Self-supporting Thin Films Research Articles

Effects of reductions and drying methods on electrochemically exfoliated graphene

Graphene research has advanced a lot in the last decade. Scientists are currently developing methods to make high-quality materials with distinctive attributes. Solar cells, electronic devices, energy storage and sensors are some of the potential applications involving graphene and derivatives. However, the reduction and drying steps of graphene obtained may influence the material properties and its future applications. The present work proposes a comparison of reduced graphene by sustainable methods following two different drying techniques. Freeze-drying prevents the aggregation of reduced graphene sheets, resulting in 2 ∼ 3D reduced graphene oxides, while oven-drying reduced graphene results in a flexible and self-supporting thin film. Reduced graphene exhibited low oxygen content (7 %), a low edge defect density and a high conductivity (2670 S cm−1).

Electrical contact effects of flexible self-supporting DNA thin films for storage devices

The development of flexible DNA thin films embedded with diverse functional nanomaterials might be beneficial for electronic devices and biosensors. In this work, we fabricated two different types of electrodes (i.e. metal paste spotted electrodes and metal layer electrodes) on flexible drug- and dye-embedded DNA thin films to examine their electrical and capacitance properties for conduction and energy storage, respectively. Enhanced current and reduced capacitance of drug-embedded DNA thin films compared with pristine DNA with Ag paste electrodes were observed due to the intrinsic characteristics of the drugs. We used the electron-beam deposition process to fabricate relatively large-area metal-coated (e.g. Au and Al) electrodes, which ensures the creation of metal layers on both sides of the flexible thin films while improving metal contact. There was a significant current increase in DNA thin films with metal layer electrodes compared with DNA thin films with Ag paste electrodes. Furthermore, capacitances measured from Au/DNA/Au and Al/DNA/Al capacitors were relatively more stable than from Ag paste DNA thin films. The physical properties of our samples might be easily controlled by manipulating functional nanomaterials in DNA thin films and various types of metal layer electrodes. Our self-supporting DNA thin films with integrated nanomaterials and durable metal layer electrodes might be employed in flexible electronic devices such as nanogenerators, skin electronics and biosensors in the future.

PET/ZnO@MXene-Based Flexible Fabrics with Dual Piezoelectric Functions of Compression and Tension.

The traditional self-supported piezoelectric thin films prepared by filtration methods are limited in practical applications due to their poor tensile properties. The strategy of using flexible polyethylene terephthalate (PET) fabric as the flexible substrate is beneficial to enhancing the flexibility and stretchability of the flexible device, thus extending the applications of pressure sensors. In this work, a novel wearable pressure sensor is prepared, of which uniform and dense ZnO nanoarray-coated PET fabrics are covered by a two-dimensional MXene nanosheet. The ternary structure incorporates the advantages of the three components including the superior piezoelectric properties of ZnO nanorod arrays, the excellent flexibility of the PET substrate, and the outstanding conductivity of MXene, resulting in a novel wearable sensor with excellent pressure-sensitive properties. The PET/ZnO@MXene pressure sensor exhibits excellent sensing performance (S = 53.22 kPa-1), fast response/recovery speeds (150 ms and 100 ms), and superior flexural stability (over 30 cycles at 5% strain). The composite fabric also shows high sensitivity in both motion monitoring and physiological signal detection (e.g., device bending, elbow bending, finger bending, wrist pulse peaks, and sound signal discrimination). These findings provide insight into composite fabric-based pressure-sensitive materials, demonstrating the great significance and promising prospects in the field of flexible pressure sensing.

