Research projects

On this page you will find some of the research projects being undertaken in the NEC.

Dates

Start date: 1 June 2011
End date: 31 May 2013

Summary

The study of materials which exhibit electrical or optical properties has played a major role in enabling all of modern technology and in particular electronics, computing and communications.  As these technologies have been developed, existing materials have also been modified and pushed close to their limits of what is technical feasible.  Optical communication and data transfer is widely known as being much quicker as information can be moved at the speed of light.  However, whenever it interacts with electronics the data transfer and processing must slow down to the speed of the microelectronic processors.  There is a strong desire and a compelling argument therefore to develop an 'optoelectronic' technology which is a hybrid of the optical and electronic systems but without the current limitations imposed by the two current technologies working independently.

Funding

EPSRC - grant EP/I018417/1

Details

This proposal will address the marriage of established ion-implantation technology with the emerging potential of chalcogenide glasses as electrically-active optoelectronic materials. The electrical properties of chalcogenides are of great technological importance, for example in phase-change memory. However, these properties are comparatively insensitive to compositional variation, or impurities present during synthesis, due to auto-compensation involving dangling-bonds and charge centres. As a result conventional glass-doping methods have proved to be insufficient to allow controlled modification of chalcogenide material's electronic properties despite their inherent semiconductor nature. The optical properties of chalcogenide materials are of equal technological interest due to their near and mid-infrared transmission and non-linear properties, to name a few. However, similarly to the electrical properties, it has generally proven difficult to modify these optical properties during preparation.

Ion-implantation is essential to modern integrated-circuit (IC) manufacture and is used for almost all doping in silicon IC's. Using the power of ion-implantation, we aim to radically expand the functionality of these emerging chalcogenide materials through post-synthesis non-equilibrium doping.  The focus of this proposal is to enable the controlled modification of their properties for the first time.

Results

Results will be disseminated in due course.

Output

Project outputs will be disseminated in due course.

Collaborations

This is a collaborative project with the universities of Southampton (Prof. Dan Hewak) and Cambridge (Prof. Stephen Elliott).

Co-investigator

Dates

Start date: 1 July 2011
End date: 20 July 2012

Summary

This project forms part of research in the theory of high electric field nanoscience.
Historically, the theories of the charged-particle (CP) optics of the focused-beam microscopies (the various types of electron microscope and ion microscope), and the projection microscopies (field electron and field ion microscopy) have not been fully integrated. The modern versions of all these instruments rely upon field emission sources (either electron or ion emission). Since the behaviour of a charged particle is independent of its mass-to-charge ratio (except when space-charge is present), an opportunity exists for greater theoretical integration.

Details

This project aims: (i) to develop an integrated theory of the CP optics of field emitters; (ii) to write tutorial-type articles setting out this theory; and (iii) to apply this theory to the operation of scanning ion microscopes based on the gas field ion source ("picoprobers"), to the issue of how to construct improved reconstruction algorithms for atom-probe tomography, and to the question of the resolving power of field electron and field microscopy for very small emitters (in particular the circumstances in which these techniques can "resolve" carbon-carbon bonds). Tasks include:
(a) handbook chapter on the theory of the gas field ion source [1,2], and confirmation of source-size estimate for the helium (scanning) ion microscope [3];
(b) integrated handbook chapter on bright field electron and ion sources [4];
(c) preliminary estimation of thermal distribution effects on the behaviour of field evaporated ions [5];
(c) development of projection formula for possible use in APT [6] (in progress);
(d) development of improved theory for the resolving power of field electron and field ion microscopies (in progress) (paper in preparation).

Results and Output

All references are outputs in the academic period 2009-2011.

References

[1] J. Orloff (ed), Handbook of Charged Particle Optics, 2nd Edition (CRC Press, Baton Rouge, 2009.)
[2] R.G. Forbes, "Gas Field Ionization Sources", Chapter 3 in Ref. [1].
[3] R.G. Forbes, "Prediction of probe radius for scanning ion microscopes (alternatively called picoprobers)", 52nd International Field Emission Symposium, Sydney, July 2010.
[4] R.G. Forbes, "Theory of bright field electron and field ion emission sources", accepted for publication in: P. Russell, I. Utke & S. Moshkalev (eds), Nanofabrication using Focused Ion and Electron Beams: Principles and Applications (Oxford University Press, New York, 2011/12).
[5] R.G. Forbes, "Estimation of the field evaporation (source-side) blurring radius", Workshop on New Frontiers of Atom-Probe Applications, Oxford, September 2009.
[6] R.G. Forbes, "Ion-optics-based projection formula, for possible use in atom-probe spatial reconstruction algorithms", 52nd Intern. Field Emission Symposium, Sydney, July 2010.

