| 1. |
- Shaali, Mehrnaz, 1981, et al.
(author)
-
Site-selective immobilization of functionalized DNA origami on nanopatterned Teflon AF
- 2017
-
In: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 5:30, s. 7637-7643
-
Journal article (peer-reviewed)abstract
- We demonstrate the use of arrays of Teflon AF nanopillars for directing the assembly of single rectangular DNA origami scaffolds, functionalized with covalently linked fluorophore molecules, in defined positions on patterned surfaces. This is achieved by introducing Teflon AF as a non-amplified negative e-beam resist, which is exposed and chemically developed to generate arrays of hydrophobic nanopillars with a minimum feature size 40 nm. Binding of the DNA origami to the pillars is facilitated by porphyrin moieties that act as hydrophobic molecular anchors, reaching 80% coverage of the available sites. This combination of top-down lithography and bottom-up self assembly is an efficient means of fabricating hierarchically structured bio-nanointerfaces in which the positioning of functional units is precisely controlled on the molecular scale inside the DNA assembly, and on the nanoscale at pre-designed locations on the substrate.
|
|
| 2. |
|
|
| 3. |
- Alexander-Webber, J. A., et al.
(author)
-
Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene
- 2016
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6
-
Journal article (peer-reviewed)abstract
- Epitaxial graphene has proven itself to be the best candidate for quantum electrical resistance standards due to its wide quantum Hall plateaus with exceptionally high breakdown currents. However one key underlying mechanism, a magnetic field dependent charge transfer process, is yet to be fully understood. Here we report measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to an almost linear increase in carrier density with magnetic field. This behaviour is strong evidence for field dependent charge transfer from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels we model the densities of donor states and predict the field dependence of charge transfer in excellent agreement with experimental results, thus providing a guide towards engineering epitaxial graphene for applications such as quantum metrology.
|
|
| 4. |
- Andzane, J., et al.
(author)
-
Effect of graphene substrate type on formation of Bi 2 Se 3 nanoplates
- 2019
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
-
Journal article (peer-reviewed)abstract
- Knowledge of nucleation and further growth of Bi 2 Se 3 nanoplates on different substrates is crucial for obtaining ultrathin nanostructures and films of this material by physical vapour deposition technique. In this work, Bi 2 Se 3 nanoplates were deposited under the same experimental conditions on different types of graphene substrates (as-transferred and post-annealed chemical vapour deposition grown monolayer graphene, monolayer graphene grown on silicon carbide substrate). Dimensions of the nanoplates deposited on graphene substrates were compared with the dimensions of the nanoplates deposited on mechanically exfoliated mica and highly ordered pyrolytic graphite flakes used as reference substrates. The influence of different graphene substrates on nucleation and further lateral and vertical growth of the Bi 2 Se 3 nanoplates is analysed. Possibility to obtain ultrathin Bi 2 Se 3 thin films on these substrates is evaluated. Between the substrates considered in this work, graphene grown on silicon carbide is found to be the most promising substrate for obtaining of 1–5 nm thick Bi 2 Se 3 films.
|
|
| 5. |
|
|
| 6. |
- Eklöf, Johnas, 1988, et al.
(author)
-
Controlling deposition of nanoparticles by tuning surface charge of SiO2 by surface modifications
- 2016
-
In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:106, s. 104246-104253
-
Journal article (peer-reviewed)abstract
- The self-assembly of nanoparticles on substrates is relevant for a variety of applications such as plasmonics, sensing devices and nanometer-sized electronics. We investigate the deposition of 60 nm spherical Au nanoparticles onto silicon dioxide (SiO2) substrates by changing the chemical treatment of the substrate and by that altering the surface charge. The deposition is characterized by scanning electron microscopy (SEM). Kelvin probe force microscopy (KPFM) was used to characterize the surface workfunction. The underlying physics involved in the deposition of nanoparticles was described by a model based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory combined with random sequential adsorption (RSA). The spatial statistical method Ripley's K-function was used to verify the DLVO–RSA model (ERSA). The statistical results also showed that the adhered particles exhibit a short-range order at distances below ~300 nm. This method can be used in future research to predict the deposition densities of charged nanoparticles onto charged surfaces.
|
|
| 7. |
- Eklöf, Johnas, 1988, et al.