Novel self-supporting thin film electrodes of FeCoNiCrMn high entropy alloy for excellent oxygen evolution reaction

The characteristics of FeCoNiCrMn high entropy alloy lead to great significance in electrocatalytic oxygen evolution reaction (OER) of water splitting. However, the preparation process of high entropy alloy for OER electrocatalyst still has limitations. And thin films of metals prepared by magnetron sputtering has a large amount of defects which facilitate the formation of active sites. In this work, FeCoNiCrMn high entropy alloy self-supporting electrodes based on nickel foam were fabricated by magnetron sputtering and applied for OER. It is confirmed that there is an optimum deposition time for the best OER performance. Furthermore, the OER performance of FeCoNiCrMn high entropy alloy electrodes can be boosted by surface reconstruction through cyclic voltammetry. As is revealed by morphology and surface chemical state characterization, there are a large amount of high entropy hydroxides and oxyhydroxides formed on the surface of FeCoNiCrMn high entropy alloy electrodes after CV reconstruction. The FeCoNiCrMn high entropy alloy electrodes reconstructed by cyclic voltammetric can reach an overpotential of 282 mV and a Tafel slope of 64.3 mVdec−1.

A novel material based on an antibacterial choline-calixarene nanoassembly embedded in thin films

Supramolecular chemistry is one of the current strategies for producing advanced materials. With the aim to develop new Thin-Films with antibacterial activity, we embedded an amphiphilic choline-calix[4]arene possessing antibacterial properties in polymeric Thin-Films based on polyether-co-amide matrix (Pebax®2533). The loading of the calix[4]arene derivative in the film was performed by solution casting. The amount of calixarene additive in the films was in the range of 0.5–5 wt%. The self-supported Thin-Films were characterized by investigating phase miscibility, morphology, spectral properties, and gas transport. The release of the calixarene derivative from the films was studied in a biomimetic medium as PBS (10 mM, pH 7.4). The presence of the additive did not affect the thermal stability of the copolymer, whereas it induced an increase in crystallinity, wettability, and gas permeability of the blend films according to its concentration. The antibacterial activity of the films was evaluated in vitro against Escherichia coli and Staphylococcus aureus strains, representative of Gram-negative and Gram-positive bacteria. The developed films displayed antibacterial activity against both strains. In particular, Pebax® − 5 wt% Chol-Calix caused within 10 h a reduction in E. coli and S. aureus of 2.57 and 2 log CFU/mL, respectively. The potential toxicity of the films was also tested on mouse embryonic fibroblasts NIH/3T3. Pebax®2533/calixarene derivative combination appears a promising approach for the development of novel flexible antibacterial materials.Graphical abstract

Mo2C@C nanofibers film as durable self-supported electrode for efficient electrocatalytic hydrogen evolution

Self-supported electrocatalytic thin films consist 3D conducting network and well-embedded electrocatalysts, which endows the advantage in mass flow kinetics and durability for large-scale water splitting. Synthesis of such self-supported electrode still remains a big challenge due to the difficulty in the control over the 3D conducting network and the simultaneous growth of catalyst with well attachment on the conducting fibers. Herein, a self-supported Mo2C@carbon nanofibers (Mo2C@C NF) film has been successfully fabricated with outstanding electrocatalytic performance under optimized pyrolysis temperature and precursors mass ratio conditions. During the carbonation process, the Mo2C nanoparticles (∼16 nm) were simultaneously grown and well dispersed on the inter-connected carbon nanofibers, which formed a 3D conducting network. The as-formed 3D carbon network was strong enough to support direct electrocatalytic application without additional ink or supporting substrates. This particular electrode structure facilitated easy access to the active catalytic sites, electron transfer, and hydrogen diffusion, resulting in the high hydrogen evolution reaction activity. A low overpotential of 86 mV was needed to achieve 10 mA cm−2 current density with outstanding kinetics metric (Tafel 43 mV dec−1) in 1 M KOH. Additionally, the self-supported Mo2C@C NF film, a binder-free electrode, exhibited extraordinary stability of more than 340 h.

