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In this work, we present a simple and solution-based synthesis approach to combine the virtues of PEDOT:PSS and carbon nanotube (CNT) by developing a composite film and their application as a hole selective layer (HSL) in organic-silicon hybrid heterojunction solar cell. The heterojunction solar cell with the optimised PEDOT: PSS-CNT HSL showed a notable open-circuit voltage ( V oc ) of 588.6 mV, short circuit current density ( J sc ) of 25.3 mA/cm2 and fill factor (FF) of 60.79% yielding a photo-conversion efficiency (η) of 9.05%. The pristine PEDOT:PSS/Si device obtained an η of 6.2% with a V oc of 502 mV. The role of CNT in the charge transport mechanism and improving V oc was corroborated by employing various characterisation methods such as J-V, C-V, and electrochemical impedance spectroscopy. The composite layer induced a strong inversion layer in silicon and enhanced the device performance. The application of PEDOT:PSS-CNT composite film is not limited to c-Si solar cells, but can also be used to fabricate flexible organic and perovskite solar cells.

p-type Cu2O thin films doped with trivalent cation boron are demonstrated for the first time as an efficient hole-selective layer for c-Si heterojunction solar cells. Cu2O and Cu2O:B films were dep...

This paper describes the fabrication of copper oxide and zinc tin oxide complementary inverters where both the p-type and n-type channels were deposited by RF magnetron sputtering. We have designed low-voltage and high gain complementary inverters by combining a set of p channel copper oxide and n channel zinc tin oxide thin film transistors (TFTs) with different aspect ratios, thus reducing the difference in mobility and threshold voltage between both types of TFTs. The complementary inverters with four different geometric aspect ratios were fabricated using top-contact configuration. The voltage gain increase with aspect ratio and a maximum value of 4.2 was reached for an aspect ratio of 2 (Wp:Wn = 7200 μm/3600 μm). The voltage gain was found to be dependent on the SS value of p-type TFTs. It is also noticed that an inverter having a geometric aspect ratio of 2 gave better voltage gain and noise margin values. For a VDD = 20 V the NMH and NML values are 7 V and 6.5 V, respectively.

In this paper, we report the fabrication of heterojunction carrier selective c-Si solar cell using a hole selective poly – 3,4 ethylene dioxythiophene (PEDOT:PSS) and an electron selective magnesium fluoride (MgF2) layers. Dopant- free asymmetric heterojunction solar cells (DASH cells) based on c-Si have gained considerable attention due to low-cost fabrication methods and ease of fabrication techniques. Carrier selective contact (CSC) based solar cells can reduce the interface recombination by selectively allowing only one type of carriers to pass through the selective layers. Here, solution-processed hole selective PEDOT:PSS was spin-coated on the c-Si, while the electron selective MgF2 layer was deposited by thermal evaporation technique. The conductivity of the PEDOT:PSS film was enhanced using secondary solvent doping with DMSO. The thickness of the MgF2 layer was optimized using the transmission line measurement. The dipole behavior of MgF2 would result in a decrease in the effective work function of the MgF2/metal stack. The as- fabricated solar cell showed a power conversion efficiency of 7.6% with an open-circuit voltage of 550 mV and a short circuit current of 31 mA/cm2.

In this chapter, the optical properties of ZnO-based multiple quantum well (MQW) structures are discussed. Quantum wells are thin layered heterostructures grown in such a way that a smaller band gap semiconductor layer (confinement layer) having very small thickness is sandwiched between two wider band gap semiconductor layers (barrier layer). The fabrication of symmetric and asymmetric MQW structures based on ZnO with ZnMgO and CuGaO2 as the barrier layer by pulsed laser ablation technique was discussed in detail. Room-temperature PL emission was observed from these MQW structures, and a systematic blueshift in the PL peak position corresponds to the quantum confinement effect was observed with decrease in the confinement layer (ZnO) thickness. The observed room-temperature PL emission from the MQW structures is found to be blue shifted as compared to the room-temperature near-band-edge PL emission from ZnO thin film grown at same experimental conditions. This high-quality MQW structures with wide band gap semiconductor as active region can be utilized as UV emitters.

Epitaxial Ba0.5Sr0.5TiO3 (BST) thin films have been grown by pulsed laser deposition on (0001) Al2O3 substrate with ZnO as buffer layer. The X-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier-filtered HRTEM images of the film–buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Dielectric studies were conducted by fabricating coplanar interdigital capacitors on the epitaxial BST thin films. Epitaxial BST thin films show significantly improved tunable performance over polycrystalline thin films.

