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Contents 1 Introduction 2 Growing Nanotubes 3 Preparing the Nanotubes 3.1 Purification 3.1.1 Heat Treatment 3.2 Suitable Solvents 3.3 Dispersion Methods 3.4 Dispersing Agents 4 Making Nanotube Samples 4.1 Preparations 4.1.1 The Substrate 4.1.1.1 Choosing the right substrate 4.1.1.2 Preparing chips from a wafer 4.1.1.3 Preparing alignment marks on the surface 4.1.2 Applying Nanotubes 4.1.2.1 Tubes in Volatile Solvents 4.1.2.2 Tubes in SDS (aq.) Solution 4.1.2.3 Prepatterning 4.1.2.4 Spraying 4.1.3 Locating Nanotubes 4.2 Contacting a Nanotube 4.2.1 E-Beam Lithography 4.2.2 Evaporation 4.2.3 Bonding 5 Measurements 6 Special Techniques 6.1 Dielectrophoresis 6.2 AFM Manipulation 6.3 Cleaning the Substrate 6.3.1 Plasma Cleaning 6.3.2 Wet Cleaning 7 Annex

[edit] Introduction

[edit] Growing Nanotubes

[edit] Preparing the Nanotubes

[edit] Purification

[edit] Heat Treatment

[edit] Suitable Solvents

DI Water

not very well suited to make nanotube solutions. Can however be a good choice when used with detergents

[edit] Dispersion Methods

[edit] Dispersing Agents

[edit] Making Nanotube Samples

[edit] Preparations

[edit] The Substrate

[edit] Choosing the right substrate

[edit] Preparing chips from a wafer

Important: Only open wafer boxes inside an operating flowbox!

• Spin a layer of protective resist on the entire wafer and bake it thoroughly
• Use a ruler and the diamond pen to scrib the wafer. Make a first cut 4 to 5 mm long, parallel to the wafer's flat. Cover the wafer with cleanroom paper and brake the wafer over an edge
• Store the rest of the wafer securely away again
• Scrib the broken off substrate in rectangular pieces
• Take a strip of scotch tape a little longer than the substrate. Glue it to the resist side. Break the substrate by pulling it over an edge holding the ends of the tape
• Carefully remove the wafer pieces from the tape with a tweezer
• Wash the chips in IPA (not in Acetone! the protective resist layer should stay on the chip until it is actually needed)

[edit] Preparing alignment marks on the surface

• Remove protective resist layer with Acetone and wash the chip in IPA
• Spin on your prefered resist system and bake the wafer
• EBL pattern the chips with a 3x3 matrix of alignment marks
• Evaporate a sufficiently thick (>35 nm) Cr/Au or Ti/Au metal layer

[edit] Applying Nanotubes

This section covers methods for random deposition of tubes. Instructions on dielectrophoretic trapping can be found in this chapter.

[edit] Tubes in Volatile Solvents

[edit] Tubes in SDS (aq.) Solution

The tubes are encapsulated in SDS micells and form a stable solution. Thus there is no need for sonication before applying.

• The substrate chip is placed on the hotplate (level 1-2; approx 100 deg C)
• One drop of nanotube solution is applied and left to dry in. This procedure is repeated two more times or until a uniform staining of the chip is visible
• The chip is put into a beaker with water. The beaker is put on the hotplate and heated until the water starts to boil
• The chip is flushed in Popanol and blown dry with nitrogen

This procedure should result in an acceptably even distribution of single tubes on the chip. If there are to many regions of aggregated tubes visible in the SEM repeat the cooking step.

[edit] Prepatterning

[edit] Spraying

[edit] Locating Nanotubes

[edit] Contacting a Nanotube

[edit] E-Beam Lithography

[edit] Evaporation

[edit] Bonding

[edit] Measurements

[edit] Special Techniques

[edit] Dielectrophoresis

[edit] AFM Manipulation

[edit] Cleaning the Substrate

[edit] Plasma Cleaning

[edit] Wet Cleaning

An effective method for removing nanotubes from a wafer without destroying other structures is to use surfactants. Here a simple recipe with SDS:

1. Sonicate samples in 1 to 10 % SDS (aq.) solution for about 5 min
2. Rinse with DI water
3. Rinse in IPA
4. Blow dry with Nitrogen

Very fragile samples can be cooked in the SDS solution instead of sonication.

[edit] Annex