Nanostructured Thin Films Research Articles

Effect of gamma irradiation on structural, morphological, optical and thermal properties of Ca doped CuO nanostructure thin films

Semiconductor optoelectronic and photonic devices are used in many harsh environment applications such as space and nuclear reactor etc. Gamma radiation in such environments significantly interacts with the semiconductor materials used in these devices, changing their structural, optical, morphological and thermal properties. Therefore, it is vital to investigate the gamma radiation effect of the material to be exposed to radiation in terms of the performance and lifetime of the application. In this study, nanostructured thin films were produced by doping different ratios (0, 0.3, 1.25, 2.5 and 5 mg/mL) of Ca to the copper oxide (CuO) is a semiconductor used in optoelectronic and photonic devices. The thin films produced were deposited on the glass substrate by the spin coating method. The effects of gamma rays on the structural, morphological, optical and thermal properties of the films were investigated by irradiating with different doses (1, 5, 15, 50, 100 and 150 kGy) used a Cobalt-60 gamma radiation source. The structural, morphological, optical and thermal properties of Ca doped CuO nanostructured thin films were investigated by using X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), atomic force microscope (AFM), mechanical profilometer, UV-Vis spectrophotometry (UV-Vis) and thermogravimetric differential thermal analyzer (TG/DTA). The band gap of thin films were been calculated using Tauc’s plot. The obtained results showed that high-dose gamma radiation caused defects in undoped and Ca doped CuO nanostructured thin films and affected their structural, morphological, thermal and optical properties. Despite the resulting defects, Ca doped CuO nanostructured thin films showed higher absorption intensity and thermal stability against gamma rays. These results showed that Ca doped CuO nanostructured thin films are suitable for many harsh environment applications such as space and nuclear reactors.

Processive Pathways to Metastability in Block Copolymer Thin Films.

Block copolymers (BCPs) self-assemble into intricate nanostructures that enhance a multitude of advanced applications in semiconductor processing, membrane science, nanopatterned coatings, nanocomposites, and battery research. Kinetics and thermodynamics of self-assembly are crucial considerations in controlling the nanostructure of BCP thin films. The equilibrium structure is governed by a molecular architecture and the chemistry of its repeat units. An enormous library of materials has been synthesized and they naturally produce a rich equilibrium phase diagram. Non-equilibrium phases could potentially broaden the structural diversity of BCPs and relax the synthetic burden of creating new molecules. Furthermore, the reliance on synthesis could be complicated by the scalability and the materials compatibility. Non-equilibrium phases in BCPs, however, are less explored, likely due to the challenges in stabilizing the metastable structures. Over the past few decades, a variety of processing techniques were introduced that influence the phase transformation of BCPs to achieve a wide range of morphologies. Nonetheless, there is a knowledge gap on how different processive pathways can induce and control the non-equilibrium phases in BCP thin films. In this review, we focus on different solvent-induced and thermally induced processive pathways, and their potential to control the non-equilibrium phases with regards to their unique aspects and advantages. Furthermore, we elucidate the limitations of these pathways and discuss the potential avenues for future investigations.

Anisotropy engineering in solution-derived nanostructured Bi2Te3 thin films for high-performance flexible thermoelectric devices

Flexible thermoelectric (TE) technology can convert human-body heat into electricity, showing great promise for powering wearable devices. Achieving simultaneous excellent flexibility and high TE performance is still a big challenge for both inorganic and organic-based flexible TE materials. Here, to overcome this challenge in the well-known Bi2Te3-based materials, we propose an anisotropy engineering strategy triggered by nanostructuring design and excess Te addition. A two-step solution-synthesis method is developed to prepare patchwork-like Bi2Te2.7Se0.3 nanorods, which can be assembled into flexible thin films by the screen-printing and spark-plasma-sintering process. Owing to the weakened anisotropy by nanostructuring, our nanorods-derived Bi2Te2.7Se0.3 thin films exhibit excellent bending flexibility. Further introducing excess Te can optimize the anisotropy as well as the interfacial connecting and oxidation resistance of these thin films. Consequently, a high power factor of ∼ 745 μWm−1K−2 at room temperature can be achieved in the n-type Bi2Te2.7Se0.3 thin film with 10 % excess Te. These n-type thin films are further assembled with p-type legs (Bi0.5Sb1.5Te3 with 4 % excess Te) into a 5-pair TE device with good flexibility and stability, showing a maximum power density of ∼ 6.06 Wm−2 at a temperature difference of ∼ 28.3 K. This work indicates that anisotropy engineering in solution-derived nanostructured thin films can be a facile way to balance the flexibility and TE properties, further advancing flexible TE devices.

