Dr Andrei Sapelkin

Dr Andrei Sapelkin

Senior Lecturer
Address:
School of Physics and Astronomy
Queen Mary, University of London
327 Mile End Road, London, E1 4NS

Telephone: 020 7882 3414
Room: G O Jones 126
Email:

My research interests

My research interests are in quantum dots (QDs) preparation, their structural and optical characterisation and their use in bio-applications. Specifically, we have been looking into effects of various synthesis routes on light emission in nanostructures. Semiconductor nano-crystals have captivated the imagination of scientists and engineers since their technological potential became evident over two decades ago.

 This is especially true for semiconductor quantum dots, where quantum size effects and carrier confinement allow unprecedented control over optical and electronic properties. Leading the way in this field, in both theoretical understanding and demonstrated applications, is indisputably the cadmium-based II-VI quantum dots discovered 1980s. However, concerns regarding their toxicity are yet to be resolved calling for the advancement of alternative nontoxic materials, including the group IV (C, Si, Ge) semiconductor and gold (Au) nanoparticles. Our interest is in bio-application of quantum dots and to this end we adopted synthesis routes that yield C, Ge and Au QDs in form of suspension. These nano-particles show low toxicity and photoluminescence in a visible range (500-700 nm) and hence could potentially be suitable for bio-application. Our synthesis methods provide a degree of control over surface termination and also over the light emission properties. We work together with our partners at QMUL, UCL and at University of Edinburgh to assess the possibility of using C, Ge and Au QDs for super-resolution imaging of live cells. This work requires a combination of in-house characterisation techniques (e.g. Raman, Photoluminescence, Fluorescence Imaging) and structural methods (e.g. XAS) available at the large scale facilities such as Diamond Light Source. Furthermore, understanding of relationship between atomic, electronic structure and optical properties requires firm theoretical support provided by members of CCMMP group at SP and by our partners at Imperial College and at KCL. Most recently we have been working on utilising quantum dots for optical super-resolution imaging (below the Abbe limit of around 250 nm) by means of spectroscopic signal separation.

   

Figure 1. A DNA ruler using QDs.

Another long standing interest is effects of high hydrostatic pressure on structural and optical properties of novel materials such as topologically disordered solids and nanostructures. This led to his interest in the development of experimental techniques for local structural characterisation of materials under pressure using synchrotron radiation. It’s well known that reduced dimensionality has profound effects on properties of matter. In our research we attempt to use reduced dimensionality to control a variety of physical properties. Crystalline Germanium is a narrow indirect band gap (0.661 eV, 1876 nm) semiconductor and appears as grey powder or metal-like crystal. However, reducing crystal size down to nanometers results in significant changes of electronic, optical and structural properties due to size effects. Furthermore, it’s well known that bulk crystalline germanium undergoes semiconductor-to-metal transition at around 10 GPa at room temperature. This is not the case for germanium quantum dots.Here pressure does clearly affect the bandgap as can be seen from the changing colour of the Ge QD sample compressed in a diamond anvil cell (DAC). However, the semiconductor phase can be observed at pressures as high 20 GPa and metallisation within an amorphous phase.

 

Figure. 2. Ge QDs evolution under pressure in a diamond anvil cell.

My teaching

Current teaching:
▪ PHY5201 – Physics Laboratory, Year 2, Semester B
▪ SPA6312 - Condensed Matter B, Year 3, Semester B
Past teaching:
▪ PHY108 – Condensed Matter Physics, Year 1, Semester A
▪ PHY550 – Solid State Physics, Year 3, Semester B
▪ PHY201 – Physics Laboratory, Year 2, Semester B

My grants

01/04/2012 -30/10/2012, PI, Smart Nanocomposite Scaffold for Tissue Engineering, British Council, £5,500 

10/04/2012 -  09/04/2015, PI, Targeted drug delivery to neurons and glia using light-and field-sensitive microcapsules, BBSRC, BB/J001473/1, £442,033

 01/10/2010 - 30/09/2013, PI, Multimodal approach to structural effects in ferromagnetic Nanomaterials, SEPnet,  £49,020

01/08/2010 - 30/07/2014, CoI, Advanced Biomaterials for Regenerative Medicine, FP7-MC-IRSES, EU, £19,800

01/06/2009 - 30/11/2011, CoI, Tunable Raman spectroscopy of carbon nanotubes under high pressure, EPSRC, £231,216

2007 - 2008, PI, Interaction of Si and Ge nanoparticles with neuron cells in vitro, University of London Central Research Fund, £3,500

01/10/2005 - 30/09/2006, PI, International Joint Project - Former Soviet Union (FSU) –2004/R2-FS' Laser Ablation in Liquid Host, Royal Society, £10,000

