Silver nanoparticles, when used as a Raman spectroscopy substrate, give rise to an effect known as surface enhancement. Oscillations of the conduction electrons on the surface of the silver nanoparticles enhance nearby electric fields, including the light incident on and scattered from these particles. This enhancement can increase the intensity of the light by a factor of up to ten billion. The cause of this enhancement, and the techniques and applications which take advantage of it, are still subjects of ongoing research. In particular, there is a strong dependence of surface enhancement on particle size an radius of curvature. Prior research projects suggest that analytical approaches to modeling surface enhancement are limited to the simplest possible shapes and smallest numbers of particles, and cannot be extended to realistic situations. This research applies computational electrodynamics to model silver nanostructures created by ferroelectric lithography.
The lithographic growth of silver nanoparticles on a ferroelectric substrate is investigated using scanning electron microscopy (SEM). The initial process of particle formation is well described by the kinetic interactions between the silver ions in a dilute silver nitrate solution and the electrons in a periodically poled lithium niobate (PPLN) substrate. However, as more silver is deposited onto the substrate, the electrostatic properties of the growing nanoparticles more profoundly influence where silver ions will continue to accumulate. By observing the nanoparticles at various stages of development, it is found that ordinary nanoparticles on a smooth, clean substrate first form as discontinuous collections of point-like particles. Further deposition results in larger, jagged particles. As these particles gather more silver, their edges become more rounded until they reach a maximum volume. Furthermore, it is shown that the condition of the substrate profoundly affects nanoparticle formation. A better understanding of how previously deposited silver affects the future deposition of silver ions still in solution will allow future research more control over wire properties, such as shape and size. This is particularly advantageous for applications that are highly dependent on nanoparticle dimensions, such as surface enhanced Raman spectroscopy (SERS), a method of detecting and characterizing single biomolecules or trace impurities.
The goal of this research is to improve the quality of nanowires grown on periodically poled (PP) ferroelectric substrates. Image analysis software is used to measure changes in particle size and separation that are caused by varying the growth parameters (i.e. the deposition time and solution concentration). A PP substrate is divided into many oppositely poled electric regions which create anomalously strong electric fields where they are connected. Covering the substrate with a solution of silver nitrate and exposing it to ultraviolet light causes promotion of electrons to the conduction band which are then free to photoreduce the silver. Since the electric field is strongest at the domain boundaries the silver tends to deposit there, creating wire-like structures. Topographic images are then taken with a Scanning Electron Microscope allowing the nanoparticles to be observed. After the pictures are archived the nanoparticles are analyzed further by the software application ImageJ to gather such statistics as the number of particles and their average size. The deposition time and solution concentration are varied during the experiment, creating nanowires of variable size, shape, and separation. Through the analysis of the particles associated with varying parameters we analyze the correlation between particle size and different combinations of depositions times and solution concentrations.
The aim of this project is to investigate the potential for patterned exposure of a ferroelectric substrate to an electron beam source to change the poling structure of the substrate. The specific substrate for this investigation is Periodically Poled Lithium Niobate. The electron beam source was a scanning electron microscope. This is a summary of the effect of spot size, magnification, and duration on the poling structure of the substrate. As of now, none of the experiments were successful in producing the poling changes which were the aim of this line of research. This investigation points towards future research which may be more fruitful than this inquiry. A section of suggested future research is included at the end of the paper.
This work studies how the speed of sound in a corrugated tube decreases relative to the speed in free space. Previous students at the University of North Carolina Asheville have engaged in research to determine this speed. The results from these studies were obtained with an uncertainty that rendered the changes of speed within the tube undeterminable due to low sampling rate. Other experimenters have published similar experiments under the assumption that the change in the speed of sound remains constant throughout the tube. This study seeks to refine previous research by measuring possible variations in the speed along the tube’s length. To accomplish this, a higher sampling rate and noise reduction procedures will be used to lower uncertainty, thereby allowing the accuracy necessary to map the change of the speed of sound as it travels through the tube. This will be done by using a ‘one-shot’ method in which frequency controlled bursts of sound are received by a decreasingly distant sound sensor.
