Formation Of Crystalline Films Research Articles

Colloidal Stabilizer‐Mediated Crystal Growth Regulation and Defect Healing for High‐Quality Perovskite Solar Cells

AbstractHigh‐quality perovskite (PVK) films is essential for the fabrication of efficient and stable perovskite solar cells (PSCs). However, unstable colloidal particles in PVK suspensions often hinder the formation of crystalline films with low defect densities. Herein, ethylenediaminetetraacetic acid (EDTA) as a colloidal stabilizer into lead iodide (PbI2) is introduced colloidal solutions. EDTA forms chelated complexes with Pb2+, enhancing the electrostatic repulsion and steric hindrance between colloidal particles. This stabilizes the particles and inhibits disordered motion (Brownian motion) and excessive aggregation. As a result, PbI2 films with a uniform hole distribution are formed, providing ample pathways for subsequent PVK film growth and sufficient space. During the film formation process, the replacement of molecules by formamidinium iodide (FAI) and EDTA slows down crystallization, ultimately leading to PVK films with large grain sizes and low defect density. By using this approach, champion power conversion efficiencies (PCEs) of 24.05% for FA0.97Cs0.03PbI3 PSC, 11.08% for CsPbBr3 PSC, and 25.19% for FA0.945MA0.025Cs0.03Pb(I0.975Br0.025)3 PSC are achieved. Moreover, the EDTA‐based FA0.97Cs0.03PbI3 device retains over 90% of its initial PCE after 1000 h at the maximum power point (MPP) under continuous illumination.

Optimizing electromagnetic interference shielding ofcarbon nanofibersreinforced nylon 6, 6 nanocomposite films in terahertz range

AbstractThe widespread development and usage of electrical and electronic devices in THz frequency band has instigated great concerns regarding the anticipated functioning of devices. The world is in dire need to develop tunable shielding materials which are not only field functional but could also provide shielding against undesired electromagnetic signals by absorption as the primary mechanism. In this work, nylon 6,6 based hybrid nanocomposite films loaded with 0–50 wt% CNFs have been prepared on the cellulosic substrates by air spray coating technique. XRD and FESEM results have established formation of crystalline films having homogeneously distributed CNFs in the polymer matrix leading to formation of an efficient conductive network. IV measurements demonstrate a significant rise in the dc conductivity in the polymer nanocomposite samples with the gradual increase of CNF content in comparison to the pristine sample. Interestingly, sample containing 50 wt% CNFs has shown dc conductivity value of 0.03 Scm−1while shielding effectiveness (SE) of 44 dB obtained through THz‐TDS. The results hold a distinctive position in these samples which have outperformed at a very low thickness of ~570 μm as compared to the results obtained by many other novel polymer composites and present themselves a light weight field functional high THz absorption materials.

Synthesis of GaSb-VDS thin film by electron beam physical vapour deposition and its electro-optical characterization as prerequisite for p-n device construction

III–V materials owing to have low effective masses, high mobilities and a direct band gap, exhibit suitability for both optoelectronic as well as tunnelling devices. Gallium Antimonide (GaSb), a III–V semiconducting compound, shows narrow band gap and high carrier mobility apposite for high-performance optoelectronics in the mid-IR range.The vertical directional solidification (VDS) is a crystal growth technique employed for the growth of high quality (>6N)bulk crystals, without the seed, without contact to the ampoule wall, without coating and without external pressure.Bulk crystalline GaSb was grown by VDS and then its fractured form is harnessed as source material for synthesis of thin film. GaSb-VDS thin semiconducting film of uniform thickness1.8μm was synthesized at 350°C by electron beam physical vapour deposition method.This thin film is p-type and will be implanted by group VI n-dopant(Telluriumions)impurities to form a junction. For same reason it is characterized for optical, electrical and morphological properties prior to support its claim as a device construction substrate. XRD, EDAX Raman, AFM, four probe and FTIR techniques were employed for the confirmation of crystalline, compositional, morphological, resistivity and optical band gap respectively.XRD of film reveals peaks close to 25°and42° corresponding to [111] and [220] crystal planes are in agreement as reported for crystalline GaSb. Raman spectra also confirm the GaSb crystalline film formation. SEM and EDAX of synthesized film found to be polycrystalline and agree the weight%of35.36and64.64 for GaandSb respectively. Four-probe technique yields the sheet resistance of 5.6Ωpersquare and optical band gap 0.728eV was obtained by FTIR. Optical band gap of the semiconducting film is obtained as 0.728eV and a Sheet resistance of5.6Ωpersquare. Uniform monolayer with low defect density is confirmed by Atomic force microscopy.It establishes formation of a p-type GaSb VDS thin film that is good for n-type implantation and show rectification tendency.

