Anomalously high effective permittivity of a system of FeNi metal nanoislands

The low-frequency effective permittivity of a system of FeNi metal nanoislands was studied. It was found that the effective permittivity of the structures under study is anomalously high, 10⁷–10⁸. The nature of the high permittivity of films is caused by structural parameters (topography) of island films and is associated with the polarization of the dipoles of charged metal nanoislands.     

Specific features of the magnetoresistance in multilayer systems of magnetic nanoislands in weak magnetic fields

New magnetic structures such as multilayer systems of magnetic nanoislands being alternating layers of nanoislands of various magnets have been proposed. The electric, magnetic, and magnetooptical properties of the systems have been studied. The magnetoresistance of ～2% related to the anisotropic effect has been revealed. In multilayer structures of magnetic nanoislands, a unidirectional axis of predominant magnetization has been found, which changes its orientation depending on the structure parameters. The magnetic field required to reorient the axis in the opposite direction has been estimated to be 2 kOe < H _A < 20 kOe. The periodic multilayer structures of magnetic nanoislands are very sensitive to hyperweak magnetic fields (to 10^?6 Oe).     

Effective permittivity of the system of metal nanoislands in strong electric fields

The effect of the electric field on the value and sign of the low-frequency effective permittivity of metal island films is studied. It is shown that the permittivity in island metal films can be both positive and negative. The permittivity of some samples changed sign with the polarity of the applied electric field. Film polarization mechanisms are considered.     

Fatigue of lead titanate and lead zirconate titanate thin films

The fatigue of lead titanate and lead zirconate titanate ferroelectric thin films, i.e., a change in the polarization as a function of the number of switching cycles in an external electric field, is investigated experimentally. The threshold numbers of switching cycles are determined to be 10¹⁰–10¹¹ for the lead titanate films and 10⁹–10¹⁰ for the lead zirconate titanate films. It is shown that a change in the temperature does not substantially affect the threshold number of switching cycles at which the switched polarization decreases drastically. However, an increase in the external field strength leads to a noticeable decrease in the threshold number of switching cycles. The process of fatigue is accompanied by an increase in the coercive field and the internal bias field. It is established that, as the number of switching cycles increases, the internal bias field changes more significantly as compared to the coercive field. The absence of a change in the phase composition in repeatedly switched samples indicates that the fatigue processes have a nonchemical nature. The anomaly observed in the frequency dependence of the permittivity in the frequency range 10⁶–10⁷ Hz due to the domain structure disappears after multiple switching cycles. This suggests that the observed fatigue phenomenon has a domain nature.     

Detection of the metal–insulator transition in disordered systems of magnetic nanoislands

We have studied the conductivity and permittivity of a series of nanoisland-type FeNi films with an effective thickness of up to 3.2 nm on different substrates. It has been observed that the quantity Re ε changes its sign at effective thickness d ^* ≈ 1.5–1.8 nm, because of the metal–insulator transition. Analysis of the temperature dependences of the conductivity has confirmed the existence of the metal–insulator transition at the same thickness d ^*. It has been concluded that the introduced effective permittivity can serve as a characteristic of island metal systems.     

Formation of ultrasmall germanium nanoislands with a high density on an atomically clean surface of silicon oxide

The experimental results of an investigation into the initial stages of growth of a germanium film on an atomically clean oxidized silicon surface are reported. It is shown that the growth of the germanium film in this system occurs through the Volmer-Weber mechanism. Elastically strained nanoislands with a lateral size of less than 10 nm and a density of 2 × 10¹² cm^?2 are formed on the oxidized silicon surface. In germanium films with a thickness greater than 5 monolayers (ML), there also arise completely relaxed germanium nanoislands with a lateral size of up to 200 nm and a density of 1.5 × 10⁹ cm^?2.     

Poole-Frenkel effect in chalcogenide semiconductors with various crystalline structures

The results of investigation of electrical conductivity of a large group of chalcogenide semiconductors having the layered, cubic, and orthorhombic structures in strong electric fields up to 10⁵ V/cm are presented. The revealed increase in electrical conductivity σ in strong electric fields has been explained by the Frenkel thermionic ionization. This has made it possible, along with other parameters (for example, activation energy and trap concentration, charge-carrier mean free path, permittivity), to evaluate the concentration and mobility of charge carriers in semiconductors under study. It has been shown that in strong electric fields in semiconductors, when the thermionic ionization of the traps occurs, their permittivity ?, which is caused by the electron polarization, is determined by the simple formula ? = n ², where n is the refractive index of light.     

