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Copper thin films are intended to serve as a cover layer of photocathodes that are deposited by ablating copper targets in a high vacuum by temporally clean 600 fs laser pulses at 248 nm. The extremely forward-peaked plume produced by the ultrashort UV pulses of high-energy contrast ensures fast film growth. The deposition rate, defined as peak thickness per number of pulses, rises from 0.03 to 0.11 nm/pulse with an increasing ablated area while keeping the pulse energy constant. The material distribution over the surface-to-be-coated can also effectively be controlled by tuning the dimensions of the ablated area: surface patterning from airbrush-like to broad strokes is available. The well-adhering films of uniform surface morphology consist of densely packed lentil-like particles of several hundred nm in diameter and several ten nm in height. Task-optimized ultrashort UV laser deposition is thereby an effective approach for the production of thin film patterns of predetermined geometry, serving e.g., as critical parts of photocathodes.

Nowadays, lasers are routine tools in the widest range of materials processing, including welding of battery packs. The properties of the laser generated weld bead are crucial in determining the electrical and mechanical behavior of the joint. Here, we report on the identification of five morphological bead types, namely, Rosenthal, single wave, elongated, pre-humping, and humping morphologies and their systematic appearance over the laser power versus scanning speed plane. We prove that each type exhibits characteristic electrical and mechanical behavior that differ not only in the magnitude of relevant materials’ properties, but also in their variability. We show for nickel-coated steel and uncoated DC01 cold rolled steel that the so-called single wave morphology is best suited for battery welding applications, since this morphology class concomitantly exhibits the lowest electrical resistance and the highest mechanical strength, both with a relatively small margin of error. The results suggest that the bead morphology could be exploited as a simple indicator of joint properties.

The material response of Borofloat, BK7, and B270 glass targets to 34 fs pulses of 800 nm central wavelength is analyzed in the 1–30 J/cm2 fluence domain. The contours of the craters change with the fluence very much the same for all three glasses up to approximately 20 J/cm2, above which the Borofloat and BK7 continue behaving similarly, while bump formation sets on for the B270 glass. Analyzing the contours single-shot ablation thresholds are determined by applying both the conventional diameter regression technique and a multiphoton absorption-based fit to depth data. The ablation threshold values are equal within the 6.1 ± 0.55 J/cm2 domain for the three glasses as well as the three-photon absorption coefficients, which lie in the same magnitude (10–25 cm3/W2). Above the ablation threshold, the diameter values follow logarithmic dependence in the fluence range investigated, reaching similar values around 45 µm at 30 J/cm2 with 51 ± 1 µm 1/e2 beam diameter on the target surface as derived from the diameter regression technique. The onset of plasma formation derived from the changes in the energy reflected from the processed surface is also found to be similar for the three glasses (9.5, 10, and 8.0 J/cm2) in good correlation with the ablation threshold values.

Wire explosion is a technically straightforward green method for nanoparticle production; however, the determination of polydisperse and multimodal particle size distribution and thereby the assessment of the efficiency of the process pose serious challenges. Fitting extinction spectra derived from the Mie theory to the measured extinction spectra of colloidal solutions produced by the explosion of copper wires of 70 μm diameter and 20 mm length by discharging a capacitor of 435 nF charged to voltages ranging from 4 to 12 kV in an aqueous environment allows for determining the size distribution of the particles in the 10–300 nm diameter range and provides information on their oxidation state as well. In underwater wire explosion of copper, the vast majority of the nanoparticles transforms into copper oxides already during the process. The size distribution remains bimodal throughout the whole charging voltage range investigated. The nanoparticles follow a lognormal size distribution with a mode at 30 nm, while the fine particle population extending from 100 to 300 nm in diameter is dominated by rather normally distributed copper droplets with modes at 160–170 nm. The energy injected into the wire controls the individual concentration of both the fine and nanoparticles with the modes and ranges remaining hardly affected. The number concentration of the nanoparticles increases monotonically with the energy, spanning more than one order of magnitude. The throughput assessed by the total mass of the nanoparticles divided by the total mass of all species identified in the sol within the 0–300 nm diameter range increases monotonically from 1% at 4 kV up to 41% at 12 kV, revealing that wire explosion can be optimized for efficient nanoparticle production.

