Publications (9)63.93 Total impact
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Article: Hybrid approaches to nanometer-scale patterning: Exploiting tailored intermolecular interactions
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ABSTRACT: In this perspective, we explore hybrid approaches to nanometer-scale patterning, where the precision of molecular self-assembly is combined with the sophistication and fidelity of lithography. Two areas––improving existing lithographic techniques through self-assembly and fabricating chemically patterned surfaces––will be discussed in terms of their advantages, limitations, applications, and future outlook. The creation of such chemical patterns enables new capabilities, including the assembly of biospecific surfaces to be recognized by, and to capture analytes from, complex mixtures. Finally, we speculate on the potential impact and upcoming challenges of these hybrid strategies.Journal of Nanoparticle Research 04/2012; 10(8):1231-1240. · 3.29 Impact Factor -
Article: Fabrication and characterization of rare-earth-doped nanostructures on surfaces.
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ABSTRACT: This article presents a simple and practical means to produce rare-earth-based nanostructures, as well as a combined characterization of structure and optical properties in situ. A nanosphere lithography strategy combined with surface chemistry enables the production of arrays of β-NaYF(4):Yb,Er nanorings inlaid in an octadecyltrichlorosilane matrix. These arrays of nanorings are produced over the entire support, such as a 1 cm(2) glass coverslip. The dimension of nanorings can be varied by changing the deposition conditions. A home-constructed, multifunctional microscope integrating atomic force microscopy, near-field scanning optical microscopy, and far-field optical microscopy and spectroscopy is utilized to characterize the nanostructures. This in situ and combined characterization is important for rare-earth-containing nanomaterials in order to correlate local structure with upconversion photoluminescence. Knowledge gained from the investigation should facilitate materials design and optimization, for instance, in the context of photovoltaic devices and biofluorescent probes.ACS Nano 08/2011; 5(8):6539-45. · 10.77 Impact Factor -
Article: Regulation of local structure and composition of binary disulfide and thiol self-assembled monolayers using nanografting.
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ABSTRACT: Nanografting is used to create spatial confinement, which enables regulation of self-assembly reaction pathways and outcome. The degree and outcome of this regulation is revealed using binary self-assembled monolayers (SAMs) of organothiols and disulfides. In naturally grown systems, these SAMs have more complex morphology when compared with corresponding binary alkanethiol SAMs. Taller molecules form nanodomains of ellipsoidal cap in shape. These domains arrange in various irregular geometries, including 1D worm-like and 2D branches. This observation differs from binary alkanethiol SAMs, where nanodomains are separated and randomly dispersed. During nanografting, more homogeneous morphology was observed compared with naturally grown layers. By varying nanoshaving speed, the nanodomain structure can be regulated from randomly dispersed to more heterogeneous and, finally, to near natural growth. This trend is very similar to mixed alkanethiol systems, where the domain size and separation increase with increasing speed. Different from the alkanethiol systems, the observed structural variations are due to the changes in surface composition, in addition to domain size, shape, and arrangement.ACS Nano 10/2010; 4(11):6863-73. · 10.77 Impact Factor -
Article: Hybrid strategies in nanolithography
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ABSTRACT: Hybrid nanoscale patterning strategies combine the registration and addressability of conventional lithographic techniques with the chemical and physical functionality enabled by intermolecular, electrostatic and/or biological interactions. This review aims to highlight and to provide a comprehensive description of recent developments in hybrid nanoscale patterning strategies that enhance existing lithographic techniques or can be used to fabricate functional chemical patterns that interact with their environment. These functional structures create new capabilities, such as the fabrication of physicochemical surfaces that can recognize and capture analytes from complex liquid or gaseous mixtures. The nanolithographic techniques we describe can be classified into three general areas: traditional lithography, soft lithography and scanning-probe lithography. The strengths and limitations of each hybrid patterning technique will be discussed, along with the current and potential applications of the resulting patterned, functional surfaces.Reports on Progress in Physics 01/2010; 73(3):036501. · 14.72 Impact Factor -
Article: Scanning electron microscopy of nanoscale chemical patterns.
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ABSTRACT: A series of nanoscale chemical patterning methods based on soft and hybrid nanolithographies have been characterized using scanning electron microscopy with corroborating evidence from scanning tunneling microscopy and lateral force microscopy. We demonstrate and discuss the unique advantages of the scanning electron microscope as an analytical tool to image chemical patterns of molecules highly diluted within a host self-assembled monolayer and to distinguish regions of differential mass coverage in patterned self-assembled monolayers. We show that the relative contrast of self-assembled monolayer patterns in scanning electron micrographs depends on the operating primary electron beam voltage, monolayer composition, and monolayer order, suggesting that secondary electron emission and scattering can be used to elucidate chemical patterns.ACS Nano 11/2007; 1(3):191-201. · 10.77 Impact Factor -
Article: 1-Adamantanethiolate monolayer displacement kinetics follow a universal form.
