Table of contents

The effect of solar cell capacitance in the electrical characterization of photovoltaic (PV) modules at Standard Test Conditions (STC) is known since the 1990s. With the efficiency of solar modules increasing in the years, the corresponding measurement artefact has been generally resolved with long pulse simulators, from few milliseconds in the 2000 s and up to hundred milliseconds nowadays. With the last improvements in module technology, with the growing interest in n-type silicon and silicon heterojunction, and with the increasing wafer and cell sizes, it is demonstrated that even 100 ms simulators are no longer enough for accurate direct I–V measurements. The need for continuous simulators is therefore becoming more frequent even for accurate measurement of commercial size modules. This work summarizes the basic physics behind the effect of capacitance on the electrical characterization of silicon PV modules, with the simplest approach of a single diode capacitive model and with examples from high efficiency modules commercially available. It reviews eight measurement methods to mitigate the effect for accurate electrical characterization at STC; finally, it presents a novel and comprehensive analysis of the uncertainty contribution to the maximum power and open-circuit voltage determination of these measurement methods. The paper is a review of the best practices in advanced testing laboratories of silicon PV modules nowadays, and it represents a contribution addressed to metrologists, researchers and module manufacturers.

In-situ analysis of the TiO₂/water interface via near ambient pressure–x-ray photoelectron spectroscopy (NAP–XPS) is demonstrated in both a lab based system (NAP-cell configuration) and synchrotron endstation (backfill configuration). Ultra-thin wetting layers of liquid water (∼10 nm) are formed on a rutile TiO₂ surface with minimal contamination present in addition to unique insight during the growth of the liquid films as indicated via NAP–XPS, in-situ sample temperature and background vapour pressure monitoring. Chemical changes at the solid/liquid interface are also demonstrated via healing of Ti³⁺ surface defect states. Photon depth profiling of the as grown liquid layers indicate that the formed films are ultra-thin (∼10 nm) and likely to be continuous in nature. This work demonstrates a novel and flexible approach for studying the solid/liquid interface via NAP–XPS which is readily integrated with any form of NAP–XPS system, thereby making a critical interface of study available to a wide audience of researchers for use in operando electrochemical and photocatalytic research.

With NO_x persisting as a problematic pollutant, understanding the interactions and reactivity of NO_x species at atmospherically relevant pressures with surfaces remains essential. Synchrotron-based ambient pressure x-ray photoelectron spectroscopy (APXPS) and near-edge x-ray absorption spectroscopy fine structure (NEXAFS) were used to investigate the interactions of NO₂ with a Cu₂O(111) surface. The NEXAFS data reveals a pressure dependence of the oxidation of the Cu₂O surface to CuO by NO₂. APXPS results show NO₂ chemi- and physisorption on the Cu₂O surface and decomposition to NO and O, or to N and O, with the amount of the species also being pressure dependent. The combination of the two spectroscopic techniques shows a comprehensive picture of NO₂ adsorption with implications for catalysis, gas sensing, and gas filtration materials.

An atmospheric, dielectric-barrier discharge µ-plasmatron was designed, fabricated, and applied to synthesize a methylated organometallic complex. The design comprises counter-current flow to packed-bed microstructures to facilitate gas–liquid and plasma–liquid mixing. Micropillars arranged in a staggered configuration served as a porous media for the optimum 2D mixing of components that replenish plasma-liquid interfaces. Longitudinal dispersion was characterized through residence time distribution (RTD) measurements. The experimental RTD data were then described by an axial dispersion model with a time delay parameter. Levenspiel number (lv) indicating the intensity of axial dispersion was estimated in the range of 20.1–374, indicating that a dispersion model should be accounted for in plasma-assisted reaction kinetics development. Stable plasma excitation of methane-helium gas mixtures was observed within the 2D porous media, by in-situ optical emission spectra, while applying an alternating high voltage across the dielectric barrier. This novel technique made it possible to confirm in-situ formations of methyl radicals. Interestingly, the porous media served as a static mixer as no discrete plasma streamers were observed. To investigate its utility, an example homogeneous cobalt catalyst was injected into the µ-plasmatron and methylated. Our findings potentially introduce a new plasma-assisted reactor design and methodology for the synthesis of methylated cobaloxime.

