Oxide Nanocomposite Thin Films Research Articles

Synthesis and characterization of graphene oxide - TiO2 thin films by sol-gel for photocatalytic applications

Titanium dioxide modified with graphene oxide (GO/TiO2) nanocomposite thin films were prepared on glass substrates by a sol-gel route using the dip coating technique for photocatalytic applications. The graphene oxide powders, fabricated through a modified Hummers' method, and the GO/TiO2 thin films were characterized by electron microscopy, XRD, Raman and UV-VIS spectroscopy to evaluate their structural, morphological and optical properties. The energy bandgap estimated for the thin films is in the range of 3.38–3.45 eV after an annealing at 450 °C; while the transmittance and the Raman intensity decreased significantly by increasing the amount of GO. The photocatalytic activity of the GO/TiO2 thin films, investigated by the blenching of methylene blue, showed a significant increment with the addition of GO; furthermore, the films exhibited potential applications in the photoreduction of CO2, in which a methanol production of 68.443 μmol cm−2 was observed after 5 h of reaction in the presence of UV light.

Polymer/Graphene oxide nanocomposite thin film for NO2 sensor: An in situ investigation of electronic, morphological, structural, and spectroscopic properties

The higher operating temperature of metal oxide and air instability of organic based NO2 sensor causes extremely urgent for development of a reliable low cost sensor to detect NO2 at room temperature. Therefore, we present a fabrication of large area Polymer/GO nano hybrid thin film for polymer thin film transistors (PTFTs) based NO2 sensors assisted via facile method named ‘spreading-solidifying (SS) method’, grown over air/liquid interface and successive investigation of effect of NO2 on film via several characterizations. The PTFTs sensor has demonstrated swift and high response towards low concentration of NO2 gas with air stability and provided real time non-invasive type NO2 sensor. Herein, we are reporting the nanohybrid PBTTT/GO composite based PTFT sensor with good repeatability and sensor response for low concentration NO2. The thin film grown via SS technique has reported very good adsorption/desorption of target analyte having response/recovery time of 75 s/523 s for 10 ppm concentration of NO2 gas. It has been observed that % change in drain current (sensor response) saturated with increasing concentration of NO2. The transient analysis demonstrates the fast sensor response and recovery time. Furthermore, in order to understand the insight of high performance of sensor, effect of NO2 on nanohybrid film and sensing mechanism, an in situ investigations was conducted via multiple technique viz. spectral, electronic, structural, and morphological characterization. Finally, the performance of sensor and the site of adsorption of NO2 at polymer chains were argued using schematic diagram. This work shows the simple fabrication process for mass production, low cost and room temperature operated gas sensors for monitoring the real-time environment conditions and gives an insight about the sensing mechanism adsorption site of NO2.

Fabrication and comprehensive investigation on structural, morphological and electrical properties of polyvinylidene fluoride–nickel oxide nanocomposite thin films

This study is mainly centered on augmenting the β-phase content in polyvinylidene fluoride (PVDF) films by adding nickel oxide (NiO) for sensors and actuators applications. PVDF–NiO nanocomposite films with varying concentration of NiO were fabricated by simple sol–gel casting technique. The impact of NiO nanofiller on physical, structural, morphological and electrical properties of PVDF–NiO nanocomposite films were investigated by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and current–voltage (I–V characteristics) measurements. The XRD pattern show the semi-crystalline structure of PVDF–NiO nanocomposite films and possesses crystalline α and β phases. The estimated structural parameters such as crystalline size, micro strain and dislocation density have also been estimated from the XRD data. XRD and FTIR spectra of PVDF–NiO nanocomposite films confirm the reduction in the intensities of α phase with the dominance of electroactive β-phase as compare to pristine PVDF. As a result, the β-phase content increases and crystallinity also increase from 52% (for pristine PVDF) to 66% (7 wt% NiO). SEM images showed the uniform distribution of NiO particles within the PVDF pattern with the increase in porosity which enhances the ionic conductivity. The significant increase in the ionic conductivity is also analyzed by I–V characteristics which make this nanocomposite suitable for miniaturized electronic devices.

