Professor Shashi Paul

Job: Professor of Nanoscience and Nanotechnology and working for Emerging Technologies Research Centre

Faculty: Computing, Engineering and Media

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: https://www.dmu.ac.uk/emterc

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Personal profile

I graduated from Indian Institute of Science, Bangalore, India 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 including neuromorphic) and biological sensors. My particular focus is on the development of materials manufacturing processes to reduce the carbon footprint and next generation electronic devices.

Research group affiliations

Institute of Engineering Sciences (IES)

Publications and outputs

Organic and Macromolecular Memory – Nanocomposite Bistable Memory Devices
Organic and Macromolecular Memory – Nanocomposite Bistable Memory Devices Paul, Shashi The primary aim in the memory devices is to produce structures that exhibit two distinct states when a certain type of stimulus (e.g. electric field or magnetic field) is applied. These two states can be viewed as the realization of memory devices. It is to be noted that the class of memory devices that is discussed in this chapter is based on the admixture of small molecules, nanoparticles, and polymers; such devices are referred to as polymer electronic memory devices. This chapter captured the key developments that have happened in the field of organic memory devices for the last two decades. This chapters include discussions on the progress in this field and address challenges that scholars are currently faced with, such as questions about the mechanism(s) of bistability, the conundrum of the experimental data, and the contradictions prevalent among the different groups and future directions. The chapter also introduces reader some basic terms, concepts and terminology often used in this field. Paul, S. (2022) Organic and Macromolecular Memory – Nanocomposite Bistable Memory Devices. In: Chen, A. (Ed.) Advances in Semiconductor Technologies: Selected Topics Beyond Conventional CMOS, Hoboken, NJ: Wiley, pp.133-151
Storing Electronic information on Semi-Metal Nanoparticles
Storing Electronic information on Semi-Metal Nanoparticles Paul, Febin; Nama Manjunatha, Krishna; Paul, Shashi This paper presents the use of selenium nanoparticles for the application of information storage in two terminal electronic memory devices. Selenium is a semi-metal with interesting electronic and optical properties that have seldom been studied in terms of electronic memory. In this study selenium nanoparticles have been demonstrated as an embedded charge storage layer between silicon oxide tunnel layer and silicon nitride blocking layer. The electrical characterisation demonstrates clear evidence that charge storage is taking place, and that it is indispensable without the presence of nanoparticles. AFM images show that selenium nanoparticles are almost uniformly distributed on Silicon substrate having a thin silicon dioxide tunnelling layer, and the electrical retention measurement shows potential for long term data storage 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. Open Access article. Paul, F., Manjunatha, K.N. and Paul, S. (2022) Storing Electronic information on Semi-Metal Nanoparticles. Materials Advances.
Flexible Silicon Photovoltaic Solar Cells
Flexible Silicon Photovoltaic Solar Cells Shende, Pratik Deorao; Nama Manjunatha, Krishna; Salaoru, Iulia; Paul, Shashi This chapter discusses research and development of emerging silicon-based flexible solar cells. More emphasis is shown on the technology, underlying principles, device architecture, fabrication process, strengths, and challenges of the flexible solar cells fabricated using silicon. This chapter considers all the counterparts of silicon, from bulk to nanostructures that are used to fabricate photovoltaic devices. Change in the structure (low-dimensional and bulk materials), morphology (surface texturing and pyramid structures), and crystallinity (amorphous, poly-crystalline, and crystalline) of silicon as an absorber layer has shown enhanced efficiencies and reliabilities in flexible silicon solar cells. Flexibility and stretchability in solar cells are achieved mainly due to the adoption of novel structures, fabrication techniques, and, most importantly, the adoption of various flexible substrates (metal foils, polymers, and thin glass). The advantages and disadvantages of solar cells are discussed in terms of achieved efficiency, fabrication method, flexibility, and chosen substrate. Shende et al. (2022) Flexible Silicon Photovoltaic Solar Cells. In: Smart and Flexible Energy Devices ( Nguyen, T.A and R.K. Gupta, Ed.) (1st ed.). CRC Press.
To Be or Not to Be – Review of Electrical Bistability Mechanisms in Polymer Memory Devices
To Be or Not to Be – Review of Electrical Bistability Mechanisms in Polymer Memory Devices Paul, Febin; Paul, Shashi Organic memory devices are a rapidly evolving field with much improvement in device performance, fabrication, and application. But the reports have been disparate in terms of the material behavior and the switching mechanisms in the devices. And, despite the advantages, the lack of agreement in regards to the switching behavior of the memory devices is the biggest challenge that the field must overcome to mature as a commercial competitor. This lack of consensus has been the motivation of this work wherein various works are compiled together to understand influencing factors in the memory devices. Different works are compared together to discover some clues about the nature of the switching occurring in the devices, along with some missing links that would require further investigation. The charge storage mechanism is critically analyzed alongside the various resistive switching mechanisms such as filamentary conduction, redox-based switching, metal oxide switching, and other proposed mechanisms. The factors that affect the switching process are also analyzed including the effect of nanoparticles, the effect of the choice of polymer, or even the effect of electrodes on the switching behavior and the performance parameters of the memory device. open access article Paul, F. and Paul, S. (2022) To Be or Not to Be – Review of Electrical Bistability Mechanisms in Polymer Memory Devices. Small
Rational design on materials for developing next generation Lithium-ion secondary battery