Real-time study of on-water chemistry: Surfactant monolayer-assisted growth of a crystalline quasi-2D polymer

<h2>Summary</h2> Unlike in the bulk, the hydrogen bond network of water is interrupted at water interfaces, and thus chemical reaction occurs at the water interface in a different manner than in the bulk, owning to, e.g., the possibility of templating molecules. On-water chemistry has generated highly crystalline, functional 2D materials through surfactant-monolayer-assisted interfacial synthesis (SMAIS). Yet, the details of the on-water reaction mechanism have remained unresolved. Here, by tracking the quasi-2D polyaniline film generation process using <i>in situ</i> surface-specific vibrational technique, we clarify how the polymerization reaction occurs at the water surfaces during SMAIS. We identify an aniline derivative with a positively charged terminal =NH₂ group as a key reaction intermediate species for highly crystalline film formation. A comparison of differently designed water interfaces reveals that intermediate species can be accumulated and ordered at the interface by the negatively charged surfactant headgroups, prompting highly crystalline, conductive polyaniline film formation. These results demonstrate the importance of interfacial electric fields and electrostatic interactions for controlled on-water chemistry.

Scalable Directed Assembly of Highly Crystalline 2,7-Dioctyl[1]benzothieno[3,2- b][1]benzothiophene (C8-BTBT) Films.

Assembly of organic semiconductors with ordered crystal structure has been actively pursued for electronics applications such as organic field-effect transistors (OFETs). Among various film deposition methods, solution-based film growth from small molecule semiconductors is preferable because of its low material and energy consumption, low cost, and scalability. Here, we show scalable and controllable directed assembly of highly crystalline 2,7-dioctyl[1]benzothieno[3,2- b][1]benzothiophene (C8-BTBT) films via a dip-coating process. Self-aligned stripe patterns with tunable thickness and morphology over a centimeter scale are obtained by adjusting two governing parameters: the pulling speed of a substrate and the solution concentration. OFETs are fabricated using the C8-BTBT films assembled at various conditions. A field-effect hole mobility up to 3.99 cm2 V-1 s-1 is obtained. Owing to the highly scalable crystalline film formation, the dip-coating directed assembly process could be a great candidate for manufacturing next-generation electronics. Meanwhile, the film formation mechanism discussed in this paper could provide a general guideline to prepare other organic semiconducting films from small molecule solutions.

Assessment of Sputtered Chromium Oxide-Nitride Coatings

Abstract The main purpose of this research work is to explore the formation of chromium oxide-nitride coatings by radio frequency (RF) magnetron sputtering using chromium as a target, oxygen and nitrogen as reactive gases, along with helium as an inert gas. The consequence of temperature variation on the formation of chromium oxide-nitride coatings and their properties is reported in this paper. The identification of respective oxide/nitride phases of chromium was done by X-ray diffraction. A wettability study of chromium oxide-nitride coatings was done using a contact angle–measuring system. Initially, at a lower deposition temperature of 200°C, the deposited films were amorphous. However, when the temperature was increased from 200°C to 600°C, the formation of crystalline films was observed, and its wettability behavior was transmuted from hydrophilic to hydrophobic. The influence of temperature variation on the tribological properties of mixed chromium oxide-nitride coatings is examined.

Reduction in the Interfacial Trap Density of Mechanochemically Synthesized MAPbI3.