Uricase grafted nanoconducting matrix based electrochemical biosensor for ultrafast uric acid detection in human serum samples.

Gold nanoparticles decorated graphene oxide (Au-rGO) nanocomposite thin films with enhanced electro-active characteristics were prepared and covalently immobilized with uricase (UOx) enzyme for sensitive and selective detection of uric acid (UA). Differential pulse voltammetry (DPV) studies revealed rapid response of fabricated electrode towards UA at low potential (0.228 V) in a wide concentration range of 50-800 μM with a sensitivity of 86.62 ± 0.19 μA mM-1 and very low detection limit of 7.32 ± 0.21 μM. The obtained Michaelis-Menten constant (km) value of 51.75 μM signifies high enzyme kinetics at electrode surface with UA. The developed biosensor was successfully applied to detect UA in human serum samples. Interferences due to components present in the real matrix were evaluated and UA determination in mixed sample was also performed. The fabricated UOx/Au-rGO/ITO biosensor demonstrated high reproducibility and a shelf-life of 6 months indicating the promising future of Au-rGO nanocomposite as an efficient transducer matrix for biosensing applications. The fast response time (1.0 ± 0.6 s) and improved sensor performance is attributed to the synergistic electronic properties of Au-nanoparticles and rGO that provided enhanced electron transfer and high electro-active species surface coverage at Au-rGO nanocomposite.

Effect of high energy Ti9+ ion beam induced modifications in titanium dioxide and tin oxide nanocomposite thin films and detailed analysis of optical, structural and morphological properties

Ion beam irradiation technique plays an important role for modifications in optical, structural, and surface morphological properties of materials. The tin oxide and titanium dioxide nanocomposite thin films were synthesized using RF magnetron deposition technique followed by irradiation with 120 MeV Ti9+ swift heavy ions (SHI). The optical band gap for pristine and irradiated samples was calculated by UV–visible technique and the value of direct band gap decreased from 3.90 eV to 3.75 eV. The refractive index, optical conductivity, Urbach energy, skin depth and optical density have been calculated from the UV–Visible technique. Photoluminescence (PL) technique confirmed the presence of SnO2-TiO2 in the material by showing three standard peaks at 421 nm, 484 nm and 529 nm. Surface morphology of thin film was studied by Atomic Force Microscopy (AFM) technique and it showed grain size dependence on the ions irradiation fluence. The crystallite size was modified by SHI and studied by X-ray diffraction (XRD) technique. The crystallite size increased from 23.97 nm to 26.07 nm as calculated using Debye-Scherrer's formula and it also increased from 54.78 nm to 67.60 nm as obtained by Williamson-Hall equation. Based on the uniform deformation model (UDM), the strain and stress in thin films and dislocation density were calculated. The calculated roughness exponent and RMS roughness varied with irradiation fluence. Depth profiling and elemental analysis were observed by Rutherford Backscattering (RBS) technique.

Surface engineering of polystyrene–cerium oxide nanocomposite thin films for refractive index enhancement

Polymer nanocomposites have gained much importance in the field of optoelectronics due to their unique optical properties. Refractive index engineering using nanoparticles is an effective strategy that could be applied for the fabrication of optical devices. Herein, we report three different strategies which are employed to enhance the refractive index of polymer thin films. These include incorporating cerium oxide nanoparticles onto the polystyrene matrix, secondly adding cerium oxide nanoparticles onto the cross-linkable polystyrene and thirdly by embedding functionalized cerium oxide nanoparticles onto the cross-linkable polystyrene. Refractive index of the polystyrene thin films was enhanced by dispersing neat CeO2 nanoparticles and functionalized CeO2 nanoparticles into the polystyrene matrix. 1.38% enhancement in the refractive index of the polymer nanocomposite thin films could be achieved using our technique. The blending of polystyrene with cerium oxide nanoparticle presents a prospective way to engineer the refractive index of polymer thin films. We firmly believe that the study will be an effective guide towards future research in the area of surface engineering of polymer thin films for refractive index enhancement.

