New Publication: Novel Au–SiO2–WO3 Core–Shell Composite Nanoparticles for Surface‐Enhanced Raman Spectroscopy with Potential Application in Cancer Cell Imaging

 

Congratulations to third year PGR Pablo Martinez Pancorbo for his latest publication- a paper on Novel Au–SiO2–WO3 Core–Shell Composite Nanoparticles for Surface‐Enhanced Raman Spectroscopy with Potential Application in Cancer Cell Imaging , published this week in Advanced Functional Materials.

Abstract

With the rapid development of nanotechnology during the last decades, the ability to detect and control individual objects at the nanoscale has enabled us to deal with complex biomedical challenges. In cancer imaging, novel nanoparticles (NPs) offer promising potential to identify single cancer cells and precisely label larger areas of cancer tissues. Herein, a new class of size tunable core–shell composite (Au–SiO2–WO3) nanoparticles is reported. These nanoparticles display an easily improvable ≈103 surface‐enhanced Raman scattering (SERS) enhancement factor with a double Au shell for dried samples over Si wafers and several orders of magnitude for liquid samples. WO3 core nanoparticles measuring 20–50 nm in diameter are sheathed by an intermediate 10–60 nm silica layer, produced by following the Stöber‐based process and Turkevich method, followed by a 5–20 nm thick Au outer shell. By attaching 4‐mercaptobenzoic acid (4‐MBA) molecules as Raman reporters to the Au, high‐resolution Raman maps that pinpoint the nanoparticles’ location are obtained. The preliminary results confirm their advantageous SERS properties for single‐molecule detection, significant cell viability after 24 h and in vitro cell imaging using coherent anti‐stokes Raman scattering. The long‐term objective is to measure SERS nanoparticles in vivo using near‐infrared light.

New Publication: Metasurface bilayer for slow microwave surface waves

Congratulations to fourth year PGR Julia de Pineda Gutiérrez, whose paper ‘Metasurface bilayer for slow microwave surface waves’ was recently published in Physical Review B. Julia’s previous publications include Microwave edge modes on a metasurface with glide symmetry and Hexagonal symmetry metasurfaces for broadband antenna applications. Julia’s thesis is on exploration of beam shaping at microwave frequencies using metasurfaces and metamaterials .

Abstract for ‘Metasurface bilayer for slow microwave surface waves’ below.

Abstract

We present a simple two-layer discontinuous crossed metal-strip array that guides microwaves having very high phase and group indices. The strips are arranged on a square lattice with a two-layer unit cell. The difference in this structure resides in the length of the metal strips, which extend to several unit cells. This work focuses on the isotropic wave dispersion at the lower frequencies. In addition, two of the higher-frequency bands give rise to a very strong negative dispersion, and strong beaming occurs, which can be tailored easily by modifying the relative orientation of the layers.

 

New Publication: 2D WS2 liquid crystals: tunable functionality enabling diverse applications

Ben Hogan

Congratulations to PGR Ben Hogan, who has just published a paper on ‘2D WS2 liquid crystals: tunable functionality enabling diverse applications’  in Nanoscale.

Ben says of his paper:

This paper describes the first observation of a liquid crystal phase for dispersions of two-dimensional tungsten disulfide particles in organic solvents. We detail the synthesis methods used to obtain the liquid crystals. We then characterise them, observing interesting and unexpected dichroism properties some of which can be controlled by the application of a magnetic field. We then demonstrate the first applications of the liquid crystals by producing highly uniform thin films of tungsten disulfide, which are then shown to be useful for developing future terahertz modulation devices. This paper represents the culmination of two and a half years of hard work, and involved collaborations with ITMO University (Russia) and Massachusetts Institute of Technology (USA)

Ben’s publications this year include Photoluminescence from NV− Centres in 5 nm Detonation Nanodiamonds: Identification and High Sensitivity to Magnetic Field and Transmission Properties of FeCl3-Intercalated Graphene and WS2 Thin Films for Terahertz Time-Domain Spectroscopy Applications.

Please see below for the abstract of ‘2D WS2 liquid crystals: tunable functionality enabling diverse applications’.

