Integrated phase-change photonics for memory and computing devices

PGR Emanuele Gemo

This video, narrated by our third year PGR Emanuele Gemo, gives a short description of the integrated phase-change photonic memory, a device allowing to store and retrieve non-volatile information on optical chips.

Emanuele’s research project is focused on the theoretical study of this class of devices, and on the proposal of solutions to improve its energy, speed and memory density performances. This device architecture has the potential to be exploited not only for memory applications, but also for in-memory computing: this aim is pursued by the EU2020 funded Fun-COMP research project, led by Prof. C.David Wright, which is a collaboration between seven academic and industrial partners focused to create a light signal based – biologically inspired neuromorphic platform, of which the phase-change photonic memory is an integral part.

The video has been created for the Fun-COMP website, to explain to an extended audience this key building block, with simple terms and yet drawing upon all the essential elements.

Emanuele co-authored “Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics”, a paper which was recently published in prestigious journal Advanced Functional Materials

Ben Hogan is awarded SPIE IDL Micro Grant

Ben Hogan, fourth year CDT PGR, has been awarded a SPIE IDL Micro Grant for $2000- one of only two UK universities to receive it this year.

The UNESCO International Day of Light is a global initiative highlighting to the citizens of the world the importance of light and light-based technologies in their lives, for their futures, and for the development of society. SPIE IDL Micro Grants support local community events and activities that highlight the critical role that light plays in our daily lives. The grants are awarded globally on a competitive basis, with 14 awarded in 2019.

Ben will use the $2000 to run three concurrent events in April and May, to promote the critical role that light plays in our daily lives to the general public.

 

 

The events that will be run are as follows:
• A photo competition for the local community, themed around light.
• A poster competition for researchers, with the aim being to convey cutting-edge research in simple terms for non-specialists.
• Lighting up RAMM – On Saturday 18th May, PGRs will provide hands-on demonstrations, activities and displays in the RAMM museum in Exeter.
• Exeter EnLIGHTens – PGRs are inviting schoolchildren of all ages (and their teachers) to pose us their questions about light. PGRs will then answer as many of their questions as possible in the form of video demonstrations of practical experiments, which will be made freely available online.

As the events progress, information and updates can be found at https://euops.wordpress.com/euops-enlightens or by following @ExUniOptPhotSoc on Twitter. Follow Ben’s research at https://twitter.com/BenHoganSci.

Porous ZnO/Carbon nanocomposites derived from metal-organic frameworks for highly efficient photocatalytic applications – A correlational study

Congratulations to XM² PGR student (third year) Mian Zahid Hussain for his latest publication on “Porous ZnO/Carbon nanocomposites derived from metal-organic frameworks for highly efficient photocatalytic applications – A correlational study” in Carbon journal. Abstract below.

Abstract

Porous ZnO/C nanocomposites derived from 3 different Zinc based metal-organic frameworks (MOFs) including MOF-5, MOF-74 and ZIF-8, were prepared at high temperature under water-steam atmosphere and their performances in photocatalytic H2 evolution reaction (HER) and photodegradation of organic dye pollutants were evaluated. The formation mechanism from MOF precursors, the structural properties, morphologies, compositions and textural properties of the derived ZnO/C composites were fully investigated based on different characterization techniques and the correlation between the precursors and the derived composites was discussed. It is evident that MOF precursors determine the crystalline structures, doping profiles, thermal stabilities and metal oxide-carbon weight percentage ratios of the resulting composites.

The correlation between MOFs and their derived nanocomposites indicates that different parameters play unalike roles in photocatalytic performances. The desired properties can be tuned by selecting appropriate MOF precursors. MOF-5 derived porous ZnO/C nanocomposite not only exhibits the highest photocatalytic dye degradation activity under visible light among these MOFs, but also outperforms those derived from MOF-74 and ZIF-8 up to 9 and 4 times in photocatalytic HER respectively. This study offers simple and environmentally friendly approaches to further develop new homogeneously dispersed functional metal oxide/carbon composites for various energy and environment-related applications.

 

Zahid has previously published on ZnO nanocomposites studies, and is currently working on a translation of Carlo Rovelli’s book “Seven Brief Lessons on Physics” into Urdu.

Leadership and Teambuilding Techniques

 

Third year students Emanuele, Jacob and Kieran working through a group exercise

On 30th and 31st January, our third year XM² postgraduate researchers took part in Leadership Training, provided by Fistral. This is the third year that we have run this course, which equips the postgraduate researchers with negotiation skills, listening techniques and how to approach group work from a psychological perspective.

