The document summarizes simulation results of quantum dot cuboid nanocrystals with different nanostructures. It first describes taking a 3D cuboid structure and simulating its 3D wavefunction, energy states, and light/dark transitions under different polarizations. It finds the characteristics are equivalent for different structures given the same boundary conditions. It then simulates a pyramid structure and finds its absorption peaks differ in number but are otherwise equivalent to the cuboid. The conclusion states that for different nanostructures, the characteristics are almost equivalent under the same boundary conditions.

1. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 3, 2012
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
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2. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 3, 2012
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
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3. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 3, 2012
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
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4. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 3, 2012
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
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5. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 3, 2012
Figure 3. Energy States
Figure 4. X Polarization
Figure 5. Z Polarization
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6. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 3, 2012
Figure 6. Absorption at angle of 45 Degree
Figure 7. Absorption sweep for angle for pyramid
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