Balasubramanian, K., Burghard, M., Electrochemically functionalized carbon nanotubes for device applications. Journal of Materials Chemistry. 18 (2008) 3071-3083.

Purpose of the study

To examine the many applications of carbon nanotubes and look at how electrochemical functionalization can expand these applications.  Using electrochemistry-based approaches, carbon nanotubes can be functionalized to serve a wide range of applications such as reinforced composites, field-emission displays, scanning probe tips, and molecular-scale electronic devices.

Methods

Several methods used to extend or enhance the applications of nanotubes based on electrochemical functionalization are surveyed in this paper.  Electrochemical functionalization involves the creation of an active species from a precursor in the vicinity of a working electron.  Methods to electrochemically functionalize nanotubes can be broken into covalent functionalization and non-covalent functionalization including electropolymerization, electrodeposition of inorganic compounds, electrodeposition of mixed carbon nanotube-polymer films, and electrophoretic deposition.

Key Points

1.    Electrochemically functionalized carbon nanotubes have a wide range of applications and this paper primarily focuses on their application as a sensing device, specifically biosensing.
2.    Due to their high surface area and chemical stability, carbon nanotubes make very good nanoscale sensors.
3.    The small size of nanotubes makes the ideal for accessing the interior of redox enzymes and other small areas needed in chemical sensing
4.    Several different biosensing methods can be carried out with functionalized nanotubes
a.    Electrochemical sensors
b.    Chemiresistors
c.    Electrochemical field-effect sensors
5.    Possible applications of future development with electrochemically functionalized carbon nanotubes include energy storage such as super-capacitors or rechargeable batteries, advanced membranes, and nanoscale probes for fluid flow

J Fang, J Fu and F Ayazi, Metal-organic thin-film encapsulation for MEMS. Journal Micromechanics and Microengineering. 18 (2008) 105002-105010.

Purpose of the study

To demonstrate proof-of-concept for a metal-organic thin-film encapsulation technique based on photolithography of multiple layers of positive-tone photo-definable polymer.  To prove this concept, a MEMS device was successfully encapsulated.

Methods

A piezoelectrically-actuated length-extensional bulk acoustic wave resonator (MEMS device) is encapsulated in a metal-organic thin-film in order to seal the device to keep out moisture and debris from the sensitive areas of MEMS devices.  To form this encapsulation, photolithography of multiple layers of Novalac-based positive-tone photoresist are assembled to construct a cavity which houses the device.  Blanket metallization is then used to seal this enclosure.

Key Points

1.    The device used in this experiment (a ZnO-on-silicon piezoelectric bulk-acoustic resonator) was fabricated by the authors of this paper, using techniques including deep reactive ion etching (DRIE), RF sputtering, and dc sputtering
2.    Advantages of this technique include
a.    The ability to complete the process with relatively low temperatures
b.    Benign release environment
c.    Residue-free cavities
d.    Can electrically isolate multiple interconnects without patterning due to its geometry
e.    Can be done for almost any positive-tone polymer
3.    The methods described in this paper can also be used to build microfluidic systems for lab-on-a-chip applications.

Carbon Nanotubes as Reinforcement Elements of Composite Nanotools

Nakabayashi, Moreau, Coluci, Galvao, Cotta, Ugarte. Carbon Nanotubes as Reinforcement Elements of Composite Nanotools. Nano Letters Vol. 8 No. 3 (2008) 842-847.

Purpose of the study

To develop reinforced carbon-carbon composite nanotools such as AFM probes and evaluate their performance and durability.

Methods

Borrowing ideas applied to the creation of reinforced concrete, the authors generated high aspect ratio nanotools by immersing a carbon nanotube in a diamond-like carbon matrix to create a reinforced carbon-carbon composite.  These devices were tested by nanomanipulation experiments performed in situ in a scanning electron microscope (SEM) and also computationally with molecular dynamics simulations.  The composite carbon nanotube was also evaluated as a tip for an AFM (atomic force microscopy).

Key Findings

1.    Carbon nanotubes can be easily reinforced with hard amorphous carbon to provide a stonger nanotube that is suitable for use as an AFM tip and also improves the life and performance of the device.
2.    The composite carbon nanotube performed well as an AFM tip generating excellent vertical and lateral image resolution and even after four hundred images, there was no reduction of imaging capabilities.  Compared to commercially available AFM tips that may experience image quality degradation after 10-20 images, this is quite an improvement.
3.    The resilience of this device is also much improved by reinforcement with the carbon composite.  It allows the nanotube to bend without breaking and contributes to the much longer device life when compared to Si based tips.
4.    Negative aspects of these devices such as flexibility and vibration can be controlled without affecting the device’s performance and life.

Overbased nanodetergents as oil additives

Hudson, Eastoe, Dowding. Nanotechnology in action: Overbased nanodetergents as lubricant oil additives. Advances in Colloid and Interface Science 123-126 (2006) 425-431

Purpose of the study

To develop a method to produce uniform nanoparticles on a large scale to be used for detergents in lubrication oils additives.

Methods

Nanodetergents consist of  two main parts: an inorganic core (typically nanoparticles of calcium carbonate and calcium hydroxide) and an oil-soluble surfactant.  The preparation of the metal carbonate nanoparticles is done by microemulsion.  Several nanodetergents were characterized using a number of different methods including small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and Transmission electron microscopy.  Molecular simulations were also performed on nanodetergents.

Key Points

1.    Improvements in nanoparticle detergent technology are driven by the need for better fuel economy and longer running engine parts as well as recent environmental legislature on emissions.
2.    According to the authors, the primary functions of nanoparticle detergents in engine oils are acid neutralization, high temperature detergency, oxidation inhibition, and rust prevention.  In general cleaner and more efficient engine performance.
3.    The detergent core is made of metallic nanoparticles typically 1-10 nm in diameter.  This core is surrounded by a surfactant layer composed of surfactants such as phenates, sulphonates, salicylates, and phosphates with sulphonates being the most widely used.
4.    Synthesis of these nanodetergents require large amounts of solvents such as xylene and methanol and future research will likely focus on decreasing the use of the solvents while still producing these nanodetergents on a large scale.

Definitions from the Paper

“The term ‘Overbased’ refers to the fact that the quantity of base incorporated in the particle cores is greater than that needed to neutralize the acid surfactant.”