Thin-film transistors based on oxide and organic materials have recently attained much progress in flexible and low-cost electronic applications. The characteristic electronic properties of these materials make it a promising candidate as channel layer for the fabrication of high-performance devices. However, the p-type oxide and n-type organic TFTs are not stable because of their inherent electronic properties and the existence of a large amount of charge carrier traps. The device performance and stability of thin-film transistors are closely associated with charge transport mechanism of the active channel layer of the device. The emerging novel transistors based on amorphous oxide and organic semiconductor materials suffer from the high density of trap states inside the channel layer. The important device parameters, such as field-effect mobility and subthreshold swing depend on the charge carrier traps inside the materials. Hence, it is a scientific challenge for researchers to explore the microscopic origin of these traps. In this chapter, the density of localized states in the band gap of n-type materials such as zinc tin oxide (ZTO) and organic N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) channel layers is analysed through temperature-dependent transfer characteristics of respective thin-film transistors.

Surface enhanced Raman scattering (SERS), is a widely used sensing technique in which Raman scattering by molecules is significantly enhanced by adsorbing the molecules onto corrugated metal surfaces enabling even single molecular detection. In the present work, we focus on the development of SERS substrate based on MoS2 film fabricated using pulsed laser deposition (PLD) technique taking advantage of the charge transfer interaction between MoS2 film and the probe molecule. Rhodamine 6G (R6G) is used as the probe molecule for the qualitative evaluation of SERS performance of the fabricated substrates. Additionally, silver nanoparticles (Ag NPs) are deposited on the PLD grown MoS2 film and is developed as SERS substrate. SERS performance is optimised by varying deposition time during the fabrication of MoS2 film and also by altering the concentration of Ag NPs. The enhancement depends on both the number of MoS2 layers and on the distribution of Ag NPs. Simulation based on finite difference time domain (FDTD) method is used to validate this result. Enhancement factor of the order of 105 and 108 is obtained for the monolayer MoS2 film and for the optimised MoS2 - Ag hybrid films respectively.

Yb3+/Er3+ co-doped Y2O3, YOF and YF3 upconversion (UC) phosphors were synthesized by co-precipitation method. The three upconversion phosphor samples show strong green (540 nm) and red (660 nm) emission bands visible to naked eyes even at the low intense incident light. The potential application of Y2O3, YOF, and YF3 UC phosphors was demonstrated by incorporating them in amorphous silicon thin film solar cells and they showed upconversion current densities of 0.36 mA/cm2, 0.23 mA/cm2, and 0.207 mA/cm2 respectively when the cell was illuminated with a 980 nm IR laser. Intensity-dependent J-V studies were carried out to understand the effectiveness of UC phosphors in improving solar cell parameters. An improvement of 7.5% in Jsc was obtained for amorphous silicon solar cell incorporated with YF3 UC phosphors under AM1.5 along with 980 nm NIR illumination.

Nano structures of MoS2 are trending up as a smart optoelectronic material nowadays. Photoluminescence, linear and non-linear optical properties of highly crystalline MoS2 quantum dot (QD)-nano flake (NF) colloidal dispersion in de-ionized water prepared by cost effective mechanical grinding assisted bath ultrasonication and centrifugation is reported in this article. Particle size, which varies with the sonication time and centrifuging speed, is confirmed by TEM and dynamic light scattering (DLS) analysis. The absorbance spectra show characteristic A, B, C and D excitonic transitions of NFs and high energy E peaks of QDs. MoS2 QD-NF dispersion exhibits appreciable photon upconversion and down conversion photoluminescence (PL) that are applicable to solar cells. The photoluminescence emission red shifts with red shift in excitation wavelength. Time correlated fluorescence decay measurement estimates the life time and it varies with the particle size. Raman spectra of spin coated MoS2 dispersion confirm the hexagonal structure and formation of few layered MoS2 in-plane (E12g) and out-of-plane (A1g) vibrational modes. Selective area diffraction patterns confirm the crystallinity and hexagonal nature of the grown nanostructures. Non-linear optical studies of the samples exhibit reverse saturable absorption (RSA) which is applicable to optical limiting devices.

Effects of quantum confinement, focusing on upconversion and downconversion photoluminescence and reverse saturable absorption, on MoS2 quantum dots produced by nanosecond UV laser ablations is not widely reported. The effect of wavelength and pulse energy of ablating laser on the size, colloidal stability, upconversion and downconversion photoluminescence and non-linear properties of MoS2 quantum dots (QDs) are reported here. MoS2 QDs are grown by pulsed laser ablation (PLA) from bulk MoS2 pellets in deionized (DI) water with UV (355 nm), visible (532 nm) and IR (1064 nm) laser beams from a nanosecond Nd-YAG laser source and ablation is repeated with varying pulse energy. The target MoS2 pellet prepared for ablation was sintered at 800 °C in nitrogen ambience for 8 h. Hexagonal structure of MoS2 pellet is confirmed by XRD and Raman spectroscopy before and after sintering. The exfoliated MoS2 QDs dispersion show appreciable photon upconversion (UPC) and down conversion (DC) photoluminescence (PL). The downconversion PL emission shows multiple peaks. QDs size is found to vary with the wavelength of the ablating laser beam. The mean particle size, measured by dynamic light scattering measurements and TEM analysis, is in the range of 2–30 nm. Absorbance measurement shows high energy peaks around 5.88 eV (211 nm) with shoulder peak at 3.79 eV (327 nm) corresponding to MoS2 QDs. MoS2 QDs dispersion show moderate dispersion stability as per zeta potential analysis. Raman analysis of spin coated few layer MoS2 QDs shows characteristic in-plane (E12g) and out-of-plane (A1g) vibrational modes of MoS2. Nonlinear optical studies of colloidal MoS2 show reverse saturable absorption (RSA) due to two photon absorption (TPA) process.

