UC Berkeley

Nanoscale materials made of carbon, boron, and nitrogen, namely BCN nanostructures, exhibit many remarkable properties making them uniquely suitable for a host of applications. Boron nitride (BN) and carbon (C) nanomaterials are structurally similar. The forms studied here originate from a two-dimensional hexagonally arranged structure of sp2 bonded atoms. These nanomaterials exhibit extraordinary mechanical and thermal properties. However, the unique chemical compositions of carbon and boron nitride result in differing electrical, chemical, biological, and optical properties. In this work, we explore the single layer sheets of sp2 bonded carbon (graphene), and their cylindrical forms (nanotubes) of carbon and boron nitride.

In the first part of this work, we look at carbon based nanomaterials. In Chapter 2, the electron field emission properties of carbon nanotubes (CNTs) and their implementation as nanoelectromechanical oscillators in an integrated device will be discussed. We show a technique hereby a single CNT is attached to a probe tip and its electron field emission characterized. We then delve into the fabrication of a field emitting CNT oscillator based integrated device using a silicon nitride membrane support. We then present the electron field emission capabilities of these devices and discuss their potential use for detection of nuclear magnetic resonance (NMR) signals.

Graphene is the subject of study in Chapter 3. We begin by extensively examining the synthesis of graphene using a chemical vapor deposition (CVD) process, ultimately establishing techniques to control graphene domain size, shape, and number of layers. We then discuss the application of the single-atom thick, but ultra-mechanically strong graphene as a capping layer to trap solutions in a custom fabricated silicon nitride membrane to enable transmission electron microscopy (TEM) of liquid environments. In this manner, the volume and position of liquid cells for electron microscopy can be precisely controlled and enable atomic resolution of encapsulated particles.

In the second portion of this work, we investigate boron nitride nanostructures and in particular nanotubes. In Chapter 4, we present the successful development and operation of a high-throughput, scalable BN nanostructures synthesis process whereby precursor materials are directly and continuously injected into a novel high-temperature, Extended-Pressure Inductively-Coupled plasma system (EPIC). The system can be operated in a near-continuous fashion and has a record output of over 35 g/hour for pure, highly crystalline boron nitride nanotubes (BNNTs). We also report the results of numerous runs exploring the wide range of operating parameters capable with the EPIC system.

In Chapter 5, we examine the impurities present in as-synthesized BNNT materials. Several methods of sample purification are then investigated. These include chemical oxidation, using both gas and liquid phase based methods, as well as physical separation techniques.

The large scale synthesis of BNNTs has opened the door for further studies and applications. In Chapter 6, we report a novel wet-chemistry based route to fill in the inner cores of BNNTs with metals. For the first time, various metals are loaded inside of BNNTs, forming a plethora of structures (such as rods, short nanocrystals, and nanowires), using a solution-based method. We are also able to initiate and observe dynamics of the metallic nanoparticles, including their movement, splitting, and fusing, within a BNNT.