This work demonstrates the production of a well-controlled, chemical gradient on the surface of graphene. By inducing a gradient of oxygen functional groups, drops of water and dimethyl-methylphosphonate (a nerve agent simulant) are "pulled" in the direction of increasing oxygen content, while fluorine gradients "push" the droplet motion in the direction of decreasing fluorine content. The direction of motion is broadly attributed to increasing/decreasing hydrophilicity, which is correlated to high/low adhesion and binding energy. Such tunability in surface chemistry provides additional capabilities in device design for applications ranging from microfluidics to chemical sensing.

Ga 2 O 3 has emerged as a promising material for next-generation power electronics. Beyond the most stable and studied β phase, metastable α-, ε-, and κ-Ga 2 O 3 have unique characteristics such as larger bandgaps, potential alloying for dopant and band engineering, and polarization, all of which can be leveraged in electronic device applications. Plasma-enhanced atomic layer deposition (PEALD) is a conformal, energy-enhanced synthesis method with many advantages including reduced growth temperatures, access to metastable phases, and improved crystallinity. In this study, PEALD was employed to deposit highly resistive, crystalline Ga 2 O 3 films from 265 to 475 °C on cplane sapphire substrates. Crystallinity, atypical at these low growth temperatures, was presumably due to the high flux of energetic ions to the growth surface independent of other growth parameters. Phase selectivity of β, α, ε(κ)-Ga 2 O 3 was demonstrated as a function of plasma gas composition, gas flow and pressure during the plasma pulse, as well as growth temperature. Factors such as atomic oxygen generation and the flux of energetic ions were found to have a significant impact on the ability to attain metastable phases. Optimum films of each phase were fully characterized to determine the feasibility of PEALD Ga 2 O 3 films. While both highquality, single-phase βand α-Ga 2 O 3 films were achieved, ε-Ga 2 O 3 films were not able to be completely isolated and even under the best conditions contained components of βand κ-Ga 2 O 3 as identified by transmission electron microscopy. Trends suggest that this could be a limitation of the underlying substrate or reactor configuration.

The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma. Unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (∼ few keV) electron beam, an approach that can be attractive to atomic layer processing applications. In particular, high electron densities (10 10 -10 11 cm −3 ) can be produced in electron beam generated plasmas, where the electron temperature remains between 0.3 and 1.0 eV. Accordingly, a large flux of ions can be delivered to substrate surfaces with kinetic energies in the range of 1 to 5 eV. This provides the potential for controllably etching and/or engineering both the surface morphology and chemistry with monolayer precision. This work describes the electron beam driven plasma processing system, with particular attention paid to system characteristics and the ability to control the generation and delivery of ions to the surface and their energies. Electron beam generated plasmas are produced by injecting a highenergy electron beam into a gas background, which will ionize, dissociate, and excite atoms or molecules as it traverses the gas volume. While the basic inelastic processes that lead to species production are the same as those in discharge plasmas, the use of energetic electron beams to drive production results in plasmas that have very different properties than conventional discharges. Some of these properties are attractive for plasma-based atomic layer processing applications where, whether etching, depositing, or chemically modifying materials, fine control over the flux and energy of ions is needed. In the case of atomic layer etching, perhaps the single most important need is to tightly control the kinetic energy of ions incident to the processing surface so as to avoid damage while maintaining a reasonable etch rate. [1][2][3] In this regard, a significant advantage of beam-driven plasmas is the inherently low electron temperature T e , which is typically a fraction of an eV in most gas mixtures of technological interest. Importantly, this is true regardless of the plasma density. Thus, one can produce a large fluence of reactive ion and neutral species where the kinetic energy of the ions is as low as a few eV.The interest in electron beam generated plasmas for materials processing can be traced back at least 4 decades. In the early 1970s Bunshah 4 described an electron beam vapor deposition system that utilizes an electron beam to both vaporize the metal and "activate" the background gas. It was also noted by Dugdale 5 that high-energy electron beam systems developed for welding could be employed for "soft vacuum vapor deposition" in a manner similar to that of Bunshah. In the 1980s, Collins and co-workers at Colorado State University, developed electron beam produced plasmas for plasma enhanced chemical vapor deposition of SiO 2 . 6,7 This system used a sheet-like beam of multi-keV electrons injected parallel to the growth substrate. A similar configurat...

The inclusion of plasma in atomic layer deposition processes generally offers the benefit of substantially reduced growth temperatures and greater flexibility in tailoring the gas-phase chemistry to produce specific film characteristics. The benefits plasmas provide, however, come at the cost of a complex array of process variables that often challenge the ability to predict, a priori, the influence of any one input parameter. In this work, the authors attempt to provide some clarity as to how plasmas are formed and controlled and how they can most optimally be employed within the framework of atomic layer deposition. To begin, the authors cover some of the fundamentals of plasma generation along with the production of energetic and reactive species and their transport within the plasma. They then focus on how different plasma generation schemes and geometries, often employed in plasma-enhanced atomic layer deposition (PEALD), differ in their production of energetic and reactive species. They also address the plasma-surface interactions that are critical for film growth and control of crystallinity. Throughout this work, the authors use both current experimental data and a review of previously published works to describe how variations in the approach to plasma generation and the interactions between plasma-produced species and the growth surface influence the plasma reactant step in PEALD processes. The authors highlight two case studies to demonstrate how these relationships can be used to control the phase purity of crystalline titanium dioxide (TiO2) films and grow crystalline growth of semiconducting indium nitride (InN).

This paper, the first in a series of two, presents experimental results demonstrating the control of electron and ion energy distribution functions in electron beam generated processing plasmas by adding trace concentrations of N 2 to an Ar background. Measurements of the electron energy distribution function, f 0 (E), are performed using a Langmuir probe while measurements of the Ar ion energy distribution function are performed using an energy-resolved mass spectrometer. The experimental results agree with modeling results, described in part II of this work, which indicate that inelastic electron collisions with nitrogen molecules provide an energy sink that can be exploited to control the electron energy distribution function.