Dr Shashi Paul

Job: Reader in NanoScience and Nanotechnologies, Director - Emerging Technologies Research Centre (EMTERC)

Faculty: Technology

School/department: School of Engineering and Sustainable Development

Research group(s): Emerging Technologies Research Centre (EMTERC)

Address: De Montfort University, The Gateway, Leicester, LE1 9BH, United Kingdom

T: +44 (0)116 207 8548

E: spaul@dmu.ac.uk

W: www.dmu.ac.uk/emterc

 

Personal profile

I graduated from Indian Institute of Science, Bangalore, India and PhD from De Montfort University, Leicester and have previously worked in Cambridge University., Durham University, and Rutgers University. My research interests include manufacturing and analysis of nano-materials and their applications into energy (e.g. photovoltaic solar cells), electronics (emerging electronic memory devices) and biological sensors.

Research group affiliations

Emerging Technologies Research Centre (EMTERC)

Publications and outputs 

  • e-Information on wires- A First Step towards 2-Terminal Silicon Nanowires for Electronic Memory Devices
    e-Information on wires- A First Step towards 2-Terminal Silicon Nanowires for Electronic Memory Devices Saranti, Konstantina; Paul, Shashi Presently, there is a rapid growth of interest in the area of flexible electronics. Benefits such as light weight, durability and low-cost are among the most appealing aspects. However, the high temperatures throughout the fabrication processes are still the main hurdle. In this study, the deposition of silicon nanowires (SiNWs) at low temperature (300˚C) using Tin (Sn) catalyst is studied. Silicon nanostructures have been the centre of research for many years for a number of applications in different areas. Chemical Vapour Deposition (CVD) and other industrial deposition techniques, for the growth of crystalline silicon micro- and nano structures use high temperatures and therefore are not compatible with temperature sensitive substrates. This work utilises a low temperature deposition method for the growth of SiNWs and creates a leeway to use flexible plastic sheets as substrates. The silicon nanowires were deposited by exploiting the Vapour-Liquid-Solid (VLS) material growth mechanism using Plasma Enhanced Chemical Vapour Deposition (PECVD) technique. The suitability of these structures, as an information storage material, for future flash and two terminals non-volatile memory devices are investigated. Strong charge storage behaviour with a retention time up to 5 hours was observed showing great potential for the future memory candidate. The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.
  • Carrier selective metal-oxides for self-doped silicon nanowire solar cells
    Carrier selective metal-oxides for self-doped silicon nanowire solar cells Manjunathan, Krishna Nama; Paul, Shashi Selection of a material that serves multiple purposes is always beneficial for any electronic device including solar cells. This study investigates nickel oxide (NiO) as a multipurpose material to overcome the potential issues observed in traditional solar cells. A proof-of concept device is fabricated to understand the efficient hole transport from NiO while blocking electrons as determined by I-V measurements showing suppression of dark current and enhancement in the power conversion from the solar cell. Enhanced surface defects in the silicon nanowires (SiNWs) leading to the poor carrier collection is possible to be improved by the selection of wide bandgap metal-oxides that show high band offset for one carrier (electron/hole) while negligible band offset for another carrier (hole/electron) is discussed. Furthermore, Fermi level de-pinning for NiO sandwiched between different metal electrodes and SiNWs, signifying that the selection of appropriate metal electrodes is another key factor in improving the efficiency of solar cells; which is experimentally studied in this work. As fabricated solar cells in this work do not use high temperature diffused P[sbnd]N junction to separate the charge carriers neither toxic gases for doping SiNWs. The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.
  • Inkjet Printing of Functional Electronic Memory Cells: A Step Forward to Green Electronics
    Inkjet Printing of Functional Electronic Memory Cells: A Step Forward to Green Electronics Salaoru, Iulia; Maswoud, Salah; Paul, Shashi Nowadays, the environmental issues surrounding the production of electronics, from the perspectives of both the materials used and the manufacturing process, are of major concern. The usage, storage, disposal protocol and volume of waste material continue to increase the environmental footprint of our increasingly “throw away society”. Almost ironically, society is increasingly involved in pollution prevention, resource consumption issues and post-consumer waste management. Clearly, a dichotomy between environmentally aware usage and consumerism exists. The current technology used to manufacture functional materials and electronic devices requires high temperatures for material deposition processes, which results in the generation of harmful chemicals and radiation. With such issues in mind, it is imperative to explore new electronic functional materials and new manufacturing pathways. Here, we explore the potential of additive layer manufacturing, inkjet printing technology which provides an innovative manufacturing pathway for functional materials (metal nanoparticles and polymers), and explore a fully printed two terminal electronic memory cell. In this work, inkjetable materials (silver (Ag) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)) were first printed by a piezoelectric Epson Stylus P50 inkjet printer as stand-alone layers, and secondly as part of a metal (Ag)/active layer (PEDOT:PSS)/metal (Ag) crossbar architecture. The quality of the individual multi-layers of the printed Ag and PEDOT:PSS was first evaluated via optical microscopy and scanning electron microscopy (SEM). Furthermore, an electrical characterisation of the printed memory elements was performed using an HP4140B picoammeter. open access journal
