Table of contents

Reactive high-power impulse magnetron sputtering with a pulsed O₂ flow control and to-substrate O₂ injection into a high-density plasma in front of the sputtered vanadium target was used for low-temperature (300 °C) deposition of VO₂ films with a pronounced semiconductor-to-metal transition onto conventional soda-lime glass substrates without any substrate bias voltage and without any interlayer. The depositions were performed using an unbalanced magnetron with a planar target of 50.8 mm diameter in argon–oxygen gas mixtures at the argon pressure of 1 Pa. The deposition-averaged target power density was close to 13 W cm⁻² at a fixed duty cycle of 1% with a peak target power density up to 5 kW cm⁻² during voltage pulses ranged from 40 µs to 100 µs. A high modulation of the transmittance at 2500 nm (between 51% and 8% at the film thickness of 88 nm) and the electrical resistivity (changed 350 times) at the transition temperature of 56–57 °C was achieved for the VO₂ films synthesized using 50 µs voltage pulses when the crystallization of the thermochromic VO₂(M1) phase was supported by the high-energy (up to 50 eV relative to ground potential) ions. Principles of this effective low-temperature deposition technique with a high application potential are presented.

In this letter, we numerically designed and experimentally demonstrated a compact photonic structure for the subwavelength focusing of light using all-dielectric absorption-free and nonmagnetic scattering objects distributed in an air medium. In order to design the subwavelength focusing flat lens, an evolutionary algorithm is combined with the finite-difference time-domain method for determining the locations of cylindrical scatterers. During the multi-objective optimization process, a specific objective function is defined to reduce the full width at half maximum (FWHM) and diminish side lobe level (SLL) values of light at the focal point. The time-domain response of the optimized flat lens exhibits subwavelength light focusing with an FWHM value of 0.19λ and an SLL value of 0.23, where λ denotes the operating wavelength of light. Experimental analysis of the proposed flat lens is conducted in a microwave regime and findings exactly verify the numerical results with an FWHM of 0.192λ and an SLL value of 0.311 at the operating frequency of 5.42 GHz. Moreover, the designed flat lens provides a broadband subwavelength focusing effect with a 9% bandwidth covering frequency range of 5.10 GHz–5.58 GHz, where corresponding FWHM values remain under 0.21λ. Also, it is important to note that the designed flat lens structure performs a line focusing effect. Possible applications of the designed structure in telecom wavelengths are speculated upon for future perspectives. Namely, the designed structure can perform well in photonic integrated circuits for different fields of applications such as high efficiency light coupling, imaging and optical microscopy, with its compact size and ability for strong focusing.

Vertical-external-cavity surface-emitting lasers (VECSELs) are the most versatile laser sources, combining unique features such as wide spectral coverage, ultrashort pulse operation, low noise properties, high output power, high brightness and compact form-factor. This paper reviews the recent technological developments of VECSELs in connection with the new milestones that continue to pave the way towards their use in numerous applications. Significant attention is devoted to the fabrication of VECSEL gain mirrors in challenging wavelength regions, especially at the yellow and red wavelengths. The reviewed fabrication approaches address wafer-bonded VECSEL structures as well as the use of hybrid mirror structures. Moreover, a comprehensive summary of VECSEL characterization methods is presented; the discussion covers different stages of VECSEL development and different operation regimes, pointing out specific characterization techniques for each of them. Finally, several emerging applications are discussed, with emphasis on the unique application objectives that VECSELs render possible, for example in atom and molecular physics, dermatology and spectroscopy.

The scaling challenges of complementary metal oxide semiconductors (CMOS) are increasing with the pace of scaling showing marked signs of slowing down. This slowing has brought about a widespread search for an alternative beyond-CMOS device concept. While the charge tunneling phenomenon has been known for almost a century, and tunneling based transistors have been studied in the past few decades, its possibilities are being re-examined with the emergence of a new class of two-dimensional (2D) materials. By stacking varying 2D materials together, with two electrode layers sandwiching a tunnel dielectric layer, it could be possible to make vertical tunnel transistors without the limitations that have plagued such devices implemented within other material systems. When the two electrode layers are of the same material, under certain conditions, one can achieve resonant tunneling between the two layers, manifesting as negative differential resistance (NDR) in the interlayer current–voltage characteristics. We call this type of device an interlayer tunnel FET (ITFET). We review the basic operation principles of this device, experimental and theoretical studies, and benchmark simulation results for several digital logic gates based on a compact model that we developed. The results are placed in the context of work going on in other groups.

