Assisted Chemical Vapor Deposition Method Research Articles

Synthesis and thermal properties of two novel cobalt (II) Schiff's base complexes as precursors for coating cobalt oxide (Co3O4) thin film by a Plasma Enhanced Metallo-Organic Chemical Vapour Deposition

Two Schiff's base complexes namely, Co(3,5-di-tertbutyl-salicylaldehydatoethylimine)2 (1) and Co(3,5-di-tertbutyl-salicylaldehydatobutylimine)2 (2) were synthesized by template method and characterized by elemental (C, H & N), FT-IR, DART-MS, TG/DTA and single crystal XRD analysis. Both 1 and 2 were found to crystallize in Orthorhombic crystal system. The complexes 1 and 2 undergoes single step volatilization in an inert N2 atmosphere giving a negligible percentage of residues at 331 °C (1) and 362 °C (2) as observed from thermogravimetry (TG) analysis. The molecular mass (M) of Co-bearing species were found to be 580 and 636 Da for 1 and 2 respectively. The equilibrium vapour pressures (pe) measurement by a TG - based transpiration technique over the temperature range of 489–550 K for 1 and 459–561 K for 2 yielded values of 107.0 (±1.8) and 105.2 (±2.1) kJ mol−1 for 1 and 2 respectively for their standard enthalpies of vapourisation (ΔHovap). Complex 2 was used as precursor for demonstrating the formation of Co3O4 thin film at a substrate temperature of 350 °C in an Ar plasma by using a home-built plasma assisted Chemical Vapour Deposition (CVD) method with a deposition pressure of 0.6–1.0 mbar. The phase identification by XRD showed the preferential growth of cubic Co3O4 in (311) plane. The morphology by SEM confirmed densely agglomerated cauliflower like structure. The particle size (D = 15.6 nm) was calculated using Debye-Scherrer's equation. A band gap value of 2.23 eV was obtained using Kubelka-Munk function.

High‐Performance Large‐Scale Vertical 1T'/2H Homojunction CVD‐Grown Polycrystalline MoTe2 Transistors

Abstract2D transition metal dichalcogenides (TMDs) have emerged as an ideal alternative to silicon in advanced electronics. Especially, MoTe2 attracts peculiar attention since it offers a unique opportunity of resolving critical electrical contacts. Currently, although MoTe2‐based coplanar semiconductor‐metal circuitry realized by epitaxial growth and chemical assembly has been demonstrated, while still suffers from the requirement of extremely accurate synthesis process control. Here, a facile strategy is demonstrated to fabricate large scale and high performance MoTe2 transistors with a 1T'/2H vertical homojunction structure by combining a spatial and phase controlled MoTe2 scalable synthesis and a scalable universal transfer method with water‐soluble poly‐vinylpyrrolidone and poly‐(vinyl alcohol) bilayer mediator. Both high quality 1T'‐ and 2H‐ MoTe2 with controlled dimensions can be scalable synthesized via a shadow mask assisted chemical vapor deposition method. These as‐synthesized MoTe2 patterns can be successfully transferred to a wide range of substrates at a high yield >80% with well‐retained properties to construct transistors with a complex vertical 1T'/2H‐MoTe2/HfAlO2 structure. The devices exhibit an on/off current ratio surpassing 104 and a typical mobility of ≈29 cm2 V−1 s−1. The developed scaled strategy of combining both scalable MoTe2 synthesis and transfer offers a feasible way for potential MoTe2‐based large‐scale electronics.

Nitrogen-phosphorus doped graphitic nano onion-like structures: experimental and theoretical studies.