Organo-lead halide perovskites have emerged as promising light harvesting materials for solar cells. The ability to prepare high quality films with a low concentration of defects is essential for obtaining high device performance. Here, we advance the procedure for the fabrication of efficient perovskite solar cells (PSCs) based on mechanochemically synthesized MAPbI3. The use of mechano-perovskite for the thin film formation provides a high degree of control of the stoichiometry and allows for the growth of relatively large crystalline grains. The best device achieved a maximum PCE of 17.5% from a current-voltage scan (J-V), which stabilized at 16.8% after 60 s of maximum power point tracking. Strikingly, PSCs based on MAPbI3 mechanoperovskite exhibit lower "hysteretic" behavior in comparison to that comprising MAPbI3 obtained from the conventional solvothermal reaction between PbI2 and MAI. To gain a better understanding of the difference in J-V hysteresis, we analyze the charge/ion accumulation mechanism and identify the defect energy distribution in the resulting MAPbI3 based devices. These results indicate that the use of mechanochemically synthesized perovskites provides a promising strategy for the formation of crystalline films demonstrating slow charge recombination and low trap density.

Formation and stability of crystalline and amorphous Al2O3 layers deposited on Ga2O3 nanowires by atomic layer epitaxy

Although the crystalline α and γ phases are the most stable forms of alumina, small-diameter (&amp;lt;6 nm) nanoparticles are known to be completely amorphous, due to the surface energy being correspondingly lower for the less stable non-crystalline phase. Al2O3 films with a thickness of 5 nm grown by low temperature (200 °C) atomic layer deposition (ALD) on small-diameter (&amp;lt;20 nm) Ga2O3 nanowires (NWs), however, are identified by transmission electron microscopy as belonging to the α, γ, and possibly θ crystalline phases of Al2O3, while films deposited on larger diameter (&amp;gt;20 nm) NWs are found to be amorphous. Indeed, until recently, all Al2O3, films deposited by low-temperature ALD using trimethylaluminum and water have been reported to be amorphous, regardless of film thickness or substrate. The formation of a crystalline ALD film can be understood in terms of the energetics of misfit dislocations that maintain the registry between the ALD film and the NW substrate, as well as the influence of strain and surface energy. The decreasing energy of co-axial misfit dislocations with NW diameter results in a corresponding decrease in the contribution of the Al2O3/Ga2O3 interface to the free energy, while the interfacial energy for an amorphous film is independent of the NW diameter. Therefore, for NW cores of sufficiently small diameter, the free energy contribution of the Al2O3/Ga2O3 interface is smaller for crystalline films than for amorphous films, thereby favoring the formation of crystalline films for small-diameter NWs. For ALD Al2O3 films of 10 nm thickness deposited on small-diameter Ga2O3 NWs, however, only the first 5 nm of the ALD film is found to be crystalline, possibly due to well-established kinetic limitations to low temperature epitaxial growth.

P-200L:Late-News Poster: Anisotropic Growth and Structural Analysis of Single Crystal Using Liquid Crystal Solvent for Molecular Alignment Controlled Organic Transistors

We have successfully developed the uniaxially-oriented single crystalline film formation technique of the soluble organic semiconductor (benzothienobenzothiophene) which combined liquid crystal solvent with rubbing-treated solution cell. As further study, we revealed that the one of crystal axes in those films was oriented along the direction of liquid crystal alignment.

Phase‐selective Route to V‐O Film Formation: A Systematic MOCVD Study Into the Effects of Deposition Temperature on Structure and Morphology

A systematic study into the MOCVD of V‐O films using the vanadyl‐acetylacetonate [VO(acac)2] precursor is carried out. The films are prepared via low pressure MOCVD on Si(001) substrates. The nature and quality of films are examined by varying operational parameters, e.g., deposition temperature, precursor vaporization rate, and flow of oxygen reacting gas. X‐ray diffraction data point to the formation of crystalline films in the range 200−550 °C. Outside of this temperature ranges amorphous phases were obtained. Field‐emission scanning electron microscope (FESEM) images indicate very homogeneous surfaces with grain shape and dimensions depending on operational conditions. Energy dispersive X‐ray (EDX) and X‐ray photoelectron spectroscopy (XPS) analyses point to the absence of any C contamination.

