Photoemission Electron Microscopy of a Plasmonic Silver Nanoparticle Trimer

In order to exploit the surface plasmon mediated growth process described above, a fundamental understanding of the plasmonic properties of the nanostructured substrates will be required.  We present a combined experimental and theoretical study to investigate the spatial distribution of photoelectrons emitted from silver-coated polystyrene nanoparticles. We use two-photon photoemission electron microscopy (2P-PEEM) to image electron emission from a silver-capped aggregate trimer. Finite difference time domain (FDTD) simulations are performed to model the intensity distributions of the electromagnetic near- fields resulting from femtosecond (fs) laser excitation of localized surface plasmon oscillations in the trimer structure. We demonstrate that the predicted FDTD near-field intensity distribution reproduces the 2P-PEEM photoemission pattern.

Doc.: http://link.springer.com/article/10.1007/s00339-012-7316-5/fulltext.html.

Samuel J Peppernick, A. G. (2012). Photoemission electron microscopy of a plasmonic nanoparticle trimer. Applied Physics A.

InxGa1–xAs Nanowire Growth on Graphene: van der Waals Epitaxy Induced Phase Segregation

This paper leverages the nascent 2D materials growth effort in CNEM to utilize graphene and MoS₂ as substrates for for In_xGa_1-xAs nanowire growth.  On graphene, there is a phase separation wherein the nanowires grow with an InAs core and an InGaAs shell. On MoS₂, only homogeneous InGaAs nanowires grow, similarly to VLS growth. The phase segregation of nanowires on graphene is a form of van der Waals epitaxy in which the InAs nanowire core is lattice matched with the graphene growth template.

Doc.: http://pubs.acs.org/doi/abs/10.1021/nl304569d

k. Mohnseny, P., Behnam, A., D. Wood, J., D. English , C., W. Lyding, J., Pop, E., & Li, X. (2013). InxGa1–xAs Nanowire Growth on Graphene: van der Waals Epitaxy Induced Phase Segregation. Nano Letters, 1553-1161 http://pubs.acs.org/doi/abs/10.1021/nl304569d

Single Ion Channel Recordings with CMOS-Anchored Lipid Membranes

Este año, Jacob K. Rosenstein, Siddharth Ramakrishnan, Jared Roseman y Jen Shepard publicaron su trabajo “Single Ion Channel Recordings with CMOS-Anchored Lipid Membranes”  en nano Letters, en el cual se presenta grabaciones de un solo canal de iones realizados con membranas lipídicas biomiméticas que se unen directamente a la superficie de un metal-óxido-semiconductor de un chip  preamplificador complementario (CMOS). Con este sistema es posible resolver corrientes de un solo canal de varios tipos de canales iónicos bacterianos, incluyendo las fluctuaciones de un solo canal alameticina en un ancho de banda de 1 MHz que representan las grabaciones más rápidas de un solo canal de iones reportado hasta la fecha. La plataforma también se utiliza para la grabación de  alta resolución de nanoporos de alfa-hemolisina. En la publicación se ilustran los resultados de la alta fidelidad de la señal, buena resolución temporal, pequeña geometría, y multiplexado de integración que se puede lograr mediante el aprovechamiento de las plataformas de semiconductores integrados para interfaces avanzadas de los canales iónicos.

 

Single Ion Channel Recordings with CMOS-Anchored Lipid Membranes

Jacob K. Rosenstein, Siddharth Ramakrishnan, Jared Roseman, and Ken Shepard. Nano Letters Just Accepted Manuscript

Disponible en: http://pubs.acs.org/doi/abs/10.1021/nl400822r?prevSearch=molecules%2Bfor%2Belectronics&searchHistoryKey=

Coherent Control of Colloidal Semiconductor Nanocrystals

Recientemente Martin Ruge, Ronald Wilcken, Mathias Wollenhaupt, Alexander Horn y thomas Baumert publicaron un artículo llamado “Coherent Control of Colloidal Semiconductor Nanocrystals” (control coherente de nanocristales semiconductores coloidales) en donde se demuestra a temperatura ambiente el control coherente de campo débil de una transición de dos fotones en nanocristales semiconductores coloidales (NCS) personalizados por láser de pulsos de femtosegundos. Para el experimento se sintetizaron conjuntos de sulfuro de cadmio (CdS) y selenuro de cadmio (CdSe) CN y se irradiaron en la fase líquida mediante pulsos láser ultracortos infrarojo que es la fase de modulación en el dominio de frecuencia. La luminiscencia generada por recombinación electrón hueco después de la excitación de dos fotones (TPE) en forma de impulsos sirvió como una medida para la excitación NC. En el experimento se aplicaron funciones de fase espectrales polinómicas de segundo-(GDD) y tercer orden (TOD), así como saltos de fase (θ-paso) y se estudió el efecto de los diferentes pulsos de láser en forma de sobre la excitación de los dos tipos de los CN. Se encontró que distintas formas de pulso permiten selectividad entre la excitación de ambos tipos NC en una mezcla. Las simulaciones numéricas basadas en el solapamiento espectral de la segunda orden de espectro óptico no lineal y el espectro de TPE de la CN están en buen acuerdo con los resultados de la medición. Expresiones analíticas derivadas de segundo orden de densidad espectral de potencia (PSD), debido a la combinación de modulación GDD-TOD y la θ paso racionalizar este hallazgo y muestran que GDD-TOD modulación proporciona un instrumento espectroscópico para investigar el espectro de TPE.

