Aerosol-assisted Chemical Vapor Deposition Research Articles

AACVD synthesized tungsten oxide-NWs loaded with osmium oxide as a gas sensor array: enhancing detection with PCA and ANNs.

This paper presents the fabrication of sensors based on tungsten trioxide nanowires decorated with osmium oxide nanoparticles using the aerosol-assisted chemical vapor deposition (AACVD) technique. This methodology allows the obtention of different osmium oxide decoration loadings on the tungsten oxide nanowires. The morphological and chemical characteristics; and the structural properties of the sensing layers of the sensors were studied using different techniques such as FESEM, HR-TEM, and ToF-SIMS. The gas sensing properties were analyzed for pure tungsten trioxide sensors and tungsten trioxide loaded with osmium exposed to nitrogen dioxide, hydrogen, and ethanol, thus assessing the impact of the loading on the sensor response. A sensor array comprising pure and osmium-loaded tungsten oxide devices coupled to multivariate pattern recognition techniques is shown to perform well in gas identification and quantification tasks, offering promising implications in the field of gas sensing technology.

A Novel Mechanism Based on Oxygen Vacancies to Describe Isobutylene and Ammonia Sensing of p-Type Cr2O3 and Ti-Doped Cr2O3 Thin Films

Gas sensors based on metal oxide semiconductors (MOS) have been widely used for the detection and monitoring of flammable and toxic gases. In this paper, p-type Cr2O3 and Ti-doped Cr2O3 (CTO) thin films were synthesized using an aerosol-assisted chemical vapor deposition (AACVD) method. Detailed analysis of the thin films deposited, including structural information, their elemental composition, oxidation state, and morphology, was investigated using XRD, Raman analysis, SEM, and XPS. All the gas sensors based on pristine Cr2O3 and CTO exhibited a reversible response and good sensitivity to isobutylene (C4H8) and ammonia (NH3) gases. Doping Ti into the Cr2O3 lattice improves the response of the CTO-based sensors to C4H8 and NH3. We describe a novel mechanism for the gas sensitivity of p-type metal oxides based on variations in the oxygen vacancy concentration.

In Situ Electrochemical Conversion of Biomass-Derived 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid by Time-Controlled Aerosol-Assisted Chemical Vapor Deposited FeNi Catalyst.

The conversion of 5-hydroxymethylfurfural (HMF) into valuable chemicals, such as 2,5-furandicarboxylic acid (FDCA), is pivotal for sustainable chemical production, offering a renewable pathway to biodegradable plastics and high-value organic compounds. This pioneering study explores the synthesis of FeNi nanostructures via aerosol-assisted chemical vapor deposition (AACVD) for the electrochemical oxidation of HMF to FDCA. By adjusting the deposition time, we developed two distinct nanostructures: FeNi-40, which features nanowires with spherical terminations, and FeNi-80, which features aggregated spherical structures. X-ray diffraction (XRD) confirmed that both nanostructures possess a phase-pure face-centered cubic (FCC) crystal structure. Electrochemical tests conducted using FeNi nanocatalysts on Ni foam revealed that FeNi-40 requires a significantly lower onset potential for HMF oxidation (1.32 V vs RHE) compared to FeNi-80 (1.40 V vs RHE). This difference is attributed to the unique nanowire morphology of FeNi-40, which provides a higher density of active sites and a larger electrochemically active surface area, thereby enhancing the efficiency of the electrochemical process. When tested in an H-type electrolyzer with a Nafion membrane, FeNi-40 demonstrated a remarkable Faradaic efficiency of 96.42% and a high product yield, underscoring the potential of morphology-controlled FeNi nanostructures to enhance the efficiency of sustainable electrochemical processes significantly.

Precursor Development and Aerosol-Assisted Chemical Vapour Deposition for BiVO4 and W-Doped BiVO4 Photoanodes: A Universal Ligand Approach.

