S. Acquaviva

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.

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.

Evidence for CN in spectroscopic studies of laser-induced plasma during pulsed irradiation of graphite targets in nitrogen and ammonia

Mass- and time-integrated optical emission spectra were recorded during direct XeCl laser ablation (308 nm, 30 ns) of graphite targets in and in atmospheres at various pressures and at different laser fluences . Spectra in vacuo were also acquired. The optical emission spectra of the laser-induced plasma are characterized by strong molecular emission bands of and CN and by lines of atomic ions . At the highest pressures the spectra are dominated by a Swan system (vibrational sequences ) and a CN violet system . Their intensities increase with an increase of gas pressure. Mass spectrometry was also performed on the ablated materials and various chemical species were found; the most common ones were C, CN and .

Atomic and molecular emissions of the laser-induced plasma during zinc and zinc oxide target ablation

Optical emission spectroscopic investigations of the plasma produced during KrF excimer laser ablation of Zn and ZnO targets, in vacuum and in oxygen gas environment, are presented. The plume luminescence is mainly due to Zn excited atoms and ions, but the contribution of atomic and molecular oxygen, as well as of particulates, cannot be neglected. In particular, we detect emissions in the spectral regions around 380 and 530 nm, corresponding to the UV and green photo-luminescence bands of the zinc oxide. Moreover, we study the temporal evolution of atomic and ionic ejected species by space- and time-resolved spectroscopy and analyze the results by means of empirical models, in order to infer information about plasma dynamics.

Fast photography of XeCl laser-induced plasma of graphite in vacuum and in nitrogen atmosphere

Fast photography with a gated intensified close-coupled device camera was applied to provide a visualization of the temporal and spatial evolution of chemical species in a plasma induced by a 308 nm laser during graphite ablation, in vacuum and in nitrogen atmosphere. A sequence of frames of the luminous plume was recorded, using narrow interference filters, and plasma expansion velocity was estimated from the acquired images. Present observations agree with optical emission spectroscopic investigations performed under the same experimental conditions.

Carbon nitride films deposited by very high-fluence XeCl excimer-laser reactive ablation

We report the characteristics of CN x films deposited by excimer laser ablation of graphite targets in low pressure N 2 atmosphere. We used a XeCl laser (A = 308 nm, τ FWHM = 30 ns) at the fluence of 32 J/cm 2 (∼ 1 GW/cm 2 ) and repetition rate of 10 Hz. Substrates were Si single crystals at room temperature. Different diagnostic techniques [scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR)] were used to characterise the deposited films. Films are plane and adhesive to their substrates. Deposition rates vary from 0.25 to 0.025 A/pulse, decreasing with increasing N 2 ambient pressure (0.5-100 Pa). N/C atomic ratios vary from 0.2 to 0.45, as inferred from RBS measurements. Raman spectroscopy evidences a prevalent amorphous structure of the films at low ambient pressures and a dominance of crystallites at high ambient pressures. XPS results show that N atoms are mainly bonded to C atoms in the sp 2 and sp 3 bonding states.

Reactive laser deposition of high quality YBaCuO and ErBaCuO films

RE 1 Ba 2 Cu 3 O 7-δ (RE = Er or Y) superconducting films were fabricated by reactive laser deposition, in situ, on YSZ(100), SrTiO 3 (100) and Si(001), under various conditions. A complete XRD investigation showed that the films grown with high substrate temperatures (T s > 740°C) combined with low fluences (1.5 J / cm 2 < 2 J / cm 2 ) and laser repetition rate (4 Hz) have the best structural characteristics, very good electrical and magnetic properties.

Effect of Laser Ablation Parameters on the Structure and Properties of Multicomponent Magnetic Films

Co and Fe-based alloy films were deposited and studied as perspective materials for the development of fast magnetic sensors. Pulsed laser ablation deposition (PLD) was used as an appropriate technique to fabricate thin films preserving the stoichiomeUy ofthe complex bulk materials. Co67Cr7Fe4SiB14, Fe75Nb3Cu1Si12B9, Fe40Ni40B20 and FexNi1-x (x=22, 36, 50) amorphous ribbons and metallic foils were ablated to deposit 10-120 nm thick films onto oxidized Si wafers using a KrF (λ= 248 urn) laser with 30 ns pulses at fluence from 2 to 7 Jcm-2. The films were analyzed by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), Rutherford backscattering spewometiy (RBS), x-ray diffraction (XRD) and reflectivity (XRR), and ferromagnetic resonance (FMR). The structural and magnetic characteristics of the films strongly depend on the laser fluence. Stoichiometry is well preserved at low laser fluences. At higher fluences lighter elements (Si, B) are partly lost. Unwanted crystallization of films is also observed at the high fluence. Magnetic characteristics are closely related to the corresponding source materials, unless the light elements are partly lost. When this happens increased magnetization of film is observed. The relaxation process in films was characterized by FMR linewidth. They are typically very narrow (110-250 G) for Fe-based alloys, indicating low values of magnetization motion damping (down to 6.06x107 radius) and therefore pointing to a perspective use of these materials for fast sensors.

Segregation of elements in the plume of laser ablated multi-component magnetic targets

Targets of Co67Cr7Fe4Si8B14 magnetic alloy were ablated in vacuum with an XeCl laser at different jIuences ranging from 2.5 to 7 J/cm2 The ablated material was collected onto unheated silicon substrates placed at different angles with respect to the nonnal o/the target at the incident laser spot. Film composition was inferred by Rutheiford backscattering spectrometry analyses. Experimental results reveal that the concentration of lighter elements is larger in films deposited at higher collecting angles. The observed effect is more evident at lower laser fluences. The compositional variations with collecting angle in the studied multi-elemental films are attributed to scaliering effects among the ablated chemical species in the plume.

Parametric studies of carbon nitride thin films deposited by reactive pulsed laser ablation

We report on parametric studies of CNx films deposited by excimer laser ablation of graphite targets in molecular nitrogen atmosphere as a function of gas pressure and laser fluence values. Substrates were Si single crystals at room temperature. Deposition rates decrease with increasing nitrogen pressure. The N/C atomic ratio generally increases with increasing nitrogen pressure and laser fluence, N atoms are mainly bonded to C atoms in the sp2 and sp3 bonding states. At relatively high pressure and laser fluences about 40 percent of the C atoms and about 50 percent of the N atoms are bounded in the C-N single bonds, generally attributed to the (beta) -C3N4 compound.