Effect of mechanical stresses on the dielectric response of PZT ferroelectric thin films

This paper reports on the results of the investigation into the effect of mechanical stresses on the dielectric properties of PZT ferroelectric thin films. An external load G applied to the sample brings about an increase in the residual tensile stress along one of the axes of the film. It is demonstrated that, in weak and moderate electric fields, an increase in the stress σ leads to an increase in the permittivity ε′ of the sample. A further increase in the strength of the measuring electric field results in the opposite effect: the permittivity ε′ decreases with increasing external load G. The observed effects are explained in terms of the specific features revealed in the behavior of the domain structure of the ferroelectric thin films in fields of internal stresses.     

Frequency dispersion of the dielectric characteristics in polymer films based on the [NiSalen] complex

The results of the measurements of the dielectric properties exhibited by metal-containing polymer structures based on Ni(II) complexes in the frequency range f = 10²–10⁵ Hz are reported. It is established that, in the range of acoustic frequencies, the permittivity ε decreases with increasing frequency, whereas the dielectric loss tangent tan δ increases. At frequencies f > 10⁴ Hz, the dependence tan δ(f) is characterized by a relaxation maximum. The possible mechanisms of dielectric polarization and charge transfer in an alternating-current electric field are considered.     

Enhancement of the photoluminescence of silicon nanocrystals under the influence of electric field

The effect of electric field generated by the application of surface acoustic waves on photoluminescence (PL) of silicon nanocrystals embedded in SiO₂ films is studied. It is shown that the application of electric field results in an increase in the intensity of nanocrystal PL, the increase amounting to 10% at a field amplitude of 6 kV cm⁻¹. The results are discussed within the frame of the self-trapped exciton model.     

Effect of low-angle boundaries on the dielectric properties of epitaxial Ba0.8Sr0.2TiO3 films

The effect of low-angle boundaries on the dielectric properties of epitaxial Ba_0.8Sr_0.2TiO₃ films is studied by comparing films differing in crystalline-block size. It is found that the permittivity diminishes considerably when the block sizes are reduced. The maximum of the temperature-dependent permittivity is shifted towards lower temperatures, and the sensitivity of the permittivity to an electric field is reduced. Moreover, it is found that the maximum in the permittivity temperature dependence is displaced towards lower temperatures when the applied measured voltage is increased and becomes higher than the coercive voltage. The width of a hysteresis loop decreases significantly when the frequency of the controlling field is reduced. The reasons for the observed behavior are analyzed.     

Microwave measurement of the permittivity of ferroelectric films by electrodeless and coplanar waveguide methods

Ferroelectric films on dielectric substrates prepared by reactive rf sputtering have been studied. The temperature and external electric field dependencies of the permittivity of the films are deduced. It is shown that deposition of metallic electrodes onto the surface of the film leads to an increase in the permittivity and to an enhancement of the dependency of on temperature and the external electric field. The observed effects may be explained by the formation of an electrode-film interface layer.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 8–12, April, 1990.     

Experimental analysis of current conduction through thermally grown SiO<Subscript>2</Subscript> on thick epitaxial 4H-SiC employing Poole-Frenkel mechanism

Electrical properties of SiO₂ grown on the Si-face of the epitaxial 4H-SiC substrate by wet thermal oxidation technique have been experimentally investigated in metal oxide-silicon carbide (MOSiC) structure with varying oxide thicknesses employing Poole-Frenkel (P-F) conduction mechanism. The quality of SiO₂ with increasing thickness in MOSiC structure has been analysed on the basis of variation in multiple oxide traps due to effective P-F conduction range. Validity of Poole-Frenkel conduction is established quantitatively employing electric field and the oxide thickness using forward I–V characteristics across MOSiC structures. From P-F conduction plot (ln(J/E) vs. E ^1/2), it is revealed that Poole-Frenkel conduction retains its validation after a fixed electric field range. The experimental methodology adopted is useful for the characterization of oxide films grown on 4H-SiC substrate.     

New resonance-polariton Bose-quasiparticles enhances optical transmission into nanoholes in metal films

We argue the existence of fundamental particles in nature, neutral Light-Particles with spin 1, and rest mass m=1.8⋅¹⁰−4me, in addition to electrons, neutrons and protons. We call these particles Light Bosons because they create the electromagnetic field which represents Planck's gas of massless photons together with a gas of Light-Particles in the condensate. In this respect, the condensed Light-Particles, having no magnetic field, represent the constant electric field. In this context, we predict an existence of polariton-plasmon Bose-quasiparticles with effective masses ml≈¹⁰−6me and mr=0.5me, which are induced by interaction of the plasmon field and the resonance Frölich-Schafroth charged bosons with electromagnetic wave in metal. Also, we prove that the enhancement optical transmission into nanoholes in metal films and Surface Enhanced Raman Spectroscopy are provided by a new resonance-polariton Bose-quasiparticles but not model of surface plasmon-polariton. In this Letter, the quantization Fresnel's equations is presented which confirms that Light-Particles in the condensate are concentrated near on the wall of grooves in metallic grating and, in turn, represent as the constant electric field which provides the launching of the surface Frölich-Schafroth bosons on the surface metal holes.     

