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P-type binary copper oxide semiconductor films for various O2 flow rates and total pressures (Pt) were prepared using the reactive magnetron sputtering method. Their morphologies and structures were detected by X-ray diffraction, Raman spectrometry, and SEM. A phase diagram with Cu2O, Cu4O3, CuO, and their mixture was established. Moreover, based on Kelvin Probe Force Microscopy (KPFM) and conductive AFM (C-AFM), by measuring the contact potential difference (VCPD) and the field emission property, the work function and the carrier concentration were obtained, which can be used to distinguish the different types of copper oxide states. The band gaps of the Cu2O, Cu4O3, and CuO thin films were observed to be (2.51 ± 0.02) eV, (1.65 ± 0.1) eV, and (1.42 ± 0.01) eV, respectively. The resistivities of Cu2O, Cu4O3, and CuO thin films are (3.7 ± 0.3) × 103 Ω·cm, (1.1 ± 0.3) × 103 Ω·cm, and (1.6 ± 6) × 101 Ω·cm, respectively. All the measured results above are consistent.

Thermally grown amorphous SiO2 (a-SiO2) on Si is widely used in microfluidic and biointerface devices, where surface charge governs capillary flows. We used amplitude-modulation Kelvin probe force microscopy (AM-KPFM) in air to test whether low-power visible light modulates a-SiO2 surface potential and to derive mathematical charging-discharging models. Single-point contact potential difference (CPD) was recorded on ~0.6 µm p-type a-SiO2 on p-type monocrystalline Si during repeated illumination cycles with continuous-wave diode lasers at 405, 505, and 685 nm delivered by optical fiber. The 405 and 505 nm wavelengths produced reproducible negative CPD shifts with steady-state values of ~−28 mV and ~−16 mV, while 685 nm stayed within noise (±2.5 mV). The 405 nm response followed bi-exponential kinetics with fast (tens of seconds) and slow (hundreds of seconds) components dominated by the slow process; after switch-off, CPD relaxed only from ~−28 to ~−23 mV over ~103 s, indicating retention for ≥103–104 s. The 505 nm charging trace fit a single slower xponential, whereas discharging could not be fit robustly. These results demonstrate wavelength-dependent optical tuning of a-SiO2 surface potential and provide compact kinetic descriptors for comparing charging, discharging, and retention.

Nanoporous gold (np-Au) has attracted significant attention for biomedical and electrochemical applications due to its high surface area, tunable morphology, and excellent biocompatibility. In this study, polycrystalline gold surfaces were modified by anodization in 0.3–0.9 M oxalic acid to produce np-Au layers. The influence of anodization conditions on surface morphology, chemical composition, electronic properties, and corrosion resistance in artificial saliva was systematically investigated. Surface morphology and porosity were analyzed by scanning electron microscopy combined with image analysis, revealing a transition from fine and uniform porosity to highly developed but structurally heterogeneous nanoporous structures with increasing oxalic acid concentration. Energy-dispersive spectroscopy confirmed surface oxidation and adsorption of oxygen- and carbon-containing species after anodization, while gold remained the dominant component. Scanning Kelvin probe measurements demonstrated significant modifications of surface electronic properties, including changes in contact potential difference, governed by nanostructure geometry and surface chemistry. Electrochemical tests in artificial saliva showed that increasing nanoporousness led to reduced thermodynamic stability, with the sample anodized in 0.3 M oxalic acid providing the most favorable balance between corrosion resistance and surface activity. These results demonstrate that oxalic acid anodization is a simple and effective approach for tailoring gold surfaces for biomedical applications, particularly in dentistry.

An orthotropic adhesion model is proposed based on the bi-potential method to solve adhesive contact problems with orthotropic interface properties between hyperelastic bodies. The model proposes a straightforward description of interface adhesion with orthotropic adhesion stiffness, whose components are conveniently expressed according to the local coordinate system. Based on this description, a set of extended unilateral and tangential contact laws has been formulated. Furthermore, we use an element-wise scalar parameter β to characterize the strength of interface adhesive bonds, and the effects of damage. Therefore, complete cycles of bonding and de-bonding of adhesive links with the account for orthotropic interface effects can be modelled. The proposed model has been tested on cases involving both tangential and unilateral contact kinematics. The test cases allowed emergence of orthotropic interface effects between elastomer bodies involving hyperelasticity. Meanwhile, the model can be implemented with minimum effort, and provides inspiration for the modelling of adhesive interface effects in areas of applications such as biomechanics.