Horseflies (Tabanidae) are polarotactic, being attracted to linearly polarized light when searching for water or host animals. Although it is well known that horseflies prefer sunlit dark and strongly polarizing hosts, the reason for this preference is unknown. According to our hypothesis, horseflies use their polarization sensitivity to look for targets with higher degrees of polarization in their optical environment, which as a result facilitates detection of sunlit dark host animals. In this work, we tested this hypothesis. Using imaging polarimetry, we measured the reflection–polarization patterns of a dark host model and a living black cow under various illumination conditions and with different vegetation backgrounds. We focused on the intensity and degree of polarization of light originating from dark patches of vegetation and the dark model/cow. We compared the chances of successful host selection based on either intensity or degree of polarization of the target and the combination of these two parameters. We show that the use of polarization information considerably increases the effectiveness of visual detection of dark host animals even in front of sunny–shady–patchy vegetation. Differentiation between a weakly polarizing, shady (dark) vegetation region and a sunlit, highly polarizing dark host animal increases the efficiency of host search by horseflies.

Recently, we proposed an alternative arrangement to traditional on- or off-axis PLD geometries, termed inverse PLD (IPLD) that is capable of producing films of improved surface morphology. Two configurations of this new target-substrate arrangement were developed, namely static and co-rotating IPLD. In the static IPLD configuration, the substrate is stationary with respect to the ablated spot; while in the co-rotating IPLD configuration the substrate is fixed to the target surface and rotates simultaneously with the target, hence offering an appealingly simple approach to homogenize film properties. Here we report the growth of CNx and Ti films, simultaneously deposited in the co-rotating and static IPLD arrangements. The homogeneity of the co-rotating films is described by a thickness inhomogeneity index, which allows for the comparison of films of different lateral dimension. A semi-analytical, semi-numerical model is proposed to derive the radial variation of the growth rate of co-rotating IPLD films from the lateral growth rate distributions measured along the symmetry axes of static IPLD films. The laterally averaged growth rate, LAGR is used to describe how the ambient pressure affects growth in the 0.5–50 Pa domain. As an example, the absolute error between the measured and calculated radial growth rate variation, obtained at 5 Pa, was less than 3%, while the LAGR of CNx layers grown by co-rotating IPLD was predicted with 20% accuracy.

Ablation of a silicone oil, Dow Corning's DC-705 with laser pulses of sub-ps duration in high vacuum is a novel approach to fabrication of Si-doped carbon nanocomposite films. Gently focused, temporally clean 700 fs pulses @ 248 nm of a hybrid dye/excimer laser system produce power densities of the order of 10 11 –10 12 W cm −2 on the target surface. The evolution of the chemical structure of film material is followed by comparing Fourier Transformed Infrared and X-ray Photoelectron spectra of films deposited at temperatures between room temperature and 250 °C. Despite the low thermal budget technique, in the spectrum of films deposited at room temperature the fingerprint of the silicone oil can clearly be identified. With increasing substrate temperature the contribution of the features characteristic of the oil gradually diminishes, but does not completely disappear even at 250 °C. This result is intriguing since the chance of oil droplets to survive in their original liquid form on the hot surface should be minimal. The results of the X-ray Photoelectron Spectroscopy suggest that the chemical structure of the film material resembles that of the oil. Both reflection mode optical microscopy and low magnification Scanning Electron Microscopy reveal that the films are inhomogeneous: areas of lateral dimensions ranging from a few to tens of micrometers, characterized by different contrasts can be identified. On the other hand, surface mapping by Scanning Electron and Atomic Force Microscopy unambiguously proves that all films possess a solid surface consisting of nanoparticles of less than 100 nm dimension, without the presence of any drop of oil. Possible explanations of the puzzling results can be that the films are polymers consisting mainly of the molecules of the target material, or composites of solid C:Si nanoparticles and oil residues.

A simple analytical model for inverse pulsed laser deposition is proposed. In the model the motion of the evaporated material is assumed to emerge as from a point source located above the surface of evaporation at some distance. The obtained thickness profiles of inverse deposited films agree well with those calculated by the test particle Monte Carlo method. The proposed approach has been applied for analysis of experimental data on inverse pulsed laser deposition of graphite in nitrogen atmosphere with nanosecond pulses of laser fluences between 1 and 7 J/cm2. The model describes well the thickness profiles and pressure dependence of film growth rate for inverse deposition.

