| 1. |
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| 2. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 3. |
- Du, Chun-Xia, et al.
(författare)
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Efficient 1.54 µm light emission from Si/SiGe/Si : Er
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 81:1-3, s. 105-108
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Tidskriftsartikel (refereegranskat)abstract
- Si/SiGe/Si:Er:O-heterojunction bipolar transistor (HBT)-type light emitting devices with Er3+ ions incorporated in the collector region have been fabricated using layered structures prepared by differential molecular beam epitaxy (MBE). Intense light emission at 1.54 µm has been observed at room temperature by hot electron impact excitation at rather low injection current and applied voltage. Separate controls of the injection current and bias voltage make it possible to perform detailed electroluminescence (EL) studies that can not be done with conventional Si:Er light emitting diodes (LEDs). Saturation of the EL intensity occurs at very low current densities indicating a 100-fold increase of the effective excitation cross-section for Si/SiGe/Si:Er:O-HBTs compared with Si:Er-LEDs. © 2001 Elsevier Science B.V.
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| 4. |
- Du, Chun-Xia, et al.
(författare)
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Electroluminescence studies of Er and SiO co-doped Si layers prepared by molecular beam epitaxy
- 2000
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Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 14:3, s. 259-265
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Tidskriftsartikel (refereegranskat)abstract
- Er/O co-doped Si light emitting diodes (LEDs) have been fabricated using layer structures prepared by molecular beam epitaxy (MBE). The Er/O doping was realized by sublimation of elemental Er and silicon monoxide simultaneously with Si during MBE growth. Intense Er-related electroluminescence (EL) at 1.54 mu m was observed at room temperature from p(+)-SiGe/i-SiGe-Si/Si:Er/n(+)-Si LEDs by electron impact excitation under reverse bias. It has been found that the EL intensity was increased with increasing growth temperature of the Si:Er/O layer in the range of 430-575 degrees C. The electrical pumping power dependence of EL intensity has been studied. An excitation cross section value of similar to 1 x 10(-16) cm(2) was estimated based on the experimental data and model fitting. The EL decay behavior under various injection and bias conditions has been studied by time-resolved EL measurements. The overall luminescence decay time is found to strongly depend on the injection parameters. Two types of de-excitation mechanisms due to Auger energy transfer to free carriers introduced by either dopant ionization or carrier injection have been discussed. Both Auger processes play an important role in reduction of the EL intensity when there is a high density of carriers with excited Er ions. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 5. |
- Du, Chun-Xia, et al.
(författare)
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Si/SiGe/Si : Er
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:12, s. 1697-1699
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Tidskriftsartikel (refereegranskat)abstract
- Si/SiGe/Si:Er:O heterojunction bipolar transistor (HBT) type light-emitting devices with Er3+ ions incorporated in the collector region have been fabricated using a layered structure grown by differential molecular-beam epitaxy. Electroluminescence measurements on processed light-emitting HBTs can be performed in either constant driving current mode or constant applied bias mode, which is an important advantage over conventional Si:Er light-emitting diodes. Intense room-temperature light emission at the Er3+ characteristic wavelength of 1.54 µm has been observed at low driving current density, e.g., 0.1 A cm-2, and low applied bias, e.g., 3 V, across the collector and emitter. © 2001 American Institute of Physics.
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| 6. |
- Du, Chun-Xia, et al.
(författare)
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Si/SiGe/Si : Er : O light-emitting transistors prepared by differential molecular-beam epitaxy
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:12, s. 1697-1699
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Tidskriftsartikel (refereegranskat)abstract
- Si/SiGe/Si:Er:O heterojunction bipolar transistor (HBT) type light-emitting devices with Er3+ ions incorporated in the collector region have been fabricated using a layered structure grown by differential molecular-beam epitaxy. Electroluminescence measurements on processed light-emitting HBTs can be performed in either constant driving current mode or constant applied bias mode, which is an important advantage over conventional Si:Er light-emitting diodes. Intense room-temperature light emission at the Er3+ characteristic wavelength of 1.54 mum has been observed at low driving current density, e.g., 0.1 A cm(-2), and low applied bias, e.g., 3 V, across the collector and emitter. (C) 2001 American Institute of Physics.
