Optical properties of nickel-incorporated amorphous carbon film deposited by femtosecond pulsed laser ablation

The present study investigates the optical properties of Ni-incorporated amorphous carbon (a-C:Ni) films covering a wide range of Ni concentration from doping to alloys. The films are deposited by sequential femtosecond pulsed laser ablation of graphite and Ni targets. The optical properties are analyzed by means of the Maxwell-Garnett theory with separated metal and carbon phases. This analysis permits to investigate the change of the carbon phase with Ni concentration. It is shown that the microstructure of the carbon phase is affected by the Ni incorporation even at low Ni concentrations (1 at.%) where a local reorganization of the carbon matrix occurs affecting the aromatic clusters. At higher Ni concentrations the films become more disordered.     

Electrical and optical properties of diamond-like carbon films deposited by pulsed laser ablation

Pulsed laser ablation of a graphite target was carried out by ArF excimer laser deposition at a laser wavelength of 193 nm and fluences of 10 and 20 J/cm² to produce diamond-like carbon (DLC) films. DLC films were deposited on silicon and quartz substrates under 1 × 10^? 6 Torr pressure at different temperatures from room temperature to 250 °C. The effect of temperature on the electrical and optical properties of the DLC films was studied. Laser Raman Spectroscopy (LRS) showed that the DLC band showed a slight increase to higher frequency with increasing film deposition temperature. Spectroscopic ellipsometry (SE) and ultraviolet–visible absorption spectroscopy showed that the optical band gap of the DLC films was 0.8–2 eV and decreased with increasing substrate temperature. These results were consistent with the electrical resistivity results, which gave values for the films in the range 1.0 × 10⁴–2.8 × 10⁵ Ω cm and which also decreased with deposition temperature. We conclude that at higher substrate deposition temperatures, DLC films show increasing graphitic characteristics yielding lower electrical resistivity and a smaller optical band gap.     

Effect of temperature on sulfur-doped diamond-like carbon films deposited by pulsed laser ablation

In this study, S-DLC films were deposited using pulsed laser ablation of a novel sulfur-graphite (SG) mixture target using an ArF excimer laser (193 nm). The SG targets were made by mixing sulfur and graphite powders at different sulfur molar percentages from 0% to 25%. The S-DLC films were deposited at room temperature, 150 °C and 250 °C. The optical and electronic properties of the doped films were studied. Laser Raman spectroscopy indicated increased graphitic behavior with temperature but decreased with higher sulfur content. Spectroscopic ellipsometry analyses found that the optical band-gap energy, extinction coefficient and reflective index, clearly depended on deposition temperature and sulfur content. Hall Effect measurements indicated n-type carrier with concentration in the range of 1 × 10¹⁴ to 2 × 10¹⁷ cm^− 3, strongly depended upon the deposition temperature and amount of sulfur.     

Nanodiamond synthesis by pulsed laser ablation in liquids

Pulsed laser ablation in liquids (PLAL) has become an attractive method for the synthesis of nanodiamond. This work deals with the growth kinetics study of structures of nano-diamonds embedded in sp² carbon synthetized by this method. The plasma created by the laser pulse has been monitored by time resolved spectroscopy to analyze the evolution of the plume and therefore the transient species created. Typical C₂ vibrational bands appear, as well as a continuous spectrum due to various phenomena. The study of both the background and the vibrational features gives information on the reaction kinetics and on the plasma density. The presence of nanodiamonds has been confirmed by Raman spectroscopy as well as TEM analysis.     

