Mikrajuddin Abdullah

Preparation of functional nanostructured particles by spray drying

Abstract When particle dimensions are reduced to the order of several nanometers, their physical and chemical properties deviate significantly from the bulk properties of such materials. Because of this, there is abundant potential for their use in future technologies including electronic and optoelectronic, mechanical, chemical, cosmetic, medical, drug, and food technologies. However, due to their extremely small sizes, the particles suffer from many problems related to their surface and thermal stability, shape preservation, handling, assembly in devices, etc. It is therefore an important challenge to solve these problems by developing slightly larger particles (e. g. on the submicrometer scale) in which the properties generated by the nanoscale material are preserved. One approach to this is to trap nanoparticles in a micrometer-sized inert matrix. This approach allows the nanoscale properties to be retained, since nanoparticles are separated from each other in the inert matrix. The inert matrix also serves as a coating medium that inhibits any chemical changes to the surface of the nanoparticles. Their larger size allows easy handling or assembly in devices. A promising method for designing and fabricating these composite structures is a spray method, in which spherical particles can be produced. In this paper, we review the nanostructural processing (synthesis) of submicrometersized particles by a spray method, which provides a restricted reaction environment (such as pores or cages) in the matrix for their synthesis and handling. The characterization and potential applications of these composites are also discussed.

Preparation of high coercivity magnetic FePt nanoparticles by liquid process

FePt nanoparticles have been synthesized using a liquid process, by mixing two precursor liquids: ferric acetyl ferric acetyl acetonate, Fe(acac)3, and platinum acetyl acetonate, Pt(acac)2 in polyol solution of sodium hydroxide at high temperatures. To avoid the agglomeration of the produced particle, aminoethoxy ethanol has been used. The particle size was monodisperse and non- agglomerating. The fraction of Fe in FexPt(100−x) was a linear function of Fe(acac)3 molar fraction. The highest room temperature coercivity (up to 10 kOe) was observed in Fe53Pt47 sample after annealed at 580 °C, which also exhibited the most ordered fct structure.

Electrical conduction of anisotropic conductive adhesives: effect of size distribution of conducting filler particles

Abstract The force–resistance relationship is investigated by considering for the first time the effect of size distribution of metallic filler particles in anisotropic conductive adhesives. It is shown, for both the elastic and plastic interactions between the metallic particle and the conducting plate, that the relationships between the applied force ( F ) and the resistance can be described as power–laws (i.e. ∝ F − n ). The universal power–law relationships are found to be independent of both the mean particle size and the standard deviation of the particle size distribution. However, the exponent constant n is much larger for a non-monosized filler particle distribution than that for a monosized one. Although the power–law relationships are independent of the standard deviation of the particle size distribution and the mean particle size, a large standard deviation of particle size distribution leads to a large resistance. The theoretical prediction of the power–law relationship is found to be supported by available experimental observations.

Optical band gap and ultralow dielectric constant materials prepared by a simple dip coating process

A simple procedure for producing silica films containing ordered porous silica films, with pore sizes in the range of 40–1000 nm, is described. The precursors were prepared by mixing polystyrene latex (PSL) colloidal spheres and silica nanoparticles. The precursors were dipped vertically onto a silicon wafer or glass substrate and the PSL particles were then completely removed at a temperature of approximately 400 °C. This method permits the pore size to be selected by appropriate adjusting of the size of the PSL particles. The presence of an optical band gap, which is dependent on the dielectric constant periodicity of the material, was clearly observed. A simple medium effective model to calculate the effective refraction index of the film combined with a Bragg diffraction equation exhibit calculation results in agreement with the measured data. The film produced using this procedure has a dielectric constant as low as 1.192, thus confirming that the proposed method has also the potential for producing ...

Direct preparation of nonagglomerated indium tin oxide nanoparticles using various spray pyrolysis methods

Indium tin oxide particles were prepared using three different spray synthetic techniques: conventional, salt-assisted, and low pressure. Optimum conditions for the preparation of small size, nonagglomerated particles were investigated for these three methods. The use of the conventional spray pyrolysis method resulted in only larger particles (submicrometer order). Salt-assisted spray pyrolysis (SASP) and low-pressure spray pyrolysis (LPSP) produced highly crystalline, dense, homogeneous, and nearly nonagglomerated nanoparticles that were less than 25 nm in size. The size of the particles was in the range 12-24 nm for the SASP method and 8-14 nm for the LPSP method. In addition, the LPSP method led to the production of single nanometer-size multicomponent particles in a single step with less heating time without the need for any post heat treatment and additives.

