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ABSTRACT: The unique energy transfer interaction between the optical protein bacteriorhodopsin (bR) and CdSe/ZnS quantum dots (QDs) provides a potential modulation mechanism for bio- nano electronic application. We have utilized ionic-self assembled monolayer (I-SAM) techniques to create a novel alternating monolayer system of QDs and bR on a conductive ITO substrate. Results demonstrate the ability to efficiently create bR/QD multilayer films along with the ability to control bR/QD spacing on the nanometer scale. I-SAM films of this nature demonstrate a sharp decrease in QD emission when deposited in close proximity to bR, suggesting possible fluorescence resonance energy transfer (FRET) effects in a bR/QD nanoscale system. The ability to modulate the QD photonic output based on proximity to bR in the I-SAM films could provide a direct method to modulate the electrical output for bio-nano sensing applications.
Nanotechnology, 2008. NANO '08. 8th IEEE Conference on; 09/2008
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ABSTRACT: We present here the results of theoretical calculations on the electron transport via a donor-bridge (π)-acceptor molecular system. A significant rectification effect is observed. A new transport mechanism involving the electronic structure of the molecular diode will be discussed.
Nanotechnology, 2007. IEEE-NANO 2007. 7th IEEE Conference on; 09/2007
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ABSTRACT: Current (I)-Voltage (V) characteristics of the self-assembled monolayer (SAM) of π-conjugated, 4,4'-1,4-phenylenebis(methylidynenitrilo)bisbenzene thiolate (PMNBT) adsorbed on Au (111) substrate have been investigated by scanning tunneling microscopy (STM). The measured tunneling current in the case of PMNBT SAM is much higher than that in the case of dodecanemonothiolate (DDMT) molecules. Furthermore, the PMNBT SAMs appear to exhibit a pronounced rectification of the tunneling current not observed in the case of DDMT. Possible reasons for the difference between the I-V characteristics of the two molecules are identified.
Nanotechnology, 2005. 5th IEEE Conference on; 08/2005
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ABSTRACT: We present the results of a first-principles quantum mechanical study of spin-dependent electron transport along a molecular wire investigating the effects of the size and the shape of the probe tip on the tunneling current. A periodic, gradient-corrected density functional method together with Bardeen, Tersoff and Hamann formalism is employed in this study. The electron tunneling through a self-assembled monolayer of benzene 1,4-dithiol on the Ni(111) substrate is found to be strongly dependent on both shape and size of the probe tip.
Nanotechnology, 2005. 5th IEEE Conference on; 08/2005
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ABSTRACT: We report the results of first-principles quantum chemical
calculations of the interactions of H/H<sup>+</sup> with oxide ring
structures of varying sizes. The calculations suggest that the binding
and stability of protons in amorphous SiO<sub>2</sub> depend upon the
topology of the interacting network. A neutral hydrogen atom, H<sup>0
</sup>, does not bind to bridging O atoms in the rings, but may occupy
voids within larger rings
IEEE Transactions on Nuclear Science 01/2002; · 1.45 Impact Factor
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ABSTRACT: A theoretical formalism based on the Buttiker multiterminal response formula has been developed and applied to model a novel three terminal molecular device, constructed from common organic donor, acceptor and π-electron conjugated spacer structures. Quantum conductivity calculations in the tight binding (extended Huckel) framework show switching behavior in the calculated I-V characteristics of the modeled transistor upon application of an external potential to the third capacitive gate terminal
Nanotechnology, 2001. IEEE-NANO 2001. Proceedings of the 2001 1st IEEE Conference on; 02/2001
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IEEE Transactions on Nuclear Science 01/2001; 48:2081-2085. · 1.45 Impact Factor
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ABSTRACT: First principles quantum mechanical calculations on model
SiO<sub>2</sub> clusters support the Lelis model of reverse annealing in
the oxide and provide the first electronic structure explanation of the
process, suggesting that delocalized holes (E<sub>δ</sub>'
centers) are annealed out permanently. Localized holes (E<sub>γ
</sub>' centers) form a metastable, dipolar complex, without restoring
the Si-Si dimer bond upon electron trapping. In the presence of an
applied negative field, these charge neutral, dipolar complexes,
(E<sub>γ</sub>'+e<sup>-</sup>), can readily release the weakly
bonded electron, exhibiting a reverse annealing process
IEEE Transactions on Nuclear Science 01/2001; · 1.45 Impact Factor
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ABSTRACT: The buildup of positive charge during annealing in forming gas at 600/spl deg/C was compared for various types of Si/SiO/sub 2/ interfaces. Our data suggest a correlation between the presence of stressed bonds in the SiO/sub 2/ network near the Si/SiO/sub 2/ interface, and the ratio of fixed vs. mobile positive charge (protons) detected near the interface after performing a forming-gas annealing. We further propose that the presence of these stressed bonds near the interface is correlated with the oxygen deficiency at the interface and with the confinement of the oxide due to the presence of a Si cover layer. A model based on first-principles quantum mechanical calculations shows a significant decrease in the overall proton binding energy with increasing network strain near the interface. These calculations support our model of mobile proton generation at Si/SiO/sub 2/ interfaces with large densities of stressed bonds.