(author)
-
Guided selective deposition of nanoparticles by tuning of the surface potential
- 2017
-
In: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 119:1
-
Journal article (peer-reviewed)abstract
- Guided deposition of nanoparticles onto different substrates is of great importance for a variety of applications such as biosensing, targeted cancer therapy, anti-bacterial coatings and single molecular electronics. It is therefore important to gain an understanding of what parameters are involved in the deposition of nanoparticles. In this work we have deposited 60 nm, negatively charged, citrate stabilized gold nanoparticles onto microstructures consisting of six different materials, (vanadium (V), silicon dioxide (SiO2), gold (Au), aluminum (Al), copper (Cu) and nickel (Ni)). The samples have then been investigated by scanning electron microscopy to extract the particle density. The surface potential was calculated from the measured surface charge density maps measured by atomic force microscopy while the samples were submerged in a KCl water solution. These values were compared with literature values of the isoelectric points (IEP) of different oxides formed on the metals in an ambient environment. According to measurements, Al had the highest surface potential followed by Ni and Cu. The same trend was observed for the nanoparticle densities. No particles were found on V, SiO2 and Au. The literature values of the IEP showed a different trend compared to the surface potential measurements concluding that IEP is not a reliable parameter for the prediction of NP deposition.
|
|
| 8. |
- Geskin, V., et al.
(author)
-
Bianthrone at a Metal Surface: Conductance Switching with a Bistable Molecule Made Feasible by Image Charge Effects
- 2015
-
In: AIP Conference Proceedings. - : AIP Publishing LLC. - 1551-7616 .- 0094-243X. ; 1642, s. 469-472
-
Conference paper (peer-reviewed)abstract
- Bianthrone is a sterically hindered compound that exists in the form of two non-planar isomers. Our experimental study of single-molecule junctions with bianthrone reveals persistent switching of electric conductance at low temperatures, which can be reasonably associated to molecular isomerization events. Temperature dependence of the switching rate allows for an estimate of the activation energy of the process, on the order of 35-90 meV. Quantum-chemical calculations of the potential surface of neutral bianthrone and its anion, including identification of transition states, yields the isolated molecule isomerization barriers too high vs. the previous estimate, though in perfect agreement with previous experimental studies in solution. Nevertheless, we show that the attraction of the anion in the vicinity of the metal surface by its image charge can significantly alter the energetic landscape, in particular, by reducing the barrier to the values compatible with the observed switching behavior.
|
|
| 9. |
- He, Hans, 1989, et al.
(author)
-
Fabrication of graphene quantum hall resistance standard in a cryogen-Table-Top system
- 2016
-
In: 2016 Conference on Precision Electromagnetic Measurements, CPEM 2016; The Westin OttawaOttawa; Canada; 10-15 July 2016. - : Institute of Electrical and Electronics Engineers Inc.. - 9781467391344 ; , s. Art no 7540516-
-
Conference paper (peer-reviewed)abstract
- We have demonstrated quantum Hall resistance measurements with metrological accuracy in a relatively easy to use and compact cryogen-free system operating at a temperature of around 3.8 K and magnetic field below 5 T. This advance in technology is due to the unique properties of epitaxial graphene on silicon carbide (SiC) which lifts the stringent requirements for quantum hall effect seen in conventional semiconductors. This paper presents the processes involved in fabrication and characterization of metrologically viable epitaxial graphene samples.
|
|
| 10. |
- He, Hans, et al.
