Crystallization Of Thin Films Research Articles

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.

Anisotropic material depletion in epitaxial polymer crystallization.

The physical properties of a semicrystalline polymer thin film are intimately related to the morphology of its crystalline domains. While the mechanisms underlying crystallization of flat-on oriented polymer crystals are well known, similar mechanisms remain elusive for edge-on oriented thin films due to the propensity of substantially thin films to adopt flat-on orientations. Here, we employ an epitaxial polymer-substrate relationship to enforce edge-on crystallization in thin films. Using matrix-assisted pulsed laser evaporation (MAPLE), we deposit films in which crystal nucleation is spatially separated from subsequent epitaxial crystallization. These experiments, together with phase-field simulations, demonstrate a highly anisotropic and localized material depletion during edge-on crystallization. These results provide deeper insight into the physics of polymer crystallization under confinement and introduce a processing motif in the crystallization of ultrathin structured films.

Directional lateral crystallization of vacuum-deposited C8-BTBT thin films via liquid crystal phase by a seeded horizontal temperature gradient cooling technique

C8-BTBT thin films with large domain sizes were grown by vacuum deposition and subsequent post-annealing and cooling crystallization via liquid crystal phase with a constant horizontal temperature gradient.

Кинетика обратимых фазовых переходов в тонких пленках Ge-=SUB=-2-=/SUB=-Sb-=SUB=-2-=/SUB=-Te-=SUB=-5-=/SUB=- при фемтосекундном лазерном облучении

Femtosecond laser irradiation of amorphous Ge2Sb2Te5 thin films initiates reversible phase transitions. The amorphization and crystallization of Ge2Sb2Te5 thin films were experimentally and theoretically confirmed. Electron and lattice temperatures kinetics during laser pulse duration were evaluated by two-temperature models calculations and experimental data. The dynamical changing of optical properties have been taking into account. Temperatures and cooling rates, which are necessary to initiate phase transitions by IR laser pulses with subpicosecond duration. The observed results open perspectives for improvement of Ge2Sb2Te5 nanophotonical devices.

Local Crystallization of Amorphous Aluminum Oxide Thin Film Using Electron Beam Irradiation by SEM

Amorphous thin film thinned for transmission electron microscopy observation is reported to crystallize by electron beam (EB) irradiation of TEM. If thin film deposited on substrates can be crystallized by EB irradiation of scanning electron microscopy (SEM), new nanoscale devices can be fabricated such as electronic nanoscale circuits in amorphous thin films. Therefore, an amorphous AlOx (am-AlOx) thin film is deposited onto a Si substrate by atomic layer deposition (ALD) and point and area scan irradiation of EBs were performed by SEM. Then, structure and elemental analyses are carried out by TEM. Only the point EB irradiated area crystallized from the surface to the interface between am-AlOx and the Si substrate, and γ-Al2O3 appeared. Moreover, the oxygen content of the not irradiated area close to the irradiated area was lower than that of the not irradiated area far from the irradiated area. These results show that the EB irradiated area was positively charged by the emission of secondary and Auger electrons under point irradiation conditions, and that oxygen was supplied by attracting its negative charge to the EB irradiated area. Also, the electrostatic repulsion between positively charged atoms and the structure relaxation due to electron excitation were additional driving forces for the crystallization.

In situphotogenerated hydroxyl radicals in the reaction atmosphere for the accelerated crystallization of solution-processed functional metal oxide thin films

We propose a disruptive method to accelerate the crystallization at low temperatures of functional metal oxide films whereby hydroxyl radicals (•OH) are photogeneratedin situfrom the atmosphere where solution-deposited layers are UV-irradiated.

Optical Properties of Crystalline Thin Films of the Organic Laser Gain Material 4,4′-Bis[(N-carbazole)styryl]biphenyl

Enhancing photoluminescence quantum yield and excellent transport associated with molecular order are important for advancing organic laser device performance. However, materials combining excellent quantum yield and transport are rare. 4,4′-Bis[(N-carbazole)styryl]biphenyl (BSB-Cz) has been heavily investigated as a promising material for laser devices. However, research on highly ordered BSB-Cz crystalline films is lacking, despite the much better transport properties to be expected. Here, we show that BSB-Cz thin-film crystals can be prepared using a simple vacuum deposition method, followed by thermal annealing. The resulting crystalline neat BSB-Cz thin films show a very high photoluminescence quantum yield of over 85% and superior optical stability compared to amorphous BSB-Cz films under intense pumping conditions. We believe that our work provides a route for advancing organic laser devices through introducing crystallinity in emitter thin films with a scalable approach.