Nanostructured ZnxMn3‒xO4 thin films by pulsed laser deposition: A spectroscopic and electrochemical study towards the application in aqueous Zn-ion batteries

Aqueous Zn-ion batteries (AZIBs) represent a safe and sustainable technology amongst the post-lithium systems, though the poor understanding of the material behaviour at the cathode prevents the full development of efficient AZIBs. ZnMn2O4 (ZMO) has been considered one of the cathode candidates owing to its analogy to the well-established LiMn2O4 cathode for lithium-ion batteries, however its electrochemical mechanism in the presence of Zn ions in aqueous environment is unclear and still debated. In this work, we synthesised nanostructured ZMO thin films by Pulsed Laser Deposition (PLD) and we evaluated, through extensive characterization by microscopic, spectroscopic, and diffraction techniques, how the deposition and annealing conditions affect the film properties. The self-supported nature and the high degree of control down to the nanoscale make a thin film an ideal model system to study the electrochemistry of the material in aqueous solution and to emphasize the impact of the film properties on its electrochemical response. We highlighted the crucial role of the oxygen pressure in the modulation of the film porosity and the combined effect of deposition pressure and annealing temperature to produce a film with tailored properties in terms of morphology, crystallinity, and Zn stoichiometry. A complex redox mechanism involving multiple concurrent reactions and the formation of zinc hydroxide sulphate hydrate (ZHS) was reported, as well as the influence of the film porosity on the voltammetric behaviour of the film at higher scan rate. Our results confirm the intricate electrochemical mechanism of the ZMO material, which does not merely involve the Zn2+ insertion/extraction but also the crucial participation of Mn2+ from the electrolyte, and pave the way for the nanoscale design of engineered ZMO-based electrodes.

Controlled Orientation of Silicon-Containing Diblock Copolymer Thin Films by Substrate Functionalization Under Vacuum

This work demonstrates a simple approach to control the orientation of the self-assembled nanostructured block copolymer thin films of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) by functionalization of the oxide layer (SiO2) on the Si substrate followed by thermal annealing under low-pressure environmental conditions. The substrate can be functionalized through two-step grafting of hydroxy-terminated polystyrene brush (PS–OH brush) followed by hydroxy-terminated polydimethylsiloxane brush (PDMS–OH brush) onto the wafer substrate. By controlling the grafting ratio of PS–OH and PDMS–OH brushes, the affinities of the PS and PDMS blocks with the substrates can be fine-tuned to provide a neutral substrate in order to form perpendicular cylinders from the bottom after thermal annealing. Owing to the vacuum-driven orientation [i.e., thermal annealing under low-pressure environment conditions (∼10–4 Pa)], the orientation of the cylinders can be controlled at the air/polymer interface. Interestingly, by combining the vacuum-driven approach with substrate functionalization, perpendicular cylinders from the air/polymer interface and substrate/polymer interface can be generated, respectively. Consequently, well-aligned perpendicular cylinders with long-range ordering can be fabricated by the self-alignment process.

Improvement of third-order NLO properties of vacuum deposited Cd1-xPbxS nanostructured thin films for optoelectronic device applications

