Precursor Evaporation Research Articles

Controlled Morphological Growth and Photonic Lasing in Cesium Lead Bromide Microcrystals.

Morphology plays a crucial role in defining the optical, electronic, and mechanical properties of halide perovskite microcrystals. Therefore, developing strategies that offer precise control over crystal morphology during the growth process is highly desirable. This work presents a simple scheme to simultaneously grow distinct geometries of cesium lead bromide (CsPbBr3) microcrystals, including microrods (MR), microplates (MP), and microspheres (MS), in a single chemical vapor deposition (CVD) experiment. By strategically adjusting precursor evaporation temperatures, flux density, and the substrate temperature, we surpass previous techniques by achieving simultaneous yet selective growth of multiple CsPbBr3 geometries at distinct positions on the same substrate. This fine growth control is attributed to the synergistic variation in fluid flow dynamics, precursor substrate distance, and temperature across the substrate, offering regions suitable for the growth of different morphologies. Pertinently, perovskite MR are grown at the top, while MP and MS are observed at the center and bottom regions of the substrate, respectively. Structural analysis reveals high crystallinity and an orthorhombic phase of the as-grown perovskite microcrystals, while persistent photonic lasing manifests their nonlinear optical characteristics, underpinning their potential application for next-generation photonic and optoelectronic devices.

Experimental determination of Si, Mg, and Ca isotope fractionation during enstatite melt evaporation

Abstract Evaporation of silicate materials from Earth or its precursors may be important in shaping their primordial compositions represented by undifferentiated meteorites, e.g., enstatite chondrites; however, the conditions under which evaporation occurs and the extent of evaporation-induced elemental and isotope fractionation remain uncertain. Here, we experimentally determine the volatility and isotope fractionation of Si, Mg, Ca, Nb, and Ta during enstatite melt evaporation at 2423–2623 K using a high-temperature conical nozzle levitator. Homogenous glasses are recovered after experiments; then we use EPMA and LA-ICP-MS to measure the elemental compositions, MC-ICP-MS to measure the Si and Mg isotopes, and TIMS to measure the Ca isotopes. Our results show that the evaporation rates of Si are larger than Mg, and the mean vapor/melt isotope fractionation factors (α = Rvapor/Rmelt; R = isotope ratio) are 0.99585 ± 0.00002 for 29Si/28Si and 0.98942 ± 0.00130 for 25Mg/24Mg. However, neither evaporative loss of Ca, Nb, and Ta nor Ca isotope fractionation was observed within analytical uncertainty. In conjunction with previous studies, we find that in an evaporation experiment the saturation degree (partial vapor pressure/equilibrium vapor pressure) of Si (SSi) is larger than SMg when Si is more volatile than Mg, and vice versa. If the Mg/Ca and Si/Ca ratios and isotopes in the bulk silicate Earth are attributed to the evaporation of enstatite chondrite-like precursors, evaporation temperatures >5000 K and SSi < SMg are required.

General synthesis of ionic-electronic coupled two-dimensional materials.

Two-dimensional (2D) AMX2 compounds are a family of mixed ionic and electronic conductors (where A is a monovalent metal ion, M is a trivalent metal, and X is a chalcogen) that offer a fascinating platform to explore intrinsic coupled ionic-electronic properties. However, the synthesis of 2D AMX2 compounds remains challenging due to their multielement characteristics and various by-products. Here, we report a separated-precursor-supply chemical vapor deposition strategy to manipulate the chemical reactions and evaporation of precursors, facilitating the successful fabrication of 20 types of 2D AMX2 flakes. Notably, a 10.4 nm-thick AgCrS2 flake shows superionic behavior at room temperature, with an ionic conductivity of 192.8 mS/cm. Room temperature ferroelectricity and reconfigurable positive/negative photovoltaic currents have been observed in CuScS2 flakes. This study not only provides an effective approach for the synthesis of multielement 2D materials with unique properties, but also lays the foundation for the exploration of 2D AMX2 compounds in electronic, optoelectronic, and neuromorphic devices.

