Property Analysis of Quantum dot Cuboid Nanocrystals with Different Nanostructures Syed Bahauddin Alam, K M Mohibul Kabir, Md. Didarul Alam, Palash Karmokar,Asfa Khan, Md. Nagib Mahafuzz, Farha Sharmin, Hasan Imtiaz Chowdhury, Md. Abdul Matin Department of EEE, *Bangladesh University of Engineering and Technology (BUET), Dhaka University of Asia Pacific (UAP), Dhaka Development Research Network (D.Net) baha_ece@yahoo.com Abstract Quantum dot nanocrystals represent a truly enabling nanotechnology and offer revolutionary fluorescence performance of long-term photostability for live-cell imaging and dynamics studies, single-excitation multicolor analysis, fixability for follow-up immunofluorescence and Narrow, symmetrical emission spectra for low interchannel crosstalk. Quantum dots are a revolutionizing material where traditional semiconductors fall short. In this paper, property analysis of quantum dot cuboid nanocrystals with different nanostructures are shown by simulation results for particular device structure and boundary conditions of Light and dark Transitions for the X, Y and Z- Polarized for different structures and so forth. Finally from the simulation, it is evident that, the characteristics are almost equivalent for different nanostructures for a particular boundary condition. Keywords: Quantum dot, nanocrystals, dimensions, Effective Mass, Energy Gap, Discretization. 1. Introduction Any solid material in the form of a particle with a diameter comparable to the wavelength of an electron. Quantum Dots is man-made artificial atoms that confine electrons to a small space. As such they have atomic-like behavior and enable the study of quantum mechanical effects on a length scale that is around 100 times larger than the pure atomic scale. Quantum dots offer application opportunities in optical sensors, lasers, and advanced electronic devices for memory and logic. This seminar starts with an overview of wavelike and particle like properties and motivates the existence of quantum mechanics. It closes the quantum mechanics point of view with these new fascinating artificial atoms. Quantum dots were predicted to exhibit interesting cooperative behavior in many-dot systems with overlapping wave functions, due to the resulting miniband structure, and also as elements in cellular neural networks.however, no scheme for using discrete quantum dots for computing was proposed during this period. These dots were not quantum dots in the energy quantization sense, but rather relied on their ultra small capacitance, which was a consequence of their very small size, to reveal measurable voltage changes with charge variations of only a single electron. Such behavior is classical, except for tunneling between dots. In confined semiconductor dots, the energy quantization is superimposed on the Coulombic effects, but is not the primary phenomenon of interest. At the heart of the fluorescence of Quantum dot nanocrystals is the formation of excitons, or Coulomb correlated electron-hole pairs. The exciton can be thought of as 15
analogous to the excited state of traditional fluorophores; however, excitons typically have much longer lifetimes (up to ~µseconds), a property that can be advantageous in certain types of "time-gated detection" studies. Yet another distinction arises from the direct, predictable relationship between the physical size of the quantum dot and the energy of the exciton (therefore, the wavelength of emitted fluorescence). This property has been referred to as "tuneability", and is being widely exploited in the development of multicolor assays. Quantum dot nanocrystals are also extremely efficient machines for generating fluorescence; their intrinsic brightness is often many times that observed for other classes of fluorophores. Another practical benefit of achieving fluorescence without involving conjugated double-bond systems is that the photostability of Quantum dot nanocrystals is many orders of magnitude greater than that associated with traditional fluorescent molecules; this property enables long-term imaging experiments under conditions that would lead to the photo-induced deterioration of other types of fluorophores. 2. 3- Dimensional Quantum Dot Simulation and Analysis: Different Boundary Conditions Fundamentally, quantum dot nanocrystals are fluorophores substances that absorb photons of light, then re-emit photons at a different wavelength. However, they exhibit some important differences as compared to traditional fluorophores such as organic fluorescent dyes and naturally fluorescent proteins, ends there. Quantum dot nanocrystals are nanometer-scale (roughly protein-sized) atom clusters, containing from a few hundred to a few thousand atoms of a semiconductor material (cadmium mixed with selenium or tellurium), which has been coated with an additional semiconductor shell (zinc sulfide) to improve the optical properties of the material. These particles fluoresce in a completely different way than do traditional fluorophores, without the involvement of electronic transitions. In this experiment, at the very beginning of the simulation we have taken 3 dimensional device Structure of Cuboids shape. In the figure 1 that shape has been shown. Here we have used the boundary conditions of: X dimensions: 5nm Y Dimensions:5.5 nm Z Dimensions:6nm Effective Mass:0.067 Energy Gap:1.43 ev Discretization:0.565nm No. Of states: 7 As light Source and polarization, light polarization angle is 45, electron Fermi level is 5ev and temperature is 300k. By following this condition, if we fabricate this device structure, we will have 3 dimensional wave function as shown in figure 2 and Energy state in figure 3. In the energy state, the approximate energy gap is 0.51 ev for the above fabrication criteria. Now, if we delve to the result of