Direct Organization of Morphology-Controllable Mesoporous SnO₂ Using Amphiphilic Graft Copolymer for Gas-Sensing Applications

Chi, Won Seok,Lee, Chang Soo,Long, Hu,Oh, Myoung Hwan,Zettl, Alex,Carraro, Carlo,Kim, Jong Hak,Maboudian, Roya American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.42

<P>A simple and flexible strategy for controlled synthesis of mesoporous metal oxide films using an amphiphilic graft copolymer as sacrificial template is presented and the effectiveness of this approach for gas-sensing applications is reported. The amphiphilic graft copolymer poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g POEM) is used as a sacrificial template for the direct synthesis of mesoporous SnO2. The graft copolymer self assembly is shown to enable good control over the morphology of the resulting SnO2 layer. Using this approach, mesoporous SnO2 based sensors with varied porosity are fabricated in situ on a microheater platform. This method reduces the interfacial contact resistance between the chemically sensitive materials and the microheater, while a simple fabrication process is provided. The sensors show significantly different gas-sensing performances depending on the SnO2 porosity, with the highly mesoporous SnO2 sensor exhibiting high sensitivity, low detection limit, and fast response and recovery toward hydrogen gas. This printable solution-based method can be used reproducibly to fabricate a variety of mesoporous metal oxide layers with tunable morphologies on various substrates for high-performance applications.</P>

Direct Fabrication of Zero- and One-Dimensional Metal Nanocrystals by Thermally Assisted Electromigration

Yuk, Jong Min,Kim, Kwanpyo,Lee, Zonghoon,Watanabe, Masashi,Zettl, A.,Kim, Tae Whan,No, Young Soo,Choi, Won Kook,Lee, Jeong Yong American Chemical Society 2010 ACS NANO Vol.4 No.6

<P>Zero- and one-dimensional metal nanocrystals were successfully fabricated with accurate control in size, shape, and position on semiconductor surfaces by using a novel <I>in situ</I> fabrication method of the nanocrystal with a biasing tungsten tip in transmission electron microscopy. The dominant mechanism of nanocrystal formation was identified mainly as local Joule heating-assisted electromigration through the direct observation of formation and growth processes of the nanocrystal. This method was applied to extracting metal atoms with an exceedingly faster growth rate (∼10<SUP>5</SUP> atoms/s) from a metal-oxide thin film to form a metal nanocrystal with any desired size and position. By real-time observation of the microstructure and concurrent electrical measurements, it was found that the nanostructure formation can be completely controlled into various shapes such as zero-dimensional nanodots and one-dimensional nanowires/nanorods.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2010/ancac3.2010.4.issue-6/nn901674p/production/images/medium/nn-2009-01674p_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn901674p'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn901674p'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn901674p'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn901674p'>ACS Electronic Supporting Info</A></P>

Graphene Nanopore with a Self-Integrated Optical Antenna

Nam, SungWoo,Choi, Inhee,Fu, Chi-cheng,Kim, Kwanpyo,Hong, SoonGweon,Choi, Yeonho,Zettl, Alex,Lee, Luke P. American Chemical Society 2014 NANO LETTERS Vol.14 No.10

<P>We report graphene nanopores with integrated optical antennae. We demonstrate that a nanometer-sized heated spot created by photon-to-heat conversion of a gold nanorod resting on a graphene membrane forms a nanoscale pore with a self-integrated optical antenna in a single step. The distinct plasmonic traits of metal nanoparticles, which have a unique capability to concentrate light into nanoscale regions, yield the significant advantage of parallel nanopore fabrication compared to the conventional sequential process using an electron beam. Tunability of both the nanopore dimensions and the optical characteristics of plasmonic nanoantennae are further achieved. Finally, the key optical function of our self-integrated optical antenna on the vicinity of graphene nanopore is manifested by multifold fluorescent signal enhancement during DNA translocation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-10/nl503159d/production/images/medium/nl-2014-03159d_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl503159d'>ACS Electronic Supporting Info</A></P>

Graphene-templated directional growth of an inorganic nanowire

Lee, Won Chul,Kim, Kwanpyo,Park, Jungwon,Koo, Jahyun,Jeong, Hu Young,Lee, Hoonkyung,Weitz, David A.,Zettl, Alex,Takeuchi, Shoji Nature Publishing Group, a division of Macmillan P 2015 Nature nanotechnology Vol.10 No.5

Assembling inorganic nanomaterials on graphene is of interest in the development of nanodevices and nanocomposite materials, and the ability to align such inorganic nanomaterials on the graphene surface is expected to lead to improved functionalities, as has previously been demonstrated with organic nanomaterials epitaxially aligned on graphitic surfaces. However, because graphene is chemically inert, it is difficult to precisely assemble inorganic nanomaterials on pristine graphene. Previous techniques based on dangling bonds of damaged graphene, intermediate seed materials and vapour-phase deposition at high temperature<SUP>,</SUP> have only formed randomly oriented or poorly aligned inorganic nanostructures. Here, we show that inorganic nanowires of gold(I) cyanide can grow directly on pristine graphene, aligning themselves with the zigzag lattice directions of the graphene. The nanowires are synthesized through a self-organized growth process in aqueous solution at room temperature, which indicates that the inorganic material spontaneously binds to the pristine graphene surface. First-principles calculations suggest that this assembly originates from lattice matching and π interaction to gold atoms. Using the synthesized nanowires as templates, we also fabricate nanostructures with controlled crystal orientations such as graphene nanoribbons with zigzag-edged directions.

