Varying Deposition Conditions Research Articles

Improvement of synaptic property of GeSe based CBRAM by engineering the deposition condition of switching matrix

A study of effect of deposition condition of germanium selenide (GeSe) switching layer to Conductive bridging random access memory (CBRAM) device property was conducted to enhance memory property and synaptic property. The devices deposited under the varied deposition conditions were analyzed by current distribution of each state (Low-resistance state [LRS], High-resistance state [HRS]), conduction mechanism analysis, chemical analysis, and synaptic analysis according to pulse conditions. When we deposited switching layer at lowest power (40 W), more Ag ions move to the switching matrix and make lower operation voltage. But there were some disadvantages, which were worst distribution and higher HRS current, less memory window, nonlinear and rapid increase of potentiation process. Conversely, although the device deposited at high voltage increased the operating voltage, but there are improvements, such as the highest memory window and improved linearity of potentiation. The best sample was conducted the synaptic property measurement, and the device successfully mimicked the biological synaptic property with the good linearity of potentiation and depression, spike-rate dependent plasticity (SRDP) and spike-timing dependent plasticity (STDP) properties.

Composition Dictates Molecular Orientation at the Heterointerfaces of Vapor-Deposited Glasses.

Physical vapor deposition (PVD) can prepare organic glasses with a preferred molecular orientation. The relationships between deposition conditions and orientation have been extensively investigated in the film bulk. The role of interfaces on the structure is less well understood and remains a key knowledge gap, as the interfacial region can govern glass stability and optoelectronic properties. Robust experimental characterization has remained elusive due to complexities in interrogating molecular organization in amorphous, organic materials. Polarized soft X-rays are sensitive to both the composition and the orientation of transition dipole moments in the film, making them uniquely suited to probe molecular orientation in amorphous soft matter. Here, we utilize polarized resonant soft X-ray reflectivity (P-RSoXR) to simultaneously depth profile the composition and molecular orientation of a bilayer prepared through the physical vapor deposition of 1,4-di-[4-(N,N-diphenyl)amino]styryl-benzene (DSA-Ph) on a film of aluminum-tris(8-hydroxyquinoline) (Alq3). The bulk orientation of the DSA-Ph layer is controlled by varying deposition conditions. Utilizing P-RSoXR to depth profile the films enables determination of both the bulk orientation of DSA-Ph and the orientation near the Alq3 interface. At the Alq3 surface, DSA-Ph always lies with its long axis parallel to the interface, before transitioning into the bulk orientation. This is likely due to the lower mobility and higher glass transition of Alq3, as the first several monolayers of DSA-Ph deposited on Alq3 appear to behave as a blend. We further show how orientation at the interface correlates with the bulk behavior of a codeposited glass of similar blend composition, demonstrating a straightforward approach to predicting molecular orientation at heterointerfaces. This work provides key insights into how molecules orient during vapor deposition and offers methods to predict this property, a critical step toward controlling interfacial behavior in soft matter.

Influence of Si segregates on the structural evolution, mechanical properties, and high-temperature fracture toughness of Cr-Si-B2±z coatings

The impact of Si-segregates and varying deposition conditions on the structural and mechanical properties of sputter deposited, high-temperature oxidation-resistant Cr-Si-B2±z coatings is studied from ambient, to elevated temperatures. Overstoichiometric, AlB2-structured Cr-Si-B2±z thin films with Si-content up to 15 at.% were synthesized on Ti-6Al-4V by magnetron-sputtering using a substrate bias of −120 V. The enhanced surface diffusion promotes mechanically superior, (001)-oriented coatings with hardness of H∼30 GPa up to a Si-content of 3 at.%. Higher Si-concentrations result in significant hardness loss to H∼20 GPa, related to a bias-independent solubility-limit in the CrB2-structure and the formation of mechanically-weak Si grain-boundary segregates. The as-deposited hardness of all Cr-Si-B2±z compositions is maintained after annealing to 800 °C, despite the initiation of material recovery. A B/Cr-ratio-independent oxidation resistance up to 1400 °C is demonstrated, underlining a minimum Si-content of 8 at.% to form a stable SiO2-based scale. In line with the room-temperature hardness, increasing Si-contents are accompanied by decreasing fracture toughness, reducing from KIC∼2.9 (Cr0.28B0.72) to ∼1.7 MPa√m (Cr0.24Si0.10B0.66). High-temperature cantilever bending up to 800 °C revealed a brittle-to-ductile-like transition for Cr0.28B0.72, resulting in an increased fracture toughness of KIC∼3.3 MPa√m. Si-alloyed coatings show decreasing fracture resistance up to 400 °C, whereas beyond, Si-segregates enable high-temperature plasticity and thus a significantly increased damage tolerance.

