HOMO and LUMO of organic compounds are basic parameters for the design and fabrication of an organic solar cell. This paper presents a technique to obtain HOMO and LUMO of an n-type polymer of [6,6]-phenyl C61-butyric acid 3-ethylthiophene ester (PCBE) and a p-type polymer of poly (3-octyl-thiophene-2, 5-diyl) (P3OT). The energy of band gap for each material has been calculated using optical absorption spectrum. Cyclic Voltammetry was used to estimate the oxidation potential and energy band diagram consequently. The experiments were carried out in a three-electrode cell consisting of a platinum working electrode, a platinum counter electrode and a SCE reference electrode. P3OT showed energy band gap equal to 1.83 eV with HOMO and LUMO equal to 5.59 eV and 3.76 eV, respectively. PCBE showed energy band gap equal to 1.96 eV with HOMO and LUMO equal to 5.87 eV and 3.91 eV, respectively. Based on energy band diagram that was constructed from this experimental result, the couple materials may be successfully used to fabricate the feasible organic solar cells.
There is great interest in gas sensing especially for toxic gases such as carbon monoxide. This paper reports the use of Langmuir-Blodgett films of hematin mixed with arachidic acid to detect carbon monoxide gas in nitrogen at room temperature. The detection was studied based on changes in the optical absorption and reflection of the film using a spectrophotometer and an optical fiber system, respectively. The absorption spectra of a 20 layers LB film decreased when exposed to 10, 100, 1000 ppm CO gas, and had fast recovery time when the gas flow was stopped. An optical fiber system consists of a laser diode as light source, a fiber reflectance probe, thin film sample on a reflecting mirror and a light detector was setup. Using this system it was found that the intensity of the reflected light increased when the film was exposed to the gas. The sensing sensitivity of the films increased after the films were annealed for one hour at 100°C. The result is explained using the atomic force microscope (AFM) images of the LB films taken before and after annealing.
Terdapat minat yang besar terhadap penderiaan gas terutama bagi gas toksik seperti karbon monoksida. Kertas ini melaporkan penggunaan filem Langmuir-Blodgett (LB) hematin bercampur asid arakidik untuk mengesan gas karbon monoksida dalam gas nitrogen pada suhu bilik. Pengesanan dikaji berasaskan perubahan serapan optik dan pantulan filem yang masing-masing menggunakan spektrofotometer dan satu sistem serat optik. Spektrum serapan bagi 20 lapisan filem LB berkurang apabila filem itu didedahkan kepada 10, 100, 1000 ppm gas CO, dan mempunyai masa pulihan yang pantas apabila aliran gas dihentikan. Satu sistem serat optik yang terdiri daripada satu sumber cahaya diod laser, penduga pantulan, sampel filem nipis di atas satu cermin pemantul dan pengesan cahaya telah dibina. Menggunakan sistem ini didapati keamatan cahaya yang terpantul meningkat selepas filem disempuhlindap selama satu jam pada 100°C. Keputusan ini dijelaskan menggunakan imej mikroskop daya atom (AFM) filem LB yang diambil sebelum dan selepas sempuhlindap.
This research explores the possibility of using fluorescence technique to detect the presence of volatile organic compounds based on a single sensing material. The material used was TiO2 nanoparticles coated with porphyrin dye. The TiO2 nanoparticles colloid is in a sol-gel form synthesized from titanium (IV) ethoxide in ethanol with addition of kalium chloride (KCl) as stabilizer. TiO2 nanoparticles were then coated with porphyrin dye, Manganase (III) 5,10,15,20 tetra (4-pyridyl)-21H, 23H porphine chloride tetrakis (metachloride). The coated nanoparticles were deposited on quartz substrate using self-assembly through dip coating technique. The sensing properties of the thin film toward volatile organic compounds; ethanol, acetone, cyclohexane and 2-propanol were studied using luminescence spectrometer. It was found that the thin film produced different emission spectra peaks for different volatile organic compounds (VOCs). Hence, it eases chemical identification process and potentially be use as fluorescence gas sensor.
This paper reports on the detection of several organic vapors using the unique characteristic of localized surface plasmon resonance (LSPR) gold nanoparticles. Gold nanoparticles on quartz substrate were prepared using seed mediated growth method. In a typical process, gold nanoparticles with average size ca. 36 nm were obtained to densely grown on the substrate. Detection of gas was based on the change in the LSPR of the gold nanoparticles film upon the exposure to the gas sample. It was found that gold nanoparticles were sensitive to the presence of volatile organic compound (VOC) gas from the change in the surface plasmon resonance (SPR) intensity. The mechanism for the detection of VOC’s gas will be discussed.
