| 1. |
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| 2. |
- Chen, Jianing, et al.
(författare)
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Surface-enhanced Raman scattering of rhodamine 6G on nanowire arrays decorated with gold nanoparticles
- 2008
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:27, s. 5-275712
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) adsorbed on Au nanoparticles attached to InP nanowires. We find that nanowire arrays act as frameworks for effective SERS substrates with a significantly higher Raman signal sensitivity than a planar framework of Au nanoparticles adsorbed two-dimensionally on a flat surface. The SERS signal displays a clear polarization-dependent effect when the nanowires are arranged in a row. We also find that the SERS signal increases with time during continuous laser illumination. The plasmon-enhanced optical forces between Au nanoparticles may either move pairs of nanoparticles closer together or attract adsorbed molecules by moving them to the junctions of Au nanoparticle aggregates. Such effects by plasmon optical forces may cause the observed increase of the SERS signal with continuous laser illumination.
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| 3. |
- Chen, Jianing, et al.
(författare)
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Tip-enhanced Raman scattering of p-thiocresol molecules on individual gold nanoparticles
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:9
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of tip-enhanced Raman scattering on Au aerosol nanoparticles deposited on gold films. Under the tunneling current state, the Au tip and the Au aerosol nanoparticle form a narrow cavity, where large electromagnetic field enhancements are created to enhance Raman scattering enormously. Colorless p-thiocresol molecules are used as probe molecules. The estimated Raman enhancement is about nine orders of magnitude for the tip/particle configuration.
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| 4. |
- Anttu, Nicklas, et al.
(författare)
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Light scattering and plasmon resonances in a metal film with sub-wavelength nano-holes
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 100, s. 052037-052037
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Konferensbidrag (refereegranskat)abstract
- We report on a theoretical study of optical extinction in a metal film of 15-230 nm in thickness patterned periodically with sub-wavelength nano-holes of 140 nm in diameter. The gold plate was on a thick SiO2 wafer and the nano-holes as well as the top side of the metal plate were filled with water or solvent. Light was sent in toward the plate from the SiO2 side. The simulations were performed by solving the Maxwell equations using the scattering matrix method. It was seen that the extinction can, depending on the periodicity of the hole array, show one or several peaks in the visible wavelength range. The positions of the peaks were redshifted when the thickness of the gold plate was decreased. It was found that the peak positions for a thick plate can be identified from a simple surface plasmon dispersion relation.
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| 5. |
- Balocco, C, et al.
(författare)
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Microwave detection at 110 GHz by nanowires with broken symmetry
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 5:7, s. 1423-1427
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Tidskriftsartikel (refereegranskat)abstract
- By using arrays of nanowires with intentionally broken symmetry, we were able to detect microwaves up to 110 GHz at room temperature. This is, to the best of our knowledge, the highest speed that has been demonstrated in different types of novel electronic nanostructures to date. Our experiments showed a rather stable detection sensitivity over a broad frequency range from 100 MHz to 110 GHz. The novel working principle enabled the nanowires to detect microwaves efficiently without a dc bias. In principle, the need for only one high-resolution lithography step and the planar architecture allow an arbitrary number of nanowires to be made by folding a linear array as many times as required over a large area, for example, a whole wafer. Our experiment on 18 parallel nanowires showed a sensitivity of approximately 75 mV dc output/mW of nominal input power of the 110 GHz signal, even though only about 0.4% of the rf power was effectively applied to the structure because of an impedance mismatch. Because this array of nanowires operates simultaneously, low detection noise was achieved, allowing us to detect -25 dBm 110 GHz microwaves at zero bias with a standard setup.
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| 6. |
- Brusheim, Patrik, et al.
(författare)
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Field-driven geometrical phases in a time-periodic quantum system
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 79:20
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Tidskriftsartikel (refereegranskat)abstract
- We apply Floquet theory to explore the geometry of the Hilbert space under the influence of a time-periodic field. The geometrical phase is found to be induced by field-driven hybridizations when the photon energy of the driving field is close to the transition energies of the states of a quantum system. The phases of two hybridized states are phase locked to each other. We show that the geometrical phase is in general related to the Rabi frequency of the hybrid states. We also show that when the photon energy is equal to the transition energy of two states the geometrical phase acquired by each state is given exactly by an integer multiple of pi, independent of the strength of the driving field. We illustrate the derived generic properties of the geometric phase with an experimentally realizable quantum-wire system. It is shown that the interference between conductance channels in the wire presents a way to identify the geometrical phase.