Green hydrogen production is a key area of importance for advancing into a completely sustainable world, not only for its use in industry and ammonia production, but also for its potential as a new fuel. One promising method for generating green hydrogen is light-driven water splitting using photoelectrodes. Here, a bismuth vanadate (BiVO4) photoanode deposition process was developed using new, bespoke dual-source precursors, tailored for use in aerosol-assisted chemical vapour deposition (AACVD). The resulting thin films were highly nanostructured and consisted of phase-pure monoclinic BiVO4. Pristine films under 1 sun solar irradiation yielded photocurrent densities of 1.23 mA cm-2 at 1.23 V vs RHE and a peak incident photon-electron conversion efficiency (IPCE) of 82 % at 674 nm, the highest performance of any CVD-grown BiVO4 film to date. A new, AACVD-compatible WO3 precursor was subsequently designed and synthesised for the deposition of W-doped BiVO4 within the same single deposition step.

Room-temperature NH3 sensor with ppb detection via AACVD of nanosphere WO3 on IO SnO2

The room temperature gas sensor has attracted sufficient attention due to the fact that low-power products are more suitable for practical environments. However, developing gas sensors with low detection limits remains challenging. In this paper, a room-temperature sensor was prepared by in situ growth of WO3 nanospheres on SnO2 inverse opal (IO) by aerosol assisted chemical vapor deposition (AACVD) method, detecting ppb level of ammonia. The WO3 nanospheres are directly fabricated on IO, and their elemental composition, morphology and structure is characterized using XRD, SEM and TEM. The results show that WO3 nanospheres have been prepared on SnO2 IO successfully. It showes that the WO3/SnO2(WS) type sensor has a detection limit as low as 1 ppb at room temperature from the gas sensitivity data. In addition, the sensor's response value to 100 ppm NH3 reached 65 %. Its excellent sensing performance depends on the distinctive morphology features of WO3 and SnO2. The hierarchical characteristic effectively enhances the sensing performance for NH3. Consequently, this presents a feasible solution for fabricating the room temperature NH3 sensor.

Surface engineering of CuO-Cu2O heterojunction thin films for improved photoelectrochemical water splitting

The efficient production of green hydrogen poses a significant challenge that requires the development of active, low-cost, and stable catalysts. Copper oxide has emerged as a highly effective photocatalyst for water splitting, offering the advantages of being nontoxic, abundant, and inexpensive. Nonetheless, the photoelectrochemical water splitting (PEC) process can be enhanced through surface modification. In this study, we utilized single-source precursors for aerosol-assisted chemical vapor deposition (AACVD) in order to deposit thin films of copper oxide (CuO-Cu2O) heterojunctions onto a substrate composed of fluorine-doped tin oxide (FTO). The chosen precursor for this purpose was copper (II) nitrate hemi(pentahydrate). To further optimize the CuO-Cu2O films, a novel acid treatment involving the addition of varying quantities of acetic acid (AA) to the precursor solution was employed. Remarkably, this acid treatment resulted in a significant improvement in the photocurrent density of the CuO-Cu2O heterojunction. Notably, a 3 mL acid-treated CuO-Cu2O thin film exhibited an impressive photocurrent measure of −6.8 mA/cm2 at 0.0 V vs RHE in 0.5 M Na2SO4 electrolyte, compared to the performance of the untreated CuO-Cu2O thin film (−2.8 mA/cm2 at 0.0 V vs RHE). This catalyst demonstrated stability and a threefold increase in hydrogen production performance. The increase in photocurrent densities is closely linked to the influence of AA on two key factors: particle growth and structural defects, such as oxygen vacancies. This relationship has been confirmed through the examination of SEM, AFM, and PL spectra results. The findings of this study not only offer a novel approach to catalyst design but also propose a practical method for photoelectrochemical water splitting. This method holds great promise for achieving sustainable and renewable energy sources, as well as efficient green hydrogen production.