The presence of multiple reactant gases as well as reaction intermediates in a heterogeneous catalytic reaction results in a complex interaction between different components of the catalyst with each gas, which can alter the surface and chemical state of the catalyst differently than in the presence of an individual gas alone. In this study, we used in situ ambient pressure x-ray photoelectron spectroscopy to study the surface state of Pt/Cu(111) single-atom alloy model system in two catalytically relevant reaction conditions: CO₂ hydrogenation and CO oxidation. We found that the activation of CO₂ results in the formation of CO, which adsorbs on Pt sites at up to 400 K. In the presence of CO₂ and H₂, Pt catalyzes the reverse water–gas shift reaction, which produces more CO and further stabilizes surface Pt atoms at 450 K. On the other hand, in CO oxidation condition, the presence of O₂ results in the formation of a thick Cu₂O layer at higher temperatures, and Pt atoms are no longer detected in the surface and subsurface layers. When O₂ is introduced to the sample before CO, the formation of a complete Cu₂O layer that covers all Pt atoms occurs immediately at room temperature. However, when CO is introduced at room temperature before O₂, the presence of adsorbed CO on Pt sites stabilizes the surface Pt atoms and prevents the formation of a complete Cu₂O layer, thus exposing the Pt atoms in 'holes' in the Cu₂O layer.

A two-camera fluorescence system for indocyanine green (ICG) signal detection has been developed and tested in a clinical feasibility trial of ten patients, with a resolution in the submillimetre scale. Immediately after systemic ICG injection, the two-camera system can detect ICG signals in vivo (∼2.5 mg ${{\text{l}}^{ - 1}}$ or 3.2 × ${10^{ - 6}}{ }$ M). Qualitative assessment has shown that the fluorescence signal does not always correlate with the cancer location in the surgical scene. Conversely, fluorescence image texture metrics when used with the logistic regression model yields good accuracy scores in detecting cancer. We have demonstrated that intraoperative fluorescence imaging for resection guidance is a feasible solution to tackle the current challenge of positive resection margins in breast conserving surgery.

We present here an investigation aimed at exploring the role of the microstructure on the magnetic properties of nanostructured cobalt ferrite. Bulk, almost fully dense, nanograined ferrites have been obtained starting from nanopowders prepared by a simple, inexpensive, water-based, modified Pechini method. This synthesis yielded largely aggregated, pure single-phase cobalt ferrite nanoparticles of ca. 35 nm average size, which have been then densified by high-pressure field-assisted sintering. Different sintering conditions (pressure up to 650 MPa and temperature up to 800 °C) and procedures have been used on both as-prepared and milled nanopowders in order to obtain materials with a spectrum of complex microstructures. In all cases, the sintering process did not produce any change in the phase composition. At the same time, using a high uniaxial pressure in combination with relatively low sintering temperatures and times, allowed for obtaining a high degree of densification while preserving the nanometric size of the crystallites. Moreover, we observed that in the densified materials the best magnetic properties are not necessarily associated with a more uniform microstructure, but rather arise from a delicate balance between moderate aggregation, grain size and high density.