Tuning Eu3+ emission in europium sesquioxide films by changing the crystalline phase

We report the growth of europium sesquioxide (Eu2O3) thin films by pulsed laser deposition (PLD) in vacuum at room temperature from a pure Eu2O3 ceramic bulk target. The films were deposited in different configurations formed by adding capping and/or buffer layers of amorphous aluminum oxide (a-Al2O3). The optical properties, refractive index and extinction coefficient of the as deposited Eu2O3 layers were obtained. X-ray photoelectron spectroscopy (XPS) measurements were done to assess its chemical composition. Post-deposition annealing was performed at 500°C and 850°C in air in order to achieve the formation of crystalline films and to accomplish photoluminescence emission. According to the analysis of X-ray diffraction (XRD) spectra, cubic and monoclinic phases were formed. It is found that the relative amount of the phases is related to the different film configurations, showing that the control over the crystallization phase can be realized by adequately designing the structures. All the films showed photoluminescence emission peaks (under excitation at 355nm) that are attributed to the intra 4f-transitions of Eu3+ ions. The emission spectral shape depends on the crystalline phase of the Eu2O3 layer. Specifically, changes in the hypersensitive 5D0→7F2 emission confirm the strong influence of the crystal field effect on the Eu3+ energy levels.

Bimodal substrate biasing to control γ-Al2O3 deposition during reactive magnetron sputtering

Al2O3 thin films have been deposited at substrate temperatures between 500{\deg}C to 600{\deg}C by reactive magnetron sputtering using an additional arbitrary substrate bias to tailor the energy distribution of the incident ions. The films were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The film structure being amorphous, nanocrystalline, or crystalline was correlated with characteristic ion energy distributions. The evolving crystalline structure is connected with different levels of displacements per atom (dpa) in the growing film as being derived from TRIM simulations. The boundary between the formation of crystalline films and amorphous or nanocrystalline films was at 0.9 dpa for a substrate temperature of 500{\deg}C. This threshold shifts to 0.6 dpa for films grown at 550{\deg}C.

Effect of doping concentration on UV accelerated chemically deposited ZnS:Mn thin films

Pure and Mn alloyed ZnS thin films have been prepared by UV accelerated chemical deposition technique which is simple, economic and easy to monitor. Influence of doping concentration on ZnS thin films was investigated through the structural, compositional, morphological, optical and luminescent studies. The XRD studies confirmed the formation of crystalline films with hexagonal structure. In doped samples the intensities of the prominent peaks increased up to 0.5 wt% Mn and then decreased. The optimum concentration means the amount required to get most suitable characteristics for photovoltaic application. The thickness of the films and the sizes of the crystallites varied in consistent with the structural results. Crystallites became larger in size on doping and appeared to be denser than undoped film. Various structural parameters like stress and micro strain were calculated. The observed strain is compressive in nature which rapidly increased with doping and then remained almost same with doping concentration. The SEM studies revealed the formation of films with almost similar morphology of spherical architectures. All the films exhibited uniform transmission in the high visible region, with a maximum of 80 % for the sample with optimum Mn concentration. Both direct and indirect band gap decreased due to the incorporation of Mn, but showed a blue shift in the fundamental absorption edge with doping concentration up to the optimum dopant content. Undoped and doped films exhibit five distinct luminescence peaks located around 391, 451, 458, 482 and 492 nm. The observed variation in the intensity of the luminescence in doped films clearly indicated the influence of thickness of the films which varied on doping.

Formation process of two-dimensional crystalline film of vacuum-evaporated n-alkane: a molecular dynamics simulation

The formation of two-dimensional crystalline film of n-pentadecane (C15H32) on a flat substrate with attractive forces similar to that of the metals or graphite substrate is investigated with molecular dynamics simulation. By controlling the deposition rate of the molecules, we observed the behavior in adsorption and conformational change of single molecule and the growing process of the n-pentadecane film. Two distinct sub-processes are recognized in the formation of the crystalline film, the formation of the molecular clusters and the coalescence of the molecular clusters. It is found that the conformational changes are gentle when only or few molecules are deposited on the substrate. However, this change becomes drastic as more molecules are gathered together. The accelerated conformational variation is attributed to the no-bonding molecular interaction.

Laser crystallization for large-area electronics

Laser crystallization is reviewed for the purpose of fabrication of polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for formation of crystalline films with a low thermal budget. Reduction of electrically active defects located at grain boundaries is essential for improving electrical properties of poly-Si films and achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent developments in laser crystallization methods with pulsed and continuous-wave lasers are also reviewed. Control of heat flow results in crystalline grain growth in the lateral direction, which is important for fabrication of large crystalline grains. We also report an annealing method using a high-power infrared semiconductor laser. High-power lasers will be attractive for rapid formation of crystalline films over a large area and activation of silicon with impurity atoms.

