Information-Rich Molecular Assembly for Patterning Applications at the Nanoscale: Outlook and Challenges

Session 2B: 12:30 PM – 3:45 PM Pacific Time on Friday, August 21.

Ricardo Ruiz*, Corie Ralston, Paul Ashby

Bottom-up molecular scale assembly with systems that exhibit a wide range of information complexity from block copolymers to colloidal nanoparticles to synthetic bio-molecules such as DNA, proteins and peptoids offer several promising pathways to complement, enhance or invent new nanofabrication schemes. These new tools to manipulate matter at the molecular scale may prove particularly useful to the semiconductor industry which, after five decades of uninterrupted scaling, is now facing some serious physical barriers to continue shrinking lithographic and device dimensions. Bottom-up assemblies of macromolecules and/or synthetic bio-molecules may provide sub-10nm patterning solutions, enable completely new architectures from 2D and 3D functional assemblies or simply provide niche solutions that would enable a wider process window to stringent fabrication processes at the nanoscale. To realize this potential, we need to bring diverse communities from silicon technology, soft-matter physics and synthetic biology together. In this workshop, we hope to provide a stage for experts in these fields to discuss recent progress and future outlook.

Symposium Schedule:

Symposium Abstracts:

12:35 PM

Directed self-assembly for block copolymers for lithographic applications

Prof. Paul Nealey
Molecular Engineering, University of Chicago

Directed self-assembly (DSA) refers to the integration of self-assembling materials with templates to impart structural precision and functionality to self-assembling materials over macroscopic, manufacturing- and device-relevant dimensions. Here I will discuss the use of lithographically defined chemically patterned surfaces to direct the assembly of block copolymers (BCPs). In the first part of my talk, I will highlight research in the DSA of films of BCPs to define the material and process parameters with which the stringent constraints for semiconductor manufacturing may be met. Key developments enabled by a combined experimental and theoretical approach include techniques for quantitative three-dimensional characterization of nanoscale structure and analysis of defect annihilation kinetics and mechanisms. In the second part of my talk I will describe a materials platform for DSA of BCPs to meet the constraints of manufacturing for near term and future patterning resolution requirements. BCPs consisting of (A-block-(B-random-C) architectures allow for the decoupling of segregation strength and surface and interfacial properties. Using high throughput synthetic and characterization strategies, we realize feature size (14 to 4 nm) specific materials with balanced surface energies between blocks for processing by thermal annealing, controllable values of segregation strength for simultaneous optimization of defectivity and dimensional uniformity, and etch selectivity.

1:00 PM

Enabling Moore’s Law with Directed Self Assembly

Dr. Gurpreet Singh
Intel Corporation

Patterning techniques based on optical lithography have enabled the rapid development of smaller, ever more powerful, yet affordable semiconductor products. Due to the large number of lithography steps in state-of-the-art patterning, the ability to print patterns at tight pitch (resolution) and the ability to accurately place these patterns with respect to each other (edge-placement error (EPE) control) are now viewed as two of the biggest challenges to scaling. Complementary patterning techniques are needed to overcome the fundamental physical limits of conventional optical lithography in terms of resolution and EPE. Spacer-based pitch division is an example for a complementary patterning technique that can scale below 20 nm pitch. However, as pitch scales below 20 nm, the lack of tight process control leads to populations in the critical dimensions (CD) of line and space patterns, which absorb a significant portion of the EPE budget. Bottom-up-patterning approaches such as directed self-assembly (DSA) offer a fundamental EPE advantage over spacer-based pitch division since the line and space CDs are chemically encoded into each molecule with unprecedented accuracy. Additionally, ease of pitch scaling and low process complexity are well-documented features of DSA. Low-χ value material systems such as PS-b-PMMA show good scalability down to 24 nm pitch whereas high-χ material systems can scale to pitches as low as 5 nm. Shared and focused learning from both academia and industry have contributed immensely to the maturity of PS-b-PMMA patterning processes. However, the same cannot be said about high-χ systems, for which a plethora of material systems exist. This presentation will highlight some key learnings from PS-b-PMMA process development (defect modes, CD control, roughness trends), provide a guide to the design of new high-χ materials and outline R&D activities specific to the successful implementation of high-χ materials. Additionally, this presentation will also highlight some of the remaining challenges for DSA that prevent its deployment to flexible design-rule applications, such as multi-pitch and multi-CD limitations, and some recent experimental advances in this regard.