Suspensions of magnetic nanoparticles offer diverse opportunities for technology innovation, spanning a large number of industry sectors from imaging and actuation based applications in biomedicine and biotechnology, through large-scale environmental remediation uses such as water purification, to engineering-based applications such as position-controlled lubricants and soaps. Continuous advances in their manufacture have produced an ever-growing range of products, each with their own unique properties. At the same time, the characterisation of magnetic nanoparticles is often complex, and expert knowledge is needed to correctly interpret the measurement data. In many cases, the stringent requirements of the end-user technologies dictate that magnetic nanoparticle products should be clearly defined, well characterised, consistent and safe; or to put it another way—standardised. The aims of this document are to outline the concepts and terminology necessary for discussion of magnetic nanoparticles, to examine the current state-of-the-art in characterisation methods necessary for the most prominent applications of magnetic nanoparticle suspensions, to suggest a possible structure for the future development of standardisation within the field, and to identify areas and topics which deserve to be the focus of future work items. We discuss potential roadmaps for the future standardisation of this developing industry, and the likely challenges to be encountered along the way.

Metalenses based on surface plasmon polaritons have played an indispensable role in ultra-thin devices designing. The amplitude, phase and polarization of electromagnetic waves all can be controlled easily by modifying the metasurface structures. Here we propose and investigate a new type of structure with Babinet-inverted nano-antennas which can provide a series of unit-cells with phase-shifts covering 2π and ensure almost same transmittance simultaneously. As a result, the wavefront can be manipulated by arraying the units in course. Metalenses with the linear asymmetrical double slit unit-cell arrays are designed and the simulative results exhibit their perfect focusing characteristics, including single-focus lenses and multi-focus lenses. The small focus size and high numerical aperture make them stand out from the traditional counterparts in application of precision sensing devices. We expect our designs will provide new insights in the practical applications for metasurfaces in data storages, optical information processing and optical holography.

An analysis of the extensive and intensive barocaloric effect (BCE) at successive structural phase transitions in some complex fluorides and oxyfluorides was performed. The high sensitivity of these compounds to a change in the chemical pressure allows one to vary the succession and parameters of the transformations (temperature, entropy, baric coefficient) over a wide range and obtain optimal values of the BCE. A comparison of different types of schematic T–p phase diagrams with the complicated $T(\,p)$ dependences observed experimentally shows that in some ranges of temperature and pressure the BCE in compounds undergoing successive transformations can be increased due to a summation of caloric effects associated with distinct phase transitions. The maximum values of the extensive and intensive BCE in complex fluorides and oxyfluorides can be realized at rather low pressure (0.1–0.3 GPa). In a narrow temperature range around the triple points conversion from conventional BCE to inverse BCE is observed, which is followed by a gigantic change of both $\vert\Delta S_{\rm BCE}\vert$ and $\vert\Delta T_{\rm AD}\vert$.

Epithelial cells cultured in a monolayer are very motile in isolation but reach a near-jammed state when mitotic division increases their number above a critical threshold. We have recently shown that a monolayer can be reawakened by over-expression of a single protein, RAB5A, a master regulator of endocytosis. This reawakening of motility was explained in terms of a flocking transition that promotes the emergence of a large-scale collective migratory pattern. Here we focus on the impact of this reawakening on the structural properties of the monolayer. We find that the unjammed monolayer is characterised by a fluidisation at the single cell level, and by enhanced non-equilibrium large-scale number fluctuations at a larger length scale. Also, with the help of numerical simulations, we trace back the origin of these fluctuations to the self-propelled active nature of the constituents, and to the existence of a local alignment mechanism, leading to the spontaneous breaking of the orientational symmetry.