Amorphous zinc tin oxide thin film transistor (ZTO TFT) was fabricated in the inverted-staggered (top contact) structure on Si/SiO2 substrate. The on-off ratio and sub-threshold swing were 2.55 × 106 and 2.3 V/dec respectively. The comparison of transfer characteristics of as prepared and 20 days air exposed ZTO TFT indicates that the threshold voltage and sub-threshold slope are highly influenced by ambient conditions. After exposure to air the device parameters such as µsat, VT and SS changed from 0.44 cm2/V s to 0.49 cm2/V s, 15 V to 18.5V and 2.3 V/dec to 9 V/dec respectively. The positive shift in threshold voltage can be due to the adsorption of oxygen molecules on the backchannel. The increase in sub-threshold swing after air exposure suggests acceptor like trap creation in the channel layer caused by adsorption of water molecules. The deposition of passivation layer on top of the device reduces the aging effect hence stability of device under ambient condition was improved. Density of states (DOS) of as prepared and 20 days air exposed TFT has been investigated for both passivated and unpassivated devices. Comparison of DOS for the TFTs suggested the formation of large number of trap levels in the ZTO channel layer by water adsorption and it was reduced by the passivation of channel layer of ZTO device.

Artificial synaptic devices play a vital role in constructing artificial neural networks, fundamental building blocks of neuromorphic computing. In this article, we report a transparent synaptic device that manifests potentiation, depression and forgetting behavior analogous to the biological synapse. This synaptic device possesses paired-pulse facilitation, spike parameters dependent synaptic weight, and voltage-induced transition from short-term memory to long-term memory. This study reveals that the pulse with a higher amplitude, higher pulse width, and lower pulse interval produces more change in synaptic weight. The mechanism behind potentiation and depression in the fabricated device is proposed in terms of oxygen vacancy migration; oxygen vacancies are generated and drift during the application of input pulses, thus forming a conducting filament. This device exhibits excellent short-term plasticity and long-term potentiation depending upon the input conditions, which are inherent properties of neuroplasticity. Forgetting, referred as the spontaneous decay of conductance, is explained by the rupturing of oxygen vacancy filament due to recombination of oxygen vacancies with non-lattice oxygen ions present in indium tin oxide electrodes. This is confirmed by studying the decay in device with metal electrodes.

Two-dimensional (2D) materials such as graphene and layered transition metal dichalcogenides (LTMDs) have attracted a great deal of attention by the scientific community because of its exceptional electronic, mechanical and optoelectronic properties. Unlike graphene, monolayer MoS 2 is a non-centrosymmetric material featured with a direct band gap energy of 1.9 eV that identifies the presence of strong luminescence. Here we report the growth of quantum confined MoS 2 nanoflakes with desired optical properties such as pronounced excitation wavelength dependent luminescence at room temperature. The emission luminescence was observed to shift from 560 to 704 nm with increasing excitation wavelength. In addition to the down-conversion photoluminescence, interestingly, MoS 2 nanoflakes also exhibited unusual upconversion photoluminescence. These enhanced optical properties of MoS 2 provide various exciting technological applications and thus opening up new possibilities in the field of bio-imaging, optical displays, photovoltaic light harvesting cells and other optical devices.

BaPbO3 (BPO) thin films of different thickness were deposited by pulsed laser deposition on p type Si/SiO2 substrates. The influence of film thickness on the structural and electrical properties is...

We report the influence of reduction time on structural, linear and nonlinear optical properties of reduced graphene oxide (rGO) thin films synthesized by spin coating method. We observed that the structural, linear and nonlinear optical properties can be tuned with reduction time in GO is due to the increased structural ordering because of the restoration of sp2 carbon atoms with the time of reduction. The nonlinear absorption studies by open aperture Z-scan technique exhibited a saturable absorption. The nonlinear refraction studies showed the self de focusing nature of rGO by closed aperture Z scan technique. The nonlinear absorption coefficient and saturation intensity varies with the time for reduction of GO which is attributed to the depletion of valence band and the conduction band filling effect. Our results emphasize duration for reduction of GO dependent optical nonlinearity of rGO thin films to a great extent and explore its applications Q switched mode locking laser systems for generating ultra short laser pulses and in optical sensors. The rGO coated films were characterized by X-Ray diffraction method (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV–Vis absorption spectroscopy (UV–Vis), Photoluminescence (PL) and Scanning electron microscope (SEM) measurements.

