Investigation of silicon quantum nanostructures and plasmonic structures for the photovoltaic applications

Some thoughts after initial literature review

The subject I will be tackling during next four years is related to application of commercially pure titanium as a structural biomaterial for modern dental implants. Pure titanium is known for its excellent biocompatible properties and corrosion resistance. It also isn’t magnetic and it does not easily conduct heat or electricity. It isn’t however strong enough to be used as a implant material. Therefore it is often alloyed with additives such as aluminum and vanadium or more recently niobium, zirconium and tantalum [1]. Other methods of metal strengthening, non-relying on use of toxic and poisonous additives (or additives in general) consist of introduction of dislocations and grain refinement by means of severe plastic deformation. So far method used most extensively for titanium grain refinement is a severe plastic deformation (SPD) technique called Equal Chanel Angular Pressing (ECAP). ECAP produces ultra-fine grained titanium with strength properties substantially improved over standard coarse grained Ti, but still worse than those of Ti–6Al–4V alloy [2]. There are reports of nano-crystalline titanium with even higher strengths obtained by ECAP conduced in room temperatures [3] or by means of hydrostatic extrusion [4]. However there is still little or no quantitative information regarding microstructure of titanium processed by such techniques. Orientation Imaging Microscopy examinations of titanium produced by these as well as other methods (for instance KOBO method), might substantially improve understanding of those materials, and hopefully this is the kind of research I will be able to conduct in the proximate future.

In October I've also had opportunity to participate in workshop on „Advanced Electron Microscopy Methods Applied to Investigations of Nanomaterials” which was held by Warsaw University of Technology (Warsaw 06-07.10.2011).

[1] Mitsuo Niinomi, Materials Science and Engineering A243 (1998) 231–236
[2] V. V. Stolyarov et al., Materials Science and Engineering A303 (2001) 82–89
[3] Xicheng Zhao et al., Scripta Materialia 59 (2008) 542–545
[4] W. Pachla et al., Journal of Materials Processing Technology 205 (2008) 173–182

PhD thesis - theoretical considerations

The first month of PhD studies I mainly devoted to formulating preliminary dissertation topic, objectives and methodology.

I decided to focus on multiscale surface functionalization of biomaterials for contact with blood in order to minimize activation of the coagulation system. Therefore most of the time I have spent doing literature review concerning surface modification techniques enhanced materials biocompatibility. Among the available methods, the layer-by-layer deposition technique introduced by Decher and co-workers in 1992 has attracted my attention because it posseses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. This method consists in alternately depositing polyelectrolytes that self-assemble and self-organize on the material’s surface, leading to the formation of polyelectrolyte multilayer films (PEM). In future studies I would like to focus on PEM made of ECM components (e.g. collagen, gelatin, fibronectin, hyaluronic acid ) in order to render them more biomimetic.

Conferences and seminars

In October I participated in the 2nd Workshop ‘Advanced Electron Microscopy Methods Applied to Investigation of Nanomaterials’, organized by Warsaw University of Technology & Hitachi High-Technologies (Warsaw, 06-07.10.2011).

I also attended in the following seminars:

• ‘Crystallographic aspects of the formation of shear bands in a strongly anisotropic structure of the alloy AA1050’ given by Dr. A. Tarasek
• ‘Energy-efficient microelectronics - The contribution of materials science and engineering’ given by Prof. E. Zschech
• ‘Using the free volume model for the description of liquid binary alloys’ given by MSc M. Trybula
• ‘Carbon is Future - Some Industrial Perspectives and Challenges’ given by Dr. O. Öttinger

Leaves have turned golden and yellow, the weather is getting cold by the day and I have embraced on a new project. Working away at my new desk doing literature search and shopping for chemical ingredients.
In the begging there is always chaos and the unknown looms blurry in the far distance but as I read on the overall entropy decreases.
The subject of my new scientific encounter are shape memory alloys SMA and in particular ferromagnetic shape memory alloys called FSMAs for short.
Shape memory alloys are a special group of metallic materials, which have the unique ability to restore some predetermined shape or size under the influence of stress, temperature or magnetic field (FSMA). This effect is caused by structural changes occurring over a range of different, external conditions.
Basically what happens here is the following: when cooled below a transformation temperature the high temperature phase called austenite, generally it is has a cubic crystal structure, turns into a low temperature martensitic phase, usually tetragonal. In this phase the material is characterized by a low yield strength and can be deformed to any shape with a relatively low force. This shape is retained as long as the material is kept below the transition temperature. (1) When heated above this temperature it reverts back to its original shape. Thanks to this property the shape memory materials find a plethora of applications including actuator and sensor systems.
A special family amongst these materials are the already above mentioned ferromagnetic materials FSMAs exhibiting shape memory effect when exposed to a magnetic field. This effect was first observed by Ullakko (2) who reported a field-induced strain in Ni2MnGa single crystal in the martensite state. This magnetic field implicated strain arises from the twin boundary rearrangement producing the macroscopic shape change. Since this discovery by Ullakko over a decade ago ferromagnetic shape memory materials have been extensively studied however much is still to be done. In the near future I am hoping to be a new contributor to this fascinating subject.

1. P. Gupta, P.S. Robi, P.P. Singha, A. Srinivasan, Journal of Materials Processing Technology 153–154 (2004) 965–970.
2. M.A. Marioni et all., Journal of Magnetism and Magnetic Materials 290–291 (2005) 35–41.

My advanture with PhD studies has begun. In October, that is, first month of my PhD studies I have done literature research. I have read a lot of papers related to grain boundaries concerning diffrent methods of boundary parametrizations, techniques of representing misorientations, tools for recognizing various characteristic types of GBs. I have written some first lines of source code of my software tool, which, in the future, will be able to perform some analysis of a single boundary and to carry out some statistical analysis of large data sets of grain boundaries. I started with functions for conversion between various rotation representations.