Since the advent of pulsed laser deposition (PLD), several different target-substrate arrangements have been proposed. Besides the most common on-axis PLD, several off-axis geometries were studied, mainly to protect the substrate from the agglomerated species (clusters, droplets, particulates) of the plasma plume, which are detrimental to the homogeneity of films. Recently we introduced a novel geometry, termed inverse pulsed laser deposition (IPLD), in which the substrate is placed parallel to and slightly above the target plane. In this paper we summarize our results on this new geometry, and show how it can extend the perspectives of pulsed laser deposition, e.g., by improving the surface morphology of the films. Effects of ambient pressure are presented and exemplified on metallic and compound IPLD films, including Ti, CN x , and Ti-oxides. AFM topographic images are used to prove that under optimized conditions IPLD is capable of growing compact and smooth films that are superior to PLD ones. A special—but easy-to-implement—IPLD arrangement is also introduced that considerably improves the homogeneity of IPLD films. In this geometry, the properties (e.g., deposition rate and roughness) of the films grown in the 1–25 Pa pressure domain are examined.

In the present contribution we report on a target–substrate arrangement to considerably improve the homogeneity of films produced in the static-substrate inverse pulsed laser deposition (IPLD) configuration. Carbon nitride films were grown in a modified IPLD geometry, by holding a silicon substrate in the target plane and jointly rotating it with the target at 5.5 rpm. The graphite target was ablated by KrF excimer laser pulses in nitrogen atmosphere of 5 Pa pressure. The laser fluence was kept at a constant value (∼7 J/cm2) in each experiment. Typically a 1 cm × 1 cm large silicon substrate was fixed to the target within the ablated track of approx. 10 mm radius. The thickness distribution of the films was measured by profilometry on masked steps. The maximum relative deviation of the film thickness was ±6% and typically around ±2.5%. The homogeneity of the refractive index and the extinction coefficient was found to be ±0.55% and ±3.58%, respectively. An additional benefit of this co-rotating IPLD geometry is its appealing simplicity, i.e. that the target and substrate are rotated by the same motor.

An inherent property of the ultrashort pulse lasers used presently for materials processing is that the main pulse is accompanied by an amplified spontaneous emission background. The temporal quality of the pulses is characterized by the temporal contrast. Due to the 5–6 orders of magnitude difference in the duration of the main pulse and the pedestal, high intensity contrast does not mean necessarily high enough difference in the respective energies. In materials processing applications consideration of the energy contrast is advisable. The importance of the contrast in determining the ablation process is exemplified by the dependence of the ablation rate of boron carbide on the cleanness of the pulses of a high brightness hybrid dye/excimer laser system. It is shown that serious consideration of the effects of the nanosecond background is mandatory when evaluating the results.

Boron carbide films with a thickness of up to 550 nm and deposit size of 40 mm × 30 mm were prepared by ablating a B4C target in high vacuum by pulses of 700 fs duration at 248 nm. Layer thickness and lateral distribution of the constituting elements along the symmetry axes of a deposit were investigated with Rutherford backscattering spectrometry (RBS) with a focussed 2.5 MeV He+ ion beam. RBS spectra were fitted with the DataFurnace computer code. The results of 2D mapping proved that both the elemental composition and the film thickness of the deposit were non-uniform. The B/C ∼ 1 ratio measured at the edge of the deposit increased up to about three toward the centre, with both the B content and the B/C ratio varying linearly with the film thickness.

Carbon nitride films have been deposited in the inverse pulsed laser deposition (IPLD) geometry by ablating a graphite target in nitrogen atmosphere while the spatial orientation of the target (and substrate) normal was varied. Two different orientations were tested, in one of which the axis of the plasma plume was made to point downwards, imposing the maximum gravitational barrier on the ablated species and make them move against the gravitational field while growing the film in order to verify the extent of a possible orientational effect. The thickness distribution of films obtained in different orientations was sampled along their axes of symmetry by stylus profilometry. The results indirectly proved that the kinetic energy of the species responsible for building the IPLD films surpassed the effect of gravitational field, even in the outer regions of the films, where the ablated species were believed to be thermalised. Evidences are also provided that utmost care should be taken to keep experimental conditions, like process pressure, spot size, etc., constant in order to get reproducible results.

