Photoelectrochemical study of MoO_3 assorted morphology films formed by thermal evaporation

Molybdenum oxide nanostructured thin films were grown on fluorine doped tin oxide（FTO）, indium doped tin oxide（ITO） and ordinary glass substrates by thermal evaporation process without vacuum and catalysts using molybdenum trioxide（MoO） powder as a source material and oxygen as a carrier gas.Various morphologies including nanobelts, disks and hexagonal rod-like nanostructures were obtained by changing the source and substrate temperatures during the growth of MoOthin films. Structural parameters, morphology, composition and surface features of the films were characterized by XRD, SEM, EDAX,XPS, AFM and Raman spectroscopy. The films were orthorhombic in structure with preferred orientation along（0 1 0） plane. Morphology analysis reveals randomly aligned nanobelts with 40 nm in thickness and a width of 800 nm and 3–12 mm in length. The disks have 1.5 μm diameters, 1 μm thickness and hexagonal rod-like nanostructures with a length, breath and width of 2 μm, 1 μm and 100 nm are formed. The samples were investigated under dark and photocurrent conditions in HSOaqueous solution as a function of applied potential. The photocurrent density of samples prepared on ITO and FTO substrate samples were compared and the results are discussed.

Effect of Mg-Film Thickness on the Formation of Semiconductor Mg_2Si Films Prepared by Resistive Thermal Evaporation Method

Mg films of various thicknesses were deposited on Si（111） substrates at room temperature by resistive thermal evaporation method, and then the Mg/Si samples were annealed at 40 ℃ for 4 h. The effects of Mg film thickness on the formation and structure of Mg2Si films were investigated. The results showed that the crystallization quality of Mg2Si films was strongly influenced by the thickness of Mg film. The XRD peak intensity of Mg2Si （220） gradually increased initially and then decreased with increasing Mg film thickness. The XRD peak intensity of Mg2Si （220） reached its maximum when the Mg film of 380 um was used. The thickness of the Mg2Si film annealed at 400℃ for 4 h was approximately 3 times of the Mg film.

Thermal Evaporation Deposition of Few-layer MoS_2 Films

We present a study of the fabrication of monolayer MoS_2 on n-Si(111) substrates by modified thermal evaporation deposition and the optoelectrical properties of the resulting film. The as-grown MoS_2 ultrathin film is about 10 nm thick, or about a few atomic layers of MoS_2. The film has a large optical absorption range of 300-700 nm and strong luminescence emission at 682 nm. The optical absorption range covered almost the entire ultraviolet to visible light range, which is very useful for making high-efficiency solar cells. Moreover, the MoS_2/Si heterojunction exhibited good rectification characteristics and excellent photovoltaic effects. The power conversion efficiency of the heterojunction device is about 1.79% under white light illumination of 10 m W/cm^2. The results show that the monolayer MoS_2 film will find many applications in high-efficiency optoelectronic devices.

Synthesis of ultralong Si_3N_4 nanowires by a simple thermal evaporation method

Largescale vaporsolid synthesis of ultralong silicon nitride （Si3N4） nanowires was achieved by using simple thermal evaporation of mixture powders of active carbon and monoxide silicon. The products were charac terized by Xray diffraction, scanning electron microscopy, energydispersive Xray spectroscopy, and transmission electron microscopy. The results suggest that the silicon nitride nanowires have a smooth surface, with lengths of up to several hundreds of microns and diameters of 100300 nm. A detailed study of both the chemical and structural composition was performed. Such ultralong sil icon nitride nanowires demonstrate potential applications as materials for constructing nanoscale devices and as reinforcement in advanced composites.

Synthesis and characterization of ZnO nanostructures prepared by a thermal evaporation process

A series of ZnO nanostructures such as nanowires,nanobelts,nanocombs and mesoporous nanoballs were fabricated by a simple carbon reduction method without catalyst.The morphologies and microstructures of all samples were characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,and energy dispersive X-ray spectroscopy.The results indicate that different deposition temperatures have great impact on different shapes of ZnO nanostructures.The growth mechanisms of these ZnO nanostructrues suggest that,by controlling the experiment parameters,different morphological configurations nanostructures can be fabricated.

Studying Thermoelectric Power Behaviors of Bi2Te3 Nanoparticles Prepared by Thermal Evaporation

Thin films of Bismuth Telluride (Bi2Te3) are prepared by thermal evaporation from nanopowders on the glass substrates. The XRD patterns of films show that all the films are polycrystalline and the crystalline increased by annealing temperature. Measuring of the thermoelectric power of thin films in the temperature range 300 to 380 K shows that Seebeck Coefficients have both negative and positive values, indicating that the films have both n-type and p-type conductivity. The re-crystallization of films is done by annealing from 130°C to 175°C and Seebeck Coefficient varied from -150 to 100 μV/K.

