Ultra-short Pulsed Laser Deposition Research Articles

Improvement of Al thin film morphology with picosecond pulsed laser deposition in burst mode

We studied the influences of the number of sub-pulses within a burst on the surface morphology of Al thin films deposited by picosecond pulsed laser. It can be demonstrated that with an increasing number of sub-pulses within a burst, both the thin film morphology and the surface roughness are gradually improved. Several physical mechanisms are proposed to explain the reduction in the size of particulates inside and on the film surface. The burst mode not only alleviates the inherent particulates generation of ultra-short pulsed laser deposition also provides a higher degree of freedom in the tunability of the film surface.

Ultra-Short Pulsed Laser Deposition of Oxides, Borides and Carbides of Transition Elements

Oxides, borides and carbides of the transition elements are materials of great interest from a technologic point of view. Many of these materials are used in the form of thin films, so several techniques are commonly used to deposit them. Among these techniques, Pulsed Laser Deposition (PLD) performed using ultra-short pulse lasers, mainly fs lasers, presents unique characteristics in respect to PLD performed using conventional short pulse lasers. Indeed, the films deposited using fs PLD are often nanostructured, and this technique often allows the target stoichiometry to be transferred to the films. In this work, we will review the use of ultra-short PLD in the production of films obtained from transition metal oxides, borides and carbides, evidencing the advantages offered by this technique, together with the problems arising with some of the studied systems. We conclude that even if ultra-short PLD is surely one of the most important and useful deposition techniques, it also presents limits that cannot be ignored.

Electrochemical Performance of Uspld Prepared Silicon Anode Electrodes

Introduction Secondary battery materials are in great demand of research and new high energy density materials are required for higher quality of batteries1. Silicon based anode is one of the most promising anode material for Li-ion batteries, because it has high theoretical capacity (4200 mAh/g, lithiated to Li4.4Si) and low operating voltage (~0.3V versus Li/Li+) 2,3 Challenges for silicon based anode are the capacity fading during the first cycle and the poor cycle performance. Experimental Si layers on copper foil were produced by Picodeon’s ultra-short pulsed laser deposition (USPLD) technology. This technology utilizes pulsed lasers with pulse lengths in the picosecond range and high pulse repetition rates (MHz). The pulsed laser beam is delivered to the surface of the target, which is placed inside a vacuum chamber, through a scanner and a telecentric lens. With this beam delivery approach a focused scan line can be produced on the target. Material is removed by the laser pulses from the target material, and movement of the substrate through the material cloud generated by this line source enables straightforward deposition of uniform layers even on larger surface areas. Cells with USPLD prepared Silicon anode and LiNi0.5Co0.2Mn0.3O2 cathode were prepared in the humidity controlled dry room. Cathode thicknesses were controlled to have different specific capacities for the silicon anode material. Different type of electrolytes and testing parameters were used to achieve better electrochemical results for USPLD silicon anodes. Results and discussion Results showed that electrochemical testing parameter and materials used in the tests have great influence on the electrochemical performance of silicon anode materials. Especially, additives used in the electrolyte seems to have a great influence on the cycle performance of silicon based anode material. Results also showed that silicon material should not charge full, instead 1500 mAh/g show much better electrochemical properties. Results also clarified some problems with half-cell and full-cell tests. We have demonstrated that the 10µm thick 100% silicon anode layer prepared by USPLD can replace 50µm graphite layer in the Li-ion cell. Total energy density is higher for silicon-NCM cell than for graphite-NCM cell after hundred cycles. Still challenge is the poor cycle performance compared to graphite anode; however, results showed that it is possible to improve cycling properties by electrolyte additives and limiting charging capacity. Silicon based anode material is a good candidate for the next generation Li-ion battery. Reference s : W Choi and D. Aurbach (2016) Nature rewiew materials 1. (2016) 16013A Huggins (1999) Journal of Power Sources, Vol 81-82, pp.13-19Hui Wu, Yi Cui (2012) Nanotoday, Vol 7, issue 5, pp 414-429

Improvements in the thread cutting torque for a 6082-T6 aluminum-based alloy with tapping tools utilizing diamond coating

