Navigation Links
Strong elasticity size effects in ZnO nanowires
Date:10/14/2008

Recently, zinc oxide (ZnO) nanowires have drawn major interest because of their semiconducting nature and unique optical and piezoelectric properties. Various applications for ZnO nanowires have been conceived, including the next generation of field effect transistors, light emitting diodes, sensors and resonators. ZnO nanowires are also envisioned as nanogenerators by exploiting the coupling of semiconducting and piezoelectric properties.

Researchers at the McCormick School of Engineering and Applied Science at Northwestern University recently performed experiments and computations to resolve major existing discrepancies about the scaling of ZnO nanowires elastic properties. These properties are essential to the design of reliable novel ZnO devices, and the insight emerging from such studies advances scientific understanding about atomic structures, which are also responsible for piezo-electric and piezo-resistive properties.

ZnO nanowires usually have a hexagonal cross-section, with diameters ranging from 5 to 500 nanometers. Interesting changes in their properties arise as the diameter of the wires decreases due to increasing surface-to-volume ratio. Unfortunately, experimental results reported in the literature on wire elasticity for a given diameter exhibit a large variability.

"This highlights one of the major challenges in the field of nanotechnology the accurate measurement of nanoscale mechanical properties," says Horacio Espinosa, professor of mechanical engineering at McCormick. "Indirect measurement techniques and ill-defined boundary conditions affected mechanical properties measurements and resulted in problematic inconsistencies."

Espinosa and his group at Northwestern resolved this discrepancy using a nanoscale material testing system based on microelectromechanical system (MEMS) technology. The system was used to perform in-situ electron microscopy tensile testing of nanowire specimens. Load and displacements were measured electronically while the deforming material was imaged with atomic resolution.

"Direct atomic imaging was instrumental in assessing the effectiveness of the test," Espinosa says.

The experimental findings revealed that the elastic stiffness of ZnO nanowires monotonically increases as their diameter decreases. Atomic level computational studies were also conducted to identify the reasons for the observed size effect.

"Our experimental method is the most direct and simplest in terms of data interpretation," says Bei Peng, a McCormick graduate student and co-author of the paper. "We feel quite certain on all the quantities we have measured. Moreover, the fact that the experimental trends and atomistic predictions agree is quite rewarding."

In this research article, the reason for the observed size dependence was also reported.

"Atoms on the surface of the wires are rearranged because they have fewer neighboring atoms as compared to atoms in the core of the nanowire," says Ravi Agrawal, a McCormick graduate student and co-author of the paper. "The resulting surface reconstruction leads to wire material properties very different to that encountered in bulk."

This phenomenon has been observed previously for various metallic nanowires with large surface-to-volume ratios, but the surface effect was confined to wires with diameters smaller than approximately 10 nm.

"Due to the ionic character of ZnO, the atoms interact via electrostatic forces, which are long-range in nature. Therefore, the size effect is found to be significant up to nanowires with diameters of about 80 nm," says Eleftherios Gdoutos, an undergraduate student and co-author of the paper.

"Our research approach based on a combined experimental-computational investigation of the mechanics of nanowires is very promising," Espinosa says. "We are currently employing MEMS devices that allow piezo-electric and piezo-resistive characterization of semiconducting nanowires. We are also investigating the effect of the identified atomic surface reconstruction on polarization and energy bands, which should impact piezo-electricity and electric conductivity."


'/>"/>

Contact: Kyle Delaney
k-delaney@northwestern.edu
847-467-4010
Northwestern University
Source:Eurekalert

Related biology technology :

1. STALLERGENES : Strong Business Growth: +17% and Earnings Per Share up 30%
2. Dawson James Securities Initiates Research Coverage on CryoCor, Inc. (Nasdaq: CRYO) with a Strong Buy Rating and $6.00 Target Price
3. Strong Demand Pushes up Both Prices and Sales Volumes for Dragons Main Products
4. U-M research: New plastic is strong as steel, transparent
5. Nobel Award in Medicine Holds Strong Messsage for Animal Activists
6. Monsanto Sees Record Sales in Fiscal Year 2007; Seeds and Traits Business Contributes to Strong Fourth Quarter and Year-End Results
7. Gen-Probe Reports Strong Financial Results for Third Quarter 2007, Raises Full-Year Guidance for Earnings Per Share and Total Revenues
8. Cephalon Announces Strong Third Quarter Financial Results
9. Edwards Lifesciences Forecasts Strong Growth in 2008
10. Genoptix Reports Strong Financial Results For Third Quarter 2007
11. STALLERGENES: 2007: A Further Year of Strong Growth: Up 16%
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:3/23/2017)... Md. , March 23, 2017  Northwest ... developing DCVax® personalized immune therapies for solid tumor ... the $7.5 million financing it announced last Friday, ... sold to several institutional investors securities totaling 28,843,692 ... per share, and 10,000,000 shares of Class C ...
(Date:3/23/2017)... (PRWEB) , ... March 23, 2017 , ... ... was recently selected by the Connecticut Technology Council (CTC) as a 2017 Women ... CTC’s thirteenth annual Women of Innovation Awards Dinner. , The dinner recognizes women ...
(Date:3/23/2017)... , March 23, 2017  Agriculture technology company ... A financing and note conversion to commercialize its Cool ... is focused on developing products that are simultaneously profitable ... million in the last 18 months. This latest round ... Bridge Venture Partners. The company,s primary ...
(Date:3/22/2017)... (PRWEB) , ... March 22, 2017 , ... ... up human tissue regeneration from small lab samples to full-size tissues, bones, even ... to establish a vascular system that delivers blood deep into the developing tissue. ...
Breaking Biology Technology:
(Date:3/23/2017)... Research and Markets has announced the addition of the "Global ... 2025" report to their offering. ... The Global Vehicle Anti-Theft System Market is ... next decade to reach approximately $14.21 billion by 2025. ... all the given segments on global as well as regional levels ...
(Date:3/20/2017)... At this year,s CeBIT Chancellor Dr. Angela ... The Chancellor came to the DERMALOG stand together with the Japanese Prime ... partner country. At the largest German biometrics company the two government leaders ... iris recognition as well as DERMALOG´s multi-biometrics system.   ... ...
(Date:3/9/2017)... , Australia , March 9, ... study data at the prestigious World Lung Imaging Workshop ... Andreas Fouras , was invited to deliver the ... pulmonary medicine. This globally recognised event brings together leaders ... share the latest developments in lung imaging. ...
Breaking Biology News(10 mins):