A novel superhydrophobic Ni-graphene coating and its corrosion resistance

A novel superhydrophobic Ni-graphene coating is synthesized on mild steel by one-step electrodeposition. The microtopography and contact angle of coatings deposited at varied deposition conditions were investigated to obtain the optimized preparation parameters. The anti-corrosion performance of the coatings was investigated by electrochemical polarization in synthetic seawater. The results illustrate that the Ni-graphene coatings deposited at GO concentration of 0.2 g·L–1 and current density of 4 A·dm–2 possessed dual roughness structures. After stored for 14 days in a vacuum drying chamber, the coating exhibited a contact angle of 156.1° and a sliding angle of 6.2°. Furthermore, the corrosion current density of the superhydrophobic coating was only 2.3×10–8 A·cm–2. This facilely prepared fluorine-free Ni-graphene superhydrophobic coating can potentially provide a pathway for corrosion control in the oil and gas industry.

SPR based refractive index modulation of nanostructured SiO2 films grown using GLAD assisted RF sputtering technique

Low refractive index materials have always gained attention for avoiding optical losses in numerous devices like Light emitting diodes (LEDs), Distributed Bragg Reflectors (DBRs) etc. Glancing angle deposition (GLAD) has proven to be an effective method for depositing porous nanostructures with low refractive index. SiO2 has the lowest refractive index in comparison to most of the materials present in nature and is therefore utilized extensively in the fabrication of optical devices with minimum optical losses. The present work focuses on the SiO2 nanostructured thin films grown using glancing angle (GLAD) configuration in RF Sputtering technique under varying deposition conditions (glancing angle and pressure) at fixed thickness. The deposited porous SiO2 nanostructured layers have well-defined nanorods of feature size smaller than 100 nm. The refractive index corresponding to all the deposited SiO2 nanostructured films came out to be smaller than the corresponding value (1.49) mentioned in the literature for bulk SiO2. The refractive index has been observed to vary in a wide range (1.05 to 1.40). Characterization of the deposited SiO2 nanostructured films was carried out using Fourier Transform Infrared (FTIR) spectroscopy, Energy Dispersive X-Ray (EDS) analysis, and Atomic Force Microscopy (AFM) to assess the qualitative properties of the deposited nanostructured SiO2 films. Surface Plasmon Resonance (SPR) and Ellipsometry studies are performed to determine the refractive index value of the deposited nanostructured SiO2 thin films. A refractive index value as low as ∼ 1.05 at a wavelength of 633 nm is achieved for SiO2 nanostructured thin film deposited at 30 mTorr deposition pressure and 80° glancing angle.

Lateral PbS Photovoltaic Devices for High Performance Infrared and Terahertz Photodetectors.

We fabricated a lateral photovoltaic device for use as infrared to terahertz (THz) detectors by chemically depositing PbS films on titanium substrates. We discussed the material properties of PbS films grown on glass with varying deposition conditions. PbS was deposited on Ti substrates and by taking advantage of the Ti/PbS Schottky junction, we discussed the photocurrent transients as well as the room temperature spectrum response measured by Fourier transform infrared (FTIR) spectrometer. Our photovoltaic PbS device operates at room temperature for wavelength ranges up to 50 µm, which is in the terahertz region, making the device highly applicable in many fields.

Optimal design of novel precursor materials for the atomic layer deposition using computer-aided molecular design

