Nanotube Quality Control N

Our goal is to develop new methods to rapidly screen bulk carbon nanotubes 

for chemical purity and homogeneity. The different synthesis routes used 

to produce these materials generate different mixtures of tube geometries, 

ANOMATERIALS

along with varying amounts of carbonaceous and metallic impurities. New 

inspection techniques are needed to enable material benchmarking, process 

optimization, and quality control. Ensuring material quality is the first step 

toward widespread commercialization of these materials.

Objective

Impact and Customers

• Sales of carbon nanotubes are projected to exceed $4.6 billion by 2015, with the materials finding applications in 

lightweight composites, microelectronics, and biomedical products. The highest growth is projected for single-walled 

carbon nanotubes, where performance is directly related to chemical purity. 

• Presently, characterization of nanotube chemistry requires multiple measurements 

using different analytical and optical techniques. As production volumes increase, 

screening tools will become more important for quickly identifying batch-to-batch 

inconsistencies, enabling quality assurance.

• Subtle changes in nanotube chemistry 

can have a dramatic impact on device 

performance and reliability. For example, 

the presence of residual catalyst particles 

can alter the current-carrying capacity of a 

single isolated nanotube. Understanding 

raw material quality is critical for predicting 

product reliability.

Approach

Materials Science and Engineering Laboratory

Thermogravimetric analysis (TGA) is widely used to gather data on nanotube 

chemistry. By monitoring weight loss as a function of temperature, one can 

determine decomposition kinetics and use this data to closely approximate the 

distribution of impurities present in a few milligrams of material. Oxidative 

stability provides an indirect measure of the carbonaceous materials present. 

The residual mass provides an estimate of the metal fraction, which primarily 

consists of the catalyst material.

One disadvantage of TGA, however, is the need for relatively large specimen sizes, which 

is particularly problematic for highly purified materials (where process yields are low). As 

an alternative to TGA, we developed an elevated temperature quartz crystal microbalance 

(QCM) technique that interrogates samples on the order of 1 microgram or less. A variety 

of coating techniques can be used to deposit the nanotube material, including drop 

casting, spin coating, and spray deposition.

0

20

40

60

80

100

120

0 200 400 600 800

Temperature, C

% Weight Remaining

Material 1

Material 2

Material 3

Material 4

residual 

mass

oxidative stability

0

20

40

60

80

100

120

0 200 400 600 800

Temperature, C

% Weight Remaining

Material 1

Material 2

Material 3

Material 4

residual 

mass

oxidative stability

853-05-04c
Materials Science and Engineering Laboratory

TGA has been used evaluate the 

compositional differences in different 

carbon nanotube materials, which arise 

from the different manufacturing and postproduction purification processes. The 

residual mass and the oxidation temperature 

data provide information on the material’s 

decomposition.

The derivative curve is used to determine 

the oxidation temperature of the material, 

as well as defining the mass loss of a single 

decomposing species (e.g., single peak) 

or of multiple decomposition events (e.g., 

double peaks, shouldered peaks). The 

oxidation temperature represents the thermal 

stability of the material. A lower oxidation 

temperature may indicate the presence of 

amorphous carbons. Higher temperatures 

can indicate multi-wall carbon nanotubes 

or other structured carbons may also be 

present.

TGA is not only a bulk analysis method but 

can also be used to characterize micro-scale 

differences within a CNT sample. Differences 

in CNT chemistry, surface functionality, and 

purification have been observed with TGA. 

Increased thermal stability of a CNT sample 

has also been observed as more layers were 

added to the nanotube structure (single, 

double, multi-wall carbon nanotubes).

Length dependency was also measured with 

the TGA. Single-walled carbon nanotube 

samples sorted as short (~ 80 nm), 

medium (~320 nm) and long (~760 nm) 

were observed to have different oxidation 

temperatures.

One major disadvantage of TGA analysis 

for CNTs is the relatively large sample size 

required, which is especially problematic 

in the case of costly high-purity samples. 

In addition to our work with conventional 

TGA, we have developed an elevated 

temperature technique based on quartz 

crystal microbalances which provides TGAlike results for a microgram scale sample 

or thin film. We validated our elevated 

temperature QCM method using materials 

with simple thermal profiles. Once the 

QCM measurements were shown to closely 

follow the TGA curve for materials with 

simple thermal decompositions, we extended 

the technique to include mixtures of these 

materials to demonstrate the capabilities of 

monitoring more complex heterogeneous 

samples.

For a relatively pure nanotube sample, we 

were able to closely approximate the TGA 

data, both in terms of mass loss at temperature 

and homogeneity. These results confirm that 

the elevated temperature QCM technique can 

be used to evaluate carbon nanotube quality 

by manufacturers to test current batch-tobatch production differences.

TGA results were supported by extensive 

transmission electron microscopy (TEM) of 

the carbon nanotube materials.

Accomplishments

Roy Geiss

Stephanie Hooker

Elisabeth Mansfield

(Materials Reliability Division)

(303) 497-6405

mansfiel@boulder.nist.gov

www.nist.gov/msel/materials_reliability

Learn More Publications

Nanomaterials

Mansfield E, Kar A, Hooker S. Applications of TGA in quality control of SWCNTs, Analytical 

and Bioanalytical Chemistry 396: 1071-1077 (2010).

Mansfield E, Geiss R, Fagan JA. Methods for TEM analysis of NIST’s single-wall carbon 

nanotube Standard Reference Material, Proc. Of SPIE, 7405: 7405A1 -7405A11 (2009).

Decker JE, Hight Walker AR, Bosnick K, Clifford CA, Dai L, Fagan JA, Hooker S, Jakubek ZJ, 

Kingston C, Makar J, Mansfield E, Postek MT, Simard, B, Sturgeon R, Wise S, Vladar AE, Yang 

L, Zeisler R. Sample Preparation Protocols for Realization of Reproducible Characterization of 

Single-Wall Carbon Nanotubes, Metrologia, 46: 682-692 (2009).

Freiman S, Hooker S, Migler K, Arepalli S, Measurement Issues in Single Wall Carbon 

Nanotubes, Recommended Practice Guide, Special Publication 960-19 (2008)

TGA for three manufactured materials

CNTs with different diameters. Single (SWCNT), 

double (DWCNT) and multi-wall carbon 

nanotubes (MWCNT) are shown.

TGA of short (green), medium (blue), and long 

(red) single-wall carbon nanotubes.

TGA (blue) and QCM (green) measurements of a 

representative carbon nanotube sample.

TEM of a double-wall carbon nanotube

End-on view of a bundle of SWCNTs