Packed-bed plasma reactors (PBPRs) have been investigated extensively to study the abatement of volatile organic compounds such as toluene. Previous studies have reported that the applied voltage (or power) is a critical parameter that affects the performance of PBPRs. However, the origin of this change in performance is not well understood. A conventional PBPR contains irregularly filled dielectric pellets that generate several micro- and mesoscopic voids in between the pellets and between pellets and dielectric walls where filamentary discharges are generated. These voids are optically inaccessible and the reaction products are often generated in gaseous form; therefore, the location of the chemical reactions within these voids could not be studied. In this work, we have qualitatively investigated the influence of the applied voltage on the locations of chemical reactions in the void using toluene oxidation as an example. Using a single layer of regularly arranged hemispherical pellets and a transparent electrode in a PBPR, the plasma generation within these voids became optically accessible. The operating conditions were tailored to enhance the deposition of solid or liquid products on the glass beads to understand the locations of chemical reactions. The intensified charged coupled device camera images of the discharge through the transparent electrode show that the distribution of plasma emission changes with the applied voltage amplitude. The distribution of the deposited/condensed solid/liquid intermediates and reaction products was found to match the plasma emission. The analysis of the reaction products and deposition/condensation locations indicates that short-living species such as energetic electrons, OH and O radicals might play an essential role in the formation of deposited chemicals on the glass beads.

There is a considerable interest in development and realization of the terahertz-frequency range oscillators and detectors. In this work a concept of temperature tunable THz oscillator is theoretically developed. As an active element we suggest holmium orthoferrite near its reorientational phase transition. We show that the heating of the orthoferrite spin system decreases the threshold of the DC electric-current required for self-oscillations due to the anisotropy constant reduction. Such concept of the temperature-tuning of magnetic properties can be applied for wide range of ferri- or antiferromagnets. We discuss a possibility of applying orthoferrite/heavy metal heterostructure as continuously tunable oscillators and detectors of THz-frequency signals.

The photoelectrochemical (PEC) properties of sputtered aluminum doped hydrogenated amorphous silicon carbide thin films grown on p-type crystalline silicon substrates were investigated in 1 M $\mathrm{H}_{2}\mathrm{SO}_{4}$ solution under chopped light illumination. Optical and structural properties of the top absorber layer were systematically assessed after post-deposition isochronical annealing treatments. Samples exhibited a noticeable improvement of the opto-electronic properties after thermal treatments. In addition, an abrupt enhancement of the photocurrent was observed reaching a saturation value of 17 mA cm⁻² at −1.75 V vs. Ag/AgCl (3.5 M KCl). In this research we propose that this enhancement effect is associated to a charge transfer kinetic mechanism influenced by surface states and the p-type substrate. The latter most likely due to the space charge region extending beyond the absorber layer reaching the substrate. Current density-potential and electrochemical impedance spectroscopy measurements in dark revealed a reduction of the $\mathrm{SiO}_{2}$ native layer at cathodic potentials higher than −1 V vs. Ag/AgCl (3.5 M KCl), which contributes to the high charge transfer kinetic of the system. We believe that these results will contribute to understand the substrate influence in the PEC performance of top absorber layers in multilayer structures for solar water splitting.

The dark current characteristics of two series of bulk GaAsBi p-i-n diodes are analysed as functions of temperature and band gap. Each temperature dependent measurement indicates that recombination current dominates in these devices. The band gap dependence of the dark currents is also consistent with recombination dominated current for the devices grown at a common growth temperature, indicating that the presence of Bi does not directly adversely affect the dark currents. However, the devices grown at different growth temperatures exhibit a faster increase in dark current with decreasing device band gap, suggesting that a reduced growth temperature causes a reduction in minority carrier lifetime.

We have calculated interband optical absorption for InAs/GaSb based type-II superlattice (SL) structures. The empirical pseudopotential method (EPM) has been used as an alternative to the k.p method since it is less sophisticated while providing similar results in the mid wavelength infrared range and long wavelength infrared range atmospherics bands for comparison. EPM results show that the bandgap wavelengths of SLs have been predicted with the underestimating of 0.4 µm. This corresponds to an uncertainty of less than 0.3 monolayer in the layer width. The theoretical estimation is comparable with the uncertainty of the layer width during the growth process. Heterostructures or SLs with their ternary and quaternary alloys can be calculated by this method to identify electronic and optical parameters for both intersubband and interband applications.