The free electron model and the electronic energy losses of protons at low velocities interacting with polycrystalline tantalum

In this letter, we report experimental data and theoretical work on the electronic energy loss and energy loss straggling of protons transmitted through self-supported thin films of tantalum in a polycrystalline tetragonal phase . Low-energy protons with energies below 10 keV and Ta films with nominal thickness of 6, 9 and 12 nm are used. The aim of this work is to understand the unexpected values of the Ta stopping power for low-energy proton backscattering reported recently, which are far from the prediction of the standard free electron gas model and semi-empirical approaches. This had led the authors to conclude the failure of the free electron model. Our transmission measurements confirm these experimental results. In this work, a qualitative discussion and quantitative explanation of our experimental results is given, using an approach based on the density functional theory within the framework of the free electron gas (FEG) model. We performed semiclassical deterministic trajectory simulations and employ the local density approximation model, using an inhomogeneous electron density distribution and the polycrystalline character of Ta samples.

Band-like Transport of Charge Carriers in Oriented Two-Dimensional Conjugated Covalent Organic Frameworks

A tunable topology and a porous network make π-conjugated covalent organic frameworks (COFs) a new class of organic semiconductors for optoelectronic, smart sensing, and catalytic applications. Although some of the COFs exhibit enhanced electric conductivity with a high charge carrier mobility, the nature and pathways of charge transport still remain elusive. In order to unveil the transport mechanism, herein, we have developed crystalline π-conjugated COFs using planar building blocks, and a wafer-scale self-supporting thin film was grown, which could be transferred onto any of the desired substrates. The COF film was found to be highly oriented and exhibited a high in-plane electronic conductivity. The conductivity was almost independent of temperature with an ultra-low activation energy of 14.3 meV, approaching a band-like transport of charge carriers within the crystalline domains. The COF films also showed a high photoresponsivity in electronic conduction against a complete visible range, demonstrated as a flexible photodetector device. This work represents a thorough investigation of the mechanism and direction of charge transport in crystalline π-conjugated COF semiconductors, which suggests their feasibility as key active materials in multi-functional organic electronics.

Impact of the experimental approach on the observed electronic energy loss for light keV ions in thin self-supporting films

Energy spectra of keV ions interacting with self-supporting foils of Au and W were recorded with a Time-of-Flight Medium-Energy Ion Scattering system in different backscattering and transmission geometries in an otherwise identical experimental setup. For He ions transmitted through Au spectra of detected particles depending on geometry show two distinct components, i.e. different energy loss distributions in the film, whereas for protons no such phenomenon was observed. The two components in the spectrum of transmitted He could be attributed to impact parameter dependent energy loss, being more prominent for He than for protons. The main origin of the necessary impact parameter selection along different trajectories is expected to be texture in the Au-foils. Electronic stopping powers obtained from both, most probable energy loss in transmission and best fits to spectrum width in backscattering are in agreement within experimental uncertainties. This observation applied for all investigated combinations of projectile and target material.

Metal-Free and Carbon-Free Flexible Self-Supporting Thin Film Electrodes

Conductive polymers are promising for application in the medical and sport sectors, e.g. for thin wearable health monitoring systems. While many today’s electrodes contain either carbon or metals as electrically conductive filler materials, product design manufacturing has an increasing interest in the development of metal free and carbon free, purely polymer based electrode materials. While conducting polymers have generally rather low electrical conductivities compared to metals or carbon, they offer broad options for industrial processing, as well as for dedicated adjustments of final product properties and design aspect, such as colour, water repellence, or mechanical flexibility in addition to their electrical properties. The development of electrically conducting polymer blends, based on conductive polymers is thus timely and of high importance for the design of new attractive flexible electrodes. We have developed material formulation and processing techniques for the fabrication of self-supporting thin film electrodes based on polyaniline (PANI) and polyvinylidene fluoride (PVDF) blends. Electrical four-point probing was used to evaluate the electrode conductivity for different processing and fabrication techniques. Optical microscopy and atomic force microscopy measurements corroborate the observed electrical conductivity obtained even at low PANI concentrations revealing the nanoscale material distribution within the blends. Our self-supporting thin film electrodes are flexible, smooth, and water repellent and were furthermore successfully tested under bending and upon storage over a period of several months. This opens new perspectives for the design of metal free and carbon free flexible electrodes for medical, health, and sports applications.

