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Scanning Tunneling Microscopy (STM)
Low-Current STM
156 MultiMode SPM Instruction Manual Rev. B
9.5 Low-Current STM
The following sections provide detailed instructions for performing low-current (sub-picoamp)
STM using two Veeco devices: the Low Current STM Converter for MultiMode AFM (Model
#MMSTMLC), or with the Basic Extender Module (Model #MMSTMLCE).
9.5.1 Description
Operation of conventional STMs with current (I
tun
) in the nanoamp range is characterized by strong
tip-sample force interactions. The forces applied to the sample during STM imaging in air actually
exceed the forces in atomic force microscopy (AFM). The effects of high STM forces were found
when imaging materials which included graphite [1a], inorganic layered compounds[1b], organic
conducting crystals [1c] and organic adsorbates on conducting substrates [1d].
For metallic surfaces, the tip-sample gap resistance, , can be used as a qualitative
measure of tip-sample separation. Where
In general, decreasing will increase the tip-sample separation and decrease the tip-sample
force.
By operating at in the GΩ range, for example, and the tip-
sample distance increases enough to allow less-destructive imaging of a variety of surfaces.
Picoampere-level STM provides the opportunity to image semi-insulating samples deposited on
conducting substrates. Indeed, it was shown that using STM at ultra high R
gap
allows imaging of
the topmost layers of alkanethiol adsorbates on gold surfaces and to reveal earlier unknown surface
features.
Check sample conductivity There are two problems associated with sample conductivity:
1). The bulk conductivity of the sample may make it difficult to image. If the resistance of the
sample is greater than 1KΩ/cm, higher bias voltages should be tried. If the resistance is greater
than 1MΩ, bias voltages of 100mV or more should be used. Samples with resistances 1MΩ or
greater will be difficult to image even with high bias voltages. These types of semiconducting
materials are not suitable for STM measurement.
2). Oxide and contamination layers on the sample surface can make imaging very difficult.
Higher bias voltages are required for these types of samples.
Head/Tip Problem Troubleshooting Tip
R
gap
V
bias
I
tun
⁄=
V
bias
bias voltage=
I
tun
setpoint current=
I
tun
R
gap
V
bias
1.0 V=
I
tun
1 pA=
- NanoScope Software Version 5 1
- 004-210-000 1
- 004-210-100 1
- Ta ble of Contents 3
- List of Figures 13
- Instruments MultiMode SPM 21
- 1.1 Introduction 22
- monitor 23
- 1.2 Safety 24
- 1.2.2 Safety Requirements 25
- 1.2.3 Safety Precautions 26
- 1.3 Microscope Specifications 33
- Microscope Specifications 34
- MultiMode 37
- 2.1 Hardware 38
- 2.1.1 MultiMode SPM 39
- 2.1.2 SPM Head 40
- 2.1.3 Scanners 41
- Hardware 43
- 2.1.4 Tipholders 44
- 2.1.5 Probes 45
- Tunneling electrons 48
- 2.3 Feedback Gains 50
- 2.3.2 Proportional Gain 51
- 2.3.3 Integral Gain 52
- 2.3.4 LookAhead Gain 52
- 2.3.6 Setpoint 53
- Feedback Gains 54
- 2.4.3 User Example 59
- 2.5 Review of TappingMode AFM 63
- Review of TappingMode AFM 64
- 2.6 Terms and Abbreviations 66
- Terms and Abbreviations 67
- 3.2 Component List 69
- Component List 70
- 3.2.1 Unpack The System 71
- 3.2.2 Vibration Isolation 75
- 3.2.3 System Power Up 76
- Silicon Cantilever Substrates 78
- Scan direction = 0 deg 80
- Scan direction = 90 deg 81
- Lever Type 86
- Preparation 89
- 5.1.1 Prepare the Sample 92
- 5.1.2 Load the Sample 93
- Reattach retaining 94
- Tip down 94
- 5.1.3 Load Probe in Tipholder 95
- 5.1.4 Install the Tipholder 97
- 5.2 Laser Alignment 98
- Laser Alignment 100
- 5.2.3 Maximize the SUM Signal 103
- Start the Microscope Program 104
- MultiMode SPM Voltage Meters 105
- RMS VERT 106
- Chapter 6 Contact AFM Mode 107
- • Setpoint: Section 6.5.4 108
- 6.1.2 Signal Settings 109
- 6.1.4 Position Tip with OMV 110
- 6.2.1 Show All Items 111
- to 0.0 112
- fidence in 115
- 0.00 nm 115
- Initiate the Engage Command 116
- 6.4.1 Cantilever Selection 118
- 6.5.1 Data type 119
- 6.5.2 Gain settings 120
- 6.5.3 Scan size and Scan rate 120
- 6.5.4 Setpoint 121
- 6.5.5 Lowpass filter 121
- 6.5.6 Highpass filter 121
- Chapter 7 TappingMode AFM 123
- 7.2.1 Switch to TappingMode 125
