arXiv subjects

Rezwanur Rahman

Publications and source records attributed to Rezwanur Rahman.

4 recordsLinked to original sources

arXiv2016

Sub-THz thermally activated-electrical conductivity of CdS thin films

The electrical conductivity of a CdS thin film, controlled by grain structures is essential to enhance its photoconductivity to be able to be fit as a window material in CdS/CdTe heterojunction solar cell. In order to characterize a thin film, electromagnetically, we employed an open cavity resonator with a sub-millimeter VNA (Vector Network Analyzer). Our technique is capable of measuring complex dielectric permittivity, $\tildeε$, of a photovoltaic film as thin as 0.1 $μ$m. We measured the real part of the complex dielectric permittivity, $ε_{re}$, and electrical conductivity, $σ_{re}$ (derived from the imaginary part, $ε_{im}$), of unannealed and annealed CdS films with thicknesses $\sim$ 0.15 $μ$m on $\sim$ 3 mm thick-borosillicate glass substrates, at room temperature. We obtain the (thermally activated) electrical conductivity between 100 and 312 GHz, which is less in annealed samples than in unannealed one by $\sim$ 2 orders of magnitude. Contrary to our expectations, the carrier concentrations extracted from these data by fitting a Drude model, are $\sim$ 10$^{16}$ cm$^{-3}$ (unannealed) and $\sim$ 10$^{14}$ cm$^{-3}$ (annealed). We investigate the connection between grain size and carrier concentration.

cond-mat.mtrl-sci↗

arXiv2015

Sub-THz complex dielectric constants of smectite clay thin samples with Na$^{+}$/Ca$^{++}$-ions

We implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm$^{-1}$ to 4.95 cm$^{-1}$) of oriented smectite samples using an open cavity resonator connected to a sub-millimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na$^{+}$ and Ca$^{++}$-ion stabilized smectite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner ($\sim$ 30 $μ$m) than the glass substrate ($\sim$ 2.18 mm). The real part of dielectric constant, $ε_{re}$, is essentially constant over this frequency range but is larger in Na$^{+}$- than in Ca$^{++}$-ion infused clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, $ε_{im}$) of both samples increases monotonically at lower frequencies ($<$ 110 GHz), but shows rapid increase for Na$^{+}$ ions in the regime $>$ 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., $ζ$-potential in the Stern layers.

cond-mat.soft↗

arXiv2015

Complex dielectric properties of organic-rich mudrocks as functions of maturity

Complex dielectric variations can address neatly the maturity of organic-rich mudrocks. We, therefore, apply an open hemispherical cavity resonator to measure complex dielectric permitivitties of five thin sections of oil (bakken) shales (with different maturity) of $\sim$ 30 $μ$m thickness on glass-substrates around 2.15 mm thick in 100 - 165 GHz. The real part of complex dielectric permittivity ($ε_{re}$) are constant but show significant differences in magnitude based on maturity: (1) lowest, $\sim$ 1.9, for immature or early maturation stage, (2) higher than the immature one, $\sim$ 3.0 (also bundled up together), for three oil-matured stages, and (3) highest, $\sim$ 4.9, for late or overmatured stage. The conductivity ($σ_{re}$) from imaginary part of the complex dielectric constant ($ε_{im}$) emphasizes two important features of conductivity of oil shales: (1) frequency dispersion, and (2) maturity-dependence. We obtain increases of $σ_{re}$ with maturity and frequency.

cond-mat.soft↗

arXiv2015

Sub-THz complex dielectric constants of montmorillionite clay thin samples with Na$^{+}$/Ca$^{++}$-ions

We implement a technique to characterize electromagnetic properties at frequencies 100 to 165 GHz (3 cm$^{-1}$ to 4.95 cm$^{-1}$) of oriented montmorillionite samples using an open cavity resonator connected to a sub-millimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na$^{+}$ and Ca$^{++}$-ion stabilized montmorillionite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner ($\sim$ 30 $μ$m) than the glass substrate ($\sim$ 2.18 mm). The real part of dielectric constant,$ε_{re}$, is essentially constant over this frequency range but is larger in Na$^{+}$- than in Ca$^{++}$-ioned clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, $ε_{im}$) of both samples increases monotonically at lower frequencies ($<$ 110 GHz), but shows rapid increase for Na$^{+}$ ions in the regime $>$ 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., $ζ$-potential in the Stern layers.

cond-mat.soft↗