脉冲激光轰击法连续制备纳米铜研究

采用脉冲激光轰击法连续制备了纳米铜及表面活性剂原位修饰的油溶性纳米铜,用UV-Vis研究了不同表面活性剂不同浓度对纳米铜／乙醇溶胶的紫外-可见光谱的影响,从而确定各表面活性剂的最佳浓度,用TEM研究了不同表面活性剂对纳米铜溶胶分散稳定性的影响,确定了最佳表面活性剂为平平加O,傅立叶红外光谱发现纳米铜／乙醇溶胶中乙醇分子基团振动波长受纳米铜颗粒的影响而出现红移现象,分散性实验表明：平平加O表面修饰纳米铜具有良好的油溶性。     

Formation of freestanding two-dimensional carbon nanosheets from poly(phenylcarbyne) through pulsed laser ablation

Freestanding, two-dimensional (2D), amorphous carbon nanosheets (CNSs) were formed from a preceramic polymer, poly(phenylcarbyne), through laser ablation using a pulsed Nd:YAG laser. CNSs of several nanometers in thickness and micrometers in size were obtained. The polymer-to-carbon transition was investigated at different laser fluences and target-to-substrate distances. Three different phases, amorphous carbon, ultrathin amorphous CNSs, and thick carbon films, were obtained as the laser fluence increased. The pulsed-laser-induced formation of the 2D CNSs includes three steps: ablation, carbonization, and landing. This study reveals an existing route of forming freestanding 2D CNSs through pulsed laser ablation.     

Fracture toughness of zirconia from a shallow notch produced by ultra-short pulsed laser ablation

Fracture toughness of submicron grain size tetragonal zirconia polycrystals doped with 3 mol% yttria (3Y-TZP) is measured by the single edge V-notch beam (SEVNB) method from a shallow sharp notch produced by ultra-short pulsed femtolaser ablation (UPLA) on the surface of a bending bar. It is shown that the radius of the notch tip achieved is in the submicron range and the damaged volume in front of the notch tip is characterized by using focus ion beam milling and scanning electron microscopy. It consists of a narrow fully microcracked region less than ∼4 μm wide and ∼15 μm deep in front of the notch. If the extension of this region and the length of the notch are used in the determination of the fracture toughness (K_Ic) in the four bending test, the values obtained for submicron grain size 3Y-TZP are in agreement those obtained by using very sharp cracks. It is concluded that the SEVNB testing method with a sharp notch induced by UPLA may be used for K_Ic testing of submicron grain size ceramics.     

Morphology,structure and density evolution of carbon nano-structures deposited by N-IR pulsed laser ablation of graphite

Carbon films were deposited by pulsed laser ablation on Si <100> substrates, heated at temperatures increasing from RT to 800 °C, from a pure graphite target, operating in vacuum (~ 10^− 4 Pa). The laser ablation was performed by an Nd:YAG laser, operating in the near IR wavelength (λ = 1064 nm).Micro-Raman and grazing incidence X-ray diffraction analysis (GI-XRD) established the progressive formation of ordered nano-sized graphitic structures, increasing substrate temperature. The surface morphology is characterised by macroscopic roughness (SEM, AFM) while the low temperature samples are characterised by very smooth surface. The film density, evaluated by X-ray reflectivity measurements, is also affected by the substrate temperature. This structural property modification induces relevant variation on the emission properties of carbon films, as evidenced by Field Emission measurements. The film structure and texturing is also strongly related to laser wavelength: the low energy associated to the IR laser radiation (1.17 eV) causes an early aromatic cluster formation at T = 400 °C associated to a sensible increase in the aromatic plane stacking distance (d₀₀₂ ~ 0.39 nm), compared to graphite. These density decrease shows a direct correlation with the electron emission properties. Roughness and presence of voids play a negative role both on the threshold electric field E_th and enhancement factor (β) The density decreasing and graphitic layer widening are notably to be ascribed to the very fast out-of-equilibrium growth and to the presence of large activated carbon species in the “plume”.     

Hydrophilic carbon onions synthesized by millisecond pulsed laser irradiation

Carbon onions with hydrophilic characteristics were synthesized through irradiating carbon black suspension using millisecond pulsed laser at room temperature. Laser energy absorption resulted in the structure transformation of carbon black and the formation of hydrophilic groups on the surface of carbon onion. Carbon onions with hollow cores and the incomplete graphitic shells were produced from the starting materials under high and low laser power density, respectively.     