Onion-like graphitic structures are of great importance in different fields. Pentagons, heptagons, and octagons are essential features of onion-like graphitic structures that could generate important properties for diverse applications such as anodes in Li metal batteries or the oxygen reduction reaction. These carbon nanomaterials are fullerenes organized in a nested fashion. In this work, we produced graphitic nano onion-like structures containing phosphorus and nitrogen (NP-GNOs), using the aerosol assisted chemical vapor deposition method. The NP-GNOs were grown at high temperature (1020 °C) using ferrocene, trioctylphosphine oxide, benzylamine, and tetrahydrofuran precursors. The morphology, structure, composition, and surface chemistry of NP-GNOs were characterized using different techniques. The NP-GNOs showed diameters of 110–780 nm with Fe-based nanoparticles inside. Thermogravimetric analysis showed that NP-GNOs are thermally stable with an oxidation temperature of 724 °C. The surface chemistry analysis by FTIR and XPS revealed phosphorus–nitrogen codoping, and several functionalities containing C–H, N–H, P–H, P–O, P Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O, CO, and C–O bonds. We show density functional theory calculations of phosphorus–nitrogen doping and functionalized C240 fullerenes. We present the optimized structures, electronic density of states, HOMO, and LUMO wave functions for P-doped and OH-functionalized fullerenes. The PO and P–O bonds attributed to phosphates or hydroxyl groups attached to phosphorus atoms doping the NP-GNOs could be useful in improving supercapacitor function.

Effect of temperature on morphologies and optical study of ZnO thin films deposited by aerosol assisted chemical vapor deposition technique

ZnO thin films were deposited on glass substrates by an aerosol assisted chemical vapor deposition method using Zn(II) semicarbazone complexes, ZnCl2(LH)2, (where LH = semicarbazones of cinnamaldehyde, 4-flouroacetophenone, benzaldehyde and 4-chlorobenzaldehyde) as precursors. X-ray diffraction patterns of as-deposited thin films show the formation of hexagonal ZnO (ICDD: 79-2205) at all the deposition temperatures, i.e. 350 °C, 400 °C and 450 °C. The UV–visible spectra show that the thin films are transparent in the visible range. The presence of the high intensity phonon mode at 438 cm−1 in the Raman spectra indicates the wurtzite phase of the ZnO thin films. Scanning electron microscopy images reveal the formation of different morphologies, hexagonal plates, nearly spherical particles and tetrapods at different temperatures. The roughnesses of the thin films were determined using atomic force microscopy.

CVD growth of self-assembled 2D and 1D WS2 nanomaterials for the ultrasensitive detection of NO2

Herein, we report for the first time on the facile synthesis of 2D layered WS2 nanosheets assembled on 1D WS2 nanostructures by combining the aerosol assisted chemical vapor deposition (AA-CVD) method with H2-free atmospheric pressure CVD, for an ultrasensitive detection of NO2. This synthesis strategy allows us a direct integration of the sensing material onto the sensor transducer with high growth yield and uniform coverage. Two different WS2 morphologies (nanotriangles and nanoflakes) were prepared and investigated. The results show that the assembly of layered WS2 nanosheets on a 3D architecture leads to an improvement in sensing performance by maintaining a high surface area in an accessible porous network. The sensors fabricated show stable, reproducible and remarkable responses towards NO2 at ppb concentration levels. The highest sensitivity was recorded for WS2 NT sensors, with an unprecedented ultra-low detection limit under 5 ppb. Additionally, this material has demonstrated its ability to detect 800 ppb of NO2 even when operated at room temperature (25 °C). Regarding humidity cross-sensitivity, our WS2 sensors remain stable and functional for detecting NO2 at ppb levels (i.e., a moderate response decrease is observed) when ambient humidity is raised to 50%. An 8-month long-term stability study has been conducted, which indicates that WS2-NT sensors show a very stable response to NO2 over time.

