Marya Lieberman

Sub-10 nm electron beam lithography using cold development of poly(methylmethacrylate)

We investigate poly(methylmethacrylate) (PMMA) development processing with cold developers (4–10 °C) for its effect on resolution, resist residue, and pattern quality of sub-10 nm electron beam lithography (EBL). We find that low-temperature development results in higher EBL resolution and improved feature quality. PMMA trenches of 4–8 nm are obtained reproducibly at 30 kV using cold development. Fabrication of single-particle-width Au nanoparticle lines was performed by lift-off. We discuss key factors for formation of PMMA trenches at the sub-10 nm scale.

Quantum-Dot Cellular Automata at a Molecular Scale

Abstract: Quantum‐dot cellular automata (QCA) is a scheme for molecular electronics in which information is transmitted and processed through electrostatic interactions between charges in an array of quantum dots. QCA wires, majority gates, clocked cell operation, and (recently) true power gain between QCA cells has been demonstrated in a metal‐dot prototype system at cryogenic temperatures. Molecular QCA offers very high device densities, low power dissipation, and ways to directly integrate sensors with QCA logic and memory elements. A group of faculty at Notre Dame has been working to implement QCA at the size scale of molecules, where room‐temperature operation is theoretically predicted. This paper reviews QCA theory and the experimental measurements in metal‐dot QCA systems, and describes progress toward making QCA molecules and working out surface attachment chemistry compatible with QCA operation.

High-resolution electron beam lithography and DNA nano-patterning for molecular QCA

Electron beam lithography (EBL) patterning of poly(methylmethacrylate) (PMMA) is a versatile tool for defining molecular structures on the sub-10-nm scale. We demonstrate lithographic resolution to about 5 nm using a cold-development technique. Liftoff of sub-10-nm Au nanoparticles and metal lines proves that cold development completely clears the PMMA residue on the exposed areas. Molecular liftoff is performed to pattern DNA rafts with high fidelity at linewidths of about 100 nm. High-resolution EBL and molecular liftoff can be applied to pattern Creutz-Taube molecules on the scale of a few nanometers for quantum-dot cellular automata.

Thermodynamic behavior of molecular-scale quantum-dot cellular automata (QCA) wires and logic devices

Quantum-dot cellular automata (QCA) offers a new paradigm for molecular electronics, a paradigm in which information transmission and processing depend on electrostatic interactions between charges in arrays of cells composed of quantum dots. Fundamental questions about the operational temperature and functional gain of devices built from molecular-scale QCA cells are addressed in this paper through a statistical-mechanical model based on electrostatic interactions. The model provides exact solutions for the thermodynamic constraints on operation of small arrays of cells (up to 15). An Ising approximation dramatically reduces the computational task and allows modeling of the thermodynamic behavior of semi-infinite QCA wires. The probability of getting the correct output from a QCA device for a given input depends on temperature, cell size, cell-cell distance, effective dielectric constant of the medium, and the number of cells in the array. Using parameters derived from molecular candidates for QCA cells, the statistical-mechanical model predicts that majority gates should give correct output at temperatures of up to 450 K, while wires of thousands to millions of QCA cells are predicted to operate as functional devices at room temperature.

DNA origami nanopatterning on chemically modified graphene.

thus far.Here we demonstrate that chemically modified grapheneis an excellent substrate material for adsorption and also forspatial patterning of DNA origami structures. Our strategy isto integrate the top-down patterning of chemically modifiedgraphene through conventional photolithography withbottom-up self-assembly of DNA origami structures uponthe patterned chemically modified graphene. Because of thesmoothness at atomic scale and chemical diversity of chemi-cally modified graphene, including GO, reduced grapheneoxide (rGO), and nitrogen-doped reduced graphene oxide(NrGO), the adsorption of DNA origami structures can besystematically tuned to allow spatial patterning on chemicallymodified graphene.Figure 1 illustrates the procedure for patterning of DNAorigami structures. A GO film was spin-cast from aqueoussolution onto an NH

Molecular patterning through high-resolution polymethylmethacrylate masks

Electron beam lithography was used to make nanometer trenches in thin polymethylmethacrylate (PMMA). After development, the wafers were dipped in an aqueous solution of the Creutz–Taube ion [(NH3)5Ru(pyrazine)Ru(NH3)5](o-toluenesulphonate)5 (CT5), and the PMMA was removed with acetone or dichloromethane. Atomic force microscopy and x-ray photoelectron spectroscopy were used to investigate the surface characteristics of wafers after dissolution of the PMMA and to confirm the binding of a monolayer of CT5 molecules on the wafer within the areas delimited by the PMMA trenches. This masking technique has so far been demonstrated to pattern 35 nm lines of a monolayer of CT5 molecules on silicon dioxide.