The development of TiO2-graphene oxide nano composite thin films for solar cells

Abstract TiO2-Graphene Oxide (TiO2-GO) nanocomposite thin films of different grades were successfully prepared using Titanium Tetra Isopropoxide (TIP) and Graphene Oxide (GO) nanosheet suspensions coated on aglass plate by a spin coating technique. TiO2-GO nanocomposite film samples were thoroughly characterized for their morphology, thickness and band gap changes by coating a thin layer of 250 nm thickness on a 2 cm × 2 cm glass plate. XRD analysis revealed the amorphous nature of the deposited layers. SEM images demonstrated the growth and distribution of the grains with some spherical/rod-like structures and partially agglomerated. AFM study indicated that the films are smooth with slightly larger surface roughness. The analysis of optical absorption data showed that the values of band gap energy decreased from 3.62 eV to 1.40 eV with increasing dopant quantity. This reduction might be attributed to electron and/or hole trapping at the donor and acceptor levels in the TiO2 band structure. Transfer Matrix Method (TMM) study on the film thickness influence on the optical properties of TiO2-GO (10 wt% GO) nanocomposite exhibited excellent properties of the film due to the inclusion of GO in the TiO2 matrix, which would be promising for application in the photovoltaic application.

Structural, optical, and photocatalytic investigation of nickel oxide@graphene oxide nanocomposite thin films by RF magnetron sputtering

Despite the recent advancement in graphene oxide (GO) as a host material in energy and environmental sectors, its composite thin films with metal oxides such as nickel oxide (NiO) and its optical, structural, chemical state, and photocatalytic activities have been poorly explored. Herein, we have reported the GO/NiO thin films preparation by a combination of chemical and physical deposition techniques (i.e. spin coating followed by DC/RF sputtering). The as-prepared composites thin films were characterised using Raman spectroscopy, X-ray diffraction/photoelectron spectroscopy scanning electron microscopy, and atomic force microscopy. The surface topography confirmed the uniform deposition of NiO over thin films of GO. The XPS results showed the formation of NiC along with the partial reduction in GO into graphene with their existing four constituents, i.e. NiO, NiC, GO, in the thin film composites. The classical plasmon, Wemple and Didomenico model, was first time applied for GO/NiO to compute energy loss functions, and dispersion energy parameters. The theoretical calculated values for the deposited GO/NiO thin films were found to be in very close agreement to the standard classical plasmon values. The change in spin orbital movement of Ni is considered due to the interaction between its nanoparticles and basal planes of GO. Thin films applied for the photodegradation of recalcitrant organic pollutant 2-chlorophenol (2-CP) revealed the dependence of photocatalytic efficiency on particle size and also on the interaction of GO with NiO rather than the ratio of NiO and GO in the films.

Pulsed photoinitiated fabrication of inkjet printed titanium dioxide/reduced graphene oxide nanocomposite thin films