Carbon nitride films have been deposited by KrF excimer laser ablation of a rotating graphite target in 5 Pa nitrogen ambient in an inverse pulsed laser deposition configuration, where the backward motion of the ablated species is utilised for film growth on substrates lying in the target plane. Topometric AFM scans of the films, exhibiting elliptical thickness distribution, have been recorded along the axes of symmetry of the deposition area. High resolution AFM scans revealed the existence of disk-like, or somewhat elongated rice-like features of 5–10 nm average thickness and ∼100 nm largest dimension, densely packed over the whole, approximately 14 × 10 cm 2 deposition area. The RMS roughness of the film decreased from 9 nm near to the laser spot down to 2 nm in the outer regions. Even the highest RMS value obtained for IPLD films was less than half of the typical, 25 nm roughness measured on simultaneously deposited PLD films.

Growth characteristics and surface morphology of boron carbide films fabricated by ablating a B 4 C target in high vacuum with a traditional KrF excimer laser and a high brightness hybrid dye/excimer laser system emitting at the same wavelength while delivering 700 fs pulses are compared. The ultrashort pulse processing is highly effective. Energy densities between 0.25 and 2 J cm −2 result in apparent growth rates ranging from 0.017 to 0.085 nm/pulse. Ablation with nanosecond pulses of one order of magnitude higher energy densities yields smaller growth rates, the figures increase from 0.002 to 0.016 nm/pulse within the 2–14.3 J cm −2 fluence window. 2D thickness maps derived from variable angle spectroscopic ellipsometry reveal that, when ablating with sub-ps pulses, the spot size rather than the energy density determines both the deposition rate and the angular distribution of film material. Pulse shortening leads to significant improvement in surface morphology, as well. While droplets with number densities ranging from 1 × 10 4 to 7 × 10 4 mm −2 deteriorate the surface of the films deposited by the KrF excimer laser, sub-ps pulses produce practically droplet-free films. The absence of droplets has also a beneficial effect on the stoichiometry and homogeneity of the films fabricated by ultrashort pulses.

Recently, we proposed a new PLD geometry, termed as inverse PLD, in which the backward motion of the ablated species was utilized for film growth on substrates lying in the target plane. Qualitative measurements revealed that in this geometry the growth rate of carbon nitride films was comparable to or even exceeded that of the traditional geometry in the critical pressure domain of reactive PLD. The knowledge of the lateral distribution of the growth rate is of primary importance for both applications and modelling. Here first quantitative data on the dependence of the lateral distribution of deposition rate of carbon nitride films, fabricated by KrF excimer laser ablation of a rotating graphite target, on N2 pressure are reported. Thickness distributions of films grown on Si substrates within the 0.5–50 Pa pressure window have been recorded along the axes of symmetry of the laser spot by stylus profilometry. At all background pressures, the thickness decreases exponentially with increasing distance from the ablating laser spot. The elliptical symmetry typical at low pressures and near to the spot shifts to circular with increasing pressure and distance. The existence of flip-over suggests that recondensation of the plasma species without scattering on the surrounding atmosphere effectively contributes to IPLD film growth.

The properties of carbon nitride films deposited in inverse pulsed laser deposition (IPLD) geometry, in which the backward motion of the ablated species is utilised for film growth on substrates lying in the target plane, are compared with those grown simultaneously in the traditional on-axis position. Within the 2–50 Pa pressure window the growth rate of the IPLD films increases nearly linearly with the logarithm of nitrogen pressure, and exceeds that of their on-axis counterparts at around 20 Pa. The IPLD films are more protected against the deposition of micron-sized particulates, consist of smaller grains and exhibit denser structure than the on-axis films, especially above 10 Pa. The chemical structure of the films is unaffected by the geometry with slightly lower nitrogen content in the IPLD case. The morphological properties of IPLD films are superior to those grown in the classical configuration, suggesting that the advantageous contribution of hyperthermal energy species has not been lost in the inverse geometry.