Synergistic Approach of TiO2@MnZnO3 Heterostructure for Efficient Photoelectrochemical Water Splitting

The superior kinetics of charge carriers and greater visible light absorption are important factors for enhancing photoelectrochemical performance. Herein, the core–shell heterostructure has been developed by encapsulating single-phase MnZnO3 over TiO2 nanotubes by aerosol-assisted chemical vapor deposition approach. The fabricated photoanodes have been characterized by employing various techniques including X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, and photoluminescence. Moreover, the mechanism for electron/hole transfer has been focused by a brief electrochemical investigation. The bilayer 1D/2D TiO2@MnZnO3 photoanode exhibited higher current density (2 mA cm−2) as compared to pristine TiO2-nanotubes (0.174 mA cm−2) at 1.52 V vs RHE. The superior photoactivity of heterostructure is attributed to the rapid transfer of photogenerated charge carriers via the Type-II mechanism. Furthermore, the reduced band gap (2.05 eV) accounts for good absorption in the visible region of light, while the interfacial electric field allowed the improved charge separation. The synergistic strategy in the present work demonstrates the promising significance of a heterojunction interface to optimize photovoltaic devices.

An Aerosol-Assisted Chemical Vapor Deposition Route to Tin-Doped Gallium Oxide Thin Films with Optoelectronic Properties.

Gallium oxide is a wide-bandgap compound semiconductor material renowned for its diverse applications spanning gas sensors, liquid crystal displays, transparent electrodes, and ultraviolet detectors. This paper details the aerosol assisted chemical vapor deposition synthesis of tin doped gallium oxide thin films using gallium acetylacetonate and monobutyltin trichloride dissolved in methanol. It was observed that Sn doping resulted in a reduction in the transmittance of Ga2O3 films within the visible spectrum, while preserving the wide bandgap characteristics of 4.8 eV. Furthermore, Hall effect testing revealed a substantial decrease in the resistivity of Sn-doped Ga2O3 films, reducing it from 4.2 × 106 Ω cm to 2 × 105 Ω cm for the 2.5 at. % Sn:Ga2O3 compared to the nominally undoped Ga2O3.

Tbx-Zn1-x-BDC MOF films synthesized in-situ by the aero-sol-assisted chemical vapor deposition

Tbx-Zn1-x-BDC MOF films were deposited in situ on glass substrates using the aerosol-assisted chemical vapor deposition (AACVD) technique with an ultrasonic spray pyrolysis system, with x ranging from 0 to 1. Various precursors and solvents were used in the precursor solutions, which were precisely nebulized onto the substrate. The resulting films were characterized using techniques such as x-ray diffraction, Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), and Photoluminescence Spectroscopy. The findings revealed the evolution of Zn-BDC and/or Tb-BDC crystalline structures within the films and changes in the physical properties of the Metal Organic Frameworks (MOFs), such as film thickness and roughness. Moreover, these insights offer vital information for the design and control of MOF films with specific properties, highlighting their potential applications in various fields.

Substrate-induced strain in molybdenum disulfide grown by aerosol-assisted chemical vapor deposition

Transition metal dichalcogenides have been extensively studied in recent years because of their fascinating optical, electrical, and catalytic properties. However, low-cost, scalable production remains a challenge. Aerosol-assisted chemical vapor deposition (AACVD) provides a new method for scalable thin film growth. In this study, we demonstrate the growth of molybdenum disulfide (MoS2) thin films using AACVD method. This method proves its suitability for low-temperature growth of MoS2 thin films on various substrates, such as glass, silicon dioxide, quartz, silicon, hexagonal boron nitride, and highly ordered pyrolytic graphite. The as-grown MoS2 shows evidence of substrate-induced strain. The type of strain and the morphology of the as-grown MoS2 highly depend on the growth substrate’s surface roughness, crystallinity, and chemical reactivity. Moreover, the as-grown MoS2 shows the presence of both direct and indirect band gaps, suitable for exploitation in future electronics and optoelectronics.

