| 1. |
- Wågberg, Lars, et al.
(författare)
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The build-up of polyelectrolyte multilayers of microfibrillated cellulose and cationic polyelectrolytes
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:3, s. 784-795
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Tidskriftsartikel (refereegranskat)abstract
- A new type of nanocellulosic material has been prepared by high-pressure homogenization of carboxymethylated cellulose fibers followed by ultrasonication and centrifugation. This material had a cylindrical cross-section as shown by transmission electron microscopy with a diameter of 5-15 nm and a length of up to 1 mu m. Calculations, using the Poisson-Boltzmann equation, showed that the surface potential was between 200 and 250 mV, depending on the pH, the salt concentration, and the size of the fibrils. They also showed that the carboxyl groups on the surface of the nanofibrils are not fully dissociated until the pH has reached pH = similar to 10 in deionized water. Calculations of the interaction between the fibrils using the Derjaguin-Landau-Verwey-Overbeek theory and assuming a cylindrical geometry indicated that there is a large electrostatic repulsion between these fibrils, provided the carboxyl groups are dissociated. If the pH is too low and/or the salt concentration is too high, there will be a large attraction between the fibrils, leading to a rapid aggregation of the fibrils. It is also possible to form polyelectrolyte multilayers (PEMs) by combining different types of polyelectrolytes and microfibrillated cellulose (MFC). In this study, silicon oxide surfaces were first treated with cationic polyelectrolytes before the surfaces were exposed to MFC. The build-up of the layers was monitored with ellipsometry, and they show that it is possible to form very well-defined layers by combinations of MFC and different types of polyelectrolytes and different ionic strengths of the solutions during the adsorption of the polyelectrolyte. A polyelectrolyte with a three-dimensional structure leads to the build-up of thick layers of MFC, whereas the use of a highly charged linear polyelectrolyte leads to the formation of thinner layers of MFC. An increase in the salt concentration during the adsorption of the polyelectrolyte results in the formation of thicker layers of MFC, indicating that the structure of the adsorbed polyelectrolyte has a large influence on the formation of the MFC layer. The films of polyelectrolytes and MFC were so smooth and well-defined that they showed clearly different interference colors, depending on the film thickness. A comparison between the thickness of the films, as measured with ellipsometry, and the thickness estimated from their colors showed good agreement, assuming that the films consisted mainly of solid cellulose with a refractive index of 1.53. Carboxymethylated MFC is thus a new type of nanomaterial that can be combined with oppositely charged polyelectrolytes to form well-defined layers that may be used to form, for example, new types of sensor materials.
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| 2. |
- Pettersson, Håkan, et al.
(författare)
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Infrared Photodetectors in Heterostructure Nanowires
- 2006
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Ingår i: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 6:2, s. 229-232
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Tidskriftsartikel (refereegranskat)abstract
- We report on spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures. The wires, typically 3 μm long with an average diameter of 85 nm, consist of InAs with a 1 μm central part of InAsP. Two different sets of wires were prepared with phosphorus contents of 15 ±3% and 35 ±3%, respectively, as determined by energy-dispersive spectroscopy measurements made in transmission electron microscopy. Ohmic contacts are fabricated to the InAs ends of the wire using e-beam lithography. The conduction band offset between the InAs and InAsP regions virtually removes the dark current through the wires at low temperature. In the optical experiments, interband excitation in the phosphorus-rich part of the wires results in a photocurrent with threshold energies of about 0.65 and 0.82 eV, respectively, in qualitative agreement with the expected band gap of the two compositions. Furthermore, a strong polarization dependence is observed with an order of magnitude larger photocurrent for light polarized parallel to the wire than for light polarized perpendicular to the wire. We believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.
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| 3. |
- Raeissi, Bahman, 1979, et al.
(författare)
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High-k-oxide/silicon interfaces characterized by capacitance frequency spectroscopy
- 2008
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Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 52:9, s. 1274-1279
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Tidskriftsartikel (refereegranskat)abstract
- Electron capture into insulator/silicon interface states is investigated for high-k dielectrics of Gd2O3 preparedby molecular beam epitaxy (MBE) and atomic layer deposition (ALD), and for HfO2 prepared byreactive sputtering, by measuring the frequency dependence of Metal Oxide Semiconductor (MOS) capacitance.The capture cross sections are found to be thermally activated and to increase steeply with theenergy depth of the interface electron states. The methodology adopted is considered useful for increasingthe understanding of high-k-oxide/silicon interfaces.
