PubMed Health⌕ Search

Biomedical subjects

David S Ginger

Publications and source records attributed to David S Ginger.

9 recordsLinked to original sources
PubMed2006

Nucleating pattern formation in spin-coated polymer blend films with nanoscale surface templates.

We use Dip-Pen Nanolithography (DPN) to generate monolayer surface templates for guiding pattern formation in spin-coated polymer blend films. We study template-directed pattern formation in blends of polystyrene/poly(2-vinylpyridine) (PS/P2VP) as well as blends of PS and the semiconducting conjugated polymer poly(3-hexylthiophene) (P3HT). We show that acid-terminated monolayers can be used to template pattern formation in PS/P3HT blends, while hydrophobic monolayers can be used to template pattern formation in PS/P2VP blends. In both blends, the polymer patterns comprise laterally-phase separated regions surrounded by vertically separated bilayers. We hypothesize that the observed patterns are formed by template-induced dewetting of the bottom layer of a polymer bilayer during the spin-coating process. We compare the effects of template feature size and spacing on the resulting polymer patterns with predictions from published models of template-directed dewetting in thin films and find the data in good agreement. For both blends we observe that a minimum feature size is required to nucleate dewetting/phase separation. We find this minimum template diameter to be approximately 180 nm in 50/50 PS/P2VP blends, and approximately 100 nm in 50/50 PS/P3HT blends. For larger template diameters, PS/P2VP blends show evidence for pattern formation beginning at the template boundaries, while PS/P3HT blends rupture randomly across the template features.

Coated Materials, Biocompatible↗
PubMed2006

Time-resolved electrostatic force microscopy of polymer solar cells.

Blends of conjugated polymers with fullerenes, polymers, or nanocrystals make promising materials for low-cost photovoltaic applications. Different processing conditions affect the efficiencies of these solar cells by creating a variety of nanostructured morphologies, however, the relationship between film structure and device efficiency is not fully understood. We introduce time-resolved electrostatic force microscopy (EFM) as a means to measure photoexcited charge in polymer films with a resolution of 100 nm and 100 micros. These EFM measurements correlate well with the external quantum efficiencies measured for a series of polymer photodiodes, providing a direct link between local morphology, local optoelectronic properties and device performance. The data show that the domain centres account for the majority of the photoinduced charge collected in polyfluorene blend devices. These results underscore the importance of controlling not only the length scale of phase separation, but also the composition of the domains when optimizing nanostructured solar cells.

Journal Article↗
PubMed2006

Efficient CdSe/CdS quantum dot light-emitting diodes using a thermally polymerized hole transport layer.

We report multilayer nanocrystal quantum dot light-emitting diodes (QD-LEDs) fabricated by spin-coating a monolayer of colloidal CdSe/CdS nanocrystals on top of thermally polymerized solvent-resistant hole-transport layers (HTLs). We obtain high-quality QD layers of controlled thickness (down to submonolayer) simply by spin-coating QD solutions directly onto the HTL. The resulting QD-LEDs exhibit narrow ( approximately 30 nm, fwhm) electroluminescence from the QDs with virtually no emission from the organic matrix at any voltage. Using multiple spin-on HTLs improves the external quantum efficiency of the QD-LEDs to approximately 0.8% at a brightness of 100 cd/m(2) (with a maximum brightness over 1,000 cd/m(2)). We conclude that QD-LEDs could be made more efficient by further optimization of the organic semiconductors.

Journal Article↗
PubMed2006

DPN-generated nanostructures as positive resists for preparing lithographic masters or hole arrays.

Experiments that utilize structures generated by dip-pen nanolithography (DPN) as positive resists for fabricating nanohole arrays and lithographic masters are described. The technique takes advantage of the difference in desorption potentials for patterned structures made from 16-mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT), respectively. In this approach, patterns of MHA on gold are generated by DPN, and surrounding areas are passivated by ODT. Electrochemistry is used to selectively remove the MHA nanofeatures made by DPN. The exposed gold can be used as an electrode to plate silver from solution, generating raised features and structures that can be transferred to PDMS to make a lithographic master, or alternatively, they can be etched to make arrays of nanoholes.

Electric Conductivity↗
PubMed2005

Patterning phase separation in polymer films with dip-pen nanolithography.

We report a rapid-prototyping method for controlling nanoscale phase separation and pattern formation in conjugated polymer blend films using Dip-Pen Nanolithography (DPN). We use DPN to generate patterned alkylthiol monolayers with feature sizes down to 50 nm on gold surfaces and show how such patterns can nucleate the formation of lateral domains in blends of poly-3-hexylthiophene (P3HT) and polystyrene (PS) cast from solution. We show that this process can be used to probe phase nucleation at heterogeneous surface sites ranging in size from 50 to 750 nm, and that polymer features smaller than 150 nm in diameter can be achieved. We anticipate this method will be useful for studying polymer film responses to nanoscale surface fluctuations as well as for correlating nanoscale phase separation with optoelectronic processes in organic films used in light-emitting diode and photovoltaic devices.

Journal Article↗
PubMed2004

The evolution of dip-pen nanolithography.

The ability to tailor the chemical composition and structure of a surface on the 1-100 nm length scale is important to researchers studying topics ranging from electronic conduction, to catalysis, to biological recognition in nanoscale systems. Dip-pen nanolithography (DPN) is a new scanning-probe based direct-write tool for generating such surface-patterned chemical functionality on the sub-100 nm length-scale, and it is a technique that is accessible to any researcher who can use an atomic force microscope. This article introduces DPN and reviews the rapid growth of the field of DPN-related research over the past few years. Topics covered range from the development of new classes of DPN-compatible chemistry, to experimental and theoretical advances in the understanding of the processes controlling tip-substrate ink transport, to the implementation of micro-electro-mechanical system (MEMS) based strategies for parallel DPN applications.

Nanotechnology↗