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| 7. |
- Du, Chun-Xia, 1966-
(författare)
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Studies of Light Emitting Devices Based on Er-doped Si and SiGe Layered Structures
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Doping with rare earth element erbium (Er) in Si has recently attracted a lot of research interest due to potential applications in Si-based opto-electronics. By using molecular beam epitaxy (MBE), precipitate-free Er-doping in Si has been made together with other co-dopants, e.g., oxygen (0) and fluorine (F), up to a level ∼1020 cm-3. Together with other capabilities of high quality growth of layered structures with desired doping profiles and heterojunctions offered by MBE, several types of dedicated Er-doped Si and Si/SiGe light emitting devices have been designed, processed, and characterized, aiming at finding a possible solution for efficient Sibased light emitters.During the thesis work, mainly three types of Er-doped Si light emitting devices: Schottky-type light emitting diode (LED), p-i-n LED, and heterojunction bipolar transistor (HBT), have been studied for light emission from either the surface or an edge. Three kinds of Er-containing sources, namely Er2O3 , ErF3 , and elementa lEr together with SiO were used for doping. In order to get comparative results from electroluminescence (EL) and photoluminescence (PL) measurements using the same sample, Schottky-type LEDs using Er/O structures were fabricated and characterized, where Er3+ ions can be excited using an impact process of hot electrons generated in the depletion region at reverse bias. A number of grown Si:Er:O and Si:Er:F p-i-n structures were processed into LEDs, and EL from these devices was studied both at forward bias and reverse bias conditions. The light emission from forward biased p-i-n diodes was concluded to be due to the carrier-recombination-mediated energy transfer process, however, luminescence could not persist to room temperature (RT) due to the strong quenching process induced by the energy back transfer process and other nonradiative processes. For reverse biased p-i-n diodes, especially for the structure designed favoring the electron tunneling, intense EL was observed via direct carrier impact excitation process, which persisted up to RT or even higher. In order to have independent control over the injection current and the applied bias, and de-couple their influence on the EL intensity, Si/SiGe/Si:Er:O-HBTs with Er3+ ions incorporated in the collector have been fabricated with layered structures prepared by differential MBE growth. Careful EL studies have been carried out by operating an HBT in a linear regime prior to the avalanche breakdown. The effective Er impact cross-section has shown a 100-fold increase compared with conventional Si:Er-LEDs. The temperature dependent EL measurements on different types of devices have indicated that an Er-induced defect level located at 150 meV below the conduction band is mainly responsible for thermal quenching of the luminescence intensity, which is the same value as obtained in PL measurements. Time-resolved EL measurements have exhibited that Auger-carrier de-excitation plays an important role in reducing EL intensity. Moreover, it has revealed that not only ionized equilibrium carriers but also injected excess carriers act as Auger de-excitation centers. Finally, the results of the thesis work suggest that if the HBT structure can be combined with a high optical activation of Er3+ ions, an efficient Si-based light emitter is possible.
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| 8. |
- Duteil, F., et al.
(författare)
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Er/O doped Si1-xGex alloy layers grown by MBE
- 2001
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Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 17:1-2, s. 131-134
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Silicon-based light emitting diodes (LEDs) containing an Er/O-doped Si1-xGex active layer have been studied. The structures were grown by molecular beam epitaxy (MBE), with Er and O concentrations of 5 × 1019 and 1 × 1020 cm-3, respectively, using Er and silicon monoxide sources. The microstructure has been studied by X-ray diffraction (XRD) and cross-sectional transmission electron microscopy, and it is found that Er/O-doped Si0.92Ge0.08 layers of high crystalline quality, can be obtained. Electroluminescence (EL) measurements have been performed on reverse-biased Er/O doped diodes both from the surface and from the edge and the emission at 1.54 µm associated with the Er3+ ions has been studied at 300 K and lower temperatures. To evaluate the possibility to use a Si1-xGex layer for waveguiding in Si-based optoelectronics, studies of the refractive index n of strained Si1-xGex as a function of the Ge concentration have been done by spectroscopic ellipsometry in the range 0.3-1.7 µm. At 1.54 µm the refractive index increases monotonically with the Ge concentration up to n = 3.542 for a Ge concentration of 21.3%. © 2001 Elsevier Science B.V.
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| 9. |
- Duteil, F., et al.
