Collaborations: The Architecture of Ahrends, Burton and Koralek (ABK) edited by Kenneth Powell

This article on one of the enduring British partnerships is not a vanity publication that we are accustomed to in our profession. Edited by Kenneth Powell, it contains illuminating essays of overlapping themes. The editor provides the overview. Jeremy Melvin writes a sensitive piece on the formation of the practice. While Elain Harwood and Frank Macdonald respectively describe early works and Irish projects of the practice Paul Finch contributes an intelligent essay on collaboration. The essays are not presented in succession but in layered colour strips on the top and bottom of pages with images in the body under the thematic titles of private/public, context, light/space and process. One does have to overcome the initial irritation of this unconventional layout before realising the importance of the ABK story. Indeed the interlocking of different narratives and the images has a resonance with the character of the practice itself, with three distinct personalities of Ahrends, Burton and Koralek, each with unique but complementary interests and predilections

Single shot ultrafast all optical magnetization switching of ferromagnetic Co/Pt multilayers

In a number of recent experiments, it has been shown that femtosecond laser pulses can control magnetization on picosecond timescales, which is at least an order of magnitude faster compared to conventional magnetization dynamics. Among these demonstrations, one material system (GdFeCo ferromagnetic films) is particularly interesting, as deterministic toggle-switching of the magnetic order has been achieved without the need of any symmetry breaking magnetic field. This phenomenon is often referred to as all optical switching (AOS). However, so far, GdFeCo remains the only material system where such deterministic switching has been observed. When extended to ferromagnetic systems, which are of greater interest in many technological applications, only a partial effect can be achieved, which in turn requires repeated laser pulses for full switching. However, such repeated pulsing is not only energy hungry, it also negates the speed advantage of AOS. Motivated by this problem, we have developed a general method for single-shot, picosecond timescale, complete all optical switching of ferromagnetic materials. We demonstrate that in exchange-coupled layers of Co/Pt and GdFeCo, single shot, switching of the ferromagnetic Co/Pt layer is achieved within 7 picoseconds after irradiation by a femtosecond laser pulse. We believe that this approach will greatly expand the range of materials and applications for ultrafast magnetic switching.Comment: 11 pages, 3 figures, supplementary material

The role of electron and phonon temperatures in the helicity-independent all-optical switching of GdFeCo

Ultrafast optical heating of the electrons in ferrimagnetic metals can result in all-optical switching (AOS) of the magnetization. Here we report quantitative measurements of the temperature rise of GdFeCo thin films during helicity-independent AOS. Critical switching fluences are obtained as a function of the initial temperature of the sample and for laser pulse durations from 55 fs to 15 ps. We conclude that non-equilibrium phenomena are necessary for helicity-independent AOS, although the peak electron temperature does not play a critical role. Pump-probe time-resolved experiments show that the switching time increases as the pulse duration increases, with 10 ps pulses resulting in switching times of ~sim 13 ps. These results raise new questions about the fundamental mechanism of helicity-independent AOS.Comment: 18 pages, 6 figures and supplementary material

Effect of electron irradiation on the properties of CdTe/CdS solar cells

Abstract Polycrystalline CdTe/CdS solar cells are used in space, as well as terrestrial, applications. The results of the studies on the effect of 8 MeV electron irradiation on p-CdTe/n-CdS thin film solar cells prepared by radio frequency (RF) sputtering are presented in this article. Solar cell parameters like short circuit current (I sc ), open circuit voltage (V oc ), fill factor (FF), conversion efficiency (Z), saturation current (I s ) and ideality factor (n) have been considered. CdTe thin film solar cells exhibit good stability against electron irradiation up to 100 kGy.

