Electrical Properties of a Tube-in-a-Tube Semiconductor

Abstract

Tube-in-a-tube (Tube^2) nanostructures were synthesized through the outer-wall

selective covalent functionalization of double-walled carbon nanotubes (DWCNTs) at

high functional densities. Upon functionalization, the properties of individual walls

within the structure decouple resulting in an electrically insulating functional outer

tube while the inner tube retains exceptional CNT properties. The exceptional

electrical properties of Tube^2 semiconductor structures were demonstrated for

applications that include molecular and biological sensors and patterning of CNTbased

structures with electronic type specificity.

Tube^2 thin film transistor (TFT) sensors exhibited simultaneous ultrahigh sensitivity

and selectivity towards chemical and biological targets. Carboxylic acid terminated

Tube^2 sensors displayed an NH3 sensitivity of 60 nM, which is comparable with

small molecule aqueous solution detection using state-of-the-art TFT sensors while

simultaneously attaining 6,000 times higher chemical selectivity towards a variety of

amine containing analyte molecules over carboxylic acids. Similarly, 23-base

ii

oligonucleotide terminated Tube^2 sensors demonstrated concomitant sensitivity

down to 5 nM towards their complementary sequence without amplification

techniques and single mismatch selectivity without the use of a gate electrode.

Unique sensor architectures can be designed with the requirement of a gate electrode,

such as the creation of millimeter-scale point sensors.

The optical features and unique structural features of Tube^2 thin films were also

exploited to address the challenge of patterning CNT nanostructures with electronic

type specificity. Patterned dot arrays and conductive pathways were created on an

initially insulating Tube^2 thin film by tuning the resonance of the direct-writing

laser with the electronic type of the inner tube (i.e., metallic or semiconducting). The

successful patterning of Tube^2 thin films was unambiguously confirmed with in situ

Raman spectral imaging and electrical characterization.

Furthermore, a hybrid 2-D carbon nanostructure comprised of a functionalized

graphene that covers a semiconducting (6,5) SWCNT network (fG/sSWCNT) was

developed. The hybrid fG/sSWCNT nanostructure exhibits similar structural and

electrical properties as a semiconducting Tube^2 thin film, but possesses a

transconductance that is an order of magnitude larger than Tube^2 and ON/OFF

ratios as high as 5400 without the useful of further processing steps such as electrical

breakdown.