Contact interaction of two bodies can be modeled using the penalty function approach while its accuracy and robustness are directly associated with the geometry of contact bodies. Particularly, in the research fields of rock mechanics, we need to treat polygonal shapes such as mineral grains/particles at a mesoscale and rock blocks at a macroscale. The irregular shapes (e.g., polygons with small angles or small edges) pose challenges to traditional contact solution approach in terms of algorithmic robustness and complexity. This paper proposed a robust potential-based penalty function approach to solve contact of polygonal particles/block. An improved potential function is proposed considering irregular polygonal shapes. A contact detection procedure based on the entrance block concept is presented, followed by a numerical integral algorithm to compute the contact force. The proposed contact detection approach is implemented into discontinuous deformation analysis with an explicit formulation. The accuracy and robustness of the proposed contact detection approach are verified by benchmarking examples. The potential of the proposed approach in analysis of kinetic behavior of complex polygonal block systems is shown by two application examples. It can be applied in any discontinuous computation models using stepwise contact force-based solution procedures.

The present article deals with the issue of thermodynamic and electro-kinetic aspects of diffusion and migration (charge transfer) of electrons (e) and holes (h) across an n-type-p-type junction under bias and a photovoltaic cell under illumination from the pedagogical motivation. From the equality of the electrochemical potential of e and h on both sides, it follows that the alignment of the Fermi energy levels gives rise to the separation of the energy bands, causing the build-up of a reversible contact potential. Physical significance of the contact potential has been extensively discussed. Under forward bias, diffusion of the majority carrier electrons in the n-type side has been detailed with simultaneously recombining through the junction “p/n” (p ← n) to the p-type side. Moreover, diffusion of the majority holes in the p-type side has been dealt with in a similar way but in the opposite direction. As a result of under forward bias, the overall resulting current flows in the direction from the p-type to the n-type side. Under forward bias, the contribution of the diffusion current by the majority carriers far outweighs the contribution of the drift current by the minority carriers. In contrast, under reverse bias, the minority electrons created within a diffusion length of e of the transition region on the p side can diffuse to the junction “n/p” (n ← p), and finally, they are swept down before recombining due to the migration (charge transfer) across the junction “n/p” (n ← p) in the direction opposite to the electric field, from p to n, that is, without any barriers. Furthermore, diffusion of the minority holes created within the transition region on the n side to the junction “p/n” (p ← n) has been dealt with likewise across the junction “p/n” (p ← n), but in the direction of the electric field, from n to p. As a result of under reverse bias, the overall resulting current flows in the direction from the n-type to the p-type side. Under reverse bias, the reverse drift current by the minority carriers dominates the diffusion current by the majority carriers. The derivation of a diode equation with bias and another modified equation under illumination necessitates a deep understanding of the Fick’s first law and modified Fick’s second formula. The photo-driven voltaic cell with illumination delivering electric power to the external load is clearly distinguished from the externally driven junction with bias. The delivered current enhanced by the incident light radiation is almost exclusively determined by the drift current by the minority carriers e and h due to their migration (charge transfer) in the direction from the n-type to the p-type. The delivered photovoltage runs in the direction as in the forward bias (from p to n). The photo-enhanced reverse drift current dominates the diffusion current by the majority carriers since the effect of the light quanta radiation is minimal on the change in the majority carrier concentration. Finally, some quizzes are raised with their answers to them, so that the readers facing the problems are motivated to solve them in the instructive perspectives.

This paper reports low temperature solution processed ZnO thin film transistors (TFTs), and the effects of interfacial passivation of a 4-chlorobenzoic acid (PCBA) layer on device performance. It was found that the ZnO TFTs with PCBA interfacial modification layers exhibited a higher electron mobility of 4.50 cm2 V−1 s−1 compared to the pristine ZnO TFTs with a charge carrier mobility of 2.70 cm2 V−1 s−1. Moreover, the ZnO TFTs with interfacial modification layers could significantly improve device shelf-life stability and bias stress stability compared to the pristine ZnO TFTs. Most importantly, interfacial modification layers could also decrease the contact potential barrier between the source/drain electrodes and the ZnO films when using high work-function metals such as Ag and Au. These results indicate that high performance TFTs can be obtained with a low temperature solution process with interfacial modification layers, which strongly implies further potential for their applications.

