Advanced Technology Institute (ATI) Seminars
Temperature sensitivity of mid-infrared type II “W” inter-band cascade lasers (ICL) emitting at 4.1μm at room temperature
Monday 1 November 2010
Thursday 25 November 2010
Monday 29 November 2010
Monday 6 December 2010
Thursday 16 December 2010
Thursday 20 January 2011
Thursday 27 January 2011
Monday 7 February 2011
Monday 21 February 2011
Thursday 24 February 2011
Monday 28 February 2011
Thursday 10 March 2011
Monday 28 March 2011
Thursday 31 March 2011
Molecular simulation of materials for energy applications: how insight on the molecular level helps to create better materials
Thursday 2 June 2011
Thursday 1 March 2012
The realization of efficient semiconductor based spin filters and manipulators is essential for semiconductor spintronics to achieve its promised potential as a route to faster and more energy efficient electronics. One of the challenges is the creation of spin polarized currents within inherently non-magnetic semiconductors. The conventional approach to achieve this has been via the incorporation of magnetic materials. However, it may be possible to produce non-magnetic spin filters with very high efficiency by exploiting the strong spin-orbit interaction present in a number of semiconductors[1-3].
Modelling and simulation in circuit quantum electrodynamics from optical nonlinearities to high fidelity qubit state measurement
Thursday 22 March 2012
High Field Magnetic White Dwarfs vs. phosphorus in silicon: spectroscopy of hydrogenic orbitals under extreme field conditions
Thursday 29 March 2012
Thursday 3 May 2012
Thursday 10 May 2012
Thursday 17 May 2012
Friday 25 May 2012
Thursday 31 May 2012
Thursday 14 June 2012
Tuesday 24 July 2012
Thursday 24 January 2013
Laser ablation plumes are an example of complex compositional environments that, in addition to atomic components and depending on the ablation conditions, are constituted by molecules, clusters, nanoparticles and larger aggregates. This talk summarizes results on the use of a novel diagnostic procedure of ablation plumes that provides a wealth of information on the spatiotemporal composition of the laser plasma. The method is based on the generation of the harmonics of a driving laser beam propagating through the plasma.
Thursday 31 January 2013
Combining plasmonics with magneto-optical materials introduces nanoscaleinteractions between light fields and magnetisation, hence opening up the possibility of using one of these fields to control the other. In this talk I will give an introduction to magneto-plasmons which, at planar interfaces, are known to exhibit non-reciprocal propagation i.e. the wave vectors for left and right propagation are unequal.
Furthermore I will discuss my work on surface plasmons in metal-insulator-metal (MIM) slot waveguides. In a MIM waveguide with magnetic dielectric the symmetry between the upper and lower interfaces is broken by the introduction of the magnetic field; the balance between the field distributions on the two interfaces can be controlled by the applied field. As a result an external magnetic field can switch on and off the coupling of an electric dipole to the surface plasmon cavity waveguide modes. In addition I will show that both the total emission of radiation from the cavity and the distribution of the far-field radiation is strongly modified by tuning the magnetisation of the MIM structure.
Thursday 7 February 2013
Indium Tin Oxide (ITO) is the most widely used transparent conductor in the display industry and also finds applications in photovoltaics, EL lighting and a variety of other optical and electronic applications. However, Indium is in short supply and ITO is expensive. It also cracks when used in the current generation of touch screen displays and it is likely to do so in next-generation rollable displays. It is therefore imperative that viable alternative technologies be developed. In this talk I will highlight some novel approaches we have developed to produce conducting transparent films, which utilize nanostructures such as carbon nanotubes, graphene and metal nanowires. We show using directed or templated assembly of such nanostructures into monolayers or thin polymer composites allows for precise control of electrical percolation. The resulting thin films are flexible, inexpensive and have potential as candidates for the next generation of transparent electrodes.
Thursday 21 February 2013
In cavity quantum electrodynamics (QED), strong coupling of atoms and light is studied via confinement of light inside a cavity. The same situation can be achieved in the microwave regime in superconducting circuits with an electrical resonator playing the role of the cavity, and a well designed solid state quantum system being used as an artificial atom. In this talk I will introduce this field of circuit QED, and discuss recent results and future plans on its use in experiments on the strong coupling and quantum control of a variety of solid state systems, such as superconducting qubits and semiconductor quantum dots.
Thursday 28 February 2013
Imaging is one of the most important tools in science and technology, and there have been solid hints that quantum mechanics can help obtain an increase in the imaging resolution over classical methods. In this talk I give an overview of a few imaging techniques and present a unified theory for determining the imaging resolution for classical and quantum imaging. This allows us to properly compare various imaging techniques, and I give a few examples where quantum imaging outperforms classical imaging.
Thursday 7 March 2013
A new edge lithography utilising conventional cleanroom fabrication to create nanometre feature sizes on large area substrates will be presented. Applications including transparent electrodes and nanoscale mapping of thermal transport in graphene will illustrate the talk. A fabrication platform for the integration of carbon nanotubes in scanning thermal microscopy to provide a better insight of nanoscale thermal transport phenomena in materials will also be discussed.
Thursday 21 March 2013
Photovoltaic devices (solar cells) based on thin films of polymeric semiconductors represent an attractive technology to harvest solar energy in a sustainable fashion, as they can in principle be manufactured using materials and techniques having low embodied energy. In this talk, I discuss the basic principles of the operation of organic photovoltaic devices, and discuss some of the materials that we are exploring at Sheffield for photovoltaic applications. I also present recent work where we use a spray-coater to deposit various functional layers in a polymeric photovoltaic device, and argue that such techniques could form a useful part of a low-cost manufacturing process.
