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.

New Publication: Realising an ultra-wideband backward-wave metamaterial waveguide

Congratulations to our XM² alumnus Sathya Sai Seetharaman who has recently published a paper in Physical Review B on ‘Realising an ultra-wideband backward-wave metamaterial waveguide’. The authors demonstrate, through experiment and numerical modeling, that the operational bandwidth of a CSRR metamaterial waveguide can be improved by restricting cross-polarization effects in the constituent meta-atoms.

Sathya is now working as a Metamaterials Scientist at Metaboards.

Abstract

Electroinductive waves have emerged as an attractive solution for designing metamaterials that support backward propagating waves. Stacked metasurfaces etched with complementary split-ring resonators (CSRRs) have also been shown to exhibit a broadband negative dispersion. We demonstrate, through experiment and numerical modeling, that the operational bandwidth of a CSRR metamaterial waveguide can be improved by restricting cross-polarization effects in the constituent meta-atoms. We report a fractional bandwidth of >56%, which, to the best of our knowledge, is broader than any previously reported value for an electroinductive metamaterial. We present a traditional coupled-dipole toy model as a tool to understand the field interactions in CSRR-based metamaterials, and to explain the origin of their negative dispersion response.

New Publication: Metamaterial-enhanced infrared attenuated total reflection spectroscopy

Congratulations to XM² PGR Cheng Shi (4th year) whose paper Metamaterial-enhanced infrared attenuated total reflection spectroscopy has been accepted by Nanoscale and is due to be published next month. Abstract below.

Abstract

The use of Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) allows solid or liquid samples to be characterised directly without specific sample preparation. In such a system, the evanescent waves generated through total internal reflection within a crystal interact with the sample under test. In this work we explore the use of a mid-infrared metasurface to enhance the interaction between molecular vibrations and the evanescent waves. A complementary ring-resonator structure was patterned onto both silicon and SiO2/Si substrates, and the spectral properties of both devices were characterised using a FTIR-ATR system. Minima in reflectance were observed corresponding to the resonance of the metasurface on the silicon substrate, and to the hybrid resonance of phonon modes and metasurface resonances on the SiO2/Si substrate, in good agreement with simulations. Preliminary experiments were undertaken using mixtures containing trace amounts of butyl acetate diluted with oleic acid. Without the use of a metasurface, the minimum concentration of butyl acetate that could be clearly detected was 10%, whereas the use of the metasurface on the SiO2/Si substrate allowed the detection of 1% butyl acetate. This demonstrates the potential of using metasurfaces to enhance trace chemical detection in FTIR-ATR systems.

Cheng’s previous publications include Metamaterial-based graphene thermal emitter (co-author) for Nano Research journal.

Carlota Ruiz De Galarreta poster presentation at Nanometa 2019

Joining fellow fourth year CDT PGRs Henry Fernandez, Charlie-Ray Mann and Tom Collier at Nanometa 2019, Carlota Ruiz De Galarreta presented a poster- “All-dielectric hybrid silicon/Ge2Sb2Te5 optical metasurfaces for tunable and switchable light control in the near infrared” (abstract below).

NANOMETA 2019 aims to bring together the international Nanotechnology, Photonics and Materials research communities where most recent and challenging results and plans are discussed in the informal setting on a glorious mountaineering resort. The technical programme included invited and selected contributed papers in the areas of:

• Plasmonics, Metamaterials and Metadevices
• Quantum and Topological Nanophotonics
• New Materials for Nanophotonics
• Optical Super-resolution

Abstract:

All-dielectric hybrid silicon/Ge2Sb2Te5 optical metasurfaces for tunable and switchable light control in the near infrared

We report a novel reconfigurable metasurface based on the combination of all-dielectric arrays of silicon meta-atoms, with deep subwavelength (< 0/100) Ge2Sb2Te5 layers. Our approach allows to selectively and individually control electric and magnetic resonances.

Henry Fernández gives talk at Nanometa 2019

Fourth year CDT PGR Henry Fernández gave a talk at the prestigious Nanometa 2019 conference in Seefield, Austria on 5th January 2019.  Nanometa aims to bring together the international Nanotechnology, Photonics and Materials research communities where most recent and challenging results and plans are discussed in the informal setting on a glorious mountaineering resort.

As the conference is very competitive, it is unusual for PhD students to give a talk. Henry spoke on “Electrical control of the Rabi splitting in a strongly coupled semiconductor microcavity”.

Fourth years PGRs Carlota Ruiz de Galarreta, Charlie-Ray Mann and Tom Collier also attended.

Henry has also been invited to give a talk in a symposium organised by the Rank Prize Funds, on the topic of two dimensional semiconductors for optoelectronics- watch this space!

New Publication: Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics

Congratulations to third year CDT PGR Emanuele Gemo , co-author of a paper, Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics, which was recently published in the prestigious journal Advanced Functional Materials. His co-authors include his supervisors Dr Anna Baldycheva and Prof C David Wright.

This work was led by researchers from the labs of Prof Harish Bhaskaran at Oxford University and Prof Dr Wolfram Pernice at Muenster University. It was carried under the auspices of the EU H2020 project Fun-COMP .

Abstract

The operation of a single class of optical materials in both a volatile and nonvolatile manner is becoming increasingly important in many applications. This is particularly true in the newly emerging field of photonic neuromorphic computing, where it is desirable to have both volatile (short‐term transient) and nonvolatile (long‐term static) memory operation, for instance, to mimic the behavior of biological neurons and synapses. The search for such materials thus far have focused on phase change materials where typically two different types are required for the two different operational regimes.

In this paper, a tunable volatile/nonvolatile response is demonstrated in a photonic phase‐change memory cell based on the commonly employed nonvolatile material Ge2Sb2Te5 (GST). A time‐dependent, multiphysics simulation framework is developed to corroborate the experimental results, allowing us to spatially resolve the recrystallization dynamics within the memory cell. It is then demonstrated that this unique approach to photonic memory enables both data storage with tunable volatility and detection of coincident events between two pulse trains on an integrated chip. Finally, improved efficiency and all‐optical routing with controlled volatility are demonstrated in a ring resonator. These crucial results show that volatility is intrinsically tunable in  normally nonvolatile GST which can be used in both regimes interchangeably.

 

Figure 1
Phase‐change photonic device. a) Illustration of device and measurement scheme. Optical WRITE pulses are used to switch the GST to a partial amorphous state while a counter propagating, variable‐power optical probe is used to control the recrystallization dynamics. b) Optical image of single device with input grating coupler (center), reference waveguide and output coupler (left), and device waveguide and input/output coupler (right). (Scale bar is 50 µm) c) False‐color SEM image of the GST vertical strip overlaying the Si3N4 waveguide. (Scale bar is 1 µm) d) FDTD simulations of the power flow from left to right through the region of GST (outlined by white dashed lines) when GST is in both the amorphous and crystalline states. e) Experimental optical transmission of device with increasing optical probe power. At low probe powers (black line), the device remains in the amorphous state for nonvolatile operation, while increasing the probe power causes recrystallization of the GST. f) Simulated optical transmission and crystallization dynamics of the device during volatile operation.