Peiman Hosseini

An optoelectronic framework enabled by low-dimensional phase-change films.

The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states—amorphous and crystalline—in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young’s modulus. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge2Sb2Te5) exploited the reversible change in their optical properties in rewritable optical data storage technologies. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent ‘smart’ glasses, ‘smart’ contact lenses and artificial retina devices.

On‐Chip Photonic Memory Elements Employing Phase‐Change Materials

Phase-change materials integrated into nanophotonic circuits provide a flexible way to realize tunable optical components. Relying on the enormous refractive-index contrast between the amorphous and crystalline states, such materials are promising candidates for on-chip photonic memories. Nonvolatile memory operation employing arrays of microring resonators is demonstrated as a route toward all-photonic chipscale information processing.

Accumulation-Based Computing Using Phase-Change Memories With FET Access Devices

Phase-change materials and devices have received much attention as a potential route to the realization of various types of unconventional computing paradigms. In this letter, we present non-von Neumann arithmetic processing that exploits the accumulative property of phase-change memory (PCM) cells. Using PCM cells with integrated FET access devices, we perform a detailed study of accumulation-based computation. We also demonstrate efficient factorization using PCM cells, a technique that could pave the way for massively parallelized computations.

Colour performance and stack optimisation in phase change material based nano-displays

We recently demonstrated a new breed of optoelectronic devices based on ultra-thin phase change materials[1]. Non-volatile, ultra-fast and ultra-thin displays based on such materials are of particular interest. In this paper we describe colour performance modelling of such displays by applying well known optical simulation techniques in an effort to refine the design of future high contrast colour phase change material-based displays.

Direct manufacturing of ultrathin graphite on three-dimensional nanoscale features

There have been many successful attempts to grow high-quality large-area graphene on flat substrates. Doing so at the nanoscale has thus far been plagued by significant scalability problems, particularly because of the need for delicate transfer processes onto predefined features, which are necessarily low-yield processes and which can introduce undesirable residues. Herein we describe a highly scalable, clean and effective, in-situ method that uses thin film deposition techniques to directly grow on a continuous basis ultrathin graphite (uG) on uneven nanoscale surfaces. We then demonstrate that this is possible on a model system of atomic force probe tips of various radii. Further, we characterize the growth characteristics of this technique as well as the film’s superior conduction and lower adhesion at these scales. This sets the stage for such a process to allow the use of highly functional graphite in high-aspect-ratio nanoscale components.

2-D Materials as a Functional Platform for Phase Change Tunable NEMS

Using modeling-based design, we demonstrate a tunable nanoelectromechanical system (NEMS) capable of operating in the 800-MHz-to-1.9-GHz frequency band without the need for continuous electrostatic tuning stimuli using reversible structural transitions of solid-state materials. We show that permanent, yet reversible, tuning of such a resonator in this region is possible, but only when the structural support platform is made of ultralight and thin 2-D elements. Using graphene as the top and bottom electrodes with a layer of the well-known phase change material Ge2Sb2Te5, we provide a pathway for highly functional NEMS that employ 2-D electrodes and phase change materials in tunable resonant circuits. Given the recent advances in graphene NEMS, and because the resonator properties are not dependent on the electronic quality, rather the mass of the graphene, such a design would enable the application of tunable phase change NEMS with no active power requirement in a variety of applications in the future.