School of Physics and Astronomy

Dr Andrei Sapelkin

Andrei

Senior Lecturer | PhD Tutor

Email: a.sapelkin@qmul.ac.uk
Telephone: 020 7882 3414
Room Number: G.O. Jones Building, Room 126

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

Research

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.

Research Group

Current members

Ying Liu, Atomic structure of low-dimensional materials

Past Members

Nikolaos Papaioannou, now with Unilever UK. 

Kemal Keseroglu, now a Research Fellow at Cincinnati Children's, USA.

Zhang Yuanpeng, now at Oak Ridge National Laboratory, USA. 

Ali Karatutlu, now an Assistant Professor at Bursa Orhangazi University, Turkey.

Mingying Song, now a Research Fellow at The State Key Laboratory of Laser Interaction with Matter, China.

Osman Ersoy, Semiconductor quantum dots

William Little, Structure and optical properties of semiconductor quantum dots.

 

Publications

Performance

My Talks

Quantum Dots for imaging Talk [PDF 3,298KB] at a British Council Sponsored Workshop, Saratov, Russia, September 2012

Quantum Dots Raman and PL Talk [PDF 2,757KB] at Renishaw Inside Raman workshop, Rutherford Appleton Laboratory, 11th-12th September 2012

Interaction of nanostructures with living cells Talk [PDF 2,091KB] at Royal Holloway, University of London, December 2011

Nanostructures under pressure Talk [PDF 1,028KB] at a CSEC, Edinburgh, 25 Feb 2010 and at CEMES-CNRS Toulouse, France 4th Oct 2010

In the Media

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