(author)
-
Polymer-encapsulated molecular doped epigraphene for quantum resistance metrology
- 2019
-
In: Metrologia. - : Institute of Physics Publishing. - 0026-1394 .- 1681-7575. ; 56:4
-
Journal article (peer-reviewed)abstract
- One of the aspirations of quantum metrology is to deliver primary standards directly to end-users thereby significantly shortening the traceability chains and enabling more accurate products. Epitaxial graphene grown on silicon carbide (epigraphene) is known to be a viable candidate for a primary realisation of a quantum Hall resistance standard, surpassing conventional semiconductor two-dimensional electron gases, such as those based on GaAs, in terms of performance at higher temperatures and lower magnetic fields. The bottleneck in the realisation of a turn-key quantum resistance standard requiring minimum user intervention has so far been the need to fine-tune the carrier density in this material to fit the constraints imposed by a simple cryo-magnetic system. Previously demonstrated methods, such as via photo-chemistry or corona discharge, require application prior to every cool-down as well as specialist knowledge and equipment. To this end we perform metrological evaluation of epigraphene with carrier density tuned by a recently reported permanent molecular doping technique. Measurements at two National Metrology Institutes confirm accurate resistance quantisation below 5n-1. Furthermore, samples show no significant drift in carrier concentration and performance on multiple thermal cycles over three years. This development paves the way for dissemination of primary resistance standards based on epigraphene
|
|
| 11. |
- He, Hans, et al.
(author)
-
Stable and Tunable Charge Carrier Control of Graphene for Quantum Resistance Metrology
- 2018
-
In: 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018). - : IEEE. - 9781538609736 - 9781538609743
-
Conference paper (peer-reviewed)abstract
- Here we demonstrate a stable and tunable method to alter the carrier concentration of epitaxial graphene grown on silicon carbide. This technique relies on chemical doping by an acceptor molecule. Through careful tuning one can produce chemically doped graphene quantum resistance devices which show long-term stability in ambient conditions and have performance comparable to that of GaAs quantum resistance standards. This development paves the way for controlled device fabrication of graphene quantum hall resistance standards, which can be reliably tailored to operate below 5 T and above 4 K out-of-the-box, without further adjustments from the end-user.
|
|
| 12. |
- He, Hans, 1989, et al.
(author)
-
Uniform doping of graphene close to the Dirac point by polymer-assisted assembly of molecular dopants
- 2018
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 9:1
-
Journal article (peer-reviewed)abstract
- Tuning the charge carrier density of two-dimensional (2D) materials by incorporating dopants into the crystal lattice is a challenging task. An attractive alternative is the surface transfer doping by adsorption of molecules on 2D crystals, which can lead to ordered molecular arrays. However, such systems, demonstrated in ultra-high vacuum conditions (UHV), are often unstable in ambient conditions. Here we show that air-stable doping of epitaxial graphene on SiC—achieved by spin-coating deposition of 2,3,5,6-tetrafluoro-tetracyano-quino-dimethane (F4TCNQ) incorporated in poly(methyl-methacrylate)—proceeds via the spontaneous accumulation of dopants at the graphene-polymer interface and by the formation of a charge-transfer complex that yields low-disorder, charge-neutral, large-area graphene with carrier mobilities ~70 000 cm2V−1s−1at cryogenic temperatures. The assembly of dopants on 2D materials assisted by a polymer matrix, demonstrated by spin-coating wafer-scale substrates in ambient conditions, opens up a scalable technological route toward expanding the functionality of 2D materials.
|
|
| 13. |
- Huang, J., et al.
