Power generation with laterally packaged piezoelectric fine wires

Rusen Yang, Yong Qin, Liming Dai and Zhong Lin Wang

Nature Nanotechnology Advance online publication, 9 November 2008

Purpose of the Study

Demonstrate a flexible power generator based on cyclic stretching–releasing of a piezoelectric fine wire that has a number of advantages over generators based on vertically aligned nanowire arrays.

Methods

The generator was fabricated by bonding a ZnO piezoelectric fine wire (PFW) laterally on a Kapton polyimide film. Both ends of the PFW is fixed to electrodes. A current/voltage measurement meter was connected to two ends of the PFW without introducing any external power source in the circuit.

Key Findings

1.   When the substrate bends and stretches the wire, a tensile strain of 0.05–0.1% is induced in the wire, and forcing electrons to flow along an external circuit to charge the wire. And when the substrate is released, electrons flow back in the opposite direction.

2.    Periodically bending and releasing the PFW therefore generates an alternating current, which can be up to ~50 mV, and the energy conversion efficiency of the wire can be as high as 6.8%.

3.    Generators based on multiple PFWs can be integrated to raise the output voltage.

Important Definitions

1.    Piezoelectricity: Piezoelectricity is the ability of some materials to generate an electric potential in response to applied mechanical stress.

2.    Kapton: Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -269 °C to +400 °C (4 K-673 K).

Improved nanofabrication through guided transient liquefaction

Stephen Y. Chou and Qiangfei Xia

Nature Nanotechnology Vol 3, May 2008, 295-300.

Purpose of the Study

Demonstrate a new approach called self-perfection by liquefaction, which can remove fabrication defects and improve nanostructures post-fabrication.

 

Methods

The self-perfection by liquefaction (SPEL) method involves selectively melting nanostructures for a short period of time (hundreds of nanoseconds) by laser pulse. It also applies a set of boundary conditions (like a flat plate) to guide the flow of the molten material into the desired geometry before solidification.

 

Key findings

1.     Using the open-SPEL method the 3σ line-edge roughness(LER) of 70-nm-wide chromium grating lines was reduced from 8.4 nm to less than 1.5 nm, which is well below the ‘red-zone limit’ of 3 nm discussed in the International Technology Roadmap for Semiconductors.

2.     After guided-SPEL (using a 40 nm gap and a 595 mJ cm^-2 pulse), the width of a silicon line was reduced from 285 nm to 175 nm, while its height increased from 50 nm to 90 nm.

3.     Self-perfection by liquefaction (SPEL) can also be extended to other metals and semiconductors, dielectrics and large-area wafers.

 

Important Definitions

1.     open-SPEL: the nanostructures are located on a substrate without any additional boundary conditions.

2.     guided-SPEL: a flat plate is placed above the nanostructures that are to be improved, with a gap between the plate and the nanostructure.

 

 

Growth and Characterization of InP Nanowires with InAsP Insertions

Maria Tchernycheva, George E. Cirlin, Gilles Patriarche, Laurent Travers, Valery Zwiller, Umberto Perinetti, and Jean-Christophe Harmand.

Nano Letters 2007 Vol.7, No.6, 1500-1504.

 

Purpose of the study

Fabricate InP nanowires with embedded InAsP insertions by Au-assisted molecular beam epitaxy.

Methods

InAsP insertions in InP nanowires were fabricated by Au-assisted molecular beam epitaxy(MBE) growth techniques. The growth temperature affects the nucleation on the nanowire lateral surface. It is therefore possible to grow the wires in two steps: to fabricate an axial heterostructure (at 420℃), and then cover it by a shell (at 390℃).

 

Key findings

1.     The wire shape was shown to change from pencil-like for 390℃growth to cylindrical for 420℃ growth.

2.     The InAsP alloy composition could be varied between InAs_0.35P_0.65 and InAs_0.5P_0.5 by changing the As to P flux ratio.

3.     The presence of InP shells around the InAsP insertions is important to observe efficient photoluminescence(PL) emission. When a shell is present, the InAsP insertions show room-temperature photoluminescence peaked in the 1.2-1.55µm wavelength range. If the axial heterostructure has no shell, luminescence intensity is drastically reduced.

4.     The micro-PL from isolated nanowires shows narrow lines with a full width at half-maximum(FWHM)  as small as 12µeV.

 

Important definitions

1.     Molecular beam epitaxy(MBE)-MBE is one of several methods of depositing single crystals, which takes place in high vacuum or ultra high vacuum. The most important aspect of MBE is the slow deposition rate (typically less than 1000 nm per hour), which allows the films to grow epitaxially.

 

Thermal Conductivity in Thin Silicon Nanowires: Phonon Confinement Effect

Inna Ponomareva, Deepak Srivastava, Madhu Menon.

Nano Letters Vol.7 No.5 (2007) 1155-1159

 

Purpose of the study

Use direct molecular dynamics simulations to calculate thermal conductivity of thin silicon nanowires(1.4~8.3nm) including the realistic crystalline structure and surface reconstruction effects.

 

Methods

The thermal conductivity is calculated using the direct method and is analogous to the experimental method. This method requires the use of nonequilibrium molecular dynamics(NEMD). The Si-Si interaction potential used in the molecular dynamics simulations is taken to be the Stillinger-Weber(SW) many-body potential. Using this method all of the nanowire structures were fully relaxed, allowing for realistic surface reconstruction.

 

Key findings

1.       There is a maximum in the thermal conductivity between 100 and 200K for tetrahedral wire with similar diameters, while for the clathrate wire, there is no peak in the temperature range considered above.

2.       Thermal conductivity of tetrahedral wires at 100K decreases with diameter decreasing from 7.7 to 3.4. However, as the nanowire diameter decrease further, the thermal conductivity starts to increase. Similar behavior was also observed in clathrate nanowires, while there is no increase in the thermal conductivity for up to 8.2 nm diameter clathrate nanowire.

3.       As the diameter of the nanowire decreases, the lowest frequency and longest wavelength excited mode shows the signature of confinement. It dominates the changes in the spectra in the low frequency region resulting in a larger amount of energy carried by the longest wavelength phonon and an increase in the thermal conductivity for the smallest diameter nanowire.

4.       The thermal conductivity increase at low temperatures can be attributed mainly to the increase in the frequency of the lowest mode with decreasing diameter.

 

Important definitions

1.       Phonon: a quantized mode of vibration occurring in a rigid crystal lattice

2.       Tetrahedron: a polyhedron composed of four triangular faces, three of which meet at each vertex.

3.       Clathrate: a structure consisting of a lattice of one type of molecule trapping and containing a second type of molecule.