Molybdenum Trioxide Thin Films Research Articles

A Simple Process for Synthesis of Transparent Thin Films of Molybdenum Trioxide in the Orthorhombic Phase (α-MoO3)

Transparent orthorhombic molybdenum trioxide (α-MoO3) thin films were prepared on glass substrates by sol–gel dip coating technique of a quality comparable to those prepared by more sophisticated techniques regarded as very costly and difficult to carry out. The prepared films were annealed in air at different temperatures in the range of 150–350°C. X-ray diffraction analysis of the films prepared at 250°C and 350°C confirmed the formation of a single-phase of MoO3 in an orthorhombic crystal system (α-MoO3). Scanning electron microscopy of the films annealed at 350°C indicated a stack of nano-layers with thickness of approximately 30 nm–40 nm. Fourier transform infrared transmittance analysis revealed the Mo=O stretching vibration, which is an indicator of the layered orthorhombic MoO3 phase. Energy dispersive x-ray analysis confirmed the existence of Mo and O in the deposited films. A maximum optical transmittance of 82% in the visible range was obtained from the films annealed at 350°C. The band gap value of the films was evaluated and it was in the range of 3.28 eV–3.40 eV. The obtained results showed that the α-MoO3 thin films prepared at 350°C exhibit good structural, chemical, and optical properties, which might be of interest to the photovoltaic and optoelectronic devices.

Molybdenum trioxide thin film recombination barrier layers for dye sensitized solar cells

MoO3 thin film recombination barrier layer suppresses electron–hole recombination at the FTO–TiO2 interface and facilitates charge transport.

Characterization of WMoO3 Thin Films and its n-WMoO3/p-Si Junction Diodes Via JNS Pyrolysis Technique

Abstract The jet nebulizer sprayed tungsten doped molybdenum trioxide (WMoO3) thin films and its P-N junction diode parameters have been studied for different doping concentrations (0, 3, 6 and 9 wt.%) of tungsten (W). The prepared films were studied by XRD, SEM, EDX, UV and I-V. The structural analyses of XRD and SEM revealed that the WMoO3 films depicted the orthorhombic structure in polycrystalline nature and showed the sub-microsized plate and flake-like structures on the surface. The presence of the elements such as W, Mo and O in the WMoO3 films prepared by jet nebulizer spray (JNS) pyrolysis technique was confirmed by the EDX spectra. From UV-vis analysis, the absorbance decreases up to 3 wt.% of WMoO3 then increases. 3 wt.% WMoO3 film exhibited the minimum band gap energy. The electrical property from I-V represents that the maximum average conductivity obtained as 5.70169×10−12 S/cm for 3 wt.% WMoO3 film. From the I-V measurements in darkness and under the illumination, the different diode parameters of ideality factor (n), barrier height (Φb) and sheet resistance (Rs) of n-WMoO3/p-Si were examined using J-V, Cheung’s and Norde methods.

Highly selective and sensitive response of 30.5 % of sprayed molybdenum trioxide (MoO3) nanobelts for nitrogen dioxide (NO2) gas detection

The molybdenum trioxide (MoO3) thin films have been successfully deposited onto the glass substrates using chemical spray pyrolysis (CSP) deposition technique at various substrate temperatures ranging from 300°C to 450°C with an interval of 50°C. The effect of substrate temperature on the structural, morphological, optical and gas sensing properties of MoO3 thin films has been thoroughly investigated. X-ray diffraction analysis reveals that all the films have an orthorhombic crystal structure and are polycrystalline in nature. FE-SEM micrographs depict the formation of nanobelts-like morphology. AFM study reveals that the RMS surface roughness of MoO3 thin films increases from 8.6nm to 12nm with increase in substrate temperature from 300°C to 400°C and then decreases to 11.5nm for substrate temperature of 450°C. Optical results show that the band gap of MoO3 thin films decreases from 3.92eV to 3.44eV. The selectivity studies show that the gas response of various gases varies as NH3<SO2<CO2<CO<H2S<NO2. Moreover, typical MoO3 film deposited at substrate temperature of 400°C is highly selective and sensitive for detection of NO2 gas in comparison with other gases. The maximum response of 30.5 % is obtained towards 100ppm NO2 gas concentration at an operating temperature of 200°C with response and recovery times of 20s and 160s, respectively. Finally, NO2 gas sensing mechanism model based on the chemisorption process is discussed.

