36 research outputs found
Brazing techniques for the fabrication of biocompatible carbon-based electronic devices
Prototype electronic devices have been critical to the discovery and demonstration of the unique properties of new materials, including composites based on carbon nanotubes (CNT) and graphene. However, these devices are not typically constructed with durability or biocompatibility in mind, relying on conductive polymeric adhesives, mechanical clamps or crimps, or solders for electrical connections. In this paper, two key metallization techniques are presented that employ commercially-available brazing alloys to fabricate electronic devices based on diamond and carbonaceous wires. Investigation of the carbon - alloy interfacial interactions was utilized to guide device fabrication. The interplay of both chemical ( adhesive ) and mechanical ( cohesive ) forces at the interface of different forms of carbon was exploited to fabricate either freestanding or substrate-fixed carbonaceous electronic devices. Elemental analysis in conjunction with scanning electron microscopy of the carbon - alloy interface revealed the chemical nature of the Ag alloy bond and the mechanical nature of the Au alloy bond. Electrical characterization revealed the non-rectifying nature of the carbon - Au alloy interconnects. Finally, electronic devices were fabricated, including a Au circuit structure embedded in a polycrystalline diamond substrate
Feasibility Assessment of an Optically Powered Digital Retinal Prosthesis Architecture for Retinal Ganglion Cell Stimulation
Clinical trials previously demonstrated the notable capacity to elicit visual
percepts in blind patients affected with retinal diseases by electrically
stimulating the remaining neurons on the retina. However, these implants
restored very limited visual acuity and required transcutaneous cables
traversing the eyeball, leading to reduced reliability and complex surgery with
high postoperative infection risks. To overcome the limitations imposed by
cables, a retinal implant architecture in which near-infrared illumination
carries both power and data through the pupil to a digital stimulation
controller is presented. A high efficiency multi-junction photovoltaic cell
transduces the optical power to a CMOS stimulator capable of delivering
flexible interleaved sequential stimulation through a diamond microelectrode
array. To demonstrate the capacity to elicit a neural response with this
approach while complying with the optical irradiance limit at the pupil,
fluorescence imaging with a calcium indicator is used on a degenerate rat
retina. The power delivered by the laser at the permissible irradiance of 4
mW/mm2 at 850 nm is shown to be sufficient to both power the stimulator ASIC
and elicit a response in retinal ganglion cells (RGCs), with the ability to
generate of up to 35 000 pulses per second at the average stimulation
threshold. This confirms the feasibility of generating a response in RGCs with
an infrared-powered digital architecture capable of delivering complex
sequential stimulation patterns at high repetition rates, albeit with some
limitations.Comment: 11 pages, 13 figure
Brazing techniques for the fabrication of biocompatible carbon-based electronic devices
Advanced surface texturing for silicon solar cells
The multi-crystalline silicon (me-Si) solar cell is considered to be one of the most
promising cells capable of achieving high efficiency at low cost and high reliability.
Improving solar cells efficiency using low cost materials requires careful design
considerations aiming to minimise the optical and electrical losses. In this work plasma
texturing was employed to reduce optical reflections from silicon surfaces well below
1%.
Plasma texturing is used to form light trapping structures suitable for silicon solar cells.
Several plasma texturing methods are investigated and associated defects are analysed.
Masked as well as mask-less texturing techniques are investigated. Conventional parallel
plate Reactive Ion Elching (RIE), Inductively Coupled Plasma (ICP) and Electron
Cyclotron Resonance (ECR) plasma system are used to compare the plasma induced
defects in silicon. The influence of various plasma etch parameters on plasma induced
defect is investigated. A correlation between the minority carriers lifetime and surface
area increased by texturing is established.
Effective lifetime measurements using Quasi Steady State Photo Conductive (QSSPC)
technique is mainly used to estimate the plasma induced defect in textured silicon
substrates. Sinton lifetime tester is used to measure the effective lifetime of the substrates.
The implied open circuit voltage is calculated from the lifetime data for textured
substrates.
In this work low temperature photoluminescence spectroscopy is also used to analyse the
defect caused by plasma on me-Si substrates. Photoluminescence (PL) data is obtained
using the 514.5 nm line of an Ar⁺ laser as an excitation source. The luminescence is
dispersed with SPEX 1700 spectrometer with a liquid nitrogen cooled Germanium
detector.
Reflectance measurements are performed on textured surfaces usmg a purpose built
integrating sphere attachment of a high accuracy spectrophotometer. Modelling is also
performed using PV-optics software to compare the experimental and theoretical results.
Finally, silicon solar cells are fabricated with measured efficiency around 18% . The
efficiency is estimated from the I-V characteristics data obtained using a calibrated
halogen lamp and a HP semiconductor parameter analyser. Spin-on-dopant source as
well as solid diffusion source is used to form the ewitter junction of the solar cells
fabricated on p-type silicon wafers. Multicrystalline silicon, CZ- silicon and FZ silicon
wafers are used to fabricate solar cells in this thesis. The effect of single and double
layer antireflection coatings on diffused reflections is also investigated
Metallisation of single crystal diamond radiation detectors
Properties such as a large band gap, high thermal conductivity and resistance to radiation damage make diamond an extremely attractive candidate for detectors in next generation particle physics experiments. This paper presents our technique for metallisation of a single crystal diamond grown by chemical vapour deposition (CVD) for use as a radiation detector, suitable for operation in places such as the Large Hadron Collider. The front and back side of the diamond are metalised with aluminium and gold on top of titanium respectively, after which the diamond is mounted and read out via a charge sensitive preamplifier. The device is found to collect charge at an efficiency of 97%