In this work, an enhanced-performance deep-ultraviolet (DUV) photodetector based on a Ga₂O₃/lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃, PZT) p-n heterojunction is fabricated and characterized for the first time. Compared to a Ga₂O₃-based device, the heterojunction device achieved a lower dark current of 2.7 $\times$ 10⁻¹¹ A, a higher photo- to dark-current ratio of 2 $\times$ 10³, a higher responsivity of 5.5 mA W⁻¹, a larger specific detectivity of 2.6 $\times$ 10¹¹ Jones and a higher external quantum efficiency of 2.7% at −2 V under 254 nm UV light illumination with an intensity of 500 μW cm⁻². The p-PZT/n-Ga₂O₃ was confirmed to be a potential candidate for the construction of DUV photodetectors with enhanced sensing performance.

In this paper, the influence of amplitude-modulated coil current waveform on polycrystalline diamond deposition was studied using modulated induction thermal plasma (M-ITP) with numerical and experimental approaches. The M-ITP is useful in undertaking the nucleation of diamond particles necessary for the first stage of diamond film deposition. First, numerical thermo-fluid calculations were conducted for Ar M-ITP with CH₄/H₂ feedstock gas to investigate the influence of a modulation waveform on particle fluxes of different hydrocarbon species onto a Si substrate. Furthermore, experiments were performed to fabricate polycrystalline diamond film deposition using M-ITP with different modulation waveforms. The modulation waveform for the coil current was set as a rectangular waveform, a saw-tooth waveform and a reverse saw-tooth waveform in the calculations and the experiments. The experimental results showed that the saw-tooth M-ITP provided a higher deposition rate, of 2.05 µm h⁻¹, than other waveforms. This could be attributed to the higher fluxes of neutral hydrocarbons in the saw-tooth M-ITP according to the calculation results.

A metamaterial absorber consisting of stacked and orthogonal elliptical graphene layers is proposed to achieve eight absorption bands in the terahertz (THz) frequency range. By adjusting the length of the short or long axis for each graphene ellipse, the corresponding absorption peak can be tuned independently. Electric field distributions are present to reveal the physical mechanism. The absorption spectrum can also be tuned by varying the chemical potential of each graphene ellipse and the manipulation for the polarization angle of the incidence. Moreover, the absorber can work properly under oblique incidences. Our work paves a way for designing tunable THz absorbers with numerous absorption bands.

OH density and rotational temperature were measured in a saturated water vapor slot-excited microwave plasma using spatio-temporally resolved laser-induced fluorescence. The microwave power was 20–100 W under continuous wave mode, whereas 40–200 W peak under pulse-modulated mode (30% duty cycle, 100 Hz). The water vapor pressure was 2.3 kPa. An approximately 2 mm thick flat-shaped plasma was generated on the surface of a slot antenna. The OH density and rotational temperature in the plasma ranged from 1 × 10¹⁴ cm⁻³ to 1 × 10¹⁵ cm⁻³ and from 1100 K to 3000 K, respectively. OH was produced via various routes originating from electron collisions (e + H₂O) and was primarily lost through recombination (OH+OH → H₂O+O) and diffusion. The production rate (k_p) of OH per H₂O molecule, which was calculated based on a simplified reaction model using the measured OH density and temperature, showed a relation of $k_p/[\textrm{H}_2\textrm{O}] \propto P^{1.8}$, where P represents the microwave power. This relationship implies a two-step production process of OH via the vibrational excitation of H₂O. Although the OH density increased with increasing microwave power, the density became saturated at high power values.