Some comments from the PGRs taking part this year- “it has been helpful to see the differing views and motivations of people. You will see the wider scope of those around you” and “very interesting and insightful”.

Fistral are returning in May to provide our first year PGRs with Project Management training.

Check out our what’s on page to see the full range of training and events.

Our third years working through hypothetical situations

 

 

 

Training and other events: February 2019 to July 2019

Please find below a table of all upcoming XM² training and other events from February 2019 until July 2019 as far as planning currently allows and subject to change.

PGRs, please highlight any XM²-training related absence times to your supervisors. In regards to annual leave or other absence time planning: All confirmed events have been sent to the PGRs via a calendar invitation, but please ensure to check the CDT in Metamaterials Outlook calendar and to liaise with your supervisors and the CDT in Metamaterials office () for approval BEFORE you make any bookings, as there might be a few more events coming up that are yet to be confirmed.

Supervisors, please be mindful of the XM² events when setting expectations on research deliverables with the PGRs.

February
19.02.19 CBC Appointments (Optional) All PGRs 09:30-12:30  13:30-16:30 Harrison 332
20.02.19 Month 6 Assessment Briefing 1st years 11:00-12:00 Physics SCR
March
06.03.19 CDT Groups All PGRs 14:30-15:30 Peter Chalk 2.1, 2.4, 2.5, 2.6
12.03.19 Beyond a PhD: Heather Lewtas All PGRs 12:30-13:30 Newman Purple
18.03.19 Presentation Skills 1st years 10:00-12:00 Physics 124
 April
01.04.19-02.04.19 NPL Visit (2 Day Visit) All PGRs 09:00-17:00 TBC
12.04.19 Beyond a PhD: James Claverley (title TBC) All PGRs 12:30-13:30 Amory Moot Room
17.04.19 CDT Colloquium: Femius Koenderink (title TBC) All PGRs 14:00-15:00 Harrison 004
18.04.19 Careers Event All PGRs 09:00-17:00 Reed Hall
May
10.05.19 CDT Colloquium: Steve
Barnett (title TBC)
All PGRs 12:30-13:30 Newman Blue
21.05.19-22.05.19 Project Management Training 1st years 09:00-16:30 Physics SCR
June
14.06.19 CDT Colloquium: Joaquin Rossier (title TBC) All PGRs 12:30-13:30 Streatham Court D
28.06.19 Beyond a Phd: Irina Khromova and Sathya Sreetharaman All PGRs 12:30-13:30 Queens LT1
July
05.07.19 CDT Colloquium: Vihar Georgiev (Title TBC) All PGRs 12:30-13:30 Queens LT1

 

Miguel Camacho Aguilar passed his viva!

Congratulations to Miguel Camacho Aguilar, who has passed his viva. His thesis title was “Microwave response of finite periodic metal structures”. The examiners were Prof. Guido Valerio from University Pierre and Marie Curie in Paris and Prof. Matthew Browning from University of Exeter.

Miguel will be starting a postdoctoral role in the group of Prof. Nader Engheta at the University of Pennsylvania on 1st March. His future work in the US will be related to metamaterials and plasmonics. Nader invented the field of metatronics, i.e., metamaterial-based optical nano circuitry, in which properly designed nano structures function as “lumped’ optical circuit elements such as optical capacitors, optical inductors and optical resistors. We wish Miguel the best of luck in his new role and career.

Below is a summary of the various publications and conferences that Miguel participated in, along with his thesis abstract. Other notable achievements include his recent Spanish national award for best Physics undergraduate student (class of 2015) and participating in Nanotech PhD student scheme with IOP Publishing in 2017.

Keep up to date with Miguel’s latest research at https://scholar.google.co.uk/citations?user=62eJgVAAAAAJ&hl=en.

Miguel is author/co-author on the following publications:

Miguel attended the following conferences during his degree:

