Zs. Czigany

Growth of fullerene-like carbon nitride thin solid films by reactive magnetron sputtering; role of low-energy ion irradiation in determining microstructure and mechanical properties

Fullerene-like (FL) carbon nitride (CNx) films were deposited on Si (100) substrates by dc reactive, unbalanced, magnetron sputtering in a N2/Ar mixture from a high-purity pyrolythic graphite cathode in a dual-magnetron system with coupled magnetic fields. The N2 fraction in the discharge gas (0%–100%) and substrate bias (−25 V; −40 V) was varied, while the total pressure (0.4 Pa) and substrate temperature (450 °C) was kept constant. The coupled configuration of the magnetrons resulted in a reduced ion flux density, leading to a much lower average energy per incorporated particle, due to a less focused plasma as compared to a single magnetron. This enabled the evolution of a pronounced FL microstructure. The nitrogen concentration in the films saturated rapidly at 14–18 at. %, as determined by elastic recoil analysis, with a minor dependence on the discharge conditions. No correlations were detected between the photoelectron N1s core level spectra and the different microstructures, as observed by high-res...

Microstructure of α-alumina thin films deposited at low temperatures on chromia template layers

Radio frequency sputtering has been used to deposit α-alumina (α-Al2O3) thin films at substrate temperatures of 280–560 °C. The films are shown to be single phased and hard. Nanoindentation gives values of 306±31 and 27±3 GPa for elastic modulus and hardness, respectively, for a substrate temperature of 280 °C. Growth of the α phase was achieved by in situ predeposition of a chromia template layer. Chromia crystallizes in the same hexagonal structure as α-alumina, with a lattice mismatch of 4.1% in the a- and 4.6% in the c-parameter, and is shown to nucleate readily on the amorphous substrates (silicon with a natural oxide layer). This results in local epitaxy of α-alumina on the chromia layer, as is shown by transmission electron microscopy. The alumina grains are columnar with grain widths increasing from 22±7 to 41±9 nm, as the temperature increases from 280 to 560 °C. This is consistent with a surface diffusion dominated growth mode and suggests that α-alumina deposition at low temperatures is possibl...

Structural features of thick c-boron nitride coatings deposited via a graded B-C-N interlayer

Structural features of thick c-boron nitride coatings deposited via a graded B-C-N interlayer (vol 142, pg 881, 2001)

Growth of fullerene-like carbon nitride thin solid films consisting of cross-linked nano-onions

Fullerene-like CNx (x≈0.12) thin solid films were deposited by reactive magnetron sputtering of graphite in a nitrogen and argon discharge on cleaved NaCl and Si(001) substrates at 450 °C. As-deposited films consist of 5 nm diam CNx nano-onions with shell sizes corresponding to Goldberg polyhedra determined by high-resolution transmission electron microscopy. Electron energy loss spectroscopy revealed that N incorporation is higher in the core of the onions than at the perimeter. N incorporation promotes pentagon formation and provides reactive sites for interlinks between shells of the onions. A model is proposed for the formation of CNx nano-onions by continuous surface nucleation and growth of hemispherical shells.

Mechanical and tribological properties of CNx films deposited by reactive pulsed laser ablation

We report the tribological, mechanical, structural and compositional characteristics of CNx films deposited by excimer laser (XeCl, ? = 308 nm, TFWHM = 30 ns) ablation of a graphite target in N2 at ...

Columnar growth structure and evolution of wavy interface morphology in amorphous and polycrystalline multilayered thin films

Abstract The connection between the columnar growth and evolution of the wavy interface morphology in amorphous and polycrystalline multilayers was investigated by transmission electron microscopy. The material systems of amorphous Si/Ge and polycrystalline Ag/Cu multilayers were chosen as model materials for the investigation. A systematic study of the growth morphology was performed on periodic multilayers as a function of the multilayer period with individual layer thickness up to 50 nm. In comparison with numerous former reports on a wide variety of multilayers, different both in the component elements and preparation methods, the following results proved to be a general property of columnar growth in multilayered thin films. In amorphous and polycrystalline multilayers the diameter of columns ( D ) depends on the thickness of the thicker layer ( H ) as D=3H+7 nm if the layer thickness does not exceed 16 nm. In both amorphous and polycrystalline multilayers the minima of the wavy interface morphology coincide with the column boundaries, consequently the lateral length of the interface waves depends on H the same way as D . In multilayers where the layer thickness exceeds 16 nm a similar coincidence of column walls and interface minima can be observed in the vicinity of the substrate. However, far from the substrate the evolution of the columnar structure and interface waves can discouple, and the observed layer thickness dependence is preserved only for the interface waves. For the explanation of the observed rule effects of deposition parameters, impurities, grain boundaries in polycrystalline films, and growth instability are discussed.

