Crystallization Of Thin Films Research Articles

Исследование спектроскопических свойств фотонных кристаллов и наноструктур

The paper proposes substantiation of dependence of dielectric permittivity, polariton dispersion and light group velocity in the sodium uranyl acetate on the wavelength. Many bands were found in the uranyl compounds transmission and absorption spectra. It was indicated that the polariton waves group velocity was decreasing anomalously in vicinity of the resonant absorption frequencies, i.e., the light was effectively stopped. This led to abnormal increase in the efficiency between the light interaction processes and the matter. Optical properties of the one-dimensional photonic crystal film formed by electrochemical etching of aluminum foil were studied. Experimental data on the transmission and reflection spectra in the region of first, second and third stop bands of the anode photonic aluminum oxide crystal were compared with theoretical dependence obtained from the known dispersion relation. Refractive indices of the first and second layers of various thin photonic crystal films, structure period and effective refractive index of the structures were theoretically calculated. Possibility of controlling position of the stop bands of one-dimensional photonic crystals in accordance with the Wulff --- Bragg’s relation was established. The studied photonic crystals could be used in experimental setups to register the light combined scattering spectra of dielectric media in the low-frequencies region

Fabrication of Surface Polymer Brushes Via Thin Film Crystallization and Solvent Annealing.

Polymer single crystals have been used as templates to synthesize polymer brushes, known as the "polymer-single-crystal-assisted-grafting-to" (PSCAGT) approach. Polymer brushes with controlled grafting densities and spatial tethering locations have been demonstrated. Previous works focused on solution crystallization, which involves large amounts of organic solvent, and the grafting density can only be tuned by varying crystallization temperatures. In this work, thin film crystallization was utilized to fabricate two-dimensional (2D) polymer crystals on flat surfaces. Subsequent chemical tethering led to polymer brushes that retained the original morphology of the crystals with high fidelity. Furthermore, we show that the grafting density of the polymer brushes fabricated using this method depends on the chain end distribution on the top/bottom surfaces of the crystal, which can be facilely controlled by annealing the crystals at various nonsolvent media. Our work broadens the scope of the PSCAGT method and provides a new route to achieve polymer brushes with controlled structures. This article is protected by copyright. All rights reserved.

Influence of molybdenum doping on the structural, electrical, and optical properties of germanium telluride thin films

This study investigates the influence of molybdenum (Mo) doping on the local atomic structure, morphology, and electrical properties of amorphous germanium telluride (GeTe) thin films. Structural and morphological studies show that Mo-doping inhibits the crystallization of amorphous GeTe thin films. Moreover, the crystallization temperature of the GeTe thin film increases from 197 to 317 °C with increasing Mo dopant concentration. The electrical properties of Mo-doped GeTe thin films are discussed in terms of the capacitance–voltage characteristics in temperatures range 27–357 °C. The optical bandgap values decrease from 0.67 to 0.55 eV when increasing Mo doping in GeTe thin film. Mo integration significantly impacts the Ge–Te bond lengths and structural symmetry, increasing the degree of disorder in amorphous GeTe thin films. This study demonstrates the effectiveness of Mo doping in enhancing the thermal stability of the amorphous phase of GeTe for its envisioned memory and brain-inspired computing applications.

3D Perovskite Passivation with a Benzotriazole-Based 2D Interlayer for High-Efficiency Solar Cells.

2H-Benzotriazol-2-ylethylammonium bromide and iodide and its difluorinated derivatives are synthesized and employed as interlayers for passivation of formamidinium lead triiodide (FAPbI3) solar cells. In combination with PbI2 and PbBr2, these benzotriazole derivatives form two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) as evidenced by their crystal structures and thin film characteristics. When used to passivate n-i-p FAPbI3 solar cells, the power conversion efficiency improves from 20% to close to 22% by enhancing the open-circuit voltage. Quasi-Fermi level splitting experiments and scanning electron microscopy cathodoluminescence hyperspectral imaging reveal that passivation provides a reduced nonradiative recombination at the interface between the perovskite and hole transport layer. Photoluminescence spectroscopy, angle-resolved grazing-incidence wide-angle X-ray scattering, and depth profiling X-ray photoelectron spectroscopy studies of the 2D/three-dimensional (3D) interface between the benzotriazole RPP and FAPbI3 show that a nonuniform layer of 2D perovskites is enough to passivate defects, enhance charge extraction, and decrease nonradiative recombination.