Manufacturing porous BaTaO2N nanosheet via nitridation of a novel oxyhalide precursor for boosted photocatalytic water oxidation reaction

BaTaO2N (BTON) with a generous adsorption edge of ca. 660 nm and high theoretical solar-to-hydrogen conversion efficiency of ca. 20.6% has been extensively investigated for photocatalytic water splitting. In this study, we have successfully prepared a porous BTON nanosheet via employing Ba2Bi3Ta2O11Cl (BBTOC) oxyhalide as a novel nitridation precursor. The oxygen evolution rate of the BTON nanosheet is 108 μmol·h−1, which is three times higher than that of BTON (25.9 μmol·h−1) prepared by conventional solid-state method. The successful construction of porous BTON nanosheet is due to the structural transformation of BBTOC nanosheet precursor and facile evaporation of Bi and Cl elements. The porous nanosheet morphology of BTON can not only promote the transfer of photogenerated charge carriers but also provide abundant reaction sites for the oxygen evolution reaction. This work demonstrates a novel and efficient strategy for preparing oxynitride for efficient solar energy conversion.

Surface Passivation for Promotes Bi-Excitonic Amplified Spontaneous Emission in CsPb(Br/Cl)3 Perovskite at Room Temperature.

Perovskite-type lead halides exhibit promising performances in optoelectronic applications, for which lasers are one of the most promising applications. Although the bulk structure has some advantages, perovskite has additional advantages at the nanoscale owing to its high crystallinity given by a lower trap density. Although the nanoscale can produce efficient light emission, its comparatively poor chemical and colloidal stability limits further development of devices based on this material. Nevertheless, bulk perovskites are promising as optical amplifiers. There has been some developmental progress in the study of optical response and amplified spontaneous emission (ASE) as a benchmark for perovskite bulk phase laser applications. Therefore, to achieve high photoluminescence quantum yields (PLQYs) and large optical gains, material development is essential. One of the aspects in which these goals can be achieved is the incorporation of a bulk structure of high-quality crystallization films based on inorganic perovskite, such as cesium lead halide (CsPb(Br/Cl)3), in polymethyl methacrylate (PMMA) polymer and encapsulation with the optimal thickness of the polymer to achieve complete surface coverage, prevent degradation, surface states, and surface defects, and suppress emission at depth. Sequential evaporation of the perovskite precursors using a single-source thermal evaporation technique (TET) effectively deposited two layers. The PL and ASEs of the bare and modified films with a thickness of 400 nm PMMA were demonstrated. The encapsulation layer maintained the quantum yield of the perovskite layer in the air for more than two years while providing added optical gain compared to the bare film. Under a picosecond pulse laser, the PL wavelength of single excitons and ASE wavelength associated with the stimulated decay of bi-excitons were achieved. The two ASE bands were highly correlated and competed with each other; they were classified as exciton and bi-exciton recombination, respectively. According to the ASE results, bi-exciton emission could be observed in an ultrastable CsPb(Br/Cl)3 film modified by PMMA with a very low excitation energy density of 110 µJ/cm2. Compared with the bare film, the ASE threshold was lowered by approximately 5%. A bi-exciton has a binding energy (26.78 meV) smaller than the binding energy of the exciton (70.20 meV).

Preparation, morphology and luminescence properties of micro-columnar structured Lu2O3:Eu films by LCVD method on quartz glass

Micron/sub-micron hard X-ray imaging is an important development direction of X-ray detection technology. Scintillation screens with excellent X-ray stopping power and high light output are desired to obtain good imaging quality. Europium-doped lutetium oxide (Lu2O3:Eu) film with micro-columnar structure is an ideal candidate for this application. In this study, micro-columnar structured Lu2O3:Eu films were prepared on quartz glass substrates by laser chemical vapor deposition (LCVD) method. The influences of preparation conditions on structure and morphology properties of films were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Photoluminescence and scintillation properties of the films, including photoluminescence excitation (PLE), photoluminescence (PL), PL decay, X-ray excitation luminescence (XEL), and afterglow curves, were recorded. The relationships between structure, morphology, luminescence properties of films, and preparation conditions were investigated and discussed as well. The preparation conditions include laser power, oxygen flow rate, and precursor evaporation temperature. In addition, dual-layer Lu2O3:Eu film was prepared for the first time by just turning off the laser.

