Predicting the wettability of patterned ITO surface using ToF‐SIMS images

Abstract

Partial least squares (PLS) regression has been increasingly used as a tool for modelling linear relations between multivariate surface analytical measurements and measures of performance. However, the use of PLS to obtain quantitative predictions has only been partially explored. In this study, we construct a PLS model using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and water contact angle (WCA) data obtained from a series of differently treated indium tin oxide (ITO) surfaces. This model displays a reasonable correlation between the WCA values and the SIMS data. To validate the model, ITO surfaces patterned with different areas of wettability were examined using ToF-SIMS imaging to produce WCA maps. The PLS model was applied to predict the spatial variation in WCA across the sample. The direct measurement of WCA on the patterned ITO surface was achieved using a small-scale interval grid from picolitre volume water droplets. We present the correlations between the predicted WCA from SIMS and the measured WCA, and highlight the discrepancies that arises in the comparison of the two datasets. This work is of direct benefit to industries where wettability is crucial but direct contact angle measurements are acquired on a scale smaller than it is possible to produce liquid drops, such as the plastic electronics and microfluidics industries.

Correlations for predicting the surface wettability for organic light-emitting-diode patterns by x-ray photoelectron spectroscopy analysis

“…Earlier work in this system, 11 using PLS analysis with SIMS with detailed spectra covering many significant spectral peaks but from maps where the signal levels were low, led to correlations of the predicted and measured contact angles that were significantly poorer than in the present work. However, the lack of quantitative signals makes the data less tractable.…”

“…11 The standard deviations of the measurements in these successive frames was typically 3°for ITO and 1°for ZPN. Ultrapure de-ionized water was used for all the contact angle measurements.…”

“…Analytical data obtained from real microchannels can then be evaluated in terms of wetting properties using the calibration curves. 11 The prediction shows ability for the quantification of surface wettability within 15°͑or 0.18 in cos ͒. Following on Baytekin and co-workers' work, 5 Urquhart and co-workers had reported that partial least-squares ͑PLS͒ analysis can be used to build models that correlate surface chemistry with the wetting angle, , to within 6°͑or 0.09 in cos ͒ for 576 acrylate-based polymers obtained from Tof-SIMS.…”

Electrochromic Properties of Metal Oxide Nanoparticles/Viologen Composite Film Electrodes

“…43 The reported water contact angle of ITO varies over a wide range from several to 85°depending on the cleaning treatment: Generally, ultraviolet ozone cleaning, oxygen plasma cleaning, and ion beam irradiation would increase the number of hydroxyl groups and therefore decrease the water contact angle. 44,45 Simple solvent cleaning as employed in this study does not have this effect and exhibited a relatively large contact angle, θ = 53°. 44,46 On the other hand, the θ values of SnO 2 films were reported to be in the range 9°−26°and, thus, indicated higher hydrophilicity.…”

Reversible wettability of electron-beam deposited indium-tin-oxide driven by ns-UV irradiation

“…The water contact angle of commercial ITO substrates typically ranges from 70 to 90 , and usually performed plasma oxygen or UV-ozone treatments significantly increase the surface hydrophilic character but can be quite long (with duration from a few to tens of minutes depending on the processing conditions, RF or UV-irradiation power, etc.). [12][13][14][15] For these reasons, alternative and possibly faster methods to treat ITO and control the film wettability are highly desirable.…”