ZnO microbowls grown on an ITO glass substrate through thermal evaporation

Novel ZnO microbowls are successfully synthesized by the thermal evaporating of a mixture of ZnS powder and Zn powder. The morphologies of the as-synthesized products can be adjusted by changing the temperature and the type of substrate. The morphologies, microstructures, and photoluminescence properties are investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscope, and photoluminescence spectroscopy respectively. The growth mechanism of the as-synthesized ZnO microbowls is proposed based on the experimental results. ZnO microbowls presented here can be used as building blocks to fabricate optical and optoelectronic micro/nano devices.

In-situ growth of a CdS window layer by vacuum thermal evaporation for CIGS thin film solar cell applications

Highly crystalline and transparent CdS films are grown by utilizing the vacuum thermal evaporation （VTE） method. The structural, surface morphological, and optical properties of the films are studied and compared with those prepared by chemical bath deposition （CBD）. It is found that the films deposited at a high substrate temperature （200 ℃） have a preferential orientation along （002） which is consistent with CBD-grown films. Absorption spectra reveal that the films are highly transparent and the optical band gap values are found to be in a range of 2.44 eV-2.56 eV. Culnl_xGaxSe2 （CIGS） solar cells with in-situ VTE-grown CdS films exhibit higher values of Voc together with smaller values of Jsc than those from CBD. Eventually the conversion efficiency and fill factor become slightly better than those from the CBD method. Our work suggests that the in-situ thermal evaporation method can be a competitive alternative to the CBD method, particularly in the physical- and vacuum-based CIGS technology.

Synthesis of uniform two-dimensional MoS_(2) films via thermal evaporation

Two-dimensional(2D)molybdenum disulfide(MoS_(2))holds great potential for various applications such as electronic devices,catalysis,lubrication,anti-corrosion and so on.Thermal evaporation is a versatile thin film deposition technique,however,the conventional thermal evaporation techniques face challenges in producing uniform thin films of MoS_(2) due to its high melting temperature of 1375℃.As a result,only thick and rough MoS_(2) films can be obtained using these methods.To address this issue,we have designed a vacuum thermal evaporation system specifically for large-scale preparation of MoS_(2) thin films.By using K2MoS4 as the precursor,we achieved reliable deposition of uniform polycrystalline MoS_(2) thin films with a size of 50 mm×50 mm and controllable thickness ranging from 0.8 to 2.4 nm.This approach also allows for patterned deposition of MoS_(2) using shadow masks and sequential deposition of MoS_(2) and tungsten disulfide(WS_(2)),similar to conventional thermal evaporation techniques.Moreover,we have demonstrated the potential applications of the obtained MoS_(2) thin films in field effect transistors(FETs),memristors and electrocatalysts for hydrogen evolution reaction(HER).

Single-atom alloys prepared by two-step thermal evaporation

Single-atom alloys(SAAs)have gained significant attention due to their remarkable atomic utilization efficiency,interactions between single atoms(SAs)and metal supports,and free-atom-like electronic structure of dopant elements.In this work,we observed the formation of SAs in pre-deposited metal particles by a two-step thermal evaporation technique,thereby establishing the first instance of discovering SAAs by thermal evaporation.The discovery of SAAs by thermal evaporation extends the range of SAAs preparation methods to include this traditional synthetic technique,which offers convenience,cost-efficiency,and universality.The formation mechanism of SAAs prepared using this technique was elucidated by density functional theory calculations.It was demonstrated that thermal evaporation can be utilized to prepare SAAs with multiple SAs,further highlighting its universal applicability.

Synthesis of Aligned ZnO Nanorod Array on Silicon and Sapphire Substrates by Thermal Evaporation Technique

High density ZnO nanorods were grown by thermal evaporation of Zn powder at 700℃ on Si （100） and sapphire （0001） substrates at atmospheric pressure without adding any catalyst. The nanorods were characterizated in terms of their structural and optical properties. The nanorods grown on Si have a diameter of 350-400 nm and a length of 1.2 μm while those on sapphire have a diameter of 600-800 nm and a length of 2.5 μm. During the structural characterization, it is noticed that the rods grow along the （0002） plane with perfect hexagonal facet. The room temperature photoluminescence spectrum showed a strong UV emission peak at 385 nm with a weak green band emission, which confirms that nanorods have good optical properties. It is observed that the oxygen partial pressure plays an important role to control the shape and size of the nanorods in thermal evaporation growth technique.

