Smart Actuators and Adhesives for Reconfigurable Matter

Ko, Hyunhyub,Javey, Ali American Chemical Society 2017 Accounts of chemical research Vol. No.

<P>In this Account, we review focused areas of smart materials with special emphasis on the material and device structure designs to enhance the response time, reversibility, multistimuli responsiveness, and smart adhesion for efficient shape transformation and functional actuations. First, the capability of fast reconfiguration of 2D and 3D structures in a reversible way is a critical requirement for programmable matter. For the fast and reversible reconfiguration, various approaches based on enhanced solvent diffusion rate through the porous or structured hydrogel materials, electrostatic repulsion between cofacial electrolyte nanosheets, and photothermal actuation are discussed. Second, the ability to reconfigure programmable matters into a variety of complex structures is beneficial for the use of reconfigurable matter in diverse applications. For the reconfiguration of planar 2D structures into complex 3D structures, asymmetric and multidirectional stress should be applied. In this regard, local hinges with stimuli responsive stiffness, multilayer laminations with different responsiveness in individual layers, and origami and kirigami assembly approaches are reviewed. Third, multistimuli responsiveness will be required for the efficient reconfiguration of complex programmable matter in response to user-defined stimulus under different chemical and physical environments. In addition, with multistimuli responsiveness, the reconfigured shape can be temporarily affixed by one signal and disassembled by another signal at a user-defined location and time. Photoactuation depending on the chirality of carbon nanotubes and composite gels with different responsiveness will be discussed. Finally, the development of smart adhesives with on-demand adhesion strength is critically required to maintain the robust reconfigurable shapes and for the switching on/off of the binding between components or with target objects. Among various connectors and adhesives, thermoresponsive nanowire connectors, octopus-inspired smart adhesives, and elastomeric, tiles with soft joints are described due to their potential applications in joints of deformable 3D structures and smart gripping systems.</P>

PCBM-Grafted MWNT for Enhanced Electron Transport in Polymer Solar Cells

Jung, Youn Su,Hwang, Yun-Hwa,Javey, Ali,Pyo, Myoungho The Electrochemical Society 2011 Journal of the Electrochemical Society Vol.158 No.3

Hierarchical polymer micropillar arrays decorated with ZnO nanowires

Ko, Hyunhyub,Zhang, Zhenxing,Takei, Kuniharu,Javey, Ali IOP Pub 2010 Nanotechnology Vol.21 No.29

<P>We introduce a simple and robust method for fabricating hierarchical fibrillar arrays based on polymer micropillar (μPLR) arrays decorated with ZnO nanowires (NWs) on mechanically flexible substrates. The hierarchical fibrillar arrays are fabricated by replica molding of polymer μPLR arrays on microfabricated silicon templates and subsequent solution-based growth of ZnO NWs. Fine control over the dimensions and aspect ratios of both the microelements and the nanoelements is demonstrated. The hierarchical μPLR<I>/</I>NW arrays show superhydrophobic surface properties, with the contact angle higher than that of planar surfaces and μPLR arrays without nanostructures. The fabrication strategy suggested here may be potentially extended to fabricate other organic/inorganic hierarchical systems for different applications. </P>

Carbon nanotube active-matrix backplanes for conformal electronics and sensors.

Takahashi, Toshitake,Takei, Kuniharu,Gillies, Andrew G,Fearing, Ronald S,Javey, Ali American Chemical Society 2011 Nano letters Vol.11 No.12

<P>In this paper, we report a promising approach for fabricating large-scale flexible and stretchable electronics using a semiconductor-enriched carbon nanotube solution. Uniform semiconducting nanotube networks with superb electrical properties (mobility of 20 cm2 V(-1) s(-1) and ION/IOFF of 10(4)) are obtained on polyimide substrates. The substrate is made stretchable by laser cutting a honeycomb mesh structure, which combined with nanotube-network transistors enables highly robust conformal electronic devices with minimal device-to-device stochastic variations. The utility of this device concept is demonstrated by fabricating an active-matrix backplane (128 pixels, physical size of 64 cm2) for pressure mapping using a pressure sensitive rubber as the sensor element.</P>

