Koshala Sarveswaran

Bio: Koshala Sarveswaran is an academic researcher from University of Notre Dame. The author has contributed to research in topics: Electron-beam lithography & DNA origami. The author has an hindex of 12, co-authored 21 publications receiving 574 citations. Previous affiliations of Koshala Sarveswaran include University of Cambridge & University of Texas at Dallas.

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

Abstract: 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.

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

Abstract: 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.

Deposition of DNA rafts on cationic SAMs on silicon [100].

Abstract: We demonstrate a guided self-assembly approach to the fabrication of DNA nanostructures on silicon substrates. DNA oligonucleotides self-assemble into “rafts” 8 37 2 nm in size. The rafts bind to cationic SAMs on silicon wafers. Electron-beam lithography of a thin poly(methyl methacrylate) (PMMA) resist layer was used to define trenches, and (3-aminopropyl)triethoxysilane (APTES), a cationic SAM precursor, was deposited from aqueous solution onto the exposed silicon dioxide at the trench bottoms. The remaining PMMA can be cleanly stripped off with dichloromethane, leaving APTES layers 0.7-1.2 nm in thickness and 110 nm in width. DNA rafts bind selectively to the resulting APTES stripes. The coverage of DNA rafts on adjacent areas of silicon dioxide is 20 times lower than on the APTES stripes. The topographic features of the rafts, measured by AFM, are identical to those of rafts deposited on wide-area SAMs. Binding to the APTES stripes appears to be very strong as indicated by “jamming” of the rafts at a saturation coverage of 42% and the stability to repeated AFM scanning in air.

Guided deposition of individual DNA nanostructures on silicon substrates.

Abstract: We demonstrate immobilization of DNA nanostructures (37 nm x 8 nm) on silicon by a combination of "top-down" fabrication and "bottom-up" self-assembly Anchor lines and pads were defined using electron beam lithography and a cationic molecular monolayer Individual DNA nanostructures bind in 85% yield onto the anchor pads and can be washed and imaged in air The strength of the binding interaction between a DNA nanostructure and its anchor pad is at least -43 kJ/mol

Alkyne–phosphinoalkyne coupling reactions on mixed-metal tungsten–cobalt centres; P–C(alkyne) bond cleavage versus P–C(alkyne) bond preservation

Abstract: Reactions of the alkyne-bridged tungsten–cobalt complexes [(η5-C5H5)(OC)2W(μ-R1CCR2)Co(CO)3] (R1 = R2 = CO2Me 1a; R1 = H, R2 = But1b) with Ph2PCCPh in refluxing toluene result in two different reaction pathways. On reaction with 1a three products are isolated namely, [(η5-C5H5)(OC)2W{μ-C2(CO2Me)2}Co(CO)3(PPh2CCPh)] 2, the result of substitution of a cobalt carbonyl ligand by a phosphorus-bound molecule of Ph2PCCPh, [(η5-C5H5)(OC)2W{μ-PhCCC(CO2Me)C(CO2Me)PPh2}Co(CO)2] 3 and [(η5-C5H5)(OC)W{μ-C(CO2Me)C(CCPh)C(OMe)O}(μ-PPh2)Co(CO)2] 4, in which phosphorus–carbon(alkyne) bond cleavage of the phosphinoalkyne has ocurred along with phosphorus–carbon bond formation (3) and/or carbon–carbon bond formation (3 and 4). In contrast, reaction of 1b with Ph2PCCPh affords two products, [(η5-C5H5)(OC)W{μ-CButCHCPhC(PPh2)}Co(CO)2] 5 and [(η5-C5H5)(OC)2W{μ-CButCHC(PPh2)CPh}Co(CO)2] 6, in which the bridging alkyne has coupled with an intact molecule of the phosphinoalkyne Ph2PCαCβPh at either its β- or α-carbon atoms, respectively. However, on reaction of 1b with the tert-butyl-substituted phosphinoalkyne, Ph2PCCBut, regiospecific coupling and oxidation of the phosphino moiety occur to give [(η5-C5H5)(OC)W{μ-CButCHCButC(PPh2O)}Co(CO)2] 8, as the sole product. The reactivity of 6 towards diiron nonacarbonyl has been explored and found to afford the trimetallic complex [(η5-C5H5)(OC)2W{μ-CButCHC(PPh2Fe(CO)4)CPh}Co(CO)2] 7 in good yield. Single crystal X-ray diffraction studies have been performed on 4, 6, 7 and 8 and possible reaction pathways for the formation of the new complexes are proposed and discussed.

Templated Self‐Assembly of Block Copolymers: Top‐Down Helps Bottom‐Up

Abstract: One of the key challenges in nanotechnology is to control a self-assembling system to create a specific structure. Self-organizing block copolymers offer a rich variety of periodic nanoscale patterns, and researchers have succeeded in finding conditions that lead to very long range order of the domains. However, the array of microdomains typically still contains some uncontrolled defects and lacks global registration and orientation. Recent efforts in templated self-assembly of block copolymers have demonstrated a promising route to control bottom-up self-organization processes through top-down lithographic templates. The orientation and placement of block-copolymer domains can be directed by topographically or chemically patterned templates. This templated self-assembly method provides a path towards the rational design of hierarchical device structures with periodic features that cover several length scales.

Engineering metallic nanostructures for plasmonics and nanophotonics

Abstract: Metallic nanostructures now play an important role in many applications. In particular, for the emerging fields of plasmonics and nanophotonics, the ability to engineer metals on nanometric scales allows the development of new devices and the study of exciting physics. This review focuses on top-down nanofabrication techniques for engineering metallic nanostructures, along with computational and experimental characterization techniques. A variety of current and emerging applications are also covered.

Etching and narrowing of graphene from the edges

Abstract: Large-scale graphene electronics requires lithographic patterning of narrow graphene nanoribbons for device integration. However, conventional lithography can only reliably pattern approximately 20-nm-wide GNR arrays limited by lithography resolution, while sub-5-nm GNRs are desirable for high on/off ratio field-effect transistors at room temperature. Here, we devised a gas phase chemical approach to etch graphene from the edges without damaging its basal plane. The reaction involved high temperature oxidation of graphene in a slightly reducing environment in the presence of ammonia to afford controlled etch rate (less than or approximately 1 nm min(-1)). We fabricated approximately 20-30-nm-wide graphene nanoribbon arrays lithographically, and used the gas phase etching chemistry to narrow the ribbons down to <10 nm. For the first time, a high on/off ratio up to approximately 10(4) was achieved at room temperature for field-effect transistors built with sub-5-nm-wide graphene nanoribbon semiconductors derived from lithographic patterning and narrowing. Our controlled etching method opens up a chemical way to control the size of various graphene nano-structures beyond the capability of top-down lithography.