Substrate controlled hydrophobicity of the Y2O3 films

The development of hydrophobic surfaces is an important factor for clean energy production from solar arrays, enabling their operation at the highest possible efficiencies for the longest possible time, without the need for physical intervention. This work reports the development of hydrophobic Y2O3 thin films on a range of transparent glass substrates. The growth of the Y2O3 films from the mono-hydrate yttrium (III) complex of 1,3-diphenyl-1,3-propanedione [Y(dbm)3(H2O)] is studied using the aerosol-assisted chemical vapor deposition (AACVD) technique. The qualitative evaluation of the deposited films and their hydrophobicity is assessed using several materials characterization techniques, such as scanning electron microscopy, grazing incident X-ray diffraction, Fourier-transform infrared, X-Ray photoelectron spectroscopy, in addition to a surface free energy and water contact angle measurements. This work demonstrates experimentally a relationship between the Y2O3 wettability and its physico-chemical characteristics in terms of surface energy, chemical composition, and morphology which is controlled by the type of glass support used. The water contact angle of the hydrophobic Y2O3 coating grown on the F-doped tin oxide glass reached 128°; currently the first deposited on transparent glass. This film exhibits the highest WCA reported up to date without the need for performing post-reaction surface treatment processes. The hydrophobic nature of the transparent Y2O3 films marks a significant leap forward in the field of anti-soiling coatings suitable for photovoltaic technology.

Synergistic engineering of palladium-cobalt nanoalloys on graphite sheet for efficient and sustainable hydrogen evolution reaction

The electrochemical hydrogen evolution reaction (HER)—a carbon-free route for hydrogen (H2) production—is of the utmost importance for H2-economy. Currently, HER performance is mainly restricted by the lack of promising alternatives to Pt-based electrocatalysts. In this study, we developed bimetallic PdCo alloy thin films with outstanding catalytic properties for the HER under acidic conditions. A simple aerosol-assisted chemical vapor deposition technique designed in-house was used to produce bimetallic alloy thin films on graphite sheets. The thin-film morphological patterns were significantly changed by varying the deposition time from 30 to 90 min. The optimized PdCo catalyst deposited for 30 min had a unique nanostructure with numerous active sites and exhibited faster HER kinetics than its analogs and pure Pd. As-prepared PdCo-30 electrode produced current densities of 10 and 1000 mA cm−2 at overpotentials of 41 and 161 mV, respectively, along with a Tafel slope of 42 mV/dec, high conductivity (0.28 Ω), and catalytic stability of ∼24 h in 0.5 M H2SO4. The excellent HER activity of the PdCo alloy was attributed to the synergy between the noble transition metal and the thin nanostructured layer of the bimetallic catalyst, which promoted formation of extensive electroactive sites on the conductive graphite surface. Density functional theory calculations confirmed the experimental findings. The Gibbs free energy (ΔGH*) of the PdCo alloy (−0.43 eV) was significantly lower than that of pure Pd (−0.57 eV), confirming the enhancement in HER activity due to the introduction of Co into the Pd lattice.

Graphite sheet-supported bimetallic RhNi thin film alloys for enhanced and durable hydrogen evolution in acidic environments

Noble metal-based materials are excellent catalysts for hydrogen production from water electrolysis, but their high cost and limited availability hinder widespread use. However, precious metals can be effectively utilized in catalysts by forming alloys with low-cost 3d transition metals, thereby reducing the need for precious metals, while enhancing the performance. In this study, aerosol-assisted chemical vapor deposition was employed to deposit bimetallic rhodium-nickel (RhNi) alloy thin films on a graphite sheet for hydrogen evolution reaction (HER) catalysis in a 0.5 M H2SO4 solution. Thin-film morphological patterns were significantly changed as the deposition time varied from 45 to 135 min. The RhNi alloy fabricated for 90 min outperformed its counterparts, displaying lower overpotential of 40 and 197 mV at 10 and 1000 mA cm−2, small Tafel kinetics (54 mV dec−1), high conductivity (0.57 Ω) and large electrochemical surface area (3312 cm2), and extended stability (48 h) compared to pure Rh metal and other reported catalysts. The superior HER performance arises from the synergistic effects between Rh and Ni metals, coupled with a uniform layer of spherical particles that enhance conductive properties and reaction rates by providing maximized active sites on graphite surface. This work provides valuable guidelines for efficiently preparing highly active and durable thin-film electrocatalyst within short time span and applying directly in fuel cell for hydrogen production.

Transparent Conductive Titanium and Fluorine Co-doped Zinc Oxide Films.