Nanomaterials and nanostructures with multi-functional properties found widespread applications such as electronics, optics, and coatings that can be fabricated using Atomic Layer Deposition (ALD). ALD is a vapor phase deposition technique to generate thin films of metals and metal oxides on a substrate. In this process, a precursor, which often comprises of organic functional groups that surround the depositing metal, chemisorbs on the substrate or reacts with the surface sites and with each other. Precursor chemisorption on the substrate leads ALD to be a self-limiting process. Thus, the precursor(s) should be chosen in a way to enhance deposition based on the ALD conditions. For a given application, it is practically impossible to carry out a large number of experiments using numerous precursors with varied deposition conditions to find the one that maximizes the growth rate in ALD. In addition, only existing precursors can be tested experimentally. The overall objective of this work is to develop a computational tool for the in-silico design of precursor materials using adsorbate solid solution theory (ASST). In the first part of this paper, we apply the ASST to derive properties of the functional groups present in the precursor using a new Group Contribution Method (GCM). The GCM is successfully derived and compared with the experimental data from ALD. The method shows good agreement and is useful for the design of novel materials. In the second part of this paper, using the thermodynamic properties as obtained from GCM, we develop a computer-aided molecular design (CAMD) framework for the optimal design of novel precursor materials with enhanced deposition properties for the ALD of metal oxides and metals. The metaheuristic efficient ant colony optimization algorithm (EACO) developed in-house is used for both parts. CAMD is a combinatorial optimization methodology, where molecules with optimal desired properties are generated from functional groups. The precursor selection optimization problem is posed as a mixed integer nonlinear programming problem, which is solved using EACO. The ALD growth kinetics is used as an objective of optimization and a solution is validated with thermodynamic constraints. Along with the number of groups, the temperature is also included in the optimization framework as decision variables. Forty-one novel titanium precursor molecular structures for ALD are generated with growth rates ranging from 1.23 Å/cycle to as high as 1.65 Å/cycle. Thus, these precursors have shown growth rates higher than the known titanium precursors. ALD growth rate is found to be a function of the combination of the precursor functional groups as well as temperature with a complex correlation among them.

Peculiarities of the synthesis of GST films by magnetron sputtering for nonvolatile optical memory cells

The structure and optical properties of thin films of the chalcogenide semiconductor Ge2Sb2Te5, deposited by magnetron sputtering, was studied. A significant change in the topology and optical properties of the films is demonstrated with varying deposition conditions. It is shown that an increase in the deposition time leads to an increase in the surface roughness. Doping with nitrogen during deposition leads to a smoothing of the film surface, and also provides a strong change in the band structure and optical properties.

(Invited) Investigations into Molecular Layer Deposition of Conjugated Amine Polymers

Conjugated amine polymers (CAPs) such as polyaniline and polypyrrole have high electrical conductivities (>500 S/cm), high specific capacities (>500 F/g), and are one of few known material classes containing redox-active sites for binding negatively-charged anions. These properties make CAPs appealing for a range of electrochemical applications including semiconductor devices, energy storage devices, sensors, and electrochemical separation processes. Unfortunately, existing synthesis routes for CAPs rely on rapid chemical or electrochemical oxidation reactions that provide limited control over the molecular structure and thickness of CAPs. This restricts the ability to use CAPs to address technological needs. In this report, we describe ongoing research in our group to deposit conformal CAP films with molecular-scale control of thickness and composition using sequential and self-limiting gas-phase surface reactions. Our approach is in line with established molecular layer deposition (MLD) techniques, and uses an oxidant as one of the MLD precursors in so-called oxidative molecular layer deposition (oMLD). Using select examples, we reveal new insights into oMLD growth behavior, characterize the molecular structures of the oMLD CAP films, and connect structural differences under varying deposition conditions with electrical and electrochemical properties of the films. The insights we report enable the deposition of electrically conductive and redox-active CAP films conformally onto high-surface area samples, opening new avenues to enable advanced electrochemical technologies based on ultrathin and conformal CAP films.

Controlled One-Step Manufacture of Charge Transfer Salt Nanowire Sensors for Gas Detection

Major barriers for commercializing nanowire sensors are complicated synthesis technique and lack of scalable device assembly methods. Charge transfer salts (CTS), like tetrathiafulvalene bromide (TTFBr), have been well known for unique electric and chemical property. This talk will bring a controlled one-step deposition method to fabricate CTS nanowire sensors. By applying certain potentials to designed substrates, TTFBr nanowires can be directly deposited onto the electrodes. Varying deposition conditions and design of substrates are able to control the geometry, density and composition of TTFBr nanowires. TTFBr nanowire sensor shows high sensitivity, selectivity, and fast response towards ammonia gas. The detection limit is less than 1ppm and the response time, at room temperature, is less than 1 minute. Other CTS, like Cu- tetracyanoquinodimethane, can also be fabricated into nanowire sensor using the same method. This research shows a promising scalable fabrication method for various nanowire sensors and is being commercialized.

