Showing papers by "Keith A. Brown published in 2016"

Giant conductivity switching of LaAlO3/SrTiO3 heterointerfaces governed by surface protonation.

Abstract: Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures. Despite intense interest, many basic questions remain about the mechanisms that give rise to interfacial conductivity and the role of surface chemistry in dictating these properties. Here we demonstrate a fully reversible >4 order of magnitude conductance change at LaAlO3/SrTiO3 (LAO/STO) interfaces, regulated by LAO surface protonation. Nominally conductive interfaces are rendered insulating by solvent immersion, which deprotonates the hydroxylated LAO surface; interface conductivity is restored by exposure to light, which induces reprotonation via photocatalytic oxidation of adsorbed water. The proposed mechanisms are supported by a coordinated series of electrical measurements, optical/solvent exposures, and X-ray photoelectron spectroscopy. This intimate connection between LAO surface chemistry and LAO/STO interface physics bears far-reaching implications for reconfigurable oxide nanoelectronics and raises the possibility of novel applications in which electronic properties of these materials can be locally tuned using synthetic chemistry.

Modulating the Bond Strength of DNA–Nanoparticle Superlattices

Abstract: A method is introduced for modulating the bond strength in DNA–programmable nanoparticle (NP) superlattice crystals. This method utilizes noncovalent interactions between a family of [Ru(dipyrido[2,3-a:3′,2′-c]phenazine)(N–N)2]2+-based small molecule intercalators and DNA duplexes to postsynthetically modify DNA–NP superlattices. This dramatically increases the strength of the DNA bonds that hold the nanoparticles together, thereby making the superlattices more resistant to thermal degradation. In this work, we systematically investigate the relationship between the structure of the intercalator and its binding affinity for DNA duplexes and determine how this translates to the increased thermal stability of the intercalated superlattices. We find that intercalator charge and steric profile serve as handles that give us a wide range of tunability and control over DNA–NP bond strength, with the resulting crystal lattices retaining their structure at temperatures more than 50 °C above what nonintercalated st...

Hard Transparent Arrays for Polymer Pen Lithography.

Abstract: Patterning nanoscale features across macroscopic areas is challenging due to the vast range of length scales that must be addressed. With polymer pen lithography, arrays of thousands of elastomeric pyramidal pens can be used to write features across centimeter-scales, but deformation of the soft pens limits resolution and minimum feature pitch, especially with polymeric inks. Here, we show that by coating polymer pen arrays with a ∼175 nm silica layer, the resulting hard transparent arrays exhibit a force-independent contact area that improves their patterning capability by reducing the minimum feature size (∼40 nm), minimum feature pitch (<200 nm for polymers), and pen to pen variation. With these new arrays, patterns with as many as 5.9 billion features in a 14.5 cm2 area were written using a four hundred thousand pyramid pen array. Furthermore, a new method is demonstrated for patterning macroscopic feature size gradients that vary in feature diameter by a factor of 4. Ultimately, this form of polymer ...

The Significance of Multivalent Bonding Motifs and "Bond Order" in DNA-Directed Nanoparticle Crystallization.

Abstract: Multivalent oligonucleotide-based bonding elements have been synthesized and studied for the assembly and crystallization of gold nanoparticles. Through the use of organic branching points, divalent and trivalent DNA linkers were readily incorporated into the oligonucleotide shells that define DNA-nanoparticles and compared to monovalent linker systems. These multivalent bonding motifs enable the change of “bond strength” between particles and therefore modulate the effective “bond order.” In addition, the improved accessibility of strands between neighboring particles, either due to multivalency or modifications to increase strand flexibility, gives rise to superlattices with less strain in the crystallites compared to traditional designs. Furthermore, the increased availability and number of binding modes also provide a new variable that allows previously unobserved crystal structures to be synthesized, as evidenced by the formation of a thorium phosphide superlattice.

Critical Undercooling in DNA-Mediated Nanoparticle Crystallization.

Abstract: The nucleation of DNA-functionalized nanoparticle superlattices is observed to exhibit a temperature hysteresis between melting (superlattice dissociation) and freezing (particle association) transitions that allows for the study of nucleation thermodynamics. Through detailed study of the assembly of these particles, which can be considered programmable atom equivalents (PAEs), we identify this hysteresis as critical undercooling—a phase transition phenomenon related to a thermodynamic barrier to nucleation. The separable nature of the DNA bonding elements and nanoparticle core enables the PAE platform to pose unique questions about the microscopic dependencies of critical undercooling and, ultimately, to control the nucleation pathway. Specifically, we find that the undercooling required to initiate nucleation increases as the nanoparticle coordination number increases (number of particles to which a single particle can bind).

Liquid-Phase Beam Pen Lithography.

Abstract: Beam pen lithography (BPL) in the liquid phase is evaluated. The effect of tip-substrate gap and aperture size on patterning performance is systematically investigated. As a proof-of-concept experiment, nanoarrays of nucleotides are synthesized using BPL in an organic medium, pointing toward the potential of using liquid phase BPL to perform localized photochemical reactions that require a liquid medium.

Silica polymer pen lithography

Abstract: Provided here are hard transparent polymer pen arrays, methods of printing indicia using the same, and methods of preparing the same.

Gradient spray coating polymer pen arrays

Abstract: The disclosure provides a method of inking a polymer pen lithography tip array (“PPL tip array”), including applying an ink composition to a PPL tip array using at least two spray applicators to deposit the ink as a non-uniform ink layer. The disclosure further provides a method of depositing at least two ink compositions on PPL tip array, including applying a first ink to a first defined area using a first spray applicator, and applying a second ink to a second defined area using a second spray applicator. The disclosure further provides a method of scaling a linear ink composition gradient provided by at least two spray applicators to a PPL tip array having a length, L, including positioning the spray applicators at a distance of about 5.0 L to about 8.0 L relative to the surface of the PPL tip array, positioning the spray applicators at a distance of about 0.5 L to about 3.0 L relative to each other, and applying an ink composition.