N. Qamhieh

Fabrication of size-selected Pd nanoclusters using a magnetron plasma sputtering source

We report on the fabrication of palladium (Pd) nanoclusters using a dc magnetron sputtering source. Plasma sputtering vaporizes the target’s material forming nanoclusters by inert gas condensation. The sputtering source produces ionized nanoclusters that enable the study of the nanoclusters’ size distribution using a quadrupole mass filter. In this work, the dependence of Pd nanoclusters’ size distribution on various source parameters, such as the sputtering discharge power, inert gas flow rate, and aggregation length have been investigated. This work demonstrates the ability of tuning the palladium nanoclusters’ size by proper optimization of the source operation conditions. The experimental nanocluster sizes are compared with a theoretical model that reveals the growth of large nanoclusters from “embryos” by a two-body collision. The model is valid for a specific range of deposition parameters (low inert gas flow rates and aggregation lengths equal or below 70 mm).

Electrical properties of Se2Sb2Te6 thin films

The electrical properties of Se2Sb2Te6 thin films are investigated using dc resistance, impedance spectroscopy and capacitance–voltage (C–V) measurements. The amorphous–crystalline transition temperature, Tc, is estimated to be 60 °C using dc resistance measurements. The impedance spectroscopy measurements are performed at different temperatures ranging from 25 to 95 °C. The impedance spectroscopy data give an estimation of the activation energy, Ev = 0.5 eV. The amorphous–crystalline interface is electrically characterized by measuring the capacitance of the film as a function of bias voltage at different temperatures ranging from 25 to 85 °C. The C–V measurements show temperature dependence and nonlinear behaviour of the capacitance with the applied bias voltages that could be attributed to the crystallization growth as the temperature gets close to Tc.

Electrical and optical properties of indium-modified Se 2 Sb 2 Te 6 films

The electrical and optical characteristics of indium-doped Se2Sb2Te6 phase-change alloy are studied in this paper. It is found that adding indium to Se2Sb2Te6 alloy increases its amorphous‐crystalline transition temperature, TC, and reduces the electrical conduction activation energy. The capacitance‐temperature measurements showed a drastic change in the capacitance of the modified film as the temperature approaches TC and eventually the capacitance becomes negative and nonlinear. The negativity and nonlinearity in the capacitance‐voltage dependence can be attributed to the growth of conductive crystalline islands with increasing temperature.

Synthesis and properties of phase-change Ge-Sb nanoparticles

We report on the synthesis and characterization of Ge15Sb85 phase-change nanoparticles by magnetron plasma sputtering and inert-gas condensation inside an ultra-high vacuum compatible system. Electrical and optical properties of Sb-rich nanoparticles for phase-change memory applications have been examined. The results show that phase-change properties of Ge15Sb85 material still exist for nanoparticles of 8.0 nm size. The amorphous to crystalline transformation proceeds at moderately elevated temperature (∼473 K) which shows that Ge15Sb85 nanoparticles are a good candidate for phase-change memory applications in terms of long data retention time. The observed phase transition in Ge15Sb85 nanoparticles is promising for down scaling the size of phase change solid-state memory devices.

Production and Growth Mechanisms of Pd Nanoclusters

Size-selected palladium nanoclusters have been produced by dc sputtering and inert gas condensation technique using mixtures of argon and helium gases. By controlling the source parameters, it was possible to produce Pd nanoclusters with size in the range of 2-10 nm. Transmission electron microscopy (TEM) images were used to confirm the produced sizes of nanocluster. It was found that increas- ing the percentage of helium to argon have two main effects: i) decreases the nanocluster size as a result of the high drift velocity of he- lium, and ii) decreases the number of measured nanoclusters due to the low sputtering yield of helium. Since He gas is primarily respon- sible for the cluster-condensation process, its partial pressure can be used to control the nanoclusters growth. The source parameters and their effects on the size and number of nanoclusters are of great importance in understanding the Pd nanoclusters growth mechanism.

Investigation of the Formation Mechanisms of Pd Nanoclusters Produced Using a Magnetron Sputtering Source

We report on the fabrication of palladium (Pd) nanoclusters using a dc magnetron sputtering source. The sputtering source produces ionized nanoclusters that enable the study of the nanoclusters’ size distribution using a quadrupole mass filter. In this work, the dependence of Pd nanoclusters’ size distribution on various source parameters, such as the inert gas flow rate, and aggregation length have been investigated in details. This work demonstrates the ability of tuning the palladium nanoclusters’ size by proper optimization of the source operation conditions.