Flash evaporation of low volatility solid precursors by a scanning infrared laser

The steady and stoichiometric delivery of metal-organic precursor mixtures is essential for the production of complex, functional nanomaterials in the gas phase. Chemical vapor synthesis (CVS) is a corresponding process which enables the production of complex oxide nanoparticles such as perovskites. While there exist a vast number of compositions that form perovskite structures, many technically relevant materials consist of transition metals and lanthanides. Their corresponding metal organic precursors often deviate significantly in their thermal behavior, resulting in a challenging delivery of precursors to the reactor. One suitable method for precursor delivery is flash evaporation by an infrared laser, where a mixture of solid precursors is instantly sublimed. Using flash evaporation, the stoichiometry of the generated vapor corresponds to the composition of precursors in the solid mixture. In this study, we present an alternative flash evaporation system based on a marking laser which rapidly scans a focused infrared beam across a precursor powder bed. By focusing the beam, higher energy densities are reached, compared to existing systems while a large area powder bed is repeatedly scanned and sublimed. Fourier-transform infrared spectroscopy (FTIR) measurements confirm the decomposition-free sublimation of precursor mixtures. Furthermore, we confirm the successful precursor delivery by the synthesis of LaFeO3 nanoparticles with an average crystallite size of 5.3 nm. The structure of the ensemble of nanoparticles is examined using X-ray diffraction (XRD) and Rietveld refinement, transmission electron microscopy (TEM), selected area diffraction (SAED), and extended X-ray absorption fine structure (EXAFS) at the Fe-K edge analyzed by reverse Monte Carlo (RMC) analysis.

Numerical analysis on burning and particle formation of a single ethanol-based droplet in flame spray pyrolysis

Ethanol is a common inexpensive solvent for industrial flame spray pyrolysis. This work presents a numerical study of a single ethanol-based droplet burning with different precursor concentrations under both dry and wet air conditions. The evaporation and decomposition of precursors, the deposition of water vapor and its diffusion and transport in the liquid phase are considered. The micro-explosion behavior and droplet burning constant were well predicted as compared to existing experimental data in literature. The results show that surface condensation, dissolution, and re-evaporation of water were controlled by the disparity of mass transfer and evaporation priorities of different components in the droplet at different temperatures. Water in the ethanol droplet increases first during the initial burning stage and then decreases with increasing temperature as water preferentially vaporized than the formed less-volatile viscous layer on the droplet surface during the droplet combustion. The ratio of particle synthesis through evaporation and thermal decomposition decreases with increasing precursor concentration. It is further identified that the presence of water from either combustion products or humid air suppresses evaporation of the precursors in ethanol droplets because water dissolved in droplets evaporates preferably than the precursor, thereby potentially inhibiting the gas-to-particle route and providing another potential option for the control of flame synthesis process.

Electroless Dealloying of Thin-Film Nanocrystalline Au-Ag Alloys: Mechanisms of Ligament Nucleation and Sources of Its Synthesis Variability.

Control of ligament size in nanoporous gold through process inputs in chemical dealloying holds the potential to exploit its size dependent properties in applications in energy and biomedicine. While its morphology evolution is regulated by the kinetics of coarsening, recent studies are focused on the early stage of dealloying (e.g., ∼ 5-42 at. % in residual alloy content) to understand mechanisms of ligament nucleation and its role in altering process-structure relationships. This paper examines this stage in chemical dealloying of nanocrystalline Au49Ag51 thin films and finds that ligaments are nucleated uniformly through its thickness due to the dealloying front rapidly propagating through the thickness of the film. Further, through the establishment of process-structure relationships with large data sets (i.e., 80 samples), this paper quantifies sources of variability that alter the kinetics of ligament growth such as aging of the precursor (e.g., grain growth) and solution evaporation. It is found that ligament diameter is better predicted by the residual silver content rather than by the dealloying time even amidst both effects and independent control of ligament diameter and solid area fraction is demonstrated within a limited window.