High-Performance Single Layered WSe₂ p-FETs with Chemically Doped Contacts

Fang, Hui,Chuang, Steven,Chang, Ting Chia,Takei, Kuniharu,Takahashi, Toshitake,Javey, Ali American Chemical Society 2012 Nano letters Vol.12 No.7

<P>We report high performance p-type field-effect transistors based on single layered (thickness, ∼0.7 nm) WSe<SUB>2</SUB> as the active channel with chemically doped source/drain contacts and high-κ gate dielectrics. The top-gated monolayer transistors exhibit a high effective hole mobility of ∼250 cm<SUP>2</SUP>/(V s), perfect subthreshold swing of ∼60 mV/dec, and <I>I</I><SUB>ON</SUB>/<I>I</I><SUB>OFF</SUB> of >10<SUP>6</SUP> at room temperature. Special attention is given to lowering the contact resistance for hole injection by using high work function Pd contacts along with degenerate surface doping of the contacts by patterned NO<SUB>2</SUB> chemisorption on WSe<SUB>2</SUB>. The results here present a promising material system and device architecture for p-type monolayer transistors with excellent characteristics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-7/nl301702r/production/images/medium/nl-2012-01702r_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl301702r'>ACS Electronic Supporting Info</A></P>

Parallel Array InAs Nanowire Transistors for Mechanically Bendable, Ultrahigh Frequency Electronics

Takahashi, Toshitake,Takei, Kuniharu,Adabi, Ehsan,Fan, Zhiyong,Niknejad, Ali M.,Javey, Ali American Chemical Society 2010 ACS NANO Vol.4 No.10

<P>The radio frequency response of InAs nanowire array transistors on mechanically flexible substrates is characterized. For the first time, GHz device operation of nanowire arrays is demonstrated, despite the relatively long channel lengths of ∼1.5 μm used in this work. Specifically, the transistors exhibit an impressive maximum frequency of oscillation, <I>f</I><SUB>max</SUB> ∼ 1.8 GHz, and a cutoff frequency, <I>f</I><SUB>t</SUB> ∼ 1 GHz. The high-frequency response of the devices is due to the high saturation velocity of electrons in high-mobility InAs nanowires. The work presents a new platform for flexible, ultrahigh frequency devices with potential applications in high-performance digital and analog circuitry.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2010/ancac3.2010.4.issue-10/nn1018329/production/images/medium/nn-2010-018329_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn1018329'>ACS Electronic Supporting Info</A></P>

Electrical Properties of Synthesized Large-Area MoS₂ Field-Effect Transistors Fabricated with Inkjet-Printed Contacts

Kim, Tae-Young,Amani, Matin,Ahn, Geun Ho,Song, Younggul,Javey, Ali,Chung, Seungjun,Lee, Takhee American Chemical Society 2016 ACS NANO Vol.10 No.2

<P>We report the electrical properties of synthesized large-area monolayer molybdenum disulfide (MoS2) field-effect transistors (FETs) with low-cost inkjet-printed Ag electrodes. The monolayer MoS2 film was grown by a chemical vapor deposition (CVD) method, and the top contact Ag source/drain electrodes (S/D) were deposited onto the films using a low-cost drop-on-demand inkjet-printing process without any masks and surface treatments. The electrical characteristics of FETs were comparable to those fabricated by conventional deposition methods such as photo- or electron beam lithography. The contact properties between the S/D and the semiconductor layer were also evaluated using the Y function method and an analysis of the output characteristic at the low drain voltage regimes. Furthermore, the electrical instability under positive gate-bias stress was studied to investigate the charge-trapping mechanism of the FETs. CVD-grown large-area monolayer MoS2 FETs with inkjet-printed contacts may represent an attractive approach for realizing large-area and low-cost thin-film electronics.</P>

