Somers, Luke A

Email Address
Research Projects
Organizational Units
Research Interests

Search Results

Now showing 1 - 3 of 3
  • Publication
    Graphitic Surface Attachment by Single-Stranded DNA and Metal Nanoparticles
    (2011-08-12) Somers, Luke A
    Graphene and carbon nanotubes are extreme mechanical and electronic materials which have been the subjects of intense study and development since their discoveries. While many of their intrinsic properties have been discovered, their interactions with other materials are only beginning to be explored. The noncovalent binding of single-stranded DNA oligonucleotides to carbon nanotubes and graphene has been seen to give rise to effective gas sensors. We examine similar systems to each of these in turn, imaging carbon nanotubes decorated with single-stranded DNA in Transmission Electron Microscope, and performing X-ray reflectivity of a single-stranded DNA film on graphite. The TEM study shows that the DNA bunches up along tubes but does not tend to clump on single tubes. Helical wrapping is not seen on single tubes. X-ray reflectivity shows that DNA on a graphite surface forms an inhomogeneous layer around 1.6 nm thick. The differences between the various thicknesses of few-layer graphene are substantial though often underappreciated. These differences are highlighted in the system of several-nanometer metal particles on few-layer graphene flakes. We formed such particles by evaporation and annealing, then examined them in Scanning Electron Microscope. We found that gold nanoparticles were circular and experienced limited growth, with the radius varying as the number of layers to the 1/3 power. A theoretical explanation is given for this observation, based on an electrostatic interaction. This theory is also consistent with observations for titanium and silver nanoparticles. Ytterbium nanoparticles on graphene form instead into filaments. A related theory is presented showing that the same electrostatic interaction is capable of overcoming surface tension to deform particles from circularity.
  • Publication
    Effect of Thermal Treatments on the Transduction Behaviors of Conductometric Hydrogen Gas Sensors Integrated with HCl-Doped Polyaniline Nanofibers
    (2008-01-01) Dan, Yaping; Somers, Luke A; Wang, Pen-Cheng; Johnson, A.T. Charlie; MacDiarmid, Alan G
    We present the effect of thermal treatments on the transduction behaviors of HCl-doped polyaniline (PANI) nanofibers integrated in conductometric devices upon exposure to 1% H2 (carried by N2). After drying in N2 at 25ºC for 12 hours, devices showed a ~10% decrease in electrical resistance upon exposure to 1% H2. However, devices subject to 12-hour drying in N2 at 25ºC followed by further thermal treatments in N2 at 100ºC, 164ºC or 200ºC for 30 minutes showed different transduction behaviors. Specifically, devices subject to thermal treatments at 100ºC and 164ºC showed a decrease in electrical resistance by ~7% and <0.5%, respectively. More interestingly, the device subject to thermal treatment at 200ºC showed a transduction behavior with opposite polarity, i.e. a ~5% increase in electrical resistance upon exposure to 1% H2. SEM, FTIR and TGA were employed to investigate the effect of thermal treatments on the morphology and chemical characteristics of HCl-doped polyaniline nanofibers. The results indicated that the change in the devices? interesting transduction behaviors might be related to the thermal treatment effects on the HCl-doped PANI nanofibers in (i) removal of adsorbed water, and (ii) crosslinking and/or degradation of polymer backbones.
  • Publication
    Nanoparticle Shape Selection by Repulsive Interactions: Metal Islands on Few-Layer Graphene
    (2010-01-01) Somers, Luke A; Johnson, Charlie; Mele, Eugene J; Zimbovskaya, Natalya A
    Metal atoms adsorbed on few-layer graphenes condense to form nanometer-size droplets whose growth is size limited by a competition between the surface tension and repulsive electrostatic interactions from charge transfer between the metal droplet and the graphene. For situations where the work-function mismatch is large and the droplet surface tension is small, a growing droplet can be unstable to a family of shape instabilities. We observe this phenomenon for Yb deposited and annealed on few-layer graphenes and develop a theoretical model to describe it by studying the renormalization of the line tension of a two-dimensional droplet by repulsive interparticle interactions. Our model describes the onset of shape instabilities for nanoparticles where the growth is size limited by a generic repulsive potential and provides a good account of the experimentally observed structures for Yb on graphene.