Solvent recovery from photolithography wastes using cellulose ultrafiltration membranes

Solvent recycling and reuse are indispensable for ensuring a sustainable chemical industry and circular economy. In this study we report the fabrication of cellulose ultrafiltration membranes and their application in recovery of propylene glycol methyl ether acetate (PGMEA) used as developer solvent in SU-8 photolithography. Cellulose membranes were fabricated via alkaline hydrolysis of cellulose acetate membranes in aqueous NaOH. Membrane permeance and molecular weight cut-off (MWCO) were tuned via changing cellulose acetate concentration in precursor solution and evaporation of volatile co-solvent, acetone. MWCO of the membranes was found to be smallest in DMSO, followed by water and largest in methanol. The difference was attributed to the different hydrodynamic diameters of the probe molecules in these solvents. SU-8 rejection from its representative developer solutions in PGMEA was assessed in dead-end filtration at up to 80% permeate recovery. After the first filtration, the collected permeate was fed to the same membrane to simulate a two-stage filtration scenario. Rejection was in the range of 87%–89% in a first stage filtration and 79%–80% in a second stage, both operated at 80% permeate recovery. Recycled solvent could be used in photolithography although with some loss of pattern fidelity, possibly owing to remaining SU-8 and photoacid generator in PGMEA. • Cellulose membrane permeance and MWCO tuned between 0.40–23.3 LHM/bar and 4–15 kDa. • Permeance is via pore flow mechanism but is also affected by swelling and steric hindrance. • SU-8 can be recovered from its PGMEA solution and reused in photolithography.

The effective and stable Cu–C@SiO2 catalyst for the syntheses of methanol and ethylene glycol via selective hydrogenation of ethylene carbonate

The co-production of ethylene glycol and methanol via ethylene carbonate hydrogenation derived from CO2 has attracted great concerns because of the promising chemical utilization of CO2 in large-scale. Copper-based catalysts are widely concerned in hydrogenation of ester due to the high catalytic efficiency and low cost, but the stability of copper-based catalyst is poor and needs to be further improved. In this study, the modification Cu–C@SiO2-R catalyst with graphite oxide was prepared by using Cu3(BTC)2 as the precursor and ammonia evaporation method, and was applied in ethylene carbonate hydrogenation to synthesis ethylene glycol and methanol. Furthermore, the catalysts were characterized in detail. The results showed that the Cu–C@SiO2-R catalyst was modified with graphite oxide, the average size of Cu particles was 2.9 nm and Cu particles had good dispersion. In addition, both Cu–C@SiO2-R and Cu@SiO2-R catalysts had similar ratio of Cu+/(Cu0+Cu+). In a batch reactor, under 453 K, 5 MPa, 4 h, the catalytic efficiency was 80.0% EC conversion 92.2% EG and 70.8% MeOH selectivity showing excellent catalytic performance capability of Cu–C@SiO2-R catalyst. In long-term experiment, the Cu–C@SiO2-R catalyst showed excellent stability after using for 264 h. The activity was 0.63 gEC gcat−1 h−1, and 100.0% EC conversion 99.9% EG and 85.8% MeOH selectivity could be achieved in a fixed bed. After the long-term experiment, the Cu+/(Cu++Cu0) ratio in Cu–C@SiO2-R catalyst kept at around 0.48. In contrast, the Cu+/(Cu++Cu0) ratio in Cu@SiO2-R catalyst decreased sharply from 0.48 to 0.38. The stability of the structure and the balance of valence of Cu were considered to be responsible to the stability of Cu–C@SiO2-R catalyst, because the graphite oxide not only kept the Cu+/(Cu0+Cu+) ratio stability, but also restrained the aggregation of Cu particles and loss of copper. This work provides an in-depth understanding of the stabilization mechanism of Cu and can be a reference for the industrial application of ethylene carbonate hydrogenation.

Finite Element Analysis of An Evaporation System to Synthesize Kesterite thin Films

Currently, there is an interest within the scientific community in thin-film solar cells with a Kesterite (Cu2ZnSnS4) type absorber layer, since they report a theoretical efficiency greater than 32 %. The synthesis of Kesterites by evaporation has allowed for efficiencies at the laboratory level of 11.6 %. Although these are good results, the design of the evaporation chamber and the distribution of the electrodes is essential to control synthesis parameters and evaporate each precursor in the corresponding stage. This project seeks to design an evaporation chamber that can achieve a vacuum of 10-5 mbar, increase the deposition surface and avoid each precursor evaporation in a non-corresponding stage. This last objective was studied using Comsol multiphysics R. (licensed product) software, with the adequate disposition of metallic precursors (zinc, copper, and tin) determined by analyzing heat distribution. It was concluded that the lower the evaporation temperature of the precursor, the smaller the height of the copper electrode in the system. This is because, with a lower height the concentration of heat in the container is lower.