In this study, the doping of boron in cuprous oxide as p-type material and its application for optoelectronic device is presented. Thin films are fabricated using metallic targets of Copper and Boron by rf magnetron co-sputtering in the Ar and O2 ambient. The X-ray diffraction spectra of the doped samples matched with cubic Cu2O phase, with no significant peak shift compared to intrinsic Cu2O film. Raman analysis confirmed the Cu2O phase in both doped and un-doped films. For doped thin films optical transparency was enhanced compared to intrinsic cuprous oxide. Band gap of doped and undoped Cu2O were 2.67 eV and 2.47 eV respectively. Heterojunction is fabricated with n-Si and the electrical properties were studied.

A resistive memory device using organo metal halide perovskite (CH3NH3PbBr3) quantum dots sandwiched between two PMMA layers with a very low SET/ RESET voltage and operating current is demonstrated in this paper. Because of the low operating voltages and currents, the operating power of the perovskite quantum dot memory device is very low. Perovskite quantum dots were prepared using the chemical method, namely ligand assisted reprecipitation method. It was then incorporated into PMMA to form a quantum dot - polymer composite. The composite was sandwiched between two PMMA layers by a successive spin coating technique. The SET voltage of the resulting device was low ∼10 mV. Operating current of the device was in micro ampere range. Hence the operating power of the device was very low and was of the order of 1 micro watt. ON/OFF current ratio of 10 was obtained for the fabricated memory device. The difference between resistances at ON and OFF states was ∼400 ohms under positive bias and ∼180 ohms under negative bias.

In the present paper, we report the development of solution processed Carbon Nano-Tube (CNT) and PEDOT:PSS composite for application in c-Si – organic heterojunction solar cell as hole selective layers. The PEDOT:PSS CNT composite film shows high conductivity and has high optical transparency. The CNT network in the composite film will act as a carrier transport bridge between the PEDOT:PSS domains. Also, the CNT will act like stress centers preventing the breakage of transport path of carriers in composite film, making the CNT-PEDOT:PSS composite an excellent candidate as hole selective layer in flexible solar cells. Thus, the CNT-PEDOT: PSS composite can considerably enhance the performance of CNT-PEDOT: PSS /n-Si solar cells through the synergistic properties of CNT and PEDOT:PSS. The power conversion efficiency of the as-designed solar cell was 9.24% with an open circuit voltage of 576 mV. Dopant-free double heterojunction solar cell making use of MgF2 electron transport layer was also fabricated.

Graphene-Zinc oxide (ZnO) hybrid has attracted much interest since the properties of both materials can be extracted. Graphene has high mobility of charge carriers and has zero band gap but ZnO is wide band gap and have large excitonic energy. Graphene-ZnO hybrid can be synthesized by different methods, and they can be explored for the potential applications like field effect devices, photo detectors, lasers, LED’s etc. In this work the study the growth mechanism of electrodeposition of ZnO on Graphene, where graphene is grown by chemical vapour deposition is presented. The deposited films are characterized using SEM, XRD, EDAX etc. The structure of the nanostructures and effectiveness of using this as optoelectronic devices will be discussed.

Surface enhanced Raman spectroscopy (SERS) is a sensitive detection technique where the Raman signal from molecules, when adsorbed on the surface of metal nanoparticles, gets enhanced to an order of 1012.. In the present work, silver nanowires are fabricated via solvothermal method and attached to the tip of optical fiber. SERS is measured from the tip of optical fiber in direct sensing mode, using Rhodamine 6G as probe molecule. The fabricated SERS substrate could detect molecules with a detection limit of 10−12 M. Multi-analyte detection capability of SERS substrate based optical fiber is also determined by detecting crystal violet.

n-type ZnO nanorods are vertically grown over p-type Mg:GaN substrate by simple hydrothermal process to form a p-GaN/n-ZnO nanorods heterojunction. The heterojunction showed good rectifying behavior. The defect states in the heterojunction are analyzed in detail using photoluminescence studies. The device response is studied for various biasing conditions and UV light pulse illumination frequencies. The present device has the fastest UV response on comparison with devices based on solution grown ZnO nanorods. The device showed reproducible results even after long exposure to room temperature and humidity environment.