Effect of varying deposition conditions of magnetite on sawdust on the physiochemical properties of the prepared composites

This work reports a novel study for deposition of magnetite (Mag) on olive wood sawdust (OW) by the coprecipitation-hydrothermal method under dominating deposition factors including deposition temperature of magnetite by OW, agitation time, magnetite deposition in presence/absence of OW, magnetite/OW mass ratio, pyrolysis of final composites. The composites were characterized by IR, XRD, TGA, surface area (by N2 and methylene blue adsorption test) and lead uptake The effect of experimental factors on physicochemical properties were addressed. Principal component analysis (PCA) was found effective for understanding the differences among composites. It was found that magnetite deposition has relatively increased the stability of OW against degradation. XRD and IR data showed that not only various deposition conditions caused deposition of various amounts of iron oxides and magnetite on wood surface; but also the amount of deposited iron oxides exceeded that of magnetite. Pb ions adsorption was significantly affected by the deposition conditions in which deposition time was the most dominant among the tested factors as 5 h stirring (at 50 °C) achieved the best lead uptake. In general, deposition of magnetite by OW reduced porosity of composites. The prepared composites were effective for Pb removal with capacitates 22–49 mg g−1 at pH 7.0. Not all physicochemical parameters were effective for composites grouping. Surface areas and Pb uptake were most responsive for experimental conditions.

Functional Data Analysis of Electrical Measurements on Thin-Film Photovoltaic Devices

Cu(In,Ga)Se2 (CIGS)-based photovoltaic cells were fabricated under varying deposition conditions for the Mo back contact and CIGS absorber layers. Specifically, O2 concentration and sputtering pressure were varied during the Mo deposition, as well as the final Mo-layer thickness. The maximum deposition temperature was then varied during the subsequent deposition of the CIGS-layer by thermal coevaporation. The JV response curve of the finished devices were recorded and used to calculate the usual solar performance characteristics (efficiency, J sc, V oc, fill-factor, R oc, and R sc). The effects of the varied fabrication conditions on these characteristics were then investigated, and CIGS-deposition temperature alone was found to have had a significant influence on J sc. Following this, the entire JV -curve was analyzed using functional data analysis (FDA). The curve shape was revealed to be affected not only by temperature, but by O2 conc. and Mo sputter pressure as well. The effect of these fabrication parameters was greatest in regions of the curve larger than V oc. External quantum efficiency measurements on the finished devices were also studied using FDA, indicating a strong influence of temperature in reducing collection across most of the visible spectrum. Mechanisms that aim to explain these observations are proposed. This work details, according to the authors’ best knowledge, the first-ever use of FDA in the analysis of photovoltaic devices.

Growth and characterization of β-Ga2O3 thin films on different substrates

β-Ga2O3 thin films were grown on the substrates of sapphire, GaN, and single crystals of β-Ga2O3, using plasma-assisted molecular beam epitaxy. By varying deposition conditions, pure-phase epitaxial β-Ga2O3 thin films were obtained, and the crystal quality of the as-grown films was optimized. A systematic characterization and a detailed analysis were performed on the films, including the nucleation process, surface morphology, crystal quality, thermal stability, as well as electrical and optical properties. Optical absorption was investigated using photothermal deflection spectroscopy, which provides detailed information about sub-gap optical absorption. Photocurrent measurements indicated a pronounced persistent photo-conductivity of β-Ga2O3. A blue-UV emission with an energy of 3–3.5 eV was observed by cathodoluminescence spectroscopy. The Fermi level position of the as-grown film was determined based on temperature-dependent electrical conductivity measurements. It is proposed that oxygen vacancies in the film form a defect band at around Ec-0.8 eV that pins the Fermi level and is related to the observed photocurrent and cathodoluminescence characteristics.

Quality management of high-efficiency planar heterojunction organic-inorganic hybrid perovskite solar cells