Since experiments cannot clarify the mechanism of current transfer to non-thermionic arc cathodes, this can only be done by means of numerical modelling based on first principles and not relying on a priori assumptions. In this work, the first quarter-period after the ignition of an AC arc on cold electrodes in atmospheric-pressure argon is investigated by means of unified one-dimensional modelling, where the conservation and transport equations for all plasma species, the electron and heavy-particle energy equations, and the Poisson equation are solved in the whole interelectrode gap up to the electrode surfaces. Results are compared with those for DC discharges and analysed with the aim to clarify the role of different mechanisms of current transfer to non-thermionic arc cathodes. It is found that the glow-to-arc transition in the AC case occurs in a way substantially different from the quasi-stationary glow-to-arc transition. The dominant mechanisms of current transfer to the cathode during the AC arc ignition on cold electrodes are, subsequently, the displacement current, the ion current, and thermionic emission current. No indications of explosive emission are found. Electron emission from the impact of excited atoms can hardly be a dominant mechanism either. The introduction of the so-called field enhancement factor, which is used for description of field electron emission from cold cathodes in a vacuum, leads to computed cathode surface temperature values that are appreciably lower than the melting temperature of tungsten even in the quasi-stationary case. This means that pure tungsten cathodes of atmospheric-pressure argon arcs can operate without melting, in contradiction with experiments.

The electronic properties at the donor (D):acceptor (A) interface are a crucial factor in determining the efficiency of organic photovoltaic devices. Here, based on first-principles calculations, the electronic properties of ten configuration complexes composed of D polymer PDPPTPT and A polymer PNDI2OD-TVT were simulated. Results show that the bandgap values of the homo-/heterojunctions decrease with the increase of the number of molecular layers, and that of AAA is close to zero. This indicates that the homogeneous stacking is favorable for charge transport; furthermore, the bandgap of the complexes is affected by the molecular arrangement. Through the differential charge density and Bader charge analysis method, it was found that charge transfer will occur intermolecularly, which promotes the formation of a dipole moment at the D:A interface, and the dipole electric field then helps the dissociation of excitons in the active layer. The amount of charge transfer at the D:A interface in the DDA, DAA and DDAA configurations is about twice that in the DA configuration alone, demonstrating that homogeneous accumulation in complexes can enhance the interface dipole interaction. The comprehensive analysis suggests that homogeneous accumulation is conducive to charge transport, that heterogeneous stacking helps to promote exciton dissociation, and that there should be an optimal ratio. Furthermore, the dipole electric fields formed at the D:A interface exhibit the characteristics of local and non-uniform distribution.

When two electrical conductors with rough surfaces are in contact, the apparent contact area can be regarded as an ensemble of small real contact spots, as noted by Holm. The currents flowing through a real contact spot are influenced by the electrical current spread from the adjacent real contact spots. Greenwood considered the interference between a pair of real contact spots. The effective constriction resistance thus obtained can be evaluated once the positions of the real contact spots have been determined. For decades, the expressions for the constriction resistance obtained by Holm and Greenwood have been widely used to interpret and characterize experimental data. Here, we take a completely different approach. Instead of explicitly considering the interference between the real contact spots using their specific positions, we regard the apparent contact area composed of an ensemble of real contact spots as a homogeneous effective conductor. The effective medium theory is not rigorous but its simplicity allows us to study the effective constriction resistance of film and bulk conductors, including the effect of conductivity anisotropy, approximately. We show that the obtained effective resistance is consistent with that obtained by Greenwood for bulk isotropic conductors. We also propose a phenomenological equation to describe the relation between the Holm radius and the number of real contact spots.

In this article, we report the observation of extremely large non-saturating linear magnetoresistance (MR) in antimony (Sb) crystal. An extremely large magnetoresistance of 43 000% at 2 K and large unsaturating MR ∼70% at room temperature is observed at the magnetic field of 9 T. Hall measurements reveal a very high mobility ∼3.8 × 10⁴ cm² V s⁻¹ of charge carriers and strong temperature dependence of carrier concentration and mobility. The respective scaling of MR and crossover field (B _c) from quadratic to linear MR with mobility and inverse of mobility describes the classical origin of large linear MR in this crystal as suggested by Parish and Littlewood model for disordered systems.