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| 7. |
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| 8. |
- Brusheim, Patrik, et al.
(författare)
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Spin filtering devices based on ferromagnetic stripe modulated double quantum-dot structures
- 2006
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 73:4
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Tidskriftsartikel (refereegranskat)abstract
- We report on a theoretical study of spin-dependent electron transport in double quantum dot structures, made from a two-dimensional electron gas, with a local magnetic field modulation. Spin-dependent conductance and probability density of electrons in the structures are calculated and the underlying physics of the results is discussed. We include in the study not only the magnetic field component perpendicular to the two-dimensional electron gas plane, but also a consideration of the in-plane component of the magnetic field. It is shown that giant spin polarization (similar to 100%) of the conductance, with tunable spin polarity, can be achieved with the double-dot structures. It is also shown that the structures can be used as efficient spin filtering devices at temperatures well above that defined by the spin splitting energy.
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| 9. |
- Brusheim, Patrik, et al.
(författare)
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Spin Hall effect and zitterbewegung in an electron waveguide
- 2006
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 74:20
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Tidskriftsartikel (refereegranskat)abstract
- We study spin-resolved probability distributions for electrons in a multichannel waveguide in the presence of a spin-orbit interaction. For a spin-polarized electron injection, a zitterbewegung pattern is predicted in the probability distribution of electrons in the waveguide. For a spin-unpolarized injection, the spin-resolved electron probability in the waveguide shows spin accumulations. In addition to the spin Hall phenomenon-namely, accumulations of opposite spins at the lateral edges of the waveguide-we predict the existence of a regular stripe pattern of spin accumulations in the internal region of the waveguide. We show that the predicted zitterbewegung and spin Hall effect stem from the same mechanism and are formed from coherent states of electrons in the waveguide.
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| 10. |
- Brusheim, Patrik, et al.
(författare)
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Spin transport and spin Hall effect in an electron waveguide in the presence of an in-plane magnetic field and spin-orbit interaction
- 2007
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 75:19
-
Tidskriftsartikel (refereegranskat)abstract
- We study electron spin transport and the spin Hall effect in a quantum waveguide in the presence of Rashba spin-orbit interaction (SOI) and a homogeneous in-plane magnetic field, as well as the energy dispersion relation and spin polarization properties of the electron states in the corresponding infinite system. A general expression for the spin polarization of the outgoing flux, resulting from an arbitrarily polarized injection source, is derived for the quantum waveguide without the assumption of spin-degenerate leads. We further derive constraints on the spin-resolved transmission coefficients by analyzing the symmetries of the system. These constraints will impose restrictions on the spin-dependent conductances as well as the spin polarization of the outgoing flux. For an applied in-plane magnetic field parallel to the waveguide, conductance oscillations as a function of the SOI strength are diminished when the Zeeman energy exceeds the Rashba energy, due to spin alignment with the applied magnetic field. Furthermore, the calculated spin and charge probability distributions in the SOI waveguide region show spin Hall patterns and zitterbewegung patterns, respectively. For an applied transverse in-plane magnetic field, the SOI induced effective magnetic field is parallel or antiparallel with the applied field. The conductance of the system is then dominantly determined by spin-conserved transport processes, and spin-flipped transport processes can occur only through interchannel scattering and are therefore greatly suppressed. Furthermore, no zitterbewegung pattern in the charge density distribution can be found in the SOI region when the electrons are injected from a lead with spin polarization along the applied in-plane transverse field direction. However, the spin polarization probability distribution can still show a spin Hall pattern in the SOI region and the sign of the spin polarization in the spin Hall pattern can be reversed by tuning the applied magnetic field strength. For the corresponding infinite waveguide systems with uniform SOI and in-plane magnetic field, we show that the interplay between the applied in-plane magnetic field and the SOI induced effective magnetic field, together with subband hybridizations, will create a wave-vector-dependent spin polarization of the Bloch states with rich features and that these features cannot be captured by employing a simple one-dimensional model.
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| 11. |
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| 12. |
- Brusheim, Patrik, et al.
