Modification of anodised aluminium surfaces using a picosecond fibre laser for printing applications.

The use of an ultrafast fibre laser at a wavelength of 1064 nm has allowed the surface modification of anodised aluminium plates coated with a 2 micron thick anodised layer for potential industrial applications. The micro- and nano-scale structuring of the anodised aluminium using picosecond pulses of approximately 25 ps duration at 200 kHz repetition rate was investigated. The interaction of the laser with the substrate created a hydrophilic surface, giving a contact angle of less than 10 degrees. On examination under a Scanning Electron Microscope (SEM), a morphology created due to laser induced spallation was observed. It has been found that these laser processed hydrophilic surfaces revert to a hydrophobic state with time. This has potential for application in the printing industry and offers reusability and sustainability of the process materials. This has been confirmed in initial trials.

Surface modification of anodised aluminium using a femtosecond laser.

Femtosecond laser pulses at 775 nm, combined with a scanning galvonometer system, have allowed the micro scale structuring of an aluminium plate coated with a 2 micron thick anodised aluminium layer for potential industrial applications. The micro-scale structuring of aluminium was investigated using ultrafast pulses of 180 fs duration at a repetition rate of 1 kHz. Under suitably optimised conditions, the interaction of the laser pulses with the substrate created a hydrophilic surface with a contact angle of less than 10 degrees. These surfaces revealed a 'lotus-leaf' like morphology when examined under a Scanning Electron Microscope (SEM). It has been found that these laser processed hydrophilic surfaces revert with time and they undergo this cycle of alternate hydrophilic/hydrophobic behaviour several times upon exposure to the laser pulses. Their potential application in the printing industries is strong due to their reusability and sustainability; initial trials on printing confirm this. This technology would offer extra advantages as a non-chemical process without the need for developer, thereby reducing the overall cost and time of printing.

The influences of particle number on hot spots in strongly coupled metal nanoparticles chain.

In understanding of the hot spot phenomenon in single-molecule surface enhanced Raman scattering (SM-SERS), the electromagnetic field within the gaps of dimers (i.e., two particle systems) has attracted much interest as it provides significant field amplification over single isolated nanoparticles. In addition to the existing understanding of the dimer systems, we show in this paper that field enhancement within the gaps of a particle chain could maximize at a particle number N>2, due to the near-field coupled plasmon resonance of the chain. This particle number effect was theoretically observed for the gold (Au) nanoparticles chain but not for the silver (Ag) chain. We attribute the reason to the different behaviors of the dissipative damping of gold and silver in the visible wavelength range. The reported effect can be utilized to design effective gold substrate for SM-SERS applications.

A preliminary investigation of the electrochemical properties of a nitrided stainless steel for dental applications.

A comparison has been made of the electrochemical behaviour of investment cast coupons of a 20Cr, 25Ni, Ti stabilized stainless steel (in the nitrided and un-nitrided conditions) with a cobalt-chromium alloy in order to make a preliminary assessment from the point of view of corrosion of the nitrided material for dental and other biomedical applications. Electrochemical tests have been carried out in vitro in artificial saliva and in Ringer's solution, with some additional tests carried out in natural saliva. Both the potential-time behaviour and the magnitude of the breakdown potential on anodic polarization suggest that the protective properties of the passivating film are substantially improved in the case of the nitrided stainless steel alloy.