This paper contributes to the old problem of droplet formation by providing detailed quantitative data on the population statistics of particulates deteriorating the surface of boron carbide films produced by PLD. Films of 180 ± 30 nm thicknesses have been fabricated by KrF excimer laser ablation of a sintered B 4 C target in high vacuum. Number densities and size distributions of the particulates are given for 14 films, deposited at laser fluences tuned between 2 and 14 J cm −2 , as a result of evaluating SEM images of the same magnification taken from minimum five different areas (altogether (2–4) × 10 −2 mm 2 ) of each film. The overwhelming majority of the droplets is small with diameters, d ≤ 1 μm. The number density of those with d ≤ 0.5 μm ranges from (1 to 7) × 10 4 mm −2 . The effect of gradual deterioration of the target surface as a result of prolonged irradiation screens practically totally the effect of changing fluence. The number of droplets of diameters in excess of 1 μm increases linearly with increasing number of shots/site resulting in maximum surface coverage values as high as 36%.

Ablation characteristics of a commercially available diamond-like carbon (DLC) film (the EVERSCANTM bar code scanner window; Diamonex Division of Morgan Advanced Ceramics Inc.) in the 0–7 J cm-2 fluence window are reported. Glass pieces covered with 6 μm thick DLC coating are ablated by 22 ns pulses of a KrF excimer laser in medium vacuum (10-1 Pa), and in Ar and O2 atmospheres of 105 Pa. The ablation depth increases strictly linearly with an increasing number of pulses, independently of the atmosphere and the applied fluence. The threshold lies at 0.13 J cm-2 and is independent of the atmosphere. While above 1 J cm-2 the ablation rate vs. fluence plots recorded in different atmospheres coincide within experimental error, processing under vacuum between 0.5 and 1 J cm-2 results in significantly higher ablation rate values. Ablation rates exceeding 100 nm/pulse above 1 J cm-2 ensure extremely efficient machining over extended areas even at relatively low fluences. Identical characteristics in Ar and O2 atmospheres suggest that solely physical (ablative) processes contribute to material removal.

The peculiarities of a novel off-axis pulsed laser deposition configuration are reported in which the material is collected on substrates placed in the target plane. Carbon nitride films have been grown by KrF excimer laser ablation of a rotating graphite target in nitrogen atmosphere. The thickness distribution of films, recorded along the axes of symmetry of the laser spot, revealed that the increase of pressure from 1 to 40 Pa led to (i) thicker films, (ii) gradually more confined deposits and (iii) a transition from elliptical to circular distribution. X-ray photoelectron spectroscopy evidenced the reduced nitrogen content of the off-axis films as compared to their traditional on-axis counterparts. Nevertheless, the chemical structure of the deposits was identical in the two geometries. In the off-axis films the further away the deposition location is from the laser spot the more nitrogen can be incorporated into the film with concomitant increase in the oxygen content, the latter pointing to possible changes in the film microstructure.

A series of boron carbide films of 180±30 nm thickness has been deposited by KrF excimer laser ablation of a sintered B 4 C target in high vacuum. Rutherford backscattering spectroscopy revealed that the chemical composition of the films grown on Si substrates, at room temperature, at laser fluences tuned between 2 and 14.3 J cm −2 varied depending not only on the actual laser fluence but also on the past record of the B 4 C target. Parallel SEM mapping of both film and target surfaces pointed to a correlation between changes in film composition, droplet density and target surface deterioration. This correlation is discussed in detail.

Carbon nitride films have been grown by a novel technique in which high power activation of the precursor gases is achieved by plasma generation with pulses of tens of nanoseconds lifetime. The effect of the substrate temperature on the chemical composition of films deposited from 13 sccm CH 4 +39 sccm N 2 at a total pressure of 300 Pa is followed by X-ray photoelectron spectroscopy (XPS). N/C ratios between 0.33 and 0.37 characterize the material obtained at room temperature. Though the N content of the films steeply decreases with increasing substrate temperature, even those grown above 800 °C do contain a few at.%. The changes in the relative abundance of the individual spectral components of the C1s and N1s lines are interpreted in terms of changes in the chemical environment of the nitrogen and carbon atoms. Comparison of the results of the XPS analysis with pieces of information on surface morphology and local composition of the films derived from parallel SEM and X-ray microanalyses suggests that the deposits consist of a great variety of carbon microstructures of different shape and dimension embedded in a rather thin layer of higher nitrogen content.

