White Light Interferometry Analysis Research Articles

Annealing study of two-dimensional patterned Ge nanostructures via nanosphere lithography

Abstract Experimental studies on patterning hexagonal Ge nanostructures have been conducted on Si substrates through deposition of Ge with colloidal particles as a mask. The deposited Ge thin film possesses, according to the X-ray diffraction measurements, in plane texture, being epitaxial and aligned with the (111) Si substrate. The size distribution of the patterned Ge nanostructures is narrow, as indicated by the atomic force microscopy and scanning electron microscopy measurements. We have obtained Ge nanostructures with lateral dimension of 490 nm (height 12 nm), 200 nm (height 6 nm) and 82 nm (height 6 nm) by using different sizes of polystyrene spheres. We have performed in depth studies of the Ge nanostructures’ behavior due to thermal and rapid thermal post-annealing processes. FT micro-Raman spectroscopy shows that there is no Si intermixing during the annealing process. In order to quantify the changes in the height and lateral dimension, we have performed atomic force microscopy and white light interferometry analysis. The changes in shape and the decrease in the area of a cross-section of Ge nanostructure will be discussed in respect to similar results shown in the literature for Ge thin films during the annealing process.

Preferential Grain Etching of AlMgSi(Zn) Model Alloys

Preferential grain etching is a problem occurring on aluminum products during alkaline etching prior to anodizing, especially if the etching bath contains small amounts of dissolved Zn. The visually uneven, “grainy” surface is caused by different etch rates for different grains, giving a terracelike surface topography. Polished samples of an AlMgSi alloy with different amounts of Zn were etched in NaOH solution. Grain orientations in selected areas were determined by electron backscatter diffraction. The low-Zn samples did not show preferential grain etching. On the higher-Zn alloys, grains with surface planes close to {111} were found to etch at a higher rate than those with other orientations. Secondary ion mass spectrometry depth profiling and imaging, combined with white light interferometry analysis, showed a clear correlation between the deep lying grains and a surface enriched in Zn, suggesting that Zn enrichment by alkaline etching occurred by selective dissolution of aluminum rather than a dissolution–redeposition mechanism. Zn-enriched grains become more active than the other grains as a result of a decrease in the rate of the water reduction reaction.

Laser ablation—laser induced breakdown spectroscopy (LA-LIBS): A means for overcoming matrix effects leading to improved analyte response

Laser-ablation laser-induced breakdown spectroscopy (LA-LIBS) is proposed as a novel analytical scheme with goals of improved analyte response, minimization of sample matrix effects, and use of non-matrix matched standards. A direct comparison of the LA-LIBS approach and a traditional direct LIBS analysis was made for a set of seven reference materials, ranging from nearly pure iron to copper-nickel and aluminum alloys. The precision of each approach was assessed using calibration curves, and the LA-LIBS configuration was demonstrated to consistently produce a superior analytical response, as assessed by the linear least-squares fit correlation coefficient and y-intercept values. Significantly, the normalized (by Fe) response of the four targeted analyte species (Al, Mn, Mg and Cu) was successfully reduced to a single calibration curve with the LA-LIBS approach. In addition, particle size measurements of the laser-ablation plume were recorded along with SEM and white-light interferometry analysis of ablation craters for assessment of the analytical sample as presented to the analytical LIBS plasma. Finally, the effect of carrier gas is explored by substitution of nitrogen with helium.

Effects of laser repetition rate on corneal tissue ablation for 193‐nm excimer laser light

The goal of the present work is to assess whether bovine corneal ablations generated at laser repetition rates of up to 400 Hz are comparable to ablations performed at rates consistent with current clinical laser systems. A combination of experiments was used to assess a comprehensive range of ablation parameters, including ablation plume dynamics via imaging and transmission, corneal ablation profiles via scanning interferometry, and high-resolution electron microscopy of collagen structure following ablation. Using white-light interferometry analysis, no statistical difference was found between corneal ablation profiles created at 60 and 400 Hz, with an average rate of 0.94 microm/pulse at 60 Hz versus 0.92 microm/pulse at 400 Hz. In addition, based on plume imaging and transmission studies, the bulk ablation plume was found to dissipate on a time-scale less than the pulse-to-pulse separation for a laser repetition rate up to about 400 Hz. A persistent, diffuse gas-phase component of the ablation products was observed and concluded to be comparable at both repetition rates. Finally, SEM and TEM analysis revealed no signs of differential thermal tissue damage, including collagen fibril analysis, for laser repetition rates up to 400 Hz. In summary, investigation of the relative effects of excimer laser repetition rate on the overall corneal ablation metrics revealed no measurable difference under conditions typical of clinical refractive procedures. This study suggests that increases in ArF laser repetition rates for clinical applications (up to approximately 400 Hz) appear feasible.