elucidate the observed difficulties in epitaxially growing metal halide perovskites directly on silicon surfaces and underscore the role of amorphous silica as an ideal passivation layer, promoting the precise layer-by-layer assembly necessary for high-efficiency tandem solar cells.

Suppression of Molecular Disordering in Liquid Crystalline Thin Films by Side-Chain Engineering

Suppression of Molecular Disordering in Liquid Crystalline Thin Films by Side-Chain Engineering

Monocrystalline Gold Metasurface to Control Anisotropic Second‐Harmonic Generation

AbstractThe tensorial nature of the nonlinear susceptibility of gold surfaces is revealed and exploited by comparing crystalline and polycrystalline thin films. The {111}‐type surfaces of crystalline gold exhibit anisotropic features that are absent at the surfaces of conventionally used polycrystalline thin films. While this anisotropy does not influence the linear optical response, it becomes apparent in the second‐harmonic generation, where the emission can be either co‐ or cross‐polarized with the excitation light, depending on the crystal orientation. It is further demonstrated that nanopatterning a {111} surface enables versatile control over the anisotropic and isotropic contributions to second‐harmonic generation in the vicinity of localized surface plasmon resonance condition. Focused ion beam‐milling is used to pattern the surface of chemically synthesized gold flake with subwavelength‐sized V‐grooves, while preserving the intrinsic crystal anisotropy as demonstrated by the nonlinear microscopy. The results highlight the potential of crystalline metasurfaces to enhance, tailor and control the nonlinear optical response, paving the way for advanced nonlinear photonic devices.

Growth of crystalline thin films of picene on semimetallic Bi(111) surface.

We report the scanning tunneling microscopy/spectroscopy (STM/STS) studies on structural and electronic properties of picene films grown on the semimetallic Bi(111) substrate held at different temperatures. Under room-temperature deposition, the picene molecules form a crystalline (001) monolayer with the standing-up orientation, indicating the weak molecule-substrate interaction. When deposited on the Bi(111) substrate held at 150K, picene molecules form a bulk-like (211̄ monolayer with building blocks of picene trimers. High-resolution STM images reveal that each trimer consists of two tilted molecules and one side-on molecule. Further reducing the deposition temperature to 90K leads to the formation of nanostripe arrays, in which the side-on molecules adopt the π-π stacking. STS measurements demonstrate that the crystalline (001) monolayer of picene exhibits a larger gap compared with picene crystals, which can be attributed to the decoupling of the upright standing molecules from the semimetallic Bi(111) substrate.

Crystallinity improvement of physical-vapor-deposited WS2 films by controlling particle energy

Abstract High-crystallinity WS2 thin films are crucial for their applications in next-generation electronic devices, particularly in logic transistors. Consequently, a physical vapor deposition (PVD) is a promising method for achieving such films because of its scalability and precise control over deposition conditions. In this study, WS2 thin film crystallinity has been investigated by controlling particle energy during the PVD process. The scattering of particles is influenced by Ar pressure, in which a throw distance of the particles is determined. The target-substrate (T-S) distance was set in conjunction with the throw distance in terms of the composition and energy of the particles at the surface on the wafer. The crystallinity of the deposited films was assessed through Raman spectroscopy, X-ray photoelectron spectroscopy, and circular transmission line method measurements. Controlling of T-S distance and Ar pressure effectively minimized film damage during the PVD process, resulting in crystallinity improvement. Therefore PVD-WS2 films hold significant potential for various applications in next-generation logic transistors.

Thin film epitaxy of high quality ferromagnetic semiconductor EuO using pulsed laser deposition equipped with Nd:YAG laser

Abstract Pulsed laser deposition with the fourth harmonic wave of Nd-doped Y3Al5O12 laser was applied to thin film epitaxy of a ferromagnetic semiconductor EuO which contains metastable Eu2+ ions. Highly crystalline, flat, and stoichiometric EuO (001) epitaxial thin films were successfully grown on YAlO3 (110) single crystal substrates. The EuO film exhibited ferromagnetism reflecting the 4f electronic configuration of Eu2+. These results indicate that Nd-doped Y3Al5O12 laser is useful for deposition of oxide thin films requiring oxygen stoichiometry.