Optical and photocatalytic properties of biomimetic cauliflowered Ca2Mn3O8–CaO composite thin films

Inspired from the μ-oxido CaMn4 cluster unit present in the photosystem-II of plant cells, various manganese-based materials, particularly calcium-manganese oxides, have been investigated by the researchers as a new class of catalysts. Herein, we report the synthesis of single source heterobimetallic complex {[CaMn(OAc)(TFA)3(THF)(H2O)2].3THF}n (where OAc ​= ​acetate, TFA ​= ​trifluoroacetate and THF ​= ​tetrahydrofuran) for the deposition of thin films of Ca2Mn3O8–CaO composite on fluorine doped tin oxide (FTO) coated glass substrates at deposition temperatures of 450–550 ​°C via the aerosol assisted chemical vapour deposition (AACVD) method. The complex was characterized by melting point, microanalysis, proton nuclear magnetic resonance (1H NMR), Fourier transformed infra-red (FT-IR) spectroscopy, thermogravimetry (TGA) and single crystal X-ray diffraction. The deposited thin films were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM) which confirmed the growth of Ca2Mn3O8–CaO composite with high purity and precise stoichiometry. The optical characterization gave direct band gap energies of 2.74, 2.68 and 2.77 ​eV for the Ca2Mn3O8–CaO thin films deposited at 450, 500 and 550 ​°C, respectively. Furthermore, photoelectrochemical studies revealed that the thin film deposited at 500 ​°C showed the photocurrent of 3.75 ​mA ​cm−2 at +0.8 ​V vs. SCE with 1.64% photo-conversion efficiency and 310 ​Ω Rct value, upon illumination with a 150 ​W (100 ​mW ​cm−2) halogen lamp. The improved photocatalytic activity of Ca2Mn3O8–CaO composite was due to the increased photo absorption ability, elevated surface area, and more efficient electron/hole transfer. In addition, this work provides an insight to design the growth of visible light active calcium-manganese based photocatalyst materials for solar energy utilization.

The synthesis of 2D MoS2 flakes with tunable layer numbers via pulsed-Argon-flow assisted CVD approach

Modified chemical vapor deposition (CVD) is highly desirable to achieve versatile synthesis of two-dimensional (2D) molybdenum sulfide (MoS2) crystals with certain layer-number and configuration. In this study, we have demonstrated growth of MoS2 domains with diverse layer numbers through the pulsed-Ar-flow assisted CVD method utilizing Mo foil and Si/SiO2 substrate to construct confined reaction space. Layer number of obtained samples under varied time width of pulsed Ar flow is regulated from monolayer to multilayer (>3). Thickness evolution may be derived from the manipulation of on-time width of pulsed Ar gas. Our result provides an optional strategy to synthesize other transition metal dichalcogenides (TMDCs) crystals with desired configurations.

Thermal stability of a-C:H:SiOx thin films in hydrogen atmosphere

a-C:H:SiOx thin films were deposited by the plasma assisted chemical vapor deposition method, using polyphenylmethylsiloxane as a precursor. The thermal stability of a-C:H:SiOx films deposited on stainless steel substrates was investigated after thermal annealing of samples in a hydrogen atmosphere for 4 h at temperatures ranging from 300 to 700 °C. The sample analysis by optical and atomic force microscopy, nanoindentation, glow discharge optical emission spectrometry and Raman spectroscopy is reported here. Characterization of the mechanical properties of films (hardness, modulus, endurance capability, elastic recovery) was accomplished using the nanoindentation method. The investigation revealed that the above mechanical characteristics of a-C:H:SiOx films are very good up to 600 °C in hydrogen compared to un-doped diamond-like coatings. The hardness of the as-deposited a-C:H:SiOx films (11–13 GPa) showed no decrease after annealing at 600 °C. It is shown that the properties of films begin to change after annealing in hydrogen at a temperature of 200 °C more than during annealing in an air atmosphere. It is demonstrated that graphitization of a-C:H:SiOx films in hydrogen occurs at higher temperatures than in air.

