Surface Resistance Of Films Research Articles

Studying the structure and electrical conductivity of thin granulated bimetallic films

The surface resistance of bimetallic granular films prepared by means of laser-induced deposition is studied. The possibility of modeling their conductivity is demonstrated, depending on their morphological properties.

The role of surface films during lithiation of amorphous and anatase TiO2 nanotubes

X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy are used to investigate the electrochemical lithiation/delithiation behaviour of self-organized amorphous TiO2 and anatase TiO2−x nanotubes. With proceeding bulk lithiation of the active material, surface films form on both nanotube arrays. Carbonates start forming with the beginning of the phase transitions and are reversibly desorbed upon delithiation, on both materials. LiF is found to mainly influence the lithiation/delithiation properties on amorphous nanotubes due to an important decrease of the surface film resistance and an increase of the surface film capacitance at potentials ≤2.0V, where large amounts of LiF adsorb at the surface. Surface film formation is found to be completely reversible on amorphous nanotubes, while CO, CO and fluoride containing adsorbates partially stay adsorbed on anatase nanotubes. The higher reversibility of the surface chemistry on amorphous TiO2 nanotubes is therefore assumed to be essential for the higher rate capability, faster kinetics, and the higher capacity retention observed for amorphous TiO2 materials. This demonstrates that lithiation properties can be substantially altered through changes of the surface chemistry, which can be used to improve kinetics and cycling stability of titania based anode materials in general.

High performance Sb2S3/carbon composite with tailored artificial interface as an anode material for sodium ion batteries

The electrochemical comparison between Sb2S3 and its composite with carbon (Sb2S3/C) involved by sodium ion carrier are explained by enhanced kinetics, particularly with respect to improved interfacial conductivity by surface modulation by carbon. Sb2S3 and Sb2S3/C are synthesized by a high energy mechanical milling process. The successful synthesis of these materials is confirmed with X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). As an anode material for sodium ion batteries, Sb2S3 exhibits an initial sodiation/desodiation capacity of 1,021/523 mAh g-1 whereas the Sb2S3/C composite exhibits a higher reversible capacity (642 mAh g-1). Furthermore, the cycle performance and rate capability of the Sb2S3/C composite are estimated to be much better than those of Sb and Sb2S3. Electrochemical impedance spectroscopy analysis shows that the Sb2S3/C composite exhibited charge transfer resistance and surface film resistance much lower than Sb2S3. X-ray photoelectron spectroscopy analyses of both electrodes demonstrate that NaF layer on Sb2S3/C composite electrode leads to the better electrochemical performances. In order to clarify the electrochemical reaction mechanism, ex-situ XRD based on differential capacity plots and ex-situ HR-TEM analyses of the Sb2S3/C composite electrode are carried out and its reaction mechanism was established.

Identifying Contact Resistances in High-Voltage Cathodes By Impedance Spectroscopy

