Publications

Pulsed laser-based material removal is a preferred micro-scribing technique for Copper (Cu) cladded onto an insulating substrate, such as a flame-retardant glass-reinforced epoxy resin (FR4), because of the less thermal diffusion as well as the process flexibility. This paper reports the pulsed laser-assisted micro-scribing of Cu (35 µm) from a dielectric material. The process was monitored by laser-induced breakdown spectroscopy technique (LIBS). For the complete removal of Cu from the substrate material, multiple laser scans were required. The Cu I line intensity in the LIBS spectra was decreasing with an increase in the microchannel depth. During the final laser scan, the FR4 substrate was getting ablated, and in the LIBS spectra, the characteristic emission lines from the substrate elements such as Calcium (Ca), Aluminum (Al), Sodium (Na) and Silicon (Si) were observed. The depth for a single laser pulse was estimated from a theoretical model, including the melt ejection due to the recoil pressure. Approximate microchannel depth was predicted based on the theoretical simulation.

High intensity lasers (>1019 W/cm2) produce relativistic electrons when they interact with matter. The high energy electrons upon incidence on a solid target produce secondary emissions like protons, neutrons, positrons, x-ray emission and γ-rays1. Gamma rays produce from this interaction can be used to induce photoneutron reaction in a material, thereby producing short-lived isotopes or isomers2. The isotopes or isomers produced can be used for diagnosing the radiation flux and directionality3. Materials with short half-lives (in μs to ms time scale) are of interest as a diagnostic for shot to shot measurement of parameters in high repetition lasers (10 Hz), since they decay well before the incidence of the subsequent pulse on the material. For understanding the working of this diagnostic, systematic studies of decay of the isotopes/isomers produced and the attenuation of γ-rays in the material are necessary. The design and efficiency of a diagnostic for characterizing γ-rays using the method of nuclear activation for 10 Hz high repetition laser is presented.

In this work, ceramic reinforcement of soft Ag–Cu–Ti filler alloy has been attempted to produce a superior filler alloy to braze cBN to steel in high vacuum conditions without compromising wettability and joint strength. 2 and 5 wt% of micro-alumina (μAl2O3) particles of average particle size (APS) 10 μm were added to Ti-activated (2 wt%) eutectic (72Ag28Cu) filler alloy as reinforcements for brazing Cubic Boron Nitride (cBN) particles (APS: 427 μm) to steel substrate. The alloy-matrix wetted μAl2O3 particles appreciably. Cu3Ti3O phase formed (confirmed through TEM/SAED-pattern analyses) and grew surrounding the μAl2O3 particles with a very thin interlayer of γ-TiO. Nano-hardness of Cu3Ti3O was measured to be 17.62.42 GPa. Cu3Ti3O together with μAl2O3 particles resulted in substantially enhanced (63–76%) abrasion-resistance characteristics of the primary alloy. 5 wt% addition of μAl2O3 to Ag–Cu–2Ti alloy displayed superior performance to 2 wt% addition. However, with higher proportion (5 wt%), wettability of the reinforced filler on cBN part got slightly impaired. Few micro-voids also surfaced on cBN-encapsulating bonding layer. Considering joint strength and wettability, 2 wt% of μAl2O3 is recommended to produce brazed cBN tools for high-impact load applications.

Laser-assisted doping of intrinsic silicon carbide (SiC) films deposited on Si (100) substrates by pulsed laser deposition (PLD) method and its influence on simultaneous annealing of the thin film is studied. PLD grown intrinsic SiC films are transformed to p-type SiC and n-type SiC, using laser-assisted doping in aqueous aluminum chloride and phosphoric solutions, respectively. Simultaneous doping and annealing of the SiC film are observed during laser-assisted doping. By precisely positioning the selectively doped region, lateral p–n diodes are formed on the SiC films without using any mask. Electric characteristics confirmed the formation of a lateral p–n diode structure. Numerical analysis of temperature distribution along the depth of the SiC films explains the mechanism of simultaneous doping and annealing during the laser treatment.

Superhydrophobic and hydrophobic surfaces on Al and Cu have a wide range of applications in electronics, industrial devices, air conditioning, and refrigeration plants, and home appliances due to their excellent electrical and thermal characteristics. In many of these applications, the wettability of their surface is essential. This work presents the fabrication of superhydrophobic and hydrophobic surfaces on Al and hydrophobic surfaces on the Cu metal sheets via laser processing and aging without any additional chemical treatment. Texturing with laser spot overlap is used to generate naturally formed nanoscale textures by scanning the whole sample surface. The influence of laser parameters on the dimension and shape of the fabricated surface textures and their impact on wettability is analyzed along with the evolution of wetting behavior over time. The laser textured surfaces, which are initially hydrophilic, are found to transform hydrophobic over time upon exposure to atmospheric conditions. Experimental evidence using X-ray photoelectron spectroscopy (XPS) and ATR-FTIR spectroscopy corroborates this transition is owing to the adsorption of organic molecules present in ambient. The depth profiling using XPS reveals carbon contamination around 60–70 nm from the sample surface. Furthermore, textures exhibiting static contact angles of up to ~154° have been achieved with Al sheets, whereas contact angles up to ~122° have been attained in the Cu sample. These experimental findings enable control of wettability of Al and Cu sheets through precise tuning of laser parameters for desired properties.