2D MoS2 has the potential to be used in demanding products such as transistors with capability of overcoming short-channel effects of silicon, ultra-thin solar cells because of huge optical absorption in 2D form, memristors, capacitors, sensors etc. However, the commercial use of 2D MoS2 is hindered by the lack of synthesis methods which provide with high quality large scale deposition. Here we demonstrate the deposition of large area 2D 2H-MoS2 from bulk to bilayers on quartz substrates by industry compatible RF sputtering technique in a sulphur sufficient environment provided by evaporation of sulphur flakes by an in-situ effusion cell. Absorbance spectra of sputtered samples showed peaks corresponding to A, B, convoluted C and D and E excitons. Raman signature peaks of MoS2, A1g near 410 cm−1 and E12g around 380 cm−1 was found in all samples. A1g-E12g value decreased with decreasing deposition time, indicating the formation of thin MoS2 layers up to bilayer which was further supported by the evolution of photoluminescence spectra. AFM measurements exhibited a uniform surface morphology. XPS ascertained the purity of the samples. Thus we could prove that radio frequency magnetron sputtering could be used as an efficient method for large area deposition of 2D MoS2.

Doped lead–zirconate–titanate (PZT) thin films are preferred for the development of micro–electro–mechanical systems (MEMS)-based acoustic sensors because of their inherent higher dielectric and piezoelectric coefficients. Patterning process is used to develop such MEMS devices which is highly complex even for undoped PZT thin films; therefore, the problem is further cumbersome for doped PZT thin films due to the presence of added dopant elements and their associated chemistry. This paper presents patterning of strontium (Sr) and lanthanum (La) co-doped PZT thin film (PSLZT) deposited on platinized silicon substrate using wet and dry etching processes for fabricating a diaphragm structure with thickness of 15–25[Formula: see text][Formula: see text]m and diameter of 1.4–2[Formula: see text]mm, suitable for acoustic sensing applications. The effects of various etching conditions have been studied and the results are reported. It is found that the dry etching is the most suited process for realizing the piezoelectric MEMS structure due to its higher etching resolution. An appreciable etching rate of 260–270[Formula: see text]nm/min with smooth vertical sidewalls is achieved. The silicon diaphragm with patterned PSLZT thin film is found to retain more than 80% of its dielectric and piezoelectric coefficients and has a resonance of 1.43[Formula: see text]MHz.

Doping in lead-zirconate-titanate (PZT) thin films is on the rise for next generation micro-electro-mechanical systems (MEMS) and energy harvesting applications, owing to their improved ferroelectric and piezoelectric properties. Strontium, lanthanum and neodymium like elements are the most exploited for such applications. This paper reports realization of a PZT thin film with strontium and lanthanum co-doping in tandem, Pb1−x−3y/2Sr x La y (Zr0.56Ti0.44)O3 x = 0.06, y = 0.03 (PSLZT), by RF sputtering process. Different process conditions like substrate temperature from 250 °C–350 °C and annealing temperature from 650 °C–750 °C are studied to achieve pyrochlore free PSLZT thin film. The structure, surface morphology, surface topography and ferroelectric characteristics are investigated using x-ray diffraction (XRD), Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FE-SEM) and P-E analyser, respectively. Nanoscale polarization switching processes and the local surface displacements are studied to ascertain that the PSLZT thin film exhibits the ferroelectric and piezoelectric properties. Experimental results reveal that the present PSLZT thin film has a polarization of 5.5 μC cm−2, leakage current density of 10−5 A cm−2 and piezoelectric charge coefficient, d33, of 87 pm V−1, which are suitable for realization of various new piezoelectric MEMS sensors.

In this work, we report the nonlinear optical absorption and asymmetric charge carrier conduction in single layer graphene films deposited by chemical vapor deposition (CVD) technique on copper foils with pretreated surface. XRD texture and pole figure analysis of the substrate are utilized for the visualization of the effect of the pretreatment on the substrate. The synthesised graphene is employed as a channel layer in a back gated field-effect transistor and the asymmetric behavior of charge carriers is analyzed. Nonlinear optical response of graphene is recorded after transferring it onto a quartz substrate. Open aperture Z-scan technique yields a nonlinear absorption coefficient of 5.34 × 106 cm GW−1. The film exhibits saturable absorption in the visible range with a saturation intensity as low as 0.134 GW cm−2.

