The parameters of laser plasmas formed using polycrystalline CuInS<Subscript>2</Subscript>, copper,and indium targets

We have studied the electron temperature (T _e) and density (N _e) of laser plasmas formed under the action of a neodymium laser in a polycrystalline CuInS₂ target, as well as in pure copper and indium targets. At a laser beam power density of ∼10⁸ W/cm², the average electron temperature of a laser plasma at a distance of r=1 mm from the CuInS₂ target falls within 0.55–0.77 eV, while the laser plasmas of copper and indium are characterized by T _e(Cu)=0.4–1.8 eV and T _e(In)=0.58–2.4 eV, respectively. The average electron density at the core of the laser torch (r=1 mm) at the CuInS₂ target reaches N _e=2.2×10¹⁶ cm⁻³. The results obtained for the polycrystalline target can be used in microelectronics for optimization of the process of laser deposition of thin films for solar cell elements.     

Design of Cu–Ce co-doped TiO<Subscript>2</Subscript> for improved photocatalysis

The fast recombination of photo-generated conduction band electrons (e _cb ^? ) and valance band holes (h _vb ⁺ ) of TiO₂ results in an unsatisfactory photocatalytic performance for organic degradation. To increase the efficiency of charge separation, TiO₂ was modified by Cu–Ce co-doping considering the better redox properties of copper–ceria oxide with respect to the single oxide, i.e., an easier electron capturing ability. An optimal Cu–Ce co-doped TiO₂ with the initial molar ratio of Cu/Ce at 3:1 was prepared by a hydrothermal method with the aim to greatly promote the charge separation, and characterized by XRD, BET, DRS, PL, HR-TEM, and XPS techniques. Upon ultraviolet light irradiation, it exhibits significantly enhanced photocatalytic activity, about 5.8 times that of Ti–HF. The presence of Cu²⁺ and Ce³⁺/Ce⁴⁺ benefits electrons captured by molecular oxygen, while an increased hydroxyl groups upon Cu–Ce co-doping consume more holes, resulting in prolonged lifetime of photo-generated carriers. Moreover, it is proved that electron transfers preferably from conduction band (CB) of TiO₂ to CB of CuO and then to nearby CeO₂.     

Electrical properties of complex bimetallic salts [M(N–N)3]2+[Cu(MNT)2]2− and heterobimetallic AgI–CuII/HgII–CuII bis(maleonitriledithiolato) bridged coordination polymers

This paper presents the solid-state electrical conductance properties of a series of complex bimetallic salts of the form [M(N–N)₃][Cu(MNT)₂] (M=Fe(II), Co(II), Ni(II), or Cd(II); N–N=1,10-phenanthroline (phen) or ethylenediamine (en); MNT²⁻=maleonitriledithiolate) and bridged heterobimetallic complexes Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] that have been prepared by treatment of complex salt Na₂[Cu(MNT)₂] (generated in situ) with one equivalent of cationic complexes [M(N–N)₃]X₂ or Hg(CH₃COO)₂ and two-equivalent of AgNO₃ in aqueous–methanol mixture and characterised by relevant spectroscopies (IR, EPR, UV-Visible) as well as by powder XRD spectra. Solution conductivity measurements in 10⁻³ M DMSO solution revealed 1:1 electrolytic behaviour of the bimetallic salts. Diamagnetism together with powder EPR spectra for Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] show strong antiferromagnetic interaction between two adjacent copper(II) centers at room temperature. Majority of the complexes exhibited compressed pellet σ_rt in 8.19×10⁻¹¹ to 5.37×10⁻⁷ S cm⁻¹ range and show semiconductivity over the 303–383 K temperature range. Conductivity of both coordination polymers are appreciably higher compared to the bimetallic salts. For the salts [Co(phen)₃][Cu(MNT)₂], [Ni(phen)₃][Cu(MNT)₂] and bridged complexes Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] the conductivity remarkably increases, i.e., 10² to 10³ order of magnitude at elevated temperature showing some sort of phase transformation producing S⋯S intermolecular contact.     