Much of the long controversy concerning the workings of electric batteries revolved around the concept of the contact potential (especially between different types of metals), originated by Alessandro Volta in the late eighteenth century. Although Volta’s original theory of batteries has been thoroughly rejected and most discussions in today’s electrochemistry hardly ever mention the contact potential, the concept has made repeated comebacks through the years, and has by no means completely disappeared. In this paper, I describe four salient foci of its revivals: dry piles, thermocouples, quadrant electrometers, and vacuum phenomena. I also show how the contact potential has maintained its presence in some cogent modern scientific literature. Why has the death of the Voltaic contact potential been such an untidy affair? I suggest that this is because the concept has displayed significant meaning and utility in various experimental and theoretical contexts, but has never been successfully given a simple, unified account. Considering that situation, I also suggest that it would make sense to preserve and develop it as a multifarious concept.

•The scanning Kelvin probe provides a fermi energy map revealing latent fingermarks.•Scanning Kelvin probe could pre-identify fingermark areas for targeted DNA recovery.•SEM/EPMA data was compared to scanning Kelvin probe images of fingermarks.•An increase in Sodium, Chlorine and Oxygen coincided with a change in CPD.•Scanning Kelvin probe worked best on non-enhanced surfaces without VMD. Most traditional techniques to recover latent fingermarks from metallic surfaces do not consider the metal surface properties and instead focus on the fingermark chemistry. The scanning Kelvin probe (SKP) technique is a non-contact, non-destructive method, used under ambient conditions, which can be utilised to recover latent prints from metallic surfaces and does not require any enhancement techniques or prevent subsequent forensic analysis. Where a fingermark ridge contacted the metal, the contact potential difference (CPD) contrast between the background surface and the fingermark contact area was 10–50mV. Measurements were performed on the untreated brass, nickel-coated brass and copper metal surfaces and compared to traditional forensic enhancement techniques such as Vacuum Metal Deposition (VMD) using Au–Zn and Au–Ag. Using VMD, the CPD change ranged from 0 to 150mV between the dissimilar metal surfaces affected by the fingermark. In general, SKP worked best without additional enhancement techniques. Scanning Electron Microscope (SEM) scans were used to identify the fingermark contact areas through a sodium, chlorine and oxygen electron probe micro-analyzer (EPMA). The fingermark was observed in the backscattered electron image as the carbon deposits scattered the electrons less than the surrounding metal surface. The fingermark is shown clearly in a Cathodoluminescence scan on the copper sample as it blocks the photon emission at band gap (2.17eV) from the underlying copper oxide (Cu2O) surface. For the first time, SEM, EPMA and Cathodoluminescence techniques were compared to SKP data. Visible and latent fingermarks were tested with latent, eccrinous fingermarks more easily imaged by SKP. Results obtained were very encouraging and suggest that the scanning Kelvin probe technique, which does not need vacuum, could have a place as a first stage analysis tool in serious crime investigation.

The dyadic Helmholtz Green’s function for electromagnetic (EM) wave transmission/ diffraction through a subwavelength nano-hole in a two-dimensional (2D) plasmonic layer is discussed here analytically and numerically, employing “contact potential”-like Dirac delta functions in 1 and 2 dimensions (δ(z) and δ(x)δ(y)≡δ(2)(r→)). This analysis is carried out employing a succession of two coupled integral equations. The first integral equation determines the dyadic electromagnetic Green’s function G^fs for the full non-perforated 2D quantum plasma layer in terms of the bulk 3D infinite-space dyadic electromagnetic Green’s function G^3D, with δ(z) representing the confinement of finite quantum plasma conductivity to the plane of the plasma layer at z=0. The second integral equation determines the dyadic electromagnetic “hole” Green’s function G^hole for the perforated 2D quantum plasma layer (containing the nano-hole) in terms of the dyadic electromagnetic Green’s function G^fs for the full non-perforated 2D plasma layer, with δ(2)(r→) describing the exclusion of the quantum plasma layer conductivity properties from the nano-hole region in the vicinity of r→=0 on the plane. Taking the radius of the subwavelength nano-hole to be the smallest length scale of the system in conjunction with the 2D Dirac delta function representation of the excluded nano-hole plasma conductivity, both of the successive coupled integral equations are solved exactly, and we present a thorough numerical analysis (based on the exact analytic solution) for the resulting dyadic “hole” Green’s function G^hole in full detail in both 3D and density plots. This result has been successfully applied to the determination of electromagnetic wave transmission/diffraction through the nano-hole of the perforated quantum plasmonic layer, jointly with the EM wave transmission through the rest of the plasma layer. This success necessarily involves spatial translational asymmetry induced by the use of spatial Dirac delta functions confining finite conductivity to the 2D quantum plasma sheet and the excision at a bit of it about the origin to represent the nano-hole perforation, thus breaking spatial translational invariance symmetry.