Preparation of Octacalcium Phosphate Thin Film with Exposing Reactive Crystalline Plane in Biological Fluid.

Octacalcium phosphate (OCP) has been used as a bone replacement material due to its higher bone affinity. However, the mechanism of affinity has not been clarified. Since the 100 crystalline plane of OCP is closely involved in the biological reactions during osteogenesis, it is important to expose the 100 crystalline plane of OCP to the biological fluid to precisely measure the interfacial reactions. In this study, the OCP plate-like crystals were fixed on a conductive substrate in the form of single-particle deposition, and the thin films with exposing 100 crystalline planes were fabricated. Then, the characteristics of hydration layers in the OCP crystals were enhanced by the exposure of 100 crystalline planes through the thin film formation, and the bioreactivity was found to be associated with the swelling and dissolution of the hydration layer in the biological fluid. Specifically, the OCP crystals were deposited on the gold sensor by electrophoretic deposition (OCP/Au-1). The results showed that the OCP plate-like crystals were selectively deposited on the gold sensor by electrophoresis. Subsequently, it was found that the ultrasonication of OCP/Au-1 resulted in the formation of an OCP crystalline thin film (m-OCP/Au-1) with the single-particle thickness on the gold sensor with exposing 100 crystalline planes. Moreover, the FT-IR spectra of m-OCP/Au-1 showed that the structure of the phosphate ions was rearranged by ultrasonication in the hydration layer, resulting in the regulation of the layered nanostructures, promoting higher crystallinity. Furthermore, the XPS spectra of m-OCP/Au-1 indicated that the hydrogen phosphate ions in the hydration layer were exposed on the 100 crystalline plane of the topmost surface. The prepared m-OCP/Au-1 was stable in citrate buffer, whereas it showed very high reactivity in phosphate buffer as the hydration layer gradually dissolved after the swelling, which was measured by the QCM-D technique. Therefore, the OCP crystalline thin films in this study were found to have higher surface reactivity due to the enhanced exposure of the hydration layer, which is assumed to be the cause of their bone-regeneration-promoting effect (i.e., higher bone affinity). The films in this study were stable at gastric acid pH and dissolved at neutral pH, which could make them useful as the orally administered drug carrier.

Atomic layer deposition of crystalline molybdenum trioxide and suboxide thin films using molybdenum(II) acetate dimer precursor

Molybdenum oxide thin films are of interest due to a large range of possible phases, high work functions, and catalytic activity. These films have applications in areas, such as sensors, chromic, and semiconductor devices. In this work, a molybdenum(II) acetate dimer precursor was used with ozone for the atomic layer deposition of molybdenum oxide thin films. The films were grown at 200–300 °C yielding highly crystalline films even at the lowest deposition temperatures. X-ray diffraction measurements showed that the as-deposited films consist of molybdenum suboxides and/or a phase-pure orthorhombic molybdenum trioxide phase depending on the deposition conditions. Time-of-flight elastic recoil detection analysis showed that the stoichiometry was close to molybdenum trioxide, and the films were exceptionally pure with main impurities being hydrogen and carbon, which were at the detection limit of the instrument (0.1 at. %). This process, allowing the deposition of very pure and highly crystalline thin films with tunable phases and oxidation states, is very promising for future industrial applications.

Comparative Optical Properties of Amorphous and Crystalline MoO3 Films by Spectroscopic Ellipsometry Study

This paper presents a comprehensive study of the optical properties of amorphous and crystalline MoO3 thin films using spectroscopic ellipsometry. MoO3 films were deposited on SiO2/Si substrates with varying oxide thicknesses using the atomic layer deposition (ALD) method. The study utilized various optical oscillator models, including Lorentz, Tauc–Lorentz and Harmonic, to analyze the dielectric functions and identify midgap states resulting from oxygen deficiencies. The findings highlight significant differences in the optical properties between amorphous and crystalline MoO3 films, demonstrating the impact of structural phases and substrate conditions. Specifically, amorphous films exhibited lower broadening and energy peaks compared to crystalline films, which showed distinct midgap states indicative of higher oxygen vacancy concentrations. These results enhance the understanding of the optical behavior of MoO3 films and their potential applications in advanced optoelectronic devices.

