| 1. |
- Blaudeck, Thomas, et al.
(författare)
-
Biocomputation Using Molecular Agents Moving in Microfluidic Channel Networks : An Alternative Platform for Information Technology
- 2022
-
Ingår i: Cyber-Physical Systems : Intelligent Models and Algorithms - Intelligent Models and Algorithms. - Cham : Springer International Publishing. - 2198-4190 .- 2198-4182. - 9783030951153 - 9783030951160 ; 417, s. 15-27
-
Bokkapitel (refereegranskat)abstract
- Deficiencies in software or computer chips cause computers or smartphones to crash and allow hackers to steal passwords. Automated test procedures could avoid these problems. However, the computing power and cooling requirements of conventional computers increase exponentially with the size of the problem, so that the technological limits for solving these problems will soon be reached. The EU project Bio4Comp aims to develop concepts for a bio-computer to help overcome these two main problems. Compared to conventional computers, computers based on biological molecular motors only consume a fraction of the energy per arithmetic operation and scale very well for problems that can be parallelized (“multitasking”). In this article, the topic network-based biocomputation (NBC) i.e. computing with biological molecules as agents that are driven by molecular motors in microfluidic networks, is presented as an alternative approach to computing, data processing, and information technology.
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| 2. |
- Boyle, Aimee L., et al.
(författare)
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Squaring the Circle in Peptide Assembly: From Fibers to Discrete Nanostructures by de Novo Design
- 2012
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 134:37, s. 15457-15467
-
Tidskriftsartikel (refereegranskat)abstract
- The design of bioinspired nanostructures and materials of defined size and shape is challenging as it pushes our understanding of biomolecular assembly to its limits. In such endeavors, DNA is the current building block of choice because of its predictable and programmable self-assembly. The use of peptide- and protein-based systems, however, has potential advantages due to their more-varied chemistries, structures and functions, and the prospects for recombinant production through gene synthesis and expression. Here, we present the design and characterization of two complementary peptides programmed to form a parallel heterodimeric coiled coil, which we use as the building blocks for larger, supramolecular assemblies. To achieve the latter, the two peptides are joined via peptidic linkers of variable lengths to produce a range of assemblies, from flexible fibers of indefinite length, through large colloidal-scale assemblies, down to closed and discrete nanoscale objects of defined stoichiometry. We posit that the different modes of assembly reflect the interplay between steric constraints imposed by short linkers and the bulk of the helices, and entropic factors that favor the formation of many smaller objects as the linker length is increased. This approach, and the resulting linear and proteinogenic polypeptides, represents a new route for constructing complex peptide-based assemblies and biomaterials.
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| 3. |
- Bromley, Elizabeth H. C., et al.
(författare)
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The Tumbleweed: towards a synthetic protein motor
- 2009
-
Ingår i: HFSP Journal. - : Informa UK Limited. - 1955-2068. ; 3:3, s. 204-212
-
Tidskriftsartikel (refereegranskat)abstract
- Biomolecular motors have inspired the design and construction of artificial nanoscale motors and machines based on nucleic acids, small molecules, and inorganic nanostructures. However, the high degree of sophistication and efficiency of biomolecular motors, as well as their specific biological function, derives from the complexity afforded by protein building blocks. Here, we discuss a novel bottom-up approach to understanding biological motors by considering the construction of synthetic protein motors. Specifically, we present a design for a synthetic protein motor that moves along a linear track, dubbed the "Tumbleweed." This concept uses three discrete ligand-dependent DNA-binding domains to perform cyclically ligand-gated, rectified diffusion along a synthesized DNA molecule. Here we describe how de novo peptide design and molecular biology could be used to produce the Tumbleweed, and we explore the fundamental motor operation of such a design using numerical simulations. The construction of this and more sophisticated protein motors is an exciting challenge that is likely to enhance our understanding of the structure-function relationship in biological motors. [DOI: 10.2976/1.3111282]
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| 4. |
- Burke, Adam, et al.
(författare)
-
InAs Nanowire Transistors with Multiple, Independent Wrap-Gate Segments.