Investigator

Dates

Start date: 1 October 2011
End date: 31 October 2011

Summary

Since its first successful isolation in 2004, graphene has attracted a huge interest in the scientific community due to its unique electronic, optical and mechanical properties. Graphene is already considered of such importance to the fields of electronics and solid state physics that the 2010 Nobel Prize for physics was awarded to Geim and Novoselov for “groundbreaking experiments regarding the two-dimensional material graphene“. Stimulated by recent reports of single molecule detection using graphene based sensors; Ab initio calculations have been employed to study the doping efficiencies of environmental toxic gases NO2, NO and NH3 on graphene.  

Funding

EPSRC

Details

We have used both the local density approximation (LDA) and the generalised gradient approximation (GGA) to obtain the molecular binding energies and have employed the Hirshfeld charge partitioning method to calculate the electron charge transfer. Spin polarised calculations were used for the open shell molecules (NO and NO2) and we explored the effects of different adsorption sites and orientations.

Results

It was found that for all orientations of the molecule and using both LDA and GGA functionals that the adsorption of NO2 results in p-type doping of graphene with 0.06e transferred to the molecule. For NO, LDA calculations show a p-type behaviour with 0.03e transferred per molecule but both n and p-type doping of 0.003 – 0.004 e/molecules is calculated using the GGA functional. Finally for NH3 both donor and acceptor behaviour (0.03 – 0.05 e/molecule) is calculated. In all cases the origin of the doping is related to the relative position of the HOMO and LUMO molecular orbitals with respect to the Dirac point of graphene and low energy density of states.

Output

Doping efficiencies and physisorption of small molecules on graphene: Understanding charge transfer, Alexander J. Samuels and David Carey, American Physical Society March Meeting, Dallas, March 2011.
Doping efficiencies and physisorption of small molecules on graphene, Alexander J Samuels and J David Carey, Oral presentation at the 1st UK-Japan Graphene workshop, Lancaster University, February 2011.
Molecular doping and charge transfer of graphene, Alexander J Samuels and J David Carey, European Materials Research Society, Spring Meeting, Strasburg, June 2010.
Charge Transfer and Environmental Doping of Graphene, Alexander J. Samuels and David Carey, Materials Research Society, Spring meeting, San Francisco, April 2010.

Investigator

PhD Student Investigator

Alexander J Samuels

Dates

Start date: 1 October 2008
End date: 1 October 2011

Summary

Irradiation of thin metal films with moderate laser power is used to form metal nanoparticle coatings which can be used in electro-optical devices such as thin film solar cells and chemical sensors. The importance of this technique is the easy scalability, suitability for industrial production with no production of hazardous wastes.

Funding

EPSRC and ESF

Details

Laser nanofabrication of size controlled metallic nanoparticles to enhance the efficiency of electro optic devices such as solar cells. Moreover use of laser nanostructuring to form nanoparticles in specific patterns on substrates for chemical sensors.

Results

Successfully demonstrated fabrication of metal nanoparticles on ceramic and polymers substrate materials with control over their size, optical and electrical properties. Incorporation into organic solar cells enchased their power conversation. Furthermore use of them into chemical sensors increased their sensitivity.