Lab on Paper: Iodometric Titration on a Printed Card

A paper test card has been engineered to perform an iodometric titration, an application that requires storage and mixing on demand of several mutually incompatible reagents. The titration is activated when a user applies a test solution to the test card: the dried reagents are reconstituted and combined through a surface-tension-enabled mixing (STEM) mechanism. The device quantifies 0.8-15 ppm of iodine atoms from iodate in aqueous solutions. This is useful, for example, to quantify iodine levels in fortified salt. A blinded internal laboratory validation established the accuracy as 1.4 ppm I and the precision as 0.9 ppm I when the test card was read by newly trained users. Using computer software to process images, the accuracy and precision both improved to 0.9 ppm I. The paper card can also detect substandard β lactam antibiotics using an iodometric back-titration. When used to quantify amoxicillin, good distinction is achieved between solutions that differ by 0.15 mg/mL over a working range of 0-0.9 mg/mL. The test card was designed to meet the World Health Organization ASSURED criteria for use in low resource settings, where laboratory-based analytical procedures are often not available.

Molecular QCA design with chemically reasonable constraints

In this article we examine the impacts of the fundamental constraints required for circuits and systems made from molecular Quantum-dot Cellular Automata (QCA) devices. Our design constraints are “chemically reasonable” in that we consider the characteristics and dimensions of devices and scaffoldings that have actually been fabricated. This work is a necessary first step for any work in QCA CAD, and can also help shape experiments in the physical sciences for emerging, nano-scale devices. Our work shows that QCA circuits, scaffoldings, substrates, and devices should all be considered simultaneously. Otherwise, there is a very real possibility that the devices and scaffoldings that are eventually manufactured will result in devices that only work in isolation. “Chemically reasonable” also means that expected manufacturing defects must be considered. In our simulations we introduce defects associated with self-assembled systems into various designs to begin to define manufacturing tolerances. This work is especially timely as experimentalists are beginning to work on merging experimental tracks that address devices and scaffolds—and the end result should facilitate correct logical operations.

Scanning tunneling microscopy and spectroscopy investigations of QCA molecules.

Quantum-dot cellular automata (QCA), a computation paradigm based on the Coulomb interactions between neighboring cells. The key idea is to represent binary information, not by the state of a current switch (transistor), but rather by the configuration of charge in a bistable cell. In its molecular realization, the QCA cell can be a single molecule. QCA is ideally suited for molecular implementation since it exploits the molecules ability to contain charge, and does not rely on any current flow between the molecules. We have examined using an UHV-STM some of the QCA molecules like silicon phthalocyanines and Fe-Ru complexes on Au (111) and Si (111) surfaces, which are suitable candidates for the molecular QCA approach.

Enabling the Development and Deployment of Next Generation Point-of-Care Diagnostics

A major goal of the 1st International Point-of-Care Diagnostic Workshop in Nairobi, Kenya was to provide a forum for open dialog concerning current challenges in, and potential solutions for, the development of the next generation of POC diagnostics. The focus was not solely on descriptions of new technologies in development but also included demonstrations of their use in a field setting. The resulting conversations identified a number of obstacles to the successful translation of prototypes into field-deployable tools. These obstacles superseded those typically encountered in research; changes must be implemented at the institutional and governmental level to enable equitable collaborations between Western and African partners, and proper funding mechanisms must be established to support these collaborations. Additionally, this workshop showcased emerging technologies for POC tests and fostered new partnerships between technology developers and African research laboratories. Equitable partnerships are critical for the successful implementation of new POC technology. The attendees agreed that the most effective methods to effect change require improved communication of needs, ideas and abilities, and a conduit for the sharing of experiences and information. We plan to implement many of the changes that are suggested here in our own research programs and to use future conferences and workshops to guide the development of both technologies and partnerships. Our successes and failures will serve as models for those scientists striving to develop technological and biomedical solutions to similar problems in global health.