IEEE Transactions on Nuclear Science 01/2000; · 1.45 Impact Factor
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ABSTRACT: The atomic structure and spin properties of two previously undescribed amorphous silicon dioxide fundamental point defects have been characterized for the first time by ab initio quantum mechanical calculations. Both defects are electrically neutral trivalent silicon centers in the oxide. One of the defects, the X-center, is determined to have an O/sub 2/Si/spl equiv/Si/sup /spl dagger// atomic structure. The other defect, called the Y-center, is found to have an OSi/sub 2//spl equiv/Si/sup /spl dagger// structure. Calculated electronic and electrical properties of the new defect centers are consistent with the published characteristics of the oxide switching trap or border trap precursors.
IEEE Transactions on Nuclear Science 01/2000; · 1.45 Impact Factor
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ABSTRACT: A model for proton mobility in a-SiO/sub 2/ is developed. Theoretical first-principles calculations are performed to test this model by obtaining pathways and activation energies for proton motion.
IEEE Transactions on Nuclear Science 01/2000; · 1.45 Impact Factor
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ABSTRACT: In order to understand the physics of radiation-induced proton
density decay in thin SiO<sub>2</sub> films, we performed ab initio
Hartree-Fock calculations of the potential energy curves for the
interaction between model oxide clusters and H in two charge states. The
calculated results led to two separate proposed mechanisms for proton
density decay in thin SiO<sub>2</sub> films: (1) electronic excitation
involving hot phonon levels of the ground electronic state at low
photon-energy radiation and (2) electron capture by protons at high
photon-energy radiation. The proposed mechanisms qualitatively explain
recent experimental observations
IEEE Transactions on Nuclear Science 01/1999; · 1.45 Impact Factor
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ABSTRACT: The atomic structure and spin properties of two previously undescribed amorphous silicon dioxide fundamental point defects have been characterized for the first time by ab initio quantum mechanical calculations. Both defects are electrically neutral trivalent silicon centers in the oxide. One of the defects, the X-center, is determined to have an O2Si≡Si† atomic structure. The other defect, called the Y-center, is found to have an OSi2 ≡Si† structure. Calculated electronic and electrical properties of the new defect centers are consistent with the published characteristics of the oxide switching trap or border trap precursors
IEEE Transactions on Nuclear Science - IEEE TRANS NUCL SCI. 01/1999; 46(6):1544-1552.
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ABSTRACT: The buildup of positive charge during annealing in forming gas at 600°C was compared for various types of Si/SiO2 interfaces. Our data suggest a correlation between the presence of stressed bonds in the SiO2 network near the Si/SiO2 interface, and the ratio of fixed vs. mobile positive charge (protons) detected near the interface after performing a forming-gas annealing. We further propose that the presence of these stressed bonds near the interface is correlated with the oxygen deficiency at the interface and with the confinement of the oxide due to the presence of a Si cover layer. A model based on first-principles quantum mechanical calculations shows a significant decrease in the overall proton binding energy with increasing network strain near the interface. These calculations support our model of mobile proton generation at Si/SiO2 interfaces with large densities of stressed bonds
IEEE Transactions on Nuclear Science - IEEE TRANS NUCL SCI. 01/1999; 46(6):1562-1567.