Carbon and carbon nitride films have been deposited by ArF excimer laser ablation of identical graphite targets in the same system, in argon and nitrogen atmospheres, respectively. Based on the comparative analysis of apparent growth rates, deposition rates of the constituting elements and mass densities, a consistent description of film formation in the 10−5–200 Pa pressure domain is presented. The results reveal that the formation, composition, and microstructure of carbon and carbon nitride films fabricated in this process window are governed by gas phase processes. Below 5 Pa the film building blocks are mainly atoms and molecules resulting in compact, dense films. At higher pressures increasing contribution of clusters to film growth leads to films of increasing porosity ready to trap (mainly water) molecules from the surrounding atmosphere.

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Carbon nitride films have been deposited by ArF excimer laser ablation of a graphite target in the 10 −2 to 100 Pa N 2 pressure range. Arrival rates of the constituting elements, mass densities and apparent growth rates have been derived from areal densities of both carbon and nitrogen atoms, determined by ion beam techniques, and film thicknesses, measured by a mechanical stylus. Below 5 Pa the film building blocks are atoms and molecules while above ∼50 Pa the formation and interaction of clusters and particles determine the film growth. The results reveal that the formation, composition and microstructure of carbon nitride films fabricated in this process window is governed by gas-phase processes.

Carbon films have been deposited by ArF excimer laser ablation of a graphite target in argon ambient of pressures between 10 � 4 and 200 Pa. Besides carbon, ex situ RBS and ERDA measurements reveal the presence of argon, hydrogen and oxygen in the films. Below 0.5 Pa the apparent growth rate, defined as the measured thickness per number of pulses, is almost constant at

Amorphous carbon nitride (a-CNx) films were grown on silicon substrates by ArF excimer laser ablation of a graphite target in the presence of nitrogen at various gas pressures. By working at elevated pressures (up to 100 Pa), large amounts of nitrogen can be incorporated into the films (up to 40 at. %, which leads to a strong enhancement of their field emission properties. This behaviour was demonstrated to be mainly related to changes in the surface morphology of the samples, in connection with the development of graphite-like structures.

Amorphous carbon nitride (a-CNx) films were grown on silicon substrates by ArF excimer laser ablation of a graphite target in the presence of nitrogen at various gas pressures. By working at elevated pressures (up to 100 Pa), high amounts of nitrogen can be incorporated into the films (N/C≤0.4) which lead to strong enhancement of their field emission properties. This behaviour was demonstrated to be mainly related to changes in the surface roughness of the samples, in connection with the development of graphite-like structures.

Results of a comparative XPS study on 26 carbon nitride samples of different chemical composition fabricated by ablating a graphite target with an ArF excimer laser in N2 atmosphere while systematically varying the pressure in the 1–100-Pa and the laser fluence in the 1.0–10-J cm−2 domains are reported. N1s core level spectra recorded on all samples are consistently fitted by four components at 398.2, 399.4, 400.7 and 402.1 eV, respectively. Changes in the relative abundance of the individual spectral components of the N1s lines as a function of laser fluence and nitrogen pressure are interpreted in terms of changes in the chemical environment around nitrogen atoms. When present in low concentration, nitrogen atoms prefer sites allowing pyramidal configuration. With increasing concentration more and more atoms form CNC type bonds, nevertheless, in all films the majority of the nitrogen atoms occupies pyramidal configurations.

Amorphous carbon nitride (CNx) films were grown on silicon substrates by ArF laser ablation (PLD) of a graphite target in presence of nitrogen at various gas pressures. These films have been measured by spectroscopic ellipsometry in the UV–vis and IR wavelength range. In the UV–vis range, the optical indices of the CNx films have been extracted accurately using a model including surface roughness. The optical indices of the films are modelized by a Forouhi dispersion law model and the thickness and roughness are adjusted at the same time. The optical gap is extracted from the extinction coefficient. In the IR spectral range, the conductivity of the films is extracted from the Drude tale model. These structural and optical results are compared to the physico-chemical results provided by Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA).