Strained BaTiO3 thin films via in-situ crystallization using atomic layer deposition on SrTiO3 substrate

The interface engineering of oxide heterostructures, such as BaTiO3 (BTO)/SrTiO3 (STO), has received considerable attention because of their interesting physical/electrical properties. In this study, the in-situ crystallization of BTO thin film was achieved using a high temperature (∼350 °C) atomic layer deposition (ALD) process, which enabled the formation of strained BTO thin films on the STO substrate. A compressive strain was introduced along the in-plane direction of the BTO film, resulting in a 1.5% decrease in the lattice constant of BTO film while an in-plane tensile strain was induced in the STO layer (0.8% increase in the lattice constant). The in-situ crystallization of BTO thin films grown by ALD allowed the formation of a strained interface at the BTO/STO heterostructure.

Modification of Two-Dimensional Tin-Based Perovskites by Pentanoic Acid for Improved Performance of Field-Effect Transistors.

Understanding and controlling the nucleation and crystallization in solution-processed perovskite thin films are critical to achieving high in-plane charge carrier transport in field-effect transistors (FETs). This work demonstrates a simple and effective additive engineering strategy using pentanoic acid (PA). Here, PA is introduced to both modulate the crystallization process and improve the charge carrier transport in 2D 2-thiopheneethylammonium tin iodide ((TEA)2 SnI4 ) perovskite FETs. It is revealed that the carboxylic group of PA is strongly coordinated to the spacer cation TEAI and [SnI6 ]4- framework in the perovskite precursor solution, inducing heterogeneous nucleation and lowering undesired oxidation of Sn2+ during the film formation. These factors contribute to a reduced defect density and improved film morphology, including lower surface roughness and larger grain size, resulting in overall enhanced transistor performance. The reduced defect density and decreased ion migration lead to a higher p-channel charge carrier mobility of 0.7 cm2 V-1 s-1 , which is more than a threefold increase compared with the control device. Temperature-dependent charge transport studies demonstrate a mobility of 2.3 cm2 V-1 s-1 at 100 K due to the diminished ion mobility at low temperatures. This result illustrates that the additive strategy bears great potential to realize high-performance Sn-based perovskite FETs.

Magnetically Modulated Hybridization of Epsilon-Near-Zero Mode in Multilayered Heterostructure

Manipulation of optical Tamm states (OTSs) near an interface between polar thin film and one-dimensional (1D) photonic crystals (PhCs) provides a framework for confinement of surface phonon polaritons (SPhPs). Here, we offer a lithography-free avenue to create structure for the realization of strong coupling between Tamm phonon polaritons (TPhPs) and epsilon-near-zero (ENZ) modes. Infrared reflectivity also reveals that the optical response of the hetero-stack can be combined with dual discrete absorption events, each associated with an individual ENZ mode. In the presence of external magnetic field, an alteration of the hybridization will be met, which enable an efficient way for the control of light-matter interaction at nanoscale in the mid-infrared (MIR) range.

Influence of the intermediate oxidation layer on the characteristics of lead zirconate titanate thin films with aluminium substrate

This paper presents a flexible piezoelectric device that has been realized by depositing lead zirconate titanate (PZT) thin films by chemical solution deposition (CSD) on a commercial aluminum foil as a substrate. The thermal treatment required for the crystallization of the PZT thin films leads to the oxidation of the substrate and a parasitic intermediate layer of alumina (Al2O3) is formed between the substrate and the first PZT layer. The comparison with and without the use of a conductive ruthenium dioxide (RuO2) interlayer, which can shunt the insulating alumina layer, showed the influence of the latter on the different characteristics of the material. The thickness of the alumina layer on the surface of the aluminum substrate after deposition of the PZT film (≈ 39 nm) was determined by calculation and confirmed by transmission electron microscopy (TEM). Dielectric characterization of the sample without considering this layer gives the permittivity of the Al2O3/PZT bilayer and not the active material alone (PZT). A relative permittivity value of 313 is measured against 558 for the single PZT layer if the alumina layer is taken into account, which means a decrease of 44%. The piezoelectric characterization is also influenced by the alumina layer, the piezoelectric coefficient is 14 pC/N while it is 26 pC/N when this layer is taken into account. This study evidences and quantitatively evaluates the influence of the oxidation layer (Al2O3) on the dielectric and piezoelectric characteristics and mechanical energy harvesting performances.

