Switching to E-Beam lithography

So after some trial and error we have found that ion beam milling will not be a suitable substitute for e-beam lithography in fabricating our controlled roughness sample.  The ion beam redeposits gallium as it mills and that could create a terrace but would have added roughness from the gallium.  Also this technique creates a V shaped channel which I am concerned will create a surface on which additional surfactant adsorption could occur and effect the adsorption on the terrace surface.  This would defeat the purpose of having a terrace separating adsorbed layer from the rest of the surface.  We will need to wait for the e-beam to be ready to use and while this is a small setback, it provides time to learn to use the Quartz crystal micro balance and practice using the liquid cell with AFM.  Happy Holidays!

Impact and implications of AFM imaging studies

Just read Surfactant adsorbed layer structure at solid/solution interfaces: impact and implications of AFM imaging studies (Surfactant Adsorbed Layer Structure; Warr, G.G., Current Opin. in Coll. & Interface Sci., 2000, 5, 88-94) and I feel that it is one of the most helpful in understanding AFM studies that I've read so far.  I believe this is because it was published when AFM was a newer technology and was just beginning to be used for adsorption studies, so less information is skipped over because it has become more common knowledge.  I found the topic of transforming cylindrical and spherical structures into mono- or bilayer sheets using ion exchange very helpful.  Structures that originally begin as cylinders or spheres transition into flat sheets over time (18 hrs in the article) and "has been attributed to slow exchange of CTA+ for the potassium ions in the mica lattice." (Warr, 90) Then by increasing the ion concentration (they used caesium as an example but mention potassium, lithium and hydrogen as well) they are able to transfer back into cylinders and spheres.  Useful information for research to be done using adsorption.

CTAB adsorbed to various substrates

Have been going over Surface-Induced Phase Behavior of Alkyltrimethylammonium Bromide Sufactants Adsorbed to Mica, Silica, and Graphite(Surface-Induced Phase Behavior; Liu,J.F.; Ducker, W.A., J. Phys. Chem., 1999, 103, 8558-8567) for the last few days before finals and had to reread some of it following finals to catch back up.  I found it very interesting and helpful in coming up with methods for preparing samples and interpreting AFM images.  As someone still fairly new to adsorption research I especially found the section on variation of chemical potential by changing one or several different parameters including temperature, concentration, concentration of a salt which acting as a co- or counter-ion, the substrate and the length of the alkyl chain.
              I feel that the best surfactant to begin the trials with would be CnTAB due to the amount of literature on its use as well as the ease of changing the length of a surfactant molecule without changing the head group by switching between n-lengths.  The article makes use of a temperature controlling apparatus on their AFM which may be of some use to us as well but if we are not able to use something to keep the temperature constant while taking images of the AFM we may be able to see the changes in morphology and phase behavior as the temperature changes with time in the process of taking the image.
         I have been reading literature to do with many substrates but have been making more notes on the methods of preparation of silica and silicon substrates because of the substrate we will be using first will be silicon which has been milled using reactive ion etching.  We will then place the samples in an oven to promote the formation of an oxide layer to the surface of the sample. An interesting test that was used was the "steam test" for silica substrates, which seems fairly simple and checks for the uniformity of the hydrophilic character of the substrate.  The test is to run steam over the sample and check for a thin layer of water over the whole sample.  If it is a patchy layer of water then the hydrophilic nature is not uniform and must be addressed before using the sample.

Integrated Hydrophobic and Hydrophilic substrate by Nanopatterned Surfaces

While looking for articles I stumbled across a paper

(Hyunjong Jin; Hsiao, A.; Liu, L.; , "Integrated hydrophobic and hydrophilic substrate by nanopatterned surfaces," Sensors, 2010 IEEE , vol., no., pp.1364-1367, 1-4 Nov. 2010)

 where a group created hydrophobic and hydrophilic areas on a single substrate sample by treating each area with different methods.  Something that I found interesting which may or may not apply to our project down the road was the variability of the hydrophobic nature of the sample and that a "difference in contact angle is mainly due to the ability of the nanotexture surface having more channels for water to [leak] in".  I am fairly new to the concept of a contact angle but from my understanding of the paper, by adding channels to our sample to create terraces and troughs we are changing the hydrophobic nature of the sample from a mechanical standpoint.  So if we perform our experiments on both hydrophobic and hydrophilic substrates we may need to make sure that we have considered the effects of changing the substrate's interaction with the solvent, water, in both a chemical and mechanical form when analyzing the differences in our data.

Self-assembly of Surfactants at the Solid-Aqueous Interface

Just would like to comment on how much easier it is to read new material that uses concepts that you are more familiar with.  I say this after reading a paper (Self Assembly of Surfactants at the Solid-aqueous interface; Tiberg, F.; Curr. Opinion in Coll. & Inter. Sci., 2000, 4, 411-419) where the author uses AFM to image the morphology of surfactants adsorbed to substrates.  After training on using AFM I have found that I understand what is being discussed much easier because I'm not unclear about the method being used to produce the images.  Also, on pg 415 there was something I found interesting and wondered if it was worth looking into in my current project,

 "The presence of highly polarisable on-ion such as caesium, induces smaller surface aggregates than the less polarisable potassium co-ion.  Highly polarisable co-ions interact with the mica surface more strongly and therefore compete more effectively with the surfactant for adsorption sites.  The main effect of counter-ions present at the solid surfactant interface is to decrease the repulsionbetween the surfactant head groups , as in bulk solution.  In summary, the effect of added salt is the result of a complex balance, which can give rise to an increase or decrease in aggregate curvature, or merely less ordered aggregate forms."

What I find intriguing is that with a reduced area of adsorption, at least the area that we are interested in, i.e. our "terraces", what kind of morphology would be seen in the presence of salts added to decrease the repulsive forces between the head groups?  Something I also find interesting is in the case where "troughs" are present, what will we see happen when salts that compete with the surfactant for binding space are present?

A note for the future, same page as before, try tetradecyl trimethyl ammonium bromide (ionic on hydrophilic surface) on silica to look for spherical micelles, see if they are the same in the case of different wall chemistry.

Nano-scale Organization

After reading a paper on surfactant organization on a substrate (Nano-scale Organization; Grant, L.M.; Tiberg, F.; Ducker, W.A., J. Phys. Chem., 1998, 102, 4288-4294), I am wondering if it would be worthwhile to perform experiments with treated as well as untreated silica as a substrate.  The results of the paper showed that with silica that was treated with varying agents, the organization of whatever surfactant they used changed depending on the hydrophobicity of the silica, driven by minimization or maximization of substrate-water interaction.  Although we are changing the substrate environment when we are working with either terraces or troughs, seeing the effects of hydrophobicity on surfactant absorption in the presence or absence of altered substrate topography could also yield interesting data.  However, it is probably best to first determine to what degree we can control the experiment with untreated silica with altered topography before trying this approach.

Q-sense Conference

Q-sense conference went very well and was very informative.  Spoke with some representatives on the possibility of using QCM-D to study the effect of lateral confinement on surfactant absorption. The frequencies involved in the QCM method may cause noise and/or difficulty in analyzing the data when using patterned surfaces but that is it still possible and will still yield accurate results.