 

Coherent Control of Colloidal Semiconductor Nanocrystals

Martin Ruge, Roland Wilcken, Mathias Wollenhaupt, Alexander Horn, and Thomas Baumer. The Journal of Physical Chemistry C Just Accepted Manuscript

Artículo original disponible en: http://pubs.acs.org/doi/abs/10.1021/jp4010136?prevSearch=molecules%2Bfor%2Belectronics&searchHistoryKey=

Surface Plasmon Mediated Chemical Solution Deposition of Gold Nanoparticles on a Nanostructured Silver Surface at Room Temperature

This paper provides proof of concept for a new method of nanoscale fabrication:  exploitation of the optical properties of a nanostructured substrate to induce nanoparticle growth.  Sub-15 nm Au nanoparticles have been fabricated on a nanostructured Ag surface at room temperature via a liquid-phase chemical deposition upon excitation of the localized surface plasmon resonance (SPR) of the substrate.  Measurement of the SPR-mediated photothermal local heating of the substrate surface by molecular thermometry indicated the temperature to be above 230 °C, which is sufficient to induce molecules of CH₃AuPPh₃ to form Au nanoparticles on the Ag surface. Particle sizes are tunable between 3 and 10 nm by adjusting the deposition time and the nanoparticle surfaces are surfactant-free.  The deposition kinetics have been measured, and are consistent with a surface-limited growth model.

Doc.: http://pubs.acs.org/doi/ipdf/10.1021/ja309392x

Jingjing Qiu †, Yung-Chien Wu †, Yi-Chung Wang †,Mark H. Engelhard ‡, Lisa McElwee-White *†, andWei David Wei *† Department of Chemistry and Center for Nanostructured Electronic Materials, University of Florida, Gainesville, Florida 32611, United States. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States. J. Am. Chem. Soc., 2013, 135 (1), pp 38–41. Publication Date (Web): December 16, 2012. American Chemical Society.

Electrones Ultrabrillantes permiten observar materiales orgánicos ultrarrápidos

La técnica, denominada difracción de electrones ultrarrápida (UED, del inglés Ultrafast Electron Diffraction), consiste en que un proceso ultrarrápido iniciado en una molécula por medio de un pulso láser de femtosegundos es resuelto en el tiempo por medio de una sonda consistente en pulsos de electrones ultrarrápidos que dan lugar a difracción, proporcionando así información estructural del sistema molecular en función del tiempo en la escala temporal de interés o, en otras palabras, su dinámica estructural.

Los trabajos pioneros en UED llevados a cabo en el grupo del Prof. Zewail, del Instituto de Tecnología de California .han permitido estudiar de esta manera reacciones químicas, dinámica molecular de estados excitados y cambios conformacionales en moléculas fuera del equilibrio, en sus escalas temporales ultrarrápidas características. Sin embargo, es en general un reto poder aplicar este método a materiales orgánicos con centros de dispersión débiles, termolábiles y de baja conductividad térmica. Estas características de los sistemas moleculares bajo estudio implican que la fuente de pulsos de electrones ultrarrápidos que proporciona la difracción deba ser extremadamente brillante con el fin de obtener difractogramas de alta calidad antes de que el calor acumulado por la excitación láser degrade la muestra o enmascare la dinámica estructural que se pretende medir. 

 

En el trabajo publicado en Nature por el grupo del Prof. Dwayne Miller del Departamento Max Planck de Dinámica Estructural de Hamburgo (Alemania) y del Departamento de Química de la Universidad de Toronto (Canada) [Nature,496, 343 (2013)] se ha demostrado cómo el empleo de una fuente de pulsos de electrones ultrabrillantes de femtosegundos ha permitido monitorizar movimientos moleculares en una sal orgánica, (EDO-TTF)₂PF₆, donde EDO-TTF es etilendioxitetratiafulvaleno, según esta sufre una transición de fase aislante-metal fotoinducida, superando los problemas mencionados. Después de la excitación de la sal orgánica con un pulso láser de femtosegundos, estos investigadores han sido capaces de medir patrones de difracción en función del tiempo, que permiten identificar cientos de reflexiones de Bragg con las que construir un mapa de la evolución estructural del sistema molecular. 