Isothermal magnetization measurements were performed on a square cuboid shaped polycrystalline ${\rm ErMnO}_{3}$ sample with a field applied along different directions, having different demagnetization factor values. The magnetocaloric property, namely the isothermal magnetic entropy change ($\Delta S_M$), is evaluated from the magnetization data with and without demagnetization factor correction. The results indicate that without demagnetization factor correction the $\Delta S_M$ values are slightly underestimated. The difference between $\Delta S_M(T)$ values with and without demagnetization factor correction increases with an increase in demagnetization factor. However, as the field increases, the variation/error in $\Delta S_M$ values due to uncertainties related to magnetization (M), field (H) and temperature (T) values becomes higher due to the demagnetization factor correction.

Magnetization dynamics in Ni₈₀Fe₂₀ (Py) diatomic nanodots (nanodots of the same thickness but with large and small diameters that are closely placed to each other so as to act as a diatomic basis structure) embedded in 2D arrays have been investigated by the Brillouin light scattering technique. A distinct variation of resonant mode characteristics for different in-plane bias magnetic field applied along two different orientations of the lattice has been observed. Micromagnetic simulations reproduced the observed dynamical behaviour and revealed the variation of spatial distribution of collective modes of constituent single nanodots with different diameter and a diatomic unit forming the large array to understand the evolution of the magnetization dynamics from a single dot to the large array via a diatomic unit. The changes in mode frequency, spatial profiles of the modes, and appearance of new modes in a diatomic unit and its array from that of the constituent single dots indicate the strong magnetostatic interaction among the dots within the diatomic unit. Also, the occurrence of the new interacting mode at different frequencies for different orientations of the bias field indicates the change in the nature of interaction among the dots within the diatomic unit with bias magnetic field. The mode profiles also show distinct behaviour for smooth and rough-edged dots. This work motivates the study of magnonic band structure formation of such a dipolarly coupled nanodot array containing a complex double-dot unit cell.

Exciton blocking effects from ultra-thin layers of N,N'-di-1-naphthalenyl-N,N'-diphenyl [1,1':4',1'':4'',1‴-quaterphenyl]-4,4‴-diamine (4P-NPD) were investigated in small molecule-based inverted organic solar cells (OSCs) using tetraphenyldibenzoperiflanthene as the electron donor material and fullerene (C₇₀) as the electron acceptor material. The short-circuit current density (J_SC) and power conversion efficiency (PCE) of the optimized OSCs with 0.7 nm thick 4P-NPD were approximately 16% and 24% higher, respectively, compared to reference devices without exciton blocking layers (EBLs). Drift diffusion-based device modeling was conducted to model the full current density–voltage (JV) characteristics and external quantum efficiency spectrum of the OSCs, and photoluminescence measurements were conducted to investigate the exciton blocking effects with increasing thicknesses of the 4P-NPD layer. Importantly, coupled optical and electrical modeling studies of the device behaviors and exciton generation rates and densities in the active layer for different 4P-NPD layer thicknesses were conducted, in order to gain a complete understanding of the observed increase in PCE for 4P-NPD layer thicknesses up to 1 nm, and the observed decrease in PCE for layer thicknesses beyond 1 nm. This work demonstrates a route for guiding the integration of EBLs in OSC devices.

The recent widespread attention on the use of the non-volatile resistance switching property of a microscopic oxide region after electrical breakdown for memory applications has prompted basic interest in the conduction properties of the breakdown region. Here, we report an interesting crossover from a negative to a positive temperature dependence of the resistance of a breakdown region in ultrathin hafnia as the applied voltage is increased. As a consequence, a near-zero temperature coefficient of resistance is obtained at the crossover voltage. The behavior may be modeled by (1) a tunneling-limited transport involving two farthest-spaced defects along the conduction path at low voltage and (2) a subsequent transition to a scattering-limited transport after the barrier is overcome by a larger applied voltage.

The low-temperature rapid solid phase crystallization route of amorphous silicon is fundamentally and technologically significant. Micrometer thick hydrogenated amorphous silicon (a-Si:H) films were exposed to a low-frequency inductively coupled hydrogen plasma under a low substrate temperature of 300 °C. The plasma treated a-Si:H was completely crystallized within half an hour. The evolution of microstructures, optical and electric properties with respect to plasma exposure duration deterministically demonstrates that the present low-temperature rapid crystallization process enables the controllable phase transition from amorphous to nanocrystalline (nc) silicon. The crystallization mechanism is discussed in terms of the unique characteristics of low-frequency inductively coupled plasma (LFICP) and the LFICP-grown precursor a-Si:H film itself. The crucial role of hydrogen atoms in the phase transition is also discussed.