Enhanced Crystallinity,Dielectric, and Energy Harvesting Performances of Surface‐Treated Barium Titanate Hollow Nanospheres/PVDF Nanocomposites

Enhancement of the energy harvesting performance and dielectric constants of poly(vinylidene fluoride) (PVDF)‐based capacitors is realized by incorporating 16 wt% of surface‐treated BaTiO₃ hollow nanospheres (HNSs) in comparison with the pristine PVDF. The fabricated BaTiO₃ HNSs with particle sizes of ≈20 nm and BET surface area of 297 m² g⁻¹ are treated by three different surface modifiers. The changes in crystallinity of the PVDF containing the surface‐treated BaTiO₃ HNSs are induced by both enlarged surface areas and increased surface functionality of the HNSs. Effects of such surface functionalities on the crystalline, dielectric, and energy harvesting performances of the nanocomposites are systematically investigated to identify the optimal surface modifier to enhance the energy density of the nanocomposites. Consequently, these changes in crystallinity lead to higher dielectric constants (ε′ ≈ 109.6) and energy density (U_e ≈ 21.7 J cm⁻³) with highly retained breakdown strength (E = 3.81 × 10³ kV cm⁻¹) compared to pristine PVDF (ε′ ≈ 11.6 and U_e ≈ 2.16 J cm⁻³ at 3.98 × 10³ kV cm⁻¹), indicating their potential as high energy density capacitors.     

In-situ reduced non-oxidized copper nanoparticles in nanocomposites with extraordinary high electrical and thermal conductivity

Copper has received considerable attention for conductive nanocomposites as an alternative to costly silver or gold. However, practical application has been impeded by its susceptibility to oxidation in air. Here we report a novel scalable synthesis method of non-oxidized copper nanoparticles (InSituCuNPs) by pre-mixing and in-situ reducing copper formate-(butylamine-octylamine) complex inside soft epoxy matrix. The solid–liquid phase change of the copper formate complex, during the nanocomposite spark-plasma-sintering process, promotes uniform dispersion. Even the outermost atoms of InSituCuNPs are not oxidized since they are surrounded by the thick matrix polymer as soon as in-situ reduced into metallic copper, resulting in high electrical (15,048 Scm⁻¹) and thermal (28.4 Wm⁻¹K⁻¹) conductivities of the nanocomposite. Furthermore, a small addition of 1-dimensional carbon nanotubes decorated with 0-dimensional copper nanoparticles (<4 nm), together with bi-functionalization, dramatically enhances connectivity between the InSituCuNPs, resulting in air-stable and record-high 31,974 Scm⁻¹ and 74.1 Wm⁻¹K⁻¹ for isotropic copper-based nanocomposites. The nanocomposite also provides a small thermal resistance (2.64 × 10⁻⁶ m²KW⁻¹) and excellent heat dissipation performance.     

Rectifying and photovoltaic effects observed in mesoporous MCM-41 silica film on silicon

Oriented mesoporous MCM-41 silica films have been synthesized on single-crystalline silicon (111) wafers by the self-assembly deposition in ammonia medium. For the first time, the I–V curves and surface photovoltaic spectra of the films has been investigated. The I–V curve of the as-synthesized film exhibits an excellent rectified ratio of σ⁺/σ⁻=3×10³ (where σ⁺, σ⁻ are the forward electrical conductivity and reverse electrical conductivity, respectively). The results of photovoltaic measurements indicate that the as-synthesized film possesses a significant surface photovoltaic increase.     

Observation of tunneling and magneto-tunneling out of a 2D Wigner crystal

We measured the escape rates of surface state electrons from an electron layer confined at the liquid helium-vacuum interface in the temperature range of 30–450mK, and for densities 0.02–2.2×10⁸ cm ^–2. Below 200mK the escape rates were temperature independent and converged to the expected single particle tunneling rates in the zero density limit, where correlations are negligible. The single particle rates were enhanced exponentially as the density was increased up to a critical densityn _c. Atn _c the escape process becomes extremely nonlinear. As the barrier is raised so that the escape rates decrease below 5.0×10^–4sec^–1, a new very weakly density and external field dependent mechanism seems to dominate the escape. Thermally activated escape was observed above 250mK and the activation energies were in good agreement with the expected values. Upon application of a magnetic field in the plane of the electron layer, the rates become strongly temperature and field dependent even at the lowest temperaturesT40mK. At these temperatures and low densities rates are suppressed four orders of magnitude in a few kGauss magnetic fields.     

Electrical properties of iron phthalocyanine thin film device using gold and aluminium electrodes

The electrical conductivity of FePc thin film sandwich structures using gold and aluminium electrodes has been investigated for the freshly prepared devices and device after exposure to oxygen for 30 days. Current density-voltage characteristics of the devices in the forward bias showed an ohmic conduction in lower voltages and a space charge limited conduction (SCLC) controlled by a single and an exponential trapping levels at two different ranges of applied voltages. The hole concentrations are obtained as P _o = 3.92 × 10¹⁶ m⁻³ with a hole mobility μ = 5.81 × 10⁻⁶ m⁻¹ V⁻¹ s⁻¹. In the SCLC region a discrete trap level of 1.88 × 10²¹ m⁻³ is found at 0.66 eV followed by an exponential trap distribution of P _e = 4.63 × 10⁴⁶ J ⁻¹ m⁻³ at N _t(e) = 2.23 × 10²⁶ m⁻³. From the current limitations in the reverse bias, the conduction is identified as an electrode limited Schottky type of conduction. In the oxygen-doped samples, both in the forward and reverse bias the order of currents are much enhanced and a transition from the ohmic conduction to a space charged conduction is observed.     