  • Exeter Microwave Metamaterials Meeting 2015 (Exeter, UK, Poster: Resonant microwave transmission through thin metal layers using 2D arrays)
  • CIMTEC 2016 (Perugia, Italy, Presentation: Resonant Transmission through Thin Metal Layers using Two Dimensional Arrays)
  • International Workshop on Metamaterials by Design (Riva del Garda, Italy, Poster: Efficient Analysis of Extraordinary Transmission Through Metallic Screens Perforated With Finite Periodic Arrays of Slots)
  • IEEE Antenna and Propagation Symposium (San Diego, USA, Presentation: Dispersion of Surface Waves Supported by Truncated Metasurfaces)
  • Metamaterials 2017 (Marseille, France, Presentation: Coupled slot metasurfaces with spoof glide symmetry)
  • European School of Antennas Siena, Italy n/a
  • Exeter Microwave Metamaterials Meeting 2017 (Exeter, UK, Presentation: Efficient analysis of the electromagnetic scattering by non-periodic hole arrays)
  • Iberian Meeting on Computational Electromagnetics (Coimbra, Portugal, Presentation: Wiener-Hopf analysis of the scattering by a two dimensional periodic semi-infinite array of dipoles)
  • IEEE Antenna and Propagation Symposium (Boston, USA, Presentation: Wiener-Hopf analysis of the scattering by a two dimensional periodic semi-infinite array of dipoles)

Miguel’s thesis abstract:

This thesis focuses on the study of the perturbations of the microwave response of large finite arrays introduced by truncations. To do so very efficient analysis methods based on the method of moments are developed and implemented for different types of truncated slot/patch arrays. The physical insight gained from the analysis of the microwave response of truncated arrays will help in the engineering of new types of metasurfaces that take full advantage of the knowledge provided in here on the different mechanisms governing the coupling between surface waves and free space radiation. The first part of the thesis deals with the efficient analysis of the electromagnetic scattering by two-dimensional and one-dimensional periodic arrays of slots, as well as by finite arrays of slots in perfectly conducting surfaces. In a second part of the thesis, the canonical problem of the electromagnetic scattering by a semi-infinite array of dipoles (the complementary problem to that of slots) is analysed using a rigorous derivation using the Wiener-Hopf approach, that allows for the analytical separation of the different contributions to the current distributions on the array. Finally, the effect introduced by the introduction of higher symmetries into the dispersion relation of modulated infinite slot metasurfaces is numerically and experimentally explored. It is shown that these lead to low-dispersive ultra-wideband metasurfaces. A design method is proposed for the design of lower-symmetric metasurfaces with similar characteristics which is validated for the design of mirror-symmetric leaky-wave metasurface antenna.

 

Presentations and Talks at Washington DC-Intermag 2019

From January 14th to 18th, fourth year XM² postgraduate researchers Angus Laurenson and Natalie Whitehead, third year XM² postgraduate researchers David Osuna Ruiz and Elizabeth Martin, second year XM² postgraduate researcher Peter Inzani and first year XM² postgraduate researcher Oliver Latcham attended MMM-Intermag 2019 in Washington DC. The Conference includes all aspects of fundamental and applied magnetism, with sessions reviewing the latest advances in magnetic materials, emerging applications, new phenomena, spin electronics, energy and power applications, biomagnetism and much more.

Our postgraduate researchers gave talks on “Improving the excitation and detection of spiral spin waves in magnetic nano-patches” (David); “Collective excitation in a Skyrmion-Bubble domain lattice stabilised in an antidot lattice” (Angus); “CFD Modelling of Ferromagnetic Micromotors” (Peter) and “Graded Index Lenses for Spin Waves” (Natalie).

Lizzie presented her poster on “Advanced Processing of Bio-Inspired Microfluidic Elasto-Magnetic Devices” and Oliver’s was on “Scattering of Acoustic Waves from 1D Arrays of Magnetic Inclusions”.

This conference was a great example of knowledge-sharing between our different cohorts.

Photos below from the event:

          

 

 

 

Mian Zahid Hussain at ICS Winter School 2019

Recently, third year CDT postgraduate researcher Mian Zahid Hussain secured a grant from Italian Chemical Society (ICS) to participate in a winter school on Catalysis which took place at Bardonecchia, Italy from 7-11 January 2019. The focus of the winter school was to provide a detailed picture of the current scientific challenges to the catalysis for energy and environmental issues.

Current chemical industry relies mostly on fossil fuels, primarily to fulfill global energy-related requirements. In the present-day efforts to develop more environmentally friendly, cleaner and renewable energy sources, it depends upon how and if the chemical industry could shift from fossil-fuel to renewable energy driven production. The young generation of researchers working in this area of catalysis needs to be trained to understand the underlying problems and to establish the connection between the shifting techno-economic landscape of energy-related production systems and catalysis development challenges. This school proposed to set the basis for such an analysis.


This winter school was informative and provided a broader overview of the field of catalysis, covering the technical, industrial and economic aspects. Zahid held a poster presentation which was appreciated by the organizing committee and fellow researchers. It also provided an excellent opportunity for networking and meeting interesting people working on similar scientific topics.