3D structure of individual nanocrystals in solution by electron microscopy

Park, Jungwon,Elmlund, Hans,Ercius, Peter,Yuk, Jong Min,Limmer, David T.,Chen, Qian,Kim, Kwanpyo,Han, Sang Hoon,Weitz, David A.,Zettl, A.,Alivisatos, A. Paul American Association for the Advancement of Scienc 2015 Science Vol.349 No.6245

<P><B>Looking at teeny tiny platinum particles</B></P><P>Electron microscopy is a powerful technique for taking snapshots of particles or images at near-atomic resolution. Park <I>et al.</I> studied free-floating platinum nanoparticles using electron microscopy and liquid cells (see the Perspective by Colliex). Using analytical techniques developed to study biological molecules, they reconstructed the threedimensional features of the Pt particles at near-atomic resolution. This approach has the scope to study a mixed population of particles one at a time and to study their synthesis as it occurs in solution.</P><P><I>Science</I>, this issue p. 290; see also p. 232</P><P>Knowledge about the synthesis, growth mechanisms, and physical properties of colloidal nanoparticles has been limited by technical impediments. We introduce a method for determining three-dimensional (3D) structures of individual nanoparticles in solution. We combine a graphene liquid cell, high-resolution transmission electron microscopy, a direct electron detector, and an algorithm for single-particle 3D reconstruction originally developed for analysis of biological molecules. This method yielded two 3D structures of individual platinum nanocrystals at near-atomic resolution. Because our method derives the 3D structure from images of individual nanoparticles rotating freely in solution, it enables the analysis of heterogeneous populations of potentially unordered nanoparticles that are synthesized in solution, thereby providing a means to understand the structure and stability of defects at the nanoscale.</P>

Imaging of pure spin-valley diffusion current in WS₂-WSe₂ heterostructures

Jin, Chenhao,Kim, Jonghwan,Utama, M. Iqbal Bakti,Regan, Emma C.,Kleemann, Hans,Cai, Hui,Shen, Yuxia,Shinner, Matthew James,Sengupta, Arjun,Watanabe, Kenji,Taniguchi, Takashi,Tongay, Sefaattin,Zettl, A American Association for the Advancement of Scienc 2018 Science Vol.360 No.6391

<P>Transition metal dichalcogenide (TMDC) materials are promising for spintronic and valleytronic applications because valley-polarized excitations can be generated and manipulated with circularly polarized photons and the valley and spin degrees of freedom are locked by strong spin-orbital interactions. In this study we demonstrate efficient generation of a pure and locked spin-valley diffusion current in tungsten disulfide (WS2)-tungsten diselenide (WSe2) heterostructures without any driving electric field. We imaged the propagation of valley current in real time and space by pump-probe spectroscopy. The valley current in the heterostructures can live for more than 20 microseconds and propagate over 20 micrometers; both the lifetime and the diffusion length can be controlled through electrostatic gating. The high-efficiency and electric-field-free generation of a locked spin-valley current in TMDC heterostructures holds promise for applications in spin and valley devices.</P>

Graphene Veils and Sandwiches

Yuk, Jong Min,Kim, Kwanpyo,Alemá,n, Benjamí,n,Regan, William,Ryu, Ji Hoon,Park, Jungwon,Ercius, Peter,Lee, Hyuck Mo,Alivisatos, A. Paul,Crommie, Michael F.,Lee, Jeong Yong,Zettl, Alex American Chemical Society 2011 NANO LETTERS Vol.11 No.8

<P>We report a new and highly versatile approach to artificial layered materials synthesis which borrows concepts of molecular beam epitaxy, self-assembly, and graphite intercalation compounds. It readily yields stacks of graphene (or other two-dimensional sheets) separated by virtually any kind of “guest” species. The new material can be “sandwich like”, for which the guest species are relatively closely spaced and form a near-continuous inner layer of the sandwich, or “veil like”, where the guest species are widely separated, with each guest individually draped within a close-fitting, protective yet atomically thin graphene net or veil. The veils and sandwiches can be intermixed and used as a two-dimensional platform to control the movements and chemical interactions of guest species.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-8/nl201647p/production/images/medium/nl-2011-01647p_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl201647p'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl201647p'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl201647p'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl201647p'>ACS Electronic Supporting Info</A></P>