Growth of nanostructured ZnO by solution process always lead to the formation of various kinds of defects. Defect states also can aid in improving different properties of the material. In the case of light-emitting diodes (LEDs), major research is focused on tuning the emission colour so as to achieve white emission without the use of any phosphors. Vertically aligned ZnO nanorods were grown over Mg:GaN substrate by hydrothermal process. High-resolution X-ray diffraction (HRXRD) analysis confirms the epitaxial growth of nanorods over the substrate. The photoluminescence (PL) studies revealed a narrow near band edge emission and a broad defect-induced deep level emission. The intensity of deep level emissions related to Zni, Vo, O i defects decreases on annealing. The V–I characteristics of the heterojunction showed excellent rectifying nature with electroluminescence emission on forward bias. Device fabricated by as-grown ZnO nanorods emits in the UV–blue region and broad emission in the visible region. While the annealed device emitted only in UV–blue region. The emission wavelengths closely matched with that of defect state emissions obtained in the PL studies. By annealing, various defect states density can be controlled, thereby emission colour tuned from white to blue.

Asymmetric (CuGaO2/ZnO/ZnMgO) and symmetric (ZnMgO/ZnO/ZnMgO) multiple quantum well (MQW) structures were successfully fabricated using pulsed laser deposition (PLD) and their comparison were made. Efficient room temperature photoluminescent (PL) emission was observed from these MQWs and temperature dependent luminescence of asymmetric and symmetric MQWs can be explained using the existing theories. A systematic blue shift was observed in both MQWs with decrease in the confinement layer thickness which could be attributed to the quantum confinement effects. The PL emission from asymmetric and symmetric MQW structures were blue shifted compared to 150 nm thick ZnO thin film grown by PLD due to quantum confinement effects.

The development of room temperature gas sensors having response towards a specific gas is attracting researchers nowadays in the field. In the present work, room temperature (29 °C) ethanol sensor based on vertically aligned ZnO nanorods decorated with CuO nanoparticles was successfully fabricated by simple cost effective solution processing. The heterojunction sensor exhibits better sensor parameters compared to pristine ZnO. The response of the heterojunction sensor to 50 ppm ethanol is, at least, 2-fold higher than the response of the ZnO bare sensor. Also the response and recovery time of ZnO/CuO sensor to 50 ppm ethanol are of 9 and 420 s whereas the values are 16 and 510 s respectively for ZnO sensor. The vertical alignment of ZnO nanorods as well as its surface modification by CuO nanoparticles increased the effective surface area of the device and the formation of p-CuO/n-ZnO junction at the interface are the reasons for the improved performance at room temperature. In addition to ethanol, the fabricated device has the capability to detect the presence of reducing gases like hydrogen sulfide and ammonia at room temperature.

Recently, flexible organic optoelectronics have got great attention because of their light weight, mechanical flexibility and cost effective fabrication process. Conjugated polymers like PEDOT: PSS are widely used for the transparent electrode applications due to its chemical stability, high conductivity, flexibility and optical transparency in the visible region. Conductivity of the PEDOT: PSS polymer can be enhanced by adding organic solvents or conducting nano fillers like CNT, graphene, etc. Carbon nanotubes are good nano fillers to enhance the conductivity and mechanical strength of PEDOT: PSS composite film. Inthe present work, the effect of gold nano particles in PEDOT: PSS/CNT composite is studied. The conductivity enhancement in PEDOT: PSS/CNT thin films can be attributed to the formation of CNT network in the polymer matrix and conformational change of the PEDOT from benzoid to quinoid structure. Even though the conductivity was enhanced, the transparency of the composite thin films decreased with increase in CNT concentration. To overcome this problem, gold nano particles were attached to CNT walls via chemical route. AuMWCNT/PEDOT: PSS composite films were prepared by spin coating method. TEM images confirmed the decoration of gold nano particles on CNT walls. Electrical and optical properties of the composite films were studied. This simple solution processed conducting films are suitable for optoelectronic applications

Graphene has generated enormous research interest during the last decade due to its significant unique properties and wide applications in the field of optoelectronics and photonics. This research studied the structural and nonlinear absorption properties of reduced graphene oxide (rGO) synthesized by Modified Hummer’s method. Structural and physiochemical properties of the rGO were explored with the help of Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (Raman). Nonlinear absorption property in rGO, was investigated by open aperture Z-scan technique by using a continuous wave (CW) laser. The Z-scan results demonstrate saturable absorption property of rGO with a nonlinear absorption coefficient, β, of −2.62 × 10−4 cm/W, making it suitable for applications in Q switching, generation of ultra-fast high energy pulses in laser cavity and mode lockers.

Vertically aligned ZnO nanorod array (ZNA) was deposited by electrodeposition technique over glass substrate coated with Al doped ZnO (AZO). The photo-luminescence spectrum of the ZNA showed a near band edge emission and deep level emission (DLE). The resolved DLE spectrum indicates the formation of various defect levels within the band gap of ZnO. P-type CuO was deposited on ZNA to form ZNA/CuO heterojunction. The voltage-current (V-I) characteristics show a turn on voltage of 0.65V. The device showed good rectification behavior and a rectification ratio of 50 at 1V. The heterojunction with a device structure AZO/ZNA/CuO/Au showed good response on ultra violet (UV) illumination. The device has stability even after long exposures to atmospheric conditions and UV light.