  • Wire-bar coating of doped Nickle oxide thin films from metal organic compounds
    Wire-bar coating of doped Nickle oxide thin films from metal organic compounds Nama Manjunatha, Krishna; Paul, Shashi This study discusses the significance of aliovalent cations, especially monovalent compared to trivalent, which provide controlled doping and increase in the conductivity of nickel oxide (NiO) thin films. This report is a first proof of concept involving simple and economical K-bar, wire-wound deposition of doped and undoped NiO films. As deposited films have similar optical and electrical properties compared to the most commonly used deposition techniques for the deposition of NiO thin films. Doping of NiO from three different metal salts that have a different valencies (Cu1+, Zn2+, and Ga3+) as dopants for NiO thin films is investigated. This will help us understand the effect of monovalent, bivalent and trivalent ions towards the doping in NiO. Change in the structural, optical and electrical properties of NiO are investigated and compared amongst different metals (dopants) with different valencies. Furthermore, these properties are investigated in-depth by varying the concentration of the dopants (between 0 at.% and 8 at.%) within the NiO film. The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.
  • Silicon Rising
    Silicon Rising Paul, Shashi Silicon, as an electronic material, has played an enormous role in promoting the modern technical evolution in almost all fields. And, needless to say, it will continue its leadership until a better material is found. We are currently going through an exploration period to search out alternative materials. A number of different materials are have been proposed as challengers, but silicon (Si) is still the front runner, as far as complementary metaloxide- semiconductor (CMOS) technologies is concerned. Silicon is widely used in electronic industries in a number of forms, such as the amorphous silicon used in thin-film transistors (TFTs) in liquid-crystal display units, poly-silicon can be found in flash memory structures and photovoltaic solar cells, and single crystals are predominately used in CMOS technologies. Among the various forms of silicon embodiments, silicon nano-structures – for example, silicon nanowires – are also currently being explored, and for the last a few decades, there has been intense interest in how toprepare nanometre scale silicon.
  • Electrical Performance and Stability of ZnO Thin-Film Transistors Incorporating Gadolinium Oxide High-k Dielectrics
    Electrical Performance and Stability of ZnO Thin-Film Transistors Incorporating Gadolinium Oxide High-k Dielectrics Ngwashi, Divine K.; Paul, Shashi; Devi, Anjana; Cross, R. B. M. This work investigates the performance and gate bias stress instability of ZnO-based thin film transistors (ZnO-TFTs) incorporating amorphous gadolinium oxide, a high-k dielectric material. ZnO thin films produced via radio frequency (RF) reactive magnetron sputtering were used as channel layers. The source/drain electrodes were achieved by the thermal evaporation of aluminium on a bottom gate inverted staggered ZnO TFT structure. Gadolinium oxide (Gd2O3) deposited by metal-organic chemical vapour deposition (MOCVD) served as the gate dielectric. The electrical characterisation of the ZnO-TFTs produced showed improvement in performance and stability in comparison to thermally-grown SiO2-based ZnO TFTs fabricated under the same conditions. The effective channel mobility, on-off current ratio and subthreshold swing of the TFTs incorporating Gd2O3 dielectric were found to be 33.5 cm2 V-1s-1, 107, and 2.4 V/dec respectively when produced. The electrical characterisation of the same devices produced with SiO2 dielectrics exhibited effective mobility, on-off current ratio and subthreshold swing of 7.0 cm2 V-1s-1, 106 and 1.4 V/dec respectively. It is worth noting that, the ZnO active layer was sputtered under room temperature with no intentional heating and post-deposition annealing treatment. On application of gate bias stressing on these thin film transistors, it was observed that threshold voltage instability increased with stress period in all device types. Transistors incorporating Gd2O3 however, were found to exhibit lesser threshold voltage related instability with regards to gate bias stressing in comparison to similar devices incorporating SiO2 as gate dielectric. It was also observed that the effective mobility in both devices tend to stabilize with prolonged gate bias application. In this work, it is demonstrated that Gd2O3 dielectric is a potential alternative to SiO2 for the fabrication of ZnO TFTs with improved performance and electrical stability under prolonged use. open access article
  • Stability of Hydrogenated Amorphous Carbon thin films for application in Electronic Devices
