Agilent Measurement Journal - Issue 3 - 2007 - (Page 12)

separation equipment coupled to sensitive mass spectrometers (MS). Example instruments include chemical analyzers such as gas chromatographs (GC) or liquid chromatographs (LC), sometimes augmented with MS instrumentation. Measurements of biological materials at the nanoscale require a highly sensitive instrument called a bioanalyzer that uses electrophoresis techniques to identify key molecules such as proteins. Looking across all disciplines, it’s clear that meaningful results depend on highly sensitive measurements that are also reliable and repeatable. Fortunately, a variety of solutions are available — some that provide direct measurements and others that act as surrogate measurements to enable indirect derivation of nanoscale characteristics and behaviors. By carefully measuring the tip/sample interaction, an AFM can detect the adhesion, friction and roughness of the surface as it scans. By measuring the force of cantilever motion, an AFM can also derive sample properties such as hardness, stiffness, elasticity, magnetic force or electrostatic force. AFMs can be conﬁgured to image materials immersed in liquids, a capability that is useful because many surfaces behave differently in such environments. In addition, AFMs are suitable for making mechanical measurements on living cells and locating molecules with high speciﬁcity. The AFM is also an important tool in the identiﬁcation and manipulation of nanoscale devices. By attaching a speciﬁc molecule to the tip of the AFM and dragging it across a surface, the molecule can be used to ﬁnd a speciﬁc nanoscale object such as a protein. Once found, the AFM tip can be used to push the protein (if the molecule repels) or pull it (if the molecule attracts). Manipulating nanoscale devices is a common use for the AFM. The AFM also can be used in conjunction with electronic instruments to make measurements on devices or surfaces. If the tip is connected to an electronic instrument (as a probe), it can measure properties such as current, voltage, capacitance or impedance as it moves across the surface. For example, connecting a network analyzer to an AFM makes it possible to extract S-parameters from nanoscale devices (Figure 2). Imaging with advanced microscopy Although scanning probe microscopes (SPM) and the popular subset of atomic force microscopes (AFM) are called “microscopes,” they are quite different from conventional optical microscopes. For instance, an AFM works much like a phonograph needle with a tip that is moved across a surface in two dimensions while sensing vertical motion (Figure 1). The resulting set of data points is combined to create a three-dimensional topography of the scanned surface. Atomic force microscope Scanning capacitance Photo detector Laser beam Network analyzer Coaxial cable Cantilever Tip Line scan Surface Photo detector Microwave diplexer Cantilever Tip atoms Force Surface atoms Surface Laser beam Coaxial resonator Figure 2. Coupling an AFM with a network analyzer creates a solution for scanning-capacitance microscopy. Figure 1. In an AFM, vertical motion of the tip is detected by bouncing laser light off the cantilever and measuring it with a photo detector. 12 Agilent Measurement Journal

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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