Nanosurf easyScan E-STM User manual

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Operating Instructions
easyScan E-STM
Version 2.1

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‘NANOSURF’ AND THE NANOSURF LOGO ARE TRADEMARKS OF NANOSURF AG, REGISTERED AND/OR
OTHERWISE PROTECTED IN VARIOUS COUNTRIES.
© JANUARY 2004 BY NANOSURF AG, SWITZERLAND, PROD.:BT00655, V2.1R1

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Table of Contents
Introduction 4
What is STM? .......................................................................................4
Scanning with the E-STM .....................................................................5
(Un)packing and Installation 8
Unpacking the instrument .....................................................................8
Hardware Installation ............................................................................9
Software installation............................................................................11
System requirements 11
Installation Procedure 11
Simulated microscope 14
Preparing for Measurement 15
Preparing and installing the STM tip ..................................................15
Preparing the sample .........................................................................17
Installing the sample ...........................................................................19
First Measurements 20
Starting the microscope......................................................................20
Approaching the tip.............................................................................21
1. Coarse approach by hand 21
2. Fine approach by piezo motor 22
3.Automatic approach 23
Start measurement .............................................................................24
Adjusting the sample’s tilt coordinates ...............................................25
Achieving atomic resolution................................................................27
Snapshots of images ..........................................................................30
STM Measurement modes .................................................................30
Judging the quality of the images .......................................................31
The graphite surface ...........................................................................33
Measuring Gold ..................................................................................34
Finish measuring ................................................................................36
Turning off and storing the instrument 36
Maintenance 38
Scan head 38
Scan electronics 39
Problems and Solutions 40
Technical Data 44

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Introduction
This manual gives instructions on how to set up and use your Nanosurf
easyScan E-STM system.The aim is to help people who don’t have a good
knowledge of physics to get pictures of atomic resolution easily.This intro-
duction chapter gives some general information on the scanning tunneling
microscopy technique, and its implementation in the easyScan STM. The
next chapter, (Un)packing and Installation, should be read when installing
your easyScan system. The chapters Preparing for Measurement and First
Measurementsshouldbe readbyallusers,astheycontainusefulinstructions
for your everyday measurements. The other chapters give more informa-
tion for advanced users.Those who need a more detailed description of the
functions of the easyScan software should refer to the Software Reference
manual.
What is STM?
Microscopy is one of the most exciting scientific techniques. The insight
into small dimensions has led to a new understanding of the structure of
materials and forms of life.
Withthehelp ofthe scanningtunneling microscope(STM) itis possible to
look into the fascinating world of the atoms.This completely new micros-
copy technique works without focusing elements and features atomic reso-
lution (laterally and vertically).
The Scanning Tunneling Microscope was developed by Gerd Binnig and
Heinrich Rohrer in the early 80’s at the IBM research laboratory in
Rüschlikon, Switzerland. For this revolutionary innovation Binnig and
Rohrer were awarded the Nobel prize in Physics in 1986.
In the STM, a small sharp conducting tip is scanned across the sample’s
surface, so close that the so-called ‘tunneling current’ can flow. With the
helpofthatcurrentthetip-surfacedistancecanbecontrolledvery precisely.
Therefore an enormous resolution is achieved so that the atomic arrange-
ment of metallic surfaces can be ‘probed’.
INTRODUCTION WHAT IS STM?

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To be able to get such excellent pictures of atomic resolution is almost in-
credible,consideringthatthesizeoftheatominrelationtothetip,isthatof
a golf ball to a mountain!
Scanning with the E-STM
In the E-STM, a platinum-iridium tip is moved in three dimensions using
piezo-crystal translators that are driven with sub-nanometer precision.
INTRODUCTIONSCANNING WITH THE E-STM