Copper oxide thin films were grown by rf magnetron sputtering on glass substrates at room temperature varying the oxygen partial pressure. Using the XRD and XPS analytical measurements, the deposition condition for the formation of Cu2O and CuO phases were optimised. The optical band gap of the Cu2O and CuO was 2.31 and 1.41 eV, respectively. The bottom gate structured transparent TFTs fabricated using p-type CuO active layers operated in enhancement mode with an on/off ratio of 104 and field-effect mobility of 0.01 cm2/V s.

Bi1.5Zn1Nb1.5O7 (BZN) epitaxial thin films were grown by pulsed laser deposition on Al2O3 with a double ZnO buffer layer through domain matching epitaxy (DME) mechanism. The pole figure analysis and reciprocal space mapping revealed the single crystalline nature of the thin film. The pole figure analysis also shows a 60 degrees twinning for the (222) oriented crystals. Sharp intense spots in the SAED pattern also indicate the high crystalline nature of BZN thin film. The Fourier filtered HRTEM images of the BZN-ZnO interface confirms the domain matched epitaxy of BZN with ZnO buffer. An electric field dependent dielectric tunability of 68% was obtained for the BZN thin films with inter digital capacitors patterned over the film. (C) 2013 Elsevier B. V. All rights reserved.

Heterojunction device performance has strong dependence on its junction interface. ZnO deposition over GaN to achieve a heterojunction is challenging as it usually requires high temperature and vacuum processing. It is even more demanding to achieve a crystalline interface while making ZnO nanorod based heterojunction. Here we report simple solution process for epitaxial growth of ZnO nanorods over GaN. High resolution x-ray diffraction studies revealed highly crystalline c-axis oriented ZnO nanorod growth by a simple hydrothermal process. ZnO/GaN heterojunction device fabricated using hydrothermally synthesized ZnO nanorods showed superior performance compared to polycrystalline sputter deposited ZnO based heterojunction.

Highly c -axis oriented ZnO thin films have been grown by pulsed laser deposition (PLD) technique on quartz, silicon (1 0 0) and Al 2 O 3 〈0 0 0 1〉 substrates using KrF excimer laser ( λ ab = 248 nm) and Q-switched fourth harmonic Nd:YAG laser ( λ ab = 266 nm). The crystalline nature, surface morphology and optical properties of the deposited films depend on the oxygen ambience, substrate nature and deposition temperature. The band gap of ZnO thin films varies with increase of substrate temperature despite of the ablation wavelength. Strong UV-PL emission without any deep level emissions confirms the growth of stoichiometric and crystalline ZnO thin films. Raman scattering studies confirms the growth of c -axis oriented ZnO thin films at different substrate temperature.

Elemental compositional analysis was carried out on various portions (edges to center) of the film on the ADITYA tokamak window using X-ray diffraction, energy-dispersive X-ray analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy. Optical transmission studies were carried out at various points along the length and breadth of the film. An automated tabletop setup was developed for cleaning the coating by back-side etching using an Nd:yttrium aluminum garnet laser operated at its second and third harmonics. Various experimental parameters were optimized so as to restore maximum transmission for the window. It was observed that a wavelength of 355 nm at an energy density of 1275 mJ/cm2 and at a repetition rate of 10 Hz was found to be best suited for this application. It was possible to restore the transmission of the coated portion to the transmission level of bare window portions using this setup.

The optical properties of Yb3+/Er3+ doped Y2O3 upconversion phosphor and the enhancement of efficiency of a-Si:H solar cell on incorporation of upconverter are investigated. The Y2O3 host material has high corrosion resistance, thermal stability, chemical stability, low toxicity and relatively low phonon energy (≈ 500 cm-1). Y2O3:Yb3+ (x %): Er3+ (y %) upconversion nanophosphors with different dopant concentrations were synthesized via simple hydrothermal method followed by a heat treatment at 1200°C for 12 hrs. Highly crystalline, quasi-spherical, body centered cubic Y2O3 structure was obtained. The structure, phase and morphology of the nanocrystals were determined using x-ray diffraction and SEM. Following pumping at 980 nm two dominant emission bands were observed at about 550 nm(green) and 660 nm(red), corresponding to 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions respectively. The dependence of emission intensity on pump power shows that the mechanism involved is two photon absorption. The upconversion phosphor along with a binder is coupled behind the a-Si:H solar cell which absorbs transmitted sub-band-gap photons and emits back the upconverted visible light which can be absorbed by the solar cell. Under suitable intensity of illumination the solar cell short circuit current is found to be increased on adding the upconversion layer.