Modeling the evaporation of CAI-like melts, and constraining the origin of CH-CB CAIs

To address the bulk compositions of CAIs from CH-CB chondrites we have used a new thermodynamic method to model the evaporation of CAI-like melts. The model calculations agree closely with the results of evaporation experiments on individual bulk compositions, and thus could provide a general means of predicting the evaporation trajectory of any CAI bulk composition melt. The model calculations and evaporation experiments show that the initial stages of CAI melt evaporation are controlled by the relative evaporation rates of MgO and SiO2, whereas the late stages are dominated by the initial CaO/Al2O3 ratio of the melt. Application of the model to the puzzling bulk compositions of very refractory CAIs from CH-CB chondrites, many of which are grossite-, hibonite-, and spinel-rich, shows that such compositions can be derived via evaporation of precursors unusually enriched in Al2O3 with CaO/Al2O3 ratios (weight %) < 0.3. This rules out most silicate-rich CAI varieties. Only spinel- and spinel-hibonite-rich fine-grained inclusions with group II REE patterns (common in CV3 chondrites), which may have been present in the region where CH CAIs formed, could be precursors for the grossite- and hibonite-rich igneous CAIs.

Experiments quantifying elemental and isotopic fractionations during evaporation of CAI-like melts in low-pressure hydrogen and in vacuum: Constraints on thermal processing of CAIs in the protoplanetary disk

It is widely believed that the precursors of coarse-grained CAIs in chondrites are solar nebula condensates that were later reheated and melted to a high degree. Such melting under low-pressure conditions is expected to result in evaporation of moderately volatile magnesium and silicon and their mass-dependent isotopic fractionation. The evaporation of silicate melts has been extensively studied in vacuum laboratory experiments and a large experimental database on chemical and isotopic fractionations now exists. Nevertheless, it remains unclear if vacuum evaporation of CAI-like melts adequately describes the evaporation in the hydrogen-rich gas of the solar nebula. Here we report the results of a detailed experimental study on evaporation of a such melt at 1600 °C in both vacuum and low-pressure hydrogen gas, using 1.5- and 2.5-mm diameter samples. The experiments show that although at 2 × 10−4 bar H2 magnesium and silicon evaporate ∼2.8 times faster than at 2 × 10−5 bar H2 and ∼45 times faster than in vacuum, their relative evaporation rates and isotopic fractionation factors remain the same. This means that the chemical and isotopic evolutions of all evaporation residues plot along a single evaporation trajectory regardless of experimental conditions (vacuum or low-PH2) and sample size. The independence of chemical and isotopic evaporation trajectories on PH2 of the surrounding gas imply that the existing extensive experimental database on vacuum evaporation of CAI-like materials can be safely used to model the evaporation under solar nebula conditions, taking into account the dependence of evaporation kinetics on PH2.The experimental data suggest that it would take less than 25 min at 1600 °C to evaporate 15–50% of magnesium and 5–20% of silicon from a 2.5-mm diameter sample in a solar nebula with PH2 ∼2 × 10−4 bar and to enrich the residual melt in heavy magnesium and silicon isotopes up to δ25Mg ∼5–10‰ and δ29Si ∼2–4‰. The expected chemical and isotopic features are compatible to those typically observed in coarse-grained Type A and B CAIs. Evaporation for ∼1 h will produce δ25Mg ∼30–35‰ and δ29Si ∼10–15‰, close to the values in highly fractionated Type F and FUN CAIs. These very short timescales suggest melting and evaporation of CAI precursors in very short dynamic heating events. The experimental results reported here provide a stringent test of proposed astrophysical models for the origin and evolution of CAIs.