Output

Publications
-Michail J. Beliatis, Simon J. Henley, and S. Ravi P. Silva, “Engineering the plasmon resonance of large area bi-metallic nanoparticle films by laser nanostructuring for chemical sensors” Optics Letters, 2011, 36 (8), 1362-1364
-Michail J. Beliatis, N. A. Martin, E. J. Leming, S. R. P. Silva, and S. J. Henley, "Laser Ablation Direct Writing of Metal Nanoparticles for Hydrogen and Humidity Sensors" Langmuir, 2011, 27 (3), 1241-1244.
Presentations
-“Synthesis and printing of metal nanoparticles with Excimer laser on functional dielectric hosts for multicoloured plasmonic optoelectronics and chemical sensors” at 2011 S2K.
-"Laser Nanostructured Substrates for Plasmonic Enhancement and Energy Conversion in Organic Photovoltaics" at 2011 E-MRS *AWARD*
-"Excimer laser synthesis of metal nanoparticles on functional dielectric hosts for multicoloured patterning and plasmonic chemical sensors" at 2011 E-MRS.
-“Tuning the surface plasmon resonance of metal nanoparticles” at Nano-Electronics Center 2010.
-“One step Laser nano-pattering for environmental sensors” at Nanomaterials Conference 2010.
-“Laser writing of nanoparticle based sensors” at Nano-Electronics Center 2009.
-“High precision laser direct writing of nanoparticle vapour sensors” at 2009 E-MRS *AWARD*

Collaborations

NPL, Alphasense Ltd., TEI Crete (Greece), FORTH Crete (Greece)

Investigator

PhD Student Investigator

Michail Beliatis

Dates

Start date: 1 January 2009
End date: 31 January 2012

Summary

Nanocrystals (NC), also known as quantum dots, has very unique physical properties which allow it to change bandgap Eg by adjusting the size. These materials are of huge technological interest since many of their electrical and thermodynamic properties show strong size dependence and can therefore be controlled through careful manufacturing processes. The interest of researchers in these materials continues today with researchers focusing on the study of their optical and electronic behaviour. Nanocrystals have the potential to be a good material for lasing devices due to their broadly tuneable emission in the NIR, good radiative quantum efficiencies, and long excited state lifetime. Studies show that quantum dots may absorb and emit light in a very narrow spectral range which if controlled, for instance by an applied magnetic field, may soon find application in the construction more efficient and precisely controllable semiconductor lasers. High degeneracy of this material at ground state make NC very hard to lasing. To overcome this problem a series of studies has to be run in order to reduce the degeneracy via splitting of the relevant energy levels. This will be approached via the use of external magnetic effects (e.g. Zeeman) or internal effects achieved via doping with magnetic ion impurities.

Funding

University Kuala Lumpur – Majlis Amanah Rakyat (MARA), Malaysia.

Details

Optical studies of NC systems require measurement of absorption spectra, photoluminescence and lifetime photoluminescence decay. NCs optical properties will be controlled by environment for temperature dependent (3 to 300 Kelvin) and external magnetic field dependent (-7 to 7 Tesla).  Other optical studies have been done with organic donor-acceptor (TTF and TCNQ) to understand charge transfer mechanism in NC systems.

Results

The absorption and photoluminescence are found to display different temperature dependent behavior though both redshift as temperature is reduced. This results in a temperature dependent Stokes shift which increases from ~75 meV with reducing temperature from 300 K until saturating at ~130 meV below ~150 K prior to a small reduction to 125 meV upon cooling from 25 K to 3 K. The PL lifetime is found to monoexponential at 3 K with a lifetime of t1 = 6.5 us.
Measurement of the photoluminescence (PL) of PbS NCs with TTF indicates that the highest occupied molecular orbital (HOMO) of TTF is closely aligned with PbS NC 1sh energy level. Whilst in the case of PbS NC in presence of the acceptor molecule (TCNQ) the direct quenching of the PL of PbS NC is observed. The absorption spectra of PbS:TTF and PbS:TCNQ mixture are taken to observe the indirect quenching from ground state of PbS to TCNQ charge transfer mechanism.

