Student Project Abstracts 2005 - Pluto - University of Washington

Toward Molecular Resolution c-AFM with Carbon Nanotube Tips:Development of Carbon Nanotube Growth TechniquesAustin McLeodNorthern Arizona UniversityNeal R. Armstrong, Paul Lee and Ken NebesnyArmstrong Lab, Department of ChemistryThe University of ArizonaCarbon nanotube tips (CNTs) will be formed for use in nanometer scale imaging in atomicforce microscopy. Optimized versions of these tips promise to provide for very high-resolutionimaging, minimization of sample damage due to the weak interactions anticipated betweenthe tip and soft materials (organic thin films), and the prospect for measuring electricalproperties of organic thin film, owing to the electrically conductive nature of the CNT.OBJECTIVES / THESISAFM nanometer-scale imaging is hindered by standard AFMtips because they have poor aspect ratios, which can cause sampledamage during the investigation of the surfaces of organic films.AFM tips modified with carbon nanotubes (CNTs) should helpgreatly to increase the resolution, owing to the small diameterof the CNT and excellent aspect ratios. The Dai group at StanfordUniversity has developed a process to grow carbon nanotubeson silicon wafer tips in mass quantities. 1 Our approach isto grow nanotubes in carpet like fashion and pick them up usingthe method of dielectrophoresis developed by Hyung Woo Lee. 2Ultimately, we anticipate growing carbon nanotubes directly ontoindividual AFM tips.Most carbon nanotubes are about 10-50 nm in diameter andbetween 100 – 1000 nm long, some have been grown to about 2mm in length, but that length will not be necessary for our work.Carbon nanotubes are typically grown from a catalytic nanoparticlesurface (the iron particle), which becomes the nucleation siteof the nanotube’s growth and a carbon source, which becomesthe structure of the nanotube. Nanotubes with a 10:1 aspect ratiowould be preferred, meaning about 100-200 nm long and 10-20nm in diameter.RESEARCH METHODS / RESULTSCarbon nanotubes are typically grown via chemical vapor depositionat low pressures, using catalytic nanoparticles to initiatetube growth and location of the tube. Usually, carbon nanotubesattach very tightly to the nanoparticles, making separation difficult.Carbon nanotubes can also be attached directly to conventionalAFM tips. A group from the Korea Advanced Instituteof Science and Technology has developed a technique to attachthe nanotubes directly to the AFM tip. 2 Our first attempts willbe to grow carbon nanotubes on silicon nitride surfaces becausethat is what AFM tips are made from, growing nanotubes directlyonto the AFM tip at the correct orientation might be difficult, so abenchmark experiment was preformed.In our first experiment we tried to grow carbon nanotubes ona silicon nitride wafer using a ferric nitrate, Fe(NO 3)3 • 9H 2 O,solution to coat the silicon surface with iron particles. Chemicalvapor deposition (CVD) was utilized to grow the SWNT in aquartz tube using acetylene as the carbon source and ultra-highpurity (UHP) nitrogen gas as the carrier gas. AFM was used tocharacterize the silicon nitride surface. AFM showed that theferric nitrate iron source yielded, what looked like, “megatubes”(Figure 1).Figure 1. AFM image of CVD with Ferric Nitrate Catalyst sourceThe next technique involved using an iron source that was alreadyon the nanometer scale. Ferrosound EMG 1111 nanoparticlesmade by Ferrotec, Inc were cleaned and separated in ethanol,CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 77