Lithium-Ion Batteries containing a high-voltage positive electrode as LiNi0.5Mn1.5O4 (LNMO) have a high operating voltage and are therefore considered for high energy batteries [1]. However, it’s high potential (4.75 V vs. Li/Li+) causes some severe side reactions, especially at elevated temperatures, such as electrolyte oxidation and transition metal dissolution [2]. A further failure mechanism of graphite/LNMO cells is the increase of the cell impedance during cycling [1]. In the literature, the impedance spectrum (in Nyquist representation) of the LNMO electrode (measured versus a reference electrode) is commonly described by a high-frequency semi-circle and one at lower frequencies [3]. The impedance spectra are interpreted as a surface film resistance (R SF ) which is attributed to the semi-circle at high frequencies and a charge transfer resistance (R CT ) for the semi-circle at low frequencies [3, 4]. The aim of this study is to examine the true origin of the semi-circle at high frequencies and its implications for the failure mechanism of high-voltage cells. This was examined by assembling graphite/LNMO and graphite/LFP Swagelok T-cells equipped with a gold-wire reference electrode (GWRE) [5] and using 1 M LiPF6 in EC/EMC (3/7 by volume) as electrolyte. The cycling procedure was carried out at 40 °C. The GWRE allows the measurement of the half-cell impedances (anode vs. RE and cathode vs. RE) during cycling, so that the impedance evolution of each electrode can be monitored independently. By means of temperature dependent impedance measurements (0°C, 10°C and 40°C) we will show that the semi-circle at high frequencies (100 kHz – 100 Hz) corresponds to a resistance at the interface between the LNMO electrode and the current collector (contact resistance, R Contact ) rather than to a surface film resistance (R SF ). This is based on the finding that the semi-circle at high frequencies shows negligible temperature dependence, whereas the semi-circle at low frequencies (100 Hz – 1 Hz) strongly depends on temperature. A low temperature dependence is typically reported for a contact resistance in Li-Ion batteries [6]. Furthermore, we will prove that the high-frequency semi-circle corresponds to a contact resistance by: (i) compressing the T-cell after 50 cycles, and (ii) coating the LNMO electrode on a glassy carbon support. In the first case (i), the high frequency semi-circle is no longer observable, and in case (ii), the increase of R Contact is lower by a factor of ten compared to a LNMO electrode coated on an aluminum substrate. As a next step, the potential dependence of the increasing R Contact will be investigated. In Figure 1, graphite/LFP cells are charged to different upper-cut-off potentials (4.0 V, 4.5 V and 5.0 V cell voltage). It can clearly be seen that between 4.5 and 5.0 V the LFP impedance shows an additional semi-circle at high frequencies (R Contact ). This leads us to the conclusion that the increase of R Contact is a potential dependent rather than a material dependent property and thus might also play a role in all high-voltage materials (e.g., in overlithiated NCM’s with upper-cut off potentials of »4.7 V vs. Li/Li+). Lastly, we will show XPS spectra of cycled current collectors and identify the origin of R Contact . Figure 1: (a) Two formation cycles (C/10) are carried out in a graphite/LFP (on carbon-coated aluminum foil) cell with a GWRE (two glassfiber separators, 60 µL of 1 M LiPF6 in EC/EMC, 3/7). Subsequently, the cell is charged to 4.5 V and 5.0 V cell voltage at C/2. (b) The Impedance is recorded at 50% SOC (indicated by black symbols in a) after each upper potential step (at 40°C from 100 kHz to 0.1 Hz with a perturbation of 0.5 mA).

Influence of electropolymerization temperature on corrosion, morphological and electrical properties of PPy doped with salicylate on iron

In this work, the influence of the electropolymerization temperature on corrosion, morphological and electrical properties of polypyrrole (PPy) film is studied. Polypyrrole is electrochemically synthesized on iron in the presence of sodium salicylate. The X-ray diffraction and scanning electron microscopy are performed in order to study the structure and morphology of electrodeposited PPy. The electroactive surface area, corrosion performance and resistance of the PPy film on iron are also investigated as a function of electropolymerization temperature. The results show that the synthesis temperature significantly affects the properties of the PPy film on iron. It is observed that at 25°C amorphous PPy is formed, whereas lowering the temperature leads to the formation of a film containing crystallites of salicylic acid. The latter reveals lower corrosion protection and a much higher level of resistance compared to the amorphous one. These characteristics were associated with the presence of insulating salicylic acid crystals in the layer structure.

Ultrasonic-assisted preparation of graphene oxide carboxylic acid polyvinyl alcohol polymer film and studies of thermal stability and surface resistivity

In this paper, flake graphite, nitric acid and acetic anhydride are used to prepare graphene oxide carboxylic acid (GO-COOH) via an ultrasonic-assisted method, and GO-COOH and polyvinyl alcohol polymer (PVA) are used to synthesize graphene oxide carboxylic acid polyvinyl alcohol polymer (GO-COOPVA) via the ultrasonic-assisted method, and GO-COOPVA is used to manufacture graphene oxide carboxylic acid polyvinyl alcohol polymer film (GO-COOPVA film) via a solidification method, and the structure and morphology of GO-COOH, GO-COOPVA and GO-COOPVA film are characterized, and the thermal stability and surface resistivity are measured in the case of the different amount of GO-COOH. Based on the characterization and measurement, it has been successively confirmed and attested that carboxyl groups implant on 2D lattice of GO to form GO-COOH, and GO-COOH and PVA have the esterification reaction to produce GO-COOPVA, and GO-COOPVA consists of 2D lattice of GO-COOH and the chain of PVA connected in the form of carboxylic ester, and GO-COOPVA film is composed of GO-COOPVA, and the thermal stability of GO-COOPVA film obviously improves in comparison with PVA film, and the surface resistivity of GO-COOPVA film clearly decreases.