Aerosol-assisted chemical vapor deposition (AACVD) was used to deposit highly transparent and conductive titanium or fluorine-doped and titanium-fluorine co-doped ZnO thin films on glass substrate at 450 °C. All films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-Vis spectroscopy, scanning electron spectroscopy (SEM), and four-point probe. The films were 600-680 nm thick, crystalline, and highly transparent (80-87 %). The co-doped film consisted of 0.70 at % titanium and 1 at % fluorine, and displayed a charger carrier mobility, charge carrier concentration, and a minimum resistivity of 8.4 cm2 V-1 s-1, 3.97×1020 cm-3, and 1.69×10-3 Ω cm, respectively. A band gap of 3.6 eV was observed for the co-doped film. Compared to the undoped and singly doped films, the co-doped film displayed a notably higher structure morphology (more homogenous grains with well-defined boundaries) suitable for transparent conducting oxide applications.

In-situ fabrication of self-supported cobalt molybdenum sulphide on carbon paper for bifunctional water electrocatalysis

The fabrication of highly efficient yet stable noble-metal-free bifunctional electrocatalysts that can simultaneously catalyse both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remains challenging. Herein, we employ the heterostructure coupling strategy, showcasing an aerosol-assisted chemical vapour deposition (AACVD) aided synthetic approach for the in-situ growth of cobalt molybdenum sulphide nanocomposites on carbon paper (CoMoS@CP) as a bifunctional electrocatalyst. The AACVD allows the rational incorporation of Co in the Mo–S binary structure, which modulates the morphology of CoMoS@CP, resulting in enhanced HER activity (ŋ10 = 171 mV in acidic and ŋ10 = 177 mV in alkaline conditions). Furthermore, the CoS2 species in the CoMoS@CP ternary structure extends the OER capability, yielding an ŋ100 of 455 mV in 1 M KOH. Lastly, we found that the synergistic effect of the Co–Mo–S interface elevates the bifunctional performance beyond binary counterparts, achieving a low cell voltage (1.70 V at 10 mA cm−2) in overall water splitting test and outstanding catalytic stability (∼90 % performance retention after 50-/30-h continuous operation at 10 and 100 mA cm−2, respectively). This work has opened up a new methodology for the controllable synthesis of self-supported transition metal-based electrocatalysts for applications in overall water splitting.

Aerosol assisted-chemical vapour deposition of tetrahedrite copper antimony sulphide thin films: the effect of zinc(II) impurities on optical properties

Non-stoichiometric semiconducting copper antimony sulphide (CAS) thin films, both undoped and with Zn2+ ions incorporated, were deposited at 500, 550 and 600 °C onto glass substrates by aerosol-assisted chemical vapour deposition (AACVD) using metal diethyldithiocarbamate precursors. Data from powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electron microscopy – energy dispersive X-ray spectroscopy suggest a correlation of composition of the non-stoichiometric sulphur-deficient tetrahedrite phase (cubic structure) microcrystalline CAS (Cu12Sb4S13) thin films with particle sizes ranging from 0.1 to 4 µm. For undoped thin films, visible optical absorption with a bandgap of ∼2.1 eV is likely associated with compositional variations involving intrinsic lattice defects, including shallow electronic states such as copper interstitials and vacancies of sulphur as deep-lying donors, and copper-antimony anti-sites and antimony vacancies as deep-lying acceptors. Additionally, tetrahedrite phase CAS (tCAS) thin films with Zn2+ ions incorporated (Znx-tCAS) exhibit tunable composition-driven electronic structure for small Zn2+ content influencing narrower bandgaps between 1.7 and 1.9 eV. The Raman data suggest that the phase purity is affected by small fractions of the famatinite (tetragonal) phase. Overall, the thin films display broad emission of fast dual radiative recombination, and an additional recombination pathway exhibited for Znx-tCAS associated with zinc-related point defects. Though further studies are required to explore in more detail the defect chemistry, these results show the utility of AACVD in tuning compositional and optical properties of undoped tCAS and Znx-tCAS thin films.