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| 4. |
- Agelis, Sacki, et al.
(författare)
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Reconfigurable optical interconnection system supporting concurrent application-specific parallel computing
- 2005
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Ingår i: 17th Symposium on Computer Architecture and High Performance Computing. - Washington, DC, USA : IEEE Computer Society. - 076952446X ; , s. 44-51
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Konferensbidrag (refereegranskat)abstract
- Application specific architectures are highly desirable in embedded parallel computing systems at the same time as designers strive for using one embedded parallel computing platform for several applications. If this can be achieved, the cost can be decreased in comparison to using several different embedded parallel computing systems. This paper presents a novel approach of running several high-performance applications concurrently on one single parallel computing system. By using a reconfigurable backplane interconnection system, the applications can be run efficiently with high network flexibility since the interconnect network can be adapted to fit the application that is being processed for the moment. More precisely, this paper investigates how the space time adaptive processing (STAP) radar algorithm and the stripmap synthetic aperture radar (SAR) algorithm can be mapped on a multi-cluster processing system with a reconfigurable optical interconnection system realized by a micro-optical-electrical mechanical system (MOEMS) crossbars. The paper describes the reconfigurable platform, the two algorithms and how they individually can be mapped on the targeted multiprocessor system. It is also described how these two applications can be mapped simultaneously on the optical reconfigurable platform. Implications and requirements on communication bandwidth and processor performance in different critical points of the two applications are presented. The results of the analysis show that an implementation is feasible with today's MOEMS technology, and that the two applications can be successfully run in a time-sharing scheme, both at the processing side and at the access for interconnection bandwidth.
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| 5. |
- Hoang, Hoai, 1976-, et al.
(författare)
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Real-time communication for industrial embedded systems using switched Ethernet
- 2006
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Ingår i: ARTES - A network for Real-Time research and graduate Education in Sweden 1997-2006. - Uppsala : Uppsala universitet. - 9150618598 ; , s. 417-427
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Bokkapitel (refereegranskat)abstract
- This paper focuses on developing and analyzing support for real-time traffic over a switched Ethernet network without any hardware or protocol modifi- cations. Network architecture with full-duplex switched Ethernet and endnodes has been assumed. The switch and the end nodes control the real-time traffic with Earliest Deadline First (EDF) scheduling on the frame level. No modification to the Ethernet standard is needed in the network that supports both real-time and non-real -time TCP/IP communication. The switch is responsible for admission control where feasibility analysis is made for each link between source and destination. All added traffic handling to support real-time communication is positioned in a thin layer (RT layer) added between the Ethernet layer and the TCP/IP suite. This assures adaptation to the surrounding protocol standards. The RT layer manages traffic on the basis of virtual connections, denoted as RT channels, as well as packet level scheduling. RT channels are created between end-nodes prior to any occurrence of real-time traffic. The comparison of two deadline-partitioning schemes, to partition the delay budget over the links for a path, is also presented. While SDPS (Symmetric Deadline Partitioning Scheme) is straightforward to implement, ADPS (Asymmetric Deadline Partitioning Scheme) is devised in order to have a more flexiblefeasibilitytest. ADPSshows promises in removing bottlenecks from links, especially when a master-slave communication is considered as the traffic pattern, and ADPS proves to be a better choice than SDPS.
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| 6. |
- Björk, Per, et al.
(författare)
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Single molecular imaging and spectroscopy of conjugated polyelectrolytes decorated on stretched aligned DNA
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 5:10, s. 1948-1953
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Tidskriftsartikel (refereegranskat)abstract
- DNA is the prototype template for building nanoelectronic devices by self-assembly. The electronic functions are made possible by coordinating electronic polymer chains to DNA. This paper demonstrates two methods for fabrication of aligned and ordered DNA nanowires complexed with conjugated polyelectrolytes (CPEs). The complex can be formed either in solution prior to stretching or after stretching of the bare DNA on a surface. Molecular combing was used to stretch the complexes on surface energy patterned surfaces, and PMMA for the bare DNA. Single molecular spectroscopy, in fluorescence, and microscopy, in atomic force microscopy, give evidence for coordination of the short CPE chains to the aligned DNA.
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| 7. |
- Temun, Attila, et al.
