Paper SS1-FrM6
Surface Deposition and Characterization of Cu Clusters Utilizing Soft-Landing Drift Tube Spectrometry

Friday, November 13, 2009, 10:00 am, Room M

Intro

The soft-landing of ion cluster onto a surface is a novel approach for the deposition of specifically selected cluster. Our approach differs from current deposition/ soft landing techniques in that it allows specific molecule to be landed with a KE of around 1-5 eV where current soft-landing techniques are in the range around 30 - 50 eV. Large KE may not be ideal for the landing of metal clusters as the energy is translated into motion along the surface resulting in aggregation along defects in the surface. We have recently developed soft-landing system using a drift tube, high pressure (1 – 100 torr), and a modified substrate to create a soft-landing around 1 - 5 eV. Surface modifications can isolate clusters and protect them from aggregation. This soft-landing method allows for the characterization of a specific soft landed metal cluster on the surface via AFM, Raman Spectroscopy, and Electrochemistry.

Method

Our soft-landing instrument allows for the direct ablation of metal samples via laser or atmospheric plasma. Laser ablation of a metal sample by a pulsed Nd:YAG laser for duration of 1-3 hrs acts as our source for ion clusters. The instrument is operated at a pressure between 1-13 torr, with a voltage between 10-500 ±V that is applied uniformly across the drift tube. Helium is used as a buffer gas and acts as a means to control cluster formation. The high pressure narrows the clusters KE from 40 eV to about 1 eV through collisions via the buffer gas. Clusters travelling within the drift tube are separated based on collisonal cross-section. A pulsed split ring assembly at the end of the drift tube isolates specifically selected clusters directly on an unprepared or modified surface. The sample surface is then removed for characterization.

Data

Drift Tube spectra collected at 8 torr shows a cluster range of n = 1-8 along with corresponding Cu_nO. Clusters that have been landed on the surface are characterized using AFM. Images show an aggregation of the clusters in a striation patterns along the surface. The bridging across a defect instead of deposition within has also been seen. This clustering, aggregation, and growth shows a soft-landing has been made on the surface keeping the Cu cations and clusters intact. Self assembly of specifically isolated cluster groups has also been shown to occur on the surface of mica. Other characterization methods and various clusters may be specifically selected and landed with time allowing further development.

Instrument operates at pressure/temperature closer to ambient conditions than currently available, allowing ions to be soft landed on various modified surfaces for isolation and characterization.