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Output

Muhammad N. Nordin, Richard. J. Curry, Konstantinos N. Bourdakos; “Charge transfer in hybrid organic-inorganic PbS nanocrystal system”; Phys. Chem. Chem. Phy.; 12; 1-7.
Isabelle Etchart,  Arnaud Huignard,  Mathieu Berard,  Muhammad N. Nordin,  Ignacio Hernandez, Richard J. Curry,  William P. Gillin  and Anthony K. Cheetham “Oxide phosphors for efficient light upconversion: Yb3+ and Er3+ co-doped Ln2BaZnO5 (Ln ¼ Y, Gd)”; Jour, of Mat, Chem.; 20; 3989-3994.
Wijittra Wichiansee, Muhammad N. Nordin, Mark Green, Richard J. Curry; “Synthesis and Optical Characterisation of Infra-red emitting HgS Quantum Dots” Journal of Material Chemistry. DOI:10.1039/c1jm10363f.
Muhammad N. Nordin, Juerong Li, Steve. K. Clowes, Richard. J. Curry, Konstantinos; “Temperature dependent on optical properties of PbS nanocrystals” Physical Review B.

PhD Student Investigator

Muhammad Noor Nordin

Dates

Start date: 1 October 2009
End date: 31 October 2012

Summary

Recently, there has been considerable interest in the organic electronic materials and their uses in the production of flexible and transparent electronic devices. However, the performance of these devices is less in comparison with those made from conventional inorganic materials. Therefore, many researchers turned to produce organic-inorganic composites in order to combine the advantages of organic materials such as flexibility and ease of processability and at the same time the advantages of inorganic materials as well. One of the most promising materials to improve the properties of such composites is carbon nanotubes which offer extraordinary properties that could be exploited to produce flexible and high performance electronic devices.

Funding

Saudi Cultural Bureau

Details

In this project we will produce well dispersed inorganic nano materials within an organic mixture in order to produce large area thin film conducting and also semiconducting composite. As part of the overall vision we will examine the dispersion of the nano-particles and relate this to the percolation limits of conduction and look to produce conductors and thin film transistors that maybe used for transparent large area electronics such as displays, circuits and sensors.

Results

Good and stable dispersion of carbon nanotubes  (CNTs) was achieved by using different chemical treatment. This dispersion was then mixed with a polymer and deposited on different types of substrates by using ink jet printing technique.

The scanning electron microscope images show a good distribution of the nanotubes in the printed sample. Moreover, we managed to align the nanotubes in the printed composite layer. The results reveal that the electrical properties of the composite are affected by the presence of the nanotubes and depend strongly on the concentration of the nanotubes in the sample.

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Output

A. S. Alshammari*, M. Shkunov and S. Ravi P. Silva, “Ink Jet Printing of Conductive Patterns For Electronic Applications”, Poster presented in the S2K conference, 21-22 June 2011, University of Surrey, Guildford, UK.

Investigators

PhD Student Investigator

Abdullah Alshammari

Dates

Start date: 3 November 2008
End date: 2 August 2012

Summary

Focused, pulsed laser light with short wavelengths is absorbed in a thin surface region for the majority of materials, allowing melting and vaporisation at the focal point. This forms the basis of a very versatile material deposition and modification system. This research concentrates on new techniques for using these high power, short pulsed, lasers for the production of technologically relevant nanomaterials, such as nanofoams, nanocoils and nanotubes.

Funding

EPSRC -EP/F048068/1

Details

This project aims to investigate techniques using high-power, short-pulsed lasers for the production of important nanomaterials, including nanoclusters, nanotubes and nanorods of carbon and zinc oxide, with controllable electrical and optical properties.  We will be addressing a full range of challenges, from obtaining a fundamental understanding of the growth processes to producing physical, chemical and biological sensors based on the products.

Results

We have fabricated mixed carbon/nickel highly conductive nanoclustered coatings by laser ablation and used these as environmental sensors and as electrodes for X-ray detectors.  We have shown that laser irradiation in solution is a rapid method of producing size and morphology controlled ZnO nanocrystals and have investigated their gas sensing properties. We have preformed extensive plume characterisation measurements using the ultra-fast imaging and spectroscopy facilities established as part of this grant and have proposed new mechanisms controlling the mixing of elements during clustering after laser ablation in background gases.