This work reports a new technique for scalable and low-temperature processing of nanostructured TiO2 thin films, allowing for practical manufacturing of TiO2-based devices such as perovskite solar cells at low-temperature or on flexible substrates. Dual layers of dense and mesoporous TiO2/graphitic oxide nanocomposite films are synthesized simultaneously using inkjet printing and pulsed photonic irradiation. Investigation of process parameters including precursor concentration (10–20 wt%) and exposure fluence (4.5–8.5 J cm−2) reveals control over crystalline quality, graphitic oxide phase, film thickness, dendrite density, and optical properties. Raman spectroscopy shows the Eg peak, characteristic of anatase phase titania, increases in intensity with higher photonic irradiation fluence, suggesting increased crystallinity through higher fluence processing. Film thickness and dendrite density is shown to increase with precursor concentration in the printed ink. The dense base layer thickness was controlled between 20 and 80 nm. The refractive index of the films is determined by ellipsometry to be 1.92 ± 0.08 at 650 nm. Films exhibit an energy weighted optical transparency of 91.1%, in comparison to 91.3% of a thermally processed film, when in situ carbon materials were removed. Transmission and diffuse reflectance are used to determine optical band gaps of the films ranging from 2.98 to 3.38 eV in accordance with the photonic irradiation fluence and suggests tunability of TiO2 phase composition. The sheet resistance of the synthesized films is measured to be 14.54 ± 1.11 Ω/□ and 28.90 ± 2.24 Ω/□ for films as-processed and after carbon removal, respectively, which is comparable to high temperature processed TiO2 thin films. The studied electrical and optical properties of the light processed films show comparable results to traditionally processed TiO2 while offering the distinct advantages of scalable manufacturing, low-temperature processing, simultaneous bilayer fabrication, and in situ formation of removable carbon nanocomposites.

Wide range and stable ink-jet printed humidity sensor based on graphene and zinc oxide nanocomposite

Nanocomposite materials are being used for different applications due to their hybrid and unique properties. In this paper, we propose a humidity sensor based on Graphene and zinc oxide nanocomposite thin film. The composite combines the advantages of both the individual materials and improves sensor performance. Addition of conductive graphene to the insulator ZnO results in fall of intrinsic impedance and also in improvement of sensitivity at low relative humidity levels. The sensor consists of silver inter-digital electrodes (IDEs) that are printed on a low cost transparent polyethyleneterephthalate (PET) substrate by DMP-3000 with dimension of 100 µm finger width, 50 µm spacing, and 500 nm thickness. To achieve a high sensitivity and wide sensing range, the active layer of composite thin film was deposited over the IDEs through spin coating to achieve a thickness of ~ 300 nm. The sensor can effective detect relative humidity in range of 0–85% RH with fast response and recovery times of 1 and 2 s respectively that are comparable to high end commercial sensors.

Fast grown self-assembled polythiophene/graphene oxide nanocomposite thin films at air–liquid interface with high mobility used in polymer thin film transistors

Successful practical application of a polymer or its nanocomposite depends on the ability to produce a high performance electronic device at a significantly lesser cost and time than those needed to manufacture conventional devices.

Self-assembled vertically aligned Ni nanopillars in CeO2 with anisotropic magnetic and transport properties for energy applications.

Self-assembled vertically aligned metal-oxide (Ni-CeO2) nanocomposite thin films with novel multifunctionalities have been successfully deposited by a one-step growth method. The novel nanocomposite structures presents high-density Ni-nanopillars vertically aligned in a CeO2 matrix. Strong and anisotropic magnetic properties have been demonstrated, with a saturation magnetization (Ms) of ∼175 emu cm-3 and ∼135 emu cm-3 for out-of-plane and in-plane directions, respectively. Such unique vertically aligned ferromagnetic Ni nanopillars in the CeO2 matrix have been successfully incorporated in high temperature superconductor YBa2Cu3O7 (YBCO) coated conductors as effective magnetic flux pinning centers. The highly anisotropic nanostructures with high density vertical interfaces between the Ni nanopillars and CeO2 matrix also promote the mixed electrical and ionic conductivities out-of-plane and thus demonstrate great potential as nanocomposite anode materials for solid oxide fuel cells and other potential applications requiring anisotropic ionic transport properties.

