arXiv subjects

A. Iraji zad

Publications and source records attributed to A. Iraji zad.

7 recordsLinked to original sources

arXiv2011

Micro helical polymeric structures produced by variable voltage direct electrospinning

Direct near field electrospinning is used to produce very long helical polystyrene microfibers in water. The pitch length of helices can be controlled by changing the applied voltage, allowing to produce both micro springs and microchannels. Using a novel high frequency variable voltage electrospinning method we found the helix formation speed and compared the experimental buckling frequency to theoretical expressions for viscous and elastic buckling. Finally we showed that the newmethod can be used to produce new periodic micro and nano structures.

cond-mat.soft↗

arXiv2010

Strain effect on quantum conductance of graphene nanoribbons from maximally localized Wannier functions

Density functional study of strain effects on the electronic band structure and transport prop- erties of the graphene nanoribbons (GNR) is presented. We apply a uniaxial strain in the x (nearest-neighbor) and y (second nearest-neighbor) directions, related to the deformation of zigzag and armchair edge GNRs (AGNR and ZGNR), respectively. We calculate the quantum conduc- tance and band structures of the GNR using the Wannier function in a strain range from -8% to +8% (minus and plus signs show compression and tensile strain). As strain increases, depending on the AGNR family type, the electrical conductivity changes from an insulator to a conductor. This is accompanied by a variation in the electron and hole effective masses. The compression x direction strain in ZGNR shifts some bands to below the Fermi level (Ef ) and the quantum conductance does not change, but the tensile x direction strain causes an increase in the quantum conductance to 10e2/h near the Ef . For transverse direction, it is very sensitive to strain and the tensile y direction strain causes an increase in the conductance while the compressive y direction strain decreases the conductance at first but increases later.

cond-mat.mtrl-sci↗

arXiv2007

Etched Glass Surfaces, Atomic Force Microscopy and Stochastic Analysis

The effect of etching time scale of glass surface on its statistical properties has been studied using atomic force microscopy technique. We have characterized the complexity of the height fluctuation of a etched surface by the stochastic parameters such as intermittency exponents, roughness, roughness exponents, drift and diffusion coefficients and find their variations in terms of the etching time.

physics.data-an↗

arXiv2005

Two-Scale Kirchhoff Theory: Comparison of Experimental Observations With Theoretical Prediction

We introduce a non-perturbative two scale Kirchhoff theory, in the context of light scattering by a rough surface. This is a two scale theory which considers the roughness both in the wavelength scale (small scale) and in the scales much larger than the wavelength of the incident light (large scale). The theory can precisely explain the small peaks which appear at certain scattering angles. These peaks can not be explained by one scale theories. The theory was assessed by calculating the light scattering profiles using the Atomic Force Microscope (AFM) images, as well as surface profilometer scans of a rough surface, and comparing the results with experiments. The theory is in good agreement with the experimental results.

physics.data-an↗

arXiv2005

Characterization of Etched Glass Surfaces by Wave Scattering

The roughness of glass surfaces after different stages of etching is investigated by reflection measurements with a spectrophotometer, light scattering, and atomic-force microscopy (in small scale), and Talysurf (in large scale). The results suggest, there are three regimes during etching, according to their optical reflectivity and roughness. The first and second regimes are studied by the Kirchhoff theory and the third one is studied by the geometric theory. Also, we compare the roughness obtained by the optical scattering to the AFM results.

physics.optics↗

arXiv2003

Stochastic Analysis and Regeneration of Rough Surfaces

We investigate Markov property of rough surfaces. Using stochastic analysis we characterize the complexity of the surface roughness by means of a Fokker-Planck or Langevin equation. The obtained Langevin equation enables us to regenerate surfaces with similar statistical properties compared with the observed morphology by atomic force microscopy.

cond-mat.stat-mech↗

arXiv2003

Height Fluctuations and Intermittency of $V_2 O_5$ Films by Atomic Force Microscopy

The spatial scaling law and intermittency of the $V_2 O_5$ surface roughness by atomic force microscopy has been investigated. The intermittency of the height fluctuations has been checked by two different methods, first, by measuring scaling exponent of q-th moment of height-difference fluctuations i.e. $C_q = < |h(x_1) - h(x_2)|^{q} >$ and the second, by defining generating function $Z(q,N)$ and generalized multi-fractal dimension $D_q$. These methods predict that there is no intermittency in the height fluctuations. The observed roughness and dynamical exponents can be explained by the numerical simulation on the basis of forced Kuramoto-Sivashinsky equation.

cond-mat.stat-mech↗