Output

S.  J.  Henley, J. Fryar, K. D. G. I. Jayawardena, S. R. P. Silva, “Laser-assisted hydrothermal growth of size-controlled ZnO nanorods”, Nanotechnology, 21, 365502 (2010)
K.D.G.I. Jayawardena, Y.Y. Tan, J. Fryar, H. Shiozawa, S.R.P. Silva, S.J. Henley, G.M. Fuge, B.S. Truscott and M.N.R. Ashfold, “Highly conductive nanoclustered carbon:nickel films grown by pulsed laser deposition” Carbon (in press) (2011)
K. D. G. I. Jayawardena, C. Opoku, J. Fryar, S. R. P. Silva, S. J. Henley, “Excimer laser accelerated hydrothermal synthesis of ZnO nanocrystals & their electrical properties” Appl. Surf. Sci., 257, 5274, (2010)
K. D. G. I. Jayawardena, J. Fryar, S. R. P. Silva and S. J. Henley, “Morphology Control of Zinc Oxide Nanocrystals via Hybrid Laser/Hydrothermal Synthesis", J. Phys. Chem. C,. 114, 12931 (2010)

Collaborations

Prof. Michael Ashfold (School of Chemistry, University of Bristol)

Investigator

Dates

Start date: 1 July 2011
End date: 20 July 2012

Summary

This project forms part of research in the theory of high electric field nanoscience.
Fowler-Nordheim (FN) tunnelling is electron tunnelling through an approximately triangular barrier. Deep FN tunnelling occurs at forwards energy levels well below the barrier top. Cold field electron emission (CFE) is electron emission in a regime where most electrons escape by deep FN tunnelling from states close to the Fermi level.
The family of Fowler-Nordheim-type equations describes CFE from the conduction band of large metallic emitters. They give the emission current i in terms of the notional emission area An, the emission current density J, the barrier field F and the local thermodynamic work-function , by expressions of the form [1]:
i  =  An J  = AnZa–1F2 PFexp[–Fb3/2/ F]. (1)
Here, a and b are the First and Second FN Constants, PF is a transmission pre-factor [2], and vF and Z are correction factors relating to the barrier and to electron supply. F is related to the applied voltage V by F=VV. The literature uses several variants of eq. (1).

Details

This project aims to put FN-type equations and their use onto a secure, well-structured and transparent intellectual basis, and to assess the approximations involved in using customisations of eq. (1). Tunnelling theory is a separate project. Progress includes:
(a) formulation of eq. (1) as a physically complete form, and provisional estimation of the uncertainties associated with the correction factors F, PF and Z [1];
(b) Restatement (with proof) of the principles involved in the summation over emitter states that is part of the derivation of FN-type equations [2];

(c) modification of eq. (1) to apply to large-area field emitters (LAFEs), by introducing the concept of area efficiency of emission [3];
(d) For the SN barrier, detailed examination of the quantitative effects of a certain class approximations involved in determining values of PF and Z (with Mayer) [4];
(e) Development of better theory for analysing i-V characteristics using FN theory (in progress, with Mousa and Fischer) [5], papers to be submitted July 2011.

Output

References [2-5] are outputs in the academic period 2009-2011.
[1] R.G. Forbes, J. Vac. Sci. Technol. B 26, 788 (2008).
[2] R.G. Forbes, J. Vac. Sci. Technol. B 28, 1326 (2010).
[3] R. G. Forbes, J. Vac. Sci. Technol. B 27, 1200 (2009).
[4] A. Mayer, J.H.B. Deane & R.G. Forbes, Poster at 23rd IVNC, Palo Alto, July 2010.
[5] A. Fischer, M.S. Mousa & R.G. Forbes, Posters at 23rd IVNC, Palo Alto, July 2010.

Collaborations

J.H.B. Deane (Surrey); A. Mayer (Belgium); M.S. Mousa (Jordan).

Investigator

Dates

Start date: 10 October 2010
End date: 1 October 2011

Summary

Zinc oxide (ZnO) nanostructures have been intensively studied due to their potential applications in diverse areas including optoelectronics and sensing. The potential for technological application of ZnO originates from its unique properties such as the wide direct band gap (~3.37 eV), large excitonic binding energy (60 meV), high mechanical strength, excellent thermal and chemical stability in harsh operating conditions, and intense piezoelectric effect. ZnO has a rich family of nanostructures and is grown in many methods using different techniques. Controlled growth of the nanostructures is very important for most of the applications like nanogenerators, gas sensors, field effect transistors, cold field emitters, and solar cells. 