The effect of ZrO2 addition on the microstructure, morphology and pressure sensing behaviour of Pb(ZrxTi1-x)O3 ceramics was studied in five different compositions of ZrO2, namely x = 0.48, 0.50, 0.52, 0.54 and 0.56. The samples were prepared through the solid-state reaction method using high purity metal oxides powders. In order to control the PbO losses due to high temperature sintering, a novel approach were explored whereby the samples were sintered in Al2O3 environment. Structural investigation using X-ray diffraction (XRD) method revealed that all samples exhibited a tetragonal crystal structure. However the c/a lattice parameters ratios exhibited a decreasing trend as the ZrO2 content was increased, indicating that PZT crystals gradually evolved towards pseudocubic structure. SEM micrographs showed different morphology of each composition with the grain size varies in the range of 1.5 μm to 3.15 μm. The performance of pressure sensing behaviour showed that sample with composition x = 0.52 exhibited the best piezoelectric properties with high sensitivity. However, all samples failed to show good stability and repeatability due to slow recovery after severe lattice strain.
The aim of this research was to investigate the ability of organometallic titanium-PANi hybrid materials as gas sensor at room temperature. To form the hybrid materials, commercially available polyaniline (PANi) powder were directly added into organometallic titanium sols which was synthesized using the sol gel method. The composite films were prepared via spin coating technique followed by electrode deposition for sensors fabrication. Five different organometallic titanium:PANi ratios namely 1 wt% to 5 wt% of PANi were prepared for this experiment. For gas sensing test, all samples were exposed to ethanol vapour. The sensing mode is based on the variation in the electrical conductivity due to the
interaction between the gas molecules and the film. It was observed that the composite sensors required appropriate ratio to exhibit optimum sensing properties. This finding proved that the hybridization process is successful and offered much cheaper and easier method for fabrication of room temperature gas sensor.
Kesan gantian Al berkepekatan rendah pada tapak-Zn sebagai lapisan anti-pantulan (LAP) untuk bahan Zn1-xAlxO ke atas pencirian struktur, morfologi dan sifat optik telah dikaji. Sampel Zn1-xAlxO dengan x = 0.00, 0.05, 0.10 and 0.15 telah disintesis dengan menggunakan kaedah sol-gel. Filem yang diperolehi dengan kaedah sol-gel telah disepuh lindap pada 400°C selama 2 jam. Kaedah pembelauan sinar-X (XRD) dan Mikroskop Elektron Imbasan (SEM) digunakan untuk mencirikan struktur dan morfologi filem. Spektrum XRD menunjukkan semua sampel mempunyai struktur heksagonal. Saiz partikel menurun apabila kepekatan Al meningkat. Filem ini mempunyai struktur filem yang padat dan tebal serta berkesan untuk memerangkap cahaya dalam filem nipis sel suria. Sifat optik telah dicirikan dengan menggunakan spektrometer UV-Vis-NIR dan fotoluminesen. Peningkatan nilai jurang tenaga penting sebagai unsur lapisan anti pantulan. Oleh itu, filem ini boleh digunakan sebagai lapisan anti-pantulan untuk sel solar.
This paper reports on structural, optical transmittance and electrical properties of fluorine-doped tin oxide (FTO) thin films deposited using an inkjet printer. The FTO ink was synthesized from a mixture of tin chloride pentahydrate (SnCl4.5H2O) and ammonium fluoride (NH4F) solutions. The thin films were deposited on glass substrates at ambient temperature or heated at 40oC and 60oC. The surface electronic state and the elemental composition of the thin films were analyzed using XPS spectroscopy. The spectra of the FTO thin films revealed that tin, oxygen, fluoride and carbon were present in the samples. The signals corresponding to Sn 3d5/2, O1s, and F1s were found at 486.6 eV, 530.5 eV and 684.5 eV, respectively. XRD analysis showed that the FTO films were in the form of crystalline with cassiterite shape. The optical and electrical properties of the films were affected by the deposition temperatures. It was observed the film deposited at 40oC has the optimum optical transmittance and sheet resistivity which were 91%T and 16 Ω/, respectively.