A tunable metamaterial absorber with a W/VO₂ square lattice nanostructure is designed and fabricated. With the excitation of plasma resonance, the tunable mechanism is achieved by the phase transition of vanadium dioxide. The optimal parameters are analyzed by using a finite difference time domain simulation method. The close-to-one absorption peak occurs around a wavelength of 5.28 µm, at which the difference of absorption between high and low temperatures is 89.74%. The findings also show that the absorber is polarization-independent and exhibits wide-angle absorption. The experimental results are in good agreement with the simulation. The results of this study show great potential for the application of energy and sensing metamaterial absorbers.

The effects of Si doping on the strain relaxation of InP-based metamorphic In_xAl_1−xAs graded buffers have been investigated. The highly Si-doped sample shows an increased ridge period along the [1 1 0] direction in the cross-hatch morphology measured by atomic force microscope. X-ray diffraction reciprocal space mapping measurements reveal that the high Si-doping induced incomplete relaxation as well as inhomogeneous residual strain along the [1 −1 0] direction, which was also observed in micro-Raman measurements. The anisotropic strain relaxation is attributed to the Si-doping enhanced anisotropy of misfit dislocations along the orthogonal directions. The α-misfit dislocations along the [1 −1 0] direction are further delayed to generate in highly Si-doped InAlAs buffer, while the β-misfit dislocations along the [1 1 0] direction are not. These results supply useful suggestions on the design and demonstration of semiconductor metamorphic devices.

A reliable bipolar resistive switching device was achieved with multi-level switching behavior in fluorine-doped titanium oxide (TiO_xF_y) film. Different resistance states can be precisely controlled by different pulse voltages, which reveals the device's high potential in neuromorphic research. The characteristics of I–V curves in each resistance state were analyzed. Nanoparticles were observed in the TiO_xF_y film by HR-TEM. The underlying physical mechanisms during resistance switching are discussed and a model of a meshy conducting path is proposed.

We report the fabrication and characterization of electrically-tunable periodically segmented waveguides (PSWs) with different duty cycles of 0.25, 0.33, 0.50 and 0.76, using the nematic liquid crystal 5CB as the guiding layer, and the negative photoresist AZ15nXT as the cladding. The experimental results show that light diffracts and re-focuses periodically on propagation through the liquid crystal (LC) core PSW, when an external voltage is applied to the periodically segmented electrodes. The performance of the fabricated LC core PSWs are analyzed in terms of effective refractive index, output power and duty cycle. The electrically-tunable LC core PSWs have potential application in the realization of optical filters, polarizers and dynamic mode size converters.

Thin-film transistors (TFTs) with solution-processed scandium (Sc) substituted indium oxide (Sc_xIn_1−xO₃, ScInO) thin films based on environmental friendly water-induced precursor were fabricated. As the Sc concentration increases from 0% to 10%, the mobility decreases from 23.7 cm² V⁻¹ s⁻¹ to 6.4 cm² V⁻¹ s⁻¹, which is attributed to the non-overlapping of the Sc³⁺ electron orbit. However, the off current decreases and the turn-ON voltage (V_ON) shifts towards the positive direction as the Sc content increases, which indicates lower carrier density after incorporation of Sc into In₂O₃. More interestingly, the incorporation of Sc into In₂O₃ can effectively improve the electrical stability of the TFT devices under gate bias stress, which is attributed to the reduction of the number of oxygen vacancies due to the relatively low standard electrode potential (−2.36) of Sc and strong bonding strength of Sc–O (680 kJ mol⁻¹). The reduction of oxygen vacancies is confirmed by the x-ray photoelectron spectroscopy (XPS) experiments.

