Browsing by Subject "Electrical properties"

Now showing 1 - 8 of 8

Open Access
Effect of O2/Ar flow ratio and post-deposition annealing on the structural, optical and electrical characteristics of SrTiO3 thin films deposited by RF sputtering at room temperature
(Elsevier, 2015) Goldenberg, E.; Bayrak, T.; Ozgit Akgun, C.; Haider A.; Leghari, S.A.; Kumar, M.; Bıyıklı, Necmi
SrTiO3 (STO) thin films have been prepared by reactive RF magnetron sputtering on Si (100) and UV fused silica substrates at room temperature. The effect of oxygen flow on film characteristics was investigated at a total gas flow of 30 sccm, for various O2/O2 + Ar flow rate ratios. As-deposited films were annealed at 700 °C in oxygen atmosphere for 1 h. Post-deposition annealing improved both film crystallinity and spectral transmittance. Film microstructure, along with optical and electrical properties, was evaluated for both as-deposited and annealed films. Abroad photoluminescence emission was observed within the spectral range of 2.75–3.50 eV for all STO thin films irrespective of their deposition parameters. Upon annealing, the optical band gap of the film deposited with 0% O2 concentration slightly blue-shifted, while the other samples grown at higher oxygen partial pressure did not show any shift. Refractive indices (n) (at 550 nm) were in the range of 2.05 to 2.09, and 2.10 to 2.12 for as-deposited and annealed films, respectively. Dielectric constant values (at 100 kHz) within the range of 30–66 were obtained for film thicknesses less than 300 nm, which decreased to ~30–38 after postdeposition annealing.
Open Access
Electro-optical performances of nanostructured SrTiOx films: The effect of plasma power, Ar/O2 ratio and annealing
(Wiley-Blackwell Publishing, Inc., 2021-01-01) Goldenberg, Eda; Bayrak, Türkan; Mohammadmoradi, O.
The present work evaluates the effects of plasma power and oxygen mixing ratios (OMRs) on structural, morphological, optical, and electrical properties of strontium titanate SrTiOx (STO) thin films. STO thin films were grown by magnetron sputtering, and later thermal annealing at 700°C for 1 h was applied to improve film properties. X-ray diffraction analysis indicated that as-deposited films have amorphous microstructure independent of deposition conditions. The films deposited at higher OMR values and later annealed also showed amorphous structure while the films deposited at lower OMR value and annealed have nanocrystallinity. In addition, all as-deposited films were highly transparent (~80%–85%) in the visible spectrum and exhibited well-defined main absorption edge, while the annealing improved transparency (90%) within the same spectrum. The calculated direct and indirect optical band gaps for films were in the range of 3.60-4.30 eV as a function of deposition conditions. The refractive index of the films increased with OMRs and the postdeposition annealing. The frequency dependent capacitance measurements at 100 kHz were performed to obtain film dielectric constant values. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 μC/cm2 charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). The leakage current density was relatively low (3 × 10−8Acm−2 at +0.8 V) indicating that STO films are promising for future dynamic random access memory applications.
Open Access
High-frequency performance of submicrometer transistors that use aligned arrays of single-walled carbon nanotubes
(American Chemical Society, 2009-04-08) Kocabaş, Coşkun; Dunham, S.; Cao, Q.; Cimino, K.; Ho, X.; Kim, H.-S.; Dawson, D.; Payne, J.; Stuenkel, M.; Zhang, H.; Banks, T.; Feng, M.; Rotkin, S. V.; Rogers, J. A.
The unique electronic properties of single-walled carbon nanotubes (SWNTs) make them promising candidates for next generation electronics, particularly in systems that demand high frequency (e.g., radio frequency, RF) operation. Transistors that incorporate perfectly aligned, parallel arrays of SWNTs avoid the practical limitations of devices that use individual tubes, and they also enable comprehensive experimental and theoretical evaluation of the intrinsic properties. Thus, devices consisting of arrays represent a practical route to use of SWNTs for RF devices and circuits. The results presented here reveal many aspects of device operation in such array layouts, including full compatibility with conventional small signal models of RF response. Submicrometer channel length devices show unity current gain (ft) and unity power gain frequencies (fmax) as high as ∼5 and ∼9 GHz, respectively, with measured scattering parameters (S-parameters) that agree quantitatively with calculation. The small signal models of the devices provide the essential intrinsic parameters: saturation velocities of 1.2 × 107 cm/s and intrinsic values of ft of ∼30 GHz for a gate length of 700 nm, increasing with decreasing length. The results provide clear insights into the challenges and opportunities of SWNT arrays for applications in RF electronics.
Open Access
Molecular and continuum perspectives on intermediate and flow reversal regimes in electroosmotic transport
(American Chemical Society, 2019) Çelebi, A. T.; Çetin, Barbaros; Beşkök, A.
Electroosmotic slip flows in the Debye–Hückel regime were previously investigated using molecular dynamics and continuum transport perspectives ( J. Phys. Chem. C 2018, 122, 9699). This continuing work focuses on distinct electrostatic coupling regimes, where the variations in electroosmotic flows are elucidated based on Poisson–Fermi and Stokes equations and molecular dynamics simulations. In particular, aqueous NaCl solution in silicon nanochannels are considered under realistic electrochemical conditions, exhibiting intermediate flow and flow reversal regimes with increased surface charge density. Electroosmotic flow exhibits plug flow behavior in the bulk region for channel heights as small as 5 nm. With increased surface charge density, constant bulk electroosmotic flow velocity first increases and then it begins to gradually decrease until flow reversal is observed. In order to capture the flow physics and discrete motions within electric double layer accurately, the continuum model includes overscreening and crowding effects as well as slip contribution and local variations of enhanced viscosity. After extraction of the continuum parameters based on molecular dynamics simulations, good agreement between simulation results and continuum predictions are obtained for surface charges as large as −0.37 C/m2.