- 2015
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:5, s. 2836-2843
-
Tidskriftsartikel (refereegranskat)abstract
- We report a method for making horizontal wrap-gate nanowire transistors with up to four independently controllable wrap-gated segments. While the step up to two independent wrap-gates requires a major change in fabrication methodology, a key advantage to this new approach, and the horizontal orientation more generally, is that achieving more than two wrap-gate segments then requires no extra fabrication steps. This is in contrast to the vertical orientation, where a significant subset of the fabrication steps needs to be repeated for each additional gate. We show that cross-talk between adjacent wrap-gate segments is negligible despite separations less than 200 nm. We also demonstrate the ability to make multiple wrap-gate transistors on a single nanowire using the exact same process. The excellent scalability potential of horizontal wrap-gate nanowire transistors makes them highly favorable for the development of advanced nanowire devices and possible integration with vertical wrap-gate nanowire transistors in 3D nanowire network architectures.
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| 5. |
- Carrad, Damon J., et al.
(författare)
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Electron-Beam Patterning of Polymer Electrolyte Films To Make Multiple Nanoscale Gates for Nanowire Transistors
- 2014
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:1, s. 94-100
-
Tidskriftsartikel (refereegranskat)abstract
- We report an electron-beam based method for the nanoscale patterning of the poly(ethylene oxide)/LiClO4 polymer electrolyte. We use the patterned polymer electrolyte as a high capacitance gate dielectric in single nanowire transistors and obtain subthreshold swings comparable to conventional metal/oxide wrap-gated nanowire transistors. Patterning eliminates gate/contact overlap, which reduces parasitic effects and enables multiple, independently controllable gates. The method's simplicity broadens the scope for using polymer electrolyte gating in studies of nanowires and other nanoscale devices.
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| 6. |
- Chen, I. Ju, et al.
(författare)
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Conduction Band Offset and Polarization Effects in InAs Nanowire Polytype Junctions
- 2017
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 17:2, s. 902-908
-
Tidskriftsartikel (refereegranskat)abstract
- Although zinc-blende (ZB) and wurtzite (WZ) structures differ only in the atomic stacking sequence, mixing of crystal phases can strongly affect the electronic properties, a problem particularly common to bottom up-grown nanostructures. A lack of understanding of the nature of electronic transport at crystal phase junctions thus severely limits our ability to develop functional nanowire devices. In this work we investigated electron transport in InAs nanowires with designed mixing of crystal structures, ZB/WZ/ZB, by temperature-dependent electrical measurements. The WZ inclusion gives rise to an energy barrier in the conduction band. Interpreting the experimental result in terms of thermionic emission and using a drift-diffusion model, we extracted values for the WZ/ZB band offset, 135 ± 10 meV, and interface sheet polarization charge density on the order of 10-3 C/m2. The extracted polarization charge density is 1-2 orders of magnitude smaller than previous experimental results, but in good agreement with first principle calculation of spontaneous polarization in WZ InAs. When the WZ length is reduced below 20 nm, an effective barrier lowering is observed, indicating the increasing importance of tunneling transport. Finally, we found that band-bending at ZB/WZ junctions can lead to bound electron states within an enclosed WZ segment of sufficient length, evidenced by our observation of Coulomb blockade at low temperature. These findings provide critical input for modeling and designing the electronic properties of novel functional devices, such as nanowire transistors, where crystal polytypes are commonly found.
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| 7. |
- Chen, I. Ju, et al.
(författare)
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Hot-Carrier Extraction in Nanowire-Nanoantenna Photovoltaic Devices
- 2020
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 20:6, s. 4064-4072
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowires bring new possibilities to the field of hot-carrier photovoltaics by providing flexibility in combining materials for band engineering and using nanophotonic effects to control light absorption. Previously, an open-circuit voltage beyond the Shockley-Queisser limit was demonstrated in hot-carrier devices based on InAs-InP-InAs nanowire heterostructures. However, in these first experiments, the location of light absorption, and therefore the precise mechanism of hot-carrier extraction, was uncontrolled. In this Letter, we combine plasmonic nanoantennas with InAs-InP-InAs nanowire devices to enhance light absorption within a subwavelength region near an InP energy barrier that serves as an energy filter. From photon-energy- and irradiance-dependent photocurrent and photovoltage measurements, we find that photocurrent generation is dominated by internal photoemission of nonthermalized hot electrons when the photoexcited electron energy is above the barrier and by photothermionic emission when the energy is below the barrier. We estimate that an internal quantum efficiency up to 0.5-1.2% is achieved. Insights from this study provide guidelines to improve internal quantum efficiencies based on nanowire heterostructures.
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| 8. |
- Chen, I. Ju, et al.