The aim of this study is to investigate the impact of multiband corrections on the current density in GaAs tunnel junctions (TJs) calculated with a refined yet simple semi-classical interband tunneling model (SCITM). The non-parabolicity of the considered bands and the spin–orbit effects are considered by using a recently revisited SCITM available in the literature. The model is confronted to experimental results from a series of molecular beam epitaxy grown GaAs TJs and to numerical results obtained with a full quantum model based on the non-equilibrium Green's function formalism and a 6-band k.p Hamiltonian. We emphasize the importance of considering the non-parabolicity of the conduction band by two different measurements of the energy-dependent electron effective mass in N-doped GaAs. We also propose an innovative method to compute the non-uniform electric field in the TJ for the SCITM simulations, which is of prime importance for a successful operation of the model. We demonstrate that, when considering the multiband corrections and this new computation of the non-uniform electric field, the SCITM succeeds in predicting the electrical characteristics of GaAs TJs, and are also in agreement with the quantum model. Besides the fundamental study of the tunneling phenomenon in TJs, the main benefit of this SCITM is that it can be easily embedded into drift-diffusion software, which are the most widely-used simulation tools for electronic and opto-electronic devices such as multi-junction solar cells, tunnel field-effect transistors, or vertical-cavity surface-emitting lasers.

The waveguide-based microwave plasma device is widely used to generate atmospheric plasma for some industrial applications. Nevertheless, the traditional tapered waveguide device has limited power efficiency and produces unstable plasma. A novel ridged waveguide with an oblique hole is proposed to produce microwave atmospheric plasma for fluid processing. By using the ridged waveguide, the microwave field can be well focused, which can sustain plasma at relatively low power. Besides, an oblique hole is used to decrease the power reflection and generate a stable plasma torch especially in the case of high flowing rates. Experiments have been performed with the air flowing rates ranging from 500 l h⁻¹ to 1000 l h⁻¹ and the microwave working frequency of 2.45 GHz. The results show that in comparison with the conventional tapered waveguide, this novel device can both sustain plasma at relative low power and increase the power transfer efficiency by 11% from microwave to plasma. Moreover, both devices are used to process the waste gas-CO and CH₄. Significantly, the removal efficiency for CO and CH₄ can be increased by 19.7% and 32% respectively in the ridged waveguide compared with the tapered waveguide. It demonstrates that the proposed device possesses a great potential in industrial applications because of its high efficiency and stable performance.

C5-PFK (C5-perfluoroketone, C₅F₁₀O) is under wide consideration as an environmentally-friendly alternative gas to SF₆ in high-voltage applications, because of its superior insulation performance. The aim of this work is to study theoretically the arc extinguishing performance and electric strength of C5-PFK.

The arc extinguishing performance of C5-PFK was evaluated by analyzing and comparing the thermophysical properties of C5-PFK, SF₆, CF₄, CO₂ and N₂ plasmas. It was difficult to obtain the species formed in C5-PFK plasmas because of the complex C5-PFK molecular decomposition process. In this work, the decomposition process of C5-PFK and the related species were analyzed by the bond energy analysis method. For the species for which parameters such as the partition function and the enthalpy of formation were not available, computational chemistry methods were used to obtain the required data. The collision integrals were calculated using the phenomenological potential model. Using these results, the local thermodynamic equilibrium composition at temperatures from 300 to 30 000 K at 1–10 atm of pure C5-PFK was calculated by the method of minimization of the Gibbs free energy, and the corresponding transport coefficients were calculated by Chapman–Enskog method. Through the comparison of the thermophysical properties, it was found that C5-PFK had similar characteristics to SF₆, with large peaks in specific heat below 4500 K, indicating potentially good thermal interruption capability. However, the specific heat peak at 7000 K corresponding to CO decomposition may detract from the thermal interruption capability. Specific heat peaks at higher temperatures are associated with the breaking of double or triple bonds, and should be avoided if possible in the new alternative gases.

The electric strength of C5-PFK was assessed using the molecular electrostatic potential, which can be accurately calculated or measured, and gives strong insights into important characteristics of the molecule. Based on the analysis of the molecular surface electrostatic potential and electric strength of C5-PFK, SF₆, CF₄, CO₂, and N₂, it is found that the positive potential area of the molecular surface has a strong correlation with the electric strength and is expected to be one of the predictors of electric strength. To verify this phenomenon, 36 kinds of particles were used for the correlation analysis. The correlation coefficient between the positive potential area and electric strength is up to 0.9 which means strong correlation.