(författare)
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Symmetry of hole spin transport in a two-terminal quantum system
- 2006
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 74:23
-
Tidskriftsartikel (refereegranskat)abstract
- We study two-terminal hole spin transport in a p-type, light-hole-heavy-hole coupled, quantum-well system under the influence of Rashba spin-orbit interaction. An expression for the spin polarization of the outgoing hole flux is derived. It is shown that the in-plane spin polarization vanishes identically whenever the outgoing lead supports only heavy-hole channels. This result is independent of the details of the system. By analyzing the symmetries of the system, constraints on the spin-dependent transmission amplitudes are derived. It is shown that under time-reversal symmetry, the total hole spin polarization vanishes whenever the outgoing lead supports only one spin-degenerate hole channel, which is also independent of the details of the system. It is further shown that generally it is difficult to achieve spin polarized currents from a laterally defined Rashba hole device without breaking its transverse reflection symmetry.
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| 13. |
- Csontos, D., et al.
(författare)
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Lande-like formula for the g factors of hole-nanowire subband edges
- 2008
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 78:3
-
Tidskriftsartikel (refereegranskat)abstract
- We have analyzed theoretically the Zeeman splitting of hole-quantum-wire subband edges. As is typical for any bound state, their g factor depends on both an intrinsic g factor of the material and an additional contribution arising from a finite bound-state orbital angular momentum. We discuss the quantum-confinement-induced interplay between bulk-material and orbital effects, which is nontrivial due to the presence of strong spin-orbit coupling. A compact analytical formula is provided that elucidates this interplay and can be useful for predicting Zeeman splitting in generic hole-wire geometries.
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| 14. |
- Csontos, D., et al.
(författare)
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Spin-3/2 physics of semiconductor hole nanowires: Valence-band mixing and tunable interplay between bulk-material and orbital bound-state spin splittings
- 2009
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 79:15
-
Tidskriftsartikel (refereegranskat)abstract
- We present a detailed theoretical study of the electronic spectrum and Zeeman splitting in hole quantum wires. The spin-3/2 character of the topmost bulk-valence-band states results in a strong variation in subband-edge g factors between different subbands. We elucidate the interplay between quantum confinement and heavy-hole-light-hole mixing and identify a certain robustness displayed by low-lying hole-wire subband edges with respect to changes in the shape or strength of the wire potential. The ability to address individual subband edges in, e.g., transport or optical experiments enables the study of hole states with nonstandard spin polarization, which do not exist in spin-3/2 systems. Changing the aspect ratio of hole wires with rectangular cross section turns out to strongly affect the g factor of subband edges, providing an opportunity for versatile in situ tuning of hole-spin properties with possible application in spintronics. The relative importance of cubic crystal symmetry is discussed, as well as the spin splitting away from zone-center subband edges.
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| 15. |
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| 16. |
- Grönqvist, Johan, et al.
(författare)
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Strain in semiconductor core-shell nanowires
- 2009
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 106:5
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Tidskriftsartikel (refereegranskat)abstract
- We compute strain distributions in core-shell nanowires of zinc blende structure. We use both continuum elasticity theory and an atomistic model, and consider both finite and infinite wires. The atomistic valence force-field (VFF) model has only few assumptions. But it is less computationally efficient than the finite-element (FE) continuum elasticity model. The generic properties of the strain distributions in core-shell nanowires obtained based on the two models agree well. This agreement indicates that although the calculations based on the VFF model are computationally feasible in many cases, the continuum elasticity theory suffices to describe the strain distributions in large core-shell nanowire structures. We find that the obtained strain distributions for infinite wires are excellent approximations to the strain distributions in finite wires, except in the regions close to the ends. Thus, our most computationally efficient model, the FE continuum elasticity model developed for infinite wires, is sufficient, unless edge effects are important. We give a comprehensive discussion of strain profiles. We find that the hydrostatic strain in the core is dominated by the axial strain-component, epsilon(ZZ). We also find that although the individual strain components have a complex structure, the hydrostatic strain shows a much simpler structure. All in-plane strain components are of similar magnitude. The nonplanar off-diagonal strain components (epsilon(XZ) and epsilon(YZ)) are small but nonvanishing. Thus the material is not only stretched and compressed but also warped. The models used can be extended for the study of wurtzite nanowire structures, as well as nanowires with multiple shells.