Carbon nitride films deposited by ArF excimer laser ablation of a graphite target in the 1–100-Pa N2 pressure and 1.0–10-J cm−2 fluence domains differ not only in their nitrogen but also in their oxygen content. The (surface) oxygen content correlates well with the compactness of the films. Oxygen contents below approximately 8 at.%, smooth surface, and mass densities above 2.2 g cm−3 are typical of films deposited at low N2 pressures (and high fluences) while deposition at/above 50 Pa results in films of oxygen contents exceeding 12 at.%, rough surface consisting of loosely connected cluster agglomerates, and density values at approximately 1.4 g cm−3. At medium pressures high fluence processing is advantageous in terms of both nitrogen content and film morphology.

Carbon nitride films deposited onto room temperature silicon substrates by ArF excimer laser ablation of a graphite target in nitrogen atmosphere have been investigated after floating off in transmission electron microscope (TEM). All films fabricated in the 1–100 Pa N2 pressure and 1–10 J cm−2 fluence domain are amorphous. It is the nitrogen pressure that governs both the composition and the morphology of the films, the effect of the laser fluence being weaker. The morphologies range from dense films grown in 1–5 Pa N2, to structures composed of carbon nitride clusters and voids between them, obtained at and above 50 Pa N2. Ablation with pulses of high fluence (10 J cm−2) results in more compact films. The oxygen content determined by energy dispersive X-ray spectrometry well correlates with the compactness of the films, being significantly higher in those fabricated at higher pressures and composed of clusters.

Carbon nitride films fabricated by ablating a graphite target in an N 2 atmosphere possess a high affinity for hydrogen incorporation. The differences in both the absolute values and the depth distribution of hydrogen within the films correlate well with changes in mass density. The dense films, deposited at and below 5 Pa N 2 pressure, contain 1.6–3.4 at.% hydrogen with two maxima in the depth distribution, namely one near the surface and another one at the substrate–film interface, suggesting both in situ and ex situ incorporation. Significantly higher hydrogen contents (12.8–16.45 at.%) uniformly distributed throughout the whole thickness characterize the less dense films grown in the 50–100-Pa pressure domain. These films are hydrogenated ex situ as a consequence of the penetration of hydrogen from the atmospheric air through their open structure. The hydrogen content of the unintentionally hydrogenated carbon nitride films is a sensitive indicator of the changes in film microstructure.

Particulate deposition on Bi film prepared by pulsed laser deposition (PLD) was studied by Rutherford backscattering spectrometry (RBS) using a 2 MeV 4 He + scanning microbeam with a lateral resolution of 2 μm. Droplets and particulate-free areas could be detected and separated in the analysis, which offers the possibility of independent measurement of the chemical composition of the thin film and the micron-sized droplets. Tomographic images illustrated thickness inhomogeneities and cross-sectional thickness profile of particulates and gave more detailed information about the surface topography than the RBS spectra themselves. An example is discussed where thicknesses larger than the probing depth could be measured. This unique combination of possibilities makes micro-RBS a powerful technique for the complete analysis of particulate thin films.

International audience; Amorphous carbon nitride films are deposited at room temperature on silicon substrates by ArF excimer laser (193 nm) ablation of a graphite target in nitrogen atmosphere. By tuning the process parameters, fine control of the carbon-carbon and carbon-nitrogen bond configuration is achieved in a broad range as followed by X-ray photoelectron spectroscopy (XPS) and infrared (IR) absorption spectroscopy. Based on the comparative and quantitative analysis of changes in measured IR versus XPS spectra as a function of reactive gas pressure, laser fluence and target-to-substrate distance, and on a critical review of the existing interpretation of IR data, an assignment of the components of the broad band extending from 900 to 1900 cm−1 in the IR spectra to specific carbon-carbon and carbon-nitrogen bond configurations is proposed.

The effects of pulsed laser irradiation on preheated solid metal surfaces have been studied. The surface of low-melting point metals (In and Bi) is irradiated by KrF excimer laser pulses of fluences below 400 mJ/cm2. Evaluation of the optical microscopic pictures of the processed metal surfaces reveals that the characteristic lateral dimension of laser-induced surface structures increases as the melting point is approached. The results are explained in terms of the lifetime of the melt pool, obtained by numerical temperature calculations. Close to the melting point, the increased lifetime of the molten phase allows ample time for smoothing of the surface before its resolidification.