(författare)
-
Thermoelectric Power Factor Limit of a 1D Nanowire
- 2018
-
Ingår i: Physical Review Letters. - 0031-9007. ; 120:17
-
Tidskriftsartikel (refereegranskat)abstract
- In the past decade, there has been significant interest in the potentially advantageous thermoelectric properties of one-dimensional (1D) nanowires, but it has been challenging to find high thermoelectric power factors based on 1D effects in practice. Here we point out that there is an upper limit to the thermoelectric power factor of nonballistic 1D nanowires, as a consequence of the recently established quantum bound of thermoelectric power output. We experimentally test this limit in quasiballistic InAs nanowires by extracting the maximum power factor of the first 1D subband through I-V characterization, finding that the measured maximum power factors conform to the theoretical limit. The established limit allows the prediction of the achievable power factor of a specific nanowire material system with 1D electronic transport based on the nanowire dimension and mean free path. The power factor of state-of-the-art semiconductor nanowires with small cross section and high crystal quality can be expected to be highly competitive (on the order of mW/m K2) at low temperatures. However, they have no clear advantage over bulk materials at, or above, room temperature.
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| 9. |
- Chen, Yang, et al.
(författare)
-
Semiconductor nanowire array for transparent photovoltaic applications
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:19
-
Tidskriftsartikel (refereegranskat)abstract
- The surface area of a building that could potentially be used for Building Integrated Photovoltaics would increase dramatically with the availability of transparent solar cells that could replace windows. The challenge is to capture energy from outside the visible region (UV or IR) while simultaneously allowing a high-quality observation of the outside world and transmitting sufficient light in the visible region to satisfactorily illuminate the interior of the building. In this paper, we show both computationally and experimentally that InP nanowire arrays can have good transparency in the visible region and high absorption in the near-infrared region. We show experimentally that we can achieve mean transparencies in the visible region of 65% and the radiative limit of more than 10% based on measured absorption and calculated emission. Our results demonstrate that nanowire arrays hold promise as a method to achieve transparent solar cells, which would fulfill the requirements to function as windows. In addition, we show that by optical design and by designing the geometry of nanowire arrays, solar cells can be achieved that absorb/transmit at wavelengths that are not decided by the bandgap of the material and that can be tailored to specific requirements such as colorful windows.
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| 10. |
- Craig, Erin M., et al.
(författare)
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Mechanochemical model for myosin V
- 2009
-
Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 106:43, s. 18261-18266
-
Tidskriftsartikel (refereegranskat)abstract
- A rigorous numerical test of a hypothetical mechanism of a molecular motor should model explicitly the diffusive motion of the motor's degrees of freedom as well as the transition rates between the motor's chemical states. We present such a Brownian dynamics, mechanochemcial model of the coarse-grain structure of the dimeric, linear motor myosin V. Compared with run-length data, our model provides strong support for a proposed strain-controlled gating mechanism that enhances processivity. We demonstrate that the diffusion rate of a detached motor head during motor stepping is self-consistent with known kinetic rate constants and can explain the motor's key performance features, such as speed and stall force. We present illustrative and realistic animations of motor stepping in the presence of thermal noise. The quantitative success and illustrative power of this type of model suggest that it will be useful in testing our understanding of a range of biological and synthetic motors.
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| 11. |
- Dabkowska, Aleksandra, et al.
(författare)
-
Fluid and Highly Curved Model Membranes on Vertical Nanowire Arrays
- 2014
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:8, s. 4286-4292
-
Tidskriftsartikel (refereegranskat)abstract
- Sensing and manipulating living cells using vertical nanowire devices requires a complete understanding of cell behavior on these substrates. Changes in cell function and phenotype are often triggered by events taking place at the plasma membrane, the properties of which are influenced by local curvature. The nanowire topography can therefore be expected to greatly affect the cell membrane, emphasizing the importance of studying membranes on vertical nanowire arrays. Here, we used supported phospholipid bilayers as a model for biomembranes. We demonstrate the formation of fluid supported bilayers on vertical nanowire forests using self-assembly from vesicles in solution. The bilayers were found to follow the contours of the nanowires to form continuous and locally highly curved model membranes. Distinct from standard flat supported lipid bilayers, the high aspect ratio of the nanowires results in a large bilayer surface available for the immobilization and study of biomolecules. We used these bilayers to bind a membrane-anchored protein as well as tethered vesicles on the nanowire substrate. The nanowire-bilayer platform shown here can be expanded from fundamental studies of lipid membranes on controlled curvature substrates to the development of innovative membrane-based nanosensors.
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| 12. |
- Dabkowska, Aleksandra, et al.