Novel erbium-doped TeO2-based oxysulfide glasses: thermal and spectroscopic properties

Er³⁺-doped TeO₂-based oxysulfide glasses have been prepared in argon atmosphere in carbon crucibles. The thermal analysis and spectroscopic properties of Er³⁺ have been considered in terms of sulfide influence. As a function of composition, we have principally measured optical absorption, spontaneous emission and lifetime measurements. Judd-Ofelt theory was introduced to calculate bandwidth and emission cross-section. The results show the product FWHM×σ_e increase from 476.88 to 635.04 10⁻²¹ cm² nm evidently with the addition of 10 mol% PbS into tellurite glass, which indicates a perfect effect on spectra property of Er³⁺ ions.     

Thermal expansion of cross-ply and woven carbon fibre–copper matrix composites

This paper presents thermal expansion data for cross-ply and woven copper matrix–carbon fibre composites (Cu–C_f MMCs) that were prepared by diffusion bonding. Thermal expansion was measured in two perpendicular in-plane directions of plate samples. For cross-ply samples (57 vol.%fibres) the mean coefficient of thermal expansion (CTE) between −20 and 300°C changed from approximately 6.5×10⁻⁶/°C to 3.5×10⁻⁶/°C during heating/cooling. The in-plane CTE increases with decreasing fibre content. Composites with woven arrangement of carbon fibres show a slightly higher CTE at elevated temperature.     

Elastic moduli,thermal expansion and microstructure of copper-matrix composite reinforced by continuous graphite fibres

Copper-matrix composites reinforced by continuous graphite fibres (C_g) were processed by hot-pressing layers of metallic prepregs, each fibre within the yarns having previously been coated with copper by electroplating. The electrodeposition and consolidation conditions were optimized to minimize the residual porosity, which could be considered as negligible. One-dimensional (1D) and two-dimensional composites were obtained by this technique. In addition to the good metallurgical quality of the matrix, examination of the fibre/matrix interphase by Auger electron spectroscopy confirmed the excellent chemical compatibility between copper and graphite. As a consequence, the ultimate tensile strength of fibres extracted from the matrix remained nearly unchanged. The thermal expansion coefficients of 1 D C_g/Cu composite materials were determined between 100 and 300°C, along the two orthogonal directions. Values ranging from 8 to 9 × 10⁻⁶ °C⁻¹ in the composite plane and from 16 to 18 × 10⁻⁶ °C⁻¹ in the orthogonal direction were obtained. These results, which are related to the strong anisotropy of the ex-pitch graphite fibre, are correlated to the theoretical values found with the rule of mixtures. The poor Young's modulus and the tensile strength values are correlated to the microstructure of the fibre/matrix interphase.     

Direct evidence of advantage of Cu(111) for graphene synthesis by using Raman mapping and electron backscatter diffraction

The advantageous crystallographic orientation of Cu surface for graphene synthesis by using thermal chemical vapor deposition (CVD) is examined by Raman mapping and electron backscatter diffraction. It is found that Cu(111) predominates over (110) and (100) for single- (SLG) or few-layer graphene (FLG) growth. To confirm this result we attempt the synthesis of graphene on Cu(111) single crystal film surfaces. We confirmed the formation of high quality and high uniformity SLG or FLG over more than 97% of the substrate surface area of 10 mm × 10 mm by Raman mapping.     

Variances of locally Minimum Variance Quadratic Unbiased Estimators (“MIVQUE's”) of Variance Components

Minimum variance quadratic unbiased estimators (MIVQUE's) of variance components from unbalanced data are functions of the components they are to estimate. To use the MIVQUE expressions for estimation under the one-way classification random model, for example, the unknown between- and within-treatments components, σ² _a and σ² _e , must be replaced by a priori estimates σ² _ao and σ² _eo the resulting estimators are called “MIVQUE's.” For the one-way classification, expressions for the variances and covariance of the “MIVQUE's” are obtained under normality. Numerical comparisons indicate that when σ² _a /σ² _e > 1 (approximately) and unless σ² _ao /σ² _eo Q σ² _a /σ² _e , (a) the “MIVQUE's” have variances near their lower bounds, and (b) the “MIVQUE” of σ² _a is more efftcient than the ANOVA estimator. When σ² _a /σ² _e < 1, the “MIVQUE's” are more dependent on accurate specification of σ² _ao /σ² _eo . The “MIVQUE” and ANOVA estimator of σ² _e have nearly equal variances unless σ² _eo /σ² _eo σ² _a /σ² _e , when the ANOVA estimator has smaller variance.     

