Yonsei University · Engineering
Professor Dahl-Young Khang's research lab specializes in the mechanics and fabrication of stretchable and flexible nanomaterials, with a focus on integrating high-performance semiconductors like silicon and carbon nanotubes into elastomeric platforms. The lab pioneers innovative approaches in nanoimprint lithography using flexible, low-surface-energy fluoropolymer molds to enable low-pressure, high-resolution patterning of sub-100 nm features without surface treatment. Central to their work is the controlled use of mechanical buckling at micro- and nanoscales to create wavy, strain-tolerant electronic structures, enabling high-performance stretchable electronics. They also apply continuum mechanics theory to quantitatively analyze nanoscale buckling behavior, particularly in single-wall carbon nanotubes, to extract intrinsic material properties such as Young’s modulus.
Figures are computed from collected data and may differ slightly.
We have produced a stretchable form of silicon that consists of submicrometer single-crystal elements structured into shapes with microscale, periodic, wavelike geometries. When supported by an elastomeric substrate, this "wavy" silicon can be reversibly stretched and compressed to large levels of strain without damaging the silicon. The amplitudes and periods of the waves change to accommodate these deformations, thereby avoiding substantial strains in the silicon itself. Dielectrics, patterns
Abstract Mechanical buckling usually means catastrophic failure in structural mechanics systems. However, controlled buckling of thin films on compliant substrates has been used to advantage in diverse fields such as micro‐/nanofabrication, optics, bioengineering, and metrology as well as fundamental mechanics studies. In this Feature Article, a mechanical buckling model is presented, which sprang, in part, from the buckling study of high‐quality, single‐crystalline nanomaterials. To check the m
We have studied the scaling of controlled nonlinear buckling processes in materials with dimensions in the molecular range (i.e., approximately 1 nm) through experimental and theoretical studies of buckling in individual single-wall carbon nanotubes on substrates of poly(dimethylsiloxane). The results show not only the ability to create and manipulate patterns of buckling at these molecular scales, but also, that analytical continuum mechanics theory can explain, quantitatively, all measurable a
A low pressure (2∼3 bar) nanoimprint lithography technique is developed that utilizes a thin fluoropolymer film (∼100 μm) mold. The flexible film mold allows imprinting of submicron pattern features at such a low pressure primarily due to “sequential” imprinting made possible by the mold flexibility and the conformal contact made between the film mold and the substrate. The surface energy of the fluoropolymer mold material is low enough that no mold surface treatment is needed for clean demoldin
Room-temperature imprint lithography showing unique features that are impossible to achieve with conventional high-temperature processes is unveiled here. Large-area nanopatterning, enabled by step-and-repeat and multiple imprinting (see Figure), leads to more versatile and practical nanoscale patterning.
A fluoropolymer mold is introduced and used to pattern sub-100 nm features with the characteristics that cause problems in patterning with a mold. The low surface energy and inertness, stiffness, and permeable nature of the mold material make it possible to pattern without surface treatment densely populated very fine features, mixed patterns of small and large features, and features with a high aspect ratio, when the mold is used with a polymer solution for the patterning. The ultraviolet trans
We demonstrate room-temperature nanoimprint lithography using solvent vapor treatment of the polymer film on a substrate. In this method, the film treated with the solvent vapor is pressed with a mold at room temperature, requiring no heating that has been needed for the lithography. We show that the mold or mask patterns down to 60 nm can well be transferred onto the polymer film without any problem of the polymer adhering to the mold. The vapor treatment of the dried polymer film results in lo
Structuring Si, ranging from nanoscale to macroscale feature dimensions, is essential for many applications. Metal-assisted chemical etching (MaCE) has been developed as a simple, low-cost, and scalable method to produce structures across widely different dimensions. The process involves various parameters, such as catalyst, substrate doping type and level, crystallography, etchant formulation, and etch additives. Careful optimization of these parameters is the key to the successful fabrication
Abstract Highly efficient organic–inorganic hybrid solar cells of Si‐poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) have been demonstrated by simultaneous structural, electrical, and interfacial engineering with low processing temperature. Si substrate has been sculpted into hierarchical structure to reduce light reflection loss and increase interfacial junction area at the same time. Regarding the electrical optimization, highly conductive organic PEDOT:PSS layer has been fo
Bulk micromachining of Si is demonstrated by the well-known metal-assisted chemical etching (MaCE). Si microstructures, having lateral dimension from 5 μm up to millimeters, are successfully sculpted deeply into Si substrate, as deep as >100 μm. The key ingredient of this success is found to be the optimizations of catalyst metal type and its morphology. Combining the respective advantages of Ag and Au in the MaCE as a Ag/Au bilayer configuration leads to quite stable etch reaction upon a prolon
Reversibly, repeatedly foldable electronics and displays are enabled by employing engineered glass or plastics substrates, where folding deformation is localized in thinned parts only. This design concept can further be extended to dual folding, leading to size reduction down to 1/4. Notably, the foldable electronics and displays can be implemented with no need to introduce any novel materials.
The crystallization behaviour of ferroelectric P(VDF–TrFE) copolymer thin films on various substrates has been investigated. The substrates used include bare Si for a high energy surface, and fluorinated self-assembled monolayer deposited Si and elastomer PDMS for low energy surfaces. Low energy surfaces have been found to enhance the crystallization rate. Additionally, the elastic moduli of those thin films, having thicknesses ranging from ∼30 nm to ∼1 μm, have been determined by the buckling m
Abstract In this topical review, the development of Si-PEDOT:PSS inorganic–organic hybrid solar cells is briefly summarized. After an introduction to the typical device structure and relevant operating mechanism, special focus is placed upon ways to enhance solar cell efficiency. The various approaches for improving cell performance have been categorized into three sub-topics: (1) micro-/nano-structuring of the Si surface for effective light manipulation and trapping, (2) interface engineering f
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