(författare)
-
Surface nanostructures for fluorescence probing of supported lipid bilayers on reflective substrates.
- 2015
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:43, s. 18020-18024
-
Tidskriftsartikel (refereegranskat)abstract
- The fluorescence interference contrast (FLIC) effect prevents the use of fluorescence techniques to probe the continuity and fluidity of supported lipid bilayers on reflective materials due to a lack of detectable fluorescence. Here we show that adding nanostructures onto reflective surfaces to locally confer a certain distance between the deposited fluorophores and the reflecting surface enables fluorescence detection on the nanostuctures. The nanostructures consist of either deposited nanoparticles or epitaxial nanowires directly grown on the substrate and are designed such that they can support a lipid bilayer. This simple method increases the fluorescence signal sufficiently to enable bilayer fluorescence detection and to observe the recovery of fluorescence after photobleaching in order to assess lipid bilayer formation on any reflective surface.
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| 13. |
- Ekvall, Mikael, et al.
(författare)
-
Three-dimensional tracking of small aquatic organisms using fluorescent nanoparticles.
- 2013
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:11
-
Tidskriftsartikel (refereegranskat)abstract
- Tracking techniques are vital for the understanding of the biology and ecology of organisms. While such techniques have provided important information on the movement and migration of large animals, such as mammals and birds, scientific advances in understanding the individual behaviour and interactions of small (mm-scale) organisms have been hampered by constraints, such as the sizes of existing tracking devices, in existing tracking methods. By combining biology, chemistry and physics we here present a method that allows three-dimensional (3D) tracking of individual mm-sized aquatic organisms. The method is based on in-vivo labelling of the organisms with fluorescent nanoparticles, so-called quantum dots, and tracking of the organisms in 3D via the quantum-dot fluorescence using a synchronized multiple camera system. It allows for the efficient and simultaneous study of the behaviour of one as well as multiple individuals in large volumes of observation, thus enabling the study of behavioural interactions at the community scale. The method is non-perturbing - we demonstrate that the labelling is not affecting the behavioural response of the organisms - and is applicable over a wide range of taxa, including cladocerans as well as insects, suggesting that our methodological concept opens up for new research fields on individual behaviour of small animals. Hence, this offers opportunities to focus on important biological, ecological and behavioural questions never before possible to address.
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| 14. |
- Fahlvik Svensson, Sofia, et al.
(författare)
-
Control and understanding of kink formation in InAs-InP heterostructure nanowires.
- 2013
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 24:34
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowire heterostructures are of special interest for band structure engineering due to an expanded range of defect-free material combinations. However, the higher degree of freedom in nanowire heterostructure growth comes at the expense of challenges related to nanowire-seed particle interactions, such as undesired composition, grading and kink formation. To better understand the mechanisms of kink formation in nanowires, we here present a detailed study of the dependence of heterostructure nanowire morphology on indium pressure, nanowire diameter, and nanowire density. We investigate InAs-InP-InAs heterostructure nanowires grown with chemical beam epitaxy, which is a material system that allows for very abrupt heterointerfaces. Our observations indicate that the critical parameter for kink formation is the availability of indium, and that the resulting morphology is also highly dependent on the length of the InP segment. It is shown that kinking is associated with the formation of an inclined facet at the interface between InP and InAs, which destabilizes the growth and leads to a change in growth direction. By careful tuning of the growth parameters, it is possible to entirely suppress the formation of this inclined facet and thereby kinking at the heterointerface. Our results also indicate the possibility of producing controllably kinked nanowires with a high yield.
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| 15. |
- Fahlvik Svensson, Sofia, et al.
(författare)
-
Lineshape of the thermopower of quantum dots
- 2012
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 14
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum dots are an important model system for thermoelectric phenomena, and may be used to enhance the thermal-to-electric energy conversion efficiency in functional materials, by tuning the Fermi energy relative to the dots' transmission resonances. It is therefore important to obtain a detailed understanding of a quantum dot's thermopower as a function of the Fermi energy. However, so far it has proven difficult to take the effects of interactions into account in the interpretation of experimental data. In this paper, we present detailed measurements of the thermopower of quantum dots defined in heterostructure nanowires. We show that the thermopower lineshape is described well by a Landauer-type transport model that uses as its input experimental values of the dot conductance, which contains information about interaction effects.
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| 16. |
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| 17. |
- Fahlvik Svensson, Sofia, et al.