Effect of residual gas pressure on the epitaxial growth of vacuum-deposited chromium on Cu{111} substrates

Transmission electron microscopy, electron diffraction and Auger electron spectroscopy were used to study the effect of vacuum conditions on the epitaxial growth of vacuum-deposited chromium films of thicknesses less than 40 nm on Cu{111} substrates. The chromium films were condensed (i) in ultrahigh vacuum at 10⁻⁹ Torr, (ii) at total pressures of 10⁻⁵, 10⁻⁶ and 5 × 10⁻⁸ Torr and (iii) at oxygen partial pressures of 5 × 10⁻⁹, 10⁻⁷ and 10⁻⁶ Torr. The presence of contaminants during the chromium evaporation suppressed the formation of Kurdjumov-Sachs orientations. A low oxygen partial pressure was most effective in altering the orientation and morphology of the deposits.     

Thiol-Branched Solid Polymer Electrolyte Featuring High Strength,Toughness, and Lithium Ionic Conductivity for Lithium-Metal Batteries

Lithium-metal batteries (LMBs) with high energy densities are highly desirable for energy storage, but generally suffer from dendrite growth and side reactions in liquid electrolytes; thus the need for solid electrolytes with high mechanical strength, ionic conductivity, and compatible interface arises. Herein, a thiol-branched solid polymer electrolyte (SPE) is introduced featuring high Li⁺ conductivity (2.26 × 10⁻⁴ S cm⁻¹ at room temperature) and good mechanical strength (9.4 MPa)/toughness (≈500%), thus unblocking the tradeoff between ionic conductivity and mechanical robustness in polymer electrolytes. The SPE (denoted as M-S-PEGDA) is fabricated by covalently cross-linking metal–organic frameworks (MOFs), tetrakis (3-mercaptopropionic acid) pentaerythritol (PETMP), and poly(ethylene glycol) diacrylate (PEGDA) via multiple C S C bonds. The SPE also exhibits a high electrochemical window (>5.4 V), low interfacial impedance (<550 Ω), and impressive Li⁺ transference number (t_Li+ = 0.44). As a result, Li||Li symmetrical cells with the thiol-branched SPE displayed a high stability in a >1300 h cycling test. Moreover, a Li|M-S-PEGDA|LiFePO₄ full cell demonstrates discharge capacity of 143.7 mAh g⁻¹ and maintains 85.6% after 500 cycles at 0.5 C, displaying one of the most outstanding performances for SPEs to date.     

Performance characteristics of guanine incorporated PVDF-HFP/PEO polymer blend electrolytes with binary iodide salts for dye-sensitized solar cells

In this work, we have investigated the influence of guanine as an organic dopant in dye-sensitized solar cell (DSSC) based on poly(vinylidinefluoride-co-hexafluoropropylene) (PVDF-HFP)/polyethylene oxide (PEO) polymer blend electrolyte along with binary iodide salts (potassium iodide (KI) and tetrabutylammonium iodide (TBAI)) and iodine (I₂). The PVDF-HFP/KI + TBAI/I₂, PVDF-HFP/PEO/KI + TBAI/I₂ and guanine incorporated PVDF-HFP/PEO/KI + TBAI/I₂ electrolytes were prepared by solution casting technique using DMF as solvent. The PVDF-HFP/KI + TBAI/I₂ electrolyte showed an ionic conductivity value of 9.99 × 10⁻⁵ Scm⁻¹, whereas, it was found to be increased to 4.53 × 10⁻⁵ Scm⁻¹ when PEO was blended with PVDF-HFP/KI + TBAI/I₂ electrolyte. However, a maximum ionic conductivity value of 3.67 × 10⁻⁴ Scm⁻¹ was obtained for guanine incorporated PVDF-HFP/PEO/KI + TBAI/I₂ blend electrolyte. The photovoltaic properties of all these polymer electrolytes in DSSCs were characterized. As a consequence, the power conversion efficiency of the guanine incorporated PVDF-HFP/PEO/KI + TBAI/I₂ electrolyte based DSSC was significantly improved to 4.98% compared with PVDF-HFP/PEO/KI + TBAI/I₂ electrolyte based DSSC (2.46%). These results revealed that the guanine can be an effective organic dopant to enhance the performance of DSSCs.     