Scalable fabrication of highly sensitive flexible temperature sensors based on silver nanoparticles coated reduced graphene oxide nanocomposite thin films

We have demonstrated the scalability of RGO-Ag nanocomposite films based temperature sensor on kapton sheet for the flexible technology platform. The RGO nanosheets are known to have the tendency to form an agglomeration, which was removed by insertion of Ag nanoparticles to the RGO sheets. This resulted in the formation of nanocomposite material having an excellent conductivity suitable for temperature sensor applications. The electro thermal performance of the RGO-Ag nanocomposite sensing film was investigated using the Hot-Cold temperature setup. The sensor developed shows exceptional temperature sensing properties, with a promise for wide range of potential application possibilities. Till today the performance of temperature sensors are limited by the flexibility, lower sensitivity, non-linearity viz. Thermistors and Platinum based sensors viz. RTD & Pt 100 while linear are expensive. In contrast, the sensor developed in our present work shows negative temperature coefficient (NTC) of −1.64×10−3Ω/Ω/K, sensitivity of 0.5553Ω/K, with a non-linearity of about 1% and hysteresis close to 1%. The measured response time (470ms) of this sensor is much faster than majority of commercially available temperature sensors with good repeatability and stability. The linearity of the developed sensor lends itself for simpler signal conditioning circuits without requiring linearization front end.

Room temperature self-assembled growth of vertically aligned columnar copper oxide nanocomposite thin films on unmatched substrates

In this work, we report the self-assembled growth of vertically aligned columnar Cu2O + Cu4O3 nanocomposite thin films on glass and silicon substrates by reactive sputtering at room temperature. Microstructure analyses show that each phase in nanocomposite films has the columnar growth along the whole thickness, while each column exhibits the single phase characteristics. The local epitaxial growth behavior of Cu2O is thought to be responsible for such an unusual microstructure. The intermediate oxygen flow rate between those required to synthesize single phase Cu2O and Cu4O3 films produces some Cu2O nuclei, and then the local epitaxial growth provides a strong driving force to promote Cu2O nuclei to grow sequentially, giving rise to Cu2O columns along the whole thickness. Lower resistivity has been observed in such kind of nanocomposite thin films than that in single phase thin films, which may be due to the interface coupling between Cu2O and Cu4O3 columns.

Hydrogen gas sensing performance of polyaniline/titania/nickel oxide nanocomposite at room temperature

Monitoring and control of hydrogen gas (H2) as a green energy resource by smart sensors is necessary for the safe H2 economy. In this work, we present a resistance-based H2 sensor based on a polyaniline/titania/nickel oxide nanocomposite (PTNN) thin film. PTNNs were synthesized by an in-situ self-assembly chemical oxidative polymerization of aniline monomers and deposited onto an epoxy glass substrate with Cu-interdigited electrodes. Synthesized samples were structurally and surface morphologically characterized. H2 sensing behavior of the fabricated sensors was investigated for different concentration of gas, and a significant response (22.1%) and response time (67s) toward 0.6vol% H2 observed at room temperature (25°C) and relative humidity (RH). PTNN sensor with Ti/Ni ratio of 1/3 was exhibited a good Long-term response up to 60days.

Investigation of enhanced electrochromic properties of α-Fe2O3/RGO nanocomposite thin film prepared by electrodeposition

The α-Fe2O3/reduced graphene oxide (α-Fe2O3/RGO) nanocomposite thin film was prepared by two steps electrodeposition method on the Fluorine doped Tin Oxide (FTO) coated glass substrate. The α-Fe2O3 and α-Fe2O3/RGO nanocomposite films were characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The thickness of the nanocomposite film was measured below 400nm.The electrochromic properties of both α-Fe2O3 and α-Fe2O3/RGO nanocomposite films were studied by cyclic voltammetry, chronoamperometry and UV–Vis spectroscopy with the standard three-electrode configuration. The results showed that the α-Fe2O3/RGO thin film have higher optical modulation, faster switching time and better cycling performance compared with pure α-Fe2O3 film. Furthermore, the combination of reduced graphene oxide into iron oxide film enhanced the optical density (ΔOD) about 18% and raised the coloration efficiency (CE) from 18 to 35cm2C−1, at the wavelength of 640nm. The enhanced electrochromic performance is basically attributed to the incorporation of the RGO into α-Fe2O3 film.