Details

Solution phase synthesis of different ZnO nanostructures is an excellent choice for large-scale synthesis because it is a simple, cost efficient, low temperature process, and friendly to the environment.  However, precise control of the nanostructure has been difficult to date – a problem that we wish to address here. Two solution phase synthesis methods: the hydrothermal and electrodeposition method are examined here to grow ZnO nanostructures. The different ZnO nanostructures are being tested as the active elements in nano-sale transistors and for gas sensors.

Results

We provide SEM images of some of the ZnO nanostructures that were produced via solution phase synthesis and an electronic device made of a single nanodisc.

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Output

Some of our results were presented at the following conferences:
• Europe’s Semiconductor Conference S2K – 2011 UK
• 8th International Conference of Nanosciences & Nanotechnologies NN11  2011 Greece

Investigator

PhD Student Investigator

Mohammad Alenezi

Dates

Start date: 1 July 2011
End date: 20 July 2012

Summary

High Electric Field NanoScience (HEFNS) is a recently introduced name for the science that underlies a large group of related effects that can occur when very high electric fields are applied to liquid or solid surfaces. HEFNS involves: (1) the science of the charged surface itself and of relevant surface processes; the physics of the emission of electrons, ions, charged clusters and charged droplets from charged surfaces; and the physics of the processes that occur in space above the emitting surface. HEFNS should be seen as an alternative scientific focus that involves many of the traditional divisions of physics but concentrates on the effects of high (positive and negative) electric fields.
The general research aims in HEFNS are as follows.
(a) Develop the basic technical physics involved in the practical use of field emitters as electron or ion sources, whether in electronic devices (e.g., displays) or in machines of modern nanotechnology (such as electron and ion microscopes, FIB machines, and atom probes).
(b) Develop an integrated understanding of the nanoscience of surfaces subject to very high electric fields (typically between 1 and 100 V/nm) and of related  processes. This can involve fundamental aspects of quantum and statistical physics.
(c) Where necessary, correct and "reconstruct" basic theory, and re-present it in a form that can be easily understood by applied scientists and engineers.

Details

This research proceeds via several linked series of short-projects, often collaborative, each of which aims to generate a publication and/or related conference reports. For the purposes of these web-pages, these short-projects have been grouped under six headings (each of which is entered as a "project"), as follows:
• wave-mechanical transmission theory for approximately triangular barriers;
• reconstruction of Fowler-Nordheim-type equations;
• theory of cold field electron emission from small emitters;
• field ion emission and its applications;
• charged-particle optics of field emitters;
• electrical thermodynamics as applied to nanoscale processes.
Details of results, outputs and funding will be found on separate sheets.
In addition, Dr R.G. Forbes has presented several general overviews of research in HEFNS or in its field electron emission component. The most significant presentations in the academic period 2009 to 2011 are listed below.

References
[1] The theory of field electron emission. Tutorial lecture, 22nd IVNC, Hamamatsu, July 2009.
[2] Recent progress in understanding field electron emission. Seminar, Free University of Brussells, July 2009.
[3] Progress in reconstructing the basic theory of field electron emission. Invited talk, High-Field-Nanoscience Workshop, Wroclaw, May 2010.
[4] High-electric-field nanoscience. Invited Tutorial Lecture, Pre-Conference Workshop, 52nd International Field Emission Symposium, Sydney, July 2010.
[5] Recent developments in the theory of cold field electron emission. Multi-poster, 1st MeVARC Workshop, Helsinki, June 2011.

Investigator

Dates

Start date: 28 September 2009
End date: 28 September 2012

Summary

Recently CNTs have emerged as a very promising way to develop interconnects lines which solve the limitations of transportation capacity and losses associated with the other metal lines in electronic circuits. Signal losses and scattering associated with interconnects are a significant concern for RF and microwave engineers, particularly at high frequency transmission. CNT-based interconnects are very desirable to be integrated in the electronic components at the giga and terahertz regimes where the high transmission characteristics are desirable. This project will open the door for many potential applications in large area electronics and microwave applications.

Funding

Ministry of Higher Education, Saudi Arabia.

Details

The project consists of CNT-polymer composites characterisation and testing the performance of these composites in practical RF applications such as antennas.

