Three-dimensional (3D) printing has been a very active area of research and development due to its capability to produce 3D objects by design. Miniaturization and improvement of spatial resolution are major challenges in current 3D printing technology development. This work reports advances in miniaturizing 3D printing to the nanometer scale using scanning probe microscopy in conjunction with local material delivery. Using polyelectrolyte polymers and complexes, we have demonstrated the concept of layer-by-layer nanoprinting by design. Nanometer precision is achieved in all three dimensions, as well as in interlayer registry. The approach enables production of designed functional 3D materials with nanometer resolution and, as such, creates a platform for conducting scientific research in designed 3D nanoenvironments as well. In doing so, it enables production of nanomaterials and scaffolds for photonics devices, biomedicine, and tissue engineering.
Multicomponent nanostructures with individual geometries have attracted much attention because of their potential to carry out multiple functions synergistically. The current work reports a simple method using particle lithography to fabricate multicomponent nanostructures of metals, proteins, and organosiloxane molecules, each with its own geometry. Particle lithography is well-known for its capability to produce arrays of triangular-shaped nanostructures with novel optical properties. This paper extends the capability of particle lithography by combining a particle template in conjunction with surface chemistry to produce multicomponent nanostructures. The advantages and limitations of this approach will also be addressed.
Incorporating single-electron tunneling (SET) of metallic nanoparticles (NPs) into modern electronic devices offers great promise to enable new properties; however, it is technically very challenging due to the necessity to integrate ultrasmall (<10 nm) particles into the devices. The nanosize requirements are intrinsic for NPs to exhibit quantum or SET behaviors, for example, 10 nm or smaller, at room temperature. This work represents the first observation of SET that defies the well-known size restriction. Using polycrystalline Au NPs synthesized via our newly developed solid-state glycine matrices method, a Coulomb Blockade was observed for particles as large as tens of nanometers, and the blockade voltage exhibited little dependence on the size of the NPs. These observations are counterintuitive at first glance. Further investigations reveal that each observed SET arises from the ultrasmall single crystalline grain(s) within the polycrystal NP, which is (are) sufficiently isolated from the nearest neighbor grains. This work demonstrates the concept and feasibility to overcome orthodox spatial confinement requirements to achieve quantum effects.
Organizational chirality on surfaces has been of interest in chemistry and materials science due to its scientific importance as well as its potential applications. Current methods for producing organizational chiral structures on surfaces are primarily based upon the self-assembly of molecules. While powerful, the chiral structures are restricted to those dictated by surface reaction thermodynamics. This work introduces a method to create organizational chirality by design with nanometer precision. Using atomic force microscopy-based nanolithography, in conjunction with chosen surface chemistry, various chiral structures are produced with nanometer precision, from simple spirals and arrays of nanofeatures to complex and hierarchical chiral structures. The size, geometry, and organizational chirality is achieved in deterministic fashion, with high fidelity to the designs. The concept and methodology reported here provide researchers a new and generic means to carry out organizational chiral chemistry, with the intrinsic advantages of chiral structures by design. The results open new and promising applications including enantioselective catalysis, separation, and crystallization, as well as optical devices requiring specific polarized radiation and fabrication and recognition of chiral nanomaterials.
While molecular-level structural information is readily available for n-alkanethiol self-assembled monolayers (SAMs) on noble metal surfaces, the same cannot be claimed for dithiol-based SAMs due to their lack of long-range-order. This work provides molecular-level structural information on dithiol SAMs by investigating 5-(octyloxy)-1,3-phenylenedimethanethiol (OPDT) SAMs on Au(111) surfaces, using combined high-resolution scanning tunneling microscopy (STM), atomic force microscopy (AFM), and nanolithography. The high coverage OPDT SAMs do not exhibit long-range order. Desorption of these OPDT SAMs leads to the formation of ordered domains known as the striped phases, whose unit mesh is revealed as commensurate with the underlying Au(111) lattice. In these domains, OPDT molecules are lying-down, with the benzene ring and the zigzag plane of the alkyl chain parallel to the Au(111) surface. At the boundaries of these ordered structures, standing-up OPDT molecules are frequently present with an intermolecular space of 1 nm (i.e., 1D ordered structures). Using these ordered structures as internal standards in situ, the structure of the high-coverage OPDT SAMs is revealed: a mixture of standing-up and lying-down molecules randomly distributed on Au(111); as such, these SAMs exhibit little long-range order or ordered domains. The two thiols of each OPDT molecule occupy triple hollow sites on Au(111) surfaces. In the standing-up configuration, the benzene ring is perpendicular to the surface. In the lying-down con-figuration, the benzene ring and zigzag plane of the alkyl chain are parallel to the Au(111) surface. This work represents a high-resolution and molecular-level structural characterization of functionalized dithiol SAMs, furthering our understanding of dithiol molecule−surface interactions and the unique properties of these SAMs.
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