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| 17. |
- He, Yuhui, et al.
(författare)
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AC Conductance of DNA molecule at low temperature
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 100, s. 052065-052065
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Konferensbidrag (refereegranskat)abstract
- Using nonequilibrium Green's function technique, we have investigated the ac conductance of poly(C)-poly(G) DNA molecule at low temperature. Our results indicate that thermal fluctuations of DNA hopping energy will play a profound role for the ac conductance. It smoothes out the conductance curves at high ac signal frequency while does not suppress it substantially. The dependences of the ac conductance on the density of states in the contacts, ac signal frequency and temperature are also investigated.
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| 18. |
- Larsson, Marcus, et al.
(författare)
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A highly tunable lateral quantum dot realized in InGaAs/InP by an etching technique
- 2008
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 103:8, s. 3-086101
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Tidskriftsartikel (refereegranskat)abstract
- We report on the realization of a quantum dot in a modulation doped InGaAs/InP heterostructure by electron beam lithography and chemical wet etching. Using etched trench defined in-plane gates and a local top gate, the tunneling barriers, electron density, and electrostatic potential of the dot can be tuned. Electrical measurements reveal clear Coulomb blockade behavior of the electron transport through the dot and the behavior of electron tunneling through its excited states.
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| 19. |
- Larsson, Marcus, et al.
(författare)
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Electron transport study of a lateral InGaAs quantum dot
- 2008
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - : Elsevier BV. - 1386-9477. ; 40:6, s. 1950-1951
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Tidskriftsartikel (refereegranskat)abstract
- We report on fabrication and electron transport measurements of lateral InGaAs quantum dots defined by wet chemical etching. The tunneling barriers and dot potential are tuned using both etching-defined in-plane gates and a local top gate. Transport measurements performed at low temperature show Coulomb diamonds with excited states in the bias spectroscopy indicating the effects of quantum confinement.
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| 20. |
- Larsson, Marcus, et al.
(författare)
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g-factor and exchange energy in a few-electron lateral InGaAs quantum dot
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:19
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the measurements of the g-factor and the exchange Interaction of electrons in a few-electron lateral quantum dot formed in an InGaAs/InP semiconductor heterostructure. The spin filling sequence of the electron states in the dot is determined by magnetotransport measurements and parallel spin filling configurations are Identified The measured g-factor (for a magnetic field applied parallel to the InGaAs quantum layer) has it Value in the range of vertical bar g*vertical bar approximate to 2 to vertical bar g*vertical bar approximate to 4 and is strongly level-dependent. By analysis of the energies of the states which favor a parallel spin filling. the lower bound of the exchange energy of electrons in the clot in the order of similar to 210 mu eV is extracted. (C) 2009 American Institute of Physics.
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Luo, Gang, et al.
(författare)
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Nanoimprint lithography for the fabrication of interdigitated cantilever arrays
- 2006
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 17:8, s. 1906-1910
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Tidskriftsartikel (refereegranskat)abstract
- We report on the realization of a novel interdigitated cantilever array with electrostatic control of the shape of the interdigitated array. It consists of an array of SiO2/metal double-finger cantilevers in a grating configuration together with an electrical connection part. The complete grating structure is fabricated with nanoimprint lithography, UV lithography and reactive ion etching. The patterns of the cantilever arrays are defined by nanoimprint lithography. The electrical contact pads are defined and aligned with the imprinted grating pattern by UV lithography. The two steps of reactive ion etching are optimized to get vertical sidewalls of the SiO2 cantilevers and finally to release them from the Si substrate. By applying a bias, the shape of the cantilever array can be altered due to the electrostatic force. The dimensions of the cantilevers and the spacing between them are optimized to achieve the desired functional operating characteristics of the structures. Since the fabrication scheme is based on nanoimprint lithography, such electrostatically controlled periodic structures may be relatively easily and non-expensively realized in various configurations, allowing them to function as optical switching elements, electrical filters, mass sensors, etc.
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| 25. |
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| 26. |
- Mikkelsen, Anders, et al.