Open Access
Monolayer diboron dinitride: direct band-gap semiconductor with high absorption in the visible range
(American Physical Society, 2020) Demirci, Salih; Rad, Soheil Ershad; Kazak, Sahmurat; Nezir, S.; Jahangirov, Seymur
We predict a two-dimensional monolayer polymorph of boron nitride in an orthorhombic structure (o-B2N2) using first-principles calculations. Structural optimization, phonon dispersion, and molecular dynamics calculations show that o-B2N2 is thermally and dynamically stable. o-B2N2 is a semiconductor with a direct band gap of 1.70 eV according to calculations based on hybrid functionals. The structure has high optical absorption in the visible range in the armchair direction while low absorption in the zigzag direction. This anisotropy is also present in electronic and mechanical properties. The in-plane stiffness of o-B2N2 is very close to that of hexagonal boron nitride. The diatomic building blocks of this structure hint at its possible synthesis from precursors having B-B and N-N bonds.
Embargo
The sub-terahertz region absorption of sputter deposited nanoscale TiAlV thin films
(Elsevier B.V., 2022-12-05) Öksüzoğlu, Ramis Mustafa; Altan, Hakan; Abdüsselamoğlu, Mehmet Sait; Özkan, Özlem Başak; Bayram, Yasin; Chakar, Erkan Syuleyman
Absorption in the sub-terahertz region in TiAlV thin films with their potential usage in detectors and plasmonic applications is a crucial point for device performance. This work aims to investigate the thickness-dependent evolution of the sub-terahertz region absorption, electrical resistivity in TiAlV thin films deposited by DC magnetron sputtering and to study the structure-property correlation. For structural analyses, X-ray diffraction and transmission electron microscopy techniques have been used. In different deposition conditions, TiAlV thin films indicating the β-Ti phase with anisotropic growth and the hexagonal AlTi3 phase with equiaxial growth have been produced. High resistivity values have been measured in films with the AlTi3 phase. In all TiAlV thin films with different structures, thickness dependent resistivity change in the range 3–23 nm, whereby a strong increase in electrical resistivity with decreasing film thickness have been observed below a thickness of 6 nm. The sub-terahertz absorption increases with increasing film thickness. The highest terahertz region absorption has been found for the films with the β-Ti phase and anisotropic growth also indicating higher electrical conductivity, which favors absorption sensitive applications in the terahertz region. © 2022 Elsevier B.V.
Open Access
Thermally stimulated currents in n-InS single crystals
(Elsevier Science, 2003) Gasanly, N. M.; Aydınlı, Atilla; Yuksek, N. S.
Thermally stimulated current measurements are carried out on as-grown n-InS single crystals in the temperature range of 10-125 K. Experimental evidence is found for four trapping centers present in InS. They are located at 20, 35, 60 and 130meV. The trap parameters have been determined by various methods of analysis, and they agree well with each other.
Open Access
X-ray photoelectron spectroscopy with electrical modulation can be used to probe electrical properties of liquids and their interfaces at different stages
(American Chemical Society, 2019) Uzundal, Can Berk; Şahin, Özgür; Aydoğan-Göktürk, Pınar; Wu, H.; Mugele, F.; Ülgüt, Burak; Süzer, Şefik
Operando X-ray photoelectron spectroscopy (o-XPS) has been used to record the binding energy shifts in the C 1s peak of a pristine poly(ethylene glycol) (PEG) liquid drop in an electrowetting on dielectric (EWOD) geometry and after exposing it to several high-voltage breakdown processes. This was achieved by recording XPS data while the samples were subjected to 10 V dc and ac (square-wave modulation) actuations to extract electrical information related to the liquid and its interface with the dielectric. Through analysis of the XPS data under ac actuation, a critical frequency of 170 Hz is extracted for the pristine PEG, which is translated to a resistance value of 14 MΩ for the liquid and a capacitance value of 60 pF for the dielectric, by the help of simulations using an equivalent circuit model and also by XPS analyses of a mimicking device under similar conditions. The same measurements yield an increased value of 23 MΩ for the resistance of the liquid after the breakdown by assuming that the capacitance of the dielectric stays constant. In addition, an asymmetry in polarity dependence is observed with respect to both the onset of the breakdown voltage and also the leakage behavior of the deteriorated (PEG + dielectric) system such that deviations are more pronounced at positive voltages. Both dc and ac behaviors of the postbreakdown system can also be simulated, but only by introducing an additional element, a diode or a polarity- and magnitude-dependent voltage source (VCVS), which might be attributed to negative charge accumulation at the interface. Measurements for a liquid mixture of PEG with 8% ionic liquid yields an almost 2 orders of magnitude smaller resistance for the drop as a result of the enhanced conductivity by the ions. Coupled with modeling, XPS measurements under dc and ac modulations enable probing unique electrochemical properties of liquid/solid interfaces.