Separation of Single-Walled Carbon Nanotubes with a Gel Permeation Chromatography System

A gel permeation chromatography system is used to separate aqueous sodium dodecyl sulfate suspensions of single-walled carbon nanotubes (SWCNTs). This automated procedure requires no precentrifugation, is scalable, and is found to yield monochiral SWCNT fractions of semiconducting SWCNTs with a purity of 61–95%. Unsorted and resulting monochiral fractions are characterized using optical absorption and photoluminescence spectroscopy

Unraveling the Interplay of Backbone Rigidity and Electron Rich Side-Chains on Electron Transfer in Peptides: The Realization of Tunable Molecular Wires

Electrochemical studies are reported on a series of peptides constrained into either a 3₁₀-helix (<b>1</b>–<b>6</b>) or β-strand (<b>7</b>–<b>9</b>) conformation, with variable numbers of electron rich alkene containing side chains. Peptides (<b>1</b> and <b>2</b>) and (<b>7</b> and <b>8</b>) are further constrained into these geometries with a suitable side chain tether introduced by ring closing metathesis (RCM). Peptides <b>1</b>, <b>4</b> and <b>5</b>, each containing a single alkene side chain reveal a direct link between backbone rigidity and electron transfer, in isolation from any effects due to the electronic properties of the electron rich side-chains. Further studies on the linear peptides <b>3</b>–<b>6</b> confirm the ability of the alkene to facilitate electron transfer through the peptide. A comparison of the electrochemical data for the unsaturated tethered peptides (<b>1</b> and <b>7</b>) and saturated tethered peptides (<b>2</b> and <b>8</b>) reveals an interplay between backbone rigidity and effects arising from the electron rich alkene side-chains on electron transfer. Theoretical calculations on β-strand models analogous to <b>7</b>, <b>8</b> and <b>9</b> provide further insights into the relative roles of backbone rigidity and electron rich side-chains on intramolecular electron transfer. Furthermore, electron population analysis confirms the role of the alkene as a “stepping stone” for electron transfer. These findings provide a new approach for fine-tuning the electronic properties of peptides by controlling backbone rigidity, and through the inclusion of electron rich side-chains. This allows for manipulation of energy barriers and hence conductance in peptides, a crucial step in the design and fabrication of molecular-based electronic devices

Photocurrent Spectroscopy of (<i>n</i>, <i>m</i>) Sorted Solution-Processed Single-Walled Carbon Nanotubes

Variable-wavelength photocurrent microscopy and photocurrent spectroscopy are used to study the photoresponse of (<i>n</i>, <i>m</i>) sorted single-walled carbon nanotube (SWNT) devices. The measurements of (<i>n</i>, <i>m</i>) pure SWCNT devices demonstrate the ability to study the wavelength-dependent photoresponse <i>in situ</i> in a device configuration and deliver photocurrent spectra that reflect the population of the source material. Furthermore, we show that it is possible to map and determine the chirality population within a working optoelectronic SWCNT device

Sorting of Double-Walled Carbon Nanotubes According to Their Outer Wall Electronic Type <i>via</i> a Gel Permeation Method

In this work, we demonstrate the application of the gel permeation technique to the sorting of double-walled carbon nanotubes (DWCNTs) according to their outer wall electronic type. Our method uses Sephacryl S-200 gel and yields sorted fractions of DWCNTs with impurities removed and highly enriched in nanotubes with either metallic (M) or semiconducting (S) outer walls. The prepared fractions are fully characterized using optical absorption spectroscopy, transmission electron microscopy, and atomic force microscopy, and the entire procedure is monitored in real time using process Raman analysis. The sorted DWCNTs are then integrated into single nanotube field effect transistors, allowing detailed electronic measurement of the transconductance properties of the four unique inner@outer wall combinations of S@S, S@M, M@S, and M@M

Separation of Double-Walled Carbon Nanotubes by Size Exclusion Column Chromatography

In this report we demonstrate the separation of raw carbon nanotube material into fractions of double-walled (DWCNTs) and single-walled carbon nanotubes (SWCNTs). Our method utilizes size exclusion chromatography with Sephacryl gel S-200 and yielded two distinct fractions of single- and double-walled nanotubes with average diameters of 0.93 ± 0.03 and 1.64 ± 0.15 nm, respectively. The presented technique is easily scalable and offers an alternative to traditional density gradient ultracentrifugation methods. CNT fractions were characterized by atomic force microscopy and Raman and absorption spectroscopy as well as transmission electron microscopy