Effect of Anionic Substitution of S by Se in CZTSSe Films Prepared from Electron Beam Evaporation

Abstract Cu2ZnSnSxSe4-x (CZTSSe) is a prominent candidate as a photon absorber layer in solar cell owing to its earth abundant constituents and high absorption coefficient with tunable bandgap. In this study, the effect of metallic stacking order and anionic substitution of S by Se on the properties of CZTSSe is investigated by varying the S/Se ratio. CZT metallic precursor films with stacking sequences SLG/Sn/Zn/Cu and SLG/Cu/Sn/Zn/Cu are fabricated on soda lime glass substrate by using electron beam evaporation of elemental metallic precursors. In order to obtain CZTSSe films with various S/Se ratio, the films are annealed in the presence of elemental S and Se environment with various ratio of elemental S and Se powder at 550 °C for 1 hour at a ramping rate of 10 °C/min with N2 as a carrier gas. The effect of variation of S/Se powder on crystallinity, morphology and composition of the films are confirmed through X-Ray diffraction, Raman spectroscopy, FEGSEM and EDS analysis. The optical bandgap of the films is estimated to decrease with increasing Se content in the films. The Se incorporation is noticed the highest in case of SLG/Sn/Zn/Cu stack and its bandgap is found to be decreasing from 1.53 to 1.2 eV with increasing Se content.

DROP DYNAMICS IN HETEROGENEOUS SPRAY FLAMES FOR NANOPARTICLE SYNTHESIS

In flame spray pyrolysis (FSP), the understanding of the atomization and spray formation of the coaxial atomizer is a key step to control the mixing of reactants, and precursor release, as well as nanoparticle formation and growth mechanisms. The drop size and drop dynamics of fuel/precursor mixtures are relevant parameters to control the particle synthesis via gas-to-particle conversion for tailoring the nanoparticle. The investigation of the multiphase flow structures, especially in the dense spray region using sophisticated nonintrusive laser diagnostics, such as phase Doppler anemometry (PDA), enables a characterization of the burner with multiscale spatial and temporal resolution. In the present work, the evolution of drop size and velocity under varying iron nitrate (FNT) concentration of the precursor is investigated allowing for an estimation of precursor release and evaporation via detailed PDA measurements. The drop size distributions of pure ethanol, and ethanol + 2-ethylhexanoic acid, as well as for FNT-based spray flames, were studied in order to reveal the influence of metal precursors on the combustion. Drop size/velocity correlations were determined in order to resolve the size class averaged evolution of drop velocities. The evolution of the drop size distribution along the axial centerline revealed a variation of the evaporation rate in space and increased evaporation rates for FNT containing spray flames. Furthermore, bimodal drop size distributions were observed for heights above the burner larger than 40 mm in FNT precursor spray flames, indicating the occurrence of possible μ-explosions of drops, that have been reported in the literature for similar systems but only in single-droplet experiments so far.

Relationship Processing–Composition–Structure–Resistivity of LaNiO3 Thin Films Grown by Chemical Vapor Deposition Methods

Precision control of resistivity/conductivity of LaNiO3 (LNO) films is essential for their integration as electrodes in the functional heterostructures. This becomes possible if the relationship between processing parameters–composition–structure–resistivity is determined. LaNiO3 films were deposited by three different chemical vapor deposition methods using different precursor supply systems: direct liquid delivery, pulsed liquid injection, and aerosol generation. The possibilities to ameliorate the efficiency of precursor evaporation and of film growth were studied. The relationship between deposition conditions and composition was determined. Detailed analysis of the epitaxial growth of LNO films on cubic and trigonal substrates and the influence of the rhombohedral distortion on the microstructural quality was done. The resistivity of LaNiO3 films, grown by chemical vapor deposition, was mainly defined by microstructural defects and La/Ni composition. The high epitaxial quality LaNiO3/LaAlO3 films with nearly stoichiometric La/Ni ratio presented low resistivity, which was very close to that of bulk LaNiO3. Their annealing in oxygen atmosphere had little effect on the resistivity, which suggests a minor presence of oxygen vacancies in the as-grown films.

Kinetic Strategies for the Formation of Graphyne Nanowires via Sonogashira Coupling on Ag(111).