    Stability of Hydrogenated Amorphous Carbon thin films for application in Electronic Devices Alotaibi, Sattam; Manjunathan, Krishna Nama; Paul, Shashi In this study, hydrogenated amorphous carbon (a-C:H) films are investigated for electronic applications as an insulating layer. a-C:H films were deposited using radio frequency-Plasma enhanced chemical vapour deposition (RF-PECVD) technique at room temperature. For the first time, the properties of a-C:H films as a function of annealing temperature is investigated, with a focus on their electrical and optical properties. This study shows that a-C:H films are stable up to 450ºC. This investigation will facilitate the use of a-C:H films as an insulating layer where the semiconductor active layers are deposited at higher temperatures (e.g. amorphous silicon deposited around 300ºC for thin film transistor TFTs). In addition to understanding the electrical and optical properties of annealed a-C:H films, we have further explored and studied its suitability in Flash-type memory devices. Various forms of diamond-like carbon are considered to have a high chemical resistance; no extensive data are available in the literature on this subject. The stability of a-C: H thin films with various reactive chemicals, commonly used in organic/printable electronic devices, is also investigated in this work. The findings may provide opportunities for adoption/integration of a-C:H in hybrid organic-inorganic electronic devices. The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.
  • A multi-faceted approach to determining the efficacy of metal and metal oxide nanoparticles against bacterial biofilms
    A multi-faceted approach to determining the efficacy of metal and metal oxide nanoparticles against bacterial biofilms Tejpal, Jyoti; Cross, R. B. M.; Owen, Lucy; Paul, Shashi; Jenkins, R. O.; Armitage, David; Laird, Katie Antibacterial efficacy of nanoscale silver, copper (II) oxide and zinc oxide were assessed against Pseudomonas aeruginosa and Staphylococcus aureus biofilms in solution and on surfaces. Using a Center for Disease Control biofilm reactor, minimum biofilm reduction concentrations, the coefficient of determination (R2) and log(10) reductions were determined. Atomic absorption spectroscopy, scanning electron microscopy and confocal laser scanning microscopy were used to assess the disruption of the biofilms. The efficacy of thin films of zinc oxide and silver deposited via magnetron sputtering and thermal evaporation respectively was also assessed. Minimum biofilm reduction concentrations of zinc oxide or silver nanoparticles were 256 or 50 µg/ml for P. aeruginosa and 16 or50 µg/ml for S. aureus respectively. When tested in combination the nanoparticles concentrations were at least halved resulting in significant (p ≤0.05) biofilm reductions of 3.77 log(10) - 3.91 log(10). Biofilm growth on thin films resulted in reductions of up to 1.82 log(10). The results suggest that nanoparticle suspensions and thin films of zinc oxide and may have potential as antimicrobial treatments for hard to eliminate biofilms in a clinical environment.
  • Inkjet printing of functional materials: a step forward to green electronics
    Inkjet printing of functional materials: a step forward to green electronics Salaoru, Iulia; Paul, Shashi; Maswoud , S. Nowadays the environmental impact of both used materials and manufacturing process of thin films is a major issue. The usage, storage, disposal protocol and the volume of waste material are also an environmental concern using conventional manufacturing pathway. The current technology to fabricate thin films requires heat generation in a deposition process and hence generation of harmful chemicals/radiation. Additionally, there are environmental limitations, for example, high vacuum equipment requires enormous amounts of electricity, thus creating a larger carbon footprint. Inkjet printing technology is a reliable alternative to traditional manufacturing protocol and most importantly, it is a solution to minimise the deleterious effects on the environment and human health. Here, we explore the potential of Additive Layer Manufacturing – inkjet printing technology to provide an innovative manufacturing pathway for functional materials, both conductive and insulating patterns, on flexible bendable substrates. In this work, ink-jettable materials were printed by a piezoelectric Epson Stylus P50 inkjet printing machine on a flexible substrate. The morphology, surface profile and the thickness uniformity of printed multi-layers were evaluated via Nikon LABOPHOT-2 optical microscope, fitted with Nikon Camera DS-Fi1. Furthermore, the conductivity and its dependency on the number of layers is investigated in this study. Even more, adhesion profile of the ink to the substrate and mechanical flexibility is also studied.
  • Binder-free Sn–Si heterostructure films for high capacity Li-ion batteries
    Binder-free Sn–Si heterostructure films for high capacity Li-ion batteries Loveridge M.J; Malik, R; Paul, Shashi; Manjunathan, Krishna Nama; Gallanti, S; Tan, C; Lain, M; Roberts, A.J; Bhagat, R This study fabricated and demonstrated a functional, stable electrode structure for a high capacity Li-ion battery (LIB) anode. Effective performance is assessed in terms of reversible lithiation for a significant number of charge–discharge cycles to 80% of initial capacity. The materials selected for this study are silicon and tin and are co-deposited using an advanced manufacturing technique (plasma-enhanced chemical vapour deposition), shown to be a scalable process that can facilitate film growth on 3D substrates. Uniform and hybrid crystalline–amorphous Si nanowire (SiNW) growth is achieved via a vapour–liquid–solid mechanism using a Sn metal catalyst. SiNWs of less than 300 nm diameter are known to be less susceptible to fracture and when grown this way have direct electrical conductivity to the current collector, with sufficient room for expansion. Electrochemical characterisation shows stable cycling at capacities of 1400 mA h g 1 (>4 the capacity limit of graphite). This hybrid system demonstrates promising electrochemical performance, can be grown at large scale and has also been successfully grown on flexible carbon paper current collectors. These findings will have impact on the development of flexible batteries and wearable energy storage. Open access article