Structural, optical and electrical properties of Ru doped MoO3 thin films and its P–N diode application by JNS pyrolysis technique

We report that the jet nebulizer spray coating is a promising route to acquire ruthenium doped molybdenum trioxide (RuMoO3) thin films for the P–N diode application at 500 °C. The influence of Ru doping (0, 3, 6 and 9 wt%) on structural, optical, dc electrical conductivity and diode properties of MoO3 was measured by various techniques. From the X-ray diffraction analysis, the films were polycrystalline with an orthorhombic structure of MoO3. The scanning electron microscope images displayed the dissimilarities of the sub-microsized plate-like structure. The elements of Ru, Mo and O presence were confirmed by the energy dispersive X-ray spectroscopy analysis. From the ultraviolet–visible analysis and current–voltage (I–V) characterization, 6 % Ru doped MoO3 film exhibited minimum absorbance in the visible region and maximum conductivity. The diode measurements were taken in darkness and under halogen light source. To calculate the diode parameter values of ideality factor (n), barrier height (Φb) and sheet resistance (Rs), we have used different methods of I–V, Cheung’s and Norde.

Morphological and optical evolution of different organic acids used MoO3 thin films by spin coating method

Molybdenum trioxide (MoO3) thin films were prepared at room temperature (RT) and at different annealing temperatures of 250, 350, 450 and 550°C. We also prepared MoO3 films using additives of water-soluble and water-insoluble organic acids. The thin films were coated using the spin coating technique and annealed at 350°C temperature. The effects of different annealing temperatures and different organic acid additives on MoO3 films were characterized by structural and optical studies. From the XRD pattern, the structure of the MoO3 films is found to vary with respect to increase in the annealing temperature. For RT and 250°C, the hexagonal structure was observed and for 350, 450 and 550°C, the orthorhombic structure was observed. The XRD pattern for all the organic acid additive used MoO3 films exposed the orthorhombic structure. SEM images show hasty variations in the surface morphology for different annealed MoO3 films and different additive used MoO3 films. The EDX analysis confirmed the presence of Mo and O elements for all the films. The UV–vis results show the absorbance and transmittance values. The band gap energy was found to be around 3.8eV for all the MoO3 films.

MOLYBDENUM TRIOXIDE THIN FILMS DOPED WITH GOLD NANOPARTICLES GROWN BY A SEQUENTIAL METHODOLOGY: PHOTOCHEMICAL METAL-ORGANIC DEPOSITION (PMOD) AND DC-MAGNETRON SPUTTERING

Gold nanoparticles (AuNPs) were deposited by DC-magnetron sputtering onto molybdenum trioxide (MoO3) thin films grown by Photochemical Metal- Organic Deposition (PMOD) on Si(100) and borosilicate glass substrates. The chemical, optical and morphology properties of the films were studied by UV/ Vis Spectroscopy, Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and X-Ray Diffraction (XRD). SEM revealed that AuNPs formed after 5 s of sputtering. AuNPs are spherical and have both an average diameter of 18 nm and a relatively narrow size distribution. As the deposition time increases, larger structures are formed by an aggregation of AuNPs. XPS studies of the AuNP/MoO3 films on Si(100) showed the presence of Mo(VI) and Mo(V), which indicated that the films were primarily non-stoichiometric molybdenum oxides. The occurrence of oxygen vacancies in the substrate play an important role to stabilize the AuNPs.

Role of substrate temperature on MoO3 thin films by the JNS pyrolysis technique for P–N junction diode application

Molybdenum trioxide (MoO3) thin films were prepared at different substrate temperatures from 350 to 500°C by the jet nebulizer spray (JNS) pyrolysis technique. The effect of the substrate temperature on the structural, optical and electrical properties of MoO3 films was characterized. The XRD pattern exposed that the crystallite size of the films increases with the increase in the substrate temperature. The SEM images showed the conversion of nanorods to sub-microsized plate-like structures by increasing the substrate temperature. The EDX analysis confirmed the presence of Mo and O elements. The UV–vis results revealed that the band gap obtained shows a decreasing trend on increasing the substrate temperature. The FTIR spectra confirmed the formation of MoO3. The dc electrical studies portrayed the minimum activation energy of 0.064eV obtained for higher substrate temperature. The P–N diode of p-Si/n-MoO3 was fabricated at the substrate temperature of 500°C. The diode parameters such as ideality factor (n), barrier height (Φb) and reverse saturation current (I0) values were calculated in darkness and under different light sources (Halogen and Metal halide lamps).

EFFECT OF ANNEALING TEMPERATURE ON STRUCTURAL AND OPTICAL PARAMETERS OF SOL–GEL ROUTED MOLYBDENUM OXIDE THIN FILM

The influence of annealing temperature on structural and optical properties of sol–gel routed spin-coated molybdenum tri oxide ( MoO 3) thin films are studied. The higher annealing temperatures improve the crystalline nature of the film. The X-ray diffraction (XRD) study reveals the formation of α-orthorhombic phase at higher annealing temperature and amorphous nature at lower annealing temperature. The optical bandgap of molybdenum tri oxide ( MoO 3) film is found to be 3.3–3.8 eV, and the refractive index of the film is found to be 2.2–2.9. The dispersion curve of the refractive index shows that an abnormal dispersion in the absorption region and normal dispersion in the transparent region are observed. The optical polarizability, optical conductivity, dielectric constant, volume and surface energy loss parameters are evaluated.