Abstract

The first observation of liquid crystalline dispersions of liquid phase-exfoliated tungsten disulfide flakes is reported in a range of organic solvents. The liquid crystals demonstrate significant birefringence as observed in the linear and circular dichroism measurements respectively. In particular, linear dichroism is observed throughout the visible range while broad-band circular dichroism can be observed in the range from 500–800 nm. Under an applied magnetic field of ±1.5 T the circular dichroism can be switched ON/OFF, while the wavelength range for switching can be tuned from large to narrow range by the proper selection of the host solvent. In combination with photoluminescence capabilities of WS2, this opens a pathway to a wide variety of applications, such as deposition of highly uniform films over large areas for photovoltaic and terahertz devices.

 

New Publication: Controlling acoustic waves using magneto-elastic Fano resonances

First year PGR Oliver Latcham has just co-authored his first paper, ‘Controlling acoustic waves using magneto-elastic Fano resonances’, published last week in Applied Physics Letters. This is an impressive achievement at the start of his degree.

His PhD project is ‘Excitation of spin waves in magnetic elements using surface acoustic waves’, supervised by Volodymyr Kruglyak, Geoff Nash and Andrey Shytov.

Earlier this year, Oliver attended MMM-Intermag 2019 with fellow CDT PGRS: fourth year XM² postgraduate researchers Angus Laurenson and Natalie Whitehead, third year XM² postgraduate researchers David Osuna Ruiz and Elizabeth Martin, and second year XM² postgraduate researcher Peter Inzani.

Abstract

We propose and analyze theoretically a class of energy-efficient magnetoelastic devices for analog signal processing. The signals are carried by transverse acoustic waves while the bias magnetic field controls their scattering from a magnetoelastic slab. By tuning the bias field, one can alter the resonant frequency at which the propagating acoustic waves hybridize with the magnetic modes, and thereby control transmission and reflection coefficients of the acoustic waves. The scattering coefficients exhibit Breit-Wigner/Fano resonant behavior akin to inelastic scattering in atomic and nuclear physics. Employing oblique incidence geometry, one can effectively enhance the strength of magnetoelastic coupling, and thus countermand the magnetic losses due to the Gilbert damping. We apply our theory to discuss potential benefits and issues in realistic systems and suggest routes to enhance the performance of the proposed devices.
The research leading to these results has received funding from the Engineering and Physical Sciences Research Council of the United Kingdom (Grant No. EP/L015331/1) and from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie Grant Agreement No. 644348 (MagIC).

New Publication: Photoluminescence from NV− Centres in 5 nm Detonation Nanodiamonds: Identification and High Sensitivity to Magnetic Field

Congratulations to fourth year PGR Ben Hogan, who has co-authored a paper on ‘Photoluminescence from NV Centres in 5 nm Detonation Nanodiamonds: Identification and High Sensitivity to Magnetic Field’, published last week in Nanoscale Research Letters. The paper was the result of a collaboration with Ioffe Institute (St. Petersburg, Russia), Université Paris-Sud & Université Paris-Saclay (Paris, France), and Hosei University (Tokyo, Japan).

Ben Hogan

Ben explains the significance of this work:

This work looks at the properties of the tiny diamonds formed during the detonation of explosives. Particularly, we look at how light can be emitted from the diamonds due to the defects that occur within them as a result of their violent creation. The diamonds have applications in imaging, as the emission is both very bright and confined to a small area, amongst others. Such diamonds have, for example, previously been used to image inside cells as their small sizes mean they can easily move within biological samples. The key results from this paper are that the method used to produce the diamonds gives a high concentration of defects, and therefore brighter emission, and the demonstration that quantum effects allow us to switch the emission on or off by using a magnetic field. 

Ben’s previous publications include ‘Transmission Properties of FeCl3-Intercalated Graphene and WS2 Thin Films for Terahertz Time-Domain Spectroscopy Applications’, co-authored with fellow fourth year PGR Kieran Walsh. His PhD project is on 2D liquid crystal composites for integrated optoelectronic devices, supervised by Dr. Anna Baldycheva & Dr. Monica Craciun.