Procedure to determine the impact of the surface film resistance on the hygric properties of composite clay/fibre plasters

The experimental determination of dynamic mass transfer properties of porous materials such as eco-efficient clay plasters is greatly influenced by the convective conditions at the surface of the material during the test. The measurement of the intrinsic vapour permeability of highly porous materials has shown to present wide discrepancies when the surface film resistance is not known. Therefore, a proper assessment of the hygric properties of clay plasters requires the determination of such resistance to vapour flow. An adapted experimental procedure was used to determine intrinsic water vapour permeability taking into account the influence of the surface film resistance. The moisture buffering test was used to measure dynamic exchange behaviour. The results gave evidence on the thickness of the active layer in the material and the impact of surface resistance on the exchange behaviour. A 1D mass transfer model was used to verify the validity of corrected vapour permeability by the surface film resistance and discuss its nature and influence on dynamic results.

Enhanced corrosion resistance of austenitic Fe-Mn-C TWIP steel by cerium(III) in 1 M hydrochloric acid pickling solution

The influence of rare earth Ce3+ ions on the corrosion behaviour of Fe-Mn-C TWIP steel in 1 M hydrochloric acid solution was studied by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Electrochemical corrosion tests showed that Ce3+ can significantly reduce corrosion deterioration up to 1.0 mM. Beyond that level the corrosion rate increases till a steady value. Surface film resistance increases with time evolution until 24 h, then decreases and stabilises. High corrosion protection of steel surface after 24 h exposure to the acidic solution containing the optimal Ce3+ ion concentration is revealed by SEM investigations.

Influence of Cold Deformation and Phase Transformation on the Electrochemical Corrosion Behavior of Nitrogen‐Alloyed Stainless Steel in Chloride Solution

Nitrogen‐alloyed stainless steels exhibit outstanding corrosion resistance in chloride solution. However, cold deformation and phase transformation can influence the materials surface properties and, therefore, corrosion behavior. A nitrogen‐alloyed stainless steel with 20 wt% chromium, 0.13 wt% nitrogen, and subject to plastic deformation of up to 36% is electrochemically tested in a 5 wt% sodium chloride solution by linear polarization and electrochemical impedance spectroscopy. The steel's corrosion behavior is distinctly influenced by its deformation state. Before polarization, a negative influence of plastic deformation on the corrosion resistance of the alloy can be determined. However, after anodic polarization, the susceptibility to corrosion due to cold deformation and phase transformation decreases. While the electrochemical resistance of the protective surface film decreases due to deformation‐induced film rupture and the formation of anodes at the surface, the permeability of the double layer also decline. This is caused by the increased activation of the surface due to the formation of local anodes and, therefore, an increase in the formation of protective species that retard further dissolution processes. In addition, increasing plastic deformation results in the surface ratio between anodes and cathodes becoming more favorable, and in a decrease in the anodic current density.

Analyzing High-Voltage Graphite/Lnmo Cells with a Novel Impedance Procedure Utilizing a Micro-Reference Electrode

