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A. Kulbickas / Medical Physics in the Baltic States 7 (2009) 30 - 33 2. Results and discussion Diamond is composed of carbon atoms. Each carbon atom is connected with four others carbon atoms in a tetrahedral geometry that is the result of a covalent bond and a face-centered arrangement in the cubic unit cell (Fig.1). The diamond surfaces properties have been carried out by using the optical microscopy. External surfaces of diamonds were immersed in contact with organic liquid crystal 5CB. External defects on diamond surfaces induced alignment of liquid crystals (LC) molecules. The actual mechanism of their orientation at the solid interface has long been unclear, because there have been technical difficulties in the analysis of the anchoring structures at a molecular level [9-13]. The measurements of the surface properties of LCs on defected diamond surfaces has been carried out by using the optical microscopy and polarizing spectroscopy. We obtained that defects on polished diamond surface are inducing homeotropic-planar transition of nematic LC. These phenomena were recorded near isotropic phase transition temperature (Fig.2-Fig.3) Fig. 1. The schematic diagram of the morphology of a typical natural diamond, the octahedral face, decorated with trigons On grown crystals were observed different alignment of LC molecules caused by anisotropic surface anchoring. This fact enables us to separate the natural mineral from synthetic grown (Fig.2). Fig. 2. Natural rough diamond demonstrating triangle growth sectors on face Moreover the LC molecules on diamond surface enable not only detect defects on solid surface but could to display his morphology of diamond (Fig.3-Fig.4). Fig. 3. LC displaying on surface synthetic diamond with fourangle growth sectors like mosaic 31 Fig. 4. The idealized synthetic diamond crystal exhibiting major octahedral {111} and cube {100} growth faces For natural diamond that are the octahedral faces, decorated with trigon etch pits have undergone partial dissolution so that rounded dodecahedral faces are beginning form. The polished slides of synthetic diamond on external diamond surface displaying unequal growth sectors {111}, {100} and they differs from natural diamond (Fig.2- Fig.4). Investigated diamonds are demonstrating bright fluorescence by illumination (Fig.5-Fig.6). Fig. 5. Fluorescence image of nanodiamonds containing nitrogen-vacancy defects Fig. 6. Fluorescence image of every nanoparticle containing nitrogen-vacancy defects Internal diamond defects could be created when one carbon atom could be substituted by nitrogen. The nitrogen-vacancy (N-V) center occurs in diamond containing single substitutional nitrogen (Fig.7). It is known that nitrogen is the most common impurity in diamond. Its usefulness in quantum computing is when it occupies next to a vacancy - a gap in the diamond crystal where a carbon should be. In this case, two of the nitrogen's electrons then stretch their orbits to cover the vacancy. In doing so, it forms a kind of molecule-like structure even though one of the atoms needed to create the molecule is actually missing. Curiously, this bizarre structure, the (N-V) centre
A. Kulbickas / Medical Physics in the Baltic States 7 (2009) 30 - 33 possesses spin, which is the quantum form of magnetism. Fig. 7. Nitrogen - vacancy defect in the diamond structure. In essence, spins are analogous to the tiny bar magnets and can code and store information by pointing in different directions. In practice, its spin can be manipulated using optical or magnetic techniques and the defect can be made to emit a single photon of light which has the characteristic of being “spin-up” or “spindown”. This in itself is not unique as many other materials have similar defects that can be used in the same way. The real advantage is that the properties of diamond mean that it can work at room temperature while other technologies being explored require very low temperatures. Surprising the (N-V) centre possesses spin at room temperature, which can be manipulated by illumination and the defect can be made to emit a single photon of light which has the characteristic of being ‘spin-up’ or ‘spin-down’ [14]. The Raman spectra at 300 K and 77K are plotted in (Fig.8a,b,c,d). In the (Fig.8b) the diamond spectra are weak at 637 nm and displaying small amount of (N-V) defects. After irradiation the line at 637 nm is stronger as result formation more (N-V) defects (Fig.8a). The (N-V) defects have formed strong optical transitions with zerophonon lines (ZPL) at 575 nm and 637 nm respectively (Fig.8 a,b,c,d). The ZPL peak at 575nm .is due the electronic transition of the neutral defect center (N-V) 0 , and the 637 nm ZPL peak corresponds to the 3 A→ 3 E transition of the negatively charged defect center (N-V) - [15–18]. Negatively charged nitrogen-vacancy (N-V) - centers in diamond have attracted much attention recently due to their unique properties, such as very long spin lifetimes at room temperature and their suitability for single photon sources [19]. Raman intensity 6,5x10 4 6,0x10 4 5,5x10 4 5,0x10 4 4,5x10 4 4,0x10 4 3,5x10 4 3,0x10 4 2,5x10 4 2,0x10 4 1,5x10 4 1,0x10 4 5,0x10 3 0,0 4,0x10 4 3,5x10 4 3,0x10 4 2,5x10 4 2,0x10 4 1,5x10 4 1,0x10 4 5,0x10 3 sample 15 514 nm con 10s nm-scale low temp a) b) sample 15 514 nm con 10s nm-scale room temp 552 0,0 500 550 Wavelength, nm 600 650 588 588 T=77K 604 612 NV - 637 NV 637 - T=300K 32 Raman intensity 1,4x10 5 1,2x10 5 1,0x10 5 8,0x10 4 6,0x10 4 4,0x10 4 2,0x10 4 0,0 5x10 4 4x10 4 3x10 4 2x10 4 1x10 4 c) d) 527 535 552 542 557 sample 25 514 nm con 10s nm-scale low temp T=77K NV 0 575 552 sample 25 514 nm con 10s nm-scale room temp T=300K 0 500 550 Wavelength, nm 600 650 Fig. 8. The intensity of Raman spectra of different (a, b) and (c, d) diamonds at the 77 K and 300 K temperatures 3. Conclusion The nitrogen defected diamonds possesses several unique properties: good fluorescence stability and spin manipulation at room temperature of the (N-V) defects. It is shown the possibility to use the (N-V) defects of nanodiamonds as cell biomarkers. Defected. nanodiamonds with (N-V) defects located close to the cell in tens nanometers distance to get information from neighbouring cells. Acknowledgements Support COST MP0803, COST P-19 and COST TD 08002 is gratefully acknowledged. Author thanks prof. R. Vaišnoras for helpful discussions. 4. References 1. Chi-Cheng Fu, et all, Characterization and application of single fluorescent nanodiamonds as cellular biomarkers, Proc Natl Acad Sci USA 104, 2007. p.727-732. 2. (a) J. Sabataityte, I. Simkiene, G.-J. Babonas, A. Reza, A. Suchodolskis, M. Baran, R. Szymczak, R. Vaisnoras, L. Rasteniene, V. Golubev, et all, Modification of photonic properties in porphyrininfiltrated opal crystals, Photonics and Nanostructures - Fundamentals and Applications, 5, 2007. p. 125-128. (b) J. Sabataityte, I. Simkiene, G.-J. Babonas, A. Reza, M. Baran, R. Szymczak, R. Vaisnoras, L. Rasteniene, V. Golubev and D. Kurdyukov, Physical studies of porphyrininfiltrated opal crystals, Materials Science and Engineering: C, 27, 2007. p. 985-989. (c) I.Simkiene, J. Sabataityte, A. Reza, G.J. Babonas, V. Golubev, D. Kurdyukov, Hybrid system of iron porphyrin on aminosilanized c-Si, Photonics and Nanostructures- Fundamentals and Applications 5,
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