Research Interests - James M. Fitz-Gerald
Research and teaching interests include
the processing, modeling, and behavior of nanofunctional and electronic
materials and their novel contributions to the electronic and biomedical
communities. The areas cover a wide spectrum from electronic thin films to
pulmonary drug delivery. My research
program is complimentary to existing research and collaborations within the
1)
Thin Film Growth, Modification and Characterization by Pulsed Laser Processing
Materials - Spanning from metals, ceramics, polymers and electronic materials
can be processed by lasers operating in the ultraviolet (wavelength: 120 - 308
nm) to produce unique materials with applications ranging from the manufacture
of computer chips to the chemical gas sensor industries.
" Electronic Thin Film Materials: Materials such as gallium
nitride (GaN) are believed to have significant potential for use as advanced
luminescent materials if bulk materials with proper doping can be grown. Due to
the non equilibrium processing conditions, it is felt that pulsed laser
deposition (PLD) may be able to synthesize bulk GaN thin films with controlled
properties such as dopant concentration and defect density.
" Luminescent Thin Films: Sulphide-based phosphor powders are
currently the brightest phosphor material available on the market, but due to
their high degradation rates and cross-contamination with molybdenum, the flat
panel display industry has not been able to utilize these materials. Thin film
sulfide materials grown from solid, sintered targets may be an answer to
controlling the diffusion of sulfur and subsequent reactions but the current
brightness of thin sulfide films are still only 40-75% of the raw powder
materials due to grain structure, stoichiometry and substrate roughness
effects.
" Bio-Compatible Polymer Thin Films: Bio-compatible polymers for both medical implant and chemical gas sensors offer a new area of research by PLD that is just beginning. In general, the ability to synthesize high-quality thin films of complex polymeric and organic materials has been difficult due to the high absorption coefficient of these materials in the ultraviolet which subsequently alters the material structures significantly, ruining the desired properties. A solution to this process has been recently developed at the Naval Research Laboratory and has been termed matrix assisted pulsed laser evaporation (MAPLE). With this new technique some complex polymer and organic material thin films have been synthesized and characterized showing > 95% structure retention and very desirable film roughness on the order of two nanometers.
2) Rapid Thermal Processing of Electronic Materials - Due to
current device fabrication, the next step in controlled atomic positioning is
pointing toward rapid thermal processing.
" Control of Temperature Profiles During Annealing: Immediate
impact exists in areas of thin film, multilayer, and in-situ direct write
devices. Rapid thermal processing operates in principle by exposing the entire
sample or portion of the sample to a high temperature (relative) environment
for a discrete period of time (nano seconds - seconds). This allows for rapid
heating of the surface layer materials without destroying the underlying
substrate material or devices of lower melting point materials. The subsequent
heating profiles generated provide limited dopant diffusion distances, which
are required for high quality devices. Rapid thermal processing can be
performed by many energy sources such as UV lamps, lasers, and hot/cold stages.
A two-fold advantage of using a laser to perform rapid annealing is the fact
that the laser treatment can directly follow the primary operation, layer - by
- layer or area by area, in some cases utilizing the same laser used to
transfer the material to the substrate. This eliminates bulk heating affects
associated with furnace heat treatments and allows for densification on the
atomic level, building from the substrate up to the final device thickness. By
utilizing the same laser to perform annealing in-situ, only a shift in the
energy density and scan speed is required. In-situ laser annealing also allows
for synthesis of multi-layer materials that can be combinations of metals,
polymers and/or ceramics. Current technologies are driving computer chip
manufacturers to build shallow junction devices on the order of 100 . Thermally enhanced diffusion has created a serious
reliability issue for these devices during implantation and subsequent dopant
activation.
3)
Synthesis of Emerging Particulate Materials and Coatings by Laser Processing
- Wide ranges of advanced technologies based on existing and emerging products
employ micron to submicron sized (0.1- 10 microns) particulate precursors for
synthesis and fabrication. Although there has been significant emphasis given
to control of the particle characteristics (shape, size, surface chemistry,
adsorption, etc.), almost no attention has been paid to designing the desirable
properties at the particulate level, which can ultimately lead to enhanced
properties of the product. By attaching atomic to nano-sized inorganic, multi
elemental particles either in discrete or continuous form onto the surface of
the core particles, that is, nano-functionalization of the particulate surface,
materials and products with significantly enhanced properties can be obtained.
" Functional Bio-Material Coatings: Laser assisted coating of dry
powder materials for enhanced drug delivery and bio-compatible stents. Current
state-of-the-art techniques cannot produce nanometric, dry powder coatings on
the surfaces of powders and irregularly shaped medical devices such as stents.
I have developed a method utilizing PLP to achieve this. Currently, this
research is focused on coatings to enhance pulmonary drug delivery of dry
powder inhalants. By controlling the thickness and structure of the coatings,
pulmonary targeting and controlled drug release has been accomplished. Due the
wide range of applications, it is difficult to predict the impact that this
research will have on the overall pharmaceutical and medical technologies over
the next 10-15 years but I believe that it will provide substantial funding for
research from commercial and academic agencies as well as citable publications.
" Luminescent and Protective Particulate Coatings: As with the sulfide-based phosphor films, sulfide-based phosphor powders exhibit rapid degradation behavior associated with sulfur reactions and charging effects on the display panel. A solution to this problem is to coat the phosphor powders with a material to slow or eliminate the diffusion of sulfur during exposure to the electron beam or stimulation source.
4) Synthesis and Characterization of
Devices by Direct-Write Techniques - This process, which was developed at
the Naval Research Laboratory, utilizes pulsed laser technology in the
fabrication of single and multi-layer device structures onto a variety of
substrate materials at room temperature including polymers, metals, glasses,
and ceramics without the use of masking or photo resists. Currently, all
materials available in powder form can be transferred (metals, polymers,
ceramics, dielectrics, insulators, and electronic materials) to form
conductors, insulators, capacitors and other electronic devices such as
antennae. In addition, feature resolution can be controlled over a wide range,
5-200 microns.
" Modeling of the Direct-Write Process: While the reason to
direct-write electronic devices is not new, this fascinating new device
fabrication technique, which combines laser, powder and chemical technology is
new. At this point a large amount of modeling remains to be conducted with
respect to the laser-powder and substrate interactions. I plan on conducting
in-situ high speed imaging, combined with microscopy and analytical
measurements to develop experimental models for the laser interactions.
" Fabrication of High Resolution Phosphors Devices: The current
state of the art for high-resolution phosphor displays is about one thousand
lines per inch, or 25 microns spacing. With this technique, the resolution
could be increased to two thousand lines per inch, pushing the high definition
technology.