Graphite/LiNi0.5Mn1.5O4 full cells show severe capacity fading, especially at elevated temperatures, frequently related to: (i) electrolyte oxidation, (ii) transition metal dissolution, and (iii) damage of the Solid Electrolyte Interphase (SEI) on the graphite anode [1]. All these effects can lead to an increase in the full-cell impedance. However, to understand the degradation mechanism of high-voltage Li-Ion batteries, anode and cathode impedances have to be investigated separately. To deconvolute the contribution of anode and cathode from the full-cell impedance, micro-reference electrodes can be used [2, 3]. This type of reference electrodes allows to record the impedance of anode and cathode during cycling without the need of full-cell disassembly to determine anode and cathode impedance in symmetric cells [4]. Commonly the semi-circles in a Nyquist plot are interpreted as combination of a charge transfer resistance (R CT) and a surface film resistance (R SF), e.g., the solid electrolyte interphase (SEI) on graphite anodes [5]. However, the contributions of the ionic resistance (R Ionic) in the pores of the electrode and also the contact resistance (RContact ) between the active material/current collector interface are often neglected, which can lead to misinterpretations in the impedance analysis [6]. In this study, we use a novel impedance approach utilizing a gold-wire reference electrode (GWRE) [2], which allows for the recording the half-cell impedances in its deconvolution into contributions from: (i) contact resistance (R Contact), (ii) ionic resistance in the pores (R Ionic), and (iii) charge transfer resistance (RCT ). This is illustrated for a cathode without surface film formation. Therefore, graphite/LiNi0.5Mn1.5O4 (LNMO) cells are assembled, which are equipped with a gold-wire reference electrode (GWRE) [2] and contain 1 M LiPF6 in EC/EMC (3/7 by volume) as electrolyte. The impedance is measured at two distinct points during cycling: (i) at 50% state of charge (SOC) and (ii) at 100% SOC. Both impedance spectra are analyzed using Matlab employing a transmission line model. Figure 1 exemplarily presents the results of the impedance analysis for more than 80 cycles of a LNMO electrode in a full-cell. We can show that the R CT has only minor contribution to the half-cell impedance of the LNMO cathode and that R Contact and R Ionic are the dominating resistances, which are slightly increasing during cycling. We explain the higher ionic resistance in the pores with electrolyte oxidation products, causing pore clogging. Furthermore, we will show results for the negative electrode (Graphite). Therefore, the anode is analyzed analogously and these results are compared with Graphite/LFP cells, where the upper cut-off potential is lower by 0.8 V (compared to a graphite/LNMO cells). Hence, electrolyte oxidation products should not affect cathode or anode. Figure 1: Fitted resistances from the Nyquist plots at 50% and 100% SOC. The Impedance is recorded at 40°C from 100 kHz to 1 Hz with a perturbation of 15 mV. The Loading of the anode was 6.6 mgGraphite/cm2 (0.95 cm2 area) and 13 mgLNMO/cm2 (0.95 cm2 area) for the cathode. A Swagelok T-cell with 60 ml 1M LiPF6 in EC/EMC (3/7 by volume) and two glass fiber separators with a gold-wire reference electrode (GWRE) was used.

Effects of ordered islands on surface resistivity: Ni on Au(111).

The change in surface resistivity due to the formation of nickel islands on gold(111) was studied by measuring the resistance of a thin film of Au as a function of Ni coverage, θ. Previous studies showed that the Au(111) herringbone reconstruction provides a template for the periodic growth of ordered islands. Ni islands grow radially until θ ≈ 0.3 ML, after which subsequent Ni atoms contribute primarily to a second layer. Since Ni atoms on Au(111) grow in ordered nanoclusters, a nonlinear dependence of resistance on θ might be anticipated. Our results, however, show a linear dependence for Ni atoms in the first layer, as if they were independent point scatterers. Above θ ≈ 0.3 ML, there is little change in resistivity, which we attribute to Ni atoms in the second layer making no significant contribution to the resistivity. Although we did not directly image the islands, our results are consistent with the growth model and structures previously observed with scanning tunneling microscopy. Our results serve as an indirect probe of the growth kinetics of this system, as well as determining the contributions of Ni islands to the surface resistivity of the Au film.

Fast formation cycling for lithium ion batteries

Abstract The formation process for lithium ion batteries typically takes several days or more, and it is necessary for providing a stable solid electrolyte interphase on the anode (at low potentials vs. Li/Li+) for preventing irreversible consumption of electrolyte and lithium ions. An analogous layer known as the cathode electrolyte interphase layer forms at the cathode at high potentials vs. Li/Li+. However, several days, or even up to a week, of these processes result in either lower LIB production rates or a prohibitively large size of charging-discharging equipment and space (i.e. excessive capital cost). In this study, a fast and effective electrolyte interphase formation protocol is proposed and compared with an Oak Ridge National Laboratory baseline protocol. Graphite, NMC 532, and 1.2 M LiPF6 in ethylene carbonate: diethyl carbonate were used as anodes, cathodes, and electrolytes, respectively. Results from electrochemical impedance spectroscopy show the new protocol reduced surface film (electrolyte interphase) resistances, and 1300 aging cycles show an improvement in capacity retention.