Laser Crystallization of Silicon for Large Area Electronics

AbstractLaser crystallization of silicon is discussed for forming polycrystalline silicon thin films used to fabricate polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for crystalline film formation with a low thermal budget. Structural and electrical properties of poly-Si films are discussed. Reduction of electrical active defects located at grain boundaries is essential for achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent development in laser crystallization methods with pulsed and continuous wave (CW) lasers is then reviewed. Control of the heat flow results in crystalline grain growth in the lateral direction, which is essential for fabrication of large crystalline grains. We also report an annealing method using a high power infrared semiconductor laser. High power lasers will be attractive for rapid crystallization of silicon films over a large area and activation of doped regions.

Epitaxial growth of pentacene films on Cu110.

The molecular structure of thin pentacene (C(22)H(14)) films grown on a Cu(110) surface has been studied by means of He atom scattering, low energy electron diffraction, thermal desorption spectroscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. Depending on the actual film thickness three different crystalline phases have been identified which reveal a characteristic reorientation of the molecular plane relative to the substrate surface. In the monolayer regime the molecules form a highly ordered commensurate (6.5x2) structure with a planar adsorption geometry. For thin multilayers (thickness <2 nm) a second phase is observed which is characterized by a lateral ((-0.65 5.69) ( 1.90 1.37)) structure and a tilting of the molecular plane of about 28 degrees around their long axis which remains parallel to the surface. Finally, when exceeding a thickness of about 2 nm subsequent growth proceeds with an upright molecular orientation and leads to the formation of crystalline films which are epitaxially oriented with respect to the substrate. The present study thus demonstrates that also on metal substrates highly ordered pentacene films with an upright orientation of the molecular planes can be grown. Photoelectron spectroscopy data indicate further that thick films do not grow in a layer-by-layer mode but reveal a significant degree of roughness.

Thermal stability and crystallization kinetics of sputtered amorphous Si 3N 4 films

The crystallization of thin silicon nitride (Si 3N 4) films deposited on polycrystalline SiC substrates was investigated by X-ray diffractometry as a function of annealing time. The amorphous Si 3N 4 films were produced by means of reactive r.f. magnetron sputtering. Annealing at temperatures between 1300 and 1700 °C led to the formation of crystalline films composed of α-Si 3N 4 and β-Si 3N 4. The fraction of β-Si 3N 4 in the films reaches approximately 40% at temperatures above 1550 °C. Both polymorphic modifications were formed simultaneously during the crystallization process. A transformation of α-Si 3N 4 to β-Si 3N 4 could not be observed in the time and temperature range investigated. The crystallization process of amorphous Si 3N 4 can be described according to the Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism, assuming a three-dimensional, interface controlled grain growth from pre-existing nuclei. The rate constants show an Arrhenius behaviour with an activation enthalpy of approximately 5.5 eV.

Preparation of crystalline MnS thin films by chemical bath deposition

Pure γ-MnS films have been deposited on commercial glass slides by chemical bath deposition (CBD) at 60 °C. Experimental results indicate that both pre-treatment of the substrates by HF etching and control of the reaction temperature play an important role in the formation of crystalline films. The optical absorption measurements reveal that the band gaps of as-deposited amorphous and γ-MnS films are 3.23 and 3.16 eV, respectively, which agree with the previously reported values.

Influence of tungsten species on the structure of anodic titania

A sputter-deposited Ti-20 at.% W alloy has been anodized at high efficiency in order to examine the influence of alloy species on the structure of anodic films on titanium. Interestingly, amorphous oxide films develop on the alloy to voltages of about 200 V, in contrast with crystalline film formation on relatively pure titanium at voltages less than 20 V. The amorphous films consist of an outer TiO2 layer and an inner layer containing units of TiO2 and WO3. The layered films form as a consequence of the migration of Ti4+ ions about 2.4 times faster than that of W6+ ions, probably owing to the relative strengths of the W6+−O and Ti4+−O bonds. Film growth proceeds by migration of both the O2− and/or OH− ions and the metal cations, typical of amorphous anodic films, with the transport number of cations, determined using a silicon species marker, of 0.39. During anodizing above about 200 V, local regions of thicker film material develop, possibly owing to nucleation and growth of crystalline material. The vo...