The effect of the mean free path of the ablated species to the target-to-substrate distance ratio on chemical composition and growth rate of carbon nitride films is reported. The composition of the films deposited at room temperature by ablating a glassy carbon target with an ArF excimer laser (193 nm) in 0.3 Torr ammonia was determined by Fourier transform infrared spectroscopy. At fixed pulse energy, the nitrogen content of the films decreases while the hydrogen content remains practically constant with increasing target-to-substrate distance. When the deposition geometry is fixed, increasing pulse energy results in an increase in the nitrogen content.

Experimental results are presented for the excimer laser ablation of highly oriented pyrolytic graphite at 193 and 248 nm for both single pulses and pulse trains in the fluence range of ∼1–15 J/cm2. The morphology and the depth of the ablated pits are monitored by atomic force microscopy, while the material characterization is performed by micro-Raman spectroscopy. A shift from ∼1.12 to ∼2.23 J/cm2 laser fluence is found in the single shot ablation threshold for the 248 nm laser wavelength compared to that at 193 nm. Broad D and G peaks in the Raman spectra indicate the formation of amorphous carbon layers as a result of laser irradiation with 193 and 248 nm pulses. This amorphous layer is present at lower fluences (several J/cm2) and after the very first shots. The modified layer created at 193 nm, compared to 248 nm, consists of optically denser material having more turbostratical/glassy character. The spectra do not show significant changes for fluences exceeding 6–7 J/cm2. A several hundred nanometers-high ring-like structure can be observed around the ablated pits. For laser fluences in excess of the estimated threshold at ∼6 J/cm2 (close to the aforementioned limit), the diameter of this structure increases with laser fluence. One hypothesis to explain the ring formation and the saturation of the Raman spectra supposes that the graphite melts and squirts on the laser irradiation. The ring, debris material and the amorphous layers disappear after heat treatment of the samples at 650°C, most probably by oxidative etching.

Lateral distribution of the 10B isotope within a boron carbide film of 550 nm maximum thickness deposited on silicon wafer using pulsed laser deposition technique has been determined taking advantage of the high cross section for (n,α) reaction and nuclear tracks detectors (NTD – LR-115 Kodak Pathe). A radioisotope neutron source (252Cf, 20 μg) and a 60 × 60 × 80 cm3 graphite cube as moderator produce a relatively uniform thermal neutron field. Details of the passive detector etching process and data processing are included. The track density reveals the boron density spatial distribution. A 3D picture is produced to visualize the boron-10 spatial distribution. The result suggests that a gradient in the boron distribution exists to almost a factor of three. The advantages of the technique are discussed.

An ArF excimer laser (22 ns, 193 nm) and a hybrid dye/excimer laser system (500 fs, 248 nm) are used to deposit amorphous carbon nitride films at room temperature by ablation of a graphite target in nitrogen atmosphere. The chemical composition and structure of the films is characterized by X-ray photoelectron spectroscopy. In the nanosecond case, the nitrogen content increases with reactive gas pressure up to 45 atomic %, while in the subpicosecond case it remains below 7 at. %. When processed with nanosecond pulses, the films’ nitrogen content steeply increases with fluence up to a maximum. The target-to-substrate distance has only minor influence on the amount of nitrogen incorporated into the films. The dependence of the carbon–carbon and carbon–nitrogen bond configurations on the processing parameters is also given.

Can particulates formation in general be avoided by using liquid targets, or only can particulates deposition be suppressed by choosing appropriate experimental circumstances? In order to answer this question, which is of general importance in pulsed laser deposition, we deposited indium, tin and bismuth films from the respective metal targets both in solid and liquid form, in vacuum. The substrates were held at room-temperature, in order to collect and preserve the droplets if formed. Ablating molten targets, the appearance of droplets of diameter exceeding microns can completely be eliminated. The particulates number density of indium and tin films decreased by two orders of magnitude as compared to the solid-target case. However, even in these cases, particulates formation could not be totally eliminated. The thickness distribution of the film material becomes broader when deposited from molten target.