- 7.2.2 Show All Items 125
- 7.2.3 Check Parameters 126
- Preparation Prior to Imaging 127
- TappingMode AFM 128
- 7.2.5 Additional preparations 129
- 7.2.6 Tune the Cantilever 129
- 7.3 Engaging The Microscope 133
- Engaging The Microscope 134
- 7.4 Withdrawing the Tip 135
- 50.00 nm/div 136
- Scan Size - 2.50 µm/div 136
- Chapter 8 Fluid Operation 141
- 8.1 Introduction 143
- 8.2 General Fluid Operation 143
- General Fluid Operation 144
- 8.2.2 Select the Probe 145
- 8.2.5 Sample Mounting 147
- Method 1 (with an O-ring) 147
- Method 2: Without an O-ring 149
- 8.2.6 Align the Laser 151
- 8.2.8 Engage the Surface 152
- 8.3 TappingMode in Fluids 154
- the Scan Rate to 1Hz 155
- TappingMode in Fluids 156
- 8.4 Troubleshooting Tips 158
- Troubleshooting Tips 159
- 8.6.1 Protein Binding Theory 162
- 8.7 Binding DNA to Mica 165
- 8.7.3 Acknowledgments 166
- Microscopy (STM) 167
- 9.1 STM Introduction 168
- 9.1.2 STM Hardware 169
- 9.1.3 Sample Surface 170
- 9.1.4 Vibration isolation 170
- 9.2 Basic STM Operation 171
- Basic STM Operation 172
- 9.3 Spectroscopy with the STM 173
- 9.3.2 Operation of STS 174
- 9.4 Troubleshooting for STM 175
- 9.5 Low-Current STM 176
- 9.5.2 Hardware Description 177
- 9.5.3 Precautions 177
- 9.5.4 Installation 178
- Low-Current STM 179
- 9.5.5 Operation 180
- 9.5.6 Servicing the Converter 182
- 9.6 Etching Tungsten Tips 184
- 9.6.1 Procedure 185
- Lateral Force 187
- 10.1 Basic LFM Operation 188
- 10.2 Advanced LFM Operation 189
- 10.2.2 Tip selection 190
- High Friction 191
- Low Friction 191
- Advanced LFM Operation 192
- Chapter 11 Force Imaging 195
- 11.1 Force Plots–An Analogy 197
- 11.2 Force Calibration Mode 198
- Force Calibration Mode 199
- 11.2.1 Example Force Plot 200
- Y Offset 204
- 11.3.3 Channel 1, 2, 3 Panels 206
- Total Force 208
- End Mode 209
- 11.3.6 Menu Bar Commands 210
- 11.4.2 Helpful Suggestions 212
- Deflection 213
- 0.48 V/div 213
- Z Position - 9.27 V/div 213
- Setpoint 213
- 11.4.3 Advanced Techniques 214
- 11.5.1 Force Plots 219
- • Main Controls 221
- • Channel 1 Panel 221
- 11.5.3 High Contact Force 223
- 11.5.4 Tip Selection 223
- 11.6 Force Modulation 224
- 11.6.3 Operating Principle 226
- Force Modulation 227
- 11.6.5 Notes About Artifacts 231
- 11.8 Force Volume 235
- LiftMode 237
- Interleave Mode Description 239
- 12.3 Lift Mode Description 240
- 12.5.2 Setpoint Selection 242
- Imaging 245
- Magnetic Force Imaging Theory 246
- 13.2.1 Procedure 248
- Drive Frequency 249
- Phase (deg) 249
- Amplitude 250
- 13.2.2 Frequency Modulation 252
- 13.3.1 Basic Extender 252
- 13.3.2 Quadrex Extender 253
- 13.3.3 NanoScope IV 253
- 13.5.1 MFM Image Verification 254
- 13.6 Advanced Topics 255
- Advanced Topics 256
- (Feedback loop 263
- NanoScope Controller 265
- Electric Force (EFM) Imaging 267
- External Voltage 269
- Source 269
- NanoScope 276
- 14.4.1 Phase Detection 277
- 14.4.2 Amplitude Detection 279
- Microscope 285
- Troubleshooting and Warranty 291
- Section 15.8.6 292
- 15.1 SPM Calibration Overview 295
- SPM Calibration Overview 297
- 15.1.2 Calibration References 300
- 15.2 Calibration Setup 301
- 15.3.1 Measure Orthogonality 303
- 15.4.1 Adjust Mag0 and Arg 304
- Mag0 Too Large Mag0 Too Small 305
- Arg Too LargeArg Too Small 306
- 15.4.2 Adjusting Fast Mag1 307
- 15.4.3 Adjust Slow Mag1 308
- Autocalibration 309
- SKIP to 310
- 28.37 µµ 311
- 15.6 Autocalibration 312
- Draw a horizontal line 315
- 15.8 Calibrating Z 319
- Calibrating Z 320
- 15.8.4 Correct Z Sensitivity 323
- Scope mode 325
- Measurement 326
- • Extended offset der 329
- Section 15.8.6) 331
- 15. Recheck accuracy at 0V 331
- 15.11.1 False engagement 333
- 15.11.3 Head does not engage 334
- 15.11.6 Lines in the image 335
- Contact AFM Troubleshooting 336
- 15.11.10 Poor image quality 337
- 15.11.14 Image goes white 338
- With Streaks Without Streaks 340
- With Rings Without Rings 341
- 15.13.1 Image drifts 343
- 15.13.2 Leaks 344
- 15.14.1 Inspection 344
- 15.14.4 Clean Guide Bushings 347
- 15.14.5 Lubricate 347
- 15.14.6 Reinstall 347
- 15.16.1 Hardware Installation 350
- 15.16.2 Select scanner 351
- 15.16.3 Inspect scanner 351
- 15.18 Warranty 353
- Warranty 354
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