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ABSTRACT: Alkanethiol molecules in solution displace 1-adamantanethiolate self-assembled monolayers on Au{111}, ultimately leading to complete molecular exchange. Specifically, here, fast insertion of n-dodecanethiolate at defects in the original 1-adamantanethiolate monolayer nucleates an island growth phase, which is followed by slow ordering of the n-dodecanethiolate domains into a denser and more crystalline form. Langmuir-based kinetics, which describe alkanethiolate adsorption on bare Au{111}, fail to model this displacement reaction. Instead, a Johnson-Mehl-Avrami-Kolmogorov model of perimeter-dependent island growth yields good agreement with kinetic data obtained by Fourier transform infrared spectrometry over 100-fold variation in n-dodecanethiol concentration. Rescaling the growth rate at each concentration collapses all the data onto a single universal curve, suggesting that displacement is a scale-free process. The rate of displacement varies as the square-root of the n-dodecanethiol concentration across the 0.01-1.0 mM range studied.Journal of the American Chemical Society 10/2007; 129(35):10741-6. · 9.91 Impact Factor -
Article: Origins of Displacement in 1-Adamantanethiolate Self-Assembled Monolayers
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ABSTRACT: We have investigated the origins of the susceptibility of 1-adamantanethiolate self-assembled monolayers on Au{111} to displacement by other thiol molecules. Using scanning tunneling microscopy, X-ray photoelectron spectroscopy, and electrochemical desportion experiments to probe separated self-assembled monolayers on Au{111} created by the displacement of 1-adamantanethiolate with n-dodecanethiolate, we have shown that there is no difference between the chemical environments at the Au{111} surface for single-component or separated self-assembled monolayers of each molecule. There are, however, differences in interaction strengths between the 1-adamantanethiolate molecules and the n-dodecanethiolate molecules that contribute to 1-adamantanethiolate displacement.04/2007; -
Article: Dynamics of Solution Displacement in 1-Adamantanethiolate Self-Assembled Monolayers
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ABSTRACT: We have investigated the dynamics of solution-phase displacement of preformed 1-adamantanethiolate self-assembled monolayers on Au{111} by n-dodecanethiol molecules on both the ensemble (millimeter) and molecular (nanometer) scales. Employing scanning tunneling microscopy, Fourier-transform infrared spectroscopy, and cyclic voltammetry, we have observed complete displacement of the preformed 1-adamantanethiolate self-assembled monolayers by n-dodecanethiol molecules via nucleation and growth. We have established and evaluated the experimental parameters that influence 1-adamantanethiolate self-assembled monolayer displacement. With established parameters, the resolution and reproducibility of chemically patterned surfaces, applicable in areas ranging from microelectronics to biocompatible systems, have been improved to fabricate and to control structures at the supramolecular 1−100 nm scale.04/2007; -
Article: Directed assembly and separation of self-assembled monolayers via electrochemical processing.
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ABSTRACT: Separated domains of 1-dodecanethiolate were fabricated via solution displacement of preformed 1-adamantanethiolate self-assembled monolayers on Au{111}. Subsequently, the 1-adamantanethiolate domains were desorbed selectively, and the substrate was exposed to a 1-octanethiol solution, creating artificially separated self-assembled monolayers of 1-dodecanethiolate and 1-octanethiolate. The molecular order of each lattice type and the apparent height differences imaged with scanning tunneling microscopy and the two distinct cathodic peaks observed with cyclic voltammetry indicated distinct separated domains of each lattice type in the separated self-assembled monolayers. By manipulating the intermolecular interaction strengths of the patterned molecules, we are able to control the structure and properties of the separated self-assembled monolayers via the exploitation of competitive adsorption and the utilization of electrochemical processing, which can be extended to other self-assembly patterning techniques such as microdisplacement printing.The Journal of Physical Chemistry B 08/2006; 110(29):14410-7. · 3.70 Impact Factor
Top co-authors
Top Journals
Institutions
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2011
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University of California, Davis
- Department of Chemistry
Davis, CA, USA
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2006–2010
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Pennsylvania State University
- Department of Chemistry
University Park, MD, USA
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