A polycrystalline nanostructured cadmium lead sulfide thin film was deposited using the thermal evaporation (PVD) technique (Cd1-xPbxS with x = 0.00, 0.01, 0.05 and 0.1 wt.% of Pb). Structural parameters of as-prepared Cd1-xPbxS thin films have been studied through X-ray diffraction. The optical investigation demonstrates that Cd1-xPbxS film's optical band gap (Eg) may be adjusted from the visible to the near-infrared region. (2.64 - 2.42 eV). The film is substantially more appropriate for absorbing layers in solar cells and optoelectronic applications due to the large decrease in ‘Eg.’ The enhanced Pb doping was found to have altered the surface morphology, verified by Field Emission Scanning Electron Microscopy (FESEM) images. The doped films also showed a significant red shift in the band edge and increased transmittance in the visible and NIR regions. The third-order nonlinear optical (TONLO) parameters of the samples were determined from the Q-switched Nd: YAG laser with 65-ps pulse duration at 1064 nm. The investigated TONLO components such as nonlinear absorption coefficient (β), nonlinear refractive index (n2) and the susceptibility χ(3)were found to be in the range from 1.16 × 10−3 to 4.12 × 10−3 (cmW−1), 1.06 × 10−8 to 3.32 × 10−8 (cm2 W−1) and 1.23 × 10−4 to 5.62 × 10−4 (esu) respectively. The results indicate that Pb-doping on CdS nanostructures on surface morphology can be used to modify NLO characteristics.Cd1-xPbxS thin film is a potential and able material for optoelectronic device applications, as seen by these encouraging NLO results.

Investigation (Cd + Co) Co-Loading Impact on Physical Properties of Nano-Structured (CuO) Thin Films

Pure CuO and (Cd+Co) double doping CuO thin films were produced using the sol- gel method and the spin coating approach, with various (Cd+Co) co-doping concentrations ((1+1), (3+3), (5+5), and (7+7) wt.%) of (Cd+Co). XRD results showed that all prepared pure and metals co-doped CuO nanostructured thin films are polycrystalline and have a monoclinic structure with preferred planes on (002) and (111) without additional peaks related to Cd and Co. The surface morphology and layer thickness of synthesized thin films were analyzed by field emission Scanning Electron Microscopy. The SEM images showed Agglomerated spherical grains form at high co-doping concentrations. The existence of Cu, Cd, Co, and O elements was confirmed by EDS measurements., The energy gap decreased from 2.139eV to 2.02 eV was investigated by the Tauc’s and Davis-Mott relations.

The impact of film deposition and annealing on the nanostructure and dielectric constant of organic semiconductor thin films.

The strategy of using a bulk-heterojunction light-absorbing layer has led to the most efficient organic solar cells. However, optimising the blend morphology to maximise light absorption, charge generation and extraction can be challenging. Homojunction devices containing a single component have the potential to overcome the challenges associated with bulk heterojunction films. A strategy towards this goal is to increase the dielectric constant of the organic semiconductor to ≈10, which in principle would lead to free charge carrier generation upon photoexcitation. However, the factors that affect the thin film dielectric constants are still not well understood. In this work we report an organic semiconductor material that can be solution processed or vacuum evaporated to form good quality thin films to explore the effect of chromophore structure and film morphology on the dielectric constant and other optoelectronic properties. 2,2'-[(4,4,4',4'-Tetrakis{2-[2-methoxyethoxy]ethyl}-4H,4'H-{2,2'-bi[cyclo-penta[2,1-b:3,4-b']dithiophene]}-6,6'-diyl)bis(methaneylylidene)]dimalononitrile [D(CPDT-DCV)] was designed to have high electron-affinity end groups and low ionisation-potential central moieties. It can be processed from solution or be thermally evaporated, with the film morphology changing from face-on to a herringbone arrangement upon solvent or thermal annealing. The glycol solubilising groups led to the static dielectric constant (taken from capacitance measurements) of the films to be between 6 and 7 (independent of processing conditions), while the optical frequency dielectric constant depended on the processing conditions. The less ordered solution processed film was found to have the lowest optical frequency dielectric constant of 3.6 at 2.0 × 1014 Hz, which did not change upon annealing. In contrast, the more ordered evaporated film had an optical frequency dielectric constant 20% higher at 4.2 and thermal annealing further increased it to 4.5, which is amongst the highest reported for an organic semiconductor at that frequency. Finally, the more ordered evaporated films had more balanced charge transport, which did not change upon annealing.

Controllable synthesis of nanostructured bismuth vanadate thin films as an efficient catalyst for photoelectrochemical water splitting

The choice of solvents and additives used in the preparation of BiVO4 films had a critical influence on the preferred orientation of the crystal planes, the surface morphology, and, consequently, the photoelectrochemical properties.