Equal-permittivity states induced in a ferroelectric

Conditions under which a ferroelectric subjected to an electric field acquires equal-permittivity paraelectric states at different temperatures are studied. The temperature dependences of the control (inducing) field intensity and feasible permittivity interval (ɛ_min-ɛ_max) are obtained. The effect of intersection of the ɛ(E, T _i ) characteristics of the ferroelectric in the paraelectric state is analyzed. With the control field and temperature varying consistently, the permittivity ɛ_i of strontium titanate films and films of the barium titanate-strontium titanate solid solution may be kept constant in a wide (200–320 K) temperature range and, at the same time, changed by more than twofold by varying the electric field.     

Local fracture of thin metallic films during electromagnetic loading

The pulsed electrodynamic fracture of thin (10–50 nm) aluminum films deposited onto polymer substrates is experimentally studied. The fracture of the films manifests itself in the form of discontinuity (crack) channel growth across an applied electric field. The roles of a magnetic pressure, thermomechanical stresses, and Joule heating at the tip of a growing crack are analyzed at high current densities (∼10¹⁰−10¹² A/m²). In contrast to the results well known for the electrodynamic fracture of bulk metallic samples, the first two factors in the films are insignificant. The effect of the electric explosion of the crack tip is found to play a key role in the beginning of fracture.     

Composition and elastic stresses in multilayer structures with Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript> nanoislands

The composition and mechanical stresses in Si_1?xGe_x nanoislands involved in multilayer and single-layer structures grown under the same conditions are determined using Raman spectroscopy. It is demonstrated that an increase in the content of silicon in the nanoislands contained in a multilayer structure does not enhance their relaxation (as compared to that in a single layer) due to the absence of a free surface. The experimental scattering spectrum of folded acoustic phonons contains bands with sufficiently small half-widths, which indicates high quality of the grown superlattices with nanoislands.     

Effects of oxygen partial pressure on the ferroelectric properties of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films

The Ba_0.8Sr_0.2TiO₃ thin films were grown on the Pt–Si substrate at 700 °C by using a pulsed laser deposition technique at different oxygen partial pressure (PO₂) in the range of 1–20 Pa and their properties were investigated. It is observed that the PO₂ during the deposition plays an important role on the tetragonal distortion ratio, surface morphology, dielectric permittivity, ferroelectric polarization, switching response, and leakage currents of the films. With an increase in PO₂, the in-plane strain for the BST films changes from tensile to compressive. The films grown at 7.5 Pa show the optimum dielectric and ferroelectric properties and also exhibit the good polarization stability. It is assumed that a reasonable compressive strain, increasing the ionic displacement, and thus promotes the in-plane polarization in the field direction, could improve the dielectric permittivity. The butterfly features of the capacitance–voltage (C–V) characteristics and the bell shape curve in polarization current were attributed to the domain reversal process. The effect of pulse amplitude on the polarization reversal behavior of the BST films grown at PO₂ of 7.5 Pa was studied. The peak value of the polarization current shows exponential dependence on the electric field.     

Field emission characteristics of thin-metal-coated nano-sheet carbon films

Nano-sheet carbon films (NSCFs) coated with very thin (≈5-nm-thick) metal layers were fabricated on Si wafer chips by means of quartz-tube-type microwave-plasma chemical-vapour-deposition method with hydrogen-methane gas mixture and an electron beam evaporation method. Field emission (FE) current densities obtained at a macroscopic average electric field, E, of ≈10 V/μm changed from 13 mA/cm² for NSCF with no coated metal to 1.7, 0.7 and 30 mA/cm² for Ti-, Al- and Au-coated NSCFs, respectively, while the threshold E varied from 4.4 V/μm for the former one to 5.3, 5.4 and 2.0 V/μm for the corresponding latter ones, respectively. As the FE currents of Au-coated NSCFs tended to be saturated in a higher E region, compared to those of NSCFs with no coated metal, no simple Fowler-Nordheim (F-N) model is applicable. A modified F-N model considering statistic effects of the FE tip structures and a space-charge-limited-current effect is successfully applied to an explanation for the FE data observed in the low and high E regions.