In-situ growth all-inorganic bismuth-based perovskite single crystal hexagonal sheets for planar photodetector

Single crystal thin films can achieve the balance between thickness and mobility, which is widely used in the field of optoelectronic devices. Herein, lead-free perovskite Cs3Bi2I9 single crystal hexagonal sheets with preferred orientation along (002) were prepared by solution method. The Bi element is positively trivalent without oxidation in the single crystal hexagonal sheets. The growth processes of Cs3Bi2I9 crystal including nucleation and crystal growth are revealed by in-situ optical and structural observation. The Cs3Bi2I9 single crystal hexagonal sheets demonstrate excellent stability without encapsulation during long time exposure to the air. Obvious fluorescence quenching effect observed by steady-state and time-resolved photoluminescence measurement indicates charge transfer from Cs3Bi2I9 to ITO electrodes. Planar photodetectors based on Cs3Bi2I9 exhibit good photosensitive property, reproducibility and stability during multiple switching cycles. This work is conducive to lead-free perovskite regulation and further applications in photoelectronic devices.

A perspective on the device physics of lead halide perovskite semiconducting detector for gamma and x-ray sensing

Metal-halide perovskites are emerging materials for radiation sensing featuring high absorption cross section, high charge mobility, and long carrier lifetime enabling superior detection efficiencies even at room temperature. Perovskite detector technologies are more complex involving different detecting modes and device architectures. To elucidate the working principles, we provide a Perspective on the device structures and the operational principles of halide perovskite direct conversion detectors for radiation sensing. We will first discuss different detection modes and introduce the commonly used device architectures and their working principles. Based on our work and pioneer developments in the field, we will next compare the performances of the reported detectors. Additionally, we will summarize the single crystal detectors and polycrystalline thin film devices and discuss their advantages and disadvantages for different applications. Finally, we provide a future Perspective on the critical problems that must be addressed to commercialize this technology.

Controlled growth of perovskite layers with volatile alkylammonium chlorides.

Controlling the crystallinity and surface morphology of perovskite layers by methods such as solvent engineering1,2 and methylammonium chloride addition3-7 is an effective strategy for achieving high-efficiency perovskite solar cells. In particular, it is essential to deposit α-formamidinium lead iodide (FAPbI3) perovskite thin films with few defects due to their excellent crystallinity and large grain size. Here we report the controlled crystallization of perovskite thin films with the combination of alkylammonium chlorides (RACl) added to FAPbI3. The δ-phase to α-phase transition of FAPbI3 and the crystallization process and surface morphology of the perovskite thin films coated with RACl under various conditions were investigated through in situ grazing-incidence wide-angle X-ray diffraction and scanning electron microscopy. RACl added to the precursor solution was believed to be easily volatilized during coating and annealing owing to dissociation into RA0 and HCl with deprotonation of RA+ induced by RA⋯H+-Cl- binding to PbI2 in FAPbI3. Thus, the type and amount of RACl determined the δ-phase to α-phase transition rate, crystallinity, preferred orientation and surface morphology of the final α-FAPbI3. The resulting perovskite thin layers facilitated the fabrication of perovskite solar cells with a power-conversion efficiency of 26.08% (certified 25.73%) under standard illumination.

One-step crystallization in (Ge2Sb2Te5)90Ga10 thin film

Owing to data storage ability of chalcogenide based Ge2Sb2Te5 phase change alloy, this composition has been tremendously explored for its application in memory devices. Upon annealing, this composition exhibit two step crystallization, i.e, amorphous -to- fcc, and then from fcc -to- hcp phase. To address the issue of power consumption in such phase transitions, the present study is reporting one-step crystallization in (Ge2Sb2Te5)90Ga10 thin film, i.e., from amorphous -to- fcc phase which is confirmed by optical transmission contrast studies. Thus, the results poses the promising data storage applicability of (Ge2Sb2Te5)90Ga10 thin film in phase change memory devices.

