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Dive into the research topics where Akram Boukai is active.

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Featured researches published by Akram Boukai.


Nature | 2008

Silicon nanowires as efficient thermoelectric materials

Akram Boukai; Yuri Bunimovich; Jamil Tahir-Kheli; Jen-Kan Yu; William A. Goddard; James R. Heath

Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT—a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another. Several groups have achieved significant improvements in ZT through multi-component nanostructured thermoelectrics, such as Bi2Te3/Sb2Te3 thin-film superlattices, or embedded PbSeTe quantum dot superlattices. Here we report efficient thermoelectric performance from the single-component system of silicon nanowires for cross-sectional areas of 10 nm × 20 nm and 20 nm × 20 nm. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk Si are achieved over a broad temperature range, including ZT ≈ 1 at 200 K. Independent measurements of the Seebeck coefficient, the electrical conductivity and the thermal conductivity, combined with theory, indicate that the improved efficiency originates from phonon effects. These results are expected to apply to other classes of semiconductor nanomaterials.


Nature | 2007

A 160-kilobit molecular electronic memory patterned at 10 11 bits per square centimetre

Jonathan E. Green; Jang Wook Choi; Akram Boukai; Yuri Bunimovich; Ezekiel Johnston-Halperin; Erica DeIonno; Yi Luo; Bonnie A. Sheriff; Ke Xu; Young Shik Shin; Hsian-Rong Tseng; J. Fraser Stoddart; James R. Heath

The primary metric for gauging progress in the various semiconductor integrated circuit technologies is the spacing, or pitch, between the most closely spaced wires within a dynamic random access memory (DRAM) circuit. Modern DRAM circuits have 140 nm pitch wires and a memory cell size of 0.0408 μm2. Improving integrated circuit technology will require that these dimensions decrease over time. However, at present a large fraction of the patterning and materials requirements that we expect to need for the construction of new integrated circuit technologies in 2013 have ‘no known solution’. Promising ingredients for advances in integrated circuit technology are nanowires, molecular electronics and defect-tolerant architectures, as demonstrated by reports of single devices and small circuits. Methods of extending these approaches to large-scale, high-density circuitry are largely undeveloped. Here we describe a 160,000-bit molecular electronic memory circuit, fabricated at a density of 1011 bits cm-2 (pitch 33 nm; memory cell size 0.0011 μm2), that is, roughly analogous to the dimensions of a DRAM circuit projected to be available by 2020. A monolayer of bistable, [2]rotaxane molecules served as the data storage elements. Although the circuit has large numbers of defects, those defects could be readily identified through electronic testing and isolated using software coding. The working bits were then configured to form a fully functional random access memory circuit for storing and retrieving information.


Nano Letters | 2009

High Density n-Si/n-TiO2 Core/Shell Nanowire Arrays with Enhanced Photoactivity

Yun Jeong Hwang; Akram Boukai; Peidong Yang

There are currently great needs to develop low-cost inorganic materials that can efficiently perform solar water splitting as photoelectrolysis of water into hydrogen and oxygen has significant potential to provide clean energy. We investigate the Si/TiO(2) nanowire heterostructures to determine their potential for the photooxidation of water. We observed that highly dense Si/TiO(2) core/shell nanowire arrays enhanced the photocurrent by 2.5 times compared to planar Si/TiO(2) structure due to their low reflectance and high surface area. We also showed that n-Si/n-TiO(2) nanowire arrays exhibited a larger photocurrent and open circuit voltage than p-Si/n-TiO(2) nanowires due to a barrier at the heterojunction.


Nano Letters | 2010

Oligo- and Polythiophene/ZnO Hybrid Nanowire Solar Cells

Alejandro L. Briseno; Thomas W. Holcombe; Akram Boukai; Erik C. Garnett; Steve W. Shelton; Jean J. M. Fréchet; Peidong Yang

We demonstrate the basic operation of an organic/inorganic hybrid single nanowire solar cell. End-functionalized oligo- and polythiophenes were grafted onto ZnO nanowires to produce p-n heterojunction nanowires. The hybrid nanostructures were characterized via absorption and electron microscopy to determine the optoelectronic properties and to probe the morphology at the organic/inorganic interface. Individual nanowire solar cell devices exhibited well-resolved characteristics with efficiencies as high as 0.036%, J(sc) = 0.32 mA/cm(2), V(oc) = 0.4 V, and a FF = 0.28 under AM 1.5 illumination with 100 mW/cm(2) light intensity. These individual test structures will enable detailed analysis to be carried out in areas that have been difficult to study in bulk heterojunction devices.


Angewandte Chemie | 2001

Preparation and Properties of Polymer‐Wrapped Single‐Walled Carbon Nanotubes

Alexander Star; J. Fraser Stoddart; David W. Steuerman; Mike Diehl; Akram Boukai; Eric W. Wong; Xin Yang; Sungwook Chung; Hyeon Choi; James R. Heath


Science | 2003

Ultrahigh-Density Nanowire Lattices and Circuits

Nicholas A. Melosh; Akram Boukai; Frédéric S. Diana; Brian D. Gerardot; Antonio Badolato; P. M. Petroff; James R. Heath


Advanced Materials | 2006

Size-Dependent Transport and Thermoelectric Properties of Individual Polycrystalline Bismuth Nanowires**

Akram Boukai; Ke Xu; James R. Heath


Nano Letters | 2006

Circuit fabrication at 17 nm half-pitch by nanoimprint lithography.

Gun Young Jung; Ezekiel Johnston-Halperin; Wei-Li Wu; Zhaoning Yu; Shih-Yuan Wang; William M. Tong; Zhiyong Li; Jonathan E. Green; Bonnie A. Sheriff; Akram Boukai; Yuri Bunimovich; James R. Heath; R. Stanley Williams


Faraday Discussions | 2006

Spiers Memorial Lecture - Molecular mechanics and molecular electronics

Robert Beckman; Kris Beverly; Akram Boukai; Yuri Bunimovich; Jang Wook Choi; Erica DeIonno; Johnny Green; Ezekiel Johnston-Halperin; Yi Luo; Bonnie A. Sheriff; J. Fraser Stoddart; James R. Heath


Archive | 2008

Methods and devices for controlling thermal conductivity and thermoelectric power of semiconductor nanowires

Akram Boukai; Yuri Bunimovich; William A. Goddard; James R. Heath; Jamil Tahir-Kheli

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James R. Heath

University of California

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Yuri Bunimovich

California Institute of Technology

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Bonnie A. Sheriff

California Institute of Technology

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Jonathan E. Green

California Institute of Technology

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Erica DeIonno

The Aerospace Corporation

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William A. Goddard

California Institute of Technology

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Yi Luo

California Institute of Technology

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