Optical Switching in Tb/Co-Multilayer Based Nanoscale Magnetic Tunnel Junctions

Magnetic tunnel junctions (MTJs) are elementary units of magnetic memory devices. For high-speed and low-power data storage and processing applications, fast reversal by an ultrashort laser pulse is extremely important. We demonstrate optical switching of Tb/Comultilayer-based nanoscale MTJs by combining optical writing and electrical read-out methods. A 90 fs-long laser pulse switches the magnetization of the storage layer (SL). The change in magnetoresistance between the SL and a reference layer (RL) is probed electrically across the tunnel barrier. Single-shot switching is demonstrated by varying the cell diameter from 300 nm to 20 nm. The anisotropy, magnetostatic coupling, and switching probability exhibit cell-size dependence. By suitable association of laser fluence and magnetic field, successive commutation between high-resistance and low-resistance states is achieved. The switching dynamics in a continuous film is probed with the magneto-optical Kerr effect technique. Our experimental findings provide strong support for the growing interest in ultrafast spintronic devices.Comment: total pages 22, Total figure

Picosecond Spin Orbit Torque Switching

Reducing energy dissipation while increasing speed in computation and memory is a long-standing challenge for spintronics research. In the last 20 years, femtosecond lasers have emerged as a tool to control the magnetization in specific magnetic materials at the picosecond timescale. However, the use of ultrafast optics in integrated circuits and memories would require a major paradigm shift. An ultrafast electrical control of the magnetization is far preferable for integrated systems. Here we demonstrate reliable and deterministic control of the out-of-plane magnetization of a 1 nm-thick Co layer with single 6 ps-wide electrical pulses that induce spin-orbit torques on the magnetization. We can monitor the ultrafast magnetization dynamics due to the spin-orbit torques on sub-picosecond timescales, thus far accessible only by numerical simulations. Due to the short duration of our pulses, we enter a counter-intuitive regime of switching where heat dissipation assists the reversal. Moreover, we estimate a low energy cost to switch the magnetization, projecting to below 1fJ for a (20 nm)^3 cell. These experiments prove that spintronic phenomena can be exploited on picosecond time-scales for full magnetic control and should launch a new regime of ultrafast spin torque studies and applications.Comment: Includes article + supplementary information. Latest version uses full name of the first author. Nature Electronics (2020

A Sweet Killer: Mesoporous Polysaccharide Confined Silver Nanoparticles for Antibacterial Applications

Silver nanoparticles (AgNP) confined within porous starch have been prepared in a simple, green and efficient manner, utilising the nanoporous structure of predominantly mesoporous starch (MS) to act as nanoparticle stabiliser, support and reducing surface. MS/AgNP materials present high surface areas (SBET > 150 m2 g−1) and mesopore volumes (Vmeso > 0.45 cm3 g−1). The interaction of the AgNP precursor and forming nanoparticle nuclei with the mesoporous domains of the porous polysaccharide, direct porosity to increasingly narrower and more defined pore size distributions, indicative of a degree of cooperative assembly. Transmission electron microscopy images indicated the presence of spherical AgNP of a size reflective of the porous polysaccharide mesopore diameter (e.g., 5–25 nm), whilst XPS analysis confirmed the metallic Ag0 state. Materials were prepared at relatively low Ag loadings (<0.18 mmol g−1), demonstrating excellent antimicrobial activity in solid and liquid phase testing against Gram negative (E. coli) and positive (S. aureus) model bacteria. The resulting materials are biocompatible and present a useful solid porous carbohydrate-based polymer vehicle to control the AgNP size regime and facilitate transference to a biological environment

Electrical performance of conducting polymer (SPAN) grown on GaAs with different substrate orientations

This article reports the effect of n-type GaAs substrate orientation, namely (100), (311)A and (311)B, on the electrical properties of sulfonated polyaniline (SPAN)/GaAs heterojunction devices. In addition, the inhomogeneity of the interface between various GaAs substrates and SPAN is investigated in terms of barrier height and ideality factor by performing I–V measurements at different temperatures (20–420K). The I–V results indicate that the value of the rectification ratio (IF/IR) at 0.5V is higher for SPAN/(311)B GaAs samples than for SPAN/(100) GaAs and SPAN/(311)A GaAs samples. Moreover, the barrier height decreases and the ideality factor increases with decreasing temperature for all three heterostructure devices. The high value of mean barrier ˚¯ b of SPAN/(311)B (calculated from the plots of ˚b0 as a function of 1/2kT) confirms that the GaAs substrate orientation results in an increase of barrier homogeneities. Furthermore,the C-V characteristics were obtained at room temperature. The C-V measurements showed that the carrier distributions at the interface and away from the interface in high index (311) GaAs orientations are more uniform and have better barrier homogeneity than those grown on the conventional (100) GaAs substrates