[Show abstract][Hide abstract] ABSTRACT: Absence of backscattering and occurrence of weak anti-localization are two
characteristic features of topological insulators. We find that the
introduction of defects results in the appearance of a negative contribution to
magnetoresistance in the topological insulator BiSbTeSe2, at temperatures below
50 K. Our analysis shows that the negative magnetoresistance originates from an
increase in the density of defect states created by introduction of disorder,
which leaves the surface states unaffected. We find a decrease in the magnitude
of the negative magnetoresistance contribution with increasing temperature and
a robustness of the topological surface states to external disorder.
Physical Review B 12/2014; 90(23). DOI:10.1103/PhysRevB.90.235427 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Graphical abstract
Nanostructured glasses have been exposed outdoors for 12 weeks to test their durability, antireflective and self-cleaning performance. It was seen that nanostructured glass sample with 200-nm high nanostructures provided superior antireflective and self-cleaning effect as compared to planar glass over the testing period. This particular nanostructured glass sample also provided the best performance when tested as the packaging cover of a solar module, with reduction in efficiency by only 0.3% over a testing period of 5 weeks.
Solar Energy 11/2014; 110:231–238. DOI:10.1016/j.solener.2014.07.003 · 3.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bismuth Selenide (Bi2Se3) is a topological insulator exhibiting helical spin
polarization and strong spin-orbit coupling. The spin-orbit coupling links the
charge current to spin current via the spin Hall effect (SHE). We demonstrate a
Bi2Se3 spin detector by injecting the pure spin current from a magnetic
permalloy layer to a Bi2Se3 thin film and detect the inverse SHE in Bi2Se3. The
spin Hall angle of Bi2Se3 is found to be 0.003 and the spin diffusion length in
Bi2Se3 to be 6.2 nm at room temperature. Our results suggest that topological
insulators with strong spin-orbit coupling can be used in functional spintronic
Physical Review B 04/2014; 90(9). DOI:10.1103/PhysRevB.90.094403 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A Bi2Se3 topological insulator field effect transistor is investigated by
using ionic liquid as an electric double layer gating material, leading to a
conductance modulation of 365% at room temperature. We discuss the role of
charged impurities on the transport properties. The conductance modulation with
gate bias is due to a change in the carrier concentration, whereas the
temperature dependent conductance change is originated from a change in
mobility. Large conductance modulation at room temperature along with the
transparent optical properties makes topological insulators as an interesting
[Show abstract][Hide abstract] ABSTRACT: Antireflection coatings on glass are highly desirable, since glasses are widely used as a packaging material in the solar industry due to their transparency and durability. In this report, we propose a novel anodizing method using grid line contacts for antireflective nanostructures on a large area glass substrate. The nanoholes on the glass substrate exhibit broadband and omnidirectional antireflective properties, leading to an 11.34% improvement in the short-circuit current and enhanced power conversion efficiency from 7.9% to 8.57%. Moreover, the enhanced optical properties persist for 3 months in an outdoor environment. The proposed anodizing method can be considered as an alternative technique for the fabrication of large area nanostructures.
Solar Energy Materials and Solar Cells 09/2013; 116:9–13. DOI:10.1016/j.solmat.2013.03.038 · 5.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Shifting of the surface plasmon resonance wavelength induced by the variation of the thickness of insulating spacer between single layer graphene and Au nanoparticles is studied. The system demonstrates a blue-shift of 29 nm as the thickness of the spacer layer increases from 0 to 15 nm. This is due to the electromagnetic coupling between the localized surface plasmons excited in the nanoparticles and the graphene film. The strength of the coupling decays exponentially with a decay length of d/R = 0.36, where d is the spacer layer thickness and R is the diameter of the Au nanoparticles. The result agrees qualitatively well with the plasmon ruler equation. Interestingly, a further increment of the spacer layer thickness induces a red-shift of 17 nm in the resonance wavelength and the shift saturates when the thickness of the spacer layer increases above 20 nm.
[Show abstract][Hide abstract] ABSTRACT: A SF6/Ar inductively coupled plasma (ICP) technique was investigated to improve etching of proton exchanged LiNbO3. The influences of He backside cooling, power, and gas flows on characteristics such as etching rate, sidewall slope angle, and surface roughness were investigated. Total gas flow is a key parameter that affects etching results, and an optimized gas flow (50 sccm) was used for lengthy etching processes (30 min). Deep (>3 μm) and highly anisotropic etching, as well as ultra smooth LiNbO3 surfaces were achieved in a single-step run. The authors’ proposed method has achieved the deepest, most vertical, minimal residue structure yet reported for single-step ICP etching.
Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2012; 30(1):1208-. DOI:10.1116/1.3674282 · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We demonstrate an enhancement of optical transmission by creating randomly distributed nanoholes in a glass surface using a simple bottom-up fabrication process. V-shaped holes with sub-100 nm diameter are created by anodized aluminum oxide template and dry etching on glass substrates. The broadband and omnidirectional antireflective effect of the proposed nanostructures is confirmed by measuring the transmittance of the patterned glasses, leading to 3% better transmission. Subsequently, the short-circuit current and the open-circuit voltage of a solar cell with nanostructures are enhanced by 3-4%, improving the solar cell efficiency from 10.47% to 11.20% after two weeks of outdoor testing.
[Show abstract][Hide abstract] ABSTRACT: Much attention has been recently focused on realizing, by chemical treatment, an artificial superhydrophobic surface with elevated roughness in order to achieve both self cleaning and antireflective effects because superhydrophobic surface with surface functionalization is believed to be effective for the self cleaning effect, mimicking a lotus leaf. Various hydrophobic, hydrophilic, superhydrophobic, and superhydrophilic glasses are evaluated by monitoring the variation of water contact angle (CA), optical transmittance, and photovoltaic performance under outdoor conditions for 12 weeks. Our results show a nanopatterned superhydrophilic glass without surface chemical treatment exhibits more efficient self cleaning and antireflective effects, leading to only 1.39% of drop of solar cell efficiency during an outdoor test for 12 weeks, while the solar cells with bare glass packaging and fluorinated superhydrophobic packaging show 7.79% and 2.62% of efficiency drop, respectively.
Solar Energy Materials and Solar Cells 01/2011; 98. DOI:10.1016/j.solmat.2011.10.011 · 5.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Negative differential conductance and tunneling characteristics of two-terminal graphene devices are observed before and after electric breakdown, respectively. The former is caused by the strong scattering under a high E -field, and the latter is due to the appearance of a tunneling barrier in graphene channel induced by a structural transformation from crystalline graphene to disordered graphene because of the breakdown. Using Raman spectroscopy and imaging, the presence of nonuniform disordered graphene is confirmed. A memory switching effect of 100 000% ON/OFF ratio is demonstrated in the tunneling regime, which can be employed in various applications.
[Show abstract][Hide abstract] ABSTRACT: Inspired by the broadband antireflection of structured nipple array of moth eye, sub-wavelength antireflective (AR) coatings have been extensively exploited. Recently, surface structures with low reflection have been fabricated with the various methods and the broadband antireflection properties have been presented. In this paper, we will focus on numerical studies of angle dependence of light transmission on the sub-wavelength structures (SWS). The optimized structures are proposed for the interface between air and glass. Finite time finite difference (FDTD) method is used to analyze the optical transmission and reflection with nanostructures.