ABSTRACTThe use of thin film diamond as a hard tool coating offers a significant wear protection in numerous machining operations and increases considerably tool's lifetime. The extreme hardness of the diamond is especially needed in machining highly abrasive materials such as aluminum-silicon alloys. Tapping is widely used for thread fabrication and it is often a time consuming process causing a delay on an automated production line. This study investigated diamond coatings in thread cutting and the aim was to gain knowledge about the performance of diamond-coated taps. PVD diamond coatings were deposited using ultra short pulsed laser deposition (USPLD) techniques. Another type of nanodiamond coating was a chrome-nanodiamond (CND) coating deposited by a two-phase electrochemical process to produce a metal matrix with embedded detonation nanodiamond (DND) particles. The main points were the analysis of tool torques of the thread machining data, sticking of aluminum alloy and wear behavior and mechanism of tested tapping tools. The tested tools were analyzed by Scanning Electron Microscopy (SEM) regarding tool wear and sticking of aluminum on tool surface caused by mechanical interaction. Coating approaches turned out to provide 13–30% improvements in cutting and 37–51% improvements in reversing for overall mean torques compared to uncoated reference tools.

Optically transparent and durable Al2O3 coatings for harsh environments by ultra short pulsed laser deposition

Nowadays, an environmental protection is needed for a number of optical applications in conditions quickly impairing the clarity of optical surfaces. Abrasion resistant optical coatings applied onto plastics are usually based on alumina or polysiloxane technology. In many applications transparent glasses and ceramics need a combination of abrasive and chemically resistant shielding or other protective solutions like coatings. In this study, we intended to test our hypothesis that clear and pore free alumina coating can be uniformly distributed on glass prisms by ultra short pulsed laser deposition (USPLD) technique to protect the sensitive surfaces against abrasives. Abrasive wear tests were carried out by the use of SiC emery paper using specified standard procedures. After the wear tests the measured transparencies of coated prisms turned out to be close those of the prisms before coating. The coating on sensitive surfaces consistently displayed enhanced wear resistance exhibiting still high quality, even after severe wear testing. Furthermore, the coating modified the surface properties towards hydrophobic nature in contrast to untreated prisms, which became very hydrophilic especially due to wear.

Decoration of silica nanowires with gold nanoparticles through ultra-short pulsed laser deposition

The ablation of a metal target at laser energy densities in the range of 1–10 TW/cm2 leads to the generation of nanoparticles (NP) of the ablated material. This aspect is of particular interest if the immobilization of NPs on three-dimensional (3D) substrates is necessary as for example in sensing applications. In this work the deposition of Au NP by irradiation of a Au bulk target with a sub-picosecond laser beam (500fs; 248nm; 10Hz) on 2D (silica and Si(100)) and 3D substrates (silica nanowire forests) is reported for different number of laser pulses (500, 1000, 1500, 2000, 2500). A uniform coverage of small Au NPs (with a diameter of few nm) on both kinds of substrates has been obtained using a suitable number of laser pulses. The presence of spherical droplets, with a diameter ranging from tens of nm up to few μm was also detected on the substrate surface and their presence can be explained by the weak electron-phonon coupling of Au. The optical characterization of the samples on 2D and 3D substrates evidenced the surface plasmon resonance peak characteristic of the Au NPs although further improvements of the size-distribution are necessary for future applications in sensing devices.

Behavior of Human Bone Marrow-Derived Mesenchymal Stem Cells on Various Titanium-Based Coatings.

The chemical composition and texture of titanium coatings can influence the growth characteristics of the adhered cells. An enhanced proliferation of the human mesenchymal stem cells (hMSCs) would be beneficial. The present study was aimed to investigate whether titanium deposited at different atmospheres would affect the cell growth properties, cellular morphology, and expression of surface markers of hMSCs. Titanium-based coatings were deposited on silicon wafers under oxygen, nitrogen, or argon atmospheres by ultra-short pulsed laser deposition using two different gas pressures followed by heating at 400 °C for 2 h. The characteristics of the coated surfaces were determined via contact angle, zeta potential, and scanning electron microscopy (SEM) techniques. Human MSCs were cultivated on differently coated silicon wafers for 48 h. Subsequently, the cell proliferation rates were analyzed with an MTT assay. The phenotype of hMSCs was checked via immunocytochemical stainings of MSC-associated markers CD73, CD90, and CD105, and the adhesion, spreading, and morphology of hMSCs on coated materials via SEM. The cell proliferation rates of the hMSCs were similar on all coated silicon wafers. The hMSCs retained the MSC phenotype by expressing MSC-associated markers and fibroblast-like morphology with cellular projections. Furthermore, no significant differences could be found in the size of the cells when cultured on all various coated surfaces. In conclusion, despite certain differences in the contact angles and the zeta potentials of various titanium-based coatings, no single coating markedly improved the growth characteristics of hMSCs.