Influence of Deposition Temperature on Cu-BDC Surface-Anchored Metal-Organic Framework Formation.

Surface-anchored metal-organic frameworks (surMOFs) are crystalline, nanoporous, supramolecular materials mounted to substrates that have the potential for integration within device architectures relevant for a variety of electronic, photonic, sensing, and gas storage applications. This research investigates the thin film formation of the Cu-BDC (copper benzene-1,4-dicarboxylate) MOF system on a carboxylic acid-terminated self-assembled monolayer by alternating deposition of solution-phase inorganic and organic precursors. X-ray diffraction (XRD) and atomic force microscopy (AFM) characterization demonstrate that crystalline Cu-BDC thin films are formed via Volmer-Weber growth. Changes in film morphology as the deposition temperature increases are seen by AFM with more isolated nanorod-like crystallites observed at lower temperatures, while vertical nanoplatelet-like structures form at higher temperatures. At 45 °C, the nanoplatelets are observed to be composed of fused nanorod segments aligned in one direction. Ellipsometry confirms that both increasing temperature and number of deposition cycles yield more film deposition in agreement with infrared reflectance-absorbance spectroscopy (IRRAS) that was further used to characterize the chemical binding and orientation in the surface-bound Cu-BDC nanostructures. In addition to observing strong preferred orientation of the nanostructures from the enhancement of the symmetric carboxylate stretch and absence of the antisymmetric stretch, IRRAS results show the emergence of a new binding motif associated with segmented nanoplatelet formation at a higher deposition temperature as well as at high surface coverage after 12 deposition cycles. From the appearance of this higher frequency symmetric carboxylate peak alongside peak splitting in BDC deformation modes, IRRAS data support the presence of a strained configuration that accompanies the appearance of Cu-BDC segmented nanoplatelets observed by AFM.

Predicting 2D Crystal Packing in Thin Films of Small Molecule Organic Materials

AbstractThe large variety of structural morphologies realized in organic semiconductors is a big challenge for the microscopic modeling of such systems. A global computational solution is still out of reach due to prevalent molecular flexibility. However, the specific case of crystalline thin films that exhibit surface alignment of molecular π‐systems for optoelectronic applications of high technological relevance, seems to be a simpler task. This study proposes an approach for the structure prediction of two‐dimensional (2D) molecular layers as precursors for the three‐dimensional (3D) structure of deposited crystalline thin films. Based on grid search sampling for the layer's degrees of freedom, it requires only a small number of trial structures to find complex packing motifs of layered molecular materials. It facilitates parallel screening among multiple molecular conformers, which is usually very difficult and expensive, using the latest 3D‐based prediction methods. The study researches theoretically and experimentally a set of known and newly crystallized compounds of evaporable flexible molecules with interesting optoelectronic properties, predicts their packing in 2D layers, and compares them with experimentally resolved crystal structures, obtaining very good agreement in the packing of these molecules within layers. The computational costs are estimated to be several orders of magnitude lower than with 3D methods.

Microstructure, mechanical properties, thermal decomposition and oxidation sequences of crystalline AlB2 thin films

Microstructure, mechanical properties, thermal decomposition and oxidation sequences of crystalline AlB2 thin films

Measurement of Anisotropy and Magnetoelastic Constants of Thin Crystalline Films by Angle- and Strain-Dependent Ferromagnetic Resonance Spectroscopy

Measurement of Anisotropy and Magnetoelastic Constants of Thin Crystalline Films by Angle- and Strain-Dependent Ferromagnetic Resonance Spectroscopy

Reversible photoswitching of proton conduction in hetero‐smectic lamellar structures formed by side‐chain liquid crystalline copolymer thin films

