Carbon Nanotube Array Selective Removal via Thermocapillary Flow

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Solution Overview

Problem

Current methods for selectively producing carbon nanotube arrays with high density of semiconducting carbon nanotubes are inefficient, as they either require complex steps or result in low density and incomplete removal of metallic carbon nanotubes, limiting their application in electronic materials and devices.

Innovation Solution

A process involving the preparation of a carbon nanotube array with both metallic and semiconducting nanotubes, followed by forming an organic layer, applying voltage to selectively remove metallic nanotubes through self-Joule heating, and then removing the organic layer, which allows for high-density semiconducting nanotube arrays with lengths up to several micrometers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If electrical breakdown method is used to remove metallic carbon nanotubes, then current can flow through metallic nanotubes for selective removal, but the method is not applicable to carbon nanotube arrays with long nanotube lengths and metallic nanotubes remain after cutting

Engineering Contradiction:

Improveselective removal of metallic nanotubesVSAvoidcomplete removal of metallic nanotubes

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

An organic layer is introduced as an intermediary substance that selectively interacts with metallic carbon nanotubes. The organic layer is torn or broken by thermocapillary flow generated in metallic nanotubes, exposing them for subsequent removal by reactive ion etching, while semiconducting nanotubes remain protected under the organic layer

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the electrical breakdown method with a combined thermal-mechanical-chemical approach. Instead of relying solely on electrical current for removal, the method uses voltage application to generate thermocapillary flow that mechanically tears the organic layer, followed by chemical etching to completely remove exposed metallic nanotubes

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If nanoscale thermocapillary flow method is used, then metallic nanotubes can be exposed for removal, but the process becomes complicated requiring additional reactive ion etching steps and the density of semiconducting nanotubes becomes low

Engineering Contradiction:

Improveexposure of metallic nanotubesVSAvoidprocess steps

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent merges multiple functions into a unified process: the organic layer serves both as a protective mask for semiconducting nanotubes and as a sacrificial layer that guides selective removal of metallic nanotubes. The voltage application step simultaneously generates thermocapillary flow to tear the organic layer and prepares metallic nanotubes for etching, combining thermal-mechanical and chemical removal in an integrated sequence

Inventive Principle:

Principle #5Merging (Combining)

3Manufacturing precision

If nanoscale thermocapillary flow method is used, then metallic nanotubes can be selectively exposed, but the density of semiconducting nanotubes in the carbon nanotube array becomes low

Engineering Contradiction:

Improveselective exposure of metallic nanotubesVSAvoiddensity of semiconducting nanotubes

Core Design Contradiction:

Manufacturing precisionVSQuantity of substance

Solution Approach 1:

The organic layer creates local quality differences across the carbon nanotube array. Areas with metallic nanotubes experience thermocapillary flow that tears the organic layer, while areas with semiconducting nanotubes maintain the organic layer intact. This local differentiation enables selective exposure and removal of metallic nanotubes while preserving the high density of semiconducting nanotubes in their original positions

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This process effectively produces carbon nanotube arrays with no metallic nanotubes, achieving high semiconducting nanotube densities and significantly improved ON/OFF ratios for field effect transistors, enabling their use in advanced electronic devices.

Implementation Method 1

voltage is applied to each carbon nanotube of the carbon nanotube array in the long axis direction so as to allow a current to flow into only the m-CNT. Due to self Joule heating of the m-CNT, the thin film in the vicinity thereof is torn and/or broken by the thermocapillary flow

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

the thin film in the vicinity thereof is torn and/or broken by the thermocapillary flow

Methodology Applied

Scientific EffectThermocapillary flow: Thermo-capillary Convection

Data Source

PatentUS11005046B2Carbon nanotube array, material, electronic device, process for producing carbon nanotube array, and process for producing field effect transistor

Publication Date: 2021.05.11 THE UNIV OF TOKYO

AI summary

In order to obtain a carbon nanotube array including no m-CNTs through simple steps using a mechanism that is different from thermocapillary flow, there are provided a process for producing a carbon nanotube array including (A) a step of preparing a carbon nanotube array in which m-CNTs and s-CNTs are horizontally aligned; (B) a step of forming an organic layer on the carbon nanotube array; (C) a step of applying voltage to the carbon nanotube array in a long axis direction of the carbon nanotubes constituting the carbon nanotube array in the air; and (D) a step of removing the organic layer, and a carbon nanotube array obtained by the process.