Effect of copper doping on physical properties of nanocrystallized SnS zinc blend thin films grown by chemical bath deposition

SnS: Cu thin films have been successfully prepared on Pyrex substrates using low cost chemical bath deposition (CBD) technique with different copper doped concentration (y = [Cu]/[Sn] = 5%, 6%, 8%, 9% and 10%). The structure, the surface morphology and the optical properties of the SnS:Cu films were studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and spectrophotometer measurements, respectively. To obtain a thickness of the order of 780 ± 31 nm for absorber material in solar cell devices, a system of multilayer has been prepared. It is found that the physical properties of tin sulphide are affected by Cu-doped concentration. In fact, X-ray diffraction study showed that better cristallinity in zinc blend structure with preferential orientations (111)^ZB and (200)^ZB, was obtained for y equal to 6%. According to the AFM analysis we can remark that low average surface roughness (RMS)value of SnS(ZB) thin film obtained with Cu-doped concentrations equal to y = 6%, is about of 54 nm. Energy dispersive spectroscopy (EDS) showed the existence of Cu in the films. Optical analyses by means of transmission T(λ) and reflection R(λ) measurements show 1.51 eV as a band gap value of SnS:Cu(6%) which is nearly equal to the theoretical optimum value of 1.50 eV for efficient light absorption. On the other hand, Cu-doped tin sulphide exhibits a high absorption coefficient up to 2 × 10⁶ cm⁻¹, indicating that SnS:Cu can be used as an absorber thin layer in photovoltaic structure such as SnS:Cu/ZnS/SnO₂:F and SnS:Cu/In₂S₃/SnO₂:F, where ZnS and In₂S₃ are chemically deposited in a previous studies.     

Thermal conductivity of copper films

The thermal conductivity of thin films of copper (400–8000 Å) has been measured in the temperature range 100–500 K. It decreases with decreasing film thickness. An electrical-thermal transport analogy has been used to calculate the size-dependent thermal conductivity of the thin copper films. The decrease of the thermal conductivity with thickness is attributed partly to the scattering of the conduction electrons from the film surfaces and partly to the scattering by lattice impurities and frozen-in structural defects in the films. The variation of the thermal conductivity with temperature agrees with the variation for bulk copper. The Lorentz ratio has been determined and is found to vary from 2.4 × 10^-8 to $\text{2.0 × 10}{}^{-8}\text{W}\text{Ω/}\text{deg}{}^2$ for film thicknesses ranging from 400 to 8000 Å.     

Massless and massive particle-in-a-box states in single- and bi-layer graphene

Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum of particle-in-a-box states for single- and bi-layer graphene, corresponding to massless and massive two-dimensional (2-D) fermions. The density of states D as a function of particle number n shows the expected relationships D(n) ∼ n ^1/2 for massless 2-D fermions (electrons in single-layer graphene) and D(n) ∼ constant for massive 2-D fermions (electrons in bi-layer graphene). The single parameters of the massless and massive dispersion relations are found, namely Fermi velocity υ _F = 1.1 × 10⁶ m/s and effective mass m* = 0.032 m _e, where m _e is the electron mass, in excellent agreement with theoretical expectations.      

Highly Anisotropic Conductors

Composite materials with ordered microstructures often lead to enhanced functionalities that a single material can hardly achieve. Many biomaterials with unusual microstructures can be found in nature; among them, many possess anisotropic and even directional physical and chemical properties. With inspiration from nature, artificial composite materials can be rationally designed to achieve this anisotropic behavior with desired properties. Here, a metallic wood with metal continuously filling the wood vessels is developed, which demonstrates excellent anisotropic electrical, thermal, and mechanical properties. The well‐aligned metal rods are confined and separated by the wood vessels, which deliver directional electron transport parallel to the alignment direction. Thus, the novel metallic wood composite boasts an extraordinary anisotropic electrical conductivity (σ_||/σ_⊥) in the order of 10¹¹, and anisotropic thermal conductivity (κ_||/κ_⊥) of 18. These values exceed the highest reported values in existing anisotropic composite materials. The anisotropic functionality of the metallic wood enables it to be used for thermal management applications, such as thermal insulation and thermal dissipation. The highly anisotropic metallic wood serves as an example for further anisotropic materials design; other composite materials with different biotemplates/hosts and fillers can achieve even higher anisotropic ratios, allowing them to be implemented in a variety of applications.