A. Castaing

Generic epitaxial graphene biosensors for ultrasensitive detection of cancer risk biomarker

A generic electrochemical method of ?bioreceptor? antibody attachment to phenyl amine functionalized graphitic surfaces is demonstrated. Micro-channels of chemically modified multi-layer epitaxial graphene (MLEG) have been used to provide a repeatable and reliable response to nano-molar (nM) concentrations of the cancer risk (oxidative stress) biomarker 8-hydroxydeoxyguanosine (8-OHdG). X-ray photoelectron spectroscopy, Raman spectroscopy are used to characterize the functionalized MLEG. Confocal fluorescence microscopy using fluorescent-labelled antibodies indicates that the anti-8-OHdG antibody selectively binds to the phenyl amine-functionalized MLEG?s channel. Current?voltage measurements on functionalized channels showed repeatable current responses from antibody?biomarker binding events. This technique is scalable, reliable, and capable of providing a rapid, quantitative, label-free assessment of biomarkers at nano-molar (<20 nM) concentrations in analyte solutions. The sensitivity of the sensor device was investigated using varying concentrations of 8-OHdG, with changes in the sensor?s channel resistance observed upon exposure to 8-OHdG. Detection of 8-OHdG concentrations as low as 0.1 ng ml?1 (0.35 nM) has been demonstrated. This is five times more sensitive than reported enzyme linked immunosorbent assay tests (0.5 ng ml?1).

Silicon carbide Schottky diodes and MOSFETs: Solutions to performance problems

Silicon carbide has long been hailed as the successor to silicon in many power electronics applications. Its superior electrical and thermal properties have delivered devices that operate at higher voltages, higher temperatures and with lower on-resistances than silicon devices. However, SiC Schottky diodes are still the only devices commercially available today. Though SiC Schottkys are now being used with silicon IGBTs in dasiahybridpsila inverter modules, the real advantages will be seen when silicon switching devices can be replaced by SiC. This paper describes the current state of SiC diode and MOSFET technology, discussing possible solutions to making these devices commercially viable.

Ellipsometric and MEIS Studies of 4H-SiC/Si/SiO2 and 4H-SiC/SiO2 Interfaces for MOS Devices

The high density of interface states of thermally grown oxides on silicon carbide has prompted research into alternative oxidation methods and post oxidation anneals. One such alternative is oxidation of a deposited sacrificial silicon layer. A recent variation of this technique is a partial oxidation of the deposited Si layer, so that a thin Si layer remains between the SiO2 and SiC layers. If the SiO2/Si interface has lower interface state densities than the SiO2/SiC interface, the SiO2/Si/SiC hetero-structure could yield improved channel mobilities in MOS devices. Moreover, by correct optimization of the MOSFET device structure, breakdown can be designed to occur in the bulk SiC layer, thus maintaining a high blocking voltage. Post oxidation annealing in N2O is another technique often used to reduce interface state densities. However, little is known about the chemical and physical nature of these N2O oxidized dielectrics. Ellipsometric and Medium Energy Ion Scattering (MEIS) investigations of conventional SiO2/SiC interfaces compared with SiO2/Si/SiC hetero-junction structures and N2O oxidized samples are reported.

Detection of monoclonal antibodies using chemically modified graphite substrates

This paper presents a novel sensor device based on chemically modified Highly Ordered Pyrolytic Graphite (HOPG). Biosensor diagnostics based on bio-functionalised semiconductor devices are an important development in ultrasensitive sensors for early detection of disease biomarkers. Electrochemical devices using chemically modified graphite (CMG) channels are excellent candidates for nano-biosensors [1]. By attaching aniline to HOPG, via coupling with an aryl diazonium salt, the amino group of the aniline molecule has been used to graft antibodies - (1) targeted against beta-actin and (2) targeted against 8-hydroxydeoxyguanosine (8-OHdG) - onto the HOPG surface. Antibody attachment to graphitic surfaces has been verified using Laser Scanning Confocal Microscopy (LSCM) to detect attached quantum-dot labeled antibodies. Furthermore, the current-voltage characteristics of virgin and chemically modified HOPG surfaces have been used to detect the presence of antibodies at nM concentrations.

Investigation of Graphene Growth on 4H-SiC

This paper reports the investigation of epitaxial graphene growth on 4H-SiC substrates. Growth has been performed under ultra high vacuum (UHV) conditions at temperatures ranging from 1150 to 1250°C, and the formation of the graphene layer has been monitored using X-ray photoelectron spectroscopy (XPS). A gradient of 100°C in temperature was introduced across the sample in order to grow a wide range of thicknesses along the sample. Atomic force microscopy (AFM) of the surface shows that the epitaxial graphene layer follows the topography of the bulk material and introduces very little surface roughness. This paper also reports the electrical characterisation of the graphene layers.

