Monday, August 27, 2012

We seem to be experiencing more technical difficulties... thank you for your patience

I am still not able to use the e-beam equipment at the University of Tulsa due to the program not having x-y control over the beams position.  The program is able to communicate with the hardware and activate the beam but because the beam does not move anywhere during the process all that is left is a burned spot where all of the beam energy is focused during the trial.  The beam technician has been working with me on this project, trying to get the x-y control back but still has had no luck and has contacted the e-beam company for support.  We are awaiting their response and hope that this will allow us to continue with the project.
One thing that I am unsure about lately is the surface integrity once the etching has been done.  Long story short, the PMMA bonding on the silica is disrupted by the e-beam, so that when the sample is immersed in a developer, the disrupted bits lift away leaving the pattern that we are looking for.  I am not worried about the resolution because that has already been shown to have high definition.  I am concerned because the developer is an alcohol and ketone, which I am hopeful will not leave a residue.  If it does, I am not sure how it will affect the adsorption of the surfactants when we move onto that stage of the research.  I am thinking I will run a few tests with the developer on a clean silicon sample and determine how much of a film, if any, the developer leaves behind after evaporation.
The other side of the project, involving etching the silicon, is also having difficulty, as the etching machine is having a performance check and will be available again shortly.  Until then, I am going to focus on the developer residue tests and nanosphere soaking, for retaining spheres and monolayer converage.

Monday, August 13, 2012

Happy Spheres are Clean Spheres and Clean Spheres Come from Trial and Error Solvent Testing

After several attempts at optimizing the SEM for taking images of the polystyrene nanospheres, the layer of contaminant that was affecting the etching process was imaged.  It does not spread throughout the entire sphere layer, but rather is in small areas strewn throughout the monolayers.  The contaminant has been seen previously but only as a lighter (contrast) region of spheres, not the contaminant itself directly.  It was imaged by increasing the power of the beam and taking several images using the backscatter detector to first identify the regions of contamination.  Then switching to the In Lens detector and imaging the previously found areas the "gunk" between and on top of the spheres could be seen.  When looking at samples which have been subjected to solvent-testing, in an effort to remove the contaminant, progress has been seen.  The tested samples show large areas of contaminant free spheres layers.  These layers still have line interruptions throughout them, and their coverage has decreased due to the loss of some spheres during the cleaning process.  Although the decrease in coverage is not ideal, having clean spheres with which to etch was the primary concern, as imaging techniques can later be used to determine the areas where spheres are still present so that when AFM is performed following etching we will know where to probe.  Having clean spheres means that etching can now be performed, and if the results are good we can use smaller spheres and work on shrinking the size of the fabricated pillars!  Moving right along!

Wednesday, August 8, 2012

Technical Difficulties

Progress has been made on the front of fabricating the "trench" structures using PMMA on silica.  The layers are a suitable depth and the program to use the e-beam has been set up to run test runs to determine the power of the beam to get clean edges and correct depth etching.  However, all of this is waiting to be used while the e-beam software and the e-beam hardware are being fixed.  The problem lies in that they are not communicating with each other, so that while they are both technically functional, the beam cannot be used because it cannot be told what to do until it can communicate with the software.  The technicians at TU have been working very hard to resolve this issue themselves but have had no luck and have had to call in the SEM manufacturers for assistance.  I am confident that once they have fixed the problems I will be able to have sample made within two weeks (one week to fine tune the parameters and one week to make the samples) and then start using them with surfactants and AFM.  I am excited about this because all of the problems that have been overcome to finally reach that point will make it more rewarding.
The other half of the fabrication process, the "terraces", is also slow moving due to problems involving surfactant on the surface of the beads and silica making it difficult to etch cleanly.  The researcher I have been working with believes that we may have had success with solvent testing, and sees a possibility of etching again next week.  I am looking forward to this because school starts soon and I would like to have all of the preparation work out of the way so that I won't have to stretch myself between school and research too much, but I am mentally preparing myself to do so anyway!  Knock on wood that the AFM is working at the end of all of this.