AbstractSpatiotemporal control of ion conductivity is a key issue for creating emerging fields of functional ion‐conducting nanomaterials. In the present paper, we demonstrate the formation of hetero‐smectic lamellar structures, which are formed by nanosegregation of hydrophobic liquid crystalline (LC) azobenzene side chains and hydrophilic acrylic acid side chains via polymer main chains in side‐chain LC (SCLC) copolymers, and the reversible photoswitching of the proton conductivity. Proton‐conducting SCLC copolymers with different acrylic acid contents are synthesized by free‐radical copolymerization. The LC nature of the synthesized polymers is investigated by polarized optical microscope observation, differential scanning calorimetry and X‐ray scattering measurements. Ultraviolet (UV)–visible absorption spectroscopy and grazing incidence X‐ray scattering measurements reveal the hetero‐smectic lamellar formation of SCLC copolymer thin films. Proton conductivity of the polymer thin films is evaluated by impedance spectroscopy measurements under different temperatures and relative humidity conditions with sequential UV light irradiation. These results indicate that stable and reversible photoswitching of the proton conductivity around one order of magnitude is attributed to the trans–cis photoisomerization of azobenzene side chains by UV light irradiation. These results offer the opportunity for applications of photo‐functional nanomaterials including emerging biomimetic ionic signal transduction devices and neuromorphic devices. © 2024 Society of Chemical Industry.

Heterostructure growth, electrical transport and electronic structure of crystalline Dirac nodal arc semimetal PtSn4

Topological semimetals have recently garnered widespread interest in the quantum materials research community due to their symmetry-protected surface states with dissipationless transport which have potential applications in next-generation low-power electronic devices. One such material, , exhibits Dirac nodal arcs and although the topological properties of single crystals have been investigated, there have been no reports in crystalline thin film geometry. We examined the growth of heterostructures on a range of single crystals by optimizing the electron beam evaporation of Pt and Sn and studied the effect of vacuum thermal annealing on phase and crystallinity. The electrical resistivity was fitted to a modified Bloch–Grüneisen model with a residual resistivity of 79.43(1) cm at 2K and a Debye temperature of 200K. Nonlinear Hall resistance indicated the presence of more than one carrier type with an effective carrier mobility of 33.6 and concentration of 1.41 at 300 K. X-ray photoemission spectra were in close agreement with convolved density of states and a work function of 4.7(2) eV was determined for the (010) surface. This study will facilitate measurements that require heterostructure geometry, such as spin and topological Hall effect, and will facilitate potential device incorporation in future quantum technologies.

High-Quality SnSe Thin Films for Self-Powered Devices and Multilevel Information Encryption.

As semiconductor technology advances toward miniaturization and portability, thin films with excellent thermoelectric performance have garnered increasing attention, particularly for applications in self-powered devices and temperature-responsive sensors. The high Seebeck coefficient of SnSe thin films makes them promising for temperature sensing, but their poor electrical conductivity limits their potential as thermoelectric generators. In this work, high-quality a-axis oriented SnSe thin films were deposited on quartz substrates by using magnetron sputtering. The substrate temperature was optimized to improve the crystallinity of the SnSe thin film, resulting in larger grain sizes, which subsequently contributes to the improved carrier mobility. The Seebeck coefficient is enhanced while optimizing the electrical conductivity, enabling the SnSe thin film to achieve both excellent sensing and power generation performance. The SnSe film deposited at 673 K exhibits a high power factor of approximately 346 μW m-1 K-2 at 620 K. A temperature-responsive sensing array was developed for multilevel information encryption, showing significant potential for applications in password encryption. The maximum output power density of the optimized thermoelectric generator with six SnSe legs is about 9 W m-2 at a temperature difference of 50 K.

Bioinspired single-shot polarization photodetector based on four-directional grating arrays capped perovskite single-crystal thin film.

Polarization photodetectors (pol-PDs) have widespread applications in geological remote sensing, machine vision, biological medicine, and so on. However, commercial pol-PDs use bulky and complicated optical systems with lenses, polarizers, and mechanical spools, which are complex and cumbersome, and respond slowly. Inspired by the desert ants' compound eyes, we developed a single-shot pol-PD based on four-directional grating arrays capped perovskite single-crystal thin film without other standard polarization optics. Our pol-PD has a high detectivity, two orders of magnitude greater than that of commercial photodetectors, and exhibits high polarization sensitivity. The high performance of our pol-PD is due to the highly crystalline perovskite single-crystal thin film and regular nanograting structure, made by a nanoimprinting crystallization method. Our single-shot pol-PD is a compact on-chip optoelectronic device that demonstrates excellent performance in a wide range of applications including accurate bionic navigation, sharp image restoration in hazy scenes, stress visualization of polymers, and detection of cancerous areas in tissues without histological staining.