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ABSTRACT: Summary form only given. Results from first-principles cluster approach quantum mechanical calculations on the electron capture mechanism by oxygen deficient center (ODC) hole traps (HTs) in SiO<sub>2 </sub> are presented. These results suggest that upon electron capture, HTs at “unstrained” ODCs are permanently annealed out while those at highly strained ODCs form a weakly bonded electron-hole (e-h) complex which can readily emit an electron and switch back to a positive charge state. Anneal characteristics of trapped holes at ODCs in buried oxide (BOX) is an issue of fundamental importance for the reliability of silicon-on-insulator (SOI) devices
SOI Conference, 1998. Proceedings., 1998 IEEE International; 11/1998
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ABSTRACT: The annihilation of mobile protons in thin SiO2 films by capture of ultraviolet-excited electrons has been analyzed for temperatures between 77 and 500 K. We observe a strong increase in proton annihilation with increasing temperature, and derive an activation energy for electron capture of about 0.2 eV. Based on quantum chemical [(OH)3Si]2�O�H+ cluster calculations, we suggest photoexcitation of electrons from excited vibrational states of the ground electronic (valence band) state to a nearby excited electronic (SiO2 gap) state. It is argued that the latter excitation can result in H0 formation at elevated temperatures. © 1998 American Institute of Physics.
Applied Physics Letters 01/1998; 72(1):28-30. · 3.84 Impact Factor
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ABSTRACT: We have performed current-voltage, capacitance-voltage and
electron-paramagnetic-resonance (EPR) characterization of
silicon-on-insulator (SOI) samples, subjected to a wide variety of
irradiation and anneal treatments. By comparing transport properties and
interfacial reaction mechanisms, we provide evidence for an intrinsic
difference in the response of mobile protons in these oxides, depending
on whether they are generated by irradiation or by H<sub>2</sub>
annealing. A radiation effects study of SOI buried oxides containing
annealing induced mobile protons is presented to gain insight into the
mechanisms behind these fundamental differences. Electrical
characterization shows that, for these devices, the initial interface
trap and mobile proton densities are largely unaffected by the
irradiation. However, if the irradiation is carried out in the presence
of positive bias applied to the top Si, the protons become trapped in
shallow levels. These proton traps are activated by the irradiation and
are located near the oxide/substrate interface. These results may lead
to improved radiation hardness of buried oxides for nonvolatile memory
and other applications
IEEE Transactions on Nuclear Science 01/1998; · 1.45 Impact Factor
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ABSTRACT: Radiation induced defect creation or revelation in metal
oxide-semiconductor (MOS) field effect transistors (FET) or bipolar
structures remains a hazard for devices exposed to hostile environments
such as those encountered in space. Certainly for MOSFETs and to some
degree for bipolar transistors, defects generated in thin, amorphous SiO
<sub>2</sub> layers are of prime concern. Despite extensive experimental
studies one can reasonably say that a complete theoretical description
of any point defect in SiO<sub>2</sub> is lacking. We report the first
ab initio quantum mechanical investigation of the structure of the E'
<sub>δ</sub> center in amorphous SiO<sub>2</sub>
(a-SiO<sub>2</sub>). Our calculations suggest that the unpaired electron
is shared by only two Si atoms, irrespective of the Si cluster
size
IEEE Transactions on Nuclear Science 01/1998; · 1.45 Impact Factor
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ABSTRACT: Ab initio Hartree-Fock and second-order Moeller-Plesset theory calculations have been performed to investigate the stability of triply-coordinated O{sup +} centers in the Si-O-Si network of amorphous SiO{sub 2}. The calculations reveal that the H{sup +} ion binds with a bridging O center to form a very stable (D{sub e} > 6 eV) trivalent O complex. Capture of an electron by the positively charged protonated complex, however, is predicted to immediately lead to the dissociation of the O-H bond. A relatively weaker, but stable bond is also formed between the bridging O atom and a {sup +}SiH{sub 3} ion.
12/1996
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Journal of the Optical Society of America B 01/1993; 10:213-221. · 2.18 Impact Factor