Thursday 25 April 2013
In an effort to enhance practicality of chalcogenide-based solid electrolyte for use in rechargeable Li+ ion batteries, much attention is being paid. The Li+-ion conduction can be conspicuously facilitated in some chalcogenide matrices mainly due to their enhanced covalence in the chemical bonds among constituent atoms compared to the case of conventional oxide counterparts. Specifically, the decrease in the Coulombic interactions between the mobile ions and the surrounding chalcogen atoms that are likely to be charged less negatively is known to contribute to the significant increase in the conductivity of Li+ ions. On the other hand, the dimensionality of the backbone structure of a chalcogenide material that is either crystalline or non-crystalline can be controlled relatively easily via compositional adjustment, which is attributed to the characteristic features of chalcogenide system, i.e., the presence of homopolar bonds and the 8-N rule. This flexibility in controlling dimensionality would provide a larger free volume to some desired chalcogenide matrices in which Li+ ions are supposed to penetrate relatively easier, thus resulting in the superior ionic conduction. The far enhanced conductivity observed from thio-LISICON seems to be quite understandable in this regard. Although several fundamental and/or technical issues remain to be resolved in putting these new Li-containing chalcogenide electrolytes to practical use, some chalcogen-based systems are fascinating indeed because these materials exhibit a great ionic conductivity tantamount to that of commercially available polymer (or even liquid) electrolyte.
Here, it is also worth mentioning that the melt-quenching and/or mechanical alloying techniques have been applied for fabricating Li-containing chalcogenides for solid electrolyte applications. We then come up with that, in addition to the typical fabrication methods, a new fabrication technique for Li-conducting chalcogenides would be more cost-effective or energy-efficient. Based on these considerations, we have aimed at exploring new solution-based processing routes for Li-containing Ge-Ga-S solid electrolyte. The Li+-ion conductivity is discussed in connection with the corresponding structural evolution which turns out to be quite sensitive to Ga concentration as well as other processing parameters.
Thursday 2 May 2013
Advances in nanoscalefabrication allow for the realization of artificial materials with properties that do not exist in nature, metamaterials. They are composed of subwavelengthelectromagnetic structures, placed at close proximity to each other. Due to mutual coupling between individual structures, they present properties to incident electromagnetic radiation that are different from those associated with the material from which the structures are comprised of. If a liquid crystal (LC) material is added to this geometry it provides a variable refractive index pathway between the CNTs and alters the plasmonicfrequency in a complex way. This is not a simple process to understand as the interaction at the surface of the CNT with the liquid crystal is a dominant effect in this geometry and is very difficult to observe experimentally. In this presentation, the most recent work we have been doing to demonstrate these unusual properties will be reviewed along with other promising hybrid nanophotonic technology options
Thursday 16 May 2013
Professor Alison Walker from the University of Bath will be giving a seminar to ATI PhD students and staff on Thursday 16 May 2013. Further details will follow.
Thursday 16 May 2013
At Bath, we have developed a model of organic devices that links morphology (packing arrangements) to device characteristics. The model, based on the dynamical Monte Carlo approach pioneered in surface physics, allows us to include interaction processes between different species on many different timescales. In this talk I will show how we have used this approach to compare organic solar cells of rod, blend and gyroid morphologies andto model the influence of interlayers, layers added to improve efficiency and lifetime, in organic light emitting devices, OLEDs. We have developed the model to allow it to distinguish between triplet and singlet excitons and allows for the interactions of these species (triplet-triplet annihilation, triplet-singlet annihilation, triplet-polaron quenching). I will show our predictions for
current-voltage-illumination characteristics (solar cells) and current-voltage-luminance characteristics (OLEDs). I will also show how through prediction of emission zone profiles in an OLED, we can gain insight into what determines changes in OLED efficiency with current and how in the longer term this approach can be used to address degradation.
Wednesday 22 May 2013
Very recently, a number of companies announced organic solar cells with power conversion efficiencies well exceeding 10% on lab scale opening pathway towards a cost-efficient exploitation of this young technology, thereby widely exhausting the efficiency potential for common single junction solar cells. Reasons for the strong efficiency limitations in organic solar cells are among others the spectrally limited absorption of organic semiconductors as well as thermalizationlosses during charge carrier relaxation after the absorption of highly energetic photons. A widely discussed concept to overcome this limitation is the use of tandem solar cell architectures, i.e. the (monolithic) integration of two solar cells in series in a single device stack. Their working principle relies on two different light absorbing semiconductors with different band-gap and hence complementary absorption in order to ensure a broader absorption of the solar spectrum and to reduce the energy losses upon the absorption of highly energetic photons. In fabrication processes, the sophisticated tandem solar cell multilayer-architectures offer many degrees of freedom such as choices for materials and layer thicknesses. Hence, understanding their working principle and optimizing their efficiency is one of the most challenging tasks in organic photovoltaics. Besides carefully chosen complementary absorbers there is a strong need for charge carrier transport layers that allow for the fabrication on an ohmicintermediate contact with low resistivity. Both require advanced solutions in particular when low-cost solution deposition processes are considered with respect to future printing processes.
As the front cell of an organic tandem solar cell needs to be transparent for a certain part of the visible spectrum in order to provide light for the back cell, this technology is closely related to a key application for organic photovoltaics: Semi-transparent devices for building or automotive integration.
In this work we present general concepts for the solution fabrication of both semi-transparent and tandem organic solar cells and how to realize devices with decent power conversion efficiencies. In particular, we present promising concepts for charge carrier transport layers for advanced device architectures and solutions how to overcome solubility limitations.