Preparation and novel photoluminescence properties of the self-supporting nanoporous InP thin films

Self-supporting nanoporous InP membranes are prepared by electrochemical etching, and are then first transferred to highly reflective (> 96%) mesoporous GaN (MP-GaN) distributed Bragg reflector (DBR) or quartz substrate. By the modulation of bandgap, the nanoporous InP samples show a strong photoluminescence (PL) peak at 541.2 nm due to the quantum size effect of the nanoporous InP structure. Compared to the nanoporous InP membrane with quartz substrate, the nanoporous membrane transferred to DBR shows a twofold enhancement in PL intensity owing to the high light reflection effect of bottom DBR.

Oxygen Reduction Reaction Activity of Nanocolumnar Pt:Ni Alloy Thin Films By High Pressure Sputtering

Self-supported nanocolumnar Pt-Ni alloy thin films (TFs) with different Pt:Ni compositions and Pt mass loadings were fabricated by high pressure sputtering (HIPS) on a microporous layer (MPL)-like surface composed of carbon particles in order to mimic the catalyst-coated gas diffusion layer (gas diffusion electrode) in a membrane electrode assembly and investigated as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cells. HIPS is a simple physical vapor deposition method that is scalable and easily applicable to industrial sputter deposition systems. At high working gas pressures, columnar and less-dense structures are formed because of angular distribution of sputtered atoms that leads to a shadowing effect. Cauliflower-like microstructures were observed from scanning electron microscopy imaging. X-ray diffraction and quartz crystal microbalance analysis revealed that by simply changing the relative deposition power between Pt and Ni source, different Pt:Ni compositions can be achieved. Benchtop cyclic voltammetry and rotating disk electrode measurements were performed for electrochemical characterization of the Pt:Ni-TF/MPL-like-layer/glassy-carbon samples in an aqueous perchloric acid electrolyte. The electrochemically active surface area (ECSA) ranged between 22-42 m2/g for varying Pt:Ni compositions. Lower Pt mass loadings showed a higher ECSA likely due to smaller nanocauliflower diameters, while the ORR activity of all compositions increased as the Pt mass loading is increased. The catalytic performance of the Pt:Ni-TFs increased in the order of 3:1 < 1:1 < 1:3 with the 1:3 films exhibiting a specific activity of 1781 µA/cm2 and mass activity of 0.66 A/mg, indicating efficient catalyst utilization. The Pt:Ni-TFs were found to exhibit higher ORR activity than traditional high surface area carbon supported Pt nanoparticles, elemental Pt nanorods, and Pt-Ni nanorods.

Skin and bubble formation in films made of methyl nanocellulose, hydrophobically modified ethyl(hydroxyethyl)cellulose and microfibrillated cellulose

The use of nanomaterials and polymers from renewable resources is important in the search for sustainable alternatives to plastic-based packaging materials and films. In this work, self-supporting thin films prepared from derivatized and non-derivatized nanocellulose and cellulose derivatives were studied. The effect of drying temperature on the film-forming behavior of compositions comprising hydrophobically modified ethyl(hydroxyethyl)cellulose (EHEC), native microfibrillated cellulose (MFC) and nanocellulose made from methyl cellulose was determined. The interaction between the components was assessed from viscosity measurements made at different temperatures, the result being linked to a thermal-dependent association during liquid evaporation, and the subsequent barrier and film-forming properties. The effect of temperature on suspensions was clearly different between the materials, confirming that there were differences in interaction and association between EHEC–MFC and methyl nanocellulose–MFC compositions. The amphiphilic EHEC affected both the suspension homogeneity and the film properties. Air bubbles were formed under certain conditions and composition particularly in MFC films, dependent on the drying procedure. The presence of air bubbles did not affect the oxygen transmission rate or the oil and grease resistance. An increasing amount of MFC improved the oxygen barrier properties of the films.