1:25 PM

Connecting Interface Width and Line Edge Roughness in Block Copolymer Lithography

Dr. Daniel Sunday
Materials Science and Engineering Division, National Institute of Standards and Technology (NIST)

Block copolymer (BCP) lithography takes advantage of a combination of top-down and bottom up assembly for cost effective patterning of features at length scales that are challenging for traditional optical methods. As features become smaller maintaining sufficiently low line edge roughness (LER) is a significant challenge, particularly for sub-10 nm patterns. The LER is expected to be directly connected to the interface width between BCP components. We use resonant soft X-ray reflectivity (RSoXR) to directly interrogate the relationship between interface width and chemistry in both novel materials and blends. Soft X-rays provide label free contrast between components in a BCP, enabling characterization of the native materials. Additionally, the ability to vary the absorbance of the film components allows for the interrogation of variations in buried structure. RSoXR measurements were conducted on a series of different BCP chemistries and blends to characterize the interface widths between the components. These results are then compared to changes in LER for equivalent patterned systems. The results show that while in many cases the two are correlated, there may be a disconnect between interface width and LER in some cases. These results also demonstrate how substrate affinity may play an important role influencing the interface width of assembled BCPs.

1:35 PM

Digital Assembly for Architected Nanomaterials

Prof. Yuebing Zheng
Mechanical Engineering, University of Texas at Austin

Architected nanomaterials made of nanoscale particles, wires and membranes as building blocks have attracted strong interests for both nanoscience discoveries and nanotechnology products. New phenomena and functions, some of which are obscure to natural matter, arise from the spatially and temporally arranged nanoscale building blocks and inspire fantastic human dreams such as development of invisibility cloaks for camouflage uniforms for militaries and invention of surgical nanorobots for non-invasive personalized therapy of diseases. However, the nanoscale poses several fabrication challenges. We merge digital techniques and directed assembly to pave a way towards mass customization and production of architected nanomaterials for targeted applications. I will present a series of our newly invented optical processes and tools, including opto-thermoelectric nanotweezers, opto-thermoelectric printing, bubble printing, optothermally-gated photon nudging, and opto-thermo-plasmonic nanolithography, which are employed to assemble and sculpt a variety of nanoparticles, nanowires and nanomembranes into functional architectures via computer design and control. These architected nanomaterials exhibit attractive functions that are tailorable by both properties (i.e., size, shape, and composition) of the building blocks and the inter-block interactions that depend on their spatial arrangement. Reconfigurable printing and assembly of the architected nanomaterials are also achieved. Furthermore, applications of these nanomaterials in surface-enhanced optical spectroscopy, molecular sensing, quantum optics, catalysis, disease diagnosis, and medicine are demonstrated.

1:45 PM

Digital Assembly for Architected Nanomaterials

Justin Ondry
Chemistry, University of California at Berkeley
Coauthors: John Philbin, Paul Alivisatos, Eran Rabani, Michael Lostica

By combining colloidal nanocrystal synthesis, self assembly, and epitaxial growth techniques, we developed a general method for preparing monolayer thick atomically attached quantum dot (QD) superlattices with high quality translational and crystallographic orientational order and state-of-the-art uniformity in the attachment thickness. The procedure begins with colloidal synthesis of hexagonal prism shaped core/shell QDs (e.g. CdSe/CdS), followed by liquid subphase self-assembly and immobilization of superlattices on a substrate. Epitaxial growth of additional semiconductor material fills in the voids between the particles resulting in a QD-in-matrix structure. The photoluminescence emission spectra of the QD-in-matrix structure retains characteristic 0D electronic confinement. Importantly, annealing of the resulting structures remove inhomogeneities in the QD-QD inorganic bridges, which our atomistic electronic structure calculations demonstrate would otherwise lead to Anderson-type localization. The step-wise nature of this procedure allows one to independently tune the size and material of the QD core, shell, QD-QD distance, and the matrix material. These four choices can be tuned to control many properties (e.g. degree of quantum confinement, quantum coupling, band alignments, etc.) depending on the specific applications. Finally, cation exchange reactions can be performed on the final QD-in-matrix, as demonstrated herein with a CdSe/CdS to HgSe/HgS cation exchange reaction.

2:05 PM

DNA Origami: The Bridge from Top to Bottom

Prof. Ashwin Gopinath
Mechanical Engineering, Massachusetts Institute of Technology (MIT)

Conventional top-down nanofabrication, over the last six decades, has enabled almost all the complex electronic, optical and micro-fluidic devices that form the foundation of our society. Parallel efforts, exploring bottom-up self-assembly processes, have also enabled design and synthesis of structures like quantum dots, carbon nanotubes and unique bio-molecules that possess technologically relevant proper- ties unachievable top-down. While both these approaches have independently matured, ongoing efforts to create “hybrid nanostructures” combining both strategies, has been fraught with technical challenges. The main roadblock is the absence of a scalable method to deterministically organize bottom-up nanocomponents within top-down nanofabricated structures.