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

IMPACT OF NANOSTRUCTURE TYPES AND THIN FILM THICKNESS ON THE PHOTOCATALYTIC PERFORMANCE OF TiO2/V2O5 COMPOSITE COATINGS

Titanium dioxide is a very promising compound for various applications. One of the important areas of applicability is photocatalysis. The wide bandgap of the titanium dioxide limits its photocatalytic activity by the utilization of the ultraviolet area of the irradiation, which is ~ 3%. Expanding the area to visible light spectra is possible by doping titanium dioxide with metals and their oxides. Vanadium pentoxide is one of the widespread dopants that allows the narrowing of the bandgap and improves the efficiency of titanium dioxide-based photoanodes. Research into the area of the improvement of titanium dioxide photocatalytic performance with the help of vanadium pentoxide is widespread and in high demand. In this research, for the first time, the effect of vanadium pentoxide thin film thickness on the photoanode based on titanium dioxide nanostructured substrates of various types was studied. An optimal thickness of that thin film was discovered that allows one to increase in the photocurrent density of the photoanode up to 400%.

A highly stable room temperature titania nanostructure-based thin film transistor (TFT) alcohol sensor

The present study is concerned with the room temperature field-induced alcohol sensitivity of nanostructured TiO2 thin films in field-effect transistor (TFT) configurations.

Effect of precursor concentration on stoichiometry and optical properties of spray pyrolyzed nanostructured NiO thin films

In this study, spray pyrolysis was used to produce nanostructured NiO thin films from high purity nickel acetate (Ni(CH3COO)2.3H2O) precursors on pre-heated ultrasonically cleaned soda-lime glass substrates. The metallic constituent concentrations in the films were varied, and the precursors were produced in distilled water at various molarities ranging from 0.1 to 0.4 M. In the study, the field-emission scanning electron microscope (FESEM) results strongly confirmed adherence of the films to the glass substrate at 350 °C. The presence of Ni and O in the samples was confirmed using Rutherford backscattering spectroscopy (RBS), X-ray diffractometry (XRD) and energy dispersive X-ray spectroscopy (EDX). For the 0.1 M NiO thin films, the thickness was approximately 43 nm, and for the 0.2 M, 0.3 M, and 0.4 M films, the thickness was 46 nm, 47 nm, and 49 nm, respectively. The XRD findings were supported by the increased Raman intensity peaks with increased precursor concentration, which confirmed the films' improved crystallinity. For the same number of passes of films deposition, as the molar concentration increases, the films thickness increases. The amount of nickel in NiO thin films increases as the molarity increases, but the amount of oxygen in NiO thin films decreases as the molarity increases. It was discovered that as molarity increases, the optical transmittance decreases and the optical band gap narrows. The qualities of NiO discovered in this study suggest the films’ potentials for usage as window layer and buffer material in thin film solar cells.

High performance multi-purpose nanostructured thin films by inkjet printing: Au micro-electrodes and SERS substrates.

Nanostructured thin metal films are exploited in a wide range of applications, spanning from electrical to optical transducers and sensors. Inkjet printing has become a compliant technique for sustainable, solution-processed, and cost-effective thin films fabrication. Inspired by the principles of green chemistry, here we show two novel formulations of Au nanoparticle-based inks for manufacturing nanostructured and conductive thin films by using inkjet printing. This approach showed the feasibility to minimize the use of two limiting factors, namely stabilizers and sintering. The extensive morphological and structural characterization provides pieces of evidence about how the nanotextures lead to high electrical and optical performances. Our conductive films (sheet resistance equal to 10.8 ± 4.1 Ω per square) are a few hundred nanometres thick and feature remarkable optical properties in terms of SERS activity with enhancement factors as high as 107 averaged on the mm2 scale. Our proof-of-concept succeeded in simultaneously combining electrochemistry and SERS by means of real-time tracking of the specific signal of mercaptobenzoic acid cast on our nanostructured electrode.

In situ moulded troilite 2H phase FeS ultrathin electrodes via pulsed laser deposition for flexible solid state high capacity supercapacitor besides boosted electrocatalytic oxygen evolution reaction

Troilite 2H phase FeS thin film nanostructures as next-generation green (clean) energy storage novel material for eco-friendly, wearable/portable multifunctional devices.

A spectrally selective visible microbolometer based on planar subwavelength thin films.