Epitaxial growth of prussian blue analogue derived NiFeP thin film for efficient electrocatalytic hydrogen evolution reaction

Hydrogen evolution reaction (HER) in water splitting plays an important role in the storage and conversion of clean energy. The development of efficient electrocatalytic materials for HER has attracted much attention in current research. In this work, a homogeneous NiFe-based prussian blue analogue (NiFe-PBA) thin film is prepared on the surface of nickel foam by liquid phase epitaxial (LPE) layer-by-layer (LBL) dipping method. Then the NiFe-PBA film reacts with PH3 produced by sodium hypophosphite to form a bimetal phosphide NiFeP film. The electrocatalytic HER properties under alkaline condition indicate that the NiFeP film only requires 99 ​mV overpotential to reach 10 ​mA ​cm−2 and the performance can be maintained for over 30 ​h without obvious degradation even at 100 ​mA ​cm−2. The results imply that the prepared NiFeP film has excellent HER performance and durable stability. This work is of great significance for the preparation of self-supporting and low-cost bimetal phosphide thin film for efficient HER.

Deposition of Thin Alumina Films Containing 3D Ordered Network of Nanopores on Porous Substrates.

Self-supporting thin films containing nanopores are very promising materials for use for multiple applications, especially in nanofiltration. Here, we present a method for the production of nanomembranes containing a 3D ordered network of nanopores in an alumina matrix, with a diameter of about 1 nm and a body centered tetragonal structure of the network nodes. The material is produced by the magnetron sputtering deposition of a 3D ordered network of Ge nanowires in an alumina matrix, followed by a specific annealing process resulting in the evaporation of Ge. We demonstrate that the films can be easily grown on commercially available alumina substrates containing larger pores with diameters between 20 and 400 nm. We have determined the minimal film thickness needed to entirely cover the larger pores. We believe that these films have the potential for applications in the fields of filtration, separation and sensing.

Self-supporting thin tin targets fabricated by ultra-high vacuum evaporation for heavy-ion induced reactions

Self-supporting thin films of 116,118Sn isotopes have been fabricated using ultra-high vacuum (UHV) facility at the Inter-University Accelerator Centre (IUAC), New Delhi. Owing to the requirements for fusion and quasi-elastic backscattering studies, several self-supporting thin target films with areal density ~ 250–600 μg/cm2 were fabricated. Attempts were also made to prepare thin films by cold rolling technique, and an areal density of ~ 1.8 mg/cm2 could be achieved after several rolling cycles. Various advanced characterization techniques viz., Rutherford Backscattering Spectrometry (RBS), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared (FTIR) Spectroscopy and Field Emission Scanning Electron Microscopy (FE-SEM) were employed to (i) ascertain levels of trace- and heavy-impurities, if present, in the fabricated target films, (ii) determine exact thickness of the films, and (iii) study morphological changes, if any, in the films after irradiation with high energy ion beam fluence of ~1015 ions/cm2. The characterization results manifested that negligible amount of impurities was present in the films, and they were quite stable under energetic ion-beam irradiations. The fabricated films were successfully used as targets in online nuclear physics experiments to measure quasi-elastic backscattering cross-sections in 7Li induced reactions.

Self-Supported Nanocolumnar Platinum Thin Film Catalysts for Oxygen Reduction Reaction