(författare)
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Luminescence and microstructure of Er/O co-doped Si structures grown by MBE using Er and SiO evaporation
- 2000
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Ingår i: Materials Science in Semiconductor Processing. - 1369-8001 .- 1873-4081. ; 3:5-6, s. 523-528
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Tidskriftsartikel (refereegranskat)abstract
- Er and O co-doped Si structures have been prepared using molecular-beam epitaxy (MBE) with fluxes of Er and O obtained from Er and silicon monoxide (SiO) evaporation in high-temperature cells. The incorporation of Er and O has been studied for concentrations of up to 2×1020 and 1×1021 cm-3, respectively. Surface segregation of Er can take place, but with O co-doping the segregation is suppressed and Er-doped layers without any indication of surface segregation can be prepared. Si1-xGex and Si1-yCy layers doped with Er/O during growth at different substrate temperatures show more defects than corresponding Si layers. Strong emission at 1.54µm associated with the intra-4f transition of Er3+ ions is observed in electroluminescence (EL) at room temperature in reverse-biased p-i-n-junctions. To optimize the EL intensity we have varied the Er/O ratio and the temperature during growth of the Er/O-doped layer. Using an Er-concentration of around 1×1020 cm-3 we find that Er/O ratios of 1:2 or 1:4 give higher intensity than 1:1 while the stability with respect to breakdown is reduced for the highest used O concentrations. For increasing growth temperatures in the range 400-575 °C there is an increase in the EL intensity. A positive effect of post-annealing on the photoluminescence intensity has also been observed.
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| 10. |
- Ederth, Thomas, et al.
(författare)
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Anomalous settlement behavior of Ulva linza zoospores on cationic oligopeptide surfaces
- 2008
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Ingår i: Biofouling (Print). - : Informa UK Limited. - 0892-7014 .- 1029-2454. ; 24:4, s. 303-312
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Tidskriftsartikel (refereegranskat)abstract
- Identification of settlement cues for marine fouling organisms opens up new strategies and methods for biofouling prevention, and enables the development of more effective antifouling materials. To this end, the settlement behaviour of zoospores of the green alga Ulva linza onto cationic oligopeptide self-assembled monolayers (SAMs) has been investigated. The spores interact strongly with lysine- and arginine-rich SAMs, and their settlement appears to be stimulated by these surfaces. Of particular interest is an arginine-rich oligopeptide, which is effective in attracting spores to the surface, but in a way which leaves a large fraction of the settled spores attached to the surface in an anomalous fashion. These 'pseudo-settled' spores are relatively easily detached from the surface and do not undergo the full range of cellular responses associated with normal commitment to settlement. This is a hitherto undocumented mode of settlement, and surface dilution of the arginine-rich peptide with a neutral triglycine peptide demonstrates that both normal and anomalous settlement is proportional to the surface density of the arginine-rich peptide. The settlement experiments are complemented with physical studies of the oligopeptide SAMs, before and after extended immersion in artificial seawater, using infrared spectroscopy, null ellipsometry and contact angle measurements.
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| 11. |
- Ederth, Thomas, et al.
(författare)
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Interactions of Zoospores of Ulva linza with Arginine-Rich Oligopeptide Monolayers
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:16, s. 9375-9383
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Tidskriftsartikel (refereegranskat)abstract
- We recently reported oil the strong interactions of zoospores of the green alga, Ulva linza with all arginine-rich oligopeptide self-assembled monolayer (SAM) [Biofouling 2008, 24, 303-312], where the arginine-rich peptide induced not only high spore settlement, but also a form of abnormal settlement, or "pseudo-settlement", whereby it proportion of spores do not go through the normal process of surface exploration, adhesive exocytosis, and loss of flagella. Further. it was demonstrated that both the total number of settled spores and the fraction of pseudosettled spores were related to the surface density of the arginine-rich peptide. Here we present a further investigation of the interactions of zoospores of ulva with a set of oligomeric, de nom designed, arginine-rich peptides, specifically aimed to test the effect of peptide primary structure on the interaction. Via variations in the peptide length and by permutations in the amino acid sequences, we gain further insight into the spore-surface interactions. The interpretation of the biological assays is supported by physicochemical characterization of the SAMs using infrared spectroscopy, ellipsometry, and contact angle measurement. Results confirm the importance of arginine residues for the anomalous pseudosettlement, and we found that settlement is modulated by variations in both the total length and peptide primary structure. To elucidate the Causes of the anomalous settlement and the possible relation to peptide-membrane interactions, we also compared the settlement of the "naked" zoospores of Ulva(which present it lipoprotein membrane to the exterior without a discrete polysaccharide cell wall), with the settlement of diatoms (unicellular algae that are surrounded by it silica cell wall), onto the peptide SAMs. Cationic SAMs do not notably affect settlement (attachment), adhesion strength, or viability of diatom cells, Suggesting that the effect of the peptides on zoospores of Ulva is mediated via specific peptide-membrane interactions.