Fabrication of PANI–ZnO nanocomposite thin film for room temperature methanol sensor

In the recent past, polymer–metal oxide nanocomposites have been identified as one of the key and new class of materials for fabricating gas sensors owing to their swift redox characteristics. In this line of thought, chemical oxidative process was employed to synthesize zinc oxide (ZnO) and polyaniline (PANI) nanocomposite thin films with different mass concentrations of ZnO to explore their gas sensing signatures. X-ray diffraction patterns and Fourier transform infrared spectra confirmed the formation of pure ZnO and PANI–ZnO composites. Field emission scanning electron micrographs revealed the leaf like structure of ZnO, porous nature of PANI and the uniformly distributed blend of these two structures for the composite films. Further, the room temperature gas/vapour sensing characteristics revealed the selective nature of nanocomposite films towards methanol vapour in the presence of other vapours with better response, swift response and recovery times of 7 and 20 s respectively.

Study of structural and optical properties of low temperature photo-activated ZnO-rGO composite thin film

Zinc oxide-reduced graphene oxide (ZnO-rGO) nanocomposite thin films were fabricated by dip-coating various substrates with a homogeneous dispersion of graphene oxide powder in a sol-gel derived ethanolic solution of zinc acetate and subsequent photo-annealing with deep-ultraviolet radiation. For comparison, ZnO thin films and ZnO-rGO thin films thermally annealed at 500°C were also prepared. The low temperature deep-ultraviolet irradiation resulted in crystallization of ZnO and reduction of graphene oxide which was confirmed by x-ray diffraction and Raman spectroscopy. Moreover, the Raman spectra also revealed that the reduction degree of graphene oxide was highest for deep-ultraviolet irradiated ZnO-rGO thin film. These results show that photo-chemical activation by deep-ultraviolet irradiation provides a low temperature, environment friendly technique to make ZnO-rGO thin films and can be used to fabricate semiconductor-graphene composite thin films on flexible substrates.

Electrochemical deposition of polyviologen-reduced graphene oxide nanocomposite thin films

In previous years, a series of polyviologen films (PVs) have been synthesized through electrochemical polymerization in our group. In order to improve their electrochemical properties, a thin composite film of these redox polymers and reduced graphene oxide were prepared using a one-step technique. In this work, the cyanopyridine based monomer and the graphene oxide flakes were initially dissolved in an ionic liquid (IL), after which the electrochemical reduction was performed. A branched polyviologen film was formed during the electrochemical process, while the graphene oxide flakes were reduced and immobilized in the polyviologens network. The resulting composite film was characterized by electrochemical, spectroscopic, and imaging techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy, UV–vis, FT-IR, Raman spectroscopy, and SEM. The analysis indicated a successful composite film formation: the redox property was enhanced by the presence of graphene in the polyviologen films. Such an easy fabrication process together with inexpensive precursor materials demonstrates a facile way for producing thin composite films for different electrochemical applications, such as electrochromic devices and sensors.

Reduced graphene oxide-SnO2 nanocomposite thin film based CNG/PNG sensor

A low temperature operated, highly sensitive and selective CNG/PNG sensor has been developed in the present work using reduced graphene oxide (rGO)–tin oxide (SnO2) nanocomposite thin film prepared via chemical route. The maximum sensing response of 60% was observed at a low operating temperature of 90°C towards 1000ppm of CNG/PNG. Concentration of rGO is optimised in the nanocomposite sensing layer to achieve the enhanced sensing response. The enhancement in sensing response characteristics is attributed to the increased surface to volume ratio of the SnO2 nanoparticles due to incorporation of rGO sheet in nanocomposite sensing layer besides providing the short conduction path across the SnO2 nanoparticles. The obtained results on sensing response and the origin of sensing mechanism are presented in detail in this communication.