In this talk, I will first introduce a directed self-assembly technique that utilizes DNA origami as a molecular adaptor to modularly position, and orient, bottom-up nano-components (like quantum dots, light emitters and proteins) within top-down nanofabricated devices. I will then present experimental results demonstrating the utility of the technique to achieve absolute, arbitrarily scalable, control over the integration of discrete emitters inside optical devices. Finally, I conclude by presenting my vision of how a DNA origami based bridge between top-down and bottom-up nanofabrication can enable a range of highly transformative, and functional, devices.

2:30 PM

Folding Beyond Proteins

Dr. Ron Zuckermann
Molecular Foundry, Berkeley Lab

A fundamental challenge in materials science is to create synthetic, organic nanostructures with the same architectural sophistication as proteins. One of the most exciting ways to do this is to mimic nature, and synthesize sequence-defined, non-natural polymer chains that spontaneously fold and assemble into precise three-dimensional structures. Peptoid polymers offer a unique platform to advance this general approach. We developed an automated synthesis method, the solid-phase submonomer method, which can efficiently synthesize high-purity, sequence-defined peptoid polymers up to 50 monomers in length. The method uses readily available primary amine synthons, allowing hundreds of chemically diverse sidechains to be cheaply introduced. We use this method, along with computational modeling, to design, synthesize, assemble and engineer a variety of protein-mimetic nanostructures, and to probe fundamental questions in polymer physics. Here, we show by direct imaging using cryo-TEM, and X-ray scattering, that all known crystalline peptoid assemblies share a fundamental secondary structure motif based on a backbone fold containing all cis-amide bonds. This unexpected universality of peptoid backbone folding offers a unique opportunity to rationally design and engineer these materials to create robust, atomically-defined nanomaterials capable of protein-like functions.

3:00 PM

Organizing Plasmonic Nanolenses using 3D DNA Origami Template

Prof. Tao Ye
Chemistry, University of California at Merced
Coauthors: Zachary Petrek, Yehan Zhang

Linear chains made of nanospheres of progressively decreasing diameters and interparticle gaps were predicted to be substantially more effective in concentrating electric fields than dimer-based plasmonic structures. However, reproducibly aligning multiple nanospheres of disparate sizes into a linear chain remains beyond the capabilities of existing top down and bottom up approaches, making it difficult to study the nanolensing effect as well as exploring the applications in sensing.

We herein report a new approach that uses a hollow DNA origami cage to exert sophisticated control over the 3D spatial arrangement of these particles. Instead of relying on 2D templates that interact with nanoparticles at one side, we used the cage to interact with multiple sides of the AuNPs and align the centers of the particles in a colinear configuration. Electron microscopy showed that our 3D hollow origami cage limits the bending angle to an average of only 10 degrees. UV-Vis measurements showed a longitudinal mode that is indicative of strong plasmonic coupling between these particles. SERS spectra showed signal enhancement consistent with FDTD simulations. Our new approach could pave the way for the synthesis of more complex hetero-multimeric nanolenses for SERS sensing, wave guiding and experimental evaluations of plasmonic theories.

3:10 PM

Building Nanoscale Assemblies by Repurposing a Self-assembling Protein Domain

Dr. Eric Young
Molecular Biophysics & Integrated Bioimaging, Berkeley Lab
Coauthors: Markus Sutter¹, Cheryl A. Kerfeld¹, Bryan H. Ferlez², Henning Kirst^1
1Berkeley Lab; ²Michigan State University

We study the structure and function of nanoscale building blocks of proteinaceous bacterial organelles. Collectively known as bacterial microcompartments (BMCs), these supramolecular organizations encapsulate enzymes within a unique selectively permeable protein shell. BMC shells primarily assemble from genes with a signature protein fold known as the BMC protein domain (protein family: pfam00936). Genetic expression of these genes typically results in ~7 nm cyclic hexameric “tiles” forming, which further associate to a higher-order architectures. Essentially, we believe pfam00936-containing proteins represent one type of idealized polymeric bionanomaterial for constructing molecularly defined nano through meso-scale assemblies. In this talk, I will summarize our work thus far in engineering pfam00936-proteins for synthetic biology and bionanomaterial applications. We can influence the behavior of higher-order assemblies with single amino acid substitutions and we have investigated real-time dynamics of functionalized pfam00936-proteins scaffolding inside living cells. Pfam00936-proteins appear highly amenable to functionalization and we currently are pursuing methods for new forms of hierarchically assembled designer, lipid-free protocell chassis.