Electrosprayed molybdenum trioxide aqueous solution and its application in organic photovoltaic cells.

A molybdenum trioxide thin film with smooth surface and uniform thickness was successfully achieved by an electrospray deposition method using an aqueous solution with a drastically low concentration of 0.05 wt%. Previous papers demonstrated that an additive solvent technique is useful for depositing the thin film by the electrospray deposition, and the high vapor pressure and a low surface tension of an additive solvent were found to be important factors. As a result, the smooth molybdenum trioxide thin film was obtained when the acetonitrile was used as the additive solvent. Furthermore, the vapor pressure of acetone is much higher than that of aqueous solution, and this indicates that the acetone is easily evaporated after spraying from the glass capillary. By optimizing a concentration of acetone in the molybdenum aqueous solution, a minimum root mean square roughness of the MoO3 thin film became 3.7 nm. In addition, an organic photovoltaic cell was also demonstrated using the molybdenum trioxide as a hole transport layer. Highest photoconversion efficiency was 1.72%, a value comparable to that using conventional thermal evaporation process even though the aqueous solution was used for the solution process. The photovonversion efficiency was not an optimized value, and the higher value can be achieved by optimizing the coating condition of the active layer.

Superior Properties of Homogeneously Aligned Twisted Nematic Liquid Crystals on Nanoscale Molybdenum Trioxide Surfaces

Homogeneously aligned twisted nematic liquid crystals (TN-LCs) were produced on molybdenum trioxide (MoO3) thin films via ion beam (IB) irradiation. Control of the pretilt angle was achieved by varying the IB incident angle. X-ray photoelectron spectroscopy (XPS) analysis revealed that the intensity of the Mo-O and O-Mo bonds at various IB incident angles exhibited the tendency that was opposite to that of the pretilt angle and the lowest intensity was produced at 45°. Superior electro-optical (EO) characteristics were also observed. Furthermore, a TN-LC cell fabricated with the MoO3 thin films exhibited high thermal stability. Such stability could be maintained at temperatures greater than 150 °C.

Physical investigations on MoO3 sprayed thin film for selective sensitivity applications

Molybdenum trioxide (MoO3) thin films have been prepared by the spray pyrolysis technique on glass substrates at 460°C using (NH4)6Mo7O24·4H2O (ACROS pure more than 99.0%) as precursor in the starting solution. X-ray analysis shows that MoO3 thin film crystallizes in orthorhombic structure with a preferred orientation of the crystallites along (020) and (040) directions. The surface topography of these films was performed by atomic force microscopy and the optical properties were investigated through reflectance and transmittance measurements. The optical band gap energy value is about 3.46eV and the Urbach energy is of the order of 191meV. Raman spectroscopy shows the bands׳ positions corresponding to α-MoO3 phase. PL measurements show two large bands located at 375nm and 575nm respectively. Finally, the electric conductivity of MoO3 thin film was investigated using impedance spectroscopy technique in the frequency range 5Hz–13MHz at various temperatures (300–500°C). The variation of the conductivity in terms of the temperature is characterized by the existence of two ranges with activation energy of 1.00, and 0.42eV. AC conductivity of MoO3 thin films is investigated through Jonsher law.

Nanostructured α-MoO3 thin film as a highly selective TMA sensor

Molybdenum trioxide thin films of different thicknesses were prepared on a glass substrate with the chemical spray pyrolysis technique. The X-ray diffraction pattern indicates the formation of an α-MoO3 phase with a polycrystalline nature. The field-emission scanning electron micrograph of the surface indicates nanostructured lamellar crystallites. The trimethylamine vapour sensing property of the film was studied by the chemiresistive method at room temperature (≈30°C). Film with a thickness of 520nm shows a response of 12% for 0.5ppm of TMA vapour in 54% relative humidity, with response and recovery times of 32s and 15s, respectively. The detection limit and sensing response of the α-MoO3 thin film in a mixed environment were analysed and reported.

Tandem organic light-emitting diode with a molybdenum tri-oxide thin film interconnector layer

A 10-nm-thick molybdenum tri-oxide (MoO3) thin film was used as the interconnector layer in tandem organic light-emitting devices (OLEDs). The tandem OLEDs with two identical emissive units consisting of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB)/tris(8-hydroxyquinoline) aluminum (Alq3) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices. At 20 mA/cm2, the current efficiency of the tandem OLEDs using the interconnector layers of MoO3 thin film was about 4.0 cd/A, which is about twice that of the corresponding conventional single-unit device (1.8 cd/A). The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200 cd/m2. The experimental results demonstrated that a MoO3 thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs. Such an interconnector layer can be easily fabricated by simple thermal evaporation, greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers. A possible explanation was proposed for the carrier generation of the MoO3 interconnector layer.