(author)
-
Hot carrier relaxation of Dirac fermions in bilayer epitaxial graphene
- 2015
-
In: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 27:16
-
Journal article (peer-reviewed)abstract
- Energy relaxation of hot Dirac fermions in bilayer epitaxial graphene is experimentally investigated by magnetotransport measurements on Shubnikov-de Haas oscillations and weak localization. The hot-electron energy loss rate is found to follow the predicted Bloch-Gruneisen power-law behaviour of T-4 at carrier temperatures from 1.4K up to similar to 100 K, due to electron-acoustic phonon interactions with a deformation potential coupling constant of 22 eV. A carrier density dependence n(e)(-1.5) in the scaling of the T-4 power law is observed in bilayer graphene, in contrast to the n(e)(-0.5) dependence in monolayer graphene, leading to a crossover in the energy loss rate as a function of carrier density between these two systems. The electron-phonon relaxation time in bilayer graphene is also shown to be strongly carrier density dependent, while it remains constant for a wide range of carrier densities in monolayer graphene. Our results and comparisons between the bilayer and monolayer exhibit a more comprehensive picture of hot carrier dynamics in graphene systems.
|
|
| 14. |
- Huang, J., et al.
(author)
-
Physics of a disordered Dirac point in epitaxial graphene from temperature-dependent magnetotransport measurements
- 2015
-
In: Physical Review B - Condensed Matter and Materials Physics. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 1098-0121 .- 1550-235X. ; 92:7
-
Journal article (peer-reviewed)abstract
- We report a study of disorder effects on epitaxial graphene in the vicinity of the Dirac point by magnetotransport. Hall effect measurements show that the carrier density increases quadratically with temperature, in good agreement with theoretical predictions which take into account intrinsic thermal excitation combined with electron-hole puddles induced by charged impurities. We deduce disorder strengths in the range 10.2-31.2 meV, depending on the sample treatment. We investigate the scattering mechanisms and estimate the impurity density to be 3.0-9.1x10(10) cm(-2) for our samples. A scattering asymmetry for electrons and holes is observed and is consistent with theoretical calculations for graphene on SiC substrates. We also show that the minimum conductivity increases with increasing disorder strength, in good agreement with quantum-mechanical numerical calculations.
|
|
| 15. |
- Janssen, Tjbm, et al.
(author)
-
Operation of graphene quantum Hall resistance standard in a cryogen-free table-top system
- 2015
-
In: 2D Materials. - : IOP Publishing. - 2053-1583. ; 2:3, s. 035015-
-
Journal article (peer-reviewed)abstract
- Wedemonstrate quantum Hall resistance measurements with metrological accuracy in a small cryogen-free system operating at a temperature of around 3.8Kand magnetic fields below 5 T. Operating this system requires little experimental knowledge or laboratory infrastructure, thereby greatly advancing the proliferation of primary quantum standards for precision electrical metrology. This significant advance in technology has come about as a result of the unique properties of epitaxial graphene on SiC.
|
|
| 16. |
- Janssen, Tjbm, et al.
(author)
-
Towards a cryogen-free table-top primary resistance standard
- 2016
-
In: 2016 Conference on Precision Electromagnetic Measurements (Cpem 2016). - : Institute of Electrical and Electronics Engineers Inc.. - 9781467391344
-
Conference paper (peer-reviewed)abstract
- We demonstrate quantum Hall resistance measurements with metrological accuracy in a small cryogen-free system operating at a temperature of around 3.8 K and magnetic fields below 5 T. We use this system to investigate the optimisation of graphene/SiC devices for maximum breakdown current. In addition we report the first characterisation of a cryogen-free cryogenic current comparator which enables entirely cryogen-free primary resistance metrology.
|
|
| 17. |
- Jõemetsa, Silver, 1990, et al.