(författare)
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Photoemission electron microscopy using extreme ultraviolet attosecond pulse trains
- 2009
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 80:12
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Tidskriftsartikel (refereegranskat)abstract
- We report the first experiments carried out on a new imaging setup, which combines the high spatial resolution of a photoemission electron microscope (PEEM) with the temporal resolution of extreme ultraviolet (XUV) attosecond pulse trains. The very short pulses were provided by high-harmonic generation and used to illuminate lithographic structures and Au nanoparticles, which, in turn, were imaged with a PEEM resolving features below 300 nm. We argue that the spatial resolution is limited by the lack of electron energy filtering in this particular demonstration experiment. Problems with extensive space charge effects, which can occur due to the low probe pulse repetition rate and extremely short duration, are solved by reducing peak intensity while maintaining a sufficient average intensity to allow imaging. Finally, a powerful femtosecond infrared (IR) beam was combined with the XUV beam in a pump-probe setup where delays could be varied from subfemtoseconds to picoseconds. The IR pump beam could induce multiphoton electron emission in resonant features on the surface. The interaction between the electrons emitted by the pump and probe pulses could be observed. (C) 2009 American Institute of Physics. [doi:10.1063/1.3263759]
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| 27. |
- Nilsson, Henrik, et al.
(författare)
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Giant, level-dependent g factors in InSb nanowire quantum dots.
- 2009
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9:9, s. 3151-3156
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Tidskriftsartikel (refereegranskat)abstract
- We report on magnetotransport measurements on InSb nanowire quantum dots. The measurements show that the quantum levels of the InSb quantum dots have giant g factors, with absolute values up to approximately 70, the largest value ever reported for semiconductor quantum dots. We also observe that the values of these g factors are quantum level dependent and can differ strongly between different quantum levels. The presence of giant g factors indicates that considerable contributions from the orbital motion of electrons are preserved in the measured InSb nanowire quantum dots, while the level-to-level fluctuations arise from spin-orbit interaction. We have deduced a value of Delta(SO) = 280 mueV for the strength of spin-orbit interaction from an avoided level crossing between the ground state and first excited state of an InSb nanowire quantum dot with a fixed number of electrons.
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| 28. |
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| 29. |
- Persson, Martin, et al.
(författare)
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Electronic structure of [100]-oriented free-standing InAs and InP nanowires with square and rectangular cross sections
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. ; 73
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a theoretical study of the electronic structure of free-standing InAs and InP nanowires grown along the [100] crystallographic direction, based on an atomistic tight-binding approach. The band structure and wave functions for nanowires with both square (nanowires) and rectangular (nanobelts) cross sections are calculated. A comparison is made between the calculations for InAs, InP, and GaAs nanowires and similar characteristics are found in the band structure and wave functions of the three material types of nanowires. It is found that the nanowires with both square and rectangular cross sections have simple, parabolic conduction bands. However, the characteristics of the valence bands in the nanowires are found to be cross-section aspect-ratio dependent. For the nanowires with a square cross section, the valence bands show rich and complex structures. In particular, the highest valence band of a square nanowire shows a double-maximum structure and has its energy maximum at k[not-equal]0, giving an indirect nanowire band gap. When the cross section of the nanowires changes from a square to a rectangular type, the top valence bands tend to develop into parabolic bands. For the nanowires with the same cross-section aspect ratio and material type, the valence band structures at different sizes are found to have similar characteristic structures, although the band energies sensitively depend on the nanowire lateral size. The wave functions of the band states of the InAs and InP nanowires at the Gamma point have been calculated. It is found that for the square nanowires the valence band states show complex structures. For the rectangular nanowires with sufficiently large aspect ratios the wave functions of the topmost valence band states show the features predicted by a one-band effective-mass model, in agreement with the fact that these valence bands become good parabolic bands in these rectangular nanowires.
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| 30. |
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| 31. |
- Roddaro, Stefano, et al.
(författare)
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Spin States of holes in ge/si nanowire quantum dots.
- 2008
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Ingår i: Physical Review Letters. - 1079-7114. ; 101:18
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Tidskriftsartikel (refereegranskat)abstract
- We investigate tunable hole quantum dots defined by surface gating Ge/Si core-shell nanowire heterostructures. In single level Coulomb-blockade transport measurements at low temperatures spin doublets are found, which become sequentially filled by holes. Magnetotransport measurements allow us to extract a g factor g;{*} approximately 2 close to the value of a free spin-1/2 particle in the case of the smallest dot. In less confined quantum dots smaller g factor values are observed. This indicates a lifting of the expected strong spin-orbit interaction effects in the valence band for holes confined in small enough quantum dots. By comparing the excitation spectrum with the addition spectrum we tentatively identify a hole exchange interaction strength chi approximately 130 mueV.
