skip to primary navigationskip to content

Past Events

Events which have already happened.
Quantum Dot Biosensors- Christian Cimorra (TFM)

Mott Seminar Room
From Dec 15, 2011 02:30 PM to Dec 15, 2011 03:30 PM
A novel sensing approach for the detection of analytes based on the photonic properties of Quantum Dots (QD) will be described with particular reference to medical applications. Photoluminescence (PL) from the QD nanocrystal lattice is contained and stabilised by capping agents, which can be designed to react to microenvironmental molecules thus conferring a quantifiable photo-physical effect. The functional agent of choice is the biomolecule Glutathione (GSH) due to its reducing potential and metal-ion complexation abilities. In addition, the relatively simple and facile synthesis methodology delivers controllable size-dependant QD architectures with tunnable emissions (480nm-410nm) offering multiplexing potential. The performance of a glucose sensing platform will be the model for the proof-of-concept.

Resistivity of Metal Oxides- Lakshay Jethi (TFM)

Mott Seminar Room
From Dec 08, 2011 02:30 PM to Dec 08, 2011 03:30 PM
Cobalt ferrite nanoparticles prepared by chemical co-precipitation route were synthesized and characterized using XRD, infra-red spectroscopy and electron paramagnetic resonance spectroscopy. These nanoparticles can be used for sensing ethanol vapours. The physical properties relevant to sensing aspects are investigated. The resistance, responsiveness, sensitivity, optimum working temperature and response time of cobalt ferrite nanoparticle based semiconductor ethanol vapour sensor are obtained from the response and recovery curves. They are practically the same with minor deviations in the studied temperature range. The results show that the largest resistance increase was observed in the 25ºC measurements. On varying the alcohol vapour concentration, the resistance of the sensor varies slightly in a particular temperature operating range. The mechanism for sensing ethanol will also be described.

Electronically Driven Major-Reversal with No Major Field-Dr Massimo Ghidini (Materials Sciences)

Mott Seminar Room
From Dec 01, 2011 02:30 PM to Dec 01, 2011 03:30 PM
The electrical reversal of magnetization is one of the key goals in the study of multiferroic and magnetoelectric materials, and was recently demonstrated in ferromagnetic films using strain1 or exchange bias2 from multiferroic single-crystal substrates. However, each reversal event required the reversal of an applied magnetic field, and so repeatable magnetic reversal under purely electrical control remains an outstanding goal. Here we perform microscopic investigations of commercially manufactured multilayer capacitors (MLCs) which serendipitously display strain-mediated magnetoelectric coupling between magnetostrictive Nielectrodes and piezoelectric BaTiO3 (BTO) dielectric layers. Magnetic force microscopy (MFM) reveals perpendicularly magnetized features in the electrode layers that exhibit electrically driven repeatable magnetization reversals with no applied magnetic field. Micromagnetic modelling supports our interpretation that this non-volatile magnetization reversal may be achieved via a dynamic process that is associated with a temporary reduction in perpendicular uniaxial magnetic anisotropy driven by strain from fast and reversible voltage-driven ferroelectric-domain switching. I will also report on the reversible control of perpendicular magnetic anisotropy in polycrystalline nickel films evaporated on single-crystal ferroelectric BTO substrates via thermal and electrical treatments. We have employed both MFM and photoemission electron microscopy with magnetic contrast from x-ray magnetic circular dichroism (XMCD-PEEM), to study the effects of thermally and electrically driven changes in the BTO substrate on the magnetic domain structure of the nickel films. I will show that the perpendicular component of the magnetization can be erased and reset by thermally cycling through the structural transitions of the substrate and more importantly, it can be reversibly electrically controlled at room temperature.

III-IV Semiconductors- Dr Ian Farrer (SP)

Mott Seminar Room
From Nov 24, 2011 02:30 PM to Nov 24, 2011 03:30 PM
MBE technology has played a crucial role in the development of nanostructures enabling the study of electron interactions at low temperatures. This talk will present an overview of Molecular Beam Epitaxy with particular reference to III-V materials in a research setting. The operation of a III-V growth system will be described with emphasis on the production of very high purity structures and the constraints that this imposes. The procedure for access to either existing wafer material or new sample requests will also be outlined.

Avenues of Metrology with Quantum Dots- Dr Mete Atatüre (AMOP)

Mott Seminar Room
From Nov 17, 2011 02:30 PM to Nov 17, 2011 03:30 PM
Self-assembled semiconductor quantum dots display discrete electronic energy levels coupled by optical transitions and they are governed by spin-dependent optical selection rules. This opens an optical channel to control and detect a single spin in a quantum dot and significant progress was witnessed based on this property in the field of quantum information science. In the quest to suppress the detrimental effects of the environment, quantum metrology emerged as a recent topic of research with potential applications. Excitonic transitions of self-assembled quantum dots can depend strongly on the ambient electric and magnetic fields, as well as strain. We will discuss how this susceptibility can be utilized in return for electric field sensing with sensitivity better than 1 V/m/√Hz and we will continue on to other avenues of quantum metrology using self-assembled quantum dots.

