AFM Workshop LS-AFM Manuale utente

LS-AFM

Users Guide

V 1.1

Part # 10-1121-16

Denitions and Symbols

The following terms and symbols are used in this document and also appear on the product

where safety-related issues occur.

General Warning or Caution

The exclamation symbol may appear in warning and caution tables in this document. This

symbol designates an area where personal injury or damage to the equipment is possible.

European Union CE Mark

The presence of the CE Mark on AFM Workshop equipment means that it has been

designed, tested and certied as complying with all applicable European Union (CE) regula-

tions and recommendations.

Warnings/Cautions/Notes

The following are denitions of the warnings, cautions and notes that may be used in this

manual to call aLSention to important information regarding personal safety, safety and

preservation of the equipment, or important tips.

WARNING

Situation has the potential to cause bodily harm or death.

CAUTION

Situation has the potential to cause damage to property or

equipment.

NOTE

Additional information the user or operator should consider.

Contents

1. Introduction to Atomic Force Microscopy..................................................................1-1

2. Introduction to the LS-AFM.........................................................................................2-1

2.1. Computer...................................................................................................2-1

2.2. Stage..........................................................................................................2-1

2.3. Ebox..........................................................................................................2-2

2.4. Video Optical Microscope.........................................................................2-2

2.4.1 Top View Video Optical Microscope.....................................2-2

2.4.2 Inverted Optical Microscope.................................................2-2

3. Software..........................................................................................................................3-1

3.1. Installation Procedure...............................................................................3-1

3.1.1. Gwyddion Image Analysis Software......................................3-1

3.2. AFM-View Software....................................................................................3-2

3.2.1. Pre-Scan Window....................................................................3-2

3.2.1.1. Files .........................................................................3-2

3.2.1.2. Modes.......................................................................3-3

3.2.1.3. Laser Align................................................................3-3

3.2.1.4. Tune Frequency........................................................3-3

3.2.1.5. Manual Z Motor Control............................................3-4

3.2.1.6. Range Check............................................................3-4

3.2.1.7. Automated Tip Approach...........................................3-5

3.2.2. Topo Scan Window.................................................3-5

3.2.2.1. Image Window..........................................................3-6

3.2.2.2. Oscilloscope Window................................................3-7

3.2.2.3 Scan Setup...............................................................3-8

3.2.2.4. Z Feedback...............................................................3-8

3.2.2.5. Display......................................................................3-9

3.2.2.6. Tip Retract...............................................................3-10

3.2.2.7. Scan ......................................................................3-10

3.2.3. System Window.....................................................................3-10

3.2.3.1. Tip Approach...........................................................3-11

3.2.3.2. Z Parameters..........................................................3-11

3.2.3.3. XYZ Calibration.......................................................3-11

3.2.3.4. XY Parameters........................................................3-12

3.2.3.5. Other Controls.........................................................3-12

3.2.4. Force Distance Curves.........................................................3-13

3.3. Video-ViewSoftware................................................................................3-14

4. Measuring Images With the LS-AFM..........................................................................4-1

4.1. Operating the Video Microscope.............................................................4-1

4.2. Preparing Samples...................................................................................4-2

4.2.1 Exchanging Samples.............................................................4-2

4.3. Exchanging Probes...................................................................................4-3

4.4. Aligning the Light Lever Force Sensor...................................................4-4

4.4.1. Tips for Aligning the Light Lever Force Sensor..................4-4

4.5. Optically-Assisted Tip Approach.............................................................4-5

4.6. Contact Mode Imaging..............................................................................4-6

4.6.1. Pre-Scan Tab..........................................................................4-6

4.6.2. Topo Scan Tab........................................................................4-8

4.7. Vibrating Mode Imaging......................................................................4-10

4.7.1. Pre-Scan Tab.......................................................................4-10

4.7.2 Topo Scan Tab......................................................................4-12

5. Troubleshooting.........................................................................................................5-1

5.1. Saturation of the Photo-Detector.............................................................5-1

5.2. Sample Not Mounted Correctly................................................................5-1

5.3. Probe Not Seated Correctly......................................................................5-1

5.4. Resonance Saturated................................................................................5-2

5.5. False Feedback..........................................................................................5-2

5.6. Scanner at End of Z Range......................................................................5-2

5.7. Defective Probe.........................................................................................5-2

6. High Resolution Imaging............................................................................................6-1

Appendix A: Setting Up the LS-AFM...........................................................................A-1

A.1. Selecting a Location................................................................................A-1

A.2. Setting Up the Optical Microscopes......................................................A-1

A.2.1 Top View Optic..........................................................................A-1

A.2.2 Inverted Optical Microscope...................................................A-2

A.3. Connecting the LS-AFM to the Cables...................................................A-3

A.4. System Check...........................................................................................A-3

A.5. Aligning the Video Microscopes to the Cantilever................................A-3