Transparent conducting films are becoming increasingly interesting because of their applications in electronics industry such as their use in solar energy applications. In this work silver nanowires were synthesized using solvothermal method by reducing silver nitrate and adding sodium chloride for assembling silver into nanowires. Absorption spectra of nanowires in the form of a dispersion in deionized water, AFM and SEM images confirm the nanowire formation. Solution of nanowire was coated over PET films to obtain transparent conducting films.

Development of cost-effective, highly reproducible non-conventional fabrication techniques for anisotropic metal nanostructures is essential to realizing potential applications of plasmonic devices, photonic devices, and surface enhanced Raman scattering (SERS) phenomenon based sensors. This report highlights the fabrication of nanotriangle arrays via nanoimprinting to overcome difficulties in creating large-area SERS active substrates with uniform, reproducible Raman signals. Electron beam lithography of anisotropic nanostructures, formation of arrays of nanotriangles in silicon and the transfer of triangular shapes to polymethylmethacrylate (PMMA) sheets via nanoimprinting have not been reported elsewhere. The reuse of silicon masters offers potential for production of low cost SERS substrates. The SERS activity and reproducibility of nanotriangles are illustrated and a consistent average enhancement factor of up to ~2.9 × 1011, which is the highest value reported for a patterned SERS substrate, is achieved.

Upconversion luminescence is an interesting area while considering its applications in a vast variety of fields. Rare earth ions like erbium is the most studied and efficient candidate for achieving upconversion. Erbium and ytterbium co-doped ZnO nanoparticles were prepared through co-precipitation method. A strong red emission has been obtained while exciting with 980 nm laser. Dependence of luminescence emission colour on ytterbium concentration has been studied.

By controlling the concentration of defects and their type in strontium sulphide phosphor, a broad range of colours in the visible spectrum can be achieved. Photoluminescence (PL) spectrum in the blue to green range of SrS:Cu,Cl is presented and explained on the basis of charge compensation process and coordination about the Cu + ion. Analysis of lattice parameter, strain and grain size were carried out on the basis of X-ray diffraction (XRD) data. From the study of diffuse reflectance spectra (DRS), red-shift in band-gap was observed with increasing doping concentration, which is due to the presence of doping induced tail states.

Ferroelectric thin films such as BST, PZT and PLZT are extensively being studied for the fabrication of DRAMS since they have high dielectric constant. The large and reversible remnant polarization of these materials makes it attractive for nonvolatile ferroelectric RAM application. In this paper we report the characterization of Ba0.7Sr0.3TiO3 (BST) thin films grown by pulsed laser ablation on oxide electrodes. The structural and electrical properties of the fabricated devices were studied. Growth of crystalline BST films was observed on La0.5Sr0.5CoO3 (LSCO) thin film electrodes at relatively low substrate temperature compared to BST grown on PtSi substrates. Electrical characterization was carried out by fabricating PtSi/LSCO/BST/LSCO heterostructures. The leakage current of the heterostructure is studied and a band structure is modeled based on the transport properties of the heterostructure. The dielectric constant of the BST film is found to be 630 at 100 kHz with a loss tangent of 0.04. The capacitance voltage characteristics show high tunability for BST thin films.

Lead zirconate titanate (PbZr x Ti1−x O3) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.

Cuprous (Cu2O) and cupric (CuO) oxide thin films have been deposited by radio frequency magnetron sputtering with two different oxygen partial pressures. The as-deposited copper oxide films were subjected to post-annealing at 300 °C for 30 min to improve the microstructural, morphological, and optical properties of thin films. Optical absorption studies revealed the existence of a large number of subgap states inside CuO films than Cu2O films. Cu2O and CuO thin film transistors (TFTs) were fabricated in an inverted staggered structure by using a post-annealed channel layer. The field effect mobility values of Cu2O and CuO TFTs were 5.20 × 10−4 cm2 V−1 s−1 and 2.33 × 10−4 cm2 V−1 s−1, respectively. The poor values of subthreshold swing, threshold voltage, and field effect mobility of the TFTs were due to the charge trap density at the copper oxide/dielectric interface as well as defect induced trap states originated from the oxygen vacancies inside the bulk copper oxide. In order to study the distribution ...

Transparent conducting indium tin oxide thin films were deposited on polyimide substrates by RF bias sputtering of ITO target. The influences of bias voltage on the structural and electrical properties of the films were investigated. In order to correlate the material characteristics with the plasma parameters during sputtering, we employed Langmuir probe and optical emission spectral studies. The films deposited onto positively biased substrates were poorly crystalline. An improvement in crystallinity was observed with increase in negative bias. The films deposited at a bias voltage of −20 V showed a preferred orientation in the [1 1 1] direction and has minimum resistivity compared to films grown at other biasing conditions. The measured plasma parameters were correlated to the film properties. The ITO films thus grown have been used as the channel layer for the fabrication of thin film transistor.