Nanocolumnar platinum thin films (Pt-TFs) were produced by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction electrocatalysts for polymer electrolyte membrane fuel cells. Conventional high-density Pt-TF by low pressure sputtering was also studied for comparison. Pt-TFs were deposited on a microporous layer (MPL)-like surface composed of carbon particles in order to mimic the catalyst coated gas diffusion layer in a membrane electrode assembly (MEA). Scanning electron microscopy and transmission electron microscopy images revealed that HIPS Pt-TFs developed a cauliflower-like columnar microstructures, which originated from a shadowing effect. At high working gas pressure conditions of HIPS, sputtered Pt atoms go through several gas phase collisions, lose their directionality, and can arrive at the substrate surface at oblique angles that results in the formation of columnar islands that shadow the gaps among them from incident flux of atoms. This shadowing effect is believed to be enhanced on the rough surface of MPL-like carbon particles that leads to the formation of nano-cauliflower structures. Electrochemical characterization of the samples was performed by cyclic voltammetry and rotating disk electrode measurements on Pt-TF/MPL-like-layer/glassy-carbon-insert samples in aqueous perchloric acid electrolyte. With this approach, we also aimed to relate the catalyst performance obtained by benchtop tests directly to MEA results. Electrochemically active surface area (ECSA) of PT-TFs were found to be ranging from 10 m2/g to 19 m2/g with increasing sputter pressure, which was determined from the charge for hydrogen adsorption and desorption in the cyclic voltammograms. In addition, carbon monoxide (CO)-stripping of Pt-TF coated gas diffusion electrodes were performed in a fuel cell station and similar ECSA values were recorded (ranging from 11 to 15 m2/g). This indicated that successful mimicking of a gas diffusion electrode in an MEA can be achieved by utilizing an MPL-like substrate surface for benchtop tests in aqueous electrolyte environment as opposed to directly depositing Pt-TFs on glassy carbon inserts. Specific activity (SA) values for conventional high-density and nanocolumnar films were similar that was approximately ~600 μA/cm2, which is believed to correspond to grain sizes of >5 nm as obtained from TEM and XRD analysis. On the other hand, mass-specific (MA) activity values increased from 0.06 A/mgPt for conventional Pt-TF to 0.13 A/mgPt for HIPS Pt-TFs. Higher MA agrees with the columnar microstructure of HIPS thin films that increases the surface to volume ratio of the Pt layer that provides a better catalyst utilization compared to conventional Pt-TFs.

Proton induced differential cross sections on 14N and 28Si from 3 to 4 MeV

In this work commercially available self-supporting thin silicon-nitride films were applied to measure the differential cross sections for the reactions 28Si(p,p′γ)28Si (Eγ = 1779 keV) and 14N(p,p′γ)14N (Eγ = 2313 keV) in the proton energy range of 3–4 MeV. For an additional validation of the data, the cross section from the present work and from the literature were integrated and compared to experimental thick target yields. Gamma-rays were detected simultaneously with backscattered particles using a HPGe detector at 55° and an ion implanted Si detector at 135° with respect to the beam direction. As a by-product, differential gamma-ray and particle production cross sections were measured for the first time in the 29Si(p,p′γ)29Si (Eγ = 1273 keV) reaction at 55°, as well as in the natN(p,po)natN, natSi(p,po)natSi and 28Si(p,p1)28Si elastic and inelastic scatterings at 135° from 3 to 4 MeV proton energies.

Preparation and Chemically Responsive Luminescent Switching of the Flexible Self-supporting TbW10-Agarose Green Emission Thin Films

Preparation and Chemically Responsive Luminescent Switching of the Flexible Self-supporting TbW10-Agarose Green Emission Thin Films

Self-supporting graphene oxide films preparation and characterization methods

Graphene oxide (GO) is prepared as a self-supporting thin film by a liquid solution of GO. The so-obtained GO films have been characterized in terms of thickness and density. The GO film composition and trace elements have been measured with Rutherford backscattering spectrometry (RBS) and Elastic recoil detection analysis (ERDA), using MeV helium ion beams. The presence of crystalline and amorphous phases has been also investigated with X-ray diffraction (XRD) and the morphology by scanning electron microscopy (SEM). Information about the GO film structure, oxidation degree and thickness has been deduced by means of Fourier transform infrared spectroscopy (FT-IR), Raman and optical spectroscopy (ultraviolet-visible-near infrared spectroscopy, UV-Vis-nIR). In particular, the GO film thickness varies from sub-micrometric values up to micrometric ones. Furthermore, the GO film heating in air up to 60 °C produces oxidation effects as deduced from the interpretation of our data.