Numerical modelling of near-anode layers in arc discharges in several gases (Ar, Xe and Hg) is performed in a wide range of current densities, anode surface temperatures, and plasma pressures. It is shown that the density of energy flux to the anode is only weakly affected by the anode surface temperature and varies linearly with the current density. This allows one to interpret the results in terms of anode heating voltage (volt equivalent of the heat flux to the anode). The computed data may be useful in different ways. An example considered in this work concerns the evaluation of thermal regime of anodes in the shape of a thin rod operating in the diffuse mode. Invoking the model of nonlinear surface heating for cathodes, one obtains a simple and free of empirical parameters model of thin rod electrodes applicable to dc and ac high-pressure arcs provided that no anode spots are present. The model is applied to a variety of experiments reported in the literature and a good agreement with the experimental data found.

The optical conductivity of a heterostructure formed by a commensurate stacking of graphene and a topological insulator (TI) is investigated using the Kubo formalism. Both the intra- and interband AC conductivities are found to be sensitive to the graphene-TI coupling. The direct interband transition in graphene which is the origin of the universal conductance is forbidden due to the topological nature is the coupling. Furthermore, the graphene-TI coupling gives rise to additional broken symmetries, resulting in both the inter- and intraband conductivity to be reduced in the graphene-TI heterostructure. By varying the Fermi energy of the heterostructure, the band that gives the largest contribution changes, which in turn affects the overall electronic transport.

As the closest isoelectronic analogue of carbon, boron nitride (BN) shares a similar structure with carbon from 1D nanotubes, 2D nanosheets, and 3D diamond structures. However, most BN structures are insulators, which limits their application. In this work, under the inspiration of the sp² hybridized carbon honeycomb, we propose a hexagonal phase of BN consisting of only sp² bonds, which exhibits intriguingly intrinsic metallicity. First-principles calculations confirm that this phase is both thermally and dynamically stable. Moreover, the calculations on the band structure, partial density states and electron localization function suggest that the metallic behavior is attributable to the delocalized B-2p electrons, leading to second-neighbor interaction between the p_z states of sp²-bonded B atoms in adjacent layers. Our findings not only enrich the BN allotrope family with 3D structures but also stimulate further experimental interest in applications of metallic BN in electronic devices.

This study investigates the permeability of new 3D Ni foam/graphene composites (Ni foam covered with graphene) using compressed air, Ar and N₂ as the probe gases. The results show that the introduction of graphene on the surface of Ni foam via in situ chemical vapour deposition is not detrimental to the permeability of the composites; on the contrary, in some cases it improves permeability. A modified Ergun-type correlation has been proposed, which represents very well the permeability of the Ni foam/graphene composites, especially at flow rates higher than 0.3 m s⁻¹. Further studies show that graphene also helps to improve the thermal conductivity of the composite. These results suggest that the graphene involvement will make the Ni foam/graphene composite a good candidate for potential applications such as filters or heat exchangers suitable for working under harsh conditions such as at high temperatures, in corrosive environments, etc.

We present a water-injected all-dielectric metamaterial that can offer an extremely wide bandwidth of electromagnetic absorption and prominent wide incident angle range. Different from conventional metal-dielectric based metamaterial absorbers, the absorption mechanism of the proposed all-dielectric metamaterial absorber is to take advantage of the dispersion of water, rather than electric or/and magnetic resonance, which thoroughly overcomes the defects of narrow bandwidth and oblique incidence from metal-dielectric based metamaterial absorber. The simulated absorption was over 90% in 8.1–22.9 GHz with the relative bandwidth of 95.5% when the incident angle reaches 60°, and the corresponding microwave experiment is performed to support the simulations. The obtained excellent absorption performance reveals a possible application of the proposed absorber, which can be exploited for electromagnetic stealth purposes, especially for electromagnetic stealth of sea targets.

