S. Ahmad

Outdoor thermal comfort of two public squares in temperate and dry region of Esfahan, Iran

This paper presents a study on outdoor thermal comfort in a temperate and dry climate based on a field survey conducted in Esfahan, Iran. Studies on outdoor thermal comfort have mostly concentrated on street canyons and few on public squares. This study utilized ASHRAEs Thermal Sensation Vote (TSV) to assess peoples acceptance of the outdoor thermal comfort conditions with a data recording technique and observing thermal adaptation behavior of the people at two public squares in the heritage areas of the city. The fieldwork was a short-term survey during an extreme period of cold winter. The study was performed for a full week at each square in December 2009 and January 2010. Air temperature, RH, wind speed and solar radiation were measured. The preliminary results revealed that people visiting the squares in cold season mostly felt comfortable with the air temperature and sunlight. They prefered a higher humidity condition and a little more wind. Areas in the squares with water elements seemed to have attracted more people with majority of the respondents satisfied with the outdoor thermal condition resulting in higher percentage of TSVs within the three central categories. People seemed to prefer a square that offers longer episodes of sun-exposed periods and higher air movement in the winter.

Current crowding effect in lateral and vertical LED configurations: 3D simulation and characterisation

Current crowding is one of the major issue that impedes the development of the efficient GaN-based high power light emitting diode (LED). Generally, there are two types of LED configurations, namely lateral configuration and vertical configuration needed to be experimentally fabricated to study the effects of current crowding on LED electrical and optical performance. In order to minimize the cost and time required to examine the full effect of the current crowding problem inside the devices, an identical free standing active LED layers with same contact size, material and thickness for both configurations are simulated by using ISE TCAD. In this work, we found that vertical LED configuration exhibits better electrical and optical performance by 20% and 21% respectively as compared to the lateral LED. The vertical configuration exhibits a better performance due to reduced series resistance, improved current spreading and better hear dissipation.

Effect of RF Power on the Formation and Morphology Evolution of ZnO Nanostructured Thin Films

The effect of RF power on the formation and morphology evolution of ZnO nanostructured thin films deposited by magnetron sputtering are presented. This project focused on electrical, optical and structural properties of ZnO thin films. The effect of variation of RF power at 50 watt-250 watt at 200 °C on glass substrate of the ZnO thin films was investigated. The thin films were examined for electrical properties and optical properties using two point probe current-voltage (I-V) measurement (Keithley 2400) and UV-Vis-NIR spectrophotometer (JASCO 670) respectively. The structural properties were characterized using field emission scanning electron microscope (FESEM) (JEOL JSM 7600F) and atomic force microscope (AFM) (Park System XE-100). The IV measurement indicated that at RF power 200 watt the conductivity of ZnO thin film show the highest. All films show high UV absorption properties using UV-VIS spectrophotometer (JASCO 670). The root means square (rms) roughness for ZnO thin film were about 4 nm measured using AFM. The image form FESEM observed that transformation of structure size started to change as the RF power increase.

High Sensitivity Humidity Sensor Based on ZnSnO3 Composite Nanocube

The performance of nanocomposites semiconducting material used as a sensor is very much depending upon physical and chemical properties of the material. In this paper we address sensitivity of ZnSnO3 thin film deposited by hydrothermal deposition in terms of its behavior towards humidity variations. The electrical, optical and structural properties of ZnSnO3 thin film deposit at different volume of solvent (50 ml and 70 ml) grown by novel deposition of ZnSnO3hydrothermal with low temperature 95°C are also reviewed. The sensor performance of ZnSnO3 thin film prepared at 50 ml volume show high sensitivity towards humidity. Using FESEM it was noted that the nanocube of ZnSnO3 thin films growth on ZnO template with the size of nanocube is 100 to 140nm by varying the volume of the solvent.

Performance of oil palm EFB fibre reinforced concrete roof slates

Natural fibres such as wood and vegetable fibre offer many advantages such as renewability, recyclability low specific gravity and high specific strength. In Malaysia most of the studies only focused on producing EFB as MDF and pulp and paper products. This paper reviews the development of natural fibres for building material and discusses the performance of oil palm empty fruit bunch (EFB) reinforced concrete roof slates produced in a preliminary experiment. Oil palm EFBs were used partially as cement replacement at levels of 0.5% and 1.0% and compared with the control specimens (0% fibre content). From the preliminary experiment, the physical properties of EFB roof slates were evaluated. Results show flexural strength and density decreased with increased fibre contents that were mixed with various water cement ratio. However, the results still exceeded the level set by the ASTM of 4 N/mm2. The preliminary results from the experiment suggest that oil palm EFBs have a potential to be a material component of reinforced mortar roofing slates with the appropriate water cement ratio and concrete mix.

Effects of Oxygen Flow Rate on Nanostructured ZnO Thin Films

Zinc Oxide (ZnO) thin films were deposited on thermally oxidized SiO2 by varying the oxygen flow rate. The deposition process were done using radio frequency (RF) magnetron sputtering at various oxygen flow rate ranging from 0 to 40 sccm. The surface morphology and crystallinity were analyzed by field emission scanning electron microscopy (FESEM) and X-Ray Diffractometer (XRD) respectively. The average thickness and deposition rate decreases with an increase of oxygen content. The grain size was measured by FESEM and it was found that it is also decreasing with the increased of oxygen flow rate. The films grown with 10 sccm oxygen shows the highest (002) peak however it is expected that the sample deposited with 40 sccm oxygen exhibit the highest sensitivity toward NH3 gas due to the highest surface to volume ratio.

Zinc Oxide Buffer Layer Insertion for Sensitivity Improvement in Aluminium-Doped Zinc Oxide-Based Humidity Sensors

The improvement of sensitivity toward humidity by insertion of buffer layer has been investigated. The insertion of hetero- or homo-buffer layer of zinc oxide (ZnO) thin film before deposition of high quality ZnO had been reported for the growth on highly mismatched substrate. Three samples are characterized with different properties which are as deposited ZnO thin film without buffer layer (as deposited ZnO thin film) , anneal ZnO thin film without buffer layer (ZnO thin film) and anneal ZnO thin film with buffer layer (ZnO/ AZO thin film). The structural properties of ZnO thin film has been characterized field emission scanning electron microscopy (FESEM) JEOL JSM 6701F, atomic force microscope AFM (Park System XE-100) and XRD (Rigaku Ultima IV). The electrical and optical properties has been characterized using 2 point probe I-V measurement (Keithley 2400) and UV-Vis spectrophotometer (JASCO 670) respectively. In this work, we have focused on investigating the humidity sensitivity of ZnO thin film deposited using RF magnetron sputtering (SNTEK RSP 5004-PVD) with and without the buffer layer (Aluminum-doped ZnO (AZO)) for humidity sensor application.

Humidity Sensor Using CVD Deposited SnO2 Thin Film

In this paper we address sensitivity of SnO2 thin film deposited by thermal chemical vapor deposition in terms of its behavior towards humidity variations. The structural, optical and electrical properties of SnO2 thin film deposit at different substrate temperature grown by thermal chemical vapor deposition (CVD) are also reviewed. FESEM image reveal smallest particle size of SnO2 at substrate temperature 500°C. Pl measurement shows red shift of SnO2 at substrate temperature 500°C. All thin film performing slightly linear sensitivities towards relative humidity (RH%).