Ultrathin Metal Coatings Research Articles

Fast measurement of the coating thickness and conductivity using eddy currents and plane wave approximation

An analytical formula for the electromagnetic field generated by a current-carrying cylindrical coil above a half-infinite conductive plate has been studied. The theoretical analysis showed that when the radius of the coil was much larger than the penetration depth, the electromagnetic wave at the plate surface could be approximated as a plane wave, and the real part of the plane wave impedance would not be affected by lift-off changes. Using normalized plane wave impedances as theoretical values and normalized coil impedances measured by swept-frequency eddy current technique as experimental values, a novel approach is proposed to rapidly and simultaneously solve the coating thickness, coating conductivity and substrate conductivity of a conductive plate with ultra-thin metallic coatings by Levenberg−Marquardt algorithm. The experimental results show that the maximum relative measurement errors of the proposed method for single- and double-coated plates are less than 8% and 18%, respectively, and the measurement time is less than 1 s, which is suitable for fast parameter detection.

Measuring ultrathin metal coatings using SPR spectroscopic ellipsometry with a prism-dielectric-metal-liquid configuration.

A new surface plasmon resonance (SPR) configuration is proposed, which consists of a prism, a dielectric layer, a metal coating, and a matching liquid. The optical constants of each layer in the proposed prism-dielectric-metal-liquid (PDML) configuration have been optimized to match the SPR conditions and reach the strongest intensity. Combining the PDML configuration with spectroscopic ellipsometry, SPR spectroscopic ellipsometry (SPRSE) with a PDML configuration was developed. The SPR wavelength can be adjusted to the desired wavelength by varying the thickness of the dielectric layer. The amplitude and phase change, magnified by the SPR in the visible and near-infrared wavelengths, were obtained to determine the optical constants and thickness of ultrathin metal coatings. The extracted optical constants were found to be in good agreement with the results obtained using transmission electron microscopy (TEM) and X-ray reflectivity (XRR) techniques. These SPRSE measurements show great potential for characterizing the interface between a metal coating and a dielectric layer, and the surface uniformity of ultrathin metal coatings.

Magnetron sputtering deposition of ultra-thin metal coatings for the visualization of protein-containing objects of nanometer size by electron microscopy

Electron microscopy is widely used in biological and medical research, enabling to obtain images of the investigated objects with nanometer resolution. Exposure of biological objects under electron beam during the visualization can, however, cause their damage. Destructive effect of the electron beam can be significantly decreased by formation of metal coating on the surface of the objects to be studied. In the present study, an approach for the formation of ultra-thin metal coatings on the surface of protein-containing structures is proposed. Magnetron sputtering in argon plasma in DC mode was employed to form 8 Å-thick tungsten films on the surface of model protein-containing objects— tobacco mosaic virus particles — for their subsequent visualization by electron microscopy.

Ultra thin metallic coatings to control near field radiative heat transfer

We present a theoretical calculation of the changes in the near field radiative heat transfer between two surfaces due to the presence of ultra thin metallic coatings on semiconductors. Depending on the substrates, the radiative heat transfer is modulated by the thickness of the ultra thin film. In particular we consider gold thin films with thicknesses varying from 4 to 20 nm. The ultra-thin film has an insulator-conductor transition close to a critical thickness of dc = 6.4 nm and there is an increase in the near field spectral heat transfer just before the percolation transition. Depending on the substrates (Si or SiC) and the thickness of the metallic coatings we show how the near field heat transfer can be increased or decreased as a function of the metallic coating thickness. The calculations are based on available experimental data for the optical properties of ultrathin coatings.

Erratum: “Ultrathin metallic coatings can induce quantum levitation between nanosurfaces” [Appl. Phys. Lett. 100, 253104 (2012)

Erratum to : Ultrathin metallic coatings can induce quantum levitation between nanosurfaces

Nanopatterning of metal-coated silicon surfaces via ion beam irradiation: Real time x-ray studies reveal the effect of silicide bonding

We investigated the effect of silicide formation on ion-induced nanopatterning of silicon with various ultrathin metal coatings. Silicon substrates coated with 10 nm Ni, Fe, and Cu were irradiated with 200 eV argon ions at normal incidence. Real time grazing incidence small angle x-ray scattering (GISAXS) and x-ray fluorescence (XRF) were performed during the irradiation process and real time measurements revealed threshold conditions for nanopatterning of silicon at normal incidence irradiation. Three main stages of the nanopatterning process were identified. The real time GISAXS intensity of the correlated peaks in conjunction with XRF revealed that the nanostructures remain for a time period after the removal of the all the metal atoms from the sample depending on the binding energy of the metal silicides formed. Ex-situ XPS confirmed the removal of all metal impurities. In-situ XPS during the irradiation of Ni, Fe, and Cu coated silicon substrates at normal incidence demonstrated phase separation and the formation of different silicide phases that occur upon metal-silicon mixing. Silicide formation leads to nanostructure formation due the preferential erosion of the non-silicide regions and the weakening of the ion induced mass redistribution.

Ultrathin metallic coatings can induce quantum levitation between nanosurfaces

There is an attractive Casimir-Lifshitz force between two silica surfaces in a liquid (bromobenze or toluene). We demonstrate that adding an ultrathin (5–50 Å) metallic nanocoating to one of the surfaces results in repulsive Casimir-Lifshitz forces above a critical separation. The onset of such quantum levitation comes at decreasing separations as the film thickness decreases. Remarkably, the effect of retardation can turn attraction into repulsion. From that we explain how an ultrathin metallic coating may prevent nanoelectromechanical systems from crashing together.

Field electron emission from diamond-like carbon films deposited using RF inductively coupled CH4-plasma source

Abstract Diamond-like carbon (DLC) films 4–400 nm thick were deposited on conductive n -Si and metal substrates using direct ion beam deposition from an RF inductively coupled CH 4 -plasma (ICP) source. The field electron emission of the films was examined as a function of deposition conditions and post-deposition surface modification by Ni ultrathin coatings. Electrical properties of the films were studied as well. A specially designed high vacuum scanning tunnelling-field emission microscope was employed for simultaneous mapping of the topography, work function and local field electron emission intensity. Stable, low voltage emission was observed after the emission electric field/current activation process. The activation mechanism was probably the formation of conductive channels in the films to supply electrons for emission from low work function surface areas. Deposition of ultrathin metal coatings on the DLC films reduced both the effective barrier height and the field emission threshold. The DLC films surface coated with ultrathin Ni films resulted in electron emission at fields as low as 20–25 V μm −1 . It was shown that DLC films with thicknesses in the range 5–15 nm demonstrated efficient field emission long-term stability. The results are interpreted based on the reduced electrical resistivity of nanometer scale thick films, and deviation of resistivity over the surface.

Surface plasmon microscopic imaging of ultrathin metal coatings

We demonstrate that ultrathin metal coatings can be imaged with high contrast by surface plasmon microscopy. Lateral resolution better than 5 μm is achieved.