(author)
-
Molecular Lipid Films on Microengineering Materials
- 2019
-
In: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 35:32, s. 10286-10298
-
Journal article (peer-reviewed)abstract
- In this study, we have systematically investigated the formation of molecular phospholipid films on a variety of solid substrates fabricated from typical surface engineering materials and the fluidic properties of the lipid membranes formed on these substrates. The surface materials comprise of borosilicate glass, mica, SiO2, Al (native oxide), Al2O3, TiO2, ITO, SiC, Au, Teflon AF, SU-8, and graphene. We deposited the lipid films from small unilamellar vesicles (SUVs) by means of an open-space microfluidic device, observed the formation and development of the films by laser scanning confocal microscopy, and evaluated the mode and degree of coverage, fluidity, and integrity. In addition to previously established mechanisms of lipid membrane–surface interaction upon bulk addition of SUVs on solid supports, we observed nontrivial lipid adhesion phenomena, including reverse rolling of spreading bilayers, spontaneous nucleation and growth of multilamellar vesicles, and the formation of intact circular patches of double lipid bilayer membranes. Our findings allow for accurate prediction of membrane–surface interactions in microfabricated devices and experimental environments where model membranes are used as functional biomimetic coatings.
|
|
| 18. |
- Kim, Kyung Ho, 1984, et al.
(author)
-
Apparent Power Law Scaling of Variable Range Hopping Conduction in Carbonized Polymer Nanofibers
- 2016
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6
-
Journal article (peer-reviewed)abstract
- We induce dramatic changes in the structure of conducting polymer nanofibers by carbonization at 800 degrees C and compare charge transport properties between carbonized and pristine nanofibers. Despite the profound structural differences, both types of systems display power law dependence of current with voltage and temperature, and all measurements can be scaled into a single universal curve. We analyze our experimental data in the framework of variable range hopping and argue that this mechanism can explain transport properties of pristine polymer nanofibers as well.
|
|
| 19. |
- Kim, Kyung Ho, 1984, et al.
(author)
-
Probing variable range hopping lengths by magneto conductance in carbonized polymer nanofibers
- 2018
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
-
Journal article (peer-reviewed)abstract
- Using magneto transport, we probe hopping length scales in the variable range hopping conduction of carbonized polyacetylene and polyaniline nanofibers. In contrast to pristine polyacetylene nanofibers that show vanishing magneto conductance at large electric fields, carbonized polymer nanofibers display a negative magneto conductance that decreases in magnitude but remains finite with respect to the electric field. We show that this behavior of magneto conductance is an indicator of the electric field and temperature dependence of hopping length in the gradual transition from the thermally activated to the activation-less electric field driven variable range hopping transport. This reveals magneto transport as a useful tool to probe hopping lengths in the non-linear hopping regime.
|
|
| 20. |
- Kim, Kyung Ho, 1984, et al.
(author)
-
Thermal stability of epitaxial graphene electrodes for conductive polymer nanofiber devices
- 2017
-
In: Crystals. - : MDPI AG. - 2073-4352. ; 7:12
-
Journal article (peer-reviewed)abstract
- We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to that of Au-nanofiber devices. We further checked the thermal stability of the graphene contacts to polyaniline devices by annealing up to T = 800 °C, the temperature at which polyaniline nanofibers are carbonized but the graphene electrode remains intact. The thermal stability and Ohmic contact of polymer nanofibers are demonstrated here, which together with the chemical stability and atomic flatness of graphene, make epitaxial graphene on SiC an attractive contact material for future all-carbon electronic devices.
|
|
| 21. |
- Lara Avila, Samuel, 1983, et al.
(author)
-
Influence of Impurity Spin Dynamics on Quantum Transport in Epitaxial Graphene
- 2015
-
In: Physical Review Letters. - : AMER PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 115:10, s. 106602-
-
Journal article (peer-reviewed)abstract
- Experimental evidence from both spin-valve and quantum transport measurements points towards unexpectedly fast spin relaxation in graphene. We report magnetotransport studies of epitaxial graphene on SiC in a vector magnetic field showing that spin relaxation, detected using weak-localization analysis, is suppressed by an in-plane magnetic field B-parallel to, and thereby proving that it is caused at least in part by spinful scatterers. A nonmonotonic dependence of the effective decoherence rate on B-parallel to reveals the intricate role of the scatterers' spin dynamics in forming the interference correction to the conductivity, an effect that has gone unnoticed in earlier weak localization studies.
|
|
| 22. |
- Lara Avila, Samuel, 1983, et al.