The selection of a reaction pathway with high energy barrier in a multipath on-surface reaction system has been challenging. Herein, we report the successful control of the reaction system of 1,1'-biphenyl-4-bromo-4'-ethynyl (BPBE) on Ag(111), in which three coupling reactions (Glaser, Ullman, Sonogashira) are involved. Either graphdiyne (GDY) or graphyne (GY) nanowires can be formed by distinct kinetic strategies. As the energetically favorable pathway, the formation of a GDY nanowire is achieved by hierarchical activation of Glaser (with lowest energy barrier) and Ullman coupling of BPBE. On the other hand, the formation of a GY nanowire originates from the high selectivity of the high-barrier Sonogashira coupling, whose indispensable kinetic parameters are high surface temperature, low molecular coverage, and low precursor evaporation rate, as derived from a series of control experiments. This work achieves the fabrication of GY nanowires via on-surface Sonogashira coupling for the first time and reveals mechanistic control strategies for potential syntheses of other functional nanostructures via cross-couplings on surfaces.

Structure of superconducting MgB2 thin films prepared by vacuum evaporation and ex-situ annealing in Ar and O2 atmospheres

Superconducting MgB2 thin films were fabricated on c-cut sapphire substrates by vacuum co-evaporation of magnesium and boron followed by an ex situ post-annealing. We show that annealing in oxygen atmosphere can significantly improve the superconducting properties of the MgB2 thin films compared to the typical annealing in argon atmosphere. In this work, influence of the ex-situ annealing atmosphere on the structure, texture and morphology of the superconducting MgB2 thin films has been studied by transmission electron microscopy, X-ray diffraction and pole figure measurements. Samples annealed at 800 °C in Ar, at 800 °C in O2 and at 500 °C in O2 have been compared. The annealing in O2 at 800 °C produces MgB2 thin films with the highest superconducting transition temperature and critical current density. We show that this is thanks to the thickest MgO layer at the surface produced in this case, which acts as a protecting barrier against out-diffusion of Mg during the annealing and leads to better stoichiometry and larger MgB2 grains compared to the samples annealed in Ar. Our method can be alternative to the customary ex-situ post annealing of Mg-B precursor in sealed vapor cell. In all samples, the MgB2 phase showed single axis texture with the (0 0 0 1) planes slightly inclined by 0° to 15° with respect to the Al2O3(0 0 0 1) substrate surface incurred with the initial precursor evaporation geometry. During the annealing, the excess Mg also reacts with the Al2O3 substrate and minor MgAl2O4 and MgO phases are produced at the substrate-layer interface.

Detailed investigations on influence of precursor stacking and sulfurization for Cu2ZnSnS4 film formation

Cu2ZnSnS4 (CZTS) is a suitable absorber material in thin film hetero-junction solar cell. In the present study, CZTS has been successfully fabricated by electron beam evaporation and the influence of precursor stacking sequences and sulfurization conditions on the formation of secondary phases have been investigated in detail. CZTS thin films are prepared by two stage process: first stage, precursor layers with two different sequences glass/Zn/Sn/Cu and glass/Sn/Zn/Cu are deposited on glass substrates at room temperature using electron beam evaporation of elemental metallic precursors; followed by the second stage, the precursor films are sulfurized in two different conditions, in presence of elemental sulfur powder and in 5% H2S + N2 environment, at 500 °C for 1 h of annealing time for the formation of CZTS films. Effects of sulfurization environment (sulfur powder and H2S) and ramping rate (1 K/min, 5 K/min and 10 K/min) on the formation of CZTS and other probable secondary phases for different stacking sequences are investigated using X-ray diffraction, Raman spectroscopy, Field emission gun scanning electron microscopy, energy dispersive X-ray spectroscopy and UV–vis spectroscopy. Deconvoluted Raman spectra revealed high crystallinity in films sulfurized at low ramping rate (1 K/min). CZTS formation is noticed to be enhanced by sulfurizing the films in the presence of sulfur powder when compared with H2S gas. Phase pure CZTS film with a bandgap of 1.53 eV is prepared using sulfurization of glass/Sn/Zn/Cu stacked film in elemental sulfur powder.