Abstract of  ‘Photoluminescence from NV Centres in 5 nm Detonation Nanodiamonds: Identification and High Sensitivity to Magnetic Field’ below:

Abstract

The content of nitrogen-vacancy (NV−) colour centres in the nanodiamonds (DNDs) produced during the detonation of nitrogen-containing explosives was found to be 1.1 ± 0.3 ppm. This value is impressive for nanodiamonds of size < 10 nm with intentionally created NV− centres. The concentration was estimated from the electron paramagnetic resonance as determined from the integrated intensity of the g = 4.27 line. This line is related with “forbidden” ∆ms = 2 transitions between the Zeeman levels of a NV− centre’s ground triplet state. Confocal fluorescence microscopy enables detection of the red photoluminescence (PL) of the NV− colour centres in nanoscale DND aggregates formed from the 5-nm nanoparticles. Subwavelength emitters consisting of NV− with sizes a few times smaller than the diffraction-limited spot are clearly distinguished. We have further observed an abrupt drop in the PL intensity when mixing and anti-crossing of the ground and excited states spin levels in NV− occurs under an applied external magnetic field. This effect is a unique quantum feature of NV− centres, which cannot be observed for other visible domain light-emitting colour centres in a diamond lattice.

 

Tom Collier submits his thesis!

Congratulations to fourth year PGR Tom Collier, who has submitted his thesis, ‘Doubled-Gated Quantum Rings and Nanohelices: from Theory to Novel Applications’.

As well as his publications and conference presentations, in April 2018, Tom made an industry visit to De La Salle University, in the Phillipines, where he worked with Dr Richard Hartmann on theoretically solving non-simply connected systems with double quantum well potentials.

During his degree, Tom took part in Pint of Science 2017, giving a public talk in The Globe Inn to bring scientific research to the wider public.

Tom’s highlights of his time with the CDT include supervising an undergraduate summer student, with whom he will be submitting a paper. Looking back over his achievements during the CDT, Tom said the following:

I managed to finish with 5 first author publications in total: 3 journal articles, 1 book chapter, and 1 extended conference proceedings. I do have 3 further draft manuscripts to be submitted eventually.

I’ve managed to tutor Natural Science students taking physics or maths modules every year of my PhD, which I’ve thoroughly enjoyed. I’ve also managed to present at a fair few conferences. All in all, it’s been a blast.

From September, Tom will be working as a patent attorney in Brighton. He cites the CDT training on Intellectual Property awareness as the inspiration for his career choice.

Tom’s publications include:

  • T. P. Collier, “Eigenvalues and eigenfunctions for angular double-well potential”, Wolfram Demonstrations Project, published: June 13, 2019
  • “Double-gated nanohelix as a novel tunable binary superlattice” accepted in Nanoscale Research Letters 29/6/19 (authors T.P. Collier and M.E. Portnoi)“Terahertz applications of non-simply-connected and helical nanostructures” Chapter 11, in Fundamental and Applied Nano-Electromagnetics II. THz Circuits, Materials, Devices, edited by A. Maffucci and S. A. Maksimenko (Springer) 2019 (authors:T. P. Collier, V. A. Saroka, C. A. Downing, A. M. Alexeev, R. R. Hartmann, and M. E. Portnoi)
  • Terahertz optoelectronics of quantum rings and nanohelices, published 27th December 2018 in Semiconductors (authors T.P. Collier, A.M. Alexeev, C.A. Downing, O.V. Kibis, M.E. Portnoi)
  • Tuning terahertz transitions in a double-gated quantum ring , published 21st December 2017 in Physical Review B (authors TP Collier, VA Saroka and ME Portnoi)
  • Tuning THz transitions in a quantum ring with two gates, published 27th April 2017 in Physics, Chemistry and Application of Nanostructures (authors TP Collier, VA Saroka and ME Portnoi)

Tom presented at the following conferences:

 

 

New Publication: Transmission Properties of FeCl3-Intercalated Graphene and WS2 Thin Films for Terahertz Time-Domain Spectroscopy Applications

Congratulations to fourth year PGRs Ben Hogan and Kieran Walsh, who are authors on ‘Transmission Properties of FeCl3-Intercalated Graphene and WS2 Thin Films for Terahertz Time-Domain Spectroscopy Applications’, which was published last month in Nanoscale Research Letters.

Ben explains the impact of the research findings:

By using new and unique methods developed at the University of Exeter, we have produced thin films of different two-dimensional (2D) materials. These thin films can then be transferred easily to almost any other surface. In this work we have then investigated the properties of the different 2D materials in the terahertz frequency range. The results show that the tested 2D materials are suitable for applications in terahertz modulation devices. Ultimately, this work, with further improvement, could lead to cheaper and improved terahertz systems with applications ranging from non-destructive materials testing, to biomedical imaging, and security and communications technologies.