Influence of annealing ambience on structural and piezoelectric properties of single crystal LiTaO3 thin film

The crystal-ion-slicing technology is a promising technology for fabricating high-quality single crystal piezoelectric thin films. This work attempted to investigate the influence of annealing ambience on the properties of LiTaO3 thin films fabricated by crystal-ion-slicing technology. Here, two 4-inch 42° rotated Y-X propagation LiTaO3 thin films were fabricated, as well as the LiTaO3 thin films were annealed in vacuum and O2 environment, respectively. The results demonstrate that the LiTaO3 thin films annealed in O2 environment possesses more homogeneous and denser structure and fewer defects. The Zratio of the resonators fabricated on the LiTaO3 thin films annealed in O2 environment is approximately 85.3 dB and the Q-factor reaches 5107, indicating the excellent piezoelectric properties of thin films.

In Situ Adsorption of Red Onion (Allium cepa) Natural Dye on Cellulose Model Films and Fabrics Exploiting Chitosan as a Natural Mordant.

Synthetic dyes and chemicals create an enormous impact on environmental pollution both in textile manufacturing and after the product's lifetime. Biobased plant-derived colorants and mordants have great potential for the development of more sustainable textile dyeing processes. Colorants isolated from biomass residues are renewable, biodegradable, and usually less harmful than their synthetic counterparts. Interestingly, they may also bring additional functions to the materials. However, the extraction and purification of the biocolorants from biomass as well as their dyeing efficiency and color fastness properties require a more thorough examination. Here, we extracted red onion (Allium cepa) skins to obtain polyphenolic flavonoids and anthocyanins as biocolorants, characterized the chemical composition of the mixture, and used a quartz crystal microbalance and thin films of cellulose nanofibrils to study the adsorption kinetics of dyes onto cellulose substrates in situ. The effect of different mordants on the adsorption behavior was also investigated. Comparison of these results with conventional dyeing experiments of textiles enabled us to determine the interaction mechanism of the dyes with substrates and mordants. Chitosan showed high potential as a biobased mordant based both on its ability to facilitate fast adsorption of polyphenols to cellulose and its ability to retain the purple color of the red onion dye (ROD) in comparison to the metal mordants FeSO4 and alum. The ROD also showed excellent UV-shielding efficiency at low concentrations, suggesting that biocolorants, due to their more complex composition compared to synthetic ones, can have multiple actions in addition to providing aesthetics.

Lattice damage and helium bubbles formation in KTaO3 crystals induced by helium ion implantation

Potassium tantalite (KTaO[Formula: see text] has shown an excellent performance in optoelectronic applications, proving its advantages with respect to fabricating single crystal thin films by ion implantation. This work introduces the damage formation of KTaO3 under 200 keV He ion implantation at room temperature and He bubbles accumulation. Ion implantation-induced lattice damage before and after annealing was quantitatively analyzed by using the Rutherford backscattering spectrometry in channeling technique. The crystals phase analysis of the samples under different fluences was studied by using the X-ray diffraction technique. For 200 keV He ions, the accumulation and migration of He bubbles were induced by the thermal annealing effect under high fluences of He[Formula: see text]. The He bubbles appear obviously coarsening and embrittlement with thermal annealing. The blistering phenomenon caused by He ion implantation is the physical basis for the smart-cut technique, which allows the preparation of high-quality single-crystal films.

Rapid electric field-enhanced crystallization of amorphous silicon thin films with an aluminum layer

A rapid aluminum induced crystallization (AIC) method of amorphous silicon (a-Si) thin film was suggested. A constant electrical current is supplied to an aluminum (Al) layer deposited on the a-Si thin film and anneals the Al/Si stack fast by Joule-heating. The Joule heating is presumed to expedite a-Si thin film crystallization. To investigate the crystallization mechanism, an in-situ temperature and reflectivity measurement was adopted during the process. The maximum crystallization temperature was 744.15 K, which was found to be similar to the typical furnace AIC process temperature and less than the Al/Si eutectic temperature of 850 K. The measured and calculated surface reflectivity demonstrated the rapid Al induced layer exchange behavior between Si and Al layers. The entire process was accomplished for only a few dozens of seconds. This rapid layer exchange is caused by sudden increase of temperature-dependent Al diffusion coefficient in a Si layer and additional electric field enhancement. The Raman peak of 519 cm−1 verified the formation of polycrystalline silicon (p-Si) after the Al etching process. Scanning electron microscopy images showed that the resulting p-Si structure was porous with an average pore size of around 1.2 μm.

