Esteban Broitman

REACTIVE MAGNETRON SPUTTER DEPOSITED CNX : EFFECTS OF N2 PRESSURE AND GROWTH TEMPERATURE ON FILM COMPOSITION, BONDING, AND MICROSTRUCTURE

The effects of growth processes on the chemical bond structure, microstructure, and mechanical properties of carbon–nitride (CNx) thin films, deposited by reactive magnetron sputtering in a pure N2 discharge, are reported. The film deposition rate RD increases with increasing N2 pressure PN2 while N/C ratios remain constant. The maximum N concentration was ∼35 at. %. RD was found to be dependent upon the film growth temperature Ts. For a given PN2, RD decreased slightly as Ts was increased from 100 to 600 °C. The variations in RD with both PN2 and Ts can be explained by ion‐induced desorption of cyano radicals CNx from both the target and growth surfaces during deposition. X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FTIR) analyses showed that N atoms in films grown at Ts≳350 °C with low nitrogen partial pressures PN2, ∼2.5 mTorr, were bound to C atoms through hybridized sp2 and sp3 configurations. For low Ts=100 °C and higher PN2, 10 mTorr, triple‐bonded C≡N was detected ...

Carbon nitride nanotubulite – densely-packed and well-aligned tubular nanostructures

Tubular carbon nitride (CNx, x=0.01–0.32) nanoparticles were successfully synthesized by d.c. magnetron sputtering. These tubes were grown in a highly packed form perpendicularly on a sodium chloride substrate. Their number density is estimated to be ∼1×104 per μm2 and is constant over macroscopic regions. Sub-nanometer scale chemical mapping shows that the nitrogen to carbon atomic ratio is rather constant across these tubes. This successful synthesis of a nanotubulite – made of a rather compact aggregation of tubular nanoparticles – could facilitate experimental approaches to measure mechanical or electrical transport properties of such nanotubes and to open the way to variable nanotube applications.

Effect of chemical sputtering on the growth and structural evolution of magnetron sputtered CNx thin films

Abstract The growth and microstructure evolution of carbon nitride CN x (0≤ x ≤0.35) films, deposited by reactive d.c. magnetron sputtering in Ar/N 2 discharges has been studied. The substrate temperature T S varied between 100 and 550°C, and the N 2 fraction in the discharge gas varied from 0 to 100%. It is found that the deposition rate and film morphology show strong dependence on T S and nitrogen fraction. For growth temperature of 100°C, the films are amorphous, and essentially unaffected by the nitrogen fraction. For T S >200°C, however, the nitrogen fraction has more significant effect on the growth and structural evolution of the films. The pure carbon films appear porous and have a high surface roughness. For increasing nitrogen fraction the films become denser and the roughness decreases by one order of magnitude. It is suggested that a chemical sputtering process, during which desorption of volatile N 2 and CN-species, predominantly C 2 N 2 , is important not only for the deposition rate and the nitrogen incorporation, but also for the resulting film structure. The chemical sputtering process becomes more pronounced at elevated temperatures with higher nitrogen fractions.

Influence of plasma parameters on the growth and properties of magnetron sputtered CNx thin films

Carbon nitride CNx thin films were grown by unbalanced dc magnetron sputtering from a graphite target in a pure N2 discharge, and with the substrate temperature Ts kept between 100 and 550 °C. A solenoid coil positioned in the vicinity of the substrate was used to support the magnetic field of the magnetron, so that the plasma could be increased near the substrate. By varying the coil current and gas pressure, the energy distribution and fluxes of N2+ ions and C neutrals could be varied independently of each other over a wide range. An array of Langmuir probes in the substrate position was used to monitor the radial ion flux distribution over the 75-mm-diam substrate, while the flux and energy distribution of neutrals was estimated through Monte Carlo simulations. The structure, surface roughness, and mechanical response of the films are found to be strongly dependent on the substrate temperature, and the fluxes and energies of the deposited particles. By controlling the process parameters, the film struc...

Electrical and optical properties of CNx(0⩽x⩽0.25) films deposited by reactive magnetron sputtering

The electrical and optical properties of carbon-nitride CNx films (O=x=0.25) deposited by unbalanced reactive magnetron sputtering from a graphite target in mixed Ar/N2 discharges at a substrate te ...

