Caterina Soldano

Charge-injection-induced dynamic screening and origin of hysteresis in field-modulated transport in single-wall carbon nanotubes

Gate modulated transport in semiconducting single-wall carbon nanotubes shows significant hysteresis in their transfer characteristics. The origin of this hysteresis is generally attributed to the screening of the gate voltage due to the movement of mobile charges/ions in the inherent presence of a trapping/detrapping mechanism in the adjacent dielectric, as in conventional silicon metal-oxide-semiconductor field-effect transistors. However, recent works have conjectured that the screening charges may originate from the nanotube itself. From an extensive study of the temperature dependence of the hysteresis behavior in nanotube field-effect transistors the authors experimentally establish this alternative mechanism, in which the screening charges are injected from the nanotube itself into the surrounding dielectric. Any detailed trapping/detrapping mechanism does not appear to play a significant role, and all experimental results can be simply explained in terms of a capacitive charging of the surrounding...

Quantitative analysis of hysteresis in carbon nanotube field-effect devices

The authors present a model to analyze hysteresis in transfer characteristics (TCs) of single-wall carbon nanotube field-effect transistors, based on capacitive charging of the surrounding dielectric by charges injected out of the nanotube. The model identifies the extent and time scale of the hysteresis and correctly describes the dependence of the magnitude of hysteresis on common experimental parameters. The authors propose and experimentally establish a “time-decay” experiment for obtaining accurate device properties in hysteresis-affected devices without actually measuring TCs. The authors further show that values obtained by this method can be used to precisely predict TCs for the same device under different experimental parameters.

Effect of ambient pressure on resistance and resistance fluctuations in single-wall carbon nanotube devices

We report low-frequency resistance fluctuation (noise) measurements in semiconducting and metallic Ti∕Au-contacted single-wall carbon nanotube devices. In both types of devices, the noise power spectra has a “1∕f” dependence, and is proportional to the squared current. Semiconducting devices were found to have three orders of magnitude higher noise levels compared to the metallic ones. In vacuum, the resistance increases but noise decreases by over an order of magnitude for both metallic and semiconducting devices. The resistance and noise levels recover to their original values when the samples are brought back to atmospheric pressure. Both noise and resistance change simultaneously when the chamber is evacuated. However, when the chamber is brought back to atmospheric pressure, the noise level takes several tens of hours longer to recover.

Temperature dependent high-bias electrical properties of C60 microrods

We present the fabrication, characterization, and temperature dependent electrical properties of individual submicron-sized hexagonal rods of C60. These rods were synthesized by liquid-liquid interfacial precipitation methods and characterized by scanning electron and transmission electron microscopies and Raman spectroscopy. The microscopic analysis reveals highly developed crystalline order. Two-probe platinum-contacted devices were fabricated using long (∼30–50μm) individual C60 rods by focused ion beam assisted deposition on insulating (Si∕SiO2) substrates. Current-voltage (IV) measurements were performed on these devices in the temperature range of 18–300K under an applied voltage of −20to20V. Our measurements reveal an overall decrease in conductivity with decreasing temperature, with structures appearing commensurately with the known positions of the phase transitions. Cyclic high-bias measurements show substantial hysteretic behavior below T∼260K, expected from a sudden and large increase in the d...

Highly Organized Carbon Nanotube-PDMS Hybrid System for Multifunctional Flexible Devices

We will present a method to fabricate a new class of hybrid composite structures based on highly organized multiwalled carbon nanotube (MWNT) and singlewalled carbon nanotube (SWNT) network architectures and a polydimethylsiloxane (PDMS) matrix for the prototype high performance flexible systems which could be used for many daily-use applications. To build 1–3 dimensional highly organized network architectures with carbon nanotubes (both MWNT and SWNT) in macro/micro/nanoscale we used various nanotube assembly processes such as selective growth of carbon nanotubes using chemical vapor deposition (CVD) and self-assembly of nanotubes on the patterned trenches through solution evaporation with dip coating. Then these vertically or horizontally aligned and assembled nanotube architectures and networks are transferred in PDMS matrix using casting process thereby creating highly organized carbon nanotube based flexible composite structures. The PDMS matrix undergoes excellent conformal filling within the dense nanotube network, giving rise to extremely flexible conducting structures with unique electromechanical properties. We will demonstrate its robustness under large stress conditions, under which the composite is found to retain its conducting nature. We will also demonstrate that these structures can be directly utilized as flexible field-emission devices. Our devices show some of the best field enhancement factors and turn-on electric fields reported so far.Copyright

Electro-Mechanically Robust, Flexible Carbon Nanotube-PDMS Composite for High Performance Field Emission

We present a method for fabricating flexible multi-wall carbon nanotubes (MWNTs)-polymer (poly-dimethylsiloxane, PDMS) composites for high performance field emission devices and other flexible electronic applications. The polymer matrix isolates individual nanotubes on its surface, reducing mutual [1] and give rise to impressive field emission properties. The MWNT-PDMS composites are extremely flexible and electro-mechanically robust since they remain electrically conducting under large strains. The above mentioned features make these MWNT-PDMS composites suitable for future applications as multifunctional flexible devices such as pressure and gas sensors as well as flexible sensors and display devices.Copyright