English Articles

New Software Simulating the Full Operation of a Scanning Tunneling Microscope and Its Application to an FPGA-Based Instrument
 

The scanning tunneling microscope is an essential tool in nanoscience and nanotechnology, because it enables imaging surfaces at the atomic level with sub-nanometer resolution. We have written a LabVIEW-based virtual instrument to simulate the operation of an STM and made it available as a free-download at our company website. This is an executable version to be run on a Windows operating system without requiring other software. We have also constructed an STM that implements the same algorithms with a field-programmable gate array (FPGA) to provide deterministic real-time control of multiple tasks

Mark J. Hagmann, Gregory R. Spencer, Jeremy Wiedemeier and

Marwan S. Mousa

Comparative Study of Field Electron Emission from Single-Walled Carbon Nanotube and Multi-Walled Carbon Nanotube Mounted on Tungsten

Field Electron Emission (FEE) from Single-Walled Carbon Nanotubes (SWCNTs) and Multi-Walled Carbon Nanotubes (MWCNTs) mounted on blunt tungsten tip has been investigated to make sure that FEE comes from the CNTs. The FEE properties were studied using Field Emission Microscope (FEM), where the distance between the emitter and screen was fixed at ~10 mm and the system was evacuated to (~10-9 mbar). The emitters were prepared during two stages, with the first one being electrolytically etching the tungsten (W) wire of (0.1 mm diameter) in 2 mol of NaOH, while the second stage involves fixing the CNTs on the etched tungsten. Current-voltage (I-V) measurements were recorded and presented in the most common way as (I-V) plot with its related Fowler-Nordheim (FN) plot. It has been found that SWCNT samples have several advantages over MWCNT samples, such as the field electron emission having been initiated at lower applied voltage values and maintaining emitting electrons at lower applied voltage values, but MWCNTs emitted higher current values compared to SWCNTs.

Marwan S. Mousa, Samer I. Daradkeh and

Emad S. Bani Ali
 

A Genetic Algorithm for Addressing Computationally Expensive Optimization Problems in Optical Engineering

We present a genetic algorithm that we developed in order to address computationally expensive optimization problems in optical engineering. The idea consists of working with a population of individuals representing possible solutions to the problem. The best individuals are selected. They generate new individuals for the next generation. Random mutations in the coding of parameters are introduced. This strategy is repeated from generation to generation until the algorithm converges to the global optimum of the problem considered. For computationally expensive problems, one can analyze the data collected by the algorithm in order to infer more rapidly the final solution. The use of a mutation operator that acts on randomly-shifted Gray codes helps the genetic algorithm escape local optima and enables a wider diversity of displacements. These techniques reduce the computational cost of optical engineering problems, where the design parameters have a finite resolution and are limited to a realistic range. We demonstrate the performance of this algorithm by considering a set of 22 benchmark problems in 5, 10 and 20 dimensions that reflect the conditions of these engineering problems. We finally show how these techniques accelerate the determination of optimal structures for the broadband absorption of electromagnetic radiations.

A. Mayer

and

Michaël Lobet

Monte Carlo Computation of the Influence of Carbon Contamination Layer on the Energy Distribution of Backscattered Electrons Emerging from Al and Au

The influence of carbon contamination layer (5nm) on the energy distribution of backscattered electrons (BSEs) emerging from the top of Al- and Au-substrates at a wide range of normal primary electron energies (E_P = 0.5-20keV) has been theoretically examined. The study is based on using a CASINO Monte Carlo model. Generally, the results show a clear effect of the contamination on the backscattering coefficient and the energy distribution of backscattered electrons. This appeared as a reduction of the number of BSE emerging from the surface with energies close to the primary energy. For primary energy less than 5keV, the contamination effects are clearly seen in the reduction of the number of BSEs emerging with energy close to E_P and the increment of the number of BSEs with low energies. The backscattered electron spectrum starts with a wide peak at low energies and becomes sharper as the primary energy increases. For high primary electron energies (10-20keV), the influence of the carbon contamination layer is restricted on the energy distribution of the backscattered electrons with energies above 95% of the primary energy. The influence of the carbon contamination layer was observed more clearly for the Au-substrate than for the Al-substrate as a reduction of the number of backscattered electrons.