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| 12. |
- Ederth, Thomas, et al.
(författare)
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Resistance of Galactoside-Terminated Alkanethiol Self-Assembled Monolayers to Marine Fouling Organisms
- 2011
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society. - 1944-8244 .- 1944-8252. ; 3:10, s. 3890-3901
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembled monolayers (SAMs) of galactoside-terminated alkanethiols have protein-resistance properties which can be tuned via the degree of methylation [Langmuir 2005, 21, 2971-2980]. Specifically, a partially methylated compound was more resistant to nonspecific protein adsorption than the hydroxylated or fully methylated counterparts. We investigate whether this also holds true for resistance to the attachment and adhesion of a range of marine species, in order to clarify to what extent resistance to protein adsorption correlates with the more complex adhesion of fouling organisms. The partially methylated galactoside-terminated SAM was further compared to a mixed monolayer of omega-substituted methyl- and hydroxyl-terminated alkanethiols with wetting properties and surface ratio of hydroxyl to methyl groups matching that of the galactoside. The settlement (initial attachment) and adhesion strength of four model marine fouling organisms were investigated, representing both micro- and macrofoulers; two bacteria (Cobetia marina and Marinobacter hydrocarbonoclasticus), barnacle cypris larvae (Balanus amphitrite), and algal zoospores (Ulva linza). The minimum in protein adsorption onto the partially methylated galactoside surface was partly reproduced in the marine fouling assays, providing some support for a relationship between protein resistance and adhesion of marine fouling organisms. The mixed alkanethiol SAM, which was matched in wettability to the partially methylated galactoside SAM, consistently showed higher settlement (initial attachment) of test organisms than the galactoside, implying that both wettability and surface chemistry are insufficient to explain differences in fouling resistance. We suggest that differences in the structure of interfacial water may explain the variation in adhesion to these SAMs.
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| 13. |
- Hansson, Göran, et al.
(författare)
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Origin of abnormal temperature dependence of electroluminescence from Er/O-doped Si diodes
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:15, s. 2104-2106
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependencies of the current-voltage characteristics and the electroluminescence (EL) intensity of molecular beam epitaxy grown Er/O-doped Si light emitting diodes at reverse bias have been studied. To minimize the scattering of electrons injected from the p-doped Si1-xGex electron emitters, an intrinsic Si layer was used in the depletion region. For many diodes, there is a temperature range where the EL intensity increases with temperature. Data are reported for a structure that shows increasing intensity up to 100°C. This is attributed to an increasing fraction of the pumping current being due to phonon-assisted tunneling, which gives a higher saturation intensity, compared to ionization-dominated breakdown at lower temperatures. © 2001 American Institute of Physics.
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| 14. |
- Karim, Amir, et al.
(författare)
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Influence of exposure to 980 nm laser radiation on the luminescence of Si : Er/O light-emitting diodes
- 2008
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 104:12, s. 123110-
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Tidskriftsartikel (refereegranskat)abstract
- Erbium (Er) codoping with oxygen (O) in Si is a well-known method for producing electroluminescent material radiating at 1.54 mu m through a 4f shell transition of Er3+ ions. In this work the influence of exposure to 980 nm radiation on the electroluminescence (EL) of reverse biased Si:Er/O light-emitting diodes (LEDs), which give a strong room temperature 1.54 mu m intensity, is presented and discussed. All the device layers, including Er/O doped Si sandwiched between two Si0.82Ge0.18 layers, have been grown on silicon on insulator substrates using molecular beam epitaxy and processed to fabricate edge emitting Si:Er/O waveguide LEDs. Electromagnetic mode confinement simulations have been performed to optimize the layer parameters for waveguiding. The temperature dependence of the 1.54 mu m EL intensity exhibits an abnormal temperature quenching with a peak near -30 degrees C, and at -160 degrees C it has decreased by a factor of 5. However, irradiating the devices with a 980 nm laser gives an enhancement of the 1.54 mu m EL intensity, which is more dramatic at low temperatures (e.g., -200 degrees C) where the quenched EL signal is increased up to almost the same level as at room temperature. The enhancement of the EL intensity is attributed to the photocurrent generated by the 980 nm laser, reducing the detrimental avalanche current.