The energy extracted from solar radiation is the most abundant and accessible source of renewable energy, which will become progressively more important as time goes on. Solar cells are regarded as one of the most promising candidates for generating renewable clean energy. Recently, a new class of semiconducting material called organic-inorganic halide perovskite has received great attention of academia, and the record power conversion efficiency (PCE) of perovskite solar cell (PSC) rapidly increased from 3.8% in 2009 to 22.7% in late 2017 through intensive research due to some advantages as follows. 1) Excellent optoelectronic property. Perovskite materials exhibit excellent properties, including long diffusion length, high carrier mobility, and high absorption coefficient. 2) Low cost. The ingredients of perovskite materials are cheap, and PSCs can be manufactured by a solution process. 3) Tunable bandgap. Perovskite materials have highly tunable bandgap (1.2-2.2 eV), contributing to the further improvement in PCE of single junction PSCs by realizing the ideal bandgap (1.3-1.4 eV) as demonstrated by the Shockley-Queisser detailed balanced calculation. The basic architectures of PSCs are divided mainly into mesoscopic and planar heterojunction structures. Compared with the former configuration, the later configuration combined with low-temperature processable interlayers provides a method of fabricating flexible PSCs and tandem PSCs. Furthermore, the nonuse of the mesoscopic structure simplifies the structure of PSCs and reduces the cost and time of fabrication. The key requirement to achieve an efficient and reproducible planar heterojunction PSCs is that the perovskite layer should be uniform, continuous, and pinhole free to minimize shunting pathways. So, significant research effort is being devoted to the quality management of perovskite films with the goal of achieving the controllable preparation, including the optimization of their morphology (uniformity, coverage, roughness) and microstructure (grain size/distribution, texture), and the elimination of defects (voids, pinholes, grain boundaries), which influence the PSC performance directly. Especially for the one-step solution coating method, the film quality of perovskite on different planar substrates under varied deposition conditions exhibits a large difference, due to the complex crystallization process and the heightened sensitivity to environmental conditions. In this paper, the characteristics of perovskite materials, the nucleation-growth mechanism of films in the one-step solution method, and the evolution of cell structures are described briefly. The latest quality control methods of high-quality perovskite films prepared by solution method are then discussed emphatically. Finally, to provide references for the future research, the development and existing problems of PSCs are addressed and prospected.

Controllable deposition of regular lead iodide nanoplatelets and their photoluminescence at room temperature

In this work, the synthesis of regular single crystalline lead iodide nanoplatelets are carried out based on the physical vapor phase deposition method. Different lead iodide nanoplatelets are obtained by tuning the location of the mica substrate along with the temperature of the tube furnace. The rules of size, thickness, density of the lead iodide nanoplatelets at varied deposition conditions are analyzed according to the crystal growth principles. It was claimed in literature that the photoluminescence of lead iodide could be obtained only at a low temperature (lower than 200 K). Here, at room temperature, we successfully obtained the photoluminescence spectra of the prepared lead iodide nanoplatelets, which possess two apparent peaks due to the biexcitons and the inelastic scattering of excitons, respectively. Our present study contributes to the development of nanoscaled high performance optoelectronic devices.

Fern-like Nickel Cobalt Sulfide Electrocatalyst Prepared By Electrodeposition and Subsequent Sulfur Ion Exchange for Water Electrolysis

Recently, the attention on development of eco-friendly sustainable energy have been gradually increased, owing to the fossil fuel depletion and global warming. Among them, the utilization of hydrogen energy produced from water electrolysis is the one of the prominent methods to solve the problems due to the environmental-friendly characteristic of hydrogen energy. Representative study on water electrolysis is focusing on highly efficient and lower cost electrode development. It has been known that the Pt and IrO2 is the most activate catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. However, they are very rare and expensive, indicating that the severe cost problem is still remained for hydrogen production from water electrolysis. To solve the problem many efforts have been conducted to the development of non-noble metal based catalysts as comparably active as Pt for HER and IrO2 for OER. In particular, the researches on transition metal compounds: M-X (M=Ni, Co, Fe and X= S or P) catalysts have been dominative during the past few years. In this study, we have fabricated the fern-like NixCoyS1-x-y catalyst for water electrolysis. Firstly, NixCoyO1-x-y was electrodeposited on the carbon paper (CP) by two-step galvanostatic deposition. The morphology and composition of fern-like NixCoyO1-x-y were controlled by varying deposition conditions. Then, annealing process was conducted to further oxidization of NixCoyO1-x-y. As a last step, sulfur ion exchange was carried out on the NixCoyO1-x-y by changing dipping time in sodium sulfide solution at 90 °C. Through field emission scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction, formation of fern-like NixCoyS1-x-y was confirmed after the sufficient dipping time. Based on the electrochemical surface area, the intrinsic activity of NixCoyS1-x-y catalysts showed compositional dependence activity for water electrolysis.

Tunable, Liquid Resistant Tip Enhanced Raman Spectroscopy Probes: Toward Label-Free Nano-Resolved Imaging of Biological Systems.

Tip enhanced Raman spectroscopy (TERS) has been established as a powerful, noninvasive technique for chemical identification at the nanoscale. However, difficulties, including the degradation of probes, limit its use in liquid systems. Here TERS probes for studies in aqueous environments have been demonstrated using titanium nitride coatings with an alumina protective layer. The probes show enhancement in signal intensity as high as 380% in liquid measurements, and the probe resonance can be tuned by varying deposition conditions to optimize performance for different laser sources and types of samples. This development of inexpensively produced probes suited for studies in aqueous environments enables its wider use for fields such as biology and biomedicine in which aqueous environments are the norm.