polarization of light source as well as X- polarized light and dark transitions, we will find that in figure 4, at 0.77eV we will get 1e-30 arb unit Light and Dark transition strength and it is maxima for that particular condition. Similarly for Y polarization, at 0.675 ev we will get highest Light and Dark transition strength. For Z polarization as shown in figure 5, we will get two identical Light and Dark transition strength points at 0.5 ev and 0.7 ev. Now, if we consider Light/ Dark transition for the angle of 45 Degree, Similarly, we will get two identical Light and Dark transition strength points at 0.5 ev and 0.7 ev. If we now cogitate at the absorption conditions as shown in Figure 6. Absorption at angle of 45 Degree, highest absorption id 51.5 arb unit by forming at energy levels of 0.47 ev and 0.56 ev, where 0.50 ev is the median of that energy level. For X and Y polarization, we will get highest Light and Dark transition strength at only one point, but for Z polarization, we will get two identical Light and Dark transition strength points. Now, we now alter the device structure. We will now fabricate through pyramid structure and after fabrication in figure 7. Absorption sweep for angle for pyramid has been shown. Here we have seen that, in three particular energy levels the Absorption are on the peak whereas for cuboid we have got 2 peaks. So from the simulation results, we have seen that, for all kind of devices: cuboid, pyramid, spheroid, dome; the properties of 3D 16
Wavefuntions are almost same. In the Energy states, energy gaps are almost equivalent. If we consider Light and dark Transitions for the X, Y and Z- Polarized for different structures, in a particular boundary condition, Fermi Level energy are almost 0.5 ev, though there are one or more than two peaks depending on the structure, polarization and light angle properties. Similarly Absorption sweep of angle theta and Integrated absorption are almost equivalent unless the number of peaks. 3. Conclusion In this paper, property analysis of quantum dot cuboid nanocrystals with different nanostructures are shown by simulation results for particular device structure and boundary conditions of Light and dark Transitions for the X, Y and Z- Polarized for different structures and so forth. Finally from the simulation, it is evident that, the characteristics are almost equivalent for different nanostructures for a particular boundary condition. References Syed Bahauddin Alam et. al, Modeling of Physics of Beta-Decay using Decay Energetics, in American Institute of Physics (AIP) Proceedings, 2012. Syed Bahauddin Alam et. al Dosimetry Control and Electromagnetic Shielding Analysis, in American Institute of Physics (AIP) Proceedings, 2012. Syed Bahauddin Alam et. al Transient and Condition Analysis for Gen-4 Nukes for Developing Countries, in American Institute of Physics (AIP) Proceedings, 2012. Syed Bahauddin Alam et al., Methodological Analysis of Bremmstrahlung Emission, published in the World Journal of Engineering and Pure and Applied Science, pp: 5-8,Volume: 1, Issue: 1, Research Reviews Publications, June 2011. Syed Bahauddin Alam et al., Mathematical Analysis of Poisoning Effect, published in the World Journal of Engineering and Pure and Applied Science, pp: 15-18, Volume:1, Issue: 1 Research Reviews Publications, June 2011. Syed Bahauddin Alam, Md. Nazmus Sakib, Md. Rishad Ahmed, Hussain Mohammed Dipu Kabir, Khaled Redwan, Md. Abdul Matin, Characteristic and Transient Analysis of Gen-4 Nuclear Power via Reactor Kinetics and Accelerator Model in 2010 IEEE International Power and Energy Conference, PECON 2010, pp. 113-118, Malaysia, 29 Nov, 2010. Syed Bahauddin Alam, Hussain Mohammed Dipu Kabir, Md. Nazmus Sakib, Celia Shahnaz, Shaikh Anowarul Fattah, EM Shielding, Dosimetry Control and Xe(135)-Sm(149) Poisoning Effect for Nuclear Waste Treatment in 2010 IEEE International Power and Energy Conference, PECON 2010, pp. 101-106, Malaysia, 29 Nov,2010. Syed Bahauddin Alam, Hussain Mohammed Dipu Kabir, Md. Rishad Ahmed, A B M Rafi Sazzad, Celia Shahnaz, Shaikh Anowarul Fattah, Nuclear Waste Transmutation by Decay Energetics, Compton Imaging, Bremsstrahlung and Nuclei Dynamics in 2010 IEEE International Power and Energy Conference, PECON 2010, pp. 107-112, Malaysia, 29 Nov, 2010. Syed Bahauddin Alam, Hussain Mohammed Dipu Kabir, A B M Rafi Sazzad, Khaled Redwan, Ishtiaque Aziz, Imranul Kabir Chowdhury, Md. Abdul Matin, Can Gen-4 Nuclear Power and Reactor Technology be Safe and Reliable Future Energy for Developing Countries? In 2010 IEEE International Power and Energy 17
Conference, PECON 2010, pp. 95-100, Malaysia, 29 Nov, 2010. Syed Bahauddin Alam, Md. Nazmus Sakib, Md Sabbir Ahsan, A B M Rafi Sazzad, Imranul Kabir Chowdhury, Simulation of Bremsstrahlung Production and Emission Process in 2nd International Conference on Intelligent Systems, Modelling and Simulation, ISMS2011, Malaysia, Phnom Penh (Cambodia), 25-27 Jan, 2011. Syed Bahauddin Alam, Md. Nazmus Sakib, Md Sabbir Ahsan, Khaled Redwan, Imranul kabir, Simulation of Beta Transmutation by Decay Energetics in 2nd International Conference on Intelligent Systems, Modelling and Simulation, ISMS2011, Malaysia, Phnom Penh (Cambodia), 25-27 Jan, 2011. Syed Bahauddin Alam, Md. Nazmus Sakib, A B M Rafi Sazzad, Imranul Kabir in Simulation and Analysis of Advanced Nuclear Reactor and Kinetics Model in 2nd International Conference on Intelligent Systems, Modelling and Simulation, ISMS2011, Malaysia, Phnom Penh (Cambodia), 25-27 Jan, 2011. Figure 1. Cuboid shape for Simulation Figure 2. 3D Wave Funtion 18
Figure 3. Energy States Figure 4. X Polarization Figure 5. Z Polarization 19
Figure 6. Absorption at angle of 45 Degree Figure 7. Absorption sweep for angle for pyramid 20
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