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 Digital
Instruments World Wide Web site (http:/
/www.di.com) to order the necessary support notes or
obtain technical support.