Characteristics of TiAlCN ceramic coatings prepared via pulsed-DC PACVD, part I: Influence of precursors’ ratio

In this study, titanium aluminium carbonitride (TiAlCN) ceramic coatings with different precursors' ratio of AlCl3/TiCl4 were deposited on H13 hot work tool steel substrates, using pulsed-DC plasma assisted chemical vapor deposition method. The coatings showed a nanocomposite microstructure consisted of fcc-TiAlN and hcp-AlN nanocrystalline grains and an amorphous carbon phase. Increasing the precursors' ratio from 0.5 to 3 led to an increase in Al content from ∼10 to ∼42 at.%. Moreover, with increasing the precursors' ratio, the surface roughness of the coating reduced initially from 21.39 to 14.44 nm, due to the creation of more nuclei of AlN and then it rose up to 18.26 nm. Coating with the precursors' ratio of 0.5 presented the highest microhardness of 3840 HV0.01,due to the less amount of chloride impurity and hcp-AlN phase. The precursors’ ratio of 0.5 resulted in the highest wear resistance and lowest coefficient of friction of around 0.17.

Aerosol-Assisted Chemical Vapor Deposition of ZnS from Thioureide Single Source Precursors

A family of 12 zinc(II) thoureide complexes, of the general form [{L}ZnMe], [{L}Zn{N(SiMe3)2}], and [{L}2Zn], have been synthesized by direct reaction of the thiourea pro-ligands iPrN(H)CS(NMe2) H[L1], CyN(H)CS(NMe2) H[L3], tBuN(H)CS(NMe2) H[L2], and MesN(H)CS(NMe2) H[L4] with either ZnMe2 (1:1) or Zn{N(SiMe3)2}2 (1:1 and 2:1) and characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis (TGA). The molecular structures of complexes [{L1}ZnMe]2 (1), [{L2}ZnMe]2] (2), [{L3}ZnMe]∞ (3), [{L4}ZnMe]2] (4), [{L1}Zn{N(SiMe3)2}]2 (5), [{L2}Zn{N(SiMe3)2}]2 (6), [{L3}Zn{N(SiMe3)2}]2] (7), [{L4}Zn{N(SiMe3)2}]2] (8), [{L1}2Zn]2 (9), and [{L4}2Zn]2 (12) have been unambiguously determined using single crystal X-ray diffraction studies. Thermogravimetric analysis has been used to assess the viability of complexes 1-12 as single source precursors for the formation of ZnS. On the basis of TGA data compound 9 was investigated for its utility as a single source precursor to deposit ZnS films on silica-coated glass and crystalline silicon substrates at 150, 200, 250, and 300 °C using an aerosol assisted chemical vapor deposition (AACVD) method. The resultant films were confirmed to be hexagonal-ZnS by Raman spectroscopy and PXRD, and the surface morphologies were examined by SEM and AFM analysis. Thin films deposited from (9) at 250 and 300 °C were found to be comprised of more densely packed and more highly crystalline ZnS than films deposited at lower temperatures. The electronic properties of the ZnS thin films were deduced by UV-Vis spectroscopy to be very similar and displayed absorption behavior and band gap (Eg = 3.711-3.772 eV) values between those expected for bulk cubic-ZnS (Eg = 3.54 eV) and hexagonal-ZnS (Eg = 3.91 eV).

Improving the bio-corrosion behavior of AISI316L stainless steel through deposition of Ta-based thin films using PACVD

In this study, the Ta and Ta/TaN films were deposited on AISI 316L stainless steel (SS) using pulsed-DC plasma assisted chemical vapor deposition (PACVD) method to simultaneously improve its corrosion resistance and biocompatibility. The results showed that the deposited Ta/TaN films represents a uniform and flawless microstructure with better adhesion to substrate compared to single layer Ta due to the enhancement of Ta nucleation suppressed by TaN interlayer and also lower lattice mismatch between Ta and TaN. The Ta and Ta/TaN films showed the better surface wettability compared to the bare SS owing to the different hydrophilic nature of their spontaneously formed oxide layers. The Ta/TaN film exhibited the excellent corrosion resistance which is mainly attributed to its dense and flaw-free microstructure. The cell viability observations revealed that due to lower corrosion rate, the adhesion and also proliferation of cells on Ta/TaN film are meaningfully higher than that of bare SS and single layer Ta. After biofilm removal, the Ta/TaN film exhibited a higher integrity and adhesion to substrate compared to the single layer Ta.

