15 June - In Situ Transmission Electron Microscopy Observation of Nanostructural Changes in Phase-Change Memory

Today Jorge will present the following paper: "In Situ Transmission Electron Microscopy Observation of Nanostructural Changes in Phase-Change Memory"


Stefan Meister,† SangBum Kim,‡ Judy J. Cha,† H.-S. Philip Wong,‡ and Yi Cui†,*

Received for review November 18, 2010

and accepted March 22, 2011.

Published online ’’’

10.1021/nn1031356

Phase-change memory (PCM) has been researched extensively as a promising alternative to flash memory. Important studies have focused on its scalability, switching speed, endurance, and new materials. Still, reliability issues and inconsistent switching in PCM devices Phase-change memory (PCM) has been researched extensively as a promising motivate the need to further study its fundamental properties. However, many investigations treat PCM cells as black boxes; nanostructural changes inside the devices remain hidden. Here, using in situ transmission electron microscopy, we observe real-time nanostructural changes in lateral Ge2Sb2Te5 (GST) PCM bridges during switching. We find that PCM devices with similar resistances can exhibit distinct threshold switching behaviors due to the different initial distribution of nanocrystalline and amorphous domains, explaining variability of switching behaviors of PCM cells in the literature. Our findings show a direct correlation between nanostructure and switching behavior, providing important guidelines in the design and operation of future PCM devices with improved endurance and lower variability.

Water Boiling Inside Carbon Nanotubes: Toward Efficient Drug Release

Vitaly V. Chaban and Oleg V. Prezhdo

ACS Nano, Article ASAP

DOI: 10.1021/nn201277a

Publication Date (Web): June 7, 2011

We show using molecular dynamics simulation that spatial confinement of water inside carbon nanotubes (CNTs) substantially increases its boiling temperature and that a small temperature growth above the boiling point dramatically raises the inside pressure. Capillary theory successfully predicts the boiling point elevation down to 2 nm, below which large deviations between the theory and atomistic simulation take place. Water behaves qualitatively different inside narrow CNTs, exhibiting transition into an unusual phase, where pressure is gas-like and grows linearly with temperature, while the diffusion constant is temperature-independent. Precise control over boiling by CNT diameter, together with the rapid growth of inside pressure above the boiling point, suggests a novel drug delivery protocol. Polar drug molecules are packaged inside CNTs; the latter are delivered into living tissues and heated by laser. Solvent boiling facilitates drug release.

Arrays of indefinitely long uniform nanowires and nanotubes

• Mecit Yaman,
• Tural Khudiyev,
• Erol Ozgur,
• Mehmet Kanik,
• Ozan Aktas,
• Ekin O. Ozgur,
• Hakan Deniz,
• Enes Korkut
• & Mehmet Bayindir

Nature Materials

 

(2011)

 

doi:10.1038/nmat3038

Received

 

08 January 2011

 

Accepted

 

28 April 2011

 

Published online

 

12 June 2011

Nanowires are arguably the most studied nanomaterial model to make functional devices and arrays^1, 2. Although there is remarkable maturity in the chemical synthesis of complex nanowire structures^3, 4, their integration and interfacing to macro systems with high yields and repeatability^5, 6, 7 still require elaborate aligning, positioning and interfacing and post-synthesis techniques^8, 9. Top-down fabrication methods for nanowire production, such as lithography and electrospinning, have not enjoyed comparable growth. Here we report a new thermal size-reduction process to produce well-ordered, globally oriented, indefinitely long nanowire and nanotube arrays with different materials. The new technique involves iterative co-drawing of hermetically sealed multimaterials in compatible polymer matrices similar to fibre drawing. Globally oriented, endlessly parallel, axially and radially uniform semiconducting and piezoelectric nanowire and nanotube arrays hundreds of metres long, with nanowire diameters less than 15 nm, are obtained. The resulting nanostructures are sealed inside a flexible substrate, facilitating the handling of and electrical contacting to the nanowires. Inexpensive, high-throughput, multimaterial nanowire arrays pave the way for applications including nanowire-based large-area flexible sensor platforms, phase-changememory, nanostructure-enhanced photovoltaics, semiconductor nanophotonics, dielectric metamaterials,linear and nonlinear photonics and nanowire-enabled high-performance composites.#