More photos from the school below:

 

 

 

 

 

 

New Publication: Laser-writable high-k dielectric for van der Waals nanoelectronics

Congratulations to second year XM² postgraduate researcher Konstantinos-Andreas Anastasiou, whose article Laser-writable high-k dielectric for van der Waals nanoelectronics has been published in Science Advances.

State of the art van der Waals heterostructures rely on the use of hexagonal boron nitride as a gate dielectric, a tunnel barrier or a high-quality substrate material. The material is transferred mostly by chemical vapour deposition on top of the two-dimensional (2D) crystals, a technique which typically contains impurities that lead to leakage current in transistor devices. Other common deposition techniques used for SiO2 and HfO2 are not directly compatible with 2D materials and they tend to damage or modify the electronic properties of the underlying 2D crystal. In this paper, the authors demonstrate a method to embed and pattern a multifunctional few-nanometer-thick high-k oxide within various van der Waals devices without degrading the properties of the neighboring 2D. Abstract below.

Abstract

Similar to silicon-based semiconductor devices, van der Waals heterostructures require integration with high-k oxides. Here, we demonstrate a method to embed and pattern a multifunctional few-nanometer-thick high-k oxide within various van der Waals devices without degrading the properties of the neighboring two-dimensional materials. This transformation allows for the creation of several fundamental nanoelectronic and optoelectronic devices, including flexible Schottky barrier field-effect transistors, dual-gated graphene transistors, and vertical light-emitting/detecting tunneling transistors. Furthermore, upon dielectric breakdown, electrically conductive filaments are formed. This filamentation process can be used to electrically contact encapsulated conductive materials. Careful control of the filamentation process also allows for reversible switching memories. This nondestructive embedding of a high-k oxide within complex van der Waals heterostructures could play an important role in future flexible multifunctional van der Waals devices.

Fig. 1 Heterostructure processing and characterization. (A) The heterostructure is fabricated via dry transfer peeling from poly(dimethylsiloxane) membrane (left), the area containing HfS2 is exposed to laser light (center), and the HfS2 is converted into HfOx (right). (B) BF STEM image showing a cross section of a Gr/HfOx device after laser-assisted oxidation (left) and EDX elemental analysis (right). a.u., arbitrary units. (C) Optical image of a graphene-HfS2/MoS2 heterostructure before (top) and after (bottom) oxidation. Black outlines the region of the graphene back gate, green outlines the HfO2, and red outlines the MoS2. (D) Current (Isd) versus applied voltage (Vsd) for the heterostructure in (C) before (red) and after (green) photo-induced oxidation. Inset shows the stacking sequence. (E) Top: Optical micrograph of a HfS2 flake encapsulated between hBN and graphene (green, HfS2; yellow, hBN; red, graphene). Bottom: Optical micrograph of the same heterostructure imaged within our vacuum chamber showing laser irradiation effects in vacuum (blue hatched area) and in air (red hatched area). Note: No obvious oxidation effects are observed when irradiated in vacuum (P ~ 10−5 mbar). (F) Two-terminal resistance versus gate voltage for a graphene on hBN (d ~ 40 nm)/SiO2 (290 nm) FET measured at T = 266 K in a helium atmosphere (blue curve) and after placing a thin HfS2 flake and subjecting it to laser oxidation (red curve; sweep rate = 10 V/min). Inset shows a Raman spectrum of graphene after oxidation plotted on a logarithmic scale showing the G peak and a negligible D peak.
Fig. 1 Heterostructure processing and characterization. (A) The heterostructure is fabricated via dry transfer peeling from poly(dimethylsiloxane) membrane (left), the area containing HfS2 is exposed to laser light (center), and the HfS2 is converted into HfOx (right). (B) BF STEM image showing a cross section of a Gr/HfOx device after laser-assisted oxidation (left) and EDX elemental analysis (right). a.u., arbitrary units. (C) Optical image of a graphene-HfS2/MoS2 heterostructure before (top) and after (bottom) oxidation. Black outlines the region of the graphene back gate, green outlines the HfO2, and red outlines the MoS2. (D) Current (Isd) versus applied voltage (Vsd) for the heterostructure in (C) before (red) and after (green) photo-induced oxidation. Inset shows the stacking sequence. (E) Top: Optical micrograph of a HfS2 flake encapsulated between hBN and graphene (green, HfS2; yellow, hBN; red, graphene). Bottom: Optical micrograph of the same heterostructure imaged within our vacuum chamber showing laser irradiation effects in vacuum (blue hatched area) and in air (red hatched area). Note: No obvious oxidation effects are observed when irradiated in vacuum (P ~ 10−5 mbar). (F) Two-terminal resistance versus gate voltage for a graphene on hBN (d ~ 40 nm)/SiO2 (290 nm) FET measured at T = 266 K in a helium atmosphere (blue curve) and after placing a thin HfS2 flake and subjecting it to laser oxidation (red curve; sweep rate = 10 V/min). Inset shows a Raman spectrum of graphene after oxidation plotted on a logarithmic scale showing the G peak and a negligible D peak.