Improved multilayer coatings by combined use of electrochemical and ultra-short pulsed laser deposition techniques

Abstract Electrochemical and ultra-short pulsed laser deposition (USPLD) methods were combined to produce multilayer coatings on various base materials that are challenging to be coated by using traditional electrochemical techniques. A thin and well-adherent metallic intermediate layer was coated on each base material by USPLD method before final nickel or nickel-trivalent chrome coating by electrochemical methods. In this way, the pretreatment steps for electrochemical deposition were simplified compared with traditional methods and hazardous chemicals were not used during the pretreatment process. The morphology, coating thickness and the elemental composition of the multilayer coatings were analyzed using scanning electron microscope (SEM) coupled with Energy Dispersive X-ray spectroscopy (EDS), and the adhesion strengths of each coating were tested by scratch and pull-off tests. The results show good adherence for all studied coatings on aluminum alloy (6082) and stainless acid-proof steel (SS316L), whereas obtaining a sufficient adhesion of coatings on glass (borosilicate) and polycarbonate (PC) requires a correct choice of coating materials and process steps. The critical loads in scratch test are approximately 20 N for coatings on aluminum and glass, at least 50 N for coatings on SS316L and approximately 5 N for coatings on PC. In pull-off tests, maximum adhesion strengths for coatings on aluminum and SS316L are approximately 25 MPa for electroless coatings and 10 MPa for electroplated coatings. Coatings on glass and PC reach adhesion strengths of approximately 4–9 MPa, which is sufficient for many applications.

Fabrication of Nb/Pb structures through ultrashort pulsed laser deposition

This work reports the fabrication of Nb/Pb structures with an application as photocathode devices. The use of relatively low energy densities for the ablation of Nb with ultrashort pulses favors the reduction of droplets during the growth of the film. However, the use of laser fluences in this ablation regime results in a consequent reduction in the average deposition rate. On the other hand, despite the low deposition rate, the films present a superior adherence to the substrate and an excellent coverage of the irregular substrate surface, avoiding the appearance of voids or discontinuities on the film surface. Moreover, the low energy densities used for the ablation favor the growth of nanocrystalline films with a similar crystalline structure to the bulk material. Therefore, the use of low ablation energy densities with ultrashort pulses for the deposition of the Nb thin films allows the growth of very adherent and nanocrystalline films with adequate properties for the fabrication of Nb/Pb structures to be included in superconducting radiofrequency cavities.

Pulsed laser ablation and deposition of niobium carbide

NbC crystalline films have been deposited in vacuum by ultra-short pulsed laser deposition technique. The films have been characterized by transmission and scanning electron microscopies and by X-ray diffraction. To clarify the ablation–deposition mechanism, the plasma produced by the ablation process has been characterized by optical emission spectroscopy and fast imaging. A comparison of the results with those obtained by ns pulsed deposition of the same target has been carried out.

Picosecond and subpicosecond pulsed laser deposition of Pb thin films

Pb thin films were deposited on Nb substrates by means of pulsed laser deposition (PLD) with UV radiation (248 nm), in two different ablation regimes: picosecond (5 ps) and subpicosecond (0.5 ps). Granular films with grain size on the micron scale have been obtained, with no evidence of large droplet formation. All films presented a polycrystalline character with preferential orientation along the (111) crystalline planes. A maximum quantum efficiency (QE) of $7.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ (at 266 nm and 7 ns pulse duration) was measured, after laser cleaning, demonstrating good photoemission performance for Pb thin films deposited by ultrashort PLD. Moreover, Pb thin film photocathodes have maintained their QE for days, providing excellent chemical stability and durability. These results suggest that Pb thin films deposited on Nb by ultrashort PLD are a noteworthy alternative for the fabrication of photocathodes for superconductive radio-frequency electron guns. Finally, a comparison with the characteristics of Pb films prepared by ns PLD is illustrated and discussed.

