Ion etching of ultranarrow structures

We describe the use of Polymethylmethacrylate as both electron beam sensitive resist and ion etch mask for high-resolution pattern transfer. By using high-resolution electron beam lithography, chemically assisted ion beam etching, and in-situ metallization, we have fabricated ultra-narrow gates with lateral dimensions below 20 nm, spaced with < 50 nm pitch on high mobility 2D electron gas material. This technique, which is thought to provide extremely small lateral electron depletion lengths and well defined confienement potentials, allows us to produce new and more complicated structures for the study of quantum transport

Microfabrication below 10 nm

We describe a new electron beam lithography method for producing structures with lateral sizes smaller than the incident beam diameter. These patterns are transferred into GaAs/AlGaAs, InGaAs/GaAs and InGaAs/InP quantum well heterostructures using chemically assisted ion beam etching, thereby forming uniform arrays of pillars with lateral dimensions at or below 10 nm. To correlate the sizes of such structures with our exposure and development conditions, reflection electron microscopy observations are used

Direct measurement of the transmission matrix of a mesoscopic conductor

We have developed an experimental approach which permits evaluation of the entire transmission matrix of a mesoscopic conductor. Results are presented from two new investigations enabled by this technique: (a) We study ballistic multiprobe conductors in the limit of weak probe coupling, and (b) we image modal features in the distribution function of electrons emerging from a quantum point contact

An Integrated Scientific Framework for Child Survival and Early Childhood Development

Building a strong foundation for healthy development in the early years of life is a prerequisite for individual well-being, economic productivity, and harmonious societies around the world. Growing scientific evidence also demonstrates that social and physical environments that threaten human development (because of scarcity, stress, or instability) can lead to short-term physiologic and psychological adjustments that are necessary for immediate survival and adaptation, but which may come at a significant cost to long-term outcomes in learning, behavior, health, and longevity. Generally speaking, ministries of health prioritize child survival and physical well-being, ministries of education focus on schooling, ministries of finance promote economic development, and ministries of welfare address breakdowns across multiple domains of function. Advances in the biological and social sciences offer a unifying framework for generating significant societal benefits by catalyzing greater synergy across these policy sectors. This synergy could inform more effective and efficient investments both to increase the survival of children born under adverse circumstances and to improve life outcomes for those who live beyond the early childhood period yet face high risks for diminished life prospects

Ion etching of ultranarrow structures

We describe the use of Polymethylmethacrylate as both electron beam sensitive resist and ion etch mask for high-resolution pattern transfer. By using high-resolution electron beam lithography, chemically assisted ion beam etching, and in-situ metallization, we have fabricated ultra-narrow gates with lateral dimensions below 20 nm, spaced with < 50 nm pitch on high mobility 2D electron gas material. This technique, which is thought to provide extremely small lateral electron depletion lengths and well defined confienement potentials, allows us to produce new and more complicated structures for the study of quantum transport

Imaging dielectric relaxation in nanostructured polymers by frequency modulation electrostatic force microscopy

We have developed a method for imaging the temperature-frequency dependence of the dynamics of nanostructured polymer films with spatial resolution. This method provides images with dielectric compositional contrast well decoupled from topography. Using frequency-modulation electrostatic-force-microscopy, we probe the local frequency-dependent (0.1–100 Hz) dielectric response through measurement of the amplitude and phase of the force gradient in response to an oscillating applied electric field. When the phase is imaged at fixed frequency, it reveals the spatial variation in dielectric losses, i.e., the spatial variation in molecular/dipolar dynamics, with 40 nm lateral resolution. This is demonstrated by using as a model system; a phase separated polystyrene/polyvinyl-acetate (PVAc) blend. We show that nanoscale dynamic domains of PVAc are clearly identifiable in phase images as those which light-up in a band of temperature, reflecting the variations in the molecular/dipolar dynamics approaching the glass transition temperature of PVAc