Optically- and Thermally-Responsive Programmable Materials Based on Carbon Nanotube-Hydrogel Polymer Composites

Xiaobo Zhang†‡§, Cary L. Pint†‡§, Min Hyung Lee†‡§, Bryan Edward Schubert†, Arash Jamshidi†‡, Kuniharu Takei†‡§, Hyunhyub Ko†‡§, Andrew Gillies†, Rizia Bardhan, Jeffrey J. Urban, Ming Wu†‡, Ronald Fearing†, and Ali Javey*†‡

Nano Lett., Article ASAP

DOI: 10.1021/nl201503e

Publication Date (Web): July 7, 2011

A simple approach is described to fabricate reversible, thermally- and optically responsive actuators utilizing composites of poly(N-isopropylacrylamide) (pNIPAM) loaded with single-walled carbon nanotubes. With nanotube loading at concentrations of 0.75 mg/mL, we demonstrate up to 5 times enhancement to the thermal response time of the nanotube-pNIPAM hydrogel actuators caused by the enhanced mass transport of water molecules. Additionally, we demonstrate the ability to obtain ultrafast near-infrared optical response in nanotube-pNIPAM hydrogels under laser excitation enabled by the strong absorption properties of nanotubes. The work opens the framework to design complex and programmable self-folding materials, such as cubes and flowers, with advanced built-in features, including tunable response time as determined by the nanotube loading.

20 July - Ultrarapid Materials Processing: Synthesis of Tungsten Carbide on Subminute Timescales

Today Hong is presenting the following paper

Ultrarapid Materials Processing: Synthesis of Tungsten Carbide on Subminute Timescales

 S. R. Vallance^1,2,S. Kingman¹,D. H. Gregory²

Article first published online: 12 DEC 2006

DOI: 10.1002/adma.200601129

The rapid synthesis of tungsten carbide through the use of microwave-assisted techniques is demonstrated. Examination of the obtained samples reveals a single-phase structure. The influence of the amount of carbon precursor added to the synthesis is investigated (see figure), providing insight into the mechanism of tungsten carbide formation. The method has potential for scale-up and synthesis of other metal carbides.  

 

Imaging, Simulation, and Electrostatic Control of Power Dissipation in Graphene Devices

Myung-Ho Bae†‡, Zhun-Yong Ong†§, David Estrada†‡, and Eric Pop*

Nano Lett., 2010, 10 (12), pp 4787–4793

DOI: 10.1021/nl1011596

Publication Date (Web): June 3, 2010

 

We directly image hot spot formation in functioning mono- and bilayer graphene field effect transistors (GFETs) using infrared thermal microscopy. Correlating with an electrical−thermal transport model provides insight into carrier distributions, fields, and GFET power dissipation. The hot spot corresponds to the location of minimum charge density along the GFET; by changing the applied bias, this can be shifted between electrodes or held in the middle of the channel in ambipolar transport. Interestingly, the hot spot shape bears the imprint of the density of states in mono- vs bilayer graphene. More broadly, we find that thermal imaging combined with self-consistent simulation provide a noninvasive approach for more deeply examining transport and energy dissipation in nanoscale devices.

Harvesting Energy from Water Flow over Graphene

Prashant Dhiman†, Fazel Yavari†, Xi Mi‡, Hemtej Gullapalli§, Yunfeng Shi‡, Pulickel M. Ajayan§, and Nikhil Koratkar*†

Nano Lett., Article ASAP

DOI: 10.1021/nl2011559

Publication Date (Web): July 12, 2011

Water flow over carbon nanotubes has been shown to generate an induced voltage in the flow direction due to coupling of ions present in water with free charge carriers in the nanotubes. However, the induced voltages are typically of the order of a few millivolts, too small for significant power generation. Here we perform tests involving water flow with various molarities of hydrochloric acid (HCl) over few-layered graphene and report order of magnitude higher induced voltages for graphene as compared to nanotubes. The power generated by the flow of 0.6 M HCl solution at 0.01 m/sec was measured to be 85 nW for a 30 × 16 μm size graphene film, which equates to a power per unit area of 175 W/m². Molecular dynamics simulations indicate that the power generation is primarily caused by a net drift velocity of adsorbed Cl^– ions on the continuous graphene film surface.