Growth of strongly textured FeCO 3 $\mathrm{FeCO}_{3}$ thin films for application in research of nuclear quantum optics with ultrashort-pulsed laser deposition

Growth of strongly textured $\mathrm{FeCO}_{3}$ thin films on substrates was achieved with ultrashort-pulsed laser deposition using 810-nm, 46-fs ablation pulses. The crystallinity and composition were verified with X-ray diffraction and Raman spectroscopy. Using Mossbauer spectroscopy, it is shown that the deposited $\mathrm{FeCO}_{3}$ thin films possess the film quality required for application in research of nuclear quantum optics. It is found that a relatively low substrate temperature is crucial for growing a strongly textured film of $\mathrm{FeCO}_{3}$ while avoiding decomposition of $\mathrm{FeCO}_{3}$ into $\mathrm{Fe}_{2}\mathrm{O}_{3}$ and $\mathrm{CO}_{2}$ . This supports the importance of the use of ultrashort-pulsed laser deposition in providing adatoms with high mobility for attaining good crystallinity. The surface morphology was characterized by surface profilometry, scanning electron microscopy and atomic force microscopy. It is found to be significantly affected by changing the ablation laser parameters, including laser fluence, pulse duration, and on-target spot size. The results show that the peak deposition flux must be below approximately 0.03 nm/pulse in order to grow a flat film.

TiO2 coating promotes human mesenchymal stem cell proliferation without the loss of their capacity for chondrogenic differentiation

Human mesenchymal stem cells (hMSCs) are used in applications, which may require a large amount of cells; therefore, efficient expansion of the cells is desired. We studied whether TiO2 coating on plastic cell culture dishes could promote proliferation of hMSCs without adverse effects in chondrogenic differentiation. TiO2-films were deposited on polystyrene dishes and glass coverslips using an ultrashort pulsed laser deposition technique. Human MSCs from three donors were expanded on them until 95% confluence, and the cells were evaluated by morphology, immunocytochemistry and quantitative RT-PCR (qRT-PCR). The chondrogenic differentiation in pellets was performed after cultivation on TiO2-coated dishes. Chondrogenesis was evaluated by histological staining of proteoglycans and type II collagen, and qRT-PCR. Human MSC-associated markers STRO-1, CD44, CD90 and CD146 did not change after expansion on TiO2-coated coverslips. However, the cell number after a 48h-culture period was significantly higher on TiO2-coated culture dishes. Importantly, TiO2 coating caused no significant differences in the proteoglycan and type II collagen staining of the pellets, or the expression of chondrocyte-specific genes in the chondrogenesis assay. Thus, the proliferation of hMSCs could be significantly increased when cultured on TiO2-coated dishes without weakening their chondrogenic differentiation capacity. The transparency of TiO2-films allows easy monitoring of the cell growth and morphology under a phase-contrast microscope.

Stepwise behaviour of magnetization temperature dependence in iron nanoparticle assembled films

An unusual stepwise behaviour is reported in the temperature dependence of the zero field cooled magnetization in iron nanoparticle dense films produced by ultra-short pulsed laser deposition assisted by irradiation of nanoparticles with a nanosecond UV laser pulse, appropriately delayed, during their flight from the target to the substrate. This behaviour, induced by the particle system’s morphology, characterized by clusters of tightly coupled nanoparticles as well as by some voids between them, is ascribed to the competition between Zeeman energy density, intracluster anisotropy energy density and intercluster exchange energy density. A phenomenological model and Monte Carlo simulations are reported, which support the proposed interpretation.

Osteoblast behavior on various ultra short pulsed laser deposited surface coatings

Ultra short pulsed laser deposition technique was utilized to create amorphous diamond, alumina and carbon nitride, and two different titania coatings on silicon wafers, thus producing five different surface deposited films with variable physico-chemical properties. The surface characterizations, including the roughness, the contact angle and the zeta potential measurements were performed before we tested the growth properties of human osteoblast-like Saos-2 cells on these surfaces (three separate experiments). The average roughness and hydrophobicity were the highest on titania-deposited surfaces, while carbon nitride was the most hydrophilic one. Osteoblasts on all surfaces showed a flattened, spread-out morphology, although on amorphous diamond the cell shape appeared more elongated than on the other surfaces. On rough titania, the area covered by the osteoblasts was smaller than on the other ones. Cell proliferation assay did not show any statistically significant differences.