09/11/2004 - 08/10/2006, PI, Bi-directional interfacing of electronics and cultured neurons, EPSRC, £208,241

 

My talks

Quantum Dots for imaging Talk at a British Council Sponsored Workshop, Saratov, Russia, September 2012

Quantum Dots Raman and PL Talk at Renishaw Inside Raman workshop, Rutherford Appleton Laboratory, 11th-12th September 2012

Interaction of nanostructures with living cells Talk at Royal Holloway, University of London, December 2011

Nanostructures under pressure Talk at a CSEC, Edinburgh, 25 Feb 2010 and at CEMES-CNRS Toulouse, France 4th Oct 2010

News

In the media

Reference to our work on Wikipedia (see Ref 16, or search Sapelkin) and in online publications

 

Research Group

Current members

Zhang Yuanpeng, Structural methods for low dimensional systems

Osman Ersoy, Semiconductor quantum dots

Kemal Keseroglu, Semiconductor QDs for super-resolution

Nikolaos Papaioannou, Syntheis, structure and properties of carbon quantum dots

Past Members

Ali Karatutlu, Synthesis of semiconductor quantum dots, now Assistant Professor at Bursa Orhangazi University, Turkey

William Little, Structure and optical properties of semiconductor quantum dots

Mingying Song, Semiconductor quantum dots for super-resolution

Selected publications

Local structure of Ge quantum dots determined by combined numerical analysis of EXAFS and XANES data.
Zhang Y, Ersoy O, Karatutlu A et al.
J Synchrotron Radiat, Volume 23, issue 1, page 253, 1st January 2016.
DOI: 10.1107/S160057751501913X

Laser-induced particle size tuning and structural transformations in germanium nanoparticles prepared by stain etching and colloidal synthesis route
Karatutlu A, Little W, Ersoy O et al.
Journal of Applied Physics, Volume 118, issue 24, 29th December 2015.
DOI: 10.1063/1.4939066

Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles.
Corsini NRC, Zhang Y, Little WR et al.
Nano Lett, Volume 15, issue 11, page 7334, 11th November 2015.
DOI: 10.1021/acs.nanolett.5b02627

Synthesis and structure of free-standing germanium quantum dots and their application in live cell imaging
Karatutlu A, Song M, Wheeler AP et al.
RSC Advances, Volume 5, issue 26, page 20566, 1st January 2015.
DOI: 10.1039/c5ra01529d

Structural origin of light emission in germanium quantum dots.
Little W, Karatutlu A, Bolmatov D et al.
Sci Rep, Volume 4, page 7372, 9th December 2014.
DOI: 10.1038/srep07372

Organo-erbium systems for optical amplification at telecommunications wavelengths
Ye HQ, Li Z, Peng Y et al.
Nature Materials, Volume 13, issue April 2014, page 382, 1st January 2014.
DOI: 10.1038/NMAT3910

Investigating the source of deep-level photoluminescence in ZnO nanorods using optically detected x-ray absorption spectroscopy
Hatch SM, Sapelkin A, Cibin G et al.
Journal of Applied Physics, Volume 114, issue 15, 21st October 2013.
DOI: 10.1063/1.4824810

Charge transfer between carbon nanotubes and sulfuric acid as determined by Raman spectroscopy
Puech P, Hu T, Sapelkin A et al.
PHYSICAL REVIEW B, Volume 85, issue 20, 9th May 2012.
DOI: 10.1103/PhysRevB.85.205412

Carbon Nanotubes on Polymeric Microcapsules: Free-Standing Structures and Point-Wise Laser Openings
Yashchenok AM, Bratashov DN, Gorin DA et al.
ADV FUNCT MATER, Volume 20, issue 18, page 3136, 23rd September 2010.
DOI: 10.1002/adfm.201000846

Nanoscale pressure effects in individual double-wall carbon nanotubes
Puech P, Flahaut E, Sapelkin A et al.
PHYS REV B, Volume 73, issue 23, 1st June 2006.
DOI: 10.1103/PhysRevB.73.233408

Interaction of B50 rat hippocampal cells with stain-etched porous silicon
Sapelkin AV, Bayliss SC, Unal B et al.
BIOMATERIALS, Volume 27, issue 6, page 842, 1st February 2006.
DOI: 10.1016/j.biomaterials.2005.06.023

Distance dependence of mean-square relative displacements in EXAFS
SAPELKIN A, Bayliss SC
Physical Review B, Volume 65, issue 17, page 172104-1, 1st April 2002.
DOI: 10.1103/PhysRevB.65.172104

X-ray absorption spectroscopy under high pressures in diamond anvil cells
Sapelkin AV, Bayliss SC
HIGH PRESSURE RES, Volume 21, issue 6, page 315, 1st January 2002.
DOI: 10.1080/08957950108202590