DEPENDENCE OF THE GROWTH RATE OF ZENGEITE CRYSTALS ON THE TEMPERATURE OF THE CRYSTALLIZATION FRONT

To clarify the mechanism of growth of zengeite crystals, the method of rapid crystallization of thin films was used in the work. The experimental dependence of the growth rate on the temperature of the crystallization front is obtained.

Low-temperature crystallization of indium oxide thin films with a photoactivable additive

In this study, we report a simple route to the low-temperature crystallization of solution-processed indium oxide thin films by introducing ammonium nitrate in the sol–gel metal oxide precursor solution as photoactivable additive and applying deep ultraviolet (DUV) irradiation onto the as-spun oxide films in an inert atmosphere. Thermal and structural analyses revealed that the initial temperatures for condensation and crystallization were reduced down to 130 and 200 °C, respectively, by the in situ generation of reactive chemical species enabled by DUV-assisted nitrate photolysis. Furthermore, transmission electron microscopy confirmed that the degree of indium oxide film crystallinity was gradually enhanced as the amount of nitrate in the precursor solution was increased. Finally, electrical characterizations showed that carrier mobility, threshold voltage, subthreshold swing, and threshold voltage shift under the positive bias stress of sol–gel indium oxide thin-film transistors were improved from 0.21 to 5.03 cm2/V s, from 4.18 to 1.64 V, from 1.33 to 0.72 V/dec, and from 6.44 to 4.04 V, respectively, by combining ammonium nitrate and DUV photoactivation.

Large increase in photo-induced conductivity of two-dimensional electron gas at SrTiO3 surface with BiFeO3 topping layer

In this work, we study and compare the photo-induced conductivity of a two-dimensional electron gas (2DEG) at the bare surface of SrTiO3 (STO) and in the heterostructure of BiFeO3 (BFO) and STO, where BFO was deposited by radio frequency magnetron sputtering. The photo-induced conductance of the BFO/STO interface shows a large increase which is 20.62 times more than the sum of photo-induced conductance from each individual BFO thin film and STO crystal. Since this photo-induced conductance of the BFO/STO heterostructure can be adjusted to become higher and lower by applying an electric field to the top surface, we attribute this large increase to the strong photo-induced electrical polarization of BFO. With the two-point setup of positive bias and negative bias, the conductivity also exhibits diode-like behavior where the forward and backward resistances are different. This work provides methods to interplay between light irradiation, electric field, and conductivity in all-oxide electronics.

Zero-Dimensional Cs3BiX6 (X = Br, Cl) Single Crystal Films with Second Harmonic Generation

The development of atomically thin single crystal films is necessary to potential applications in the 2D semiconductor field, and it is significant to explore new physical properties in low-dimensional semiconductors. Since, zero-dimensional (0D) materials without natural layering are connected by strong chemical bonds, it is challengeable to break symmetry and grow 0D Cs3BiX6 (X = Br, Cl) single crystal thin films. Here, we report the successful growth of 0D Cs3BiX6 (X = Br, Cl) single crystal films using a solvent evaporation crystallization strategy. Their phases and structures are both well evaluated to confirm 0D Cs3BiX6 (X = Br, Cl) single crystal films. Remarkably, the chemical potential dependent morphology evolution phenomenon is observed. It gives rise to morphology changes of Cs3BiBr6 films from rhombus to hexagon as BiBr3 concentration increased. Additionally, the robust second harmonic generation signal is detected in the Cs3BiBr6 single crystal film, demonstrating the broken symmetry originated from decreased dimension or shape change.

Computer simulation of AlCoCuFeNi high-entropy alloy thin film deposition and crystallization

The processes of deposition and crystallization of high-entropy AlCoCuFeNi alloy thin film on a substrate of silicon (100) are studied by classical molecular dynamics simulation. Total simulation time reaches 50 ns. The embedded atom model is used to describe the interaction among Al–Co–Cu–Ni–Fe. Interaction between the atoms of Al, Co, Cu, Fe, Ni, and the Si substrate is described using the Lennard–Jones potential, and the interaction between the silicon atoms was modeled using the Stillinger–Weber potential. It is found that at the first stage of deposition small clusters are formed and the process of crystallization starts after ~ 5 ns of simulation, at the characteristic sizes of clusters of about 2 nm. At the end of the simulation, after the 50 ns of modeling, the simulated film contains a face-centered cubic phase, a body-centered cubic phase, a hexagonal close-packed phase, and an amorphous phase. An analysis of the radial distribution of atoms makes it possible to determine the distances between the nearest neighbors and estimate the lattice parameters of these phases.