Production of Size-Selected CuXSn1-X Nanoclusters

Composites of copper–tin (CuxSn1-x) nanoclusters were synthesized using the magnetron dc sputtering gas–condensation technique. Targets with controlled ratios of Sn to Cu were used to produce CuxSn1-x with different compositions. The effects on the nanocluster size and yield of the sputtering discharge power, inert gas flow rate, and aggregation length were investigated using a quadrupole mass filter. The sputtering discharge power was optimized to maximize the nanocluster yield. The results show that as the inert gas flow rate increases the nanocluster size increases and then decreases. These dependences could be understood in terms of the dominant nanocluster production mechanisms. This work demonstrates the ability of controlling the CuxSn1-x nanoclusters’ size and composition by optimizing the source operation conditions.

Optical and electrical characterization of Co doped Ge-Sb-S films

T alpha (α)-hematite (Fe2O3) nanomaterial is attractive due to its band gap, chemical robustness, availability in the nature and excellent photoelectrochemical (PEC) properties to split water into oxygen and hydrogen. However, the α-Fe2O3 suffers from low conductivity, slow surface kinetic, low carrier diffusion and greater electron-hole combination. The electronic properties such as carrier mobility and diffusion of α-Fe2O3 can be improved through doping, synthesis of composite material or formation of structured films. Recently, 2D-molybdenum disulfide (MoS2) has shown interesting photocatalytic activity due to its bonding, chemical composition, doping and nanoparticles grown on other 2D-film. Recently, our group has studied photoelectrochemical properties of hybrid film of regioregular poly (3-hexylthiophene-2, 5-diyl) (P3HT) with nanodiamond as well as P3HT-MoS2. In the present study, we have studied photoelectrochemical properties of polyhexylthiophene (RRPHTh)-nanodiamond (ND) and α-Fe2O3-MoS2 nanocomposite based electrodes films. The photoelectrochemical properties of α-Fe2O3-MoS2 as n-type and ND-RRPHTh as p-type electrodes in photoelectrochemical cell in various electrodes have been studied. We have obtained 3 to 4 times higher photocurrent and energy conversion efficiencies than the parent electrode based photoelectrochemical cell. We have synthesized nanocomposite α-Fe2O3MoS2 using sol-gel technique. The nanocomposite α-Fe2O3-MoS2 as well as ND-RRPHTh films were characterized using SEM, X-ray diffraction, UV-vis, FTIR and Raman techniques. The electrochemical techniques were used to understand the photocurrent in electrode/electrolyte interface of α-Fe2O3-MoS2 as well as ND-RRPHTh films in both acid base based electrolyte. The α-Fe2O3-MoS2 and ND-RRPHTh electrodes reveal improved production of hydrogen compared to α-Fe2O3 and aluminum doped α-Fe2O3 and MoS2 doped α-Fe2O3 nanostructured films. The band structure has been used to understand the mechanism of photoelectrochemical water splitting in p-n types based photoelectrochemical cell.Thermal degradation of two tung oil based reactive diluents, linseed oil alkyd and different amounts of two reactive diluents having paint formulations were investigated using TGA and DSC under non-isothermal conditions and dynamic nitrogen atmosphere and air. Activation energies were obtanied from Freidman method and Freeman-Carroll method and subsequently the preexponential factor, A, and reaction order,n,for reactive diluents and alkyd were also determined according to general rate equation. From kinetic analysis of the thermal degradation of using TGA, it was founded that thermal degradation of two diluents and alkyd has taken place in one stage but thermal degradation of all paint formulations have taken place in more than two stages. As shown from Freidman method and Freeman-Carroll method, the chemical composition and atmosphere of reactive diluents influenced the thermal degradation. Increasing reactive diluents decreased slightly the thermal stability of linseed oil alkyd.

Electrical and Optical Properties of Indium-Modified SeSbTe Thin Films for Low Power Memory Devices

The electrical and optical characteristics of indium doped Se2Sb2Te6 phase-change alloy are studied. It is found that adding indium to Se2Sb2Te6 alloy (In0.3Se2Sb2Te6) increased the crystallization temperature and reduced the electrical conduction activation energy. The capacitance-temperature measurements showed a drastic change in the capacitance of the modified film when the temperature approaches the crystallization temperature, and eventually the capacitance becomes negative and nonlinear. The negativity and nonlinearity in the capacitancevoltage dependence can be attributed to the growth of conductive crystalline islands by increasing the temperature.