Stress development during deposition of CNx thin films

We have investigated the influence of deposition parameters on stress generation in CNx (0.3<x<0.5) thin films deposited onto Si(001) substrates by reactive magnetron sputtering of C in pure N2 discharges. Film stress, σ, which in all cases is compressive, decreases with an increase in the N2 pressure, PN2, due to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. The film stress σ is also a function of the film growth temperature, Ts, and exhibits a maximum value of ∼5 GPa at 350 °C. Under these conditions, the films have a distorted microstructure consisting of a three-dimensional, primarily sp2 bonded, network. In contrast, films deposited at Ts<200 °C with a low stress are amorphous. At 350 °C<Ts<600 °C, σ gradually decreases as Ts is increased and the microstructure becomes more graphitic and contains fewer defects. Nanoindentation measurements show that the films grown at 350 °C exhibit the highest hardness and ela...

Growth, structure, and mechanical properties of CNxHy films deposited by dc magnetron sputtering in N2/Ar/H2 discharges

Hydrogenated carbon nitride films were deposited by reactive dc magnetron sputtering in mixed Ar/N2/H2 discharges at temperatures of 100 and 350 °C. The total pressure was kept constant at 0.33 Pa and the gas mixtures were varied in order to study the effect of the hydrogen on the resulting film structure and properties. Chemical sputtering effects taking place during deposition were found to be an important factor for the growth and structural evolution. When H2 is mixed into the discharge gas, the growth rate decreases considerably and the films become denser due to desorption of volatile species, like hydrocarbons, NH3 and HCN. For a H2 fraction above 15%, no net film growth takes place. The hydrogen concentration incorporated into the films was highest (up to ∼33 at. %) for low growth temperatures and low nitrogen concentrations. Furthermore, the results indicate that substantial amount of hydrogen are bonded to nitrogen. The incorporation of hydrogen in the structure interrupts the relatively long ba...

Thermal stability of carbon nitride thin films

The thermal stability of carbon nitride films, deposited by reactive direct current magnetron sputtering in N-2 discharge, was studied for postdeposition annealing temperatures T-A up to 1000 degre ...

Reactive magnetron sputtering of CNx thin films at different substrate bias

Abstract The chemical binding states of C and N atoms, and optical properties of carbon nitride (CNx) thin films deposited by unbalanced magnetron sputtering, have been investigated as a function of the negative substrate bias (Vs). The film deposition rate increased slightly with increasing Vs, having a weak maximum at floating potential (~50 V), and decreased sharply to zero for Vs>150 V, while N/C ratios did not exhibit any significant variation. Raman spectroscopy was used to reveal that the structure of the film is predominantly amorphous. Fourier transform infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) analyses showed that N atoms in the films were bound to C atoms through sp2 and sp3 configurations. Triple C–N bonds were also detected by FTIR. The ratio of sp3 to sp2 bonds increased with increasing Vs. The maximum sp3 concentration in CNx films was estimated to be ~20%. The optical band gap of CNx films was also found to increase with an increase in Vs.

Nanoscale piezoelectric response of ZnO nanowires measured using a nanoindentation technique

We report the piezoelectric properties of ZnO nanowires (NWs) obtained by using a nanoindenter with a conductive boron-doped diamond tip. The direct piezoelectric effect was measured by performing nanoindentations under load control, and the generated piezoelectric voltage was characterized as a function of the applied loads in the range 0.2-6 mN. The converse piezoelectric effect was measured by applying a DC voltage to the sample while there was a low applied force to allow the tip being always in physical contact with the NWs. Vertically aligned ZnO NWs were grown on inexpensive, flexible, and disposable paper substrates using a template-free low temperature aqueous chemical growth method. When using the nanoindenter to measure the direct piezoelectric effect, piezopotential values of up to 26 mV were generated. Corresponding measurement of the converse piezoelectric effect gave an effective piezoelectric coefficient d33(eff) of ∼9.2 pm V(-1). The ZnO NWs were also characterized using scanning electron microscopy, X-ray diffraction, and high-resolution transmission electron microscopy. The new nanoindentation approach provides a straightforward method to characterize piezoelectric material deposited on flexible and disposable substrates for the next generation of nanodevices.