Effects of the starting materials of Na0.44MnO2 cathode materials on their electrochemical properties for Na-ion batteries

Na0.44MnO2 is one of the most promising cathode materials in the development of sodium ion batteries (SIBs). Here, a solid-state method is described for the synthesis of regular Na0.44MnO2 nanorods about 200nm in size at a low temperature without further annealing being required. In this work, we have investigated effects of different precursors on preparation of Na0.44MnO2 and found that the size and width of the Na0.44MnO2 nanorods were influenced by the MnCO3 precursors. The electrochemical properties for SIBs of Na0.44MnO2 nanorods synthesized from three different preparation methods were thoroughly researched. Na0.44MnO2 nanorods prepared by hydrothermal synthesis of MnCO3 (HS-Na0.44MnO2) produced a superior cathode material than other Na0.44MnO2 which uses commercial MnCO3 (C-Na0.44MnO2) and co-precipitation synthesis of MnCO3 (CP-Na0.44MnO2) as precursors. The HS-Na0.44MnO2 exhibits high discharge capacity (about 139.6mAhg−1), good cycling stability (98.2% after 40 cycles at the current density of 20mAg−1) and excellent rate performance, which is a much better performance than those in previous reports. The superior electrochemical performance of HS-Na0.44MnO2 is mainly due to the relatively smaller size, uniform morphology and excellent crystallinity. Furthermore, the electrochemical impedance spectroscopy (EIS) showed that the surface film resistance and charge transfer resistance of the HS-Na0.44MnO2 is smaller than others, which leading to the better electrochemical performance.

Thin Film Surface Chemo-Resistivity Tuning Using Metal Deposition Via Slrr

The interaction of SH-, or S2- with Au surface has been phenomenon of considerable interest in last decade. The Au-S adsorption bond was studied as convenient linker for many complex molecules such as alkane-thiols, proteins, 3D molecular structures for molecular electronics, or for biological sensors applications [[1]]. The adsorption of SH-, or S2- to the Au is enabled by formation of strong S-Au bond (few eV energy) [[2]], which is stable in a wide potential range from Au surface oxidation (1.2 V vs. SHE) to reductive dissociation of Au-S bond (~-0.6 V vs. SHE). The change in the energetics of the surface states due to HS-, S2- adsorption does affect the surface resistance of ultrathin Au films. This effect is mainly due to S-adsorbate induced changes to quality of electron scattering from the surface states [[3]]. Therefore, an adsorption process of SH-, or S2-on Au can be indirectly observed by measuring the change in the overall resistance of the Au thin films. In this talk we will present data studying chemo-resistive properties of Au ultrathin films exposed to solutions containing Cl- and HS- ions in 0 – 100 ppm range, Figure 1. The surface modification of these films was done by deposition of few monolayers of Au, Pd and AuPd via SLRR of Pb UPD [[4]]. The change in resistivity of Au films as a function of the solution composition was measured by AC method in order to minimize the effect of parasitic current path through the solution. As deposited Au films showed very small surface chemo-resistance while the films modified by few monolayers of Au, Pd and AuPd deposit have shown much better performance. To analyze our data we have developed comprehensive analytical model which links the adsorption process of different anions from the solution to the change in the diffused scattering coefficient for electrons from the surface [[5]]. Experimental results and analysis show that modifications of the Au surface, with several monolayers of Au and Pd, increases probability for electron scattering from the surface and improves the chemo-resistance of ultrathin Au films. The significance of our findings is discussed for chemical sensors design shining a new light on the importance of surface preparation for chemo-resistive sensor performance, Figure 1. The authors acknowledge the support from Baker Hughes Corporation and NSF Chemistry division under the contract # 0955922. [1] Nanoelectronics, Nanowires, Molecular Electronics, and Nanodevices, K. Iniewski, Mc Graw Hill, New York (2013). [2] Y. Jin, C. Yu, R.J. Denman, W. Zhang, Recent Advances in Dynamic Covalent Chemistry, Chemical Society Reviews 42, 6634 (2013) [3] Ultrathin Electrochemical Chemo- and Biosensors, eds. O.S. Wolfbeis, and V. M. Mirsky, Springer (2013), p. 120 [4] S. R. Brankovic , J. X. Wang and R.R. Adzic, Surface Science , 474, L173, (2001). [5] E. H. Sondheimer, Advances in Physics, 1, 1 (1952). Figure 1