Wafer-Scale Graphene Integrated Circuit

Science 10 June 2011: 
Vol. 332 no. 6035 pp. 1294-1297 
DOI: 10.1126/science.1204428


Yu-Ming Lin,* Alberto Valdes-Garcia, Shu-Jen Han, Damon B. Farmer, Inanc Meric,†
Yanning Sun, Yanqing Wu, Christos Dimitrakopoulos, Alfred Grill,
Phaedon Avouris,* Keith A. Jenkins


A wafer-scale graphene circuit was demonstrated in which all circuit components, including graphene field-effect transistor and inductors, were monolithically integrated on a single silicon carbide wafer. The integrated circuit operates as a broadband radio-frequency mixer at frequencies up to 10 gigahertz. These graphene circuits exhibit outstanding thermal stability with little reduction in performance (less than 1 decibel) between 300 and 400 kelvin. These results open up possibilities of achieving practical graphene technology with more complex functionality and performance.

Combined Atomic Force Microscope-Based Topographical Imaging and Nanometer-Scale Resolved Proximal Probe Thermal Desorption/Electrospray Ionization–Mass Spectrometry

Olga S. Ovchinnikova, Maxim P. Nikiforov, James A. Bradshaw, Stephen Jesse, and Gary J. Van Berkel

Publication Date (Web): June 6, 2011 (Article)

DOI: 10.1021/nn200939e

 

Nanometer- scale proximal probe thermal desorption/electrospray ionization mass spectrometry (TD/ESI–MS) was demonstrated for molecular surface sampling of caffeine from a thin film using a 30 nm diameter nanothermal analysis (nano-TA) probe tip in an atomic force microscope (AFM) coupled via a vapor transfer line and ESI interface to a MS detection platform. Using a probe temperature of 350 °C and a spot sampling time of 30 s, conical desorption craters 250 nm in diameter and 100 nm deep were created as shown through subsequent topographical imaging of the surface within the same system. Automated sampling of a 5 × 2 array of spots, with 2 μm spacing between spots, and real time selective detection of the desorbed caffeine using tandem mass spectrometry was also demonstrated. Estimated from the crater volume (2 × 10⁶ nm³), only about 10 amol (2 fg) of caffeine was liberated from each thermal desorption crater in the thin film. These results illustrate a relatively simple experimental setup and means to acquire in an automated fashion submicrometer scale spatial sampling resolution and mass spectral detection of materials amenable to TD. The ability to achieve MS-based chemical imaging with 250 nm scale spatial resolution with this system is anticipated.

 

 

01 June - Gold Nanoparticles as Surface Defect Probes for WS2 Nanostructures

Today Fang will present the paper:


Gold Nanoparticles as Surface Defect Probes for WS2 Nanostructures


Chen Shahar,†,§ Roi Levi,†,§ Sidney R. Cohen,‡ and Reshef Tenne*



WS2 inorganic nanotubes (INT) and inorganic fullerene-like nanoparticles (IF) are well-known for their high mechanical strength and as superior solid lubricants. The outermostWS2 layer is considered to be fully bonded; thus, it was suggested that the interactions of these WS2 nanostructures with their surroundings are governed by purely van der Waals (vdW) interactions. However, in the case of IF-WS2 nanoparticles, the faceted surface may contain sites with nonsaturated coordination, which, in turn, react with the surrounding media. Gold nanoparticles (GNP)were used as probes for the IF-WS2 surface defects, mapped by both scanning and transmission electron microscopy. The interaction between the GNP and the reactive surface was investigated using INT-WS2 as a model and was characterized by atomic force microscopy (AFM).