1.2. Microscope Specifications
Following is a list of basic specifications:
1.2.1. Image size and resolution.
Images consist of raster-scanned, electronic renderings of sample surfaces. There are three default sizes: 128 x 128 pixels, 256 x 256 pixels, and 512 x 512 pixels. In addition, six width-to-height aspect ratios may be specified by the user: 1:1, 2:1, 4:1, 8:1, 16:1, and 32:1. Thus, it is possible to obtain “strip scans” which require less time to capture.
The controller provides 16-bit resolution on all three axes, with three independent 16-bit digital-to-analog converters (DACs) in X and Y for control of the scan pattern, scaling and offset. This configuration provides 16-bit resolution of the lateral scanning motion at any scan size, and the ability to perform atomic resolution imaging throughout the full lateral range of the scanner. The patented digital feedback is governed by integral and proportional gain controls, providing immediate response to scanning parameter changes.
The MultiMode can scan up to 200 mm laterally (in X and Y) and 10 mm vertically (Z axis). A table summarizing each scanner’s capabilities is provided in Chapter 2.
MultiMode™SPM Instruction Manual 1-5
Part I: Introduction Introduction to the MultiMode™ SPM
1.2.2. Scanning techniques with the MultiMode SPM.
The MultiMode is so called because it offers multiple SPM modes, including AFM, ECAFM, ECSTM, STM and TappingMode. While many early SPMs offered only one dedicated operating mode (e.g., STM), the MultiMode was the world’s first multiple-use SPM. It remains one of Digital Instrument’s most versatile instruments.
A complete range of Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) techniques is available with the MultiMode SPM. Some of these techniques are available only through Digital Instruments.
• Contact AFM — Measures topography by sliding the probe’s tip across the sample surface. Operates in both air and fluids. See Chapter 6.
• TappingMode™ AFM — Measures topography by tapping the surface with an oscillating tip. This eliminates shear forces which can damage soft samples and reduce image resolution. TappingMode is available in air and fluids (patented). This is now the technique of choice for most AFM work. See Chapter 8.
• Phase Imaging — Provides image contrast caused by differences in surface adhesion and viscoelasticity. Requires an Extender™ Electronics Module (patent pending). See Chapters 8 and 13.
• Non-contact AFM — Measures topography by sensing Van der Waals attractive forces between the surface and the probe tip held above the surface. Provides lower resolution than either contact AFM or TappingMode.
• Magnetic Force Microscope (MFM) — Measures magnetic force gradient distribution above the sample surface. Performed using LiftMode to track topography (Extender Electronics Module recommended). See Chapter 13.
• Electric Force Microscope (EFM) — Measures electric field gradient distribution above sample surfaces. Performed using LiftMode to track topography (Extender Electronics Module recommended). See Chapter 13.
• Surface Potential Microscopy — Measures differences in local surface potential across the sample surface. Performed using LiftMode to track topography (Extender Electronics Module only). See Chapter 13.
• LiftMode™ — A combined, two-pass technique that separately measures topography (using TappingMode) and another selected property (e.g., magnetic or electric force), using the topographical information to track the probe tip at a constant height above the surface (patented). See Chapter 12.
• Force Modulation — Measures relative elasticity/stiffness of surface features (patented). Force modulation is only one of several types of force imaging which are possible. See Chapter 11.
• Lateral Force Microscopy (LFM) — Measures frictional forces between the probe tip and sample surface. See Chapter 10. Introduction to the MultiMode™ SPM Part I: Introduction
• Scanning Tunneling Microscopy (STM) — Measures topography of surface electronic states using a tunneling current which is dependent on the separation between the probe tip and a conductive sample surface. An optional Low-Current STM Converter allows operation in the subpicoamp tunneling current region which can be useful when scanning poorly conductive samples. Tunneling spectroscopy may also be performed. See Chapter 9.
• Electrochemical Microscopy (ECSTM and ECAFM) — Measures the surface structure and properties of conducting materials immersed in electrolyte solutions with or without potential control. See ECSTM/ECAFM manuals.
• Lithography — Use of a probe tip to mechanically scribe or indent a sample surface. May be used to generate patterns, test surfaces for microhardness, etc. Performed using AFM and STM. See the Command Reference Manual and Support Note 225.
Most of these imaging techniques are discussed in this manual. If you do not find sufficient information here, refer to Bruker website (http://www.bruker.com/products/surface-analysis/atomic-force-microscopy.html) to order the necessary support notes or obtain technical support.