FIB Patterned Templates for Guided Nanostructure Formation

FIB PATTERNED TEMPLATES FOR GUIDED NANOSTRUCTURE FORMATION Hao Wang, PhD University of Pittsburgh, 2013 There are many factors that limit significant advances in device technology, including the ability to arrange materials at shrinking dimensions and the ability to successfully integrate new materials having better properties with silicon. Methods for self-assembly of quantum dots are greatly desired for new devices which have smaller sizes, lower energy consumption, higher performance, and new functionality. In order to create such new devices, a patterning method must be used that can arrange quantum dots at the appropriate length scales. A focused ion beam (FIB) is one method of laterally arranging nanosized islands of dissimilar materials on silicon by creating template patterns directly on the Si substrate with nanoscale resolution. With the intention of promoting self-assembly of nanostructures, surface topography features and chemical/compositional variations are used in the near surface region of the templates. Two changes are taking place simultaneously during the milling process: surface topography is created as material being removed while implanted Ga is added. The implanted Ga can form clusters or nanocrystals when heating.1,2 Both processes are of potential interest for lateral positioning of nanostructures. One possible concern for device applications is the effect of the implanted Ga which is a result of the milling process. Implantation can result in damage to the lattice, unwanted doping of the substrate, and/or nucleation of Ga nanocrystals from the implanted material. On the other hand, it may also be desirable in some scenarios to take advantage of the implanted material and nucleate nanostructures directly from it. For example, Ga surface islands could result upon annealing with the potential to be converted to Ga-based compounds, such as GaN, on Si through chemical reactions. GaN is a direct band gap material and of interest for electrically pumped ultraviolet-blue LEDs(light-emitting diodes), lasers, and potentially for single photon sources.3–6 For a lattice mismatched system such as SiGe/Si, the topography created by the FIB can lead to the formation of strain-relieving islands at the preferential sites. For the case of SiGe/Si, the physical evaporation of Si and Ge under UHV(ultra-high vacuum) conditions, that deposition of epitaxial strained SiGe on top of a FIB patterned Si substrate can lead to preferential island formation at FIB patterned pit edges under appropriate growth conditions.

Plasmas Processes Applied on Metals and Alloys

This book focuses on recent advances in plasma technology and its application to metals, alloys, and related materials. Surface modifications, material syntheses, cutting and surface coatings are performed using low-pressure plasma or atmospheric-pressure plasma. The contributions of this book include the discussion of a wide scope of plasma technologies applied to materials. Plasma is a versatile tool that can be applied in many types of material processing. New material processing applications of plasmas and new plasma technologies are being developed rapidly. We hope that this book can contribute new knowledge to the plasma material research society

Toward biomaterial-based implantable photonic devices

Optical technologies are essential for the rapid and efficient delivery of health care to patients. Efforts have begun to implement these technologies in miniature devices that are implantable in patients for continuous or chronic uses. In this review, we discuss guidelines for biomaterials suitable for use in vivo. Basic optical functions such as focusing, reflection, and diffraction have been realized with biopolymers. Biocompatible optical fibers can deliver sensing or therapeutic-inducing light into tissues and enable optical communications with implanted photonic devices. Wirelessly powered, light-emitting diodes (LEDs) and miniature lasers made of biocompatible materials may offer new approaches in optical sensing and therapy. Advances in biotechnologies, such as optogenetics, enable more sophisticated photonic devices with a high level of integration with neurological or physiological circuits. With further innovations and translational development, implantable photonic devices offer a pathway to improve health monitoring, diagnostics, and light-activated therapies. Keywords: biomaterials; biocompatible; biodegradable; optics; photonicsUnited States. Department of Defense (Award FA9550-13-1-0068)National Institutes of Health (U.S.) (Award P41-EB015903)National Institutes of Health (U.S.) (Award R01-CA192878)National Science Foundation (U.S.) (Award CBET-1264356)National Science Foundation (U.S.) (Award ECCS-1505569

Influence of Embedded Metallic Nanocrystals on GaAs Thermoelectric Properties.