Ultra-low density carbon foams produced by pulsed laser deposition

We report on the manufacturing of ultra-low density carbon foam produced by pulsed laser deposition. Mean mass density, morphology and structure were investigated within a broad range of process parameters. We have been able to obtain carbon foam layers having tunable mean density and thickness in the range 1–1000 mg/cm³ and 5–80 μm, respectively. Surface uniformity has been achieved over ∼1 μm² areas with mean pore size around 10 nm. The morphological/structural properties have been investigated by means of quartz crystal microbalance, scanning electron microscopy and Raman spectroscopy. Based on these results, this work shows how pulsed laser deposition can be exploited as a versatile tool for the deposition of carbon foams with tunable and tailored density, thickness and uniformity.     

Diamond-like carbon by pulsed laser deposition from a camphoric carbon target: effect of phosphorus incorporation

DLC thin films were grown by XeCl excimer pulsed-laser deposition (PLD) at room temperature using a camphoric carbon (CC) target. To carry out doping, CC soot was mixed with varying amounts (1–7% by mass) of phosphorus (P) powder. The resistivity was observed to increase initially for the films deposited from a target containing 1% P. The resistivity then decreased sharply at first, and gradually thereafter, for the films deposited from targets with a higher P content. Raman, optical gap and the electrical resistivity studies suggest that the P incorporation in carbon films results in controlled doping for the films deposited from targets containing up to 5% P, and a higher P content induces graphitization by narrowing the optical gap.     

Rearrangements of sp/sp hybridized bonding with phosphorus incorporation in pulsed laser deposited semiconducting carbon films by X-ray photoelectron spectroscopic analysis

The carbon films were grown on p-type silicon substrate at room temperature by pulsed (XeCl) laser deposition technique using camphoric carbon target containing 1%, 3%, 5% and 7% of phosphorus (P) by mass. The analysis of X-ray photoelectron spectroscopy spectra of the C1s region in these films shows the presence of sp² and sp³ hybridized carbon and a sp² satellite peak due to π–π shake up. The sp² content is seen to remain almost constant with P content. The FWHM of the sp² peak increases up to 5% P but decreases for 7% P probably due to clustering of sp² chains and this clustering in the sp² phase probably decreases the band gap for the 7% P film. With P incorporation, the tetrahedral bonding configurations of the carbon network do not change appreciably, therefore, suggesting the scope of phosphorus as a potential dopant in carbon films.     

Polymeric fullerene oxide films produced by decomposition of hexanitro[60]fullerene

A new poly(fullerene oxide) thin film material has been fabricated by thermal activation and electron bombardment on hexanitro[60]fullerene (HNF) film deposited on a Au substrate, all under vacuum conditions. The reaction products in the polymerization process are analyzed by XPS, UPS, IR, TGA-MS and LDI-MS techniques. It is found that the main effect of thermal and radiation treatments is to induce cleavage of -NO bonds from HNF molecules resulted in the release of nitric oxide gas and the formation of fullerene-bound oxyradicals, C₆₀-O₆. Spectroscopic evidence strongly suggests that rearrangement of fullerenic nitro moieties into nitrito groups is involved in the HNF decomposition process prior to the generation of reactive oxyradical intermediates. Consequently, the intermolecular coupling reaction of these oxyradicals leads to carbon polymer networks containing oxygen-bridged fullerenes. The thermally generated polymeric thin film is stable up to 900 K. Electron bombardment is also effective in both the decomposition of -NO₂ groups and the removal of -OH groups present in HNF films. UV irradiation at 365 nm alone is shown to be not as efficient for the polymer formation.     

Growth of diamond nanocrystals by pulsed laser ablation of graphite in liquid

Nanocrystalline diamond has been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation (Nd:YAG, 532 nm) of a graphite target in water. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and laser Raman spectroscopy have been used to characterise the nanocrystals and to confirm that they are diamond. Time-averaged optical emission spectroscopy showed the presence of H, C and O atoms in the ablation plume. Imaging of the light emitted from the plume showed that H atoms were formed in two regions, in the liquid above the graphite surface, and also in the air just above the water surface. The results are consistent with the idea that atomic H is a necessary requirement for the growth of diamond via this method.     