Versatile approaches to tune a nanocolumnar structure for optimized electrical properties of In2O3 based gas sensor

In this study, we demonstrate tuning of electrical properties and sensing responses of In2O3 nanocolumnar structure via varying glancing angle (GLAD) deposition conditions by e-beam evaporator. The varied deposition conditions include glancing angle, vacuum level and deposition rate. The electrical property of In2O3 nanostructured thin films, demonstrated by the base resistance, change up to 3 orders of magnitude from 110Ω to 103104Ω depending on the porosity of nanocolumnar structure and oxygen vacancy concentration. This variation in electrical property transfers to the tuning of gas sensing response, and we achieve tuning the same material (In2O3) based gas sensors to better perform for specific type of gases (either oxidizing or reducing). The highest responses achieved in this work reached up to 176 for oxidizing gases (5ppm NO2, Rgas/Rair) and 929 for reducing gases (50ppmC2H5OH, Rair/Rgas). Therefore, we demonstrate that gas sensors can be optimized for specific type of target gases with the same material, via simple control of deposition conditions. Along with the high reproduciblility and sensitivity, this puts the nanocolumnar thin film based gas sensors by GLAD with huge potential for further miniaturization and mass production, suitable for the upcoming IoT era.

Combinatorial refinement of thin-film microstructure, properties and process conditions: iterative nanoscale search for self-assembled TiAlN nanolamellae.

Because of the tremendous variability of crystallite sizes and shapes in nano-materials, it is challenging to assess the corresponding size-property relationships and to identify microstructures with particular physical properties or even optimized functions. This task is especially difficult for nanomaterials formed by self-organization, where the spontaneous evolution of microstructure and properties is coupled. In this work, two compositionally graded TiAlN films were (i) grown using chemical vapour deposition by applying a varying ratio of reacting gases and (ii) subsequently analysed using cross-sectional synchrotron X-ray nanodiffraction, electron microscopy and nanoindentation in order to evaluate the microstructure and hardness depth gradients. The results indicate the formation of self-organized hexagonal-cubic and cubic-cubic nanolamellae with varying compositions and thicknesses in the range of ∼3-15 nm across the film thicknesses, depending on the actual composition of the reactive gas mixtures. On the basis of the occurrence of the nanolamellae and their correlation with the local film hardness, progressively narrower ranges of the composition and hardness were refined in three steps. The third film was produced using an AlCl3/TiCl4 precursor ratio of ∼1.9, resulting in the formation of an optimized lamellar microstructure with ∼1.3 nm thick cubic Ti(Al)N and ∼12 nm thick cubic Al(Ti)N nanolamellae which exhibits a maximal hardness of ∼36 GPa and an indentation modulus of ∼522 GPa. The presented approach of an iterative nanoscale search based on the application of cross-sectional synchrotron X-ray nanodiffraction and cross-sectional nanoindentation allows one to refine the relationship between (i) varying deposition conditions, (ii) gradients of microstructure and (iii) gradients of mechanical properties in nanostructured materials prepared as thin films. This is done in a combinatorial way in order to screen a wide range of deposition conditions, while identifying those that result in the formation of a particular microstructure with optimized functional attributes.

Nanostructured manganese oxide and manganese oxide/polyethylenedioxythiophene rods electrodeposited onto nickel foam for supercapacitor applications

A template-free anodic electrodeposition process was utilized to deposit Mn oxide and Mn oxide/PEDOT rods onto Ni foam substrates for use as supercapacitor electrodes. Deposit morphology was optimized by varying deposition conditions and by characterization using electron microscopy. The deposits were poorly crystalline, and electron diffraction patterns could be indexed to either a cubic spinel structure (Mn3O4) or a hexagonal birnessite structure (MnO2). The deposits had an overall oxidation state of Mn3+ before cycling and Mn4+ after 500 cycles. The maximum capacitance values for deposits with and without PEDOT were 159 and 120 F g−1 (500 and 290 mF cm−2), respectively, measured using CV at a scan rate of 5 mV s−1. The addition of the PEDOT coating reduced Mn oxide dissolution during cycling up to 500 cycles. Uncoated samples showed an increase in capacitance during cycling, which is attributed to the oxidation state change and the redeposition of Mn oxide in areas of high conductivity. Capacitance retentions after 2000 cycles were 46 and 120 % for deposits with and without PEDOT, respectively.