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The sample to be examined approaches the tip within a distance of 1 nano-
meter (1nm= 1 / 1 000 000 000 m). Classical physics would prohibit the
appearance of electrons in the small gap between a tip and a sample, but if
a sharp tip and a conducting surface are put under a low voltage (U~0.1V)
a very small tunneling current (I~1nA) may nevertheless flow between tip
and sample. This tunneling current is due to a quantum physics effect.
The strength of the tunneling current depends exponentially on the dis-
tance between the tip and the sample (usually referred to as z-distance).
This extreme dependence on the z-distance makes it possible to measure
thetip-sample movementvery precisely.Oneofthe threepiezocrystals, the
z-piezo, can now be used in a feedback loop that keeps the tunneling cur-
rent constant by appropriately changing the z-distance.
To obtain an image of the sample, the tip is scanned using the x- and y-
piezo crystals.The feedback loop will now let the tip follow the structure of
the sample's surface. A height image can now be made by recording the
position of the z-feedback loop as a function of the x-y piezo position.This
‘landscape’(ortopography)oftheatomicsurfaceisthendrawnonthecom-
puter screen line by line.
x
z
I = const.
The feedback loop maintains a constant tunneling current between the tip and the sample
during motion in the x-direction by changing the z-direction (viewed from top)
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Scan-images of graphite as views from the ‘side’ and the ‘top’
The sample can also be scanned in a second mode: When the feedback
loop is slowed down very much (P-Gain=0, I-Gain=2), the tip scans at a
fixed distance from the sample (constant height mode).This time the vari-
ations in the tunneling current are measured and drawn line by line on the
computerscreen.However,thismodeonlyworkswhenthesampleisatomi-
cally flat, because the tip would otherwise ‘crash’ in to the sample
What is so special about the Nanosurf easyScan E-STM?
The E-STM was designed to allow people without training as a physicist to
do experiments in the world of atoms. Its design is compact, simple and
comfortable to operate. With the E-STM, it is possible to do any STM
experiment which can be carried out in air. The special sample approach
system allows simple handling of samples and tips, whilst at the same time
providing maximum stability of the tip-sample distance. All functions can
be carried out using a computer and the E-Line software.
INTRODUCTIONSCANNING WITH THE E-STM

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(Un)packing and Installation
This chapter describes the installation of the Nanosurf easyScan E-STM.
Important!
To enable measurements of atomic resolution to be made the following
precautions must be taken to keep equipment dust and grease free:
•Never toucheither thewirefortips (figure components, 8e), the sample(8
g) nor the open part of the STM scan head (2) with your fingers.
• Only touch the sample holder (8 f) at the black plastic end.
Unpacking the instrument
Before unpacking the instrument suitcase, check for the following items:
Documents and
software(9)
1
2
3
54 8
67
c d
bfg
e
a
Components:The easyScan DFM system
(UN)PACKING AND INSTALLATION UNPACKING THE INSTRUMENT

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1- easyScan E-SPM electronics
2- STM scan head
3- Power supply LPS-1
4- RS232 cable between computer and control electronics
5- Mains cable
6- Vibration isolation platform
7- Magnifying cover with 10x magnifier
8-Toolset,containinga:wirecutterb:half-roundpliers,c:pointedtweez-
ers, d: rounded tweezers, e: 30 cm Pt/Ir 0.25mm wire for tips, f: sample
holder, g: sample set: HOPG (graphite), gold thin film, three empty
sample supports
9- easyScan E-Line CD, containing the easyScan E-Line software
- this manual
- software reference manual
- a test sheet and a sheet with the calibration information.
- a Case for storing and transporting the instrument
Additionally, the following material is needed that is not included with the
contents of delivery:
•AcomputerthatmeetstherequirementsdescribedinthesectionSoftware
Installation.
• Solvent to clean the tools (e.g. ethanol, acetone)
Hardware Installation
Important!
- Please check that the mains voltage corresponds to that of the power sup-
ply (3).
- Make sure that your mains connection is protected against excess voltage.
(UN)PACKING AND INSTALLATIONHARDWARE INSTALLATION

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Chooseasteadytablewhereyoucanworkundisturbed.To ensurethefault-
less operation of the STM it has to be kept away from vibrations, heat
emission and air current.
- Put the STM scan head (2) onto the vibration isolation platform (6). Fix
the scan head cable under the strain relief clip.
- Connect the STM scan head to the easyScan E-SPM electronics (1).
- Make sure your computer is turned off. Then connect the control elec-
tronics to a free serial port (or RS232, or COM Port) on your computer
with the RS232 cable (4). If you are using the ‘USB adapter: ES’, DO
NOT connect it now.
- Connect the power supply (3) to the E-SPM electronics, and plug in the
mains cable (5).
- Finally turn on the power supply.
Now the E-SPM electronics and the microscope are connected, and the
LED on the E-SPM electronics flashes.
(UN)PACKING AND INSTALLATION HARDWARE INSTALLATION