A.5.1 Aligning the Top View Optic...................................................A-3

A.5.2 Aligning the Inverted Microscope with the Cantilever.........A-4

A.6. First Alignment of the Light Lever..........................................................A-5

A.7. Grounding the LS-AFM............................................................................A-6

Appendix B: LS-AFM Files...........................................................................................B-1

B.1. Parameter Files........................................................................................B-1

B.2. Scanner Files............................................................................................B-2

B.3. Data Files..................................................................................................B-2

Appendix C: Calibration................................................................................................C-1

Appendix D: Noise Floor...............................................................................................D-1

Appendix E: Probes.......................................................................................................E-1

Appendix F: Technical Information..............................................................................F-1

F.1. Electronic Block Diagrams......................................................................F-1

F.2. EBox and Modes Pin Assignments.........................................................F-2

Appendix G: Optimizing GPID Parameters...................................................................G-1

Appendix H: Renaming National Instruments DAQ Device........................................H-1

Appendix I: Analyzing Force/Distance Curves.................................................................I-1

Appendix I: Inverted Optical Microscope.........................................................................J-1

V 1.1 / LS-AFM Users Guide Section 1-1

In an AFM (atomic force microscope), a probe is scanned

over a surface and the motion of the probe is monitored

to create a three-dimensional image of the surface.

These unique instruments are capable of measuring

high-resolution images in both ambient air and liquids,

with surface features of only a few nanometers in size.

The three-dimensional motion of the sample (or

probe) is generated by piezoelectric ceramics. These

sensitive ceramics allow motions as small as a frac-

tion of a nanometer. Typically, the sample (or probe) is

moved in a raster pattern as the probe glides across

the surface.

A light lever sensor is used for controlling the force of

the probe on the surface while the sample is scanned.

The light lever reects a laser beam off the surface of

a cantilever into a photo-detector. As the probe inter-

acts with a surface, the cantilever deects, and this

motion is sensed by the photo-detector.

With this light lever, forces as small as a pico-new-

ton are possible. With such small forces, very small

probes may be used. With micro-machining methods,

probes can have diameters of only a few nanometers.

The light lever can be made more sensitive by vibrat-

ing the cantilever with a small piezoelectric ceramic

and modulating the light. When the vibrating probe

interacts with the surface, the amplitude of vibration

may be monitored and used to control the probe's

force on the surface.

Modern atomic force microscopes include not only a

probe and piezoelectric scanner, but additional hard-

ware for bringing the probe rapidly into the proximity

of a surface. A video optical microscope is very help-

ful for operating an AFM. The video microscope helps

with aligning the light lever and probe approach, and

for nding features for scanning.

For an in-depth description of AFM instrumentation,

we recommend the book Atomic Force Microscopy

by Peter Eaton and Paul West. This book provides a

complete theoretical, as well as practical explanation

for the design and application of AFMs.

1. Introduction to Atomic Force Microscopy

Section 2-1 V 1.1 / LS-AFM Users Guide

2. Introduction to the LS-AFM

When fully assembled, the LS-AFM comprises four subunits. They are the control computer,

the Ebox, the stage, and the video optical microscope.

LS-AFM stage combined with the

video microscope. The key compo-

nents in the stage are the light lever

force senor, piezoelectric scanner,

XY positioner and Z motor.

Standard control computer

2.2 Stage

Samples are held and scanned on the AFM stage.

On the upright inside the stage is a linear translator

which moves both the light lever force sensor and

the piezoelectric scanner in a vertical direction. The

stage also includes a base plate tted with precision

XY translators.

Optimal images are measured with the AFM stage if

it is in a vibration- and acoustic-free environment. If

necessary, a vibration and acoustic isolation system

should be used. Appendix A provides more information

on the best location for the AFM stage.

On the back cover of the stage is a modes connector.

Signals required for implementing additional modes

such as conductive AFM, STM, and EFM are provided.

Additional information on the cable conguration is

provided in Appendix A.

2.1 Computer

The control computer is a standard IBM/PC-type

computer with a Microsoft Windows operating sys-

tem. There are two programs required to operate

the LS-AFM: the AFM control software and the

software for the color video camera.

V 1.1 / LS-AFM Users Guide Section 2-2

2.3 Ebox

The Ebox sends and receives signals from the computer through a single USB cable.

Electronic signals are then sent to the stage through a 60-pin ribbon cable. Additionally, a

grounding cable is connected between the stage and the Ebox. All cables are connected at

the rear of the Ebox. Besides the cable to the stage, there is a plug for an auxiliary 50-pin

cable that gives access to the Ebox's internal electronic signals.

Front and back views of the LS-AFM Ebox showing indicator lights

and connectors for ribbon cables and USB

2.4.1. Top View Video Optical Microscope

Aligning the light lever force sensor is greatly facili-

tated by the aid of the video optical microscope.