Polymerization of monomers initiated by silyl centers in SiO deposits prepared by pulsed laser ablation

Deposits from silicon monoxide prepared by pulsed laser ablation were allowed to react with acrylic and vinyl monomers—styrene, methyl methacrylate and 1,2 ethylene glycol dimethacrylate. It was revealed by means of FTIR, electron paramagnetic resonance (EPR), and NMR spectroscopies that silyl ?Si· reacts with monomer molecules and initiates the consecutive polymerization. Crosslinking is proved by the occurrence of bending δ(? CH₂) absorption peak at about 750 cm^?1 in FTIR spectra. Because of very low concentration of the propagating radical for styrene we used a radical scavenger N‐phenyl‐t‐butylnitrone for trapping. The measured EPR parameters were compared with the calculated ones. In case of styrene, NMR analysis manifested the presence of Si? C bonds in SiC_xO_y (x + y = 2) units, which can be taken as direct evidence of the reaction between silyl centers and monomer molecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4488–4492, 2006     

Spectroscopic study on pulsed laser ablation of graphite target in ECR nitrogen plasma for carbon nitride film deposition

The influence of nitrogen plasma generated by electron cyclotron resonance (ECR) microwave discharge on deposition of carbon nitride films by means of ECR plasma assisted reactive pulsed laser deposition was investigated by a comparative study on the optical emission of the plume produced by pulsed laser ablation of a graphite target in ECR nitrogen plasma, in vacuum and in low-pressure nitrogen gas ambient. Spatial and temporal spectroscopic measurements show that in vacuum optical emission lines originating from carbon atoms and ions dominate the plume emission, while in low-pressure N₂ ambient weak CN emissions appear. In nitrogen plasma, the plume emission exhibits itself very differently. It evolves from consisting of emissions almost from mono-atomic carbon atoms and ions to being dominated by emissions from CN molecules. The presence of the reactive nitrogen plasma greatly enhanced the CN emissions and eliminated the emission lines from carbon atoms and ions. The appearance of the CN emissions occurs after the emissions from carbon atoms and ions have decayed considerably, indicating that the dominant mechanism for the formation of CN molecules is gaseous phase reaction. Carbon nitride films with nitrogen content of about 40 at.% were obtained. Possible processes for CN molecule formation in gaseous phase and mechanisms responsible for efficient nitrogen incorporation and carbon nitride film deposition were suggested.     

Fabrication of micro-scale textured grooves on green ZrO2 ceramics by pulsed laser ablation

The green ZrO₂ ceramics were fabricated by cold isostatic pressing. Pulsed laser ablation with a wavelength of 1064 nm was performed to fabricate micro-scale textured grooves on the surface of green ZrO₂ ceramics. The influence of laser parameters on surface quality was studied. The heat-affected zone around the machined grooves and micromorphology of laser-irradiated surface were investigated. Results showed that micro-scale textured grooves with a width of 30–50 µm and a depth of 15–50 µm on the green ZrO₂ ceramic surfaces were successfully fabricated by pulsed laser ablation. The laser parameters had a profound influence on the surface quality of micro-scale textured grooves. Better surface quality could be obtained with frequency below 40 Hz, power below 6 W, and scanning velocity above 200 mm/s. A sintering layer was found on the laser-irradiated surfaces when frequency was above 60 Hz, power was above 10 W, and scanning velocity was below 150 mm/s. Analysis of this sintering layer revealed clear melting and resolidification of ZrO₂ particles.     

Highly conductive nanoclustered carbon:nickel films grown by pulsed laser deposition

An enhancement by 5 orders of magnitude of the electrical conductivity of nanoclustered carbon films is reported by incorporation of metallic atoms, but without significant morphological changes. Films were deposited by 248 nm pulsed laser ablation of both a pyrolytic graphite target and a mixed carbon–nickel (C:Ni) target, and structural analysis revealed that similar film morphologies were obtained when deposition was carried out using either target. Compositional analysis demonstrated a preferential incorporation of nickel over carbon in the resulting films (cf. the composition of the target). This non-stoichiometric transfer was also observed for films grown by 193 nm laser ablation of the C:Ni target, for which the enhancement was more pronounced, indicating that the ablation mechanism and the subsequent transfer are important in determining the eventual film composition.