ZnS thin films deposition by thermal evaporation for photovoltaic applications

ZnS thin films were deposited on glass substrates by thermal evaporation from millimetric crystals of ZnS. The structural, compositional and optical properties of the films are studied by X-ray diffraction, SEM microscopy, and UV-VIS spectroscopy. The obtained results show that the films are pin hole free and have a cubic zinc blend structure with （111） preferential orientation. The estimated optical band gap is 3.5 eV and the refractive index in the visible wavelength ranges from 2.5 to 1.8. The good cubic structure obtained for thin layers enabled us to conclude that the prepared ZnS films may have application as buffer layer in replacement of the harmful CdS in CIGS thin film solar cells or as an antireflection coating in silicon-based solar cells.

A novel approach to fabricate Zn coating on Mg foam through a modified thermal evaporation technique

Zn enriched coatings with distinct microstructures and properties were fabricated on Mg foams by a modified thermal evaporation technique using a tubular resistance furnace. As the temperature and kinetic energy of Zn vapor varied along the tubular system, a spatial variation of preparation conditions was created and the obtained coatings were found to follow two growth mechanisms： a thermal diffusion pattern in high-temperature zone and the a relatively low-temperature deposition model. AZn-based deposition coating with dense texture and nearly uniform structure was acquired while Mg foam was placed 20 cm far from the evaporation source, where the Zn vapor deposition model dominated the coating growth.Mechanical properties and bio-corrosion behaviors of the samples were investigated. Results showed that the Zn coatings brought dramatic improvements in compression strength, but exhibited differently in biodegradation performance. It was confirmed that the diffusion layer accelerated corrosion of Mg foam due to the galvanic effect, while the Zn-based deposition coating displayed excellent anti-corrosion performance, showing great potential as bone implant materials. This technique provides a novel and convenient approach to tailor the biodegradability of Mg foams for biomedical applications.

Microstructure evolution and growth mechanism of core-shell silicon-based nanowires by thermal evaporation of SiO

Core-shell structured SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires were prepared on the surface of carbon/carbon(C/C)composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO3)2 as the catalyst.The average diameters of SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires are about 145 nm,and the core-shell diameter ratios are about 0.41 and 0.53,respectively.The SiO_(2)shells of such two nanowires resulted from the reaction between SiO and CO and the reaction of SiO itself,respectively,based on the model analysis.The growth of these two nanowires conformed to the vapor-liquid-solid(VLS)mode.In this mode,CO played an important role in the growth of nanowires.There existed a critical partial pressure of CO(pC)determining the microstructure evolution of nanowires into whether SiC@SiO_(2)or Si@SiO_(2).The value of pC was calculated to be 4.01×10^(-15) Pa from the thermodynamic computation.Once the CO partial pressure in the system was greater than the pC,SiO tended to react with CO,causing the formation of SiC@SiO_(2)nanowires.However,the decomposition of SiO played a predominant role and the products mainly consisted of Si@SiO_(2)nanowires.This work may be helpful for the regulation of the growth process and the understanding of the growth mechanism of silicon-based nanowires.

Effect of Oxygen Admittance Temperature on the Growth of ZnO Microcrystals by Thermal Evaporation Technique

Hexagonally well-faceted microcrystals of ZnO have been grown by thermal evaporation of Zn powder in oxygen ambient at 700℃ under atmospheric pressure. It has been observed that the properties （size and quality） of ZnO microcrystals have a strong dependence on the reactor temperature at which the oxygen gas is admitted into the growth zone. The microcrystals grown with oxygen admittance at 450℃ have a length of 1 μm and a diameter of 0.75 μm while that grown with oxygen admittance at 600 ℃ have a length of 1.5-2 μm and a diameter of 1 μm. Room temperature photoluminescence spectra show a ultraviolet （UV） emission peak at 385 nm with a green band emission at around 500 nm. The UV-to-green band emission ratio for the microcrystals grown with oxygen admittance at 450℃ is observed to be 1.25 and the ratio decreases to 0.45 for the sample grown with oxygen admittance at 600℃.