(author)
-
Towards quantum-limited coherent detection of terahertz waves in charge-neutral graphene
- 2019
-
In: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 3:11, s. 983-988
-
Journal article (other academic/artistic)abstract
- Spectacular advances in heterodyne astronomy1,2 have been largely due to breakthroughs in detector technology3. To exploit the full capacity of future terahertz (∼300 GHz–5 THz) telescope space missions4, new concepts of terahertz coherent receivers are needed, providing larger bandwidths and imaging capabilities with multipixel focal plane heterodyne arrays5. Here we show that graphene uniformly doped to the Dirac point, with material resistance dominated by quantum localization and thermal relaxation governed by electron diffusion, enables highly sensitive and wideband coherent detection of signals from 90 to 700 GHz and, prospectively, across the entire terahertz range. We measure on proof-of-concept graphene bolometric mixers an electron diffusion-limited gain bandwidth of 8 GHz (corresponding to a Doppler shift of 480 km s−1 at 5 THz) and intrinsic mixer noise temperature of 475 K (which would be equivalent to ~2 hν/kB at ν = 5 THz), limited by the residual thermal background in our setup. An optimized device will result in a mixer noise temperature as low as 36 K, with the gain bandwidth exceeding 20 GHz, and a local oscillator power of <100 pW. In conjunction with the emerging quantum-limited amplifiers at the intermediate frequency6,7, our approach promises quantum-limited sensing in the terahertz domain, potentially surpassing superconducting technologies, particularly for large heterodyne arrays
|
|
| 23. |
- Lartsev, Arseniy, 1987, et al.
(author)
-
A prototype of RK/200 quantum Hall array resistance standard on epitaxial graphene
- 2015
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 118:4, s. art nr. 044506-
-
Journal article (peer-reviewed)abstract
- Epitaxial graphene on silicon carbide is a promising material for the next generation of quantum Hall re-sistance standards. Single Hall bars made of graphene have already surpassed their state-of-the-art GaAsbased counterparts as an RK/2 (RK = h/e^2) standard, showing at least the same precision and higher break-down current density. Compared to single devices, quantum Hall arrays using parallel or series connectionof multiple Hall bars can offer resistance values spanning several orders of magnitude and (in case of parallelconnection) significantly larger measurement currents, but impose strict requirements on uniformity of thematerial. To evaluate the quality of the available material, we have fabricated arrays of 100 Hall bars con-nected in parallel on epitaxial graphene. One out of four devices has shown quantized resistance that matchedthe correct value of RK/200 within the measurement precision of 1e-4 at magnetic fields between 7 and 9Tesla. The defective behaviour of other arrays is attributed mainly to non-uniform doping. This result con-firms the acceptable quality of epitaxial graphene, pointing towards the feasibility of well above 90% yieldof working Hall bars.
|
|
| 24. |
- Makarovsky, O., et al.
(author)
-
Enhancing optoelectronic properties of SiC-grown graphene by a surface layer of colloidal quantum dots
- 2017
-
In: 2D Materials. - : IOP Publishing. - 2053-1583. ; 4:3
-
Journal article (peer-reviewed)abstract
- We report a simultaneous increase of carrier concentration, mobility and photoresponsivity when SiC-grown graphene is decorated with a surface layer of colloidal PbS quantum dots, which act as electron donors. The charge on the ionised dots is spatially correlated with defect charges on the SiC-graphene interface, thus enhancing both electron carrier density and mobility. This charge-correlation model is supported by Monte Carlo simulations of electron transport and used to explain the unexpected 3-fold increase of mobility with increasing electron density. The enhanced carrier concentration and mobility give rise to Shubnikov-de Haas oscillations in the magnetoresistance, which provide an estimate of the electron cyclotron mass in graphene at high densities and Fermi energies up to 1.2 x 10(13) cm(-2) and 400 meV, respectively.
|
|
| 25. |
- Shaali, Mehrnaz, 1981, et al.