A New Anion Receptor for Improved Interface Between the Lithium- and Manganese-Rich Layered Oxide Cathode and the Electrolyte

Significant progress has been made in lithium-ion batteries for applications in electric vehicles and grid energy storage. The deep market penetration of the LIB technology would be further accelerated if methods to further increase energy density, stability and cycle life can be identified and developed. Although intensively studied in the last several decades, cathode materials are still considered a major limiting factor in LIB performance. In the past few years, remarkable efforts have been dedicated to studying a family of lithium- and manganese-rich layered oxides, with a general formula of Li1+x M1-x O2 (M=Mn, Ni, Co etc). [1] Depending on the composition, the oxides can deliver capacities exceeding 250 mAh/g at an average potential of about 4.6 V vs. Li+/Li. While they have the potential to drastically improve the energy density of lithium-ion batteries, there are several critical problems, including a large first-cycle irreversible capacity loss associated with the activation process, subsequent-cycle voltage decay characterized by a continuous decrease in average discharge voltage during cycling, transition-metal dissolution into the electrolyte, sluggish kinetics, and a high impedance at low state of charge (SOC), prevent their application in commercial batteries. In addition, the high charging potential of these materials along with the catalytic properties of the high-valent transition metals in the charged cathode oxidize carbonate solvents and decompose the electrolyte. [2] These reactive interactions between the electrode and the electrolyte, or side reactions, not only leave surface deposits onto the cathode, but also modify the intrinsic properties, including elemental, chemical and structural, of the cathode surface. While the stability of resulted cathode-electrolyte interface (CEI) layer, like solid electrolyte interface of anode, is largely influenced by the chemical nature (both organic and inorganic) and the distribution of the side reaction products, studies have shown that a build-up in CEI can increase the charge transfer resistance and deteriorate electrochemical performance. Previous research has demonstrated the important role of electrolyte additives in influencing the CEI and battery performance.[3] For example, boron-based anion receptors that can dissolve electrolyte decomposition byproducts, such as LiF, Li2O and Li2O2, are capable of enhancing long-term cycling of LIBs. To date, however, most studies have focused on the compositional engineering of additives. The general knowledge of how electrolyte additives influence the changes on the cathode particle surface and interfere with the electrolyte/electrode side reactions is nearly nonexistent. Such studies would have a profound impact on additive development that not only benefits the entire electrolyte community but also the cathode community. Herein, We report a new electrolyte additive, tris (2, 2, 2-trifluoroethyl) borate (TTFEB), to improve the discharge capacity, coulombic efficiency and cycle life of cells with a lithium- and manganese-rich layered cathode (in Fig1). TTFEB suppressed the growth of insulating inorganic byproducts at the cathode/electrolyte interface, inhibited the growth of surface film resistance, and alleviated the cell polarization during cycling. Furthermore, surface transition-metal (mostly Mn) reduction and structural transformation in cathode were mitigated when the electrode was cycled in a TTFEB containing electrolyte. The work highlights the importance of electrolyte additives in preserving the structure of cathode materials and helps us understand the underlying mechanism of the improved electrochemical performance enabled by electrolyte additives.

Influence of Mn-Ni alloying elements on surface film and pitting resistance of Cr-Mn austenitic stainless steels

This research focused on surface film and corrosion resistance of three commercial type 200 austenitic stainless steels including L4, L1 and LH with different Mn/Ni mass ratio in Chinese market. X-ray photoelectron spectrum (XPS) results showed that Fe, Cr and Mn oxide layer thickness and passive film thickness were reduced as Mn/Ni mass ratio increased. Mn enrichment was only found in LH passive film. Mn oxide percentage in LH passive film was also the highest. These disadvantages deteriorated pitting resistance of LH, which was proved by anodic polarization result. Mn/Ni mass ratio should not be higher than 1.7 to ensure good corrosion resistance and low raw material cost.