For the past several years, there has been significant interest in low-dimensional structures, such as superlattices, nanocrystals, and nanowires, for thermoelectric applications due to their ability to enhance the figure-of-merit. These nanostructured materials must be optimized to maximize the Seebeck coefficient (S) and electrical conductivity (σ) while minimizing the thermal conductivity (κ). Due to the possibility of nucleating nanocrystals within an amorphous matrix, ion-beam-synthesized nanocomposites show promise as possible thermoelectric materials. To optimize these ion-beam-synthesized nanocomposites, an understanding of the microstructure and thermoelectric properties is essential. Here, we report on the formation of metallic In (Bi) nanocrystals (NCs) embedded in GaAs by In (Bi) ion implantation and rapid thermal annealing (RTA). The role of microstructure on the thermoelectric properties of ion-implanted GaAs is discussed via a comparison of GaAs:Bi, GaAs:In and GaAs:N films. We report on the relationship between microstructure and thermoelectric properties of ion-beam-synthesized In NCs in GaAs. We developed a sputter-mask method to enhance the retained ion dose. During annealing, In NCs are nucleated within a polycrystalline GaAs matrix. Electrons and phonons are scattered at interfaces, reducing σ, κ, and consequently the thermoelectric efficiency in comparison to that of unimplanted GaAs. We also report on the formation of Bi NCs embedded in GaAs and their influence on the thermoelectric properties. Implantation-induced defects reduce the free carrier concentration, n, and, consequently, σ, while annealing results in a partial recovery of n and σ. Phonon scattering at Bi NC boundaries serves to reduce κ by ~30% for all films. We discuss the role of microstructure on the electrical and thermal conductivity of the GaAs:Bi films through a comparison with GaAs:In and GaAs:N films, demonstrating a general trend of n and σ reduction following ion-implantation, while a partial recovery of n and σ, and a reduction in κ due to phonon scattering, follows RTA. This thesis reveals new insights into the structure-property relationship of ion-implanted GaAs. Embedded metallic NCs show promise for thermoelectric applications via κ reduction. Based on these results, it is suggested that epitaxial growth of embedded NCs will result in a reduction in κ while simultaneously preserving σ.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107186/1/mvwarren_1.pd

Biological cell–substrate interactions with few-layered nanomaterials

Biology, fundamental to understanding life, remains a vitally important area of research. There is still much left for humankind to understand even after decades of research. This is clear now more than ever; as I write this, research has been disrupted for about 12 months due to various COVID-19 restrictions. Biology, therefore, is ripe for the fresh, new advances that result from interdisciplinary collaboration. Recent years have seen the exciting development of new few-layered materials, providing new possibilities in biology, as well as other areas. To this end, the work presented herein considers the interactions between different cell lines and various synthesised nanomaterial substrates. To distinguish effects due to the inherent biology of the cell and effects due to the nanomaterial substrate, well-defined substrates are crucial to interdisciplinary research. Thin films created by the Langmuir–Schaefer (L–S) deposition technique are a good candidate. This technique provides an easily controllable method of producing single-layer substrates. Here, a method resulting in improved understanding of the physical and chemical influences on L–S film formation is described. Surface pressure-surface coverage data can be normalised to nanosheet size to account for edge effects. This new approach allows the L–S film density to be determined from standard dispersion properties alone. In addition, this work produced the first demonstration of the production of single layer hexagonal boron nitride films using this method. To test nanomaterial–cellular interactions, various cell lines were seeded onto MoS2 L–S substrates. To the best of our knowledge, this study resulted in the first demonstration of the internalisation of MoS2 through mechanotransduction. The material showed localisation to the endoplasmic reticulum, which combined with the innate fluorescence or Raman signal of the MoS2 nanosheet, could lead to a new theranostic tool. This study was expanded to consider cell interactions with other transition metal dichalcogenide materials, WS2 and MoSe2, to investigate the difference between structure and chemistry seen by the cell. This work provides a step change to studying nanomaterial–cellular interactions, opening the door to new therapies and diagnostics