Kieran presents at LOPEC
Ben Hogan

Abstract of Transmission Properties of FeCl3-Intercalated Graphene and WS2 Thin Films for Terahertz Time-Domain Spectroscopy Applications below:

Abstract

Time-resolved terahertz spectroscopy has become a common method both for fundamental and applied studies focused on improving the quality of human life. However, the issue of finding materials applicable in these systems is still relevant. One of the appropriate solution is 2D materials. Here, we demonstrate the transmission properties of unique graphene-based structures with iron trichloride FeCl3 dopant on glass, sapphire and Kapton polyimide film substrates that previously were not investigated in the framework of the above-described problems in near infrared and THz ranges. We also show properties of a thin tungsten disulfide WS2 film fabricated from liquid crystal solutions transferred to a polyimide and polyethylene terephthalate substrates. The introduction of impurities, the selection of structural dimensions and the use of an appropriate substrate for modified 2D layered materials allow to control the transmission of samples for both the terahertz and infrared ranges, which can be used for creation of effective modulators and components for THz spectroscopy systems.

New Publication: Vibrational strong coupling with surface plasmons and the presence of surface plasmon stop bands

Kishan Menghrajani

Congratulations to 4th year PGR Kishan Menghrajani, who is lead author on ‘Vibrational strong coupling with surface plasmons and the presence of surface plasmon stop bands’, published in ACS Photonics.

The authors present results from experiments and numerical simulations to show that surface plasmon modes provide convenient open cavities for vibrational strong coupling experiments. In addition to providing momentum matching between surface plasmon modes and incident light, gratings may also produce a modification of the surface plasmon properties, notably their dispersion. The authors further show that for the parameters used in our experiment, surface plasmon stop bands are formed, and they find that both stop-band edges undergo strong coupling.

Kishan’s previous publications include ‘Hybridization of Multiple Vibrational Modes via Strong Coupling Using Confined Light Fields’.

Hybridization of Multiple Vibrational Modes via Strong Coupling Using Confined Light Fields

Congratulations to our fourth year PGRs Kishan Menghrajani, the main author of the paper Hybridization of Multiple Vibrational Modes via Strong Coupling Using Confined Light Fields, which was recently published in Advanced Optical Materials. The co-authors were fourth year PGR Henry Fernandez and supervisors Geoffrey R. Nash and William L. Barnes.

The paper is on strong coupling of multiple vibrational resonances of the same molecular unit with confined light fields. The results suggest that strong coupling might be used to manipulate vibrational resonances in a richer and subtler way than previously considered, opening a path to greater control of molecular systems and molecular processes via vibrational strong coupling.

Both Kishan and Henry have been busy this year, with Kishan presenting at Liebniz Institute of Photonics Technology and earlier this year, Henry giving a talk at the prestigious Nanometa conference.

For more information on Kishan’s research, you can follow him on Twitter and for more on Henry’s research, please check out ResearchGate.

Kishan Menghrajani
Henry Fernandez

Impact of pump wavelength on terahertz emission of a cavity-enhanced spintronic trilayer

 

FIG. 1.
Schematic of a spintronic trilayer with added dielectric cavity, grown on 0.5 mm of sapphire (Al2O3). The near-infrared pump pulse, incident through the substrate, is partially absorbed in the metallic layers, launching a spin current from the ferromagnetic (FM) layer into the nonmagnetic (NM) layers. The inverse spin Hall effect converts this ultrashort out-of-plane spin current into an in-plane charge current resulting in the emission of THz radiation into the optical far-field. A weak in-plane magnetic field (B) determines the magnetization direction and the linear polarization of the emitted THz field.

Congratulations to third year CDT PGR Rosamund Herapath for her recent publication of Impact of pump wavelength on terahertz emission of a cavity-enhanced spintronic trilayer in Applied Physics Letters.

In this paper, the authors enhance the THz generation of a novel, thin-film THz emitter by adding a set of dielectric overlayers. In doing so, they not only increase the intensity of the THz emitter by a factor of 4 in intensity, but also reduces the amount of IR pump beam transmitted (This will enable the emitter to be used within delicate systems).

She presented her findings in December 2018 at University of Warwick.