Investigation of Si/4H-SiC hetero-junction growth and electrical properties

This paper describes the growth and characterisation of Si/SiC heterojunction structures. Heterojunction structures are of interest for low on-resistance diodes and as potential solutions to fabricating SiC MOS devices with lower interface state densities. The formation of the Si/SiC heterojunction using Chemical Vapour Deposition (CVD), Molecular Beam Epitaxy (MBE), Electron Beam Evaporation under UHV conditions (EBE-UHV) and Layer Transfer (LT) are reported. The physical nature of Si/SiC structures has been investigated using scanning electron microscopy (SEM). Results of electrical characterisation of the Si/SiC heterojunctions, are also reported. Finally, thermal oxidation of a Si / SiC heterojunction structures has been performed. The C(V) characteristics of the resulting oxides are compared to conventional thermal oxides on SiC.

Graphene Nano-Biosensors for Detection of Cancer Risk

Biosensor diagnostics based on bio-functionalized semiconductor devices are an important development in ultrasensitive sensors for early detection of disease biomarkers. Electrochemical devices using chemically modified graphene (CMG) channels are excellent candidates for nanobiosensors. This paper presents the development of novel antibody functionalized epitaxial graphene devices for bio-sensing applications. Epitaxial graphene has been grown on silicon carbide (SiC) substrates under high vacuum and high temperature conditions (1200 – 1700°C). A generic electrochemical surface functionalisation chemistry, which can be used to attach a variety of “bio-receptors” to graphitic surfaces, has been developed. The attached bio-receptors are capable of specific and selective interaction with disease biomarkers. When a target biomarker molecule interacts with the “bio-receptor” functionalized surface, the charge density at that surface is affected. This change can be detected as an electrical signal from the biosensor, enabling highly sensitive (nM) detection of biomarker analytes. This paper reports the fabrication of graphene channel sensors for detection of disease biomarkers.

Photochemistry in Electronics

Photochemistry plays a critical role in modern semiconductor electronics, primarily through the use of photoactive polymers or photoresists in the lithographic processes used to fabricate semiconductor devices. Photoactive polymers have been extensively researched in order to develop resists that are chemically robust and that are able to produce sharp, well defined, high resolution features through photolithography. This chapter introduces photolithography and photoresists, and presents review of the photochemistry of some of the more important commercial photoresists. Miniaturisation of semiconductor devices for consumer electronics and sensors now places increasing demands on lithography processes. This has lead to the development of sub-micrometer and now nanometer scale devices. A review of electron beam lithography and other high-resolution lithography techniques concludes this chapter.

Fabrication of ultrasensitive graphene nanobiosensors

The development of miniaturised systems for detection of disease biomarkers, at clinically relevant concentrations in biological samples, is key in the early diagnosis and monitoring of diseases. This paper presents the development of novel antibody functionalized epitaxial graphene devices for bio-sensing applications. Epitaxial graphene has been grown on silicon carbide (SiC) substrates under high vacuum and high temperature conditions (1200 – 1700°C). A generic electrochemical surface functionalisation chemistry, which can be used to attach a variety of “bio-receptors” to graphitic surfaces, has been developed. The attached bio-receptors are capable of specific and selective interaction with disease biomarkers. When a target biomarker molecule interacts with the “bio-receptor” functionalised surface, the charge density at that surface is affected. This change can be detected as an electrical signal from the biosensor, enabling highly sensitive detection of biomarker analytes.

XPS investigation of titanium contact formation to ZnO nanowires

Ti is often used to form an initial Ohmic interface between ZnO and Au due to its low work function, and the TiO2/ZnO heterojunction is also of great importance for many practical applications of nanoparticles. Here, Ti has been controllably deposited onto hydrothermally grown ZnO nanowires and the formation of metal-semiconductor contact has been investigated using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and scanning electron microscopy. XPS results showed that that the Ti initially reacts with surface oxygen species to form TiO2, and further deposition results in the formation of oxides with oxidation state numbers lower than four, and eventually metallic Ti on top of the TiO2. The formation of TiC was also observed. XPS showed that the onset of metallic Ti coincided with a Zn 3p core level shift to lower binding energy, indicating upwards band bending and the formation of a rectifying contact. Annealing caused a near-complete conversion of the metallic Ti to TiO2 and caused the Zn 3p to shift back to its original higher binding energy, resulting in downwards band bending and a more Ohmic contact. PL measurements showed that the optical properties of the nanowires are not affected by the contact formation.