Ion mass spectrometry investigations of the discharge during reactive high power pulsed and direct current magnetron sputtering of carbon in Ar and Ar/N2

Ion mass spectrometry was used to investigate discharges formed during high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a graphite target in Ar and ...

Imaging of fullerene-like structures in CNx thin films by electron microscopy, Sample preparation artefacts due to ion-beam milling

The microstructure of CN(x) thin films, deposited by reactive magnetron sputtering, was investigated by transmission electron microscopy (TEM) at 200kV in plan-view and cross-sectional samples. Imaging artefacts arise in high-resolution TEM due to overlap of nm-sized fullerene-like features for specimen thickness above 5nm. The thinnest and apparently artefact-free areas were obtained at the fracture edges of plan-view specimens floated-off from NaCl substrates. Cross-sectional samples were prepared by ion-beam milling at low energy to minimize sample preparation artefacts. The depth of the ion-bombardment-induced surface amorphization was determined by TEM cross sections of ion-milled fullerene-like CN(x) surfaces. The thickness of the damaged surface layer at 5 degrees grazing incidence was 13 and 10nm at 3 and 0.8keV, respectively, which is approximately three times larger than that observed on Si prepared under the same conditions. The shallowest damage depth, observed for 0.25keV, was less than 1nm. Chemical changes due to N loss and graphitization were also observed by X-ray photoelectron spectroscopy. As a consequence of chemical effects, sputtering rates of CN(x) films were similar to that of Si, which enables relatively fast ion-milling procedure compared to carbon compounds. No electron beam damage of fullerene-like CN(x) was observed at 200kV.

The effect of the carbon matrix on the mechanical properties of nanocomposite films containing nickel nanoparticles

The correlation of structural electronic and mechanical properties of carbon–nickel composite thin films has been investigated. The films were deposited on oxidized silicon substrates by dc magnetron sputtering of Ni and C targets in argon at different temperatures between 25 and 800 °C. Composition variation was achieved by variation of the power of the Ni target with constant power on the C target. Structural investigations were performed by transmission electron microscopy (including high resolution) both in plan view and cross section. The nanocomposite films consisted of metallic nanocrystals embedded in a carbon matrix. The carbon matrix was disordered or graphite-like carbon; the crystalline phase consisted of Ni3C or Ni nanoparticles, depending on the deposition temperature. The temperature coefficient of resistivity measurements at low temperature confirmed the various structures of the carbon matrix. The samples in which the prevailing matrix was disordered carbon show the tunneling effect and samples with graphite-like carbon matrix show metallic behavior. The hardness of the films varies between 2 GPa (hardness of Ni) and 13 GPa depending on the deposition temperature, but is independent of the Ni content. The highest hardness of ~11–13 GPa and modulus of elasticity of ~120 GPa were obtained when the crystalline Ni3C nanoparticles were separated by a 2–3 nm thin carbon matrix consisting of amorphous and graphite-like carbon phases. In these films the hardness to modulus of elasticity ratio (H/E) is ~0.1.

Structural and mechanical properties of diamond-like carbon films deposited by direct current magnetron sputtering

The microstructure, morphology, and mechanical properties of diamond-like carbon (DLC) films deposited by direct current magnetron sputtering were investigated for microelectromechanical systems applications. Film properties were found to vary markedly with the ion energy (Eion) and ion-to-carbon flux ratio (Jion/JC). Cross-sectional high-resolution transmission electron microscopy revealed an amorphous microstructure. However, the presence of nanometer-sized domains at Eion∼85 eV was detected. Film stresses, σ, which were compressive in all cases, ranged from 0.5 to 3.5 GPa and depended on the flux ratio as well as ion energy. The hardness (H), Young’s moduli (e), and elastic recovery (R) increased with Eion to maximum values of H=27 GPa, e=250 GPa, and R=68% at Eion=85 eV and Jion/JC=4.4. However, near edge x-ray absorption fine structure and electron energy-loss spectrum analysis showed that the sp2/sp3 content of the films does not change with Eion or Jion/JC. The measured change in mechanical propert...