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| 32. |
- Sun, Jie, et al.
(författare)
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A novel SR latch device realized by integration of three-terminal ballistic junctions in InGaAs/InP
- 2008
-
Ingår i: IEEE Electron Device Letters. - 0741-3106. ; 29:6, s. 540-542
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, a novel sequential logic device based on three-terminal ballistic junctions (TBJs) is proposed and demonstrated. Two TBJs and two in-plane gates are laterally integrated in a high-electron-mobility InGaAs/InP quantum-well material by a single-step lithography process. Electrical measurements reveal that the integrated device functions as a set-reset (SR) latch with voltage gains at room temperature. The demonstrated device provides a new and simple circuit design for SR latches in digital electronics.
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| 33. |
- Sun, Jie, et al.
(författare)
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A sequential logic device realized by integration of in-plane gate transistors in InGaAs/InP
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951. ; 92:1
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Tidskriftsartikel (refereegranskat)abstract
- An integrated nanoelectronic circuit is fabricated from a high-mobility In0.75Ga0.25As/InP heterostructure. The manufactured device comprises two double in-plane gate transistors with a current channel of 1.1 mu m in length and 100 nm in width. The two transistors are coupled to each other in a configuration that the source of one transistor is directly connected with one in-plane gate of the other transistor. Electrical measurements reveal that this device functions as an SR (set-reset) latch (a sequential logic device) with a gain of similar to 4 in the logic swing at room temperature. The demonstrated device provides a simple circuit design for SR latches.
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| 34. |
- Sun, Jie, et al.
(författare)
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Frequency mixing and phase detection functionalities of three-terminal ballistic junctions
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:19
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Tidskriftsartikel (refereegranskat)abstract
- Three-terminal ballistic junctions (TBJs) are fabricated from a high-mobility InP/In0.75Ga0.25As heterostructure by electron-beam lithography. The voltage output from the central branch is measured as a function of the voltages applied to the left and right branches of the TBJs. The measurements show that the TBJs possess an intrinsic nonlinearity. Based on this nonlinearity, a novel room-temperature functional frequency mixer and phase detector are realized. The TBJ frequency mixer and phase detector are expected to have advantages over traditional circuits in terms of simple structure, small size and high speed, and can be used as a new type of building block in nanoelectronics.
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| 35. |
- Sun, Jie, et al.
(författare)
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Gate-defined quantum devices realized on an InGaAs/InP heterostructure by incorporating a high-kappa dielectric material
- 2009
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Ingår i: 2009 IEEE Nanotechnology Materials and Devices Conference. ; , s. 183-185
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Konferensbidrag (refereegranskat)abstract
- Gate-defined quantum devices in an InGaAs/InP heterostructure are achieved by introducing a HfO2 layer as the gate dielectric. The high-kappa layer is grown by atomic layer deposition and the fabrication process is described in detail. Electrical measurements at low temperature reveal the Coulomb blockade effect. Magnetotransport characterization is also carried out for the devices made from this promising spintronic material and the current peaks are found to shift in spin pairs with the applied B-field perpendicular to the wafer.
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| 36. |
- Sun, Jie, et al.
(författare)
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Gate-defined quantum-dot devices realized in InGaAs/InP by incorporating a HfO2 layer as gate dielectric
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:4
-
Tidskriftsartikel (refereegranskat)abstract
- Gate-defined quantum dots in an InGaAs/InP heterostructure are realized by incorporating a high-kappa HfO2 material as a gate dielectric using atomic layer deposition. The fabricated quantum-dot devices show Coulomb blockade effect at low temperature. The Coulomb blockade current peaks are found to shift in pairs with the magnetic field applied perpendicular to the quantum-dot plane, due to the filling of electrons into spin-degenerate orbital states. When the magnetic field is applied parallel to the quantum-dot plane, spin splittings of orbital states are observed and the extracted effective g-factors are found to be different for different orbital states.