 

másinformación: http://www.rsef.org/fisica-al-dia/item/361-electrones-ultrabrillantes-permiten-observar-materiales-org%C3%A1nicos-ultrarr%C3%A1pidos

Faster Than Silicon: Redesigned Material Could Lead to Lighter, Faster Electronics

The same material that formed the first primitive transistors more than 60 years ago can be modified in a new way to advance future electronics, according to a new study.

Chemists at The Ohio State University have developed the technology for making a one-atom-thick sheet of germanium, and found that it conducts electrons more than ten times faster than silicon and five times faster than conventional germanium.

The material's structure is closely related to that of graphene -- a much-touted two-dimensional material composed of single layers of carbon atoms. As such, graphene shows unique properties compared to its more common multilayered counterpart, graphite. Graphene has yet to be used commercially, but experts have suggested that it could one day form faster computer chips, and maybe even function as a superconductor, so many labs are working to develop it.

Joshua Goldberger, assistant professor of chemistry at Ohio State, decided to take a different direction and focus on more traditional materials.

"Most people think of graphene as the electronic material of the future," Goldberger said. "But silicon and germanium are still the materials of the present. Sixty years' worth of brainpower has gone into developing techniques to make chips out of them. So we've been searching for unique forms of silicon and germanium with advantageous properties, to get the benefits of a new material but with less cost and using existing technology."

In a paper published online in the journal ACS Nano, he and his colleagues describe how they were able to create a stable, single layer of germanium atoms. In this form, the crystalline material is called germanane.

Researchers have tried to create germanane before. This is the first time anyone has succeeded at growing sufficient quantities of it to measure the material's properties in detail, and demonstrate that it is stable when exposed to air and water.

In nature, germanium tends to form multilayered crystals in which each atomic layer is bonded together; the single-atom layer is normally unstable. To get around this problem, Goldberger's team created multi-layered germanium crystals with calcium atoms wedged between the layers. Then they dissolved away the calcium with water, and plugged the empty chemical bonds that were left behind with hydrogen. The result: they were able to peel off individual layers of germanane.

Studded with hydrogen atoms, germanane is even more chemically stable than traditional silicon. It won't oxidize in air and water, as silicon does. That makes germanane easy to work with using conventional chip manufacturing techniques.

The primary thing that makes germanane desirable for optoelectronics is that it has what scientists call a "direct band gap," meaning that light is easily absorbed or emitted. Materials such as conventional silicon and germanium have indirect band gaps, meaning that it is much more difficult for the material to absorb or emit light.

"When you try to use a material with an indirect band gap on a solar cell, you have to make it pretty thick if you want enough energy to pass through it to be useful. A material with a direct band gap can do the same job with a piece of material 100 times thinner," Goldberger said.

The first-ever transistors were crafted from germanium in the late 1940s, and they were about the size of a thumbnail. Though transistors have grown microscopic since then -- with millions of them packed into every computer chip -- germanium still holds potential to advance electronics, the study showed.

According to the researchers' calculations, electrons can move through germanane ten times faster through silicon, and five times faster than through conventional germanium. The speed measurement is called electron mobility.

With its high mobility, germanane could thus carry the increased load in future high-powered computer chips.

"Mobility is important, because faster computer chips can only be made with faster mobility materials," Golberger said. "When you shrink transistors down to small scales, you need to use higher mobility materials or the transistors will just not work," Goldberger explained.

Next, the team is going to explore how to tune the properties of germanane by changing the configuration of the atoms in the single layer.

Lead author of the paper was Ohio State undergraduate chemistry student Elizabeth Bianco, who recently won the first place award for this research at the nationwide nanotechnology competition NDConnect, hosted by the University of Notre Dame. Other co-authors included Sheneve Butler and Shishi Jiang of the Department of Chemistry and Biochemistry, and Oscar Restrepo and Wolfgang Windl of the Department of Materials Science and Engineering.

The research was supported in part by an allocation of computing time from the Ohio Supercomputing Center, with instrumentation provided by the Analytical Surface Facility in the Department of Chemistry and Biochemistry and the Ohio State University Undergraduate Instrumental Analysis Program. Funding was provided by the National Science Foundation, the Army Research Office, the Center for Emergent Materials at Ohio State, and the university's Materials Research Seed Grant Program

Elisabeth Bianco, Sheneve Butler, Shishi Jiang,Oscar D. Restrepo,Wolfgang Windl, and Joshua E. Goldberger.

Doc.:http://pubs.acs.org/doi/pdf/10.1021/nn4009406