Preparation and optical properties of hexagonal and orthorhombic molybdenum trioxide thin films

h-MoO3 and α-MoO3 films were successfully fabricated on glass substrates by two ways: ion exchange and chemical deposition. The as-synthesized products were characterized through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optical properties of MoO3 films were investigated in detail. The result showed that h-MoO3 film possesses two fluorescence emission peaks at 440 and 630nm, but α-MoO3 film just possesses one at 440nm. The emission peak at 440nm might come from the band-to-band transition of MoO3, and the emission peak at 630nm probably originated from the presence of oxygen vacancies in h-MoO3 film. The photochromic behavior of the as-prepared films was also observed, in which h-MoO3 film exhibited higher photochromic response than α-MoO3 film. It was related to some defects of oxygen vacancies in the especial h-MoO3 structure.

Effect of the substrate temperature on the physical properties of molybdenum tri-oxide thin films obtained through the spray pyrolysis technique

Abstract Polycrystalline molybdenum tri-oxide thin films were prepared using the spray pyrolysis technique; a 0.1 M solution of ammonium molybdate tetra-hydrated was used as a precursor. The samples were prepared on Corning glass substrates maintained at temperatures ranging between 423 and 673 K. The samples were characterized through micro Raman, X-ray diffraction, optical transmittance and DC electrical conductivity. The species MoO 3 (H 2 O) 2 was found in the sample prepared at a substrate temperature of 423 K. As the substrate temperature rises, the water disappears and the samples crystallize into α-MoO 3 . The optical gap diminishes as the substrate temperature rises. Two electrical transport mechanisms were found: hopping under 200 K and intrinsic conduction over 200 K. The MoO 3 films' sensitivity was analyzed for CO and H 2 O in the temperature range 160 to 360 K; the results indicate that CO and H 2 O have a reduction character. In all cases, it was found that the sensitivity to CO is lower than that to H 2 O.

Electrical measurement of non-destructively p-type doped graphene using molybdenum trioxide

We demonstrate effective non-destructive p-type doping of graphene via surface modification with molybdenum trioxide (MoO3) thin film using electrical transport measurements. The p-type doping via MoO3 modification of graphene leads to the downward shift of Fermi level towards the valence band. MoO3 modified graphene retains its high charge carrier mobility, facilitating the observation of quantum Hall effect. In-situ ultraviolet photoelectron spectroscopy studies also show that air exposure of MoO3 modified graphene reduces the doping efficiency.

Soft X-ray Spectroscopy of C60/Copper Phthalocyanine/MoO3 Interfaces: Role of Reduced MoO3 on Energetic Band Alignment and Improved Performance

The interfacial electronic structure of C-60/copper phthalocyanine (CuPc)/molybdenum trioxide (MoO3) thin films grown in situ on indium tin oxide (ITO) substrates has been studied using synchrotron radiation-excited photoelectron spectroscopy in an attempt to understand the influence of oxide interlayers on the performance of small molecule organic photovoltaic devices. The MoO3 layer on ITO is found to significantly increase the work function of the substrate and induces large interface dipoles and band bending at the CuPc/MoO3 interface. The large band bending confirms the formation of an internal potential that assists hole extraction from the CuPc layer to the electrode. The electronic structure of the MoO3 layer on ITO was also examined using various soft X-ray spectroscopies to probe the conductive nature of the MoO3 thin film.

Liquid phase deposition synthesis of hexagonal molybdenum trioxide thin films

SEM photograph of typical h-MoO 3. nH 2O thin film nuclei obtained after 36 h at 40 °C by the LPD method. [Display omitted]

Structural, optical and electrochromic properties of Nb-doped MoO 3 thin films

Niobium (Nb) doped molybdenum trioxide (MoO 3) thin films have been synthesized using spray pyrolysis deposition technique. The structural changes were observed with the help of X-ray diffraction technique. With increasing Nb concentration, the structure of MoO 3 undergoes a phase transformation from α-orthorhombic to amorphous with nano-sized grains. The thread like reticulated morphology is converted into spongy like structure at higher Nb concentration (9 at% Nb). It is seen that Nb doping can lead to significant surface morphology changes in MoO 3 films. It was found that the coloration efficiency increases with doping concentration. With increasing Nb concentration charge capacity, reversibility and electrochemical stability increases. The improvement is attributed to the amorphous structure of the doped samples that favors easy intercalation and deintercalation processes. Hence, we have successfully demonstrated formation of an adequate host for electrochromic devices with Nb (9 at%) doped MoO 3 samples.