Rational design on materials for developing next generation Lithium-ion secondary battery Mambazhasseri Divakaran, Arun; Minakshi, Manickam; Arabzadeh Bahri, Parisa; Paul, Shashi; Kumari, Pooja; Mambazhasseri Divakaran, Anoop; Nama Manjunatha, Krishna Lithium-ion batteries (LIBs) gained global attention as the most promising energy storing technology for the mobile and stationary applications due to its high energy density, low self-discharge property, long life span, high open-circuit voltage and nearly zero memory effects. However, to meet the growing energy demand, this energy storage technology must be further explored and developed for high power applications. The conventional lithium-ion batteries mainly based on Li-ion intercalation mechanism cannot offer high-charge capacities. To transcend this situation, alloy-type anode and conversion-type anode materials are gaining popularity. This review article focuses on the historical and recent advancements in cathode and anode materials including the future scope of the lithium nickel manganese cobalt oxide (NMC) cathode. Equal emphasis is dedicated in this review to discuss about lithium based and beyond lithium-based anode materials. This review additionally focuses on the role of technological advancements in nanomaterials as a performance improvement technique for new novel anode and cathode materials. Also, this review offers rational cell and material design, perspectives and future challenges to promote the application of these materials in practical lithium-ion batteries. research groups involved: 1. Emerging Technologies Research Centre, De Montfort University, Leicester, United Kingdom 2. Engineering and Energy, Murdoch University, Murdoch, Australia 3. Malaviya National Institute of Technology, Jaipur, India 4.School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom 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. Divakaran, A.M., Minakshi, M., Bahri, P.A., Paul, S., Kumari, P., Divakaran, A.M., Manjunatha, K.N. (2020) Rational design on materials for developing next generation Lithium-ion secondary battery, Progress in Solid State Chemistry,
Comparative Study of Silicon Nanowires Grown From Ga, In, Sn, and Bi for Energy Harvesting
Comparative Study of Silicon Nanowires Grown From Ga, In, Sn, and Bi for Energy Harvesting Manjunathan, Krishna Nama; Salaoru, Iulia; Milne, W.I; Paul, Shashi A high density of silicon nanowires for solar cell applications was fabricated on a single crystalline silicon wafer, using low eutectic temperature metal catalysts, namely, gallium, indium, tin, and bismuth. The use of silicon nanowires is exploited for light trapping with an aim to enhance the efficiency of solar cells. Additionally, we have optimized the deposition parameters so that there is merely deposition of amorphous silicon along with the growth of silicon nanowires. Thus, it may improve the stability of silicon-based solar cells. The different catalysts used are extensively discussed with experimental results indicating stable growth and highly efficient silicon nanowires for photovoltaic applications. To test the stability, we measured the open-circuit voltage for four hours and the change in voltage was ±0.05 V. The fabrication of all-crystalline silicon solar cells was demonstrated using the conventional mature industrial manufacturing process that is presently used for the amorphous silicon solar cells. To summarize, this research compares various post-transition metals as a catalyst for the growth of nanowires discussing their properties, and such silicon nanowires can be utilized in several other applications not only limited to photovoltaic research. 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. Manjunathan, K. N., Salaoru, I., Milne, W.I. and Pauls, S. (2020) Comparative Study of Silicon Nanowires Grown From Ga, In, Sn, and Bi for Energy Harvesting. IEEE Journal of Photovoltaics,
Single step ohmic contact for heavily doped n-type silicon
Single step ohmic contact for heavily doped n-type silicon Paul, Febin; Nama Manjunathan, Krishna; Paul, Shashi; Govindarajan, S. This work focusses on the metal-semiconductor contact on n-type c-Si wafers and explore the possibility of using magnesium (Mg) to form electron–selective contacts instead of using the conventional Au-Sb films which requires high temperature annealing between 350 and 500 °C. Aluminium (Al) capping layer was added over the magnesium contacts to prevent oxidation of magnesium. Various electrical measurements were performed over thermally evaporated Mg/Al contacts to investigate the conduction properties on both p-type and n-type silicon, where a Schottky behaviour was observed for the p doped silicon, but an ohmic behaviour (V ∝ I) for the n-type doped c-Si samples. The results were further optimised after investigating various thicknesses of the Mg interlayer, with 10 nm of Mg interlayer found to have the least resistance. The resistivity of the optimised structure (n-Si/Mg-10 nm/Al) was calculated, and measurements according to the Transmission Line Method (TLM) showed a contact resistivity of 462mΩ cm2 ± 20mΩ cm2. Further investigations were also conducted on the effect of high temperature annealing of the magnesium contact, which showed an increase in resistance with increase in annealing temperature, with the lowest resistance obtained without annealing. Additional investigations focussed on the morphological analysis of the deposited magnesium and its impact on the electrical characteristics. 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. Paul, F., Nama Manjunathan, K., Govindarajan, S., Paul, S . (2019) Single step ohmic contact for heavily doped n-type silicon. Applied Surface Science, 144686.
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. Saranti, K., Paul, S. (2019) e-Information on wires- A First Step towards 2-Terminal Silicon Nanowires for Electronic Memory Devices. ACS Applied Electronic Materials,
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. Manjunathan, K.N. and Paul, S. (2019) Carrier selective metal-oxides for self-doped silicon nanowire solar cells. Applied Surface Science, 492, pp. 856-861
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 Salaoru, I. Maswoud, S. and Paul, S. (2019) Inkjet Printing of Functional Electronic Memory Cells: A Step Forward to Green Electronics. Micromachines, 10, 417