Plasmon characteristics in a monolayer of 2H-TiS₂ in the presence of strain are carefully analyzed by employing the density functional theory along with random phase approximation. The anisotropic properties of 2H-TiS₂ are carefully analyzed under biaxial strains. An anisotropic semi-Dirac cone in the electronic band-structure is observed at a specific biaxial strain configuration. This unique characteristic can be explained by the hybridization of orbitals at the conduction band minimum and valence band maximum which can be effectively tuned by applying strain. The effect of anisotropic electronic band-structure on the properties of plasmons is investigated by utilizing the electron energy loss spectrum analysis. A $\sqrt{q}$ dispersion along the Γ−K direction and a linear dispersion along the $\Gamma-M^{^{\prime}}$ were found. The linear dispersion characterizes an extrinsic acoustic plasmon mode that can be tuned by the carrier concentration.

We investigate a diffusion process with a time-dependent diffusion coefficient, both exponentially increasing and decreasing in time, $D(t) = D_0 e^{\pm 2 \alpha t}$. For this (hypothetical) nonstationary diffusion process we compute—both analytically and from extensive stochastic simulations—the behavior of the ensemble- and time-averaged mean-squared displacements (MSDs) of the particles, both in the over- and underdamped limits. Simple asymptotic relations derived for the short- and long-time behaviors are shown to be in excellent agreement with the results of simulations. The diffusive characteristics in the presence of ageing are also considered, with dramatic differences of the over- versus underdamped regime. Our results for $D(t) = D_0 e^{\pm 2 \alpha t}$ extend and generalize the class of diffusive systems obeying scaled Brownian motion featuring a power-law-like variation of the diffusivity with time, $D(t) \sim t^{\alpha -1}$. We also examine the logarithmically increasing diffusivity, $D(t) = D_0 \log [t/ \tau_0]$, as another fundamental functional dependence (in addition to the power-law and exponential) and as an example of diffusivity slowly varying in time. One of the main conclusions is that the behavior of the massive particles is predominantly ergodic, while weak ergodicity breaking is repeatedly found for the time-dependent diffusion of the massless particles at short times. The latter manifests itself in the nonequivalence of the (both nonaged and aged) MSD and the mean time-averaged MSD. The current findings are potentially applicable to a class of physical systems out of thermal equilibrium where a rapid increase or decrease of the particles' diffusivity is inherently realized. One biological system potentially featuring all three types of time-dependent diffusion (power-law-like, exponential, and logarithmic) is water diffusion in the brain tissues, as we thoroughly discuss in the end.

Ferroelectric organic field-effect transistors (FE-OFETs) are fabricated to implement the functions of a neural synapse, including one-directional signal transmission and synaptic plasticity. Stochastic resonance (SR) experiments are conducted with FE-OFETs that use regioregular poly(3-hexylthiophene-2,5-diyl) as the semiconductor layer and poly(vinylidene fluoride-co-hexafluoropropylene) as the insulator layer. The input–output correlation is observed to increase as the external noise intensity rises, with a cutoff frequency of 1 Hz, demonstrating the experimental occurrence of SR in the fabricated FE-OFETs. Furthermore, vibrational resonance experiments are performed to clarify the frequency-dependence of the SR behavior. The peak input–output correlation shifts toward higher amplitudes of a secondary sine wave that is applied instead of external noise as the frequency of the input signal rises from $f_\textrm{signal}$ = 0.5–1 Hz. The FE-OFETs exhibit more adaptive behavior than paraelectric OFETs, with a threshold voltage that changes dynamically according to the frequency characteristics of the input signal and/or external noise. Furthermore,the immediate response to abrupt environmental changes via the SR phenomenon and flexible behavior based on past experience via hysteresis effects can be implemented by a single FE-OFET element.