(författare)
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Assessment of digital cameras for micro-structural sensing of low contrast surface features
- 2005
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Ingår i: Proceedings of the First International Conference on Multi-Material Micro Manufacture 2005, Karlsruhe, DE. - Amsterdam : Elsevier. - 0080448798 ; , s. 253-257
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Konferensbidrag (refereegranskat)abstract
- Evaluation of three digital cameras are presented focusing on their capabilities and applicability in the detection of low-contrast surface features on the micrometer level. The key to a successful identification of surface flaws on microstructured surfaces, such as silicon wafers is the ability to determine minor deviations in the reflectance of an object surface. Micro-topography of a surface, surface structure and surface roughness has a strong influence on the amount and direction of scattered light. Different portions of the surrounding illumination are reflected on different parts of an uneven surface, hence the resulting contrast-variation on the illuminated surface has a strong correlation to the surface structure itself. In our work we discuss the possibilities of using either of the investigated cameras for the automated visual inspection of micro-structured surfaces. The cameras - two of them equipped with CCD and one with CMOS image sensors - are studied in an environment which is similar to standard surface appearance measurements, involving human observers. The specimens, featuring different surface structures are imaged in a well-controlled environment under varying illumination conditions. Experimental results of spatial resolution and contrast sensitivity are presented.
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| 8. |
- Temun, Attila, et al.
(författare)
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Localizing micro-defects on rough metal surfaces
- 2006
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Ingår i: Proceeding of the 2nd International Conference on Multi-Material Micro Manufacture 2006, Grenoble, FR. - Amsterdam : Elsevier. - 9780080452630 ; , s. 169-172
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Konferensbidrag (refereegranskat)abstract
- In this paper we present a study of reflectance measurements to a direct metrological problem. Our aim is to estimate progressive surface wear by detecting minute defect development in surface microtopography on Ra 0.7 μm rough stainless steel surfaces subject to mechanical wear from hard particle deposits on a metal bar. The investigation was carried out by using a standard CMOS digital camera with a macro objective. It demonstrates how surface scattering measurements can provide a viable alternative in circumstances where traditional roughness measurement techniques fail to deliver the expected results and, due to certain restraints, laboratory-type surface measurements are not applicable either. Our work is based upon measuring variations in the amount and direction of scattered light, reflected from the inspected surfaces, featuring microirregularities. We will show that it is possible to identify the extent of surface flaws by statistically evaluating the recorded brightness information. The developments in this paper can provide basis for a future quality control system devoted to on-line surface measurements of micro components.
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| 9. |
- Bryllert, Tomas, et al.
(författare)
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Vertical wrap-gated nanowire transistors
- 2006
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Ingår i: Nanotechnology. - 0957-4484. ; 17:11, s. 227-230
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Tidskriftsartikel (refereegranskat)abstract
- We present a process for fabricating a field-effect transistor based on vertically standing InAs nanowires and demonstrate initial device characteristics. The wires are grown by chemical beam epitaxy at lithographically defined locations. Wrap gates are formed around the base of the wires through a number of deposition and etch steps. The fabrication is based on standard III - V processing and includes no random elements or single nanowire manipulation.
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| 10. |
- Dahlin, Andreas, et al.
(författare)
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Synchronized Quartz Crystal Microbalance and Nanoplasmonic Sensing of Biomolecular Recognition Reactions
- 2008
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 2:10, s. 2174-2182
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Tidskriftsartikel (refereegranskat)abstract
- We present a method providing synchronized measurements using the two techniques: quartz crystal microbalance with dissipation (QCM-D) monitoring and localized surface plasmon resonance (LSPR). This was achieved by letting a thin gold film perforated with short-ranged ordered plasmon-active nanoholes act as one of the electrodes of a QCM-D crystal. This enabled transmission-mode optical spectroscopy to be used to temporally resolve colorimetric changes of the LSPR active substrate induced upon bionnolecular binding events. The LSPR response could thus be compared with simultaneously obtained changes in resonance frequency, Delta f, and energy dissipation, AD, of the QCM-D device. Since the LSPR technique is preferentially sensitive to changes within the voids of the nanoholes, while the QCM-D technique is preferentially sensitive to reactions on the planar region between the holes, a surface chemistry providing the same binding kinetics on both gold and silica was used. This was achieved by coating the substrate with poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), which was shown to bind in the same manner on silica and gold modified with a carboxyl-terminated thiol. In this way, the combined setup provided new information about structural changes upon PLL-g-PEG adsorption. We also demonstrate subsequent binding of NeutrAvidin and an immunoreaction utilizing biotin-modified IgG. The combined information from the synchronized measurements was also used in a new way to estimate the sensing volume of the LSPR sensor.
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