13 July - Quantum Dot Light-Emitting Devices with Electroluminescence Tunable over the Entire Visible Spectrum

Today Krisztian is presenting the paper:

Quantum Dot Light-Emitting Devices with Electroluminescence Tunable over the Entire Visible Spectrum

Polina O. Anikeeva†^‡, Jonathan E. Halpert†^§, Moungi G. Bawendi^§ and Vladimir Bulovi*

Nano Lett., 2009, 9 (7), pp 2532–2536

DOI: 10.1021/nl9002969

Publication Date (Web): June 10, 2009

Improvements in quantum dot light-emitting device (QD-LED) performance are achieved by the choice of organic charge transporting layers, by use of different colloidal QDs for the different parts of the visible spectrum, and by utilizing a recently demonstrated robust QD deposition method. Spectrally narrow electroluminescence of our QD-LEDs is tuned over the entire visible wavelength range from λ = 460 nm (blue) to λ = 650 nm (deep red). By printing close-packed monolayers of different QD types inside an identical QD-LED structure, we demonstrate that different color QD-LEDs with QDs of different chemistry can be fabricated on the same substrate. We discuss mechanisms responsible for efficiency increase for green (4-fold) and orange (30%) QD-LEDs as compared to previous reports and outline challenges associated with achieving high-efficiency blue QD-LEDs.

06 July - Electrically Induced Ferromagnetism at Room Temperature in Cobalt-Doped Titanium Dioxide

1. Today Peiman is presenting the following paper:

1. 
   

1. Science 27 May 2011: 
   Vol. 332 no. 6033 pp. 1065-1067 
   DOI: 10.1126/science.1202152

1. Y. Yamada¹,*, 
2. K. Ueno²,³,*, 
3. T. Fukumura³,⁴,†, 
4. H. T. Yuan⁵,⁶, 
5. H. Shimotani⁵,⁶, 
6. Y. Iwasa⁵,⁶, 
7. L. Gu², 
8. S. Tsukimoto²,
9. Y. Ikuhara²,⁷,⁸, and 
10. M. Kawasaki¹,²,⁵,⁶

The electric field effect in ferromagnetic semiconductors enables switching of the magnetization, which is a key technology for spintronic applications. We demonstrated electric field–induced ferromagnetism at room temperature in a magnetic oxide semiconductor, (Ti,Co)O₂, by means of electric double-layer gating with high-density electron accumulation (>10¹⁴ per square centimeter). By applying a gate voltage of a few volts, a low-carrier paramagnetic state was transformed into a high-carrier ferromagnetic state, thereby revealing the considerable role of electron carriers in high-temperature ferromagnetism and demonstrating a route to room-temperature semiconductor spintronics.

Experimental Acoustic Ground Cloak in Air

APS » Journals » Phys. Rev. Lett. » Volume 106 » Issue 25

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Phys. Rev. Lett. 106, 253901 (2011) [4 pages]

Bogdan-Ioan Popa^*, Lucian Zigoneanu, and Steven A. Cummer^† 

We present the design, fabrication, and performance analysis for a class of two-dimensional acoustic cloaking coatings in air. Our approach takes advantage of transformation acoustics and linear coordinate transformations that result in shells which are homogeneous, broadband, and compact. The required material parameters are highly anisotropic; however, we show that they are easily achievable in practice in metamaterials made of perforated plastic plates. The good performance of the fabricated design is assessed from measurements of the sound field produced around the cloak by a broadband source. The remarkably low complexity of the device made of perforated plastic plates shows that sound in air can be fully and effectively manipulated using realizable transformation acoustics devices.