Field emission from single multi-wall carbon nanotubes

Electron field emission characteristics of individual multiwalled carbon nanotubes have been investigated by a piezoelectric nanomanipulation system operating inside a scanning electron microscopy chamber. The experimental setup ensures a high control capability on the geometric parameters of the field emission system (CNT length, diameter and anode-cathode distance). For several multiwalled carbon nanotubes, reproducible and quite stable emission current behaviour has been obtained with a dependence on the applied voltage well described by a series resistance modified Fowler-Nordheim model. A turn-on field of about 30 V/um and a field enhancement factor of around 100 at a cathode-anode distance of the order of 1 um have been evaluated. Finally, the effect of selective electron beam irradiation on the nanotube field emission capabilities has been extensively investigated.Comment: 16 pages, 5 figure

Vacuum gauge from ultrathin MoS2 transistor

We fabricate monolayer MoS2 field effect transistors and study their electric characteristics from 10^-6 Torr to atmospheric air pressure. We show that the threshold voltage of the transistor increases with the growing pressure. Hence, we propose the device as an air pressure sensor, showing that it is particularly suitable as a low power consumption vacuum gauge. The device functions on pressure-dependent O2, N2 and H2O molecule adsorption that affect the n-doping of the MoS2 channel.Comment: 10 pages, 4 figure - conference pape

Local probing of the field emission stability of vertically aligned multiwalled carbon nanotubes

Metallic cantilever in high vacuum atomic force microscope has been used as anode for field emission experiments from densely packed vertically aligned multi-walled carbon nanotubes. The high spatial resolution provided by the scanning probe technique allowed precise setting of the tip-sample distance in the submicron region. The dimension of the probe (curvature radius below 50nm) allowed to measure current contribution from sample areas smaller than 1um^2. The study of long-term stability evidenced that on these small areas the field emission current remains stable (within 10% fluctuations) several hours (at least up to 72 hours) at current intensities between 10-5A and 10-8A. Improvement of the current stability has been observed after performing long-time Joule heating conditioning to completely remove possible adsorbates on the nanotubes.Comment: 15 pages, 7 figure

Gas dependent hysteresis in MoS2_2 field effect transistors

We study the effect of electric stress, gas pressure and gas type on the hysteresis in the transfer characteristics of monolayer molybdenum disulfide (MoS2) field effect transistors. The presence of defects and point vacancies in the MoS2 crystal structure facilitates the adsorption of oxygen, nitrogen, hydrogen or methane, which strongly affect the transistor electrical characteristics. Although the gas adsorption does not modify the conduction type, we demonstrate a correlation between hysteresis width and adsorption energy onto the MoS2 surface. We show that hysteresis is controllable by pressure and/or gas type. Hysteresis features two well-separated current levels, especially when gases are stably adsorbed on the channel, which can be exploited in memory devices.Comment: 8 pages, 5 figure

two dimensional effects in fowler nordheim field emission from transition metal dichalcogenides

We report field emission from bilayer MoS 2 and monolayer WSe 2 synthesized by CVD on SiO 2/Si substrate. We show that the emitted current follows a Fowler-Nordheim model modified to account for the two-dimensional confinement of charge carriers. We derive the figures of merit of field emission and demonstrate that few-layer transition-metal dichalcogenides are suitable for field emission applications

Space charge limited current and photoconductive effect in few-layer MoS2

We analyse the conduction mechanism and the electrical photoresponse of chemical-vapor deposited MoS2 few-layers on SiO2/Si substrate. We perform temperature dependent I-V measurements and report a space-charge limited conduction due to the presence of an exponential distribution of trap states in the MoS2 band-gap. We estimate the density of trap states as 1010 – 1011 cm −2 from the temperature-independent critical drain-source voltage. We also investigate the MoS2 photocurrent under white light at different incident powers. We use a modified Hornbeck-Hayens model to study the photoconductive effect and for an alternative estimation of the trap state density

Low density polyethylene coated by graphene nanoplatelets

An advantageous micromechanical technique to deposit large area graphene nanoplatelet (GNP) thin films on a low-density polyethylene substrate is proposed. This method, based on the application of shear-stress and friction forces to a graphite platelets/ethanol paste on the surface of a polymeric substrate, allows to obtain films of overlapped nanoplatelets mainly made of 13-30 graphene layers. X-ray diffraction (XRD), atomic force and transmission electron microscopy (TEM) measurements support the occurrence of a partial exfoliation of the graphite platelets due to shear-stress and friction forces applied during film formation. Scanning electron microscopy (SEM) observations point out that the surface of the polymer is uniformly coated by GNP unities, and the TEM analysis reveals the tendency of the nanoplatelets to align parallel to the interfacial plane. It has been found that the deposited samples, under white light illumination, exhibit a negative photoconductivity and a linear photoresponse as a function of the applied voltage and the optical power density in the -120÷120 mV and 20.9÷286.2 mWcm-2 ranges, respectively. These structural and electrical characteristics will be compared to those of LDPE films coated with thin layers deposited by spraying a commercial graphite-based product

High field emission current density from Ga2O3 nanopillars

Field emission from gallium oxide amp; 946; Ga2O3 nanopillars, etched by Ne ion milling on amp; 946; polymorph 100 single crystals, is reported. A stable field emission current, with a record density over 100 amp; 8201;A cm2 and a turn on field of amp; 8764;30 amp; 8201;V amp; 956;m, is achieved. We expect that the high field enhancement factor of about 200 at a cathode anode distance of 1 amp; 8201; amp; 956;m can be further increased by optimizing the shape of the nanopillar apex. This work demonstrates that the material properties combined with an appropriate nano patterning can make amp; 946; Ga2O3 competitive or better than other well established field emitter

Feestanding carbon nanotube network based temperature sensor

The present invention introduces a small-size temperature sensor, which exploits a random or oriented network of un-functionalized, single or multi-walled, carbon nanotubes to monitor a wide range of temperatures. Such network is manufactured in the form of freestanding thin film with an electric conductance proven to be a monotonic function of the temperature, above 4.2 K. Said carbon nanotube film is wire-connected to a high precision source-measurement unit, which measures its electric conductance by a standard two or four- probe technique. Said temperature sensor has a low power consumption, an excellent stability and durability, a high sensitivity and a fast response; its manufacturing method is simple and robust and yields low-cost devices. Said temperature sensor, freely scalable in dimension, is suitable for local accurate measurements of rapidly and widely changing temperatures, while introducing a negligible disturb to the measurement environment