Exceptional Thermoelectric Performance of Cu2(Zn,Fe,Cd)SnS4 Thin Films.

High-quality Cu2(Zn,Fe,Cd)SnS4 (CZFCTS) thin films based on the parent CZTS were prepared by aerosol-assisted chemical vapor deposition (AACVD). Substitution of Zn by Fe and Cd significantly improved the electrical transport properties, and monophasic CZFCTS thin films exhibited a maximum power factor (PF) of ∼0.22 μW cm-1 K-2 at 575 K. The quality and performance of the CZFCTS thin films were further improved by postdeposition annealing. CZFCTS thin films annealed for 24 h showed a significantly enhanced maximum PF of ∼2.4 μW cm-1 K-2 at 575 K. This is higher than all reported values for single-phase quaternary sulfide (Cu2BSnS4, B = Mn, Fe, Co, Ni) thin films and even exceeds the PF for most polycrystalline bulk materials of these sulfides. Density functional theory (DFT) calculations were performed to understand the impact of Cd and Fe substitution on the electronic properties of CZTS. It was predicted that CZFCTS would have a smaller band gap than CZTS and a higher density of states (DoS) near the Fermi level. The thermal conductivity and thermoelectric figure of merit (zT) of the CZFCTS thin films have been evaluated, yielding an estimated maximum zT range of 0.18-0.69 at 550 K. The simple processing route and improved thermoelectric performance make CZFCTS thin films extremely promising for thermoelectric energy generation.

Aerosol assisted chemical vapor deposition routes for the selective formation of gas sensitive iron oxide structures

Iron oxide (Fe2O3) structures with various morphologies are synthesized by aerosol-assisted chemical vapor deposition (AACVD) method. The structures are formed reproducibly by tuning different AACVD synthesis parameters, including temperatures, solvents, and samples' position in the reaction chamber. The properties of these structures are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Results demonstrate the formation of six types of crystalline Fe2O3 structures - flattened pyramids (fPy), pyramids (Py), porous pyramids (pPy), sheets (Sh), bricks (Br), and quasi-spherical particles (qsP). The formation of these structures is mainly connected with the use of acetone or acetone/ethanol mixture as solvents and their effect on boosting the influence of the temperature or sample’s position, respectively, on the properties of the structures. The gas sensing tests of the structures with higher aspect ratios or porosity (pPy, Py, fPy, and Sh) showed responses to various gases (acetone, ethanol, toluene, carbon monoxide, hydrogen, methane, ammonia, and nitrous oxide), reporting maximum sensitivity and selectivity to acetone and ethanol. The best results recorded are for the porous pyramids which show sensitivities of 5.1 % ppm−1 and 3.9 % ppm−1 (in the range of 10–40 ppm) to acetone and ethanol, respectively.

Aerosol-Assisted Chemical Vapor Deposition of 2H-WS2 From Single-Source Tungsten Dithiolene Precursors.

The tungsten carbonyl dimethyldithiolene (dmdt) complexes W(CO)4(dmdt), W(CO)2(dmdt)2, and W(dmdt)3 were evaluated as potential single-source precursors for the chemical vapor deposition of WS2. The results of TGA-MS, DIP-MS, and pyrolysis with NMR analysis were consistent with a thermal decomposition pathway in which loss of 2-butyne through a retro[3+2]cycloaddition of the dithiolene ligand generated terminal sulfido ligands. Aerosol-assisted chemical vapor deposition onto silicon substrates was performed using all three complexes, yielding 2H-WS2 thin films as characterized by Raman spectroscopy and GI-XRD. Film morphology and elemental composition of the films were determined using SEM, EDS, and XPS. Four-point probe measurements afforded a film resistivity of 8.37 Ωcm for a sample deposited from W(dmdt)3 in toluene at 600 °C.

The aerosol-assisted chemical vapour deposition of Mo-doped BiVO4 photoanodes for solar water splitting: an experimental and computational study

A series of Mo-doped BiVO4 photoanodes are studied using experimental and DFT methods. Mo doping replaces V sites, increasing electronic conductivity and improving solar water splitting performance.