Agilent Measurement Journal - Issue 3 - 2007 - (Page 13)

Traditional optical and electron microscopy techniques are widely used in nanotechnology research. Electron microscopes, used in both scanning and transmission conﬁgurations, make it possible to see small details on large surfaces. The scanning electron microscrope (SEM) uses a focused electron beam to see areas as small as 1 nm on the surface of a sample (Figure 3). As the beam is scanned (rastered) across the surface, many types of signals (e.g., secondary electrons, backscattered electrons or Auger electrons) are collected and used to generate an image. Analyzing chemical composition Chemists were among the earliest nanotechnology researchers, building molecules at the nanoscale. Gas and liquid chromatography are the most popular tools for the separation of complex mixtures of molecules by their chemistry. In liquid chromatography, the chemical mixtures of interest are transported by a liquid solvent through a column packed with solid particles (stationary phase), causing the molecules to progress through the column at different rates based on their chemical afﬁnity to the stationary phase. In gas chromatography, the chemical mixture is similarly transported in gas phase by a carrier gas through a column treated to have variable afﬁnity for the constituents of the mixture (Figure 5). Scanning electron microscope Electrons Detector Sample injector Flow controller Material must have a conductive surface Figure 3. An SEM streams electrons at a conductive surface and creates an image based on the reﬂected information. Waste Another popular imaging tool is the transmission electron microscope (TEM). These expensive machines project high-energy electrons through the sample, making it possible to image at very high resolution because electron wavelengths are much smaller than 1 nm (Figure 4). For the TEM to work properly — and provide atomic resolution — the sample material must be reduced in thickness to a few hundred nanometers. Carrier gas Column Column oven Detector Figure 5. A gas chromatograph ionizes chemical compounds and detects individual molecules of the constituent materials. Tunneling electron microscope Electrons Material must be in a thin slice An MS can measure the mass-to-charge ratio of individual molecules (Figure 6). It is quite often used in conjunction with a gas chromatograph (GC/MS) or liquid chromatograph (LC/MS), either of which can separate a complex mixture for subsequent quantitative identiﬁcation by the MS. As an example, Yonsei University in Korea uses an LC/MS to examine byproducts from the creation of core-shell nanoparticles, which have a core of one element surrounded by a shell of another element.1 Detector Figure 4. A TEM sends high-powered electrons through the sample to create a 3D view. Agilent Measurement Journal 13

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 3 - 2007

Applying Ingenuity to the Measurement of Emerging Technologies Contents Emerging Innovations Department Delivering Bigger Benefits by Optimizing Customer Workflows Measuring Material Properties at the Nanoscale Utilizing In Situ Atomic Force Microscopy in Life Science, Pharmaceutical and other Bio-Related Applications WiMAX™: Plotting a New Path to Global Mobility Addressing the Triple Complexity of Triple-Play Networks What Next for Mobile Telephony? Exploring the Inner Workings of Tire-Pressure Monitoring Systems Developing, Assessing and Applying a High-Resolution Thin-Film Magnetic Probe Making Accurate Settling-Time Measurements Using a Vector Network Analyzer Applying Metabolomics Methods to the Study of Bacterial Leaf Blight in Rice Plants Measuring Stream Dynamics with Fiber Optics survey

Agilent Measurement Journal - Issue 3 - 2007

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