A. Perrone

Boron carbonitride films deposited by pulsed laser ablation

Abstract Boron carbonitride (BCN) thin films were deposited on Si (100) substrates at room temperature by sequential pulsed laser ablation (PLA) of graphite and hexagonal boron nitride (h-BN) targets in vacuum and in nitrogen atmosphere in the pressure range 1–100 Pa. Different analysis techniques as transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) pointed out the synthesis of h-BCN and c-BCN. The grain size of the crystalline c-BCN phase was estimated to be in the range 30–80 nm. The size of the crystallites in h-BCN phase was 4.6 μ m, with a transversal dimension of about 30 nm. Complementary microhardness measurements evidenced the high microhardness (values up to 2.9 GPa) of the deposited films.

Deposition of high quality TiN films by excimer laser ablation in reactive gas

A new laser method is proposed for the deposition of high purity, hard fcc TiN layers of unlimited thickness. The film thickness can be very finely controlled mainly through the intermediary of the number of applied laser pulses as the deposition rate is of only 0.02–0.05 nm/pulse. The ablation is promoted from a Ti target by high intensity multipulse excimer laser irradiation in a low pressure N2 ambient gas while the forming compound is collected on a Si single‐crystalline wafer. The best results have been obtained for an ambient pressure of p=10–30 mTorr and a distance between the target and support of d=10 mm. It is shown that the formation of a liquid phase within the irradiated zone, maintained even after the end of a laser pulse, is the most important requisite for TiN formation. TiN is then ablated as a stoichio‐ metric phase.

Deposition of CN films by reactive laser ablation

Abstract A study of the characteristics of films deposited at room temperature on Si and KBr substrates by XeCl laser ablation of graphite in low pressure (0.25–2.5 mbar) N2 and NH3 is presented. Hard films, with a very high electrical resistivity were obtained. N C atomic ratios up to 0.6 were calculated from backscattering measurements. Different diagnostic techniques (XPS, IR absorption spectroscopy, etc.) prove the formation of carbon nitride with a prevalent graphitic structure.

Oxidation interference in direct laser nitridation of titanium: relative merits of various ambient gases

Abstract A comparison is performed between the relative merits of using an ambient NH 3 atmosphere or a stoichiometrically equivalent N 2 -H 2 (1:3) mixture for the direct laser nitridation of titanium samples by multipulse excimer laser ( λ = 308nm) irradiation. It is shown that the N 2 -H 2 mixture proves more effecient in inhabiting the unwanted interference of the oxidation process and that the whole process proceeds through the action of an erosion plasma on a molten layer covering the laser-irradiated area.

Study of CN binding states in carbon nitride films deposited by reactive XeCl laser ablation

Carbon nitride films, deposited on 〈111〉 Si substrates at room temperature by XeCl laser ablation of graphite targets in low pressure (1, 5, 10 and 50 Pa) N2 atmosphere at the fluence of 16 J/cm2 (∼0.5 GW/cm2) have been submitted to accurate X-ray photoelectron spectroscopy (XPS) investigations in order to study the CN chemical bonding in the films. Multiple binding energy values have been obtained. The N 1s peak of the XPS spectra indicates three different binding states of nitrogen atoms to C atoms, while the C 1s peak, apart from the binding states to nitrogen atoms, indicates other bonding states with regard to carbon atoms.

Optical emission spectroscopy of molecular species in plasma induced by laser ablation of carbon in nitrogen

Abstract The results obtained from the study of time-integrated molecular spectra emitted by a plasma induced by excimer laser (XeCl, λ=308 nm, τ=30 ns) ablation of a graphite target in nitrogen atmospheres are presented. The dominant molecular species are found to be CN and C2. The intensities of CN and C2 bands have been studied for laser fluences in the range 3–12 J/cm2, for N2 pressure in the range 1–250 Pa, and distances along the plasma axis of 1–14 mm. The values of roto-vibrational temperatures of CN radicals were calculated by fitting the experimental spectra with computer-simulated spectra. The self-absorption effects have been considered, and the optical path of the CN radical (the product between CN(X) density and plasma radius, R) was also estimated from the fitting procedure. The formation and the excitation of CN radicals, which could be important in the CNx materials deposition process, are discussed. It is shown that a possible mechanism could be the surface reaction of atomic nitrogen with the carbon clusters or particles existing in the plasma plume.

Characterization of C-N thin films deposited by reactive excimer laser ablation of graphite targets in nitrogen atmosphere

Abstract Carbon nitride films were deposited at room temperature on 〈111〉 Si substrates by XeCl laser ablation of graphite in low pressure (1–50 Pa) N2 atmosphere at a fluence of 12 J/cm2. N/C atomic ratios up to 0.5 were inferred from Rutherford backscattering measurements. Different diagnostic techniques (ARXPS, FTIR transmission spectroscopy, EDS, SEM and XRD) were used to characterize the deposited films. XRD spectra indicate a polycrystalline structure of the films.

Direct carbide synthesis by multipulse excimer laser treatment of Ti samples in ambient CH4 gas at superatmospheric pressure

Successful carbidation of Ti in a layer forming on the surface of a Ti sample submitted to multipulse excimer (λ=308 nm) laser treatment in CH4 at a slightly superatmospheric pressure is reported. The layer is only surface contaminated with oxygen while its main part consists of fcc TiC. The layer apparently ends with a tail of carbides with low C content, extending deeper into the sample’s bulk. The characteristics of the synthesized layer are suggested to be related to the peculiarities of the chemical synthesis which are enhanced by gas propulsion into a melted layer under the recoil action of a plasma evolving in front of the sample. A cavitation mechanism inside the melted surface layer in order to account for plasma initiation is proposed. This mechanism also facilitates the strong substance propulsion into the sample’s bulk.

Excimer laser reactive ablation: An efficient approach for the deposition of high quality TiN films

The successful deposition of TiN films on Si wafers by excimer (λ=308 nm) multipulse laser ablation of Ti in a low pressure N2 jet is reported in this article. The films are particularly pure, entirely consisting of polycrystalline fcc TiN. One difficulty still seems to be related to the presence of small droplets probably ejected in a liquid phase. According to the analyses, TiN is formed on Ti target with small contributions only, if any, of the next transit through gas and final deposition onto the Si wafer support.

Spectroscopic studies during pulsed laser ablation deposition of C–N films

Abstract Mass and optical emission spectra were recorded during XeCl laser ablation of graphite targets in vacuo and in low pressure (up to 2.5 mbar) N2 and NH3 atmospheres to study the role of gas phase reactions in C–N compound formation. Mass spectra were recorded during ablation in vacuo (10−6 mbar) and in N2 at 1×10−4 mbar. In vacuo, during the first stage of ablation, the mass spectrum was characterized by the peaks at 12 and 26 amu (C and CN). The CN peak intensity was slowly decreasing with the laser pulse number, to disappear after ∼3000 laser pulses. In contrast, the peak at 26 amu is permanent during the whole ablation when N2 is introduced in the chamber. The optical emission spectra recorded during ablation in vacuo are dominated by the bands of the C2 Swan system. Weak bands from CN can also be distinguished. Spectra recorded during ablation in NH3 are also dominated by the bands of the C2 Swan system. During ablation in N2 (10−4–2.5 mbar), strong bands of the CN violet system are detected. Their intensities increase with increasing N2 pressure and, at the same pressure, with increasing laser fluence. It was observed that the N atom density recorded in the deposited C–N films is increasing with the intensity of the CN emission.