Click here to view a full listing of Shashi Paul's publications and outputs

Key research outputs

Memory effect in thin films of insulating polymer and C60 nanocomposites, Paul, S., Chhowalla, M. and Kanwal, A., Nanotechnology (2006), 17(1), pp. 145-151.

Langmuir-Blodgett film deposition of metallic nanoparticles and their application to electronic memory structures, Paul, S et al, Nano letters (2003), 3, 191-195.

Realisation of Non-volatile Memory Devices using Small Organic Molecules and Polymer”, S. Paul, IEEE Transaction on Nanotechnology, 2007, 6 , 191-195.

Ferroelectric nanoparticles in polyvinyl acetate (PVAc) matrix-A method to enhance the dielectric constant of polymers. D Black, I Salaoru, S Paul, Nanoscience and Nanotechnology Letters (2010), Volume 2, Issue 1, March 2010, Pages 41-45.

Prime, D. and Paul, S. (2010) First contact-charging of gold nanoparticles by electrostatic force, Applied Physics Letters, 96 (4) 043120.

Research interests/expertise

Cheap and Flexible Electronics

Emerging Memory Devices (e.g. Molecular, Organic and low temperature Si memory devices)

Spin Valves

Growth Nano-structures (e.g nanoparticles, nanowires, nanotubes) and their applications in emerging areas of electronics (e.g healthcare and THz generation)

Self Assembly

Instrumentation Development for growth of nano-materials and understanding their physical properties

Green Growth Processes for Electronics Materials

Photovoltaic

Biological Sensors

Areas of teaching

Physics of Semiconductor Devices (ENGT5128)

Research Methods (ENGT5244)

Biosensors (ENGT5257)

Nanomaterials and Nanoelectronics (ENG5242)

Research Method (REST7013)

Research Method (EMTERC)

Qualifications

MSc, PhD

Courses taught

MSc in Micro Electronics and Nano Technology

MSc in Electronics Engineering

Membership of external committees

The 4th International Conference “Smart Materials, Structures and Systems”- a part of CIMTEC2012 conference organising programme committee

Dr S Paul is member of international programme committee for the forthcoming Conference on Renewable Energies and Power Quality (ICREPQ) by the European Association for the Development of Renewable Energies, Environment and Power Quality (EA4EPQ)", (http://www.icrepq.com/), 28-30 March, 2012, Santiago de Compostela, Spain.