A. M. D. Assa’d

Ionic Liquids: Sustainable Media for Nanoparticles

In this paper, an incompressible viscous fluid flow over a flat plate is presented. In the past decade, ionic liquids have attracted great interest both in scientific research world and amongst the most diverse technological and industrial sectors. This fact, together with the growing contribution of the industrial sector, is turning ionic liquids into a key component for the most diverse fields of science, such as nanotechnology, electrochemistry, green chemistry, physics, materials science and engineering, among many others. First, before talking about the ionic liquids’ applications, one should answer this question; what are the main properties that make ionic liquids so attractive? In general, ionic liquids are salts formed by very asymmetric and large ions, due to which they have attractive cation-anion forces weaker than those that occur in conventional ionic salts, such as table salt, which causes them to be liquids in a wide range of temperatures, including the ambient temperature in most cases. The term "ionic liquid" is considered a synonym of a "molten salt", although in practice it began to be used when molten salts started to be popular at low temperatures. Indicatively, a compound is usually called a molten salt when the melting temperature is above 100 °C, while an ionic liquid melts at lower temperatures. Due to the growing applications of ionic liquids as engineering fluids, their ability to functionalize or surface-modify materials in the form of nanoparticles has recently been described. Therefore, ionic liquids have been used as solvents for nanoparticle synthesis with a wide variety of sizes and morphologies.

Azeez A. Barzinjy, Samir M. Hamad

and

Ashna F. Arkawazi

Numerical Testing by a Transfer-Matrix Technique
of Simmons’ Equation for the Local Current Density
in Metal-Vacuum-Metal Junctions

 

We test the consistency with which Simmons’ model can predict the local current density obtained for flat metal-vacuum-metal junctions. The image potential energy used in Simmons’ original papers had a missing factor of 1/2. Beside this technical issue, Simmons’ model relies on a mean-barrier approximation for electron transmission through the potential-energy barrier between the metals. In order to test Simmons’ expression for the local current density when the correct image potential energy is included, we compare the results of this expression with those provided by a transfer-matrix technique. We also consider the current densities provided by a numerical integration of the transmission probability obtained with the WKB approximation and Simmons’ mean-barrier approximation. The comparison between these different models shows that Simmons’ expression for the local current density actually provides results that are in good agreement with those provided by the transfer-matrix technique, for a range of conditions of practical interest. We show that Simmons’ model provides good results in the linear and field-emission regimes of current density versus voltage plots. It loses its applicability when the top of the potential-energy barrier drops below the Fermi level of the emitting metal.

Alexandre Mayer, Marwan S. Mousa, Mark J. Hagmann
and

Richard G. Forbes
 

 JJP, 2019, 12(1), 63-77

Preparation and Preliminary Characterization of Hybrid Alginate – Carrageenan Aerogel: Effect of Gelation Methods

Aerogels are a class of nanoporous structured material with a high specific surface area, large porosity and open pore structure. Usually, they are produced by substituting the solvent of a stable gel with air without affecting the 3-D network of the gel. It is possible to engineer the produced material by controlling the precursors, gelling mechanism and drying process. In this work, hybrid aerogel based on alginate and three different types of carrageenan was produced using supercritical fluid technology. CO2-induced gelation, as well as GdL-induced gelation, were evaluated for their effect on final textural properties of the produced aerogel. CO2-induced gelation method shows enhanced aerogel properties and can be further investigated for the scale-up application. Nevertheless, GdL-induced gelation is easier to perform and produced a smaller specific surface area aerogel if compared with CO2-induced gelation method. Hybrid alginate-carrageenan aerogels were produced with high surface area (390-566) m2∙g-1 and large pore volume (4.2-6.8) m3∙g-1 and with a mesoporous structure (3.2 – 26.8) nm. The produced aerogels have great potential for future biotechnological and pharmaceutical applications.

M. Alnaief,

B. Mohammad, Mohannad Aljarrah

and

R. M. Obaidat

Effect of Relaxation and Cooling Process on Field Electron Emission from Single-Walled Carbon Nanotubes Embedded in Glass

Several experiments examined the properties of Field Electron Emission (FEE) from Single-Walled Carbon Nanotubes (SWCNTs), where extensive studies were conducted to improve the emission current density (stability and repeatability) and emission current image concentration. In this study, the effect of relaxation and cooling processes on FEE from SWCNTs embedded in glass has been investigated to keep the ongoing investigation for factors that positively affect the FEE process. It has been found that the relaxation process can ameliorate the FEE, where the “switch-on” phenomenon occurs at lower applied voltage after performing the relaxation process. Also, the saturation region extends down to lower applied voltage values after the relaxation process. In case of the effect of cooling process on FEE, the “switch-on” phenomenon occurs at higher applied voltage values after applying the cooling process. Also, the saturation region extends down to higher applied voltage values and the threshold value has been found to significantly being lowered as the result of the cooling process, where the emission current disappeared at applied voltage values of ~20 V. In terms of the effects of the cooling process on emission current images, the emission current image is distributed throughout the screen. Furthermore, it has been experiencing a massive emission current fluctuation after performing the cooling process.

Marwan S. Mousa

and

Samer I. Daradkeh