Ultra-short pulsed laser deposition of thin silver films for surface enhanced Raman scattering

Nanostructured thin films have been obtained by ultra-short pulsed laser deposition (PLD) of silver performed in vacuum. The ablation source used in these experiments was a frequency doubled (λ=527nm) Nd:glass laser with a pulse duration of 250fs. The films have been characterized by UV–vis spectroscopy, atomic force microscopy and transmission electron microscopy. The surface enhanced Raman scattering activity results, investigated by Raman scattering of rhodamine B adsorbed onto rough silver substrates, are strongly related to the effective surface area (ESA) of the silver surfaces. Surprisingly, silver films obtained by ultra-short PLD are very similar to those obtained by short PLD. With the aim of explaining this likeness, the dynamics of plasmas induced by short and ultra-short laser pulses have been studied by optical emission spectroscopy and fast imaging. Composition, velocity, excitation temperature and density of short and ultra‐short plasmas are quite similar, showing that film properties are strongly related to the plasma features.

Y thin films by ultrashort pulsed laser deposition for photocathode application

In this work, the deposition of Y thin films by laser beams with 0.5ps and 5ps pulse durations at different laser fluences (1.2–6.4J/cm2) is reported. The morphology of the deposited films and of the ablated target surface is investigated by scanning electron microscopy analyses. The present results show that the films, well adherent to the substrates, are characterized by a high abundance of sub-micrometric particulates with average size less than 0.3μm, whose density decreases with increasing laser fluence. The formation of columnar structures observed on the target surface seems to be responsible of the poor film homogeneity. Acceptable deposition rate in the range of 0.08–0.16Å/pulse with 5ps pulse duration is found; on the contrary with 0.5ps pulse duration, it is not possible to get information on deposition rate as a function of the laser fluence due to the high non-uniformity of the films. A comparison with the results previously obtained in ns regime is presented and discussed. The achievements of our investigation will be useful to optimize the synthesis of photocathodes based on Y films for the production of bright electron beams in radio-frequency photoinjectors.

Thin films deposited by femtosecond pulsed laser ablation of tungsten carbide

Ultra-short Pulsed Laser Deposition has been applied to the production of thin films from a tungsten carbide target. The gaseous phase obtained by the laser ablation shows a very weak primary plume, in contrast with a very strong secondary one. The deposited films, investigated by Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and X-Ray Diffraction, present a mixture of WC and other phases with lower carbon content. All films are amorphous, independently from the substrate temperature. The characteristics of the deposits have been explained in terms of thermal evaporation and cooling rate of molten particles ejected from the target.

Diamond-like carbon thin films produced by femtosecond pulsed laser deposition of fullerite

Diamond-like carbon films have been deposited from a fullerite target by ultra-short pulsed laser deposition technique. The results indicate that the films morphology and structure, determined by scanning electron microscopy, atomic force microscopy and energy dispersive X-ray diffraction, depend strongly on the substrate temperature. X-ray photoelectron, X-ray Auger electron, Raman and surface enhanced Raman scattering spectra indicate that the fs-DLC films composition involves a mixed sp, sp2 and sp3 carbon network consisting of aromatic rings and sp3 diamond-like structures linked by chains of different lengths and composition. The films deposited at room temperature, presenting the higher content of sp3 carbon (48%), also contain C60 crystalline phase and show a very high hardness of 49GPa.

Nanoparticles and Thin Film Formation in Ultrashort Pulsed Laser Deposition of Vanadium Oxide

The ultrashort pulsed laser deposition of vanadium oxide thin films has been carried out by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The characteristics of the plasma produced by the laser-target interaction have been studied by ICCD imaging and optical emission spectroscopy. The results confirm that an emitting plasma produced by ultrashort laser pulses is formed by both a primary and a secondary component. The secondary component consists of particles with a nanometric size, and their composition and spatial angular distribution influence the deposited films. In fact, these films, analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are formed by the aggregation of a large number of nanoparticles whose composition is explained by a model based on equilibrium thermal evaporation from particles directly ejected from the target. On these basis, the presence in the films of a mixture of V(2)O(5) and VO(2) is discussed.