Fabrication and Characterization of Thinner Solid-State Nanopores

Solid State nanopores that are fabricated by the ion beam sculpting process and electron beam drilling have shown great promise as a sensing device for DNA and protein molecules. Even though biological pores such as the alpha-Haemolysin have been in use for quite some time, the use of solid state Nanopores in single biomolecule detection has been on the rise since the mid 1990s. Solid State nanopores have an advantage over biological pores in that they are more robust, stable, and can be sculpted to any desired size for use in translocation experiments. One of the major challenges in Nanopore fabrication by ion beam sculpting has been limited by the user\u27s ability to control the closure rate of pores in the fabrication process. Another challenge in nanopore sensing is the resolution limitation due to the thickness of the pore. This is because most of the nanopores fabricated by the ion beam sculpting method are often thicker than they should. This thesis will focus on the modification of nanopore fabrication using the ion beam sculpting system at the University of Arkansas by first baking the samples in vacuum under specified temperature conditions. Baking the samples will give the user better control over pore closure. This Thesis will also focus on thinning the sculpted pores by Reactive Ion Etching in an attempt to increase its resolution for single biomecule translocation experiments

Ion-beam Sculpting at Nanometre Length Scales

Manipulating matter at the nanometre scale is important for many electronic, chemical and biological advances, but present solid-state fabrication methods do not reproducibly achieve dimensional control at the nanometre scale. Here we report a means of fashioning matter at these dimensions that uses low-energy ion beams and reveals surprising atomic transport phenomena that occur in a variety of materials and geometries. The method is implemented in a feedback-controlled sputtering system that provides fine control over ion beam exposure and sample temperature. We call the method "ion-beam sculpting", and apply it to the problem of fabricating a molecular-scale hole, or nanopore, in a thin insulating solid-state membrane. Such pores can serve to localize molecular-scale electrical junctions and switches, and function as masks to create other small-scale structures. Nanopores also function as membrane channels in all living systems, where they serve as extremely sensitive electro-mechanical devices that regulate electric potential, ionic flow, and molecular transport across cellular membranes. We show that ion-beam sculpting can be used to fashion an analogous solid-state device: a robust electronic detector consisting of a single nanopore in a Si3N4 membrane, capable of registering single DNA molecules in aqueous solution.PhysicsEngineering and Applied SciencesMolecular and Cellular Biolog

Design and Focused Ion Beam Fabrication of Single Crystal Diamond Nanobeam Cavities

We present the design and fabrication of nanobeam photonic crystal cavities in single crystal diamond for applications in cavity quantum electrodynamics. First, we describe three-dimensional finite-difference time-domain simulations of a high quality factor (Q ~ 10^6) and small mode volume (V ~ 0.5 ({\lambda}/n)^3) device whose cavity resonance corresponds to the zero-phonon transition (637nm) of the Nitrogen-Vacancy (NV) color center in diamond. This high Q/V structure, which would allow for strong light-matter interaction, is achieved by gradually tapering the size of the photonic crystal holes between the defect center and mirror regions of the nanobeam. Next, we demonstrate two different focused ion beam (FIB) fabrication strategies to generate thin diamond membranes and nanobeam photonic crystal resonators from a bulk crystal. These approaches include a diamond crystal "side-milling" procedure as well as an application of the "lift-off" technique used in TEM sample preparation. Finally, we discuss certain aspects of the FIB fabrication routine that are a challenge to the realization of the high-Q/V designs

Multistate spin-transfer-torque random access memory

Spin-transfer-torque random access memory (STT-RAM) is an emerging non-volatile memory technology that stores information as the relative alignment of two ferromagnets in a magnetic tunnel junction stack. Due to high scalability, speed and endurance STT-RAM is being considered as a promising candidate for future universal memory. To improve storage density various multi-state configurations have been proposed for STT-RAM. Previously, using micromagnetic simulations, it was shown that shape anisotropy of a cross-shaped ferromagnet can be used to achieve multi-state operation in a STT-RAM bit. In this work, we attempt to demonstrate the multi-state operation of such cross-shaped ferromagnet experimentally. We have explored different approach to fabricate cross-shaped magnetic tunnel junctions. Using magnetic force microscopy we demonstrate equilibrium magnetization states of a patterned cross-shaped ferromagnet. Challenges and future perspectives have been discussed.Electrical and Computer Engineerin

Ion-sculpting of Nanopores in Amorphous Metals, Semiconductors and Insulators

We report the closure of nanopores to single-digit nanometer dimensions by ion sculpting in a range of amorphous materials including insulators (SiO$_2$ and SiN), semiconductors (a-Si), and metallic glasses (Pd$_{80}$Si$_{20}$) — the building blocks of a single-digit nanometer electronic device. Ion irradiation of nanopores in crystalline materials (Pt and Ag) does not cause nanopore closure. Ion irradiation of c-Si pores below 100 °C and above 600 °C, straddling the amorphous-crystalline dynamic transition temperature, yields closure at the lower temperature but no mass transport at the higher temperature. Ion beam nanosculpting appears to be restricted to materials that either are or become amorphous during ion irradiation.Engineering and Applied SciencesPhysic

Nanopore Fabrication by Controlled Dielectric Breakdown

Nanofabrication techniques for achieving dimensional control at the nanometer scale are generally equipment-intensive and time-consuming. The use of energetic beams of electrons or ions has placed the fabrication of nanopores in thin solid-state membranes within reach of some academic laboratories, yet these tools are not accessible to many researchers and are poorly suited for mass-production. Here we describe a fast and simple approach for fabricating a single nanopore down to 2-nm in size with sub-nm precision, directly in solution, by controlling dielectric breakdown at the nanoscale. The method relies on applying a voltage across an insulating membrane to generate a high electric field, while monitoring the induced leakage current. We show that nanopores fabricated by this method produce clear electrical signals from translocating DNA molecules. Considering the tremendous reduction in complexity and cost, we envision this fabrication strategy would not only benefit researchers from the physical and life sciences interested in gaining reliable access to solid-state nanopores, but may provide a path towards manufacturing of nanopore-based biotechnologies.Comment: 19 pages, 4 figures. Supplementary information contains 22 pages, 11 figures and 2 tables - A version of this manuscript was first submitted for publication on April 23rd, 2013. It is currently under review at another journa