Using molecular dynamics (MD) simulations, we investigate the elastic–plastic mechanical performances of monolayer graphene oxide (GO) under uniaxial tension. The brittle–ductile–brittle transition and nonlinear–linear–nonlinear elastic transition is found in the uniaxial tension of GO, which displays strong correlations to the content, distribution and proportion of oxygen functional groups. In principle, the tensile behavior of graphene with epoxy groups exhibits ductile fracture features due to the unique epoxy-to-ether transformation in structural evolution. Our simulation results also reveal that wrinkling could cause a competing mechanism of strain-hardening or -softening, and in turn, the nonlinear–linear elasticity transition. Moreover, we propose a continuum mechanical model with a modified stress–strain relation to understand the unique deformation performances, which is consistent with the MD results. These findings might provide valuable insight and design guidelines for optimizing the specific mechanical properties and deformation behaviors of graphene and its derivatives.

Broadband absorption enhancement is obtained in organic solar cells using zirconium nitride (ZrN) plasmonic nanostructures. Due to the thickness limitations imposed on organic solar cells, their absorption efficiency is limited. Plasmonic nanostructures have the ability to increase their optical efficiency by increasing the light path length inside the active material. Here, refractory plasmonics, a new type of plasmonic nanostructures, is used in organic solar cells instead of traditional metal plasmonics. ZrN, as an example of refractory plasmonics, has a high localized surface plasmon resonance quality factor in the visible range while being cheap, abundant, and C-MOS compatible. Here, several ZrN plasmonic nanostructures are studied including ZrN nanospheres, nanocubes, and nanoshells. Their Mie scattering and absorption efficiencies in a polymer environment are calculated. In addition, the effect of their incorporation on the absorbed power and short circuit current of organic solar cell is analyzed. ZrN nanodisks are also studied in different locations inside the solar cell with the best performance found for nanodisks placed at the interface between the active and the buffer layer. The highest absorption enhancement reported here is obtained when ZrN cubical nanoshells are added. A 34.7% increase in short circuit current is calculated for this structure.

The electric field amplitude (E_o) dependent dynamic ferroelectric hysteresis and polarization current density curves measured at room temperature for Na_0.5Bi_0.5TiO₃ (NBT), showed three different stages of polarization reversal mechanism. The scaling relationship confirmed the dominance of domain wall motion at Stage I (i.e. upto E_o  <  35 kV cm⁻¹), followed by domain switching at Stage II (35 kV cm⁻¹  <  E_o  <  60 kV cm⁻¹). Interestingly, a unique behaviour with two sub stages was observed in Stage III (60 kV cm⁻¹  <  E_o  <  90 kV cm⁻¹), with two distinct switching mechanisms viz., polarization rotation at Stage III-A and polarization extension at Stage III-B. X-ray diffraction analysis based on the Rietveld refined atomic positional co-ordinates, in electrically poled system strongly favors the polarization extension mechanism proposed at Stage III-B. The measured E_o-dependent longitudinal piezoelectric response (d₃₃ and g₃₃) values match closely with our proposed polarization reversal mechanism.

The ion flux from various metals (Al, Ti, Cu, Sn and W) ablated with 20 ns Nd:YAG laser radiation at a wavelength of 1064 nm was investigated by an ion collector operating in time-of-flight (TOF) configuration. The laser irradiance at the target was varied in the range of 1.7  ×  10⁸–5.73  ×  10⁸ W cm⁻². Ion yield from various metals showed a linearly increasing trend with increasing laser irradiance, whereas ion yield was found to decrease with an increasing atomic mass of the target. Our results clearly indicate that ion yield is not a function of the volatility of the metal. TOF ion spectra showed at least two groups of low intensity peaks due to fast ions. The first group of ion peaks, which was present in the spectra of all five metals, was due to surface contamination. The additional fast ion structures in the spectra of Sn and W can be related to the ion acceleration due to the prompt electron emission from these high-Z metals. The ion velocity follows the anticipated inverse square root dependence on the ion mass. For the range of laser irradiance investigated here, the most probable energy of the Cu ions increases from about 100–600 eV. The fast increase in ion energy above ~3  ×  10⁸ W cm⁻² is related to the increase of the Columb part of the ion energy due to the production of multiply charged ions.