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| 2. |
- Elfström, Niklas, et al.
(författare)
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Surface Charge Sensitivity of Silicon Nanowires : Size Dependence
- 2007
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 7:9, s. 2608-2612
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nanowires of different widths were fabricated in silicon on insulator (SOI) material using conventional process technology combined with electron-beam lithography. The aim was to analyze the size dependence of the sensitivity of such nanowires for biomolecule detection and for other sensor applications. Results from electrical characterization of the nanowires show a threshold voltage increasing with decreasing width. When immersed in an acidic buffer solution, smaller nanowires exhibit large conductance changes while larger wires remain unaffected. This behavior is also reflected in detected threshold shifts between buffer solutions of different pH, and we find that nanowires of width > 150 nm are virtually insensitive to the buffer pH. The increased sensitivity for smaller sizes is ascribed to the larger surface/volume ratio for smaller wires exposing the channel to a more effective control by the local environment, similar to a surrounded gate transistor structure. Computer simulations confirm this behavior and show that sensing can be extended even down to the single charge level.
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| 3. |
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| 4. |
- Sprunken, Dan, et al.
(författare)
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Influence of the Local Environment on Determining Aspect-Ratio Distributions of Gold Nanorods in Solution Using Gans Theory
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111, s. 14299-
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Tidskriftsartikel (refereegranskat)abstract
- We apply Gans theory to fit the absorption spectra of gold nanorods with aspect ratios R < 2.5 in solution using both the longitudinal and transversal surface plasmon resonance absorption peaks and the dielectric constant of the medium as a fitting parameter. By fitting the broadened absorption peaks using the absorption spectra of a set of nanorods with a range of aspect ratios, we determine the size distribution of the nanorods in solution. The optimum value of dielectric constant is substantially higher than the dielectric constant of the solvent, which is most likely due to a change in the effective dielectric constant in the vicinity of the nanorods. The validity of our method is confirmed by comparing the calculated size distributions with transmission electron microscope images, and we obtain a good agreement between the experiments and our calculations. Furthermore, several other recent experimental results are compared with our fitting method, and we find that the discrepancy between Gans theory and those experimental results can be explained by using higher values of dielectric constant. 1.
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| 5. |
- Sychugov, Ilya, et al.
(författare)
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Composition Control of Electron Beam Induced Nanodeposits by Surface Pretreatment and Beam Focusing
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:52, s. 21516-21519
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Tidskriftsartikel (refereegranskat)abstract
- Cross-sectional transmission electron microscopy with elemental analysis was used to investigate shape and composition of nanostructures fabricated by electron beam induced deposition. The nanostructures were deposited on a thin edge of the silicon membrane allowing characterization without intermediate distorting preparation steps, such as focused ion beam milling. The effect of the surface carbon contaminants and the electron beam focusing on nanostructure composition was studied. It is shown how carbon content of nanostructures can be reduced by sample preheating, forming metal nanostructures with higher purity advantageous for circuitry and lithography applications.
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| 6. |
- Sychugov, Ilya, et al.
(författare)
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Effect of photonic bandgap on luminescence from silicon nanocrystals
- 2007
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 32:13, s. 1878-1880
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Tidskriftsartikel (refereegranskat)abstract
- The modification of the luminescence of silicon nanocrystals experiencing the effect of a photonic bandgap in a 2D photonic crystal was investigated. The time-integrated photoluminescence spectra detected in the plane of the photonic crystal revealed a dip in the light emission corresponding to the wavelength of the bandgap, whose position changes according to the geometry of the prepatterned pillar array. The calculated emission pattern for a pointlike dipole placed in such a structure suggests an inhibition of the spontaneous emission rate at certain directions as a physical reason for the observed modification of luminescence.
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| 7. |
- Sychugov, Ilya, et al.
(författare)
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Effect of substrate proximity on luminescence yield from Si nanocrystals
- 2006
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 89:11, s. 111124-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the proximity of a high refractive index substrate on the luminescence of Si nanocrystals was investigated by time-integrated and time-resolved photoluminescence. The luminescence yield was found to be ∼2.5 times larger for emitters distanced from the substrate compared to those in proximity with the substrate, while luminescence decay measurements revealed only a slight increase in the luminescence lifetime (∼15%). Results are discussed in terms of local density of optical modes surrounding a pointlike light emitter with important implications for the collection efficiency of luminescence and the estimation of internal quantum efficiency for a quantum dot.
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| 8. |
- Sychugov, Ilya, et al.
(författare)
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Light emission from silicon nanocrystals: probing a single quantum do
- 2006
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 252:15, s. 5249-5253
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of low-temperature photoluminescence measurements performed on single silicon nanocrystals is presented. The luminescence emission linewidth of Si nanocrystals is found to be less than thermal broadening at low temperature, confirming the atomic-like nature of their energetic states. Beside the main peak the low-temperature spectra reveal a similar to 6 meV replica, the origin of which is discussed. For some of the investigated dots, we also observe a similar to 60 meV transverse optical (TO) phonon replica. The regular arrangement of individual nanocrystals used in this work enables combined high-resolution transmission electron microscopy (TEM) and low-temperature photoluminescence characterization of the same single quantum dot.
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| 9. |
- Sychugov, Ilya, et al.
(författare)
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Luminescence blinking of a Si quantum dot in a SiO2 shell
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : The American Physical Society. - 1098-0121 .- 1550-235X. ; 71:11, s. 115331-1-115331-5
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of on-off luminescence intermittency - blinking - in silicon nanocrystals was studied using a single-dot microphotoluminescence technique. From recordings of the luminescence intensity trace, on- and off-time distributions were extracted revealing exponential behavior, as expected for systems with blinking of a purely random nature. The corresponding switching rates for on-off and off-on processes exhibit different dependence on the excitation intensity. While the on-off switching rate grows quadratically with the excitation, the inverse process is nearly pumping power independent. Experimental findings are interpreted in terms of a dot "charging" model, where a carrier may become trapped in the surrounding matrix due to thermal and Auger-assisted processes. Observed blinking kinetics appear to be different from that of porous silicon particles.
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| 10. |
- Sychugov, Ilya, et al.
(författare)
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Measuring interface electrostatic potential and surface charge in a scanning electron microscope
- 2009
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Ingår i: Journal of Vacuum Science & Technology B. - : AVS Publications. - 1071-1023 .- 1520-8567. ; 27:6, s. 2357-2360
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Tidskriftsartikel (refereegranskat)abstract
- A novel method for electrostatic potential measurements at the interface is described. It involves placing a two-dimensional grid below the sample and observing it in a scanning electron microscope. Primary electron beam displacement, caused by surface charges, can be then measured for every grid knot. Using geometric parameters of the setup, a quantitative mapping of the potential can be extracted. It is shown that this method can achieve a tens of millivolt sensitivity and a submicron spatial resolution in electrostatic potential measurements.
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