Silica Films Containing Ordered Pores Prepared by Dip Coating of Silica Nanoparticles and Polystyrene Beads Colloidal Mixture

Silica films containing three dimensionally (3D) ordered pores were prepared by a simple dip coating method. A colloidal sol containing silica particles in the nanometer size range and a polystyrene latex (PSL) colloidal sol containing particles of tens of nanometers to one micrometer in size were used as precursors. The pore periodicity, which in turn produces the dielectric periodicity, can be easily altered by changing the size of the PSL beads. Films having a high surface smoothness were obtained by using small silica particles, large PSL particles, and a low withdrawal speed in the dip-coating. When the films were irradiated with a white light source, the reflective spectrum was changed by varying the incident angle, indicating its possible use as a monochromator. The change in the reflective spectrum was explained using effective medium approximation combined with a simple Bragg reflection equation.

Home‐made PIC 16F877 microcontroller‐based temperature control system for learning automatic control

A closed‐loop temperature control system, which is composed of a thermal plant and a controller, has been developed to support undergraduate students in learning automatic control delivered in the Special Topics in Instrumentation Physics course. The thermal plant was made from a plastic box covering a lamp and a fan, which heats and drains the air in the plastic box, respectively, as well as a temperature sensor. The controller with a proportional control action was realized by employing the PIC 16F877 microcontroller. The control signal updates pulse‐width modulators (PWMs) in which driver circuits turn on or off the lamp and the fan. A mathematical model of the closed‐loop control system was derived and a theoretical transient response was then obtained. It is found that the experimental transient responses were always much lower than the set point and the steady‐state errors were high for the proportional sensitivity (KP) lower than 10. For KP higher than 10, the transient responses tend to approach the set point to cause small steady‐state errors. These characteristics are consistent with the theoretical transient response. Further examination revealed that the closed‐loop system is a higher order system due to the action of the PWMs and the driver circuits.

Model of a tunneling current in an anisotropic Si/Si1−xGex/Si heterostructure with a nanometer-thick barrier including the effect of parallel–perpendicular kinetic energy coupling

A theoretical model of an electron tunneling current in an anisotropic Si/Si1−xGex/Si heterostructure was developed. The parallel and perpendicular kinetic energies were coupled and the coupling was included in expressing the electron transmittance through the anisotropic heterostructure. The model was applied to the anisotropic Si(1 1 0)/Si0.5Ge0.5/Si(1 1 0) heterostructure with a 25 nm thick strained Si0.5Ge0.5 potential barrier, in which each layer of the heterostructure has three valleys (valleys 1, 2 and 3) with different inverse effective mass tensors and a conduction band discontinuity of 216 meV. The Si(1 1 0)/SiGe structure implies that only the four equivalent valleys (valleys 1 and 2) are considered in calculations. It was found that the transmittance for valley 1 is the same as that for valley 2 due to the same barrier height. The transmittance decreases as the electron phase velocity increases because the electron phase velocity enhances the barrier height. Moreover, the total tunneling current density for the phase velocity higher than 3 × 105 m s−1 differs significantly from that obtained without including the kinetic energy coupling. As the electron phase velocity gets higher, the total tunneling current density lowers. This implies that the coupling effect cannot be ignored for electrons with high phase velocity.

A simple spectrophotometer using common materials and a digital camera

A simple spectrophotometer was designed using cardboard, a DVD, a pocket digital camera, a tripod and a computer. The DVD was used as a diffraction grating and the camera as a light sensor. The spectrophotometer was calibrated using a reference light prior to use. The spectrophotometer was capable of measuring optical wavelengths with a theoretical accuracy as high as 0.2 nm. Using this spectrophotometer, wavelengths are determined via image processing.

A new architecture for solar cells involving a metal bridge deposited between active TiO2 particles

The efficiency of titanium dioxide (TiO2)-based film solar cells fabricated by combined spray and electroplating methods was improved by forming metal bridges in the pores between TiO2 nanoparticles. The interfaces between TiO2 nanoparticles and metal bridges formed Schottky contacts, which minimized recombination of electron-hole pairs and increased electron transfer. A maximum efficiency of 4.38% was achieved for cells plated at 50 mA and 55 °C. This efficiency is higher than that reported for solar cells with a similar structure [Saehana et al., AIP Conf. Proc. 1284, 154 (2010); 1415, 163 (2011); IJBAS/IJENS 11, 15 (2011)]. We also identified that both current and temperature influence the morphology of the metal bridges and efficiency of the solar cell.