Phase pure deposition of flower-like thin films by aerosol assisted chemical vapor deposition and solvent mediated structural transformation in copper sulfide nanostructures

Bis(O-isobutyldithiocarbonato)copper(II) complex [Cu(SCSOCH2CH(CH3)2)2] was used as a single source precursor to synthesize both copper sulfide thin films and nanoparticles. The copper sulfide thin films were deposited by the aerosol assisted chemical vapor deposition method, whereas the nanoparticles were synthesized by the hot injection route. The deposited copper sulfide thin films showed different morphologies based on spherical to flower or flakes-like crystallites depending on the temperature of deposition. Powder X-ray diffraction studies of the deposited films revealed formation of pure Covellite-hexagonal phase of copper sulfide, with high crystallinity at elevated temperature. The diffraction pattern of nanoparticles synthesized in dodecanthiol, and 1-octadecene at 150°C, 190°C and 230°C showed the formation of monodispersed nanoparticles of Cu1.78S Roxbyite phase with an average size of ca. 12±1nm. Interestingly, when oleylamine was used as a capping solvent, the formation of Covellite and Digenite phases were obtained at temperatures of 110°C and 190°C respectively. Electron microscopic studies showed formation of rod shaped particles at 110 and 150°C, whereas at higher temperatures formation of fairly spherical nanoparticles were observed.

Carbon sponge-type nanostructures based on coaxial nitrogen-doped multiwalled carbon nanotubes grown by CVD using benzylamine as precursor

Carbon sponges-type nanostructures (CSTN) based on coaxial nitrogen-doped multiwalled carbon nanotubes (CA-MWCNTs) were synthesized using the aerosol assisted chemical vapor deposition method involving the decomposition of a mixture of ferrocene, benzylamine, thiophene, and ethanol at 1020 °C under a flow of H2/Ar. Sample morphology and composition profiles were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA). SEM and TEM characterizations demonstrated that the CA-MWCNTs consisted of a core MWCNT surrounded by graphite materials with low crystallinity which was confirmed by XRD and Raman spectroscopy. Depending where the CSTN were collected along the reactor, three types of core MWCNTs morphologies were found: (1) N-doped MWCNTs with a bamboo shape and zigzagged growth, (2) straight MWCNTs, and (3) wavy MWCNTs. The carbon CSTN showed to be highly hydrophobic with outstanding oil absorption properties. XPS characterizations suggest the presence of water-fearing chemical groups such as ester- and ethoxy-groups anchored on the surface of the CA-MWCNTs. The mechanism in which the three types of MWCNTs are formed, the nature of the shell disordered graphite materials, and the hydrophobicity of the carbon sponges-type are thoroughly discussed.

Optical and optoelectronic properties of morphology and structure controlled ZnO, CdO and PbO thin films deposited by electric field directed aerosol assisted CVD

A simple and convenient electric field directed aerosol assisted chemical vapor deposition method is developed for the deposition of morphology and structure controlled thin films of ZnO, CdO and PbO with enhanced visible light photoelectrochemical activity. The films are generated from commonly available metal acetates solution in THF at 400 °C. The FESEM/EDX, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, UV–Vis spectrophotometry was carried out to investigate morphology, structure, stoichiometry and optical band gap of the fabricated films. The photelctrochemical properties investigated in the presence of 0.1 M Na2SO4 of the as-produced ZnO, CdO and PbO thin films show current densities of 207, 263, 237 and 1.55, 215, 1.67 µA cm−2 in light and dark respectively. These results show a slight improvement in photocurrent density of the films prepared under the influence of electric field as compared to the films deposited in the absence of electric field. This difference may have arisen due to compact structure and uniform morphology created under the influence of electric field.