Tuneable interface exchange for optical magnetisation control- Dr Theo Trypiniotis (TFM)

Mott Seminar Room
From Nov 10, 2011 02:30 PM to Nov 10, 2011 03:30 PM
Beyond studies of spin dependent transport which have traditionally dominated the field of spintronics, an increasing number of investigations of more ‘exotic’ spin related phenomena are being reported in the last few years. In this talk I will present the extension of our work in spin transport, into the use of spin accumulation for the optical control of magnetisation. We can routinely use optical spin orientation in III -V semiconductors as a reliable spin source for spin transport investigations. We have recently successfully combined the above with ferromagnetic resonance (FMR) measurements on epitaxial ferromagnetic-metal/semiconductor interfaces. The optically controlled spin polarised carrier population at the interface affects the ferromagnet magnetisation via an interface exchange interaction the signature of which is measured in the FMR response. We have demonstrated an effective exchange field of the order of tens of Gauss at room temperature, which offers a new method for the optical control of magnetization.

The Spin Hall Effect- Dr Jörg Wunderlich (Hitachi Lab)

Mott Seminar Room
From Nov 03, 2011 02:30 PM to Nov 03, 2011 03:30 PM
We realized an all semiconductor spin Hall effect transistor by combining the Spin transistor concept proposed by Datta and Das with the (inverse) spin Hall effect (iSHE) detection. We first discuss the Spin Hall effect in a device where spins are optically generated in the depletion layer of a reverse biased pn-junction and injected into a 2-dimensional electron gas (2DEG). In the 2DEG, the spin-orbit interaction (SOI) can be modulated with electrostatic gates to control locally the spin-polarziation. This concept of spin-manipulation is tested by using the SHE. The SHE is also used to demonstrate a spin AND logic function in a 2D channel with two gates. Finally, we demonstrate the inverse SHE detection in a semiconductor combined with an electrical spin injection and manipulation, and to perform a quantitative analysis of the measured iSHE voltages. In our GaAs microchannel with an Fe injection electrode, the spin current in a lateral semiconductor channel is detected by the iSHE and the spin polarization is simultaneously measured by the non-local spin valve effect using an additional Fe electrode. The spins in the channel are manipulated via the Hanle spin precession induced by an applied magnetic eld and via a drift of electrons induced by an applied electrical bias. The output spin signal is suppressed or enhanced depending on the applied drift, rendering the device an electrically controlled spin amplifier.

Spin Injection into Germanium- Chen Shen (TFM)

Mott Seminar Room
From Oct 27, 2011 02:30 PM to Oct 27, 2011 03:30 PM
In this study, we generate spin polarised electrons in GaAs near an epitaxial Fe/GaAs interface using optical spin orientation. By applying high forward bias, we remove or invert the Schottky barrier. A spin filtering current was obtained as a function of bias for opposite magnetic fields. The results reveal a clear spin filtering in the absence of a tunnelling barrier and suggest a successful experimental demonstration of ballistic spin transport across an epitaxial Fe/GaAs interface. Using a simple transport model based on a transfer matrix approach within an effective mass approximation, we semi-quantitatively obtain the polarisation of the interfacial density of states by fitting our experimental data. By comparing with the theoretical results based on a tight-binding approach by Honda* et al.*[1], our experimental results suggest the interface is a mixture of Fe-As and Fe-Ga terminated structure.

Electrodeposition with Bitrex- Jos Cooper (TFM)

Mott Seminar Room
From Oct 20, 2011 02:30 PM to Oct 20, 2011 03:30 PM
We investigate the effects of denatonium benzoate (Bitrex) on the electrodeposition of copper films from a boric acid bath using scanning electron microscopy, cyclic voltammetry, electrochemical quartz microbalance (EQCM) measurements and corrosion studies. In the absence of Bitrex, pure copper films grown by this method are optically black owing to the appearance of complex surface nanostructures. The addition of Bitrex acts as a levelling agent preventing the formation of these nanostructures even for concentrations as low as 0.02mM producing a lustrous film with low surface roughness. Bitrex is also found to improve the corrosion resistance by up to a factor of 20 and increase the current efficiency by over a factor of two. Bitrex is hypothesised to act directly on the cathode, partially inhibiting the growth or lowering the deposition current.

MISM Conference Overview Magnetotactic Bacteria- Dr Adrian Ionescu (TFM)

Mott Seminar Room
From Oct 13, 2011 02:30 PM to Oct 13, 2011 03:30 PM
Dr Adrian Ionescu (TFM)