Two birds with One Stone

Having trouble getting responses for the last couple of days.  Have been working on getting 50 nm spheres to create more continuous layers on the silica by changing the solvent ratios some more but to the naked eye there doesn't seem to be any apparent improvement in sample coverage overall.  This does not mean that it is not improving on a micro scale, just that I will need to use an SEM to tell.  This is in the mean time while I have been waiting to hear back from contacts who are graciously helping us with creating the channels (trough) for the other half of the project.  So far though I have not been able to get responses from them or the people who are helping us with the etching to create nanopillars either.  It is a difficult thing to try and schedule something else into an already packed summer for them I'm sure, but it makes me nervous because I don't want to get to a point where I've got more to accomplish than time to do it all.  

As already mentioned the plan is for the troughs to be fabricated in PMMA using e-beam lithography which the group who have been contacted to help us are adept at.  I'm excited to start this because it appears that this technique will be more precise and require less leg work to get a sample ready for surfactant trials.  Once I've gotten to a place where I can get nanopillars done it will essentially be the same deal, where to create a new sample I already have a protocol done, but this is the part where I have to perfect the protocol, and that's where the bulk of the work has gone so far.  As a added benefit from this though I have increased my knowledge of the substrate and its properties, which means that creating this sample will have served a dual purpose, which I look at as an accomplishment. 

Some challenges faced so far

I have been trying to get things started with the e-beam lithography to begin creating the trough structures to look at how adsorption in a channel will occur.  One thing I like about this project is that we are given the opportunity for symmetry.  That is, we are looking at the adsorption of surfactants on the top of small area open surfaces (the terraces) as well as adsorption where the surface is still small but confined.  The difficulty with this is that surfactants are, of course, very small.  Therefore, in order for the effects of the "confinement" to be noticed, or different than any other surface, the surface must be on the order of a few surfactant molecules long or smaller.  That is why this project is so challenging so far is that creating such structures isn't like picking up an x-acto knife and cutting a small piece of substrate.  It must also be smooth and, for the most part, flat so that the size of the surface is the variable causing changes.
Using the smallest size spheres is how these surfaces will be achieved, but the smaller the spheres the harder it is to obtain self assembled monolayers of the beads.  So what we tried with the etching last time is using a small amount of O2 etching along with the primary etchant.  The O2 will shrink the beads linearly with etch time, so the structure formed will (should) have a terrace smaller than the original bead size!
I am really looking forward to working with the e-beam lithography because aside from just being plain cool it will be more precise and repeatable.  Exciting things are happening!! Now if I could only get over this cold....

Sick and Graduate Research Schedule

Was sick for the first part of the weekend.  One thing that is both a blessing a curse about graduate research is that for the most part you dictate your own schedule.  Being sick means that you take off the days you can but you come in an extra day somewhere else to make up the slack.  It is very much reliant on weekly goals to keep on track and make sure things are moving forward.  Therefore I come to work in the morning and leave when I feel that I am no longer productive, no set come in or leave time.  Just try to accomplish what I set out to do for the day and then make a goal for the next day.  My current goal is to try and set up the RIE using PMMA for creating trenches, the opposite of what I have been working on lately.  Will continue to update on the progress of this endeavor.

Methanol Soaking Step

SEM was used to view the state and orientation of the 200 nm spheres on a silica surface.  There was a good amount of monolayer coverage (more than multi-layer), although those monolayers had line interruptions through out it.  A grid was used to find a spot which after soaking was performed could be found again for comparing the sphere positions.
After soaking the silica sample in methanol for 15 hours (overnight) the surface had a much deeper purple color.  When SEM was used to determine whether or not the soaking moved the spheres around significantly, it could be seen that the soaking had little to no effect on the position of the spheres, however not much could be said about the SDS on the sample surface.  From this information we can say that the soaking step can only be helpful, because the sphere positions did not change so if the SDS wasn't removed no harm was done to the sample.  If the SDS film was loosened or removed then when RIE is done there should be less of a mask from the SDS and the spheres should be able to create a better mask for creating the nanopillars.  All this is good news and hopefully next week or the week after, depending on the RIE availability, we will be able to try etching again with a shorter etch time and see what kind of shapes we can get!!  Exciting!!

Effect of pH Conclusion

The pH of the 50 nm sphere solution was tested and found to be roughly 4.5.  From the literature, at 8.5 pH silica has a negative charge which hinders the adsorption of anionic surfactants (1).  Because our pH is much lower than this value we can say that the surface of the silica has a slightly positive charge which would increase the adsorption of the SDS (anionic) in the sphere solution.  The theory that this would increase the sphere adsorption as well would require further experimentation which is not the primary focus of this project. Therefore, we will conclude that the pH effect on the sphere adsorption is not a factor to be explored in enhancing the monolayer coverage for this project. 

However, the SDS adsorption to the silica as a result of the low pH may be a factor is creating a sharp relief.  It has been recommended that the samples be soaked in methanol to loosen the SDS on the surface of the silica.  To make sure that this soaking step does not affect the sphere monolayer, SEM will be performed prior to the soak and then again after the soak to determine the effect, if any, on the already deposited spheres.  

Post Memorial Day update

Hope everyone had a good Memorial Day Weekend! Today will be a short post.  Due to complications with the SEM I am not able to use it until later this week at the earliest.  Something important came up this weekend I was not able being the pH testing of the sphere diffusions as I had hoped but I should be able to do that tomorrow. On the personal side, following this weekend it is easier to understand the concept that the world continues to turn even when you want to take a moment to stand still.

Short term goals for the next 3 weeks

Next week I will be trying to remove some of the stuck on SDS from the surface of a deposited sample using a methanol soaking.  This step was recommended by the research scientist helping me with the etching process.  The idea would be to loosen and help the spreading out of the SDS in order that it does not create an etch mask on the surface of the silica.  I am not convinced that the spheres will remain in place during this process, but the worst that could happen is that the spheres became disordered and I know that it may make remove some of the SDS but at the cost of compromising the sphere locations.  I am hoping to etch again in the beginning of June using a different etch time and perhaps with smaller spheres.  We are getting close to the point where we will determine if this process will give us the surface we are looking for.  I anticipate that the answer to this question will be answered mid-June.  Memorial day weekend will be relaxing, only in the fact that I can spread out the work I hope to get done this weekend over three days instead of two, but still I am thankful for the holiday.  Everyone have a safe and enjoyable weekend!!