Nanoscale Semiconductor “X” on Substrate “Y” – Processes, Devices, and Applications

Madsen, Morten,Takei, Kuniharu,Kapadia, Rehan,Fang, Hui,Ko, Hyunhyub,Takahashi, Toshitake,Ford, Alexandra C.,Lee, Min Hyung,Javey, Ali WILEY‐VCH Verlag 2011 ADVANCED MATERIALS Vol.23 No.28

<P><B>Abstract</B></P><P>Recent advancements in the integration of nanoscale, single‐crystalline semiconductor ‘X’ on substrate ‘Y’ (XoY) for use in transistor and sensor applications are presented. XoY is a generic materials framework for enabling the fabrication of various novel devices, without the constraints of the original growth substrates. Two specific XoY process schemes, along with their associated materials, device and applications are presented. In one example, the layer transfer of ultrathin III–V semiconductors with thicknesses of just a few nanometers on Si substrates is explored for use as energy‐efficient electronics, with the fabricated devices exhibiting excellent electrical properties. In the second example, contact printing of nanowire‐arrays on thin, bendable substrates for use as artificial electronic‐skin is presented. Here, the devices are capable of conformably covering any surface, and providing a real‐time, two‐dimensional mapping of external stimuli for the realization of smart functional surfaces. This work is an example of the emerging field of “<I>translational nanotechnology</I>” as it bridges basic science of nanomaterials with practical applications.</P>

Contact printing of compositionally graded CdS_xSe_1−x nanowire parallel arrays for tunable photodetectors

Takahashi, Toshitake,Nichols, Patricia,Takei, Kuniharu,Ford, Alexandra C,Jamshidi, Arash,Wu, Ming C,Ning, C Z,Javey, Ali IOP Pub 2012 Nanotechnology Vol.23 No.4

<P>Spatially composition-graded CdS<SUB>x</SUB>Se<SUB>1−x</SUB> (x = 0–1) nanowires are grown and transferred as parallel arrays onto Si/SiO<SUB>2</SUB> substrates by a one-step, directional contact printing process. Upon subsequent device fabrication, an array of tunable-wavelength photodetectors is demonstrated. From the spectral photoconductivity measurements, the cutoff wavelength for the device array, as determined by the bandgap, is shown to cover a significant portion of the visible spectrum. The ability to transfer a collection of crystalline semiconductor nanowires while preserving the spatially graded composition may enable a wide range of applications, such as tunable lasers and photodetectors, efficient photovoltaics, and multiplexed chemical sensors.</P>

III–V Complementary Metal–Oxide–Semiconductor Electronics on Silicon Substrates

Nah, Junghyo,Fang, Hui,Wang, Chuan,Takei, Kuniharu,Lee, Min Hyung,Plis, E.,Krishna, Sanjay,Javey, Ali American Chemical Society 2012 Nano letters Vol.12 No.7

<P>One of the major challenges in further advancement of III–V electronics is to integrate high mobility complementary transistors on the same substrate. The difficulty is due to the large lattice mismatch of the optimal <I>p</I>- and <I>n</I>-type III–V semiconductors. In this work, we employ a two-step epitaxial layer transfer process for the heterogeneous assembly of ultrathin membranes of III–V compound semiconductors on Si/SiO<SUB>2</SUB> substrates. In this III–V-on-insulator (XOI) concept, ultrathin-body InAs (thickness, 13 nm) and InGaSb (thickness, 7 nm) layers are used for enhancement-mode <I>n</I>- and <I>p</I>- MOSFETs, respectively. The peak effective mobilities of the complementary devices are ∼1190 and ∼370 cm<SUP>2</SUP>/(V s) for electrons and holes, respectively, both of which are higher than the state-of-the-art Si MOSFETs. We demonstrate the first proof-of-concept III–V CMOS logic operation by fabricating NOT and NAND gates, highlighting the utility of the XOI platform.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-7/nl301254z/production/images/medium/nl-2012-01254z_0002.gif'></P>