The 3rd International Conference “Smart Materials, Structures and Systems” held in Acireale Catania District), Sicily, Italy, on June 8 to 13, 2008. Organised a special session on “Recent Development in Electrical Writable Organic Memory Devices”.

The 4th International Conference “Smart Materials, Structures and Systems” will be held in Acireale Catania District), Sicily, Italy, on June 8 to 13, 2008. Dr S Paul is organising a special session on “Emerging Non-volatile Memory Devices”.

Visiting Professor in the Physics department of Alexandru Ioan Cuza University of Iasi, Romania. From 24/12/2011 to 24/12/2013.

Membership of professional associations and societies

Association Name, period start, period end, description

Member IEEE (January, 2012 to December 2012)

Member Materials Research Society

Forthcoming events

Organising a special symposium on Emerging Memory Devices in CIMTEC2012

Conference attendance

Attended a number of international conferences (e.g.: IEEE, MRS, CIMTEC)

Current research students

First supervisor for:

Nare Gabrielyan
Sultan Alotaibi 
Faleh Alotaiby 
Keith McGrath 
Khalid Mahood 
Konstantina Saranti 

Second supervisor for:

Jyoti Tejpal

Externally funded research grants information

EPSRC funding (#EP/E047785/1) on “Nano-Scale Re-Writable Non-Volatile Polymer Memory Arrays” (from 08/07/2007 to 08/11/2009) – PI (£207k).

EPSRC funded CASE studentship for new academics (~£57k) from October, 2005 to March, 2009.

National Physical Lab funding for understandin “Electrical Charging Mechanism in C60”, (from October-2005 –July-2011 – PI (~£20k).

Low-temperature Si Nonvolatile memory- PI, European Integrated Activity of Excellence and Networking for Nano and Micro- Electronics Analysis (ANNA) (FP6), http://www.anna-i3.org, NCSR 'Demokritos' – IMEL funded (5500 Euros) directly to use their facilities (December, 2010).

Internally funded research project information

RIF project: A Cleaner, Greener, Low Carbon Fabrication Process for Photovoltaic (PV) Solar Cells (PI). Start date: 01/04/10; End date: 01/07/10.

DMU PhD Bursary on Plastic compatiable Electronic Memory Devices, October-2011 to September 2014.

Professional esteem indicators

Guest editor of the issue of the Philosophical Transaction of the Royal Society A, on the theme of “Making Nano-Bits Remember: A Recent Development in Organic Electronic Memory Devices”. Volume 367, Issue 1905, 28 October 2009.

Reviewer for a number of journals in the field of electronic materials and devices.

Visiting Professor, Faculty of Physics, Alexandru Ioan Cuza University of Iasi, Romania.

Case studies

Nano-bits Enabled Application in storing electronic information and creating electrical energy:

Ribbon award – MRS Fall Meeting 2004, Boston, USA

News in Science -2004: http://www.sciencenews.org/view/generic/id/5717/title/Buckyballs_store_1s_and_0s_in_new_memory_device

Gold nanoparticles for memory storage: http://www.theengineer.co.uk/news/gold-nanoparticles-for-memory-storage/1001480.article

Organic electronic memory chip to be demonstrated in the UK

Huge breakthrough in tiny technology by DMU: http://www.findaphd.com/custadverts/dmu/2010.asp

De Montfort University Shows the Benefits of Gold Nanoparticles for Organic Electronics: http://nanopatentsandinnovations.blogspot.com/2010/03/de-montfort-university-shows-benefits.html

De Montfort University Shows the Benefits of Gold Nanoparticles for Organic Electronics: http://nanopatentsandinnovations.blogspot.com/2010/03/de-montfort-university-shows-benefits.html

Flexible memory has wide ranging application

shashipaul

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