Derrick Wen Hui Fam

Fabrication of Single‐ and Multilayer MoS2 Film‐Based Field‐Effect Transistors for Sensing NO at Room Temperature

Single- and multilayer MoS(2) films are deposited onto Si/SiO(2) using the mechanical exfoliation technique. The films were then used for the fabrication of field-effect transistors (FETs). These FET devices can be used as gas sensors to detect nitrous oxide (NO). Although the single-layer MoS(2) device shows a rapid response after exposure to NO, the current was found to be unstable. The two-, three-, and four-layer MoS(2) devices show both stable and sensitive responses to NO down to a concentration of 0.8 ppm.

Applications of atomic layer deposition in solar cells

Atomic layer deposition (ALD) provides a unique tool for the growth of thin films with excellent conformity and thickness control down to atomic levels. The application of ALD in energy research has received increasing attention in recent years. In this review, the versatility of ALD in solar cells will be discussed. This is specifically focused on the fabrication of nanostructured photoelectrodes, surface passivation, surface sensitization, and band-structure engineering of solar cell materials. Challenges and future directions of ALD in the applications of solar cells are also discussed.

Label-free electronic detection of bio-toxins using aligned carbon nanotubes.

A facile route for sensitive label-free detection of bio-toxins using aligned single walled carbon nanotubes is described. This approach involves patterning of a catalyst on the surface of a quartz substrate using a sub-100 μm stripe-patterned polydimethylsiloxane stamp for aligned carbon nanotube generation followed by fabrication of field effect transistor (FET). Atomic force microscopy, field emission scanning electron microscopy and Raman spectroscopy are employed to characterize the synthesized nanotubes. Unlike previous reports, the adopted approach enables direct electronic detection of bio-toxins with sensitivities comparable to ELISA. As a proof of concept, the fabricated FET responds to nM concentration levels (with a LOD of ∼2 nM) of epsilon toxin produced by Clostridium perfringens and a prominent food toxin. This facile approach could be customized to detect other classes of toxins and biomarkers upon appropriate functionalization of the aligned carbon nanotubes. Finally, we demonstrate the use of the FET-platform for detection of toxin in more complex matrices such as orange juice.

The Extended Growth of Graphene Oxide Flakes Using Ethanol CVD .

We report the extended growth of Graphene Oxide (GO) flakes using atmospheric pressure ethanol Chemical Vapor Deposition (CVD). GO was used to catalyze the deposition of carbon on a substrate in the ethanol CVD with Ar and H2 as carrier gases. Raman, SEM, XPS and AFM characterized the growth to be a reduced GO (RGO) of <5 layers. This newly grown RGO possesses lower defect density with larger and increased distribution of sp(2) domains than chemically reduced RGO. Furthermore this method without optimization reduces the relative standard deviation of electrical conductivity between chips, from 80.5% to 16.5%, enabling RGO to be used in practical electronic devices.

The mechanism of graphene oxide as a growth template for complete reduced graphene oxide coverage on an SiO2 substrate

Reduced Graphene Oxide (rGO) has the distinct advantage of an aqueous and industrial-scalable production route. However large deviation in the electrical resistivity of fabricated rGO devices, caused by inhomogeneous coverage of rGO on the substrate, prevents its practical application in electronic devices. This critical problem could be solved by using an ethanol chemical vapour deposition (CVD) treatment on graphene oxide (GO). With the treatment, not only GO is reduced to rGO, but also rGO preferentially grows outwards from the edges of the existing GO template and enlarge in size until rGO completely covers the substrate. The growth sequence is presented and our results indicate that the growth supports the free radical condensate growth mechanism. After the ethanol CVD treatment, the standard deviation in electrical resistivity decreased significantly by 99.95% (1.60 × 106 to 7.72 × 102 Ω per square) in comparison with hydrazine-reduced rGO substrates. As no carbon signatures on the substrate were observed when no template was used, this work indicates that GO could act as a template for subsequent formation of rGO.

A carbon monoxide gas sensor using oxygen plasma modified carbon nanotubes

Carbon monoxide (CO) is a highly toxic gas that can be commonly found in many places. However, it is not easily detected by human olfaction due to its colorless and odorless nature. Therefore, highly sensitive sensors need to be developed for this purpose. Carbon nanotubes (CNTs) have an immense potential in gas sensing. However, CNT-based gas sensors for sensing CO are seldom reported due to the lack of reactivity between CO and CNTs. In this work, O(2) plasma modified CNT was used to fabricate a CNT gas sensor. The plasma treated CNTs showed selectively towards CO, with the capability of sensing low concentrations of CO (5 ppm) at room temperature, while the pristine CNTs showed no response. UV spectra and oxygen reduction reaction provided evidence that the difference in sensing property was due to the elimination of metallic CNTs and enhancement of the oxygen reduction property.

Horizontally Aligned Carbon Nanotube Based Biosensors for Protein Detection

A novel horizontally aligned single-walled carbon nanotube (CNT) Field Effect Transistor (FET)-based biosensing platform for real-time and sensitive protein detections is proposed. Aligned nanotubes were synthesized on quartz substrate using catalyst contact stamping, surface-guided morphological growth and chemical vapor deposition gas-guided growth methods. Real-time detection of prostate-specific antigen (PSA) using as-prepared FET biosensors was demonstrated. The kinetic measurements of the biosensor revealed that the drain current (Id) decreased exponentially as the concentration of PSA increased, indicating that the proposed FET sensor is capable of quantitative protein detection within a detection window of up to 1 µM. The limit of detection (LOD) achieved by the proposed platform was demonstrated to be 84 pM, which is lower than the clinically relevant level (133 pM) of PSA in blood. Additionally, the reported aligned CNT biosensor is a uniform sensing platform that could be extended to real-time detections of various biomarkers.

Mono-distributed single-walled carbon nanotube channel in field effect transistors (FETs) using electrostatic atomization deposition

This communication reports on the novel work of creating a transistor channel based on functionalized single-walled carbon nanotubes (SWNTs) via electrostatic atomization deposition. The current method of drop-cast though convenient was unable to produce replicable transistor device due to its inherent inability in controlling the volume of liquid being drop-cast. Hence, this method of electrostatic atomization was introduced to consistently obtain a uniformly distributed SWNT channel resulting in a good transistor device.