Solution deposition has potential for highly cost-effective fabrication of thin film transistors (TFTs) on flexible substrates. Shape memory polymer (SMP), with improved thermal mechanical response, may enable large-area flexible devices, as well as add control to the product shape and modulus. Until date, TFTs made on SMP substrates have been limited to vacuum-deposition methods. While TFTs processed through more economical solution-based techniques achieve device performance close to their vacuum-processed counterparts, they have not yet been demonstrated on SMP substrates due to the required high calcination temperatures (> 500 °C). To take full advantages of SMP, low temperature (< 200 °C) solution-based processing is highly desirable. Compatibility of the deposition process with the substrate and previously deposited films is essential. Here, we develop a process that incorporates direct UV patterning that would allow for fabrication of oxide TFTs on SMP using a reduced number of processing steps. Rigid In<sub>2</sub>O<sub>3</sub> TFTs, deposited from solution-combustion synthesis, are fabricated on Si substrates with different solution-deposited dielectrics to evaluate their potential for transferring to SMP.
Nanocomposites are a promising new dielectric material for on-chip and chip-to-chip waveguides that operate at millimeter (mm)-wave frequencies because of their higher relative permittivity compared to neat polymers and their compatibility with printed circuit board processing. For dielectric waveguides, extremely low loss is critical; thus, understanding the origins of loss is an important step for these applications. In this paper, we investigate the sources of loss in TiO<sub>2</sub>/polypropylene (PP) nanocomposites, in which polypropylene-graft-maleic anhydride (PP-g-MA) is added as a compatibilizer. Compared to nanocomposites made without PP-g-MA, we find that PP-g-MA improves the distribution of nanoparticles in the PP matrix and significantly lowers loss. We also examine the contribution to dielectric loss from PP-g-MA by measuring samples that contain no TiO<sub>2</sub> nanoparticles, and find that while increasing the amount of PP-g- MA in PP results in a higher loss, it is small compared to the loss that comes from the addition of TiO<sub>2</sub> nanoparticles.
Zinc oxide (ZnO) is a technologically important material because of its multi-functional properties, with applications ranging from piezoelectric transducers and varistors to wide-bandgap semiconductor for UV emitters and detectors. In addition to polycrystalline ceramic powders and epitaxial thin films, recent advances in ZnO have been in vapor and solution phase growth of complex nanostructures. For these nanostructures to be useful, a means to place them strategically on the surface is needed. Here we will describe using micro-contact printing to pattern self-assembled monolayer (SAM) molecules that locally inhibit crystal growth on surfaces. These chemically patterned surfaces are then used as templates for ZnO nanorod growth in aqueous solutions. We demonstrate good control of crystal placement
with feature size down to 1 µm. In addition, we find that restricting active nucleation regions results in a marked increase in nucleation density. These results are the first demonstration of combining soft lithography and bio-inspired crystal growth to make nanostructures of ZnO. The success illustrated here indicates that such a combination may be applicable to a much broader range of materials systems than previously envisioned.
Proc. SPIE. 2547, Laser Techniques for Surface Science II
KEYWORDS: Quantum wells, Diffusion, Electroluminescence, Near field scanning optical microscopy, Near field, Surface properties, Laser damage threshold, Spatial resolution, Laser optics, Near field optics
Near-field scattering optical microscopy (NSOM) is used to characterize the emission output and to obtain photoconductivity maps of InGaAsP multiple quantum well lasers. The high spatial resolution of NSOM (approximately (lambda) /20) allows detailed imaging of the laser structure. Emission measurements not only provide direct visualization of the laser mode but also reveal unwanted emission due to InP electroluminescence. Near-field photoconductivity experiments yield high resolution measurement of carrier transport throughout the structure yielding valuable information on current leakage, defect formation, and the quality of p-n junctions.
Transient photoluminescence, photoluminescence excitation and picosecond photoinduced absorption studies on stretch oriented phenylenevinylene polymer films are presented. A coherent picture of the processes occurring after light absorption emerges which can account for the data. The implications of this picture for photoconductivity and electroluminescence are considered.
We have investigated the surface morphology of relaxed, compositionally graded Ge<SUB>x</SUB>Si<SUB>1-x</SUB> structures to study the influence of defect-related strain fields on film growth. Quantitative topographic measurements via scanning force microscopy show that the roughness associated with the cross-hatch patterns, due to underlying misfit dislocations beneath the surface, increases as the final Ge concentration or the grading rate increases. We further show that strain fields arising from the termination of threading dislocations at the surface result in shallow depressions. In addition to the as grown samples, we have also studied the morphology of processed Si, Ge, and Ge<SUB>x</SUB>Si<SUB>1-x</SUB> surfaces. Protrusions are observed on top of the long-wavelength morphology when the Ge<SUB>0.75</SUB>Si<SUB>0.25</SUB> films are annealed at 900 degree(s)C for as short as 1 minute. These protrusions are unique to the alloy films and not seen in pure Si or Ge. We offer an explanation of this process induced morphological change and discuss the effect of tip shape on images.