(författare)
-
Nonlinear thermovoltage and thermocurrent in quantum dots
- 2013
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum dots are model systems for quantum thermoelectric behavior because of their ability to control and measure the effects of electron-energy filtering and quantum confinement on thermoelectric properties. Interestingly, nonlinear thermoelectric properties of such small systems can modify the efficiency of thermoelectric power conversion. Using quantum dots embedded in semiconductor nanowires, we measure thermovoltage and thermocurrent that are strongly nonlinear in the applied thermal bias. We show that most of the observed nonlinear effects can be understood in terms of a renormalization of the quantum-dot energy levels as a function of applied thermal bias and provide a theoretical model of the nonlinear thermovoltage taking renormalization into account. Furthermore, we propose a theory that explains a possible source of the observed, pronounced renormalization effect by the melting of Kondo correlations in the mixed-valence regime. The ability to control nonlinear thermoelectric behavior expands the range in which quantum thermoelectric effects may be used for efficient energy conversion.
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| 18. |
- Fahlvik Svensson, Sofia, et al.
(författare)
-
Using Polymer Electrolyte Gates to Set-and-Freeze Threshold Voltage and Local Potential in Nanowire-based Devices and Thermoelectrics
- 2015
-
Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 25:2, s. 255-262
-
Tidskriftsartikel (refereegranskat)abstract
- The strongly temperature-dependent ionic mobility in polymer electrolytes is used to freeze in specific ionic charge environments around a nanowire using a local wrap-gate geometry. This makes it possible to set both the threshold voltage for a conventional doped substrate gate and the local disorder potential at temperatures below 220 K. These are characterized in detail by combining conductance and thermovoltage measurements with modeling. The results demonstrate that local polymer electrolyte gates are compatible with nanowire thermoelectrics, where they offer the advantage of a very low thermal conductivity, and hold great potential towards setting the optimal operating point for solid-state cooling applications.
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| 19. |
- Fairbanks, M. S., et al.
(författare)
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Measuring hybridization in GaInAs/InP electron billiard arrays
- 2010
-
Ingår i: Physica E: Low-dimensional Systems and Nanostructures. - : Elsevier BV. - 1386-9477. ; 42:4, s. 1205-1207
-
Konferensbidrag (refereegranskat)abstract
- We study low temperature magnetoconductance fluctuations in arrays of electron billiards in an effort to quantitatively measure hybridization between array elements. In contrast to previous research in the 'open' regime, which is mostly limited to the canonical AlxGa1-xAs/GaAs heterostructure, our devices are etched into the Ga0.25In0.75As/InP heterostructure. To chart hybridization (i.e. the extent of the coherent electron wavefunction) in the arrays, we use a Fourier analysis to examine the frequency content of the universal conductance fluctuations in one and two element arrays. This analysis reveals strong evidence of wavefunction hybridization over all measured coupling strengths between the array elements. (c) 2009 Elsevier B.V. All rights reserved.
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| 20. |
- Fast, Jonatan, et al.
(författare)
-
Hot-carrier optoelectronic devices based on semiconductor nanowires
- 2021
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 8:2
-
Tidskriftsartikel (refereegranskat)abstract
- In optoelectronic devices such as solar cells and photodetectors, a portion of electron-hole pairs is generated as so-called hot carriers with anexcess kinetic energy that is typically lost as heat. The long-standing aim to harvest this excess energy to enhance device performance hasproven to be very challenging, largely due to the extremely short-lived nature of hot carriers. Efforts thus focus on increasing the hot carrierrelaxation time and on tailoring heterostructures that allow for hot-carrier extraction on short time and length scales. Recently, semiconductornanowires have emerged as a promising system to achieve these aims, because they offer unique opportunities for heterostructure engineeringas well as for potentially modified phononic properties that can lead to increased relaxation times. In this review we assess thecurrent state of theory and experiments relating to hot-carrier dynamics in nanowires, with a focus on hot-carrier photovoltaics. To providea foundation, we begin with a brief overview of the fundamental processes involved in hot-carrier relaxation and how these can be tailoredand characterized in nanowires. We then analyze the advantages offered by nanowires as a system for hot-carrier devices and review the statusof proof-of-principle experiments related to hot-carrier photovoltaics. To help interpret existing experiments on photocurrent extractionin nanowires we provide modeling based on non-equilibrium Green’s functions. Finally, we identify open research questions that need to beanswered in order to fully evaluate the potential nanowires offer toward achieving more efficient, hot-carrier based, optoelectronic devices.
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| 21. |
- Fast, Jonatan, et al.