Asymmetric Thermally Activated Delayed Fluorescence Materials Rendering High-performance OLEDs Through both Thermal Evaporation and Solution-processing

Exploring high-efficiency thermally activated delayed fluorescence(TADF)materials is of great importance regarding to organic light-emitting diode(OLED).Herein,we present a design strategy for developing asymmetric TADF materials based on a diphenyl sulfone-phenoxazine structure,resulting in efficient TADF emitters(CzPXZ and t-CzPXZ)with aggregation-induced emission properties,while t-CzPXZ is modified with tert-butyl groups.The two compounds exhibit high solid-state luminescence,efficient TADF,and significantly impressive device performances by both thermal evaporation and solution processing.For an instance,CzPXZ and t-CzPXZ enable the thermally-evaporated OLEDs with high external quantum efficiencies(EQEs)of over 20%.Meanwhile,t-CzPXZ allows the solution-processed device with a high EQE of 16.3%with low-efficiency roll-off,attributing to the enhanced molecular solubility and suppressed excitons quenching through tert-butyl modification on t-CzPXZ.The results reveal that the proposed asymmetric structure is a promising approach for developing high-efficiency TADF materials and OLEDs.

Synthesis of Single-Crystal TiO_2 Nanowire Using Titanium Monoxide Powder by Thermal Evaporation

TiO 2 nanowires were synthesized successfully in a large quantity by thermal evaporation using titanium monoxide powder as precursor. X-ray diffraction results showed that all the products were pure rutile phase of TiO 2 . According to microstructural observations, the nanowires have two typical morphologies, a long straight type and a short tortuous type. The straight nanowires were obtained at a wide temperature range of 900–1050 ℃, while the tortuous ones were formed below 900 ℃. Transmission electron microscopy characterization revealed that both the straight and the tortuous nanowires are single-crystal rutile TiO 2 . The preferential growth direction of the nanowires was determined as [110] orientation according to electron diffraction and high-resolution image analyses. The morphological change of TiO 2 nanowires was discussed by considering the different atomic diffusion rates of Ti atoms caused by the phase transformation in Ti substrate at around 900 ℃.

Growth mechanism for zinc coatings deposited by vacuum thermal evaporation

The vacuum thermal evaporation technique was used to simultaneously deposit zinc coatings onto interstitial free steel plates and single-crystal silicon wafers in a high vacuum environment.The effect of substrate temperature on the mor-phology and crystal orientation of zinc coatings was investigated.When the substrate temperature was 25 and 50℃,the zinc crystallites were plate-like and grew under a particular angle to the substrate surface.After the substrate was heated to 100℃,the zinc crystallites were regular hexagonal and arranged almost parallel to the substrate surface.In addition,observation of pure zinc coatings with different thicknesses showed that the growth of zinc coating was mainly in the Volmer-Weber mode.When the process parameters were appropriate,the zinc coating was composed of closely arranged columnar crystallites,and the crystallites grew preferentially along[0001]direction.

Metal-catalyzed growth of In_2O_3 nanotowers using thermal evaporation and oxidation method

Large-scale In2O3 nanotowers with different cross sections were synthesized by a thermal evaporation and oxidation technique using metal as the catalyst. The morphologies and structural characterizations of In2O3 nanotowers are dependent on growth processes, such as different metal （Au, Ag or Sn） catalysts, the relative position of the substrate and evaporation source, growth temperature, gas flow rate, and growth time. In2O3 nanotowers cannot be observed using Sn as the catalyst, which indicates that metal liquid droplets play an important role in the initial stages of the growth of In2O3 nanotowers. The formation of an In2O3 nanotower is attributed to the competitive growth model between a lateral growth controlled by vapor-solid mechanism and an axial vaporliquid-solid growth mechanism mediated by metal liquid nanodroplets. The synthesized In2O3 nanostructures with novel tower-shaped morphology may have potential applications in optoelectronic devices and gas sensors.

Rapid thermal evaporation for cadmium selenide thin-film solar cells

Cadmium selenide(CdSe)belongs to the binary II-VI group semiconductor with a direct bandgap of~1.7 eV.The suitable bandgap,high stability,and low manufacturing cost make CdSe an extraordinary candidate as the top cell material in silicon-based tandem solar cells.However,only a few studies have focused on CdSe thin-film solar cells in the past decades.With the advantages of a high deposition rate(~2µm/min)and high uniformity,rapid thermal evaporation(RTE)was used to maximize the use efficiency of CdSe source material.A stable and pure hexagonal phase CdSe thin film with a large grain size was achieved.The CdSe film demonstrated a 1.72 eV bandgap,narrow photoluminescence peak,and fast photoresponse.With the optimal device structure and film thickness,we finally achieved a preliminary efficiency of 1.88%for CdSe thin-film solar cells,suggesting the applicability of CdSe thin-film solar cells.