Poly(4-styrenesulfonate) templated polyaniline-carboxymethyl cellulose blend: Morphology and surface resistivity of the spin-coated films

ABSTRACTPoly (4-styrenesulfonate) (PSS) templated polyaniline-carboxymethyl cellulose blend forming stable aqueous colloidal suspensions was prepared through simple synthesis. Morphology of the spin-coated films obtained from different concentrations of colloidal suspensions was studied through atomic force microscopy (AFM). The AFM images were found to be drastically altered at lower concentrations showing a regular network-like structure. Room-temperature surface resistivity for the network featured spin-coated film showed semiconducting behavior. This indicates the efficacy of dilution as a new design element for network structures, further exhibiting resistivity.

Imaging of electrical response of NiO x under controlled environment with sub-25-nm resolution

The spatially resolved electrical response of polycrystalline NiOx films, composed of 40 nm crystallites, was investigated under different relative humidity (RH) levels. The topological and electrical properties (surface potential and resistance) were characterized with sub-25-nm resolution using Kelvin probe force microscopy and conductive scanning probe microscopy under argon atmosphere with 0%, 50%, and 80% RH. The dimensionality of surface features obtained through autocorrelation analysis of topological maps increased linearly with increased RH, as water was adsorbed onto the film surface. Surface potential decreased from 280 to 100 mV and resistance decreased from 5 GΩ to 3 GΩ, in a nonlinear fashion when RH was increased from 0% to 80%. Spatially resolved surface potential and resistance of the NiOx films was found to be heterogeneous throughout the film, with distinct surface features that grew in size from 60 to 175 nm at 0% and 80% RH levels, respectively. The heterogeneous character of the topological, surface potential, and resistance properties of the polycrystalline NiOx film observed under dry conditions decreased with increased RH, yielding nearly homogeneous surface properties at 80% RH, suggesting that the nanoscale potential and resistance properties converge with the mesoscale properties as water is adsorbed onto the NiOx film.

Manufacturing and mechanical, thermal and electrical characterization of graphene loaded chitosan composites

Abstract A detailed characterization of Graphene (Gr) loaded chitosan films was conducted in this study. Thermal characterization of Gr loaded CS films was made by using thermogravimetric analysis and thermal conductivity measurement. 1, 2, and 3 wt% loading of Gr into CS increased the thermal conductivity of CS by 25, 258 and 244%, respectively. The effect of Gr loading into CS on electrical resistivity properties of CS was determined by surface resistivity measurements. 1 wt% loading of Gr decreased the surface resistivity of CS film from 4.7 × 10 5 Ω/sq to 4.4 × 10 3 Ω/sq. Viscoelastic properties of CS–Gr composite film samples were analyzed by using dynamic mechanical analysis. Mechanical, morphological, crystallographic properties of composite films were determined by tensile tests, scanning electron microscopy (SEM) observations, and X-ray diffraction analyses, respectively. The storage modulus of CS was increased by 32% with 1 wt% Gr loading into CS. With the loading of 1 wt% of Gr, tensile strength and Young's modulus of CS film increased by 128%, and 52%, respectively. The hydrophilicity of the CS and CS–Gr composites films was examined by contact angle measurements.

On solutions of Maxwell’s equations with dipole sources over a thin conducting film

We derive and interpret solutions of time-harmonic Maxwell’s equations with a vertical and a horizontal electric dipole near a planar, thin conducting film, e.g., graphene sheet, lying between two unbounded isotropic and non-magnetic media. Exact expressions for all field components are extracted in terms of rapidly convergent series of known transcendental functions when the ambient media have equal permittivities and both the dipole and observation point lie on the plane of the film. These solutions are simplified for all distances from the source when the film surface resistivity is large in magnitude compared to the intrinsic impedance of the ambient space. The formulas reveal the analytical structure of two types of waves that can possibly be excited by the dipoles and propagate on the film. One of these waves is intimately related to the surface plasmon-polariton of transverse-magnetic polarization of plane waves.