Browsing by Subject "Electrical conductivity"

Now showing 1 - 9 of 9

Open Access
Hydrogenated carbon monolayer in biphenylene network offers a potential paradigm for nanoelectronic devices
(American Chemical Society, 2022-09-15) Demirci, S.; Gorkan, T.; Çallıoǧlu, Şafak; Özçelik, V. O.; Barth, J.; Aktürk, E.; Çıracı, Salim
A metallic carbon monolayer in the biphenylene network (specified as C ohs) becomes an insulator upon hydrogenation (specified as CH ohs). Patterned dehydrogenation of this CH ohs can offer a variety of intriguing functionalities. Composite structures constituted by alternating stripes of C and CH ohs with different repeat periodicity and chirality display topological properties and can form heterostructures with a tunable band-lineup or Schottky barrier height. Alternating arrangements of these stripes of finite size enable one to also construct double barrier resonant tunneling structures and 2D, lateral nanocapacitors with high gravimetric capacitance for an efficient energy storage device. By controlled removal of H atom from a specific site or dehydrogenation of an extended zone, one can achieve antidoping or construct 0D quantum structures like antidots, antirings/loops, and supercrystals, the energy level spacing of which can be controlled with their geometry and size for optoelectronic applications. Conversely, all these device functions can be acquired also by controlled hydrogenation of a bare C ohs monolayer. Since all these processes are applied to a monolayer, the commensurability of electronically different materials is assured. These features pertain not only to CH ohs but also to fully hydrogenated Si ohs.
Open Access
k · p Parametrization and linear and circular dichroism in strained monolayer (janus) transition metal dichalcogenides from first-principles
(American Chemical Society, 2021-04-08) Aksu Korkmaz, Yağmur; Bulutay, Ceyhun; Sevik, C.
Semiconductor monolayer transition metal dichalcogenides (TMDs) have brought a new paradigm by introducing optically addressable valley degree of freedom. Concomitantly, their high flexibility constitutes a unique platform that links optics to mechanics via valleytronics. With the intention to expedite the research in this direction, we investigated ten TMDs, namely MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2, MoSSe, MoSeTe, WSSe, and WSeTe, which particularly includes their so-called janus types (JTMDs). First, we obtained their electronic band structures using regular and hybrid density functional theory (DFT) calculations in the presence of the spin–orbit coupling and biaxial or uniaxial strain. Our DFT results indicated that against the expectations based on their reported piezoelectric behavior, JTMDs typically interpolated between the standard band properties of the constituent TMDs without producing a novel feature. Next, by fitting to our DFT data we generated both spinless and spinful k · p parameter sets which are quite accurate over the K valley where the optical activity occurs. As an important application of this parametrization, we considered the circular and linear dichroism under strain. Among the studied (J)TMDs, WTe2 stood out with its largest linear dichroism under uniaxial strain because of its narrower band gap and large K valley uniaxial deformation potential. This led us to suggest WTe2 monolayer membranes for optical polarization-based strain measurements, or conversely, as strain tunable optical polarizers.
Open Access
Liquid bulk rotation induced by electric field at free surface
(American Institute of Physics Inc., 2015) Saghaei, T.; Moradi, A.-R.; Shirsavar, R.; Habibi, M.
In this paper, we induce rotation in a bulk of polar liquid with one free surface, by applying external crossed electric fields. We show that the induced rotation is due to the imposed stresses at the free surface of the liquid. A simple theoretical model was developed based on solving the Navier-Stokes equation that enables us to calculate the average induced stress in the liquid bulk, using experimental measurements of the angular velocity of the liquid. Our results indicate that the induced stresses and the angular velocities of the rotating liquid are independent from the electrical conductivity of the liquid. However, the induced stresses linearly depend on the external electric field and the applied electric voltage for passing the electric current through the bulk. Both experimental results and the theoretical model show that the angular velocity, linearly changes with depth. © 2015 AIP Publishing LLC.
Open Access
Mechanochemical activation and patterning of an adhesive surface toward nanoparticle deposition
(American Chemical Society, 2015) Baytekin, H. T.; Baytekin, B.; Huda, S.; Yavuz, Z.; Grzybowski, B. A.
Mechanical pulling of adhesive tape creates radicals on the tapes surface. These radicals are capable of reducing metal salts to the corresponding metal nanoparticles. In this way, the mechanically activated tape can be decorated with various types of nanoparticles, including Au, Ag, Pd, or Cu. While retaining their mechanical properties and remaining "sticky, " the tapes can exhibit new properties derived from the presence of metal nanoparticles (e.g., bacteriostaticity, increased electrical conductivity). They can also be patterned with nanoparticles only at selective locations of mechanical activation.
