Both planar GaN substrates and individual GaN nanowires have been functionalized with single-stranded DNA, an important process for use of GaN devices for label-free biosensing. A functional aminopropyltrimethoxysilane layer was deposited on hydroxylated GaN, as confirmed by XPS. A bifunctional glutaraldehyde layer was then coupled to the silane, presenting carbonyl groups for subsequent condensation reaction with amine-terminated, fluorescently labeled DNA. Atomic force and scanning electron microscopy studies indicated the functional layers are smooth, uniformly deposited, and at least 20 nm thick on both the planar surfaces and on individual nanowires. An oxygen plasma treatment was used in conjunction with a silicone mask to pattern the functionalized surfaces and nanowires. DNA remained immobilized on the nanowires following their release into suspension via sonication and dielectrophoretic alignment, demonstrating the potential of this functionalization chemistry for ‘bottom-up’ fabrication and self-assembly of nanowire sensor arrays.

Bilayer consisting of polypyrrole, PPy, as the inner and poly(2,5-dithienyl-( N -3-phosphorylpropyl)pyrrole, p(TPTC3-normalPO3H2) as the outer layers was electropolymerized in layer-by-layer steps. Due to the presence of phosphonic acid functionality tethered to the backbone of outer polymer, the system is capable of binding organic and inorganic bases and offers an easy and conven- ient access to sensor devices. The ion transport through the polypyrrole film depends on its thickness. The thin layer of pTPTC3-PnormalO3normalH2 does not hinder the redox and ion-transport characteristics of the PPy layer.

The extendability of conventional subtractive lithographic processing using spin-coated polymeric single layer resists (SLR) faces many challenges as feature sizes in microelectronics push below 100 nm. In addition, the opacity of the polymeric materials traditionally used as SLR resins to future exposure sources presents new challenges as the radiation penetration depth decreases (e.g. 157 nm, EUVL, low keV e-beam). One solution to these problems is the use of surface imaging materials and processes. In such surface imaging methods, exposure in only a thin surface layer is used to create a pattern in a substantially thicker etch barrier layer. Conventional surface imaging approaches have mainly focused on silylation techniques which have experienced a variety of problems. This paper presents an update on two novel surface imaging methods under investigation: (1) surface monolayer initiated polymerization (SMIP) and (2) organometallic-organic bilayer resists.The SMIP process involves using a monolayer that contains a polymerization initiator functionality. Exposure of the monolayer to radiation can deactivate the initiators in selected areas and the remaining initiators can subsequently be used to directly grow patterned polymer structures. This process allows complete decoupling of the imaging properties of the monolayer from the etch properties of the polymer etch barrier. In essence, the polymerization process is used to amplify the pattern initially formed in the monolayer. Recent results are presented that demonstrate the use of x-ray photoelectron spectroscopy in conjunction with dose array experiments to analyze the sensitivity of the initiators used for this process.The other novel surface imaging method presented in this work uses organometallic-organic bilayers. In these systems, thin films of radiation sensitive organometallic precursors are used as an imaging layer in conjunction with thick organic etch barrier layers. Upon exposure, the organometallic precursor film is selectively converted to metal oxide. After exposure, the unexposed regions of the film can be developed away. Subsequent dry pattern transfer in an oxygen plasma can be used to transfer the pattern defined in the thin oxide layer through the organic etch barrier layer. Organometallic precursor films with sensitivities on the order of 70 μC/cm2 are demonstrated which result in oxide films that possess an etch selectivity of 100:1 with respect to novolac in oxygen plasmas. 500 nm line-space patterns are demonstrated as a first lithographic imaging proof-of-concept.

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An in situ study of the t -butyllithium initiated polymerization of butadiene in d -heptane via small angle neutron scattering and H 1 -NMR Surface monolayer initiated polymerization (SMIP) is a potential method for achieving high resolution patterning of surfaces and materials that could be used as an alternative to conventional lithographic methods based on photoresist thin films. This article reports on the photochemical kinetic rate constants of two candidate azo-type surface bound photoradical initiator molecules. X-ray photoelectron spectroscopy was utilized to monitor the relative concentration of azo initiator on a silicon surface as a function of exposure dose to 248 nm radiation. This photochemical decomposition data showed that the photoreaction for both initiators followed first order kinetics with photoreaction rate constants in the range of 4.5ϫ 10 −3 cm 2 /mJ to 9.7ϫ 10 −3 cm 2 / mJ. The difference in the observed rate constants for the two azo initiators was attributed primarily to differences in their quantum efficiencies. These differences in quantum efficiency were attributed to the size of the nontethered fragment that would be produced from the initiator, with larger fragments producing slower photochemical decomposition kinetics. Thus, photoradical initiators with small non-surface bound fragments are desirable in terms of increasing the photosensitivity of such SMIP processes. For successful positive tone imaging using a SMIP process with photoradical initiators, it was estimated that approximately 99% of the monolayer must be decomposed in order to produce images in the resulting polymer layers. Using this information in conjunction with the photochemical reaction rate constants for the azo initiators, exposure doses on the order of 400 mJ/ cm 2 and larger would be required for the present initiators.