(författare)
-
Hot-carrier separation in heterostructure nanowires observed by electron-beam induced current
- 2020
-
Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 31:39
-
Tidskriftsartikel (refereegranskat)abstract
- The separation of hot carriers in semiconductors is of interest for applications such asthermovoltaic photodetection and third-generation photovoltaics. Semiconductor nanowiresoffer several potential advantages for effective hot-carrier separation such as: a high degree ofcontrol and flexibility in heterostructure-based band engineering, increased hot-carriertemperatures compared to bulk, and a geometry well suited for local control of light absorption.Indeed, InAs nanowires with a short InP energy barrier have been observed to produce electricpower under global illumination, with an open-circuit voltage exceeding the Shockley-Queisserlimit. To understand this behaviour in more detail, it is necessary to establish control over theprecise location of electron-hole pair-generation in the nanowire. In this work we performelectron-beam induced current measurements with high spatial resolution, and demonstrate therole of the InP barrier in extracting energetic electrons.We interprete the results in terms ofhot-carrier separation, and extract estimates of the hot carriers’ mean free path.
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| 22. |
- Fast, Jonatan, et al.
(författare)
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Optical-Beam-Induced Current in InAs/InP Nanowires for Hot-Carrier Photovoltaics
- 2022
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:6, s. 7728-7734
-
Tidskriftsartikel (refereegranskat)abstract
- Using the excess energy of charge carriers excited above the band edge (hot carriers) could pave the way for optoelectronic devices, such as photovoltaics exceeding the Shockley-Queisser limit or ultrafast photodetectors. Semiconducting nanowires show promise as a platform for hot-carrier extraction. Proof of principle photovoltaic devices have already been realized based on InAs nanowires, using epitaxially defined InP segments as energy filters that selectively transmit hot electrons. However, it is not yet fully understood how charge-carrier separation, relaxation, and recombination depend on device design and on the location of optical excitation. Here, we introduce the use of an optical-beam-induced current (OBIC) characterization method, employing a laser beam focused close to the diffraction limit and a high precision piezo stage, to study the optoelectric performance of the nanowire device as a function of the position of excitation. The photocurrent response agrees well with modeling based on hot-electron extraction across the InP segment via diffusion. We demonstrate that the device is capable of producing power and estimate the spatial region within which significant hot-electron extraction can take place to be on the order of 300 nm away from the barrier. When comparing to other experiments on similar nanowires, we find good qualitative agreement, confirming the interpretation of the device function, while the extracted diffusion length of hot electrons varies. Careful control of the excitation and device parameters will be important to reach the potentially high device performance theoretically available in these systems.
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| 23. |
- Gluschke, Jan-Göran, et al.
(författare)
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Characterization of Ambipolar GaSb/InAs Core-Shell Nanowires by Thermovoltage Measurements.
- 2015
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 9:7, s. 7033-7040
-
Tidskriftsartikel (refereegranskat)abstract
- In semiconductor heterostructures with a type II band alignment, such as GaSb-InAs, conduction can be tuned from electron- to hole-dominated using an electrostatic gate. However, traditional conductance measurements give no direct information on the carrier type, and thus limit the ability to distinguish transport effects originating from the two materials. Here, we employ thermovoltage measurements to GaSb/InAs core-shell nanowires, and reliably identify the dominant carrier type at room temperature as well as in the quantum transport regime at 4.2 K, even in cases where the conductance measurement does not allow for such a distinction. In addition, we show that theoretical modeling using the conductance data as input can reproduce the measured thermovoltage under the assumption that electron and hole states shift differently in energy with the applied gate voltage.
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| 24. |
- Gluschke, Jan-Göran, et al.
(författare)
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Fully tunable, non-invasive thermal biasing of gated nanostructures suitable for low-temperature studies.
- 2014
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 25:38
-
Tidskriftsartikel (refereegranskat)abstract
- There is much recent interest in the thermoelectric (TE) characterization of single nanostructures at low temperatures, because such measurements yield information that is complementary to traditional conductance measurements, and because they may lead to novel paradigms for TE energy conversion. However, previously reported techniques for thermal biasing of nanostructures are difficult to use at low temperatures because of unintended global device heating, the lack of ability to continuously tune the thermal bias, or limited compatibility with gating techniques. By placing a heater directly on top of the electrical contact to a single InAs nanowire, we demonstrate fully tunable thermal biases of up to several tens of Kelvin, combined with negligible overall heating of the device, and with full functionality of a back gate, in the temperature range between 4 K and 300 K.
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| 25. |
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