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

Organic and inorganic materials for plastic electronics (including printing techniques for their deposition)
Emerging Electronic Memory Devices (including neuromorphic)
New Growth Processes/Methods for Nano-structures/materials
Photovoltaic Solar Cells (organic and inorganic)
Energy Storage (Electrical and Heat)

Areas of teaching

Electrical & Electronic Principles 1 (ENGD1103)
Emerging Materials and Processes (ENGD3114)
Energy Conversion & Storage Systems (ENGD3121)
Physics of Semiconductor Devices (ENGT5128)
Study Skills and Research Methods (ENGT5214)

Qualifications

MSc, PhD

Courses taught

MSc(Electronics Engineering)- Programme Leader, B.Engg (Mechanical Engineering), BSc(Energy Engineering) and a common module to all engineering disciplines in the school of engineering and sustainable development

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

1. Febin Paul (1st supervisor)
2. Swapnodoot Ganguly (2nd supervisor)
3. Chris Yang (1st supervisor)
4. Abdulrahaman Ogunji (1st supervisor)
5. Pratik Deorao Shende (1st supervisor)
6. Shashikala Madaiah (1st supervisor)
7. Maher Nahhas(1st supervisor)

Externally funded research grants information

Awarded an ICURe (Innovation & Commercialisation of University Research - funded by UKRI) £27k (from 1/1/2021 to 31/1/2021) for ‘Storing Electrical Energy in Silicon-Tin’ to explore commercialisation of his research. The CURe Programme offers university research teams with commercially-promising ideas funding and support to ‘get out of the lab’ and validate their ideas in the marketplace.
Energy Catalyst-3 - Creating electricity by reducing cost, payback time and Carbon footprint - An exploitation of a novel method into manufacturing Crystalline Silicon Photovoltaic solar Cells. (£70k) with 3 industrial partners.
EPSRC High Value Manufacturing (HVM) Catapult fellowship to work on the project “Manufacturing Silicon Nano-structure at low temperature – route to increase charge capacity and lower the cost of Li-Ion batteries” (£36,070)- February-2016 to February-2018.
EPSRC funding (#EP/E047785/1) on “Nano-Scale Rewritable Non-Volatile Polymer Memory Arrays”, principal investigator (£207k) – July-2007- November-2009.
National Physical Lab funding “Electrical Charging Mechanism in C60”, principal investigator (£20k)- October-2005 – September-2010.
EPSRC CASE Studentship (£57k) – October-2005 – March 2009.
“Low-temperature Si Nonvolatile memory”, principle investigator, European Integrated Activity of Excellence and Networking for Nano and Micro- Electronics Analysis (FP6), December-2010
Hosting visitor from Iraq (6k) – 2013
Consultancy (AFM analysis) – 1k -2008.
EPSRC-DTA studentship (~40k) – 2008 for 3 years.

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.

Published patents

GB2482915 - A low temperature method for the production of polycrystalline silicon, aligned silicon columns and silicon nanowires (Date Lodged: 20 August 2010, Granted on 5/2/2013).
GB2484743 - Organic photoconductive material (Filing date: 23 October 2010, Publication Date 25 April 2012, Granted in October, 2014).
2 patent applications submitted in 2020.

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

Flexible memory has wide ranging application

ORCID number

0000-0002-7077-8235