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| 37. |
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| 38. |
- Sun, Jie, et al.
(författare)
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Novel nanoelectronic device applications based on the nonlinearity of three-terminal ballistic junctions
- 2007
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Ingår i: Physics of Semiconductors, Pts A and B. - : AIP. - 0094-243X .- 1551-7616. ; 893, s. 1471-1472
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Konferensbidrag (refereegranskat)abstract
- Nanometer-scale electron devices containing three-terminal ballistic junctions are fabricated by electron-beam lithography on InP/InGaAs two-dimensional electron gas materials. Based on the intrinsic nonlinearity of the devices, frequency mixer, phase detector and RS flip-flop memory functioning at room temperature are successfully achieved. The devices have simple structure layout and small size, and are expected to function at high speed.
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| 39. |
- Sun, Jie, et al.
(författare)
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Novel room-temperature functional analogue and digital nanoelectronic circuits based on three-terminal ballistic junctions and planar quantum-wire transistors
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 100, s. 052073-052073
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Konferensbidrag (refereegranskat)abstract
- Three-Terminal ballistic junctions (TBJs) and planar quantum-wire transistors (QWTs) are emerging nanoelectronic devices with various novel electrical properties. In this work, we realize novel nanoelectronic analogue and digital circuits with TBJs and planar QWTs made on In0.75Ga0.25As/InP two-dimensional electron gas (2DEG) material. First we show that a single TBJ can work as a frequency mixer or a phase detector. Second, we fabricate an integrated nanostructure containing two planar QWTs, which can be used as an RS flip-flop element. Third, we make a nanoelectronic circuit by the integration of two TBJs and two planar QWTs. This circuit shows the RS flip-flop functionalities with much larger noise margins in both high and low level inputs. All measurements in this work are done at room temperature.
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| 40. |
- Suyatin, Dmitry, et al.
(författare)
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Electrical properties of self-assembled branched InAs nanowire junctions
- 2008
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:4, s. 1100-1104
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Tidskriftsartikel (refereegranskat)abstract
- We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.
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| 41. |
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| 42. |
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| 43. |
- Søndergaard, Niels, et al.
(författare)
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Strain distributions in lattice-mismatched semiconductor core-shell nanowires
- 2009
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 27:2, s. 827-830
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Konferensbidrag (refereegranskat)abstract
- The authors study the elastic deformation held in lattice-mismatched core-shell nanowires with single and multiple shells. The authors consider infinite wires with a hexagonal cross section under the assumption of translational symmetry. The strain distributions are found by minimizing the elastic energy per unit cell using the finite element method. The authors find that the trace of the strain is discontinuous with a simple, almost piecewise variation between core and shell, whereas the individual components of the strain can exhibit complex variations. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3054200]
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| 44. |
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| 45. |
- Wallin, Daniel, et al.
(författare)
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Detection of charge states in nanowire quantum dots using a quantum point contact
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90
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Tidskriftsartikel (refereegranskat)abstract
- The authors demonstrate operation of a charge readout scheme for quantum dots in a semiconductor nanowire using a quantum point contact defined in a GaAs/AlGaAs two-dimensional electron gas beneath the nanowire. The quantum dots were fabricated by epitaxial growth of InP barriers along a n-type InAs nanowire. Applying negative voltages to two split-gate electrodes aligned to the nanowire induces a quantum point contact in the two-dimensional electron gas such that charging of quantum dots in the nanowire modulates the quantum point contact transmission, thus resulting in the desired detector response.
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| 46. |
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| 47. |
- Wallin, Daniel, et al.
(författare)
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Electrical properties and logic function of multibranch junction structures
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:25
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Tidskriftsartikel (refereegranskat)abstract
- We report on room-temperature electrical measurements of multibranch junction (MBJ) devices made from a semiconductor heterostructure. We show that the MBJ devices exhibit an interesting electrical property. If the voltage output at one branch is measured as a function of the voltages inputs to all the other branches, the output voltage is determined predominately by the most negative, or the lowest, voltage applied. The property arises from the nature of the voltage-induced ballistic electron transport in the MBJ device, and can in general be observed in other nanoscale MBJ structures. We also demonstrate the realization of very compact multi-input logic gates with the MBJ structures.
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| 48. |
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| 49. |
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| 50. |
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