Open Access
Metal-insulator transitions in bilayer electron-hole systems in transition metal dichalcogenides
(American Physical Society, 2021-11-29) Chui, S. T.; Wang, N.; Tanatar, Bilal
We investigated metal-insulator transitions for double-layer two-dimensional electron-hole systems in transition metal dichalcogenides stacked on opposite sides of thin layers of boron nitride. The interparticle interaction is calculated by including the screening due to the polarization charges at different interfaces, including that at the encapsulation and at the substrate of experimental structures. We compute and compare the energies of the metallic electron-hole plasma and the proposed insulating exciton solid with fixed-node diffusion Monte Carlo simulation including the high valley degeneracy of the electron bands. We found that for some examples of current experimental structures, the transition electron/hole density is in an experimentally accessible range between 4.1×10 12cm−2 and 14.5×10 12cm−2 for spacer thicknesses between 2.5 and 7.5 nm. Our result raises the possibility of exploiting this effect for logic device applications.
Open Access
Microfluidics for reconfigurable electromagnetic metamaterials
(AIP Publishing, 2009) Kasirga, T. S.; Ertas, Y. N.; Bayındır, Mehmet
We propose microfluidics as a useful platform for reconfigurable electromagnetic metamaterials. Microfluidic split-ring resonators (MF-SRRs) are fabricated inside a flexible elastomeric material by employing rapid prototyping. The transmission measurements performed for mercury-injected MF-SRR exhibits sharp magnetic resonances at microwave wavelengths. We further calculate transmission properties of the MF-SRR array and the effect of electrical conductivity of the liquid inside the channel on the magnetic resonance. The measured results agree well with numerical calculations. Our proposal may open up directions toward switchable metamaterials and reconfigurable devices such as filters, switches, and resonators.
Open Access
Modulation of electronic properties in laterally and commensurately repeating graphene and boron nitride composite nanostructures
(American Chemical Society, 2015) Özçelik, V. O.; Durgun, Engin; Çıracı, Salim
Graphene and hexagonal boron nitride (h-BN) nanoribbons of diverse widths and edge geometries are laterally repeated to form commensurate, single-layer, hybrid honeycomb structures. The resulting composite materials appear as continuous, one atom thick stripes of graphene and BN having the average mechanical properties of constituent structures. However, depending on the widths of constituent stripes they can be metal or semiconductor with band gaps in the energy range of the visible light. These two-dimensional (2D) composite materials allow strong dimensionality in electrical conductivity and undergo transition from 2D to one-dimensional (1D) metal in a 2D medium, resulting in multichannel narrow conductors. As for the composite ribbons, such as one dielectric BN stripe placed between two graphene stripes with bare zigzag edges, charge separation of opposite polarity is possible under applied electric field and they exhibit resonant tunneling effects at nanoscale. Graphene/BN composite materials also form stable single-wall nanotubes with zigzag or armchair geometries.
Open Access
Nanomaterials for neural regeneration
(John Wiley & Sons, 2016-03-11) Sever, Melike; Mammadov, Büşra; Geçer, Mevhibe; Güler, Mustafa O.; Tekinay, Ayşe B.; Güler, Mustafa O.; Tekinay, Ayşe B.
The central nervous system (CNS) consists of a dense network of cells leaving a smaller volume for the extracellular matrix (ECM) components (10‐20% for the brain unlike most other tissues (Cragg, 1979)). The reaction of the nervous tissue to any injury leading to scar tissue formation acts as a barrier for regeneration in the CNS, while it supports regeneration in the peripheral nervous system (PNS). By mimicking several unique characteristics of the natural environment of cells, synthetic materials for neural regeneration can be improved chemically and biologically. Especially bioactivation of materials can be achieved by addition of small chemical moieties to the scaffold particularly found in specific tissues or addition of biologically active molecules derived from natural ECM. The ECM‐derived short peptides are promising candidates to be presented as functional domains on the scaffold surface for use in neural regeneration.
Open Access
A PN-type quantum barrier for InGaN/GaN light emitting diodes
(Optical Society of American (OSA), 2013) Zhang, Z.-H.; Tan, S.T.; Ji, Y.; Liu W.; Ju, Z.; Kyaw, Z.; Sun X.W.; Demir, Hilmi Volkan
In this work, InGaN/GaN light-emitting diodes (LEDs) with PN-type quantum barriers are comparatively studied both theoretically and experimentally. A strong enhancement in the optical output power is obtained from the proposed device. The improved performance is attributed to the screening of the quantum confined Stark effect (QCSE) in the quantum wells and improved hole transport across the active region. In addition, the enhanced overall radiative recombination rates in the multiple quantum wells and increased effective energy barrier height in the conduction band has substantially suppressed the electron leakage from the active region. Furthermore, the electrical conductivity in the proposed devices is improved. The numerical and experimental results are in excellent agreement and indicate that the PN-type quantum barriers hold great promise for high-performance InGaN/GaN LEDs. © 2013 Optical Society of America.