(author)
-
Nanopatterning of Mobile Lipid Mono layers on Electron-Beam-Sculpted Teflon AF Surfaces
- 2015
-
In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 9:2, s. 1271-1279
-
Journal article (peer-reviewed)abstract
- Direct electron-beam lithography is used to fabricate nanostructured Teflon AF surfaces, which are utilized to pattern,surface-supported monolayer phospholipid films with 50 nm lateral feature size. In comparison with unexposed Teflon AF coatings, e-beam-irradiated areas show reduced surface tension and surface potential. For phospholipid monolayer spreading experiments, these areas can be designed to function as barriers that enclose unexposed areas of nanometer dimensions and confine the lipid film within. We show that the effectiveness of the barrier is defined by pattern geometry and radiation dose. This surface preparation technique represents an efficient, yet simple, nanopatterning strategy supporting studies of lipid monolayer behavior in ultraconfined spaces. The generated structures are useful for imaging studies of biomimetic membranes and other specialized surface applications requiring spatially controlled formation of self-assembled, molecularly thin films on optically transparent patterned polymer surfaces with very low autofluorescence.
|
|
| 26. |
- Yager, Tom, et al.
(author)
-
High mobility epitaxial graphene devices via aqueous-ozone processing
- 2015
-
In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 106:6, s. 063503-
-
Journal article (peer-reviewed)abstract
- We find that monolayer epitaxial graphene devices exposed to aggressive aqueous-ozone processing and annealing became cleaner from post-fabrication organic resist residuals and, significantly, maintain their high carrier mobility. Additionally, we observe a decrease in carrier density from inherent strong n-type doping to extremely low p-type doping after processing. This transition is explained to be a consequence of the cleaning effect of aqueous-ozone processing and annealing, since the observed removal of resist residuals from SiC/G enables the exposure of the bare graphene to dopants present in ambient conditions. The resulting combination of charge neutrality, high mobility, large area clean surfaces, and susceptibility to environmental species suggest this processed graphene system as an ideal candidate for gas sensing applications.
|
|
| 27. |
- Yager, Thomas, 1987, et al.
(author)
-
Low contact resistance in epitaxial graphene devices for quantum metrology
- 2015
-
In: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 5:8, s. 087134-
-
Journal article (peer-reviewed)abstract
- We investigate Ti/Au contacts to monolayer epitaxial graphene on SiC (0001) for applications in quantum resistance metrology. Using three-terminal measurements in the quantum Hall regime we observed variations in contact resistances ranging from a minimal value of 0.6 Ω up to 11 kΩ. We identify a major source of high-resistance contacts to be due bilayer graphene interruptions to the quantum Hall current, whilst discarding the effects of interface cleanliness and contact geometry for our fabricated devices. Moreover, we experimentally demonstrate methods to improve the reproducibility of low resistance contacts (
|
|
| 28. |
- Yager, Tom, et al.
(author)
-
Wafer-scale homogeneity of transport properties in epitaxial graphene on SiC
- 2015
-
In: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 87, s. 409-414
-
Journal article (peer-reviewed)abstract
- Magnetotransport measurements on Hall bar devices fabricated on purely monolayer epitaxial graphene on silicon carbide (SiC/G) show a very tight spread in carrier concentration and mobility across wafer-size dimensions. In contrast, SiC/G devices containing bilayer graphene domains display variations in their electronic properties linked to the amount of bilayer content. The spread in properties among devices patterned on the same SiC/G wafer can thus be understood by considering the inhomogeneous number of layers often grown on the surface of epitaxial graphene on SiC. (C) 2015 Elsevier Ltd. All rights reserved.
|
|