 

 

New Publication: Multi-layer graphene as a selective detector for future lung cancer biosensing platforms

Congratulations to XM² PGR Ben Hogan (4th year) who has co-authored a recently published paper on ‘Multi-layer graphene as a selective detector for future lung cancer biosensing platforms’ in the journal Nanoscale.

Lung cancer is one of the most common and aggressive cancers, with mortality rates of about 1.4 million per year, worldwide. The lack of clinical symptoms of early-stage lung cancer is a critical global challenge which leads to late-stage diagnosis and hence inability to cure patients. One potential solution is to monitor the makeup of people’s breath, in order to detect changes occurring due to the presence of cancer in the lungs. This paper shows that patterned multilayer graphene is a suitable electrode for the specific and selective analysis of breath samples in future devices.

Ben’s previous publications include Probing Raman Scattering for Particle Tracking (co-author) and From colloidal CdSe quantum dots to microscale optically anisotropic supercrystals through bottom-up self-assembly (co-author). Follow on Twitter for his latest research- @BenHoganSci.

Abstract

Highly selective, fast detection of specific lung-cancer biomarkers (CMs) in exhaled human breath is vital to the development of enhanced sensing devices. Today, e-nose is a promising approach for the diagnosis of lung cancer. Nevertheless, considerable challenges to early-stage disease diagnostics still remain: e.g. decrease in sensor sensitivities in the presence of water vapor, sensor drift leading to the inability to calibrate exactly, relatively short sensor lifetimes, and difficulty discriminating between multiple diseases.

However, there is a wide scope for breath diagnostics techniques, and all advanced electrodes applicable to e-nose devices will benefit them. Here, we present the promising sensing capabilities of bare multi-layer graphene (MLG) as a proof of concept for advanced e-nose devices and demonstrate its utility for biomolecule discrimination of the most common lung CMs (ethanol, isopropanol, and acetone). We report on a comparative study involving exposure of the three CM solutions on flat MLG (f-MLG) and patterned MLG (p-MLG) electrodes, where the electrical conductivity of p-MLG is significantly increased while applying acetone. Based on sensitivity tests, we demonstrate the ability to monitor the electrical response of graphene electrodes employing graphene of various wettabilities. Specifically, the f-MLG electrode displays almost 2 times higher sheet resistance (30 Ω sq−1) compared to the hydrophilic p-MLG (12 Ω sq−1). We show significant sensitivity to selected specific molecules of pristine f-MLG and p-MLG while applying CM solutions with a 1.4 × 105 ppm concentration.

Fig. 1 Chemical vapor deposition growth of multi-layer graphene (a schematic image). Methane was used as a carbon source, which under high temperature and an argon atmosphere decomposed into C and H2, as seen from the chemical reaction (a). Resulted carbon atoms were created in nucleation centers on both sides of the Ni foil through penetration and “dissolution” in the catalyst volume32,33 (b). Following the nucleation stage, the first graphene layers were grown directly on the top and bottom sides of Ni foil (c). Formation of multiple layers of graphene occurred according to the “underlayer growth model” with each newly grown layer pushing up the previously grown one (d).

 

 

 

 

 

 

 

 

 

 

Finally, we show the selectivity of f-MLG and p-MLG-based sensors when exposed to 2.0 × 105 ppm solutions containing different CM combinations. Both sensors were selective in particular to acetone, since the presence of acetone leads to a sheet resistance increase. We demonstrate that an advanced e-nose approach integrated with MLG electrodes has significant potential as a design concept for utilization of molecular detection at variable concentrations such as in early-stage disease diagnosis. This early-stage approach will provide convenient and reusable complex monitoring of CMs compared to typical contact sensors which require target analysis and are limited by disposable measuring. Moreover, further integration of the Internet of Things will introduce advanced e-nose devices as a biotechnological innovation for disease resilience with the potential for commercialization.