The video microscope can help locate features on

a surface for scanning. With the aid of the video

microscope, tip approach can be undertaken much

more rapidly. Images from the video microscope

are displayed on the computer’s video monitor.

2.4.2. Inverted Optical Microscope

The inverted optical microscope, below the AFM, is

used for high resolution optical viewing of transpar-

ent samples.

V 1.1 / LS-AFM Users Guide Section 3-1

3. Software

The TT-2 AFM includes three separate software modules in the AFM Installation les:

AFM Workshop Acquisition Software, Video Microscope Software, and Gwyddion Image

Analysis Software. This installation guide is targeted towards a computer running Windows

OS.

3.1 Installation Procedure

NOTE: If the target computer has a previous version of LabVIEW installed, it

is imperative that it rst be completely removed.

Locate the provided AFM installation les for the USB camera, Gwyddion, and AFM software

and follow the prompts.The user will be asked to input his/her scanner size, so that the setup

procedure will copy the les that correlate with that scanner size onto the desktop. Reboot

when directed. All instructions can be found in the readme le.

NOTE: A Windows Security pop-up will appear when installing the Video

Microscope driver that states that Windows cannot verify the publisher of the

driver software. Choose the option to “Install this driver software anyway.”

Upon initializing the AFM-View software, the user will be asked to conrm the serial number

of the National Instruments DAQ card in the Ebox. The software will display this pop-up

every time the user plugs in a different Ebox.

3.1.1 Gwyddion Image Analysis Software

Gwyddion is open-source software and the latest version of this image-analysis software

is available on the Internet at: http://gwyddion.net/. The functions of the Gwyddion image

analysis software are:

1. Processes such as leveling, deglitching, and smoothing which alter the images.

2. Display functions which change how the data is viewed, including 2-D, 3-D, light shad-

ing, and color mapping.

3. Analysis options that are used for obtaining measurements from images, such as line

proling and histogram analysis.

Section 3-2 V 1.1 / LS-AFM Users Guide

3.2.1.1 Files

Two les are required to operate the AFM-View software. The Parameter File contains

parameters that are used to operate the microscope. The Scanner File contains calibration

parameters for a specic scanner. Upon launching the AFM-View software, default les are

loaded into the software. Changing the les used by the program is possible with the File

buttons. These les may be edited to change parameters with a text editor such as Notepad.

Appendix B lists the contents of both the conguration and scanner les.

3.2 AFM-View Software

Once launched, the AFM-View software has four screens that can be viewed by pressing the

tabs at the top right-hand side of the screen. The rst tab is for the Pre-Scan window (section

3.2.1.) and the second tab is for the Scan window (section 3.2.2.). These two windows are

all that are needed for measuring AFM images. The third tab labeled System (section 3.2.3.)

is used for several other functions, such as measuring the Z noise oor and XYZ scanner

calibration. There is a fourth tab that, when activated, permits force-distance curve measure-

ments (section 3.2.4.).

3.2.1 Pre-Scan Window

The Pre-Scan window contains all of the functions that require adjustment before an image

is measured. In this window, when a function is being used it appears within a green frame.

When the green frame is activated, no other functions can be performed at this time.

V 1.1 / LS-AFM Users Guide Section 3-3

3.2.1.2 Modes

There are two scanning modes: Vibrating mode and Non-Vibrating (contact) mode. The

modes are selected with the Scan Mode button. When Vibrating mode is selected, the fre-

quency sweep window is activated. When Non-Vibrating mode is selected, the frequency

sweep window is deactivated.

3.2.1.3 Laser Align

The position of the laser on the four-quadrant photo-detector is presented numerically and

visually in the Laser Align window. These two indicators are both updated in real time and

are used for aligning the light lever. There is a switch for turning the laser On and Off. This

switch will automatically turn the laser off after the system has been inactive for a certain

length of time.

NOTE: After the TT-2 AFM light lever is set up for the rst time (see Appendix

A.6), the thumb screws used for laser alignment should not need to be turned

more than a few turns.

3.2.1.4 Tune Frequency

The Tune Frequency window is used for selecting the optimal conditions for producing vibrat-

ing-mode images. There are two oscilloscope windows: the upper window shows the ampli-

tude of the probe’s vibration, while the lower window shows the phase between the drive

frequency and the measured frequency. The variable controls are:

1. Amplitude and Phase sliders: Adjusting the amplitude scroll bar will alter the driving

amplitude of the probe’s vibration. Adjusting the phase scroll bar alters the phase

degree. For optimal scanning, the amplitude should not exceed 2.5V or the resonance

will become saturated (see section 5.4).

2. Lower, Selected, and Upper Frequency: The lower, selected, and upper frequencies cor-

respond to green, blue, and red vertical bars in the oscilloscope windows, respectively.

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