Secondary electron emission from thin self-supporting films of silver

The paper deals with the measurement of secondary electron emission and the scattering of primary electrons on thin self-supporting films of Ag. The measured values of the practical range agree with the older results obtained by Kanter. New results are those concerning the maximum depth from which the primaries are scattered back to the front surface and the maximum range of secondaries, which has been found to be about 300 å.     

Electrical conduction of organic ultrathin films evaluated by an independently driven double-tip scanning tunneling microscope

The electrical transport properties of organic thin films within the micrometer scale have been evaluated by a laboratory-built independently driven double-tip scanning tunneling microscope, operating under ambient conditions. The two tips were used as point contact electrodes, and current in the range from 0.1 pA to 100 nA flowing between the two tips through the material can be detected. We demonstrated two-dimensional contour mapping of the electrical resistance on a poly(3-octylthiophene) thin films as shown below. The obtained contour map clearly provided an image of two-dimensional electrical conductance between two point electrodes on the poly(3-octylthiophene) thin film. The conductivity of the thin film was estimated to be (1-8) × 10(-6) S cm(-1). Future prospects and the desired development of multiprobe STMs are also discussed.     

Electrical properties of silver iodide

The electrical conductivity of γ- and β-AgI pellets was measured as a function of temperature over the range between 20 and 145 °C. The electronic contributions to the conductivity were studied by using the polarization cell (?) Ag/sample/graphite(+) in addition to experiments in an iodine atmosphere. The increase in conductivity of β-AgI due to the addition of Pbl₂ was also investigated.     

Electrical and optical properties of silver doped indium oxide thin films prepared by reactive DC magnetron sputtering

Silver doped indium oxide (In_2−x Ag_x O_3−y) thin films have been prepared on glass and silicon substrates at room temperature (300 K) by reactive DC magnetron sputtering technique using an alloy target of pure indium and silver (80: 20 atomic %. The magnetron power (and hence the metal atom sputter flux) is varied in the range 40-80 W. The energy dispersive analysis of X-ray (EDAX) results show that the silver content in the film decreases with increasing magnetron power. The grain size of these films is of the order of 100 nm. The resistivity of these films is in the range 10⁻²-10⁻³ Ω cm. The work function of the silver-indium oxide films (by Kelvin Probe) are in the range: 4.64-4.55 eV. The refractive index of these films (at 632.8 nm) varies in the range: 1.141-1.195. The optical band gap of indium oxide (3.75 eV) shrinks with silver doping. Calculations of the partial ionic charge (by Sanderson's theory) show that silver doping in indium oxide thin films enhance the ionicity.     

Electrical measurements of nanoscale bismuth cluster films

A range of percolating atomic cluster films, with nanoscale overall dimensions, have been studied using a combination of in situ and ex situ electrical transport measurements, together with field emission electron microscopy and atomic force microscopy. Bismuth clusters with mean diameter 20 nm were deposited between electrical contacts defined by electron beam lithography. The morphology of the films can be understood within percolation theory, and the electrical measurements show complex behaviour characteristic of both percolation effects and modification of the cluster films by current flow and by oxidation.     

Light emission from Ag cluster films excited by conduction current

The light emission spectra obtained for a silver cluster film, excited by the passage of electrical current through it, were measured by the charge‐coupled device (CCD) combined with a monochromator in the spectral range 200 ≑ 1050 nm (6.2 ≑ 1.18 eV). This film is a two‐dimensional ensemble of Ag clusters linked by tunneling on a dielectric substrate. It was shown that the light emission spectra had a number of features, and the shape of spectrum depends on a voltage applied to the film. With increasing the voltage the spectrum starts to extend to high energies. The light emission in the visible spectral region was observed already at 1 V applied to the film, i.e., the photon energy can exceed the excitation energy. It means that this phenomenon is not trivial. In order to explain these results, an assumption about the electron gas heating in metal clusters may be used.     

A low voltage time of flight electron emission microscope

This paper presents the design of a low voltage time of flight electron emission microscope (TOF-EEM), which should in principle be capable of acquiring spectral chemical information at nano-metre spatial resolution. The system will be able to operate as a photoelectron emission microscope (PEEM), an X-ray photoemission electron microscope (XPEEM), or a secondary electron emission microscope (SEEM). For each pixel in its highly magnified topographic image, the TOF-EEM column should be able to provide the emission spectrum with milli-electron-volt resolution. The system is designed to operate at secondary electron beam voltages of typically less than 100 V, and has the possibility of dynamically correcting for chromatic aberration. Provisional simulation results predict that the TOF-EEM column should be able to provide an image resolution of better than 2 nm.     

Electrical properties of chromium films

We have investigated experimentally the influence of a constant electric current on the magnitude and temperature dependence of the resistance of chromium films prepared by vacuumthermal condensation. The results are interpreted in terms of the Fröhlich conductivity model.     