In this work, we experimentally demonstrate a new type of compact, low-cost, visible microbolometer based on metal-insulator-metal (MIM) planar subwavelength thin films, which exploits resonant absorption for spectral selectivity without additional filters and has the advantages of compact design, simple structure, cost-efficiency, and large format fabrication. The experimental results show that a proof-of-principle microbolometer exhibits spectrally selective properties in the visible frequency range. At a resonant absorption wavelength of 638 nm, a responsivity of about 10 mV W-1 is achieved at room temperature at a bias current of 0.2 mA, which is about one order of magnitude higher than that of the control device (a bare Au bolometer). Our proposed approach provides a viable solution for the development of compact and inexpensive detectors.

Hydrothermally prepared ultra-stable multilayer nanoflake NiO-based electrochromic films

Electrochromic materials cycle between colored and bleached states under various applied voltage and have applications in smart windows and displays. The formation of a micro–nano structure in electrochromic thin films using hydrothermal methods can improve their properties. However, the conventional constant-temperature hydrothermal method yields films that easily peel from the conductive substrate during electrochromic cycling, resulting in performance losses. Therefore, we investigated the effect of a gradient-temperature hydrothermal protocol on the electrochromic performance of NiO thin films. First, a layer of small, strongly adhered crystal grains was seeded on an indium tin oxide substrate. Thereafter, NiO nanoflake layers were grown by adjusting the reaction temperature. The prepared film could be operated for 14,000 electrochromic cycles, four-times more than those of the conventionally prepared films, without significant performance loss. Therefore, our proposed method enhances the cyclic stability of micro–nanostructured NiO thin films significantly and will aid the development of high-performance electrochromic thin films having broad applications.

Fabrication, structural, morphological, and optical studies of CdS:Cu nanostructured thin films: effect of Cu concentration

Fabrication, structural, morphological, and optical studies of CdS:Cu nanostructured thin films: effect of Cu concentration

Lateral and vertical evolution of the compositional and morphological profiles in nanostructured photocatalytic titania thin films

Thin films of nanostructured titania comprising different levels of lateral and vertical microstructural order and surface chemistry were prepared via the anodization of titanium. We segmented and demystified the contributions that lead to nanostructured titania and affected its photocatalytic behaviour to: (1) specific compositional (less dominant) and (2) specific (surface) morphological differences (substantial), in the as-achieved films. To shed more light on the contributions, we partitioned these films by chemically and morphologically distinctive constituents; (1) top porous non-stoichiometric titania, (2) mid tubular nanoformations, and (3) bottom dense titania.Morphology of the films was described using electron microscopy, and synchrotron grazing incidence X-ray scattering/diffraction. Narrow range of synthetic conditions allowed preparing of ordered, macroscopically homogeneous nanotubes for photovoltaics. Interestingly, somewhat different, distorted tubular nanoformations were better suited for the photo-degradation of salicylic acid (fit by pseudo-second order). In this case, rutile traces in anatase tubular formations were commonly observed, synergistically boosting photodegradation. Broad characterisations reasons the photodegradation in order of importance to: (1) controlling the evolution of type of porosity and presence of defects in the films, (2) controlling the ratio and vertical profile of anatase-to-rutile, and (3) observing the surface chemistry changes, i.e. the presence of substoichiometric titania.

Competitive Registration Fields for The Development of Complex Block Copolymer Structures by A Layer-by-Layer Approach.

Block copolymer (BCP) self-assembly in thin films is an elegant method to generate nanometric features with tunable geometrical configurations. By combining directed assembly and hybridization methods, advances in nano-manufacturing have been attested over the past decades with flagship applications in lithography and optics. Nevertheless, the range of geometrical configurations is limited by the accessible morphologies inherent to the energy minimization process involved in BCP self-assembly. Layering of nanostructured BCP thin films has been recently proposed in order to enrich the span of nanostructures derived from BCP self-assembly with the formation of non-native heterostructures such as double-layered arrays of nanowires or dots-on-line and dots-in-hole hierarchical structures. In this work, the layer-by-layer method is further exploited for the generation of nano-mesh arrays using nanostructured BCP thin films. In particular, a subtle combination of chemical and topographical fields is leveraged in order to demonstrate design rules for the controlled registration of a BCP layer on top of an underneath immobilized one by the precise tuning of the interfacial chemical field between the two BCP layers.