In this paper an efficient method is proposed to measure the geometric dimensions of a microchannel bonded by a
transparent top plate by employing the techniques of quick vertical scan of featured surfaces, detailed multi-layer
sampling of depth response curves (DRC), and measurement of the refractive index of transparent top plate. The featured
surfaces with profile fluctuation in the micro scale are scanned with high vertical resolution. The absolute height of each
surface is determined by the peak point of the corresponding DRC. Since the DRCs are only sampled in the central area
the processing speed is acceptable even with a large scanning length. The results of the measured depth should be
corrected by the refractive index. Only in the same material does the focal point move at the same speed during the
scanning motion. In this study an inverse measurement scheme is proposed to calculate the refractive index of a
transparent plate without prior calibration. Any measurable steps on the sample surface can be used as the sampling area.
By scanning the same area from both sides different sectional profiles can be extracted. The ratio of the different steps is
the refractive index.
Titanium dioxide (TiO<sub>2</sub>) films were rendered hydrophilic through ultraviolet (UV) light irradiation (254nm) and returned
to their previous hydrophobic condition when exposed to a sealed pressurized nitrogen atmosphere. UV light irradiation
on TiO<sub>2</sub> films resulted in super-hydrophilic surfaces with water contact angles of <5°. Alternatively, exposure of the
films to an N<sub>2</sub> environment resulted in relatively hydrophobic surfaces with water contact angles of >40°. The switching
of TiO<sub>2</sub> surface wettability could be repeated on the same surface with little hysteresis in water contact angle values. The
mechanism behind the hydrophilic and hydrophobic reversal in TiO<sub>2</sub> surfaces is proposed to be due to UV light mediated
photocatalysis and physio- adsorption of N<sub>2</sub> molecules respectively. The non-intrusive control of TiO<sub>2</sub> surface wettability
could be an attractive alternative to other wettability-based microfluidic valving strategies like electrowetting and
photochromic wetting variation. The above results are discussed in terms of the potential use of the films in wettability
based valving and repeated wettability patterning of TiO<sub>2</sub> surfaces for open and sealed microfluidic systems.
Material removal at the sub-micron level has been a topic of interest in the past few years, particularly with respect to the
fabrication of miniaturized devices. While numerous techniques have been developed and refined from their larger mesoscale
counterparts (e.g. microEDM, micromilling), most have inherent limitations such as tool dimensions restricting the
minimum feature which can be produced.
In this work, we are proposing a novel technique of using the electrokinetic phenomenon for precise material removal at
rates in the order of nanometers/min. An AC electric field with a DC offset is applied to a flowing fluid containing
suspended particles which will then collide with the workpiece material causing material wear and tear and thus material
Results showed that the technique was feasible in achieving sub-micron material removal in micro-channels up to a
depth of several hundred nanometers. With no chemicals involved in the process, the technique offers the further
attraction of being a benign nano-manufacturing process with potential usage in the biochip and microfluidics areas.