RESEARCH
In this work we are interested in developing approaches for the design and assembly of nanoscale materials and devices for molecular electronic, photonic and sensor applications. In our work we utilize a combination of top-down and bottom-up approaches to control and manipulate materials on the nanoscale. In much of our work we take advantage of self-organizing materials for the design of robust structures, which can be manipulated and controlled through the engineering of specific inter-molecular forces and chemical interactions with surfaces. We combine self-assembly with soft-lithographic and scanned probe lithographic techniques to enable the design of nanoscale test architectures. These include confined molecular assemblies for molecular electronics, polymer-metal heterojunctions for organic electronics and nanoscale metallic structures for plasmonic devices.
HOMO Levels
Schematic of zinc porphyrin thiol inserted into dodecanethiol SAM
Spatially Confined Chemistry
Plasmonics – Enhanced Chemical Sensing
The union of electronics and optics research has lead to the development of the area known as plasmonics. Here we are interested in the controlled placement of metallic nanostructures to create plasmon enhanced devices such as optical sources and detectors.
Using photobrightened QDs coupled with metal nanoparticles, we have developed a platform for the ultrasensitive detection of Cu with a detection limit of 5 nM.
Patterns of CdSe nanorings were fabricated by using an evaporative templating method. This involves the introduction of an aqueous solution containing both quantum dots and polystyrene microspheres onto the surface of a planar hydrophilic glass substrate. The quantum dots became confined to the meniscus of the microspheres during evaporation, which drove ring assembly via capillary forces at the polystyrene sphere/glass substrate interface.
Schematic diagram of Water-Stain Lithography (left) and the AFM image of the CdSe nanorings (right).
AFM images of CdSe nanoparticle rings (scale bars are 200 nm). The height of each nanoring was controlled by changing the ratio between the nanoparticles and the microspheres before mixing them together.
We have also developed optical approaches (“lithosynthesis”) by which the optical properties of quantum dots (emission intensity and wavelength) can be directly tuned on a surface in a patterned fashion using local photo-oxidation reactions.
By controlling molecular interactions, nanowires of porphyrins can be assembled into nanowires which exhibit semiconducting behavior. We are integrating these materials with carbon nanotubes to create novel solar cell materials.
Shape controlled semiconductors
By tuning the ratio of the surfactants (Oleic acid/oleylamine) and the precursors, reaction temperature and solvents, materials in nano-scale with different shape and size can be synthesized. These materials offer control over optical and magnetic properties of semiconductor nanoparticles.
By tuning the ratio of the surfactants (Oleic acid/oleylamine) and the precursors, reaction temperature and solvents, materials in nano-scale with different shape and size can be synthesized. These materials offer control over optical and magnetic properties of semiconductor nanoparticles.
(a) Porphyrin nanofibers formed from diacids of tetra-carboxyphenyl porphryins. (TCPP) (b) Cryo-TEM image of TCPP nanofibers. (c) Alignment of nanofibers across gate electrodes. (d) Photocurrents in the porphyrin nanofibers.
Singles atomic layers of graphite (graphene) offer significant potential for new electronics. Here we use SPL to control the shapes of these layers. Raman mapping can be used to follow local chemical changes. Porphyrins bound to graphene can be used to dope the material affording a means of photogating transport.
Nanotribology – Controlling friction on the atomic scale
The details of friction and wear on the nanoscale are of significant consequence for a number of developing technologies including microelectromehanical systems (MEMS) devices. The generation of defects at surfaces in sliding contacts is the catalyst for the eventual wear of the materials. In this project we are investigating the wear of oxide surfaces at the nanoscale, including probing how local environment such as the presence of water impacts the formation and nucleation of defects at the atomic level. Associated with the investigations of friction and wear, we have developed force microscopy studies designed to directly probe the interactions at nanoscale asperities in sliding contacts using AFM. In contrast to the above studies on atomically smooth crystalline surfaces, this approach provides a means to assess adhesion and wear in nanoscale asperity-asperity contacts, which more closely mimic the interactions found between real surfaces in contact. In fact, with sufficiently sharp tips, bond quantization and energetic exchange with solvent becomes visible.Use of Silica Nanoparticle Film to Model Asperity-Asperity Contacts
Two examples of MEMS devices including a micromotor and an accelerometer. Water vapor can condense in device junctions yielding stiction. This can be reduced by control of surface roughness and chemistry. Intermittent contact between device components nucleates defects ultimately yielding wear debris.
Adhesion↓with↑Chain Length
Adhesion↑with↑Chain Length
The intercalation of 3-phenyl-1-propanol into disordered SAMs allows for active molecular lubricants to be trapped and activated under pressure…
R.L. Jones, N.C. Pearsall and J.D. Batteas, “Disorder in Alkylsilane Monolayers Assembled on Surfaces with Nanoscopic Curvature,” J. Phys. Chem. C. 113 (2009) 4507-4514.
R.L. Jones, B.L. Harrod and J.D. Batteas, “Intercalation of 3-phenyl-1-propoanol into OTS SAMs on Silica Nanoasperties to Create Self-Repairing Films for MEMS Lubrication,” Langmuir 26 (2010) 16355-16361.