Field electron emission of carbon-based nanocone films

Diamond nanocone, graphitic nanocone, and mixed diamond and graphitic nanocone films have been synthesized through plasma enhanced hot filament chemical vapor deposition (HFCVD). The field emission properties of these films have been experimentally investigated. The studies have revealed that all three kinds of nanocone films have excellent field electron emission (FEE) properties including low turn-on electric field and large emission current at low electric field. Compared with the diamond nanocone films (emission current of 86 μA at 26 V/μm with the turn-on field of 10 V/μm), the graphitic nanocone films exhibit higher FEE current of 1.8×10² μA at 13 V/μm and a lower turn-on filed of 4 V/μm. The mixed diamond and graphitic nanocone films have been found to posses FEE properties similar to graphitic nanocone films (emission current of 1.7×10² μA at 20 V/μm with the turn-on field of 5 V/μm), but have much better FEE stability than the graphitic nanocone films. PACS 81.07.Bc; 81.05.Uw; 79.70.+q     

Field emission studies of silver nanoparticles synthesized by electron cyclotron resonance plasma

Field emission has been studied for silver nanoparticles (25-200 nm), deposited within a cylindrical silver target in an electron cyclotron resonance (ECR) plasma. Particle size distribution was controlled by optimum biasing voltages between the chamber and the target. Presence of non-oxidized silver was confirmed from the X-Ray diffraction analysis; however, thin protective layer of oxide was identified from the selective area electron diffraction pattern obtained with transmission electron microscopy. The silver nanoparticles were seen to exhibit hilly pointed like structures when viewed under the atomic force microscopy (AFM). The emissive properties of these particles were investigated by field emission microscopy. It is found that this technique of deposition is ideal for formation of nanoparticles films on different substrate geometries with size controllability as well as its application to emission devices.     

Secondary electron emission of sputtered alumina films

Secondary electron emission yieldδ was measured for thin films of alumina prepared byrf sputtering technique. Single pulse method was used along with 4-gridleed optics system to determineδ. Maximum value of 4·3 was obtained at primary energy of 350 eV. The Dionne’s theory was used to analyse the results and the emission probability escape depth and absorption coefficient of secondaries were also estimated. Fairly good correlation is observed between experimental and theoretical values ofδ for beam energies upto 1 keV.     

Electrical breakdown and high-energy electron emission under dielectric charging

A Monte-Carlo calculation model for electron transport in crystalline dielectrics charged by irradiation is improved with allowance for impact ionization and cascading processes. The electron transport in SiO ₂ is simulated for high-strength electric fields. It is found that a breakdown in a dielectric can occur in the electric field strength range 11.5–12.5 MV/cm. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 52–58, March, 2008.     

Polarization properties of porous gold and silver films

Using the method of polarization modulation of electromagnetic radiation and the Kretschmann geometry, we perform comparative studies of surface plasmon resonance in porous and continuous gold and silver films. The spectral dependences of the polarization difference of the reflection coefficients of nano-composites are obtained for the first time and are supplemented by angular characteristics of this parameter. We show that these dependences characterize particular features of the optical properties related to the structure, morphology, and topology of porous films. We reveal that surface plasmon-polaritons and local plasmons in porous films can be excited both by radiation that is p polarized with respect to the plane of incidence, as is the case with continuous films, and by s polarized radiation. We demonstrate that the measurement results can yield information on the structural properties of films, such as their thickness, roughness height, degree of dispersion of nanoparticles, and so on.     

Electrical properties of evaporated a-CdTe films

The electrical dc conductivity of amorphous CdTe thin films evaporated in a high vacuum system has been measured in situ as deposited on a cold substrate and after various annealings from 100 K up to 365 K. The investigated features are analysed according to the Mott model.     

Electrical conduction in nanostructured carbon and carbon-metal films grown by supersonic cluster beam deposition

We have studied the electrical conduction in nanostructured carbon (ns-C) films produced by deposition of a supersonic beam of neutral carbon clusters. The d.c. conduction properties of these films have been measured in situ during the deposition process and ex situ as a function of the temperature in vacuum and in ambient of different gases (H₂, N₂, CH₄, He). The ns-C films exhibit an ohmic behavior with a room temperature resistivity in the range of 10⁷-10⁹ W{\rm\Omega} cm depending on the growth and storage conditions. Conductivity vs. temperature measured in vacuum in the range 290-400 K is characterized by activation energies in the range of 0.3-1.7 eV, the current response does not differ significantly in gas atmosphere. Nanocomposite carbon-metal films have been obtained by adding small amounts of metallorganic precursors containing molybdenum and cobalt during the formation of carbon clusters prior to deposition. The films are characterized by porous carbon networks containing small metal and metal carbide clusters. Electrical transport properties of these films have been studied as a function of temperature, gas pressure and relative humidity. In particular, the electrical conductivity of the sample produced with molybdenum showed to be much sensitive to changes in gas pressure and relative humidity, being characterised by fast and reversible responses.     

Field emission properties of polymer-converted carbon films by heat treatment

Carbon films were prepared on single crystal silicon substrates by heat-treatment of a polymer-poly(phenylcarbyne) at 800 °C in Ar atmosphere. The heat-treatment caused the change of the polymer into carbon film, which exhibited good field emission properties. Low turn-on emission field of 4.3 V/μm (at 0.1 μA/cm²) and high emission current density of 250 μA/cm² (at 10 V/μm) were observed for the polymer-converted carbon films. This behavior was demonstrated to be mainly related to the microstructure of the carbon films, which consisted of fine carbon nanoparticles with high sp² bonding. The carbon films, which can be deposited simply with large areas, are promising for practical applications in field emission display.