Studies of thermal stability of a-C:H:Si coatings produced by radio-frequency plasma assisted chemical vapour deposition (RF-PACVD) method

Studies of thermal stability of a-C:H:Si coatings produced by radio-frequency plasma assisted chemical vapour deposition (RF-PACVD) method

The chemical composition and band gap of amorphous Si:C:N:H layers

In this work we presented the correlation between the chemical composition of amorphous Si:C:N:H layers of various content of silicon, carbon and nitrogen, and their band gap. The series of amorphous Si:C:N:H layers were obtained by plasma assisted chemical vapour deposition method in which plasma was generated by RF (13.56MHz, 300W) and MW (2.45GHz, 2kW) onto monocrystalline silicon Si(001) and borosilicate glass. Structural studies were based on FTIR transmission spectrum registered within wavenumbers 400–4000cm−1. The presence of SiC, SiN, CN, CN, CC,CN, SiH and CH bonds was shown. The values band gap of the layers have been determined from spectrophotometric and ellipsometric measurements. The respective values are contained in the range between 1.64eV – characteristic for typical semiconductor and 4.21eV – for good dielectric, depending on the chemical composition and atomic structure of the layers.

Electrochemical sensing of nitrite using a copper–titanium oxide composite derived from a hexanuclear complex

An electrochemical nitrite ions sensor electrode, CuO–2TiO2, has been developed using single molecular precursor [Cu2Ti4(O)2(OH)4(TF)8(THF)6]·THF in aerosol assisted chemical vapour deposition technique.

Aerosol assisted chemical vapor deposition (AACVD) of CdS thin films from heterocyclic cadmium(II) complexes

Cadmium dithiocarbamato complexes of piperidine (1) and tetrahydroquinoline (2) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, NMR and TGA analyses. The X-ray single crystal structure of bis(piperidinedithiocarbamato)cadmium(II) complex (1) was determined. The synthesized compounds were used as single source precursors to deposit CdS films on glass substrates at 350, 400 and 450°C using the aerosol assisted chemical vapor deposition (AACVD) method. The surface morphology and the size of the CdS films were determined by AFM and SEM analyses; the crystalline phases by p-XRD analyses and the elemental composition by EDX measurements. The particle sizes were found to be in the range between 50–110nm and 100–220nm for complex (1) and (2), respectively. The electronic properties of the CdS films were analyzed by UV–Vis and Raman spectroscopic methods. Results revealed that the morphology, size and composition of the films are influenced by the deposition temperature.

The Possibility of Deposition of Diamond and DLC Coatings by PACVD Method

The Diamond like carbon (DLC) and diamond coatings were deposited on a steel substrate using plasma assisted chemical vapor deposition (PA CVD) method. The parameters of deposition were analyzed in relation to the effectiveness of the process and the quality of coatings. It was found that the DLC coatings formed only at specific conditions of temperature and pressure of precursor gases. The characterization of coatings were performed by Raman spectromicroscopy, X-ray diffraction and infrared spectromicroscopy which allowed us to recognize the dominant phases and the distribution of bonds inside the coatings. The chemical bonds such as sp2 C-C, sp3 CH3/CH2 and sp3 CH were found in microstructure coatings. The maps of distribution of bonds in the coatings were also prepared. Additionally, their microstructure was investigated by scanning electron microscopes which have revealed a spherical grains morphology of the coatings.

Thermally activated band conduction and variable range hopping conduction in Cu2ZnSnS4 thin films

The temperature dependence of electrical conductivity of the Cu2ZnSnS4 (CZTS) thin films has been measured in order to identify the dominant conduction mechanism. These CZTS film have been deposited by ultrasonic assisted chemical vapor deposition method at different substrate temperatures in a single step process. All the films exhibit p-type semiconducting behaviour. In the high temperature range (> 250 K), the dominance of thermally activated band conduction is observed, whereas in the lower temperature region (250−70 K), the hopping conduction is present. Detailed analysis of the temperature dependence of conductivity of the films reveals that in the temperature range from 250–170 K, nearest neighbour hopping dominates, whereas in the lower temperature region (170–70 K), the dominant hopping conduction is Mott's 3D variable range hopping and not Efros-Shklovskii variable range hopping. The value of Mott's temperature is found to decrease for the CZTS films deposited at higher temperature, which has been attributed to enhanced density of states at the Fermi level.