The samples characterised consisted of CVD grown multiwalled CNTs (average length 1.5 µm, average diameter 9.5 nm) mixed with polymethyl methacrylate (PMMA) to   produce composites with 10 wt.% CNT loading. The composites were screen printed unto alumina substrate to fabricate coplanar waveguides (CPW) of several millimeters in length. The scattering or S-parameters of our CPW structures were measured using an HP 8510C vector network analyzer (VNA) connected to a wafer-probing station.

Results

We have characterized the high frequency behaviour of CNT-PMMA composite materials up to 220 GHz. The results have shown decreasing in signal losses with increasing frequency and we interpreted the role played by the capacitive coupling between the nanotubes in determining the high frequency conduction in these CNT composites. The next step in our project is to measure the performance of flexible microstrip patch antennas made from these composites.

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Output

Ali H. Alshehri, Malgorzata Jakubowska, Marcin Sloma, Michal Horaczek, Diana Rudka, Charles Free and J. David Carey; ‘Performance of Carbon Nanotube-Polymer Composites at Frequencies up to 220 GHz.’ Submitted.

Collaborations

Professor Malgorzata Jakubowska, Faculty of Mechatronics, Warsaw University of Technology, Warsaw, Poland.

Investigator

PhD Student Investigator

Ali Alshehri

Summary

The theory of the wave-mechanical transmission of particles across barriers has both fundamental and applied relevance. There are many devices (for example, electron microscope sources) where field-induced electron tunnelling – often called "Fowler-Nordheim (FN) tunnelling" –is involved, and many machines (for example, ion beam accelerators) where vacuum breakdown and arcing need to be prevented.
Simple approximate theories of tunnelling have existed since the 1920s. It is difficult to formulate exact theories, due to mathematical problems in the theory of differential equations that have been under study since the early 1800s. The problem is made worse by lack of transparency/completeness in literature discussions of FN tunnelling.

Details

This project aims to clarify and improve existing discussions of transmission theory, in order to facilitate more accurate numerical treatments. Associated tasks have been/are:
(a) reformulation of exact theory of transmission across the exact triangular (ET) barrier [1,2], and statement of the known difficulties in the FN 1928 treatment [3];
(b) in the context of the usual approximate theory of transmission across the widely-used Schottky-Nordheim (SN) barrier, re-development of the theory of the Principal SN Barrier Function v [4], development of exact series expansion for v [5], demonstration [6] that a new approximate expression found for v [7] is superior to all (12 or so) approximations of equivalent complexity previously suggested, and archiving statement [8] of the post-1928 attempts to calculate v accurately.
(c) Development of alternative "more general" formula for transmission coefficient [9]; exploration of the Kemble approximation as applied to the ET and SN barriers (to be done); exploration of reliability of existing transmission formulae for Schottky emitters, and comparison's with Mayer's approach [10] (to be done).
Results and Output
References [1-3, 6, 8] are outputs in the academic period 2009-2011.

Output

References
[1] R.G. Forbes & J.H.B. Deane, Proc. R. Soc. Lond A, online: doi: 10.1098/rspa2011.0025.
[2] R.G. Forbes & J.H.B. Deane, at 24th Intern. Vacuum Nanoelectronics Conf., July 2011.
[3] R.G. Forbes, Poster at 24th Intern. Vacuum Nanoelectronics Conf., Wuppertal, July 2011.
[4] R.G. Forbes & J.H.B. Deane, Proc. R. Soc. Lond. A 463, 2907 (2007).
[5] J.H.B. Deane & R.G. Forbes, J. Phys. A: Math. Theor. 41, 395301 (2008).
[6] R.G. Forbes & J.H.B. Deane, J. Vac. Sci. Technol. B 28, 2CA33 (2010).
[7] R.G. Forbes, Appl. Phys. Lett. 89 113122 (2006).
[8] R.G. Forbes, Poster at 23rd Intern. Vacuum Nanoelectronics Conf., Palo Alto, July 2010.
[9] R.G. Forbes, J. Appl. Phys. 103, 114911 (2008).
[10] A. Mayer, J. Phys. Condens. Matter 22, 1 (2010).

Collaborations

J H B Deane, Department of Mathematics, University of Surrey.

Investigator

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