Akram Boukai
California Institute of Technology
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Publication
Featured researches published by Akram Boukai.
Nature | 2008
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
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
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
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
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
Nicholas A. Melosh; Akram Boukai; Frédéric S. Diana; Brian D. Gerardot; Antonio Badolato; P. M. Petroff; James R. Heath
Advanced Materials | 2006
Akram Boukai; Ke Xu; James R. Heath
Nano Letters | 2006
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
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
Akram Boukai; Yuri Bunimovich; William A. Goddard; James R. Heath; Jamil Tahir-Kheli