The influence of PANI additions on methanol sensing properties of ZnO thin films at room temperature had been investigated. Commercial polyaniline powder (PANI) was mixed into 3 mL ZnO solution in five different weight percentages namely 1.25, 2.50, 3.75, 5.00 and 6.25% to obtain ZnO/PANI composite solutions. These solutions were spin coated onto glass substrate to form thin films. Microstructural studies by FESEM indicated that ZnO/PANI films showed porous structures with nanosize grains. The thickness of the film increased from 55 to 256 nm, proportionate to increment of PANI. The presence of 2 adsorption peaks at ~310 nm and ~610 nm in UV-Vis spectrum proved that addition of PANI has modified the adsorption peak of ZnO film. Methanol vapour detection showed that addition of PANI into ZnO dramatically improved the sensing properties of the sensor. The sensors also exhibited good repeatability and reversibility. Sensor with the amount of PANI of 3.75 wt% exhibited the highest sensitivity with response and recovery time was about 10 and 80 s, respectively. The possible sensing mechanism of the sensor was also discussed in this article.
ZnO nanowires have been synthesized using a catalyst-free carbothermal reduction approach on SiO2-coated Si substrates in a flowing nitrogen atmosphere with a mixture of ZnO and graphite as reactants. The collected ZnO nanowires have been characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and photoluminescence spectroscopy. Controlled growth of the ZnO nanowires was achieved by manipulating the reactants heating temperature from 700 to 1000 oC. It was found that the optimum temperature to synthesize high density and long ZnO nanowires was about 800 0C. The possible growth mechanism of ZnO nanowires is also proposed.
This paper reports on the synthesis and characterization of CdTe-CdSe core-shell quantum dots (QDs) with luminescent from 650 to 720 nm. The QDs were synthesized using a wet-chemical process at a moderate temperature (300 °C) following two-steps process of core and shell synthesis. The photoluminescence characterization on the QDs showed that the QDs emitted light in the range of red regime with quantum yield as high as 37%. Owing to their unique photoluminescence characteristics (high quantum yield and narrow spectrum), the QDs may find a potential application in a variety of applications such as LED, solar cell and bio-labeling.
The aim of this project was to investigate the effect of ZnO addition on the structural properties of ZnO-PANi/carbon black thin films. The sol gel method was employed for the preparation of ZnO sol. The sol was dried for 24 h at 100°C and then annealed at 600°C for 5 h. XRD characterization of the ZnO powder showed the formation of wurtzite type ZnO
crystals. The ZnO powder were mixed into PANi/carbon black solution which was dissolved into M-Pyrol, N-Methyl-2-Pyrrolidinone (NMP) to produce a composite solution of ZnO-PANi/carbon black. The weight ratio of ZnO were 4 wt%, 6 wt% and 8 wt%. The composite solutions were deposited onto glass substrates using a spin-coating technique to fabricate
ZnO-PANi/carbon black thin films. AFM characterization showed the decreasing of average roughness from 7.98 nm to 2.23 nm with the increment of ZnO addition in PANi/carbon black films. The thickness of the films also decreased from 59.5 nm to 28.3 nm. FESEM image revealed that ZnO-PANi/carbon black thin films have changed into agglomerated
surface morphology resulting in the increment of porosity of the films.
Identified as potential materials for optoelectronic applications, the polymer/inorganic nanocomposites are actively studied. In this work, the effect of amorphous silica nanoparticles (NPs) content on the optical properties of Poly (9,9’-di-n-octylfluorenyl- 2.7-diyl) (PFO) thin films has been investigated. Different ratios of PFO/SiO2 NPs composites have been prepared using solution blending method. Then, the blends were spin-coated onto glass substrates at 2000 rpm for 30 s and subsequently dried at room temperature. XRD and TEM were used to determine the structural properties, while UV-Vis and PL spectrophotometers were employed to investigate the optical properties of the films. XRD confirms that there was no variation on structure of both PFO and SiO2 NPs resulted from the blending process. TEM micrographs display that majority of amorphous SiO2 NPs were well coated with PFO. The absorption spectra of the composite thin films were red-shifted, indicating the increment in conjugation length of the PFO/SiO2 composite. In addition, the calculated values of the optical energy gap, the width of the energy tails and vibronic spacing of the composite films exhibited SiO2 content dependence.