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| 15. |
- Larsson (Kaiser), Andréas, et al.
(författare)
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UV-patterned poly(ethylene glycol) matrix for microarray applications
- 2007
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:11, s. 3511-3518
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Tidskriftsartikel (refereegranskat)abstract
- A versatile method to fabricate polymeric matrixes for microarray applications is demonstrated. Several different design strategies are presented where a variety of organic films, such as plastic polymers and self-assembled monolayers (SAMs) on planar silica and gold substrates, act as supports for the graft polymerization procedure. An ensemble of poly(ethylene glycol) methacrylate monomers are combined to obtain a matrix with desired properties: low nonspecific binding and easily accessible groups for postimmobilization of ligands. The free radical graft polymerization process occurs under irradiation with UV light in the 254−266 nm range, which offers the possibility to introduce patterns by means of a photomask. The arrays are created on inert and homogeneous coatings prepared either by graft polymerization of a methoxy-terminated PEG−methacrylate or self-assembly of a methoxy-terminated oligo(ethylene glycol) thiol. Carboxylic acid groups, introduced in the array spots either during graft polymerization or upon wet chemical conversion of hydroxyls, grant the capability to immobilize proteins and other molecules via free amine groups. Immobilization of fluorescent species as well as biotin followed by exposure to a fluorescently labeled antibody directed toward biotin display both excellent integrity of the spots and low nonspecific binding to the surrounding framework. Beside patterns of uniform height and size, an array of spots with varying thickness (a sort of gradient) is demonstrated. Such gradient samples enable us to address critical issues regarding the mechanism(s) behind spatially resolved free radical polymerization of methacrylates. It also offers a convenient route to optimize the matrix properties with respect to thickness, loading capacity, protein diffusion/penetration, and nonspecific binding.
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| 16. |
- Ni, Wei-Xin, et al.
(författare)
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1.54 µm light emitting devices based on Er/O-doped Si layered structures grown by molecular beam epitaxy
- 2001
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Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 17:1-2, s. 65-69
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Two types of Si:Er light emitting devices have been processed and characterized with an aim to efficiently use hot electrons for impact excitation. One is a p+-SiGe/i-Si/n-Si:Er:O/n+-Si tunneling diode with a design favoring electron tunneling from the SiGe valence band to the Si conduction band and subsequent acceleration. Another type of Si:Er light emitters is based on a heterojunction bipolar transistor (HBT) structure containing an Er-doped active layer in the collector. In these devices, one can introduce hot electrons from the HBT emitter in a controlled way with a collector bias voltage prior to the avalanche breakdown to improve the impact excitation efficiency. Intense electroluminescence was observed at 300 K at low current (0.1 A cm-2) and low bias (3 V). An impact cross-section value of 1 × 10-14 cm2 has been estimated, which is a 100-fold increase compared with the values reported from any other type of Er-doped LEDs. © 2001 Elsevier Science B.V.
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| 17. |
- Ni, Wei-Xin, et al.
(författare)
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Light emitting SiGe/i-Si/Si : Er
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 369:1, s. 414-418
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Tidskriftsartikel (refereegranskat)abstract
- p+-SiGe/i-Si/n-Si:Er:O/n+-Si tunneling diodes have been processed using layer structures prepared by molecular beam epitaxy (MBE). Electroluminescence has been observed at room temperature from these devices at reverse bias. The devices have been used for characterizing the optical activation of Er3+ ions in MBE Si:Er:O layers grown at different conditions. In the range of 400-575 °C, a high substrate temperature is favored for formation of Er emission centers, but this is limited by the silicidation process occurring above 600 °C. Several important device parameters such as the impact excitation cross section and various EL decay processes have been carefully studied. A fast decay (approximately 4 µs) due to the Auger carrier transfer process is observed.
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