Applications and Measurements

Various nanostructures have been explored for applications to hydrogen sensors. Nanogaps on an elastomeric substrate and hybrid nanowires are such examples. For instance, Pd nanogaps on PDMS substrate showed perfect On-Off response, and Pd-coated rough Si nanowires exhibited quasi On-Off response and a very low H₂ detection limit (5 ppm).

J. S. Noh, H. Kim, B. S. Kim, E. Lee, H. H. Cho, and W. Lee, “High Performance Vertical Hydrogen Sensors Using Pd-coated Rough Si Nanowires”, Journal of Materials Chemistry 21, 15935 (2011). (Inside cover article)

Interest about the environmental protection has been ever growing. Photocatalysis, which is the light-assisted decomposition of pollutants, has been proposed as a potential solution. To activate the photocatalysis, high-performance photo-responding catalysts are necessary. To this aim, hybrid nanostructures composed of ZnO nanorods and Ag nanowires have been developed, which showed enhanced photocatalytic activity. Moreover, flake-like Co-doped ZnO thin films and their composites with Ag nanowires revealed greatly enhanced photoelectrochemical (PEC) water-splitting activity under visible light.

Q. T. H. Ta, S. Park, and J. S. Noh, “Ag nanowire/ZnO Nanobush Hybrid Structures for Improved Photocatalytic Activity”, Journal of Colloid and Interface Science 505, 437 (2017).

Q. T. H. Ta, E. Cho, A. Sreedhar, and J. S. Noh, “Mixed-dimensional, Three-level Hierarchical Nanostructures of Silver and Zinc Oxide for Fast Photocatalytic Degradation of Multiple Dyes”, Journal of Catalysis 371, 1 (2019).

A. Sreedhar, I. N. Reddy, Q. T. H. Ta, E. Cho, and J. S. Noh, “Highly Supportive Hydrogen Peroxide as A Hole Scavenger to Improve the Visible Light Water Splitting Activity of Flake-like Co-doped ZnO Thin Films”, Solar Energy 191, 151 (2019).

The thermoelectric performance of nanoscale materials is superior to their bulk counterparts. In particular, nanowires show a greatly enhanced thermoelectric figure-of-merit. This mainly arises from a great reduction of thermal conductivity with a moderate decrease of electrical conductivity, which enables a phonon-glass electron-crystal (PGEC). The reduction of thermal conductivity is attributed to boundary or interface scattering of phonons. Using a Bi-Te core/shell nanowire with rough interface, a very low lattice thermal conductivity (0.43 W/m×K) was achieved.

J. Kang, J. W. Roh, W. Shim, J. Ham, J. S. Noh, and W. Lee, “Reduction of Lattice Thermal Conductivity in Single Bi-Te Core/Shell Nanowires with Rough Interface”, Advanced Materials 23, 3414-3419 (2011). (Cover article)

Stretchable gas sensors can be realized by decorating reduced graphene oxide/silver nanowires (rGO/AgNWs) hybrids on a polyurethane (PU) sponge via a simple dip-coating method. Those rGO/AgNWs/PU composite gas sensors could detect both oxidizing and reducing gases at room temperature even under a large strain up to 60%. Fabric gas sensors may be a more advanced class of stretchable gas sensors, which make us step closer to wearable gas sensors. For realization of these gas sensors, several nanostructures such as rGO, ZnO nanorods, Pd nanoparticles, and AgNWs can be integrated onto a fabric. The fabric gas sensors normally worked under diverse strain states including a 100% of tensile strain.

Y. Luan, S. Zhang, T. H. Nguyen, W. Yang, and J. S. Noh, “Polyurethane Sponges Decorated with Reduced Graphene Oxide and Silver Nanowires for Highly Stretchable Gas Sensors”, Sensors and Actuators B-Chemical 265, 609 (2018).

T. H. P. Doan, Q. T. H. Ta, A. Sreedhar, N. T. Hang, W. Yang, and J. S. Noh, “Highly Deformable Fabric Gas Sensors Integrating Multidimensional Functional Nanostructures”, ACS Sensors 5, 2255 (2020).

Stretchable electronics gain much attraction due to growing demand in the fields like sensory skins, wearable devices, and health monitors. Various circuit elements need to endure a certain level of strains. Interconnect is a basic element for every electronic circuit. Highly conductive and stretchable interconnects were demonstrated using a typical elastomer, PDMS, and a typical conducting polymer, PEDOT:PSS. A third component, PDMS-b-PEO played as an miscibility improver between the two immiscible components.

J. S. Noh, “Highly Conductive and Stretchable Poly(dimethylsiloxane): Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonic acid) Blends for Organic Interconnects”, RSC Advances 4, 1857-1863 (2014).

An elaborate combination of Ag nanowires (AgNWs) and zinc ferrite (ZnFe2O4) nanoparticles can effectively inhibit the biofilm formation of Candida albicans, which is the prevailing species for invasive candidiasis. The high biofilm inhibition efficiency of ZnFe2O4@AgNWs hybrid nanostructures is attributed to the cell membrane damage induced by AgNWs and ROS generation induced by ZnFe2O4 nanoparticles. Meanwhile, bacterial contaminants such as E. coli and S. aureus can be inactivated using another nanocomposites (Fe3O4/Pd/mpg-C3N4). At a concentration of 100 ug/mL, the nanocomposites could degrade both bacterial strains almost completely within 2 h of solar light irradiation.

D. Thakur, S. Govindaraju, K. S. Yun, and J. S. Noh, “The Synergistic Effect of Zinc Ferrite Nanoparticles Uniformly Deposited on Silver Nanowires for the Biofilm Inhibition of Candida albicans”, Nanomaterials 9, 1431 (2019).

D. Thakur, Q. T. H. Ta, and J. S. Noh, “Photon-Induced Superior Antibacterial Activity of Palladium-Decorated, Magnetically Separable Fe3O4/Pd/mpg-C3N4 Nanocomposites”, Molecules 24, 3888 (2019).

Nanocracks in a metal film on an elastomeric substrate can be utilized as a strain sensor. They have specific patterns and width distribution depending on the material and the applied strain. The width of nanocracks in general becomes larger with an increase in the applied strain, leading to an increase in electrical resistance. Highly flexible and transparent strain sensors were demonstrated using Ti thin films on a PDMS substrate.

J. S. Noh, “Cracked Titanium Film on an Elastomeric Substrate for Highly Flexible, Transparent, and Low-power Strain Sensors”, Nanoscale Research Letters 8, 441 (2013).

As the size of devices scale down deep into the nanometer scale, devices with a traditional structure step closer to their performance limit. To continue the scale-down of technology node, new technologies such as high-k/metal gate stack and 3D transistors have been developed. Major electronics companies like Intel, TSMC, and Samsung have been expanding the range of incorporation of these advanced technologies into their ICs. Omega gate transistors are a type of 3D transistors with extended channels under a Si body. They have attributes in between tri-gate transistors and FinFETs.

S. H. Park, J. S. Noh, and J. Jeon, “Semiconductor device having a metal gate with a low sheet resistance and method of fabricating metal gate of the same”, US Patent 08115264 (2012).