Multimodal Characterization of Crystal Structure and Formation in Rubrene Thin Films Reveals Erasure of Orientational Discontinuities

AbstractMultimodal multiscale characterization provide opportunities to study organic semiconducting thin films with multiple length scales, across multiple platforms, to elucidate crystallization mechanisms of the various microstructures that impact functionality. With polarized scanning transmission X‐ray and 4D‐scanning transmission electron microscopy, hybrid crystalline structures in rubrene thin films in which large crystalline domains surround a common nucleus and transition to a spherulite morphology at larger radii is observed. These high‐resolution techniques reveal how azimuthal orientational discontinuities at smaller radii are erased as spherulite morphology takes hold. In situ crystallization in the films with optical microscopy is also captured, discovering the importance of considering the initial temperature increase of a film during thermal annealing over the crystallization timescale. This kinetic information of the radial crystallization rate and of corresponding film heating kinetics is used to estimate the temperature at which the larger crystalline regions transition into a spherulite. By combining the results obtained from the different characterization modes, it is learned that thermal conditions can sensitively affect the crystallization of rubrene and other organic thin films. The observations suggest opportunities for more complex temperature‐dependent processing to maximize hybrid structures’ functionality in organic thin films and demonstrate that multimodal studies deepen the understanding of structure‐function dynamics.

Epitaxial stabilisation of uranium silicide line compounds

Epitaxial single crystal thin films of U3Si, U3Si5, α−USi2, and USi3, alongside poly-crystalline U3Si2 have all been synthesised using DC magnetron sputtering. These idealised samples provide the bases on which fundamental studies can be conducted for the understanding of advanced technology fuel (ATF) candidates: U3Si, U3Si2, and U3Si5. The silicon-rich phases, USi2 and USi3 are of interest as intermediate oxidation products, forming as a result of the surface oxidation of the fuel candidates. Films were characterised using x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS), with XRD results indicating the stabilisation of [001]-oriented surfaces for all epitaxial phases with the exception of hexagonal U3Si5, which was found to be [100]-oriented. The XPS area analysis results from the U-4f and Si-2s core levels indicate that all phases are stoichiometric within error.

An active straight waveguide polarization rotator in single crystal thin film barium titanate-on-insulator

Electro-optic materials play an essential role in telecommunications. In active devices like Mach–Zehnder modulators, typically the diagonal Pockels coefficients are employed to induce an optical phase shift through electrical tuning of the refractive index along an optic axis. On the other hand, waveguide polarization rotators are usually passive devices where asymmetric structures or specially designed couplers are used. In this Letter, we exploit off diagonal Pockels coefficients to demonstrate an active straight waveguide polarization rotator using a c-axis single crystal thin film barium titanate (BTO)-on-insulator, with a maximum power conversion of ∼30% from the input TE (or TM) mode into its orthogonal mode observed. The device is switched on or off through an applied voltage and is demonstrated in a simple straight waveguide. A TM output extinction ratio of 26.1 dB is achieved in the device with a TE input. The r51 value in the BTO thin film is estimated to be around 600 pm/V. This work adds a different polarization rotation scheme to the active photonics family.

Research progress of applications of freestanding single crystal oxide thin film

Flexible electronics have aroused great interest of researchers because of their wide applications in information storage, energy harvesting and wearable device. To realize extraordinary functionalities, freestanding single crystal oxide thin film is utilized due to its super elasticity, easy-to-transfer, and outstanding ferro/electric/magnetic properties. Using the state-of-art synthesis methods, functional oxide films of various materials can be obtained in freestanding phase, which eliminates the restrictions from growth substrate and is transferable to other flexible layers. In this work, we first introduce wet etching and mechanical exfoliation methods to prepare freestanding single crystal oxide thin film, then review their applications in ferroelectric memory, piezoelectric energy harvester, dielectric energy storage, correlated oxide interface, and novel freestanding oxide structure. The recent research progress and future outlooks are finally discussed.