Nano electronics

Electronic devices based on nanowires

By applying electron-beam lithography, we may fabricate nano-metre sized electronic devices by attaching metal leads onto nanowires. In this way, we made electronic devices based on VOx nanowires and helical carbon nanofibres. For the VOx samples, we found the device resistance has a strong dependence on gas pressure and species: Typically the resistance increases in the N2 environment and in contrast, decrease in the O2 environment. This suggests the VOx device to be a potential gas sensor. This work has been published in Nanotechnology 22, 115501(2011)

Electronic devices based on nanowires

For the devices based on helical carbon nanofibres, we found that the charge conduction in the fibres is through variable range hoping. In a low temperature of 2K, we can observe an oscillatory resistance as a function of gate voltage. This may be due to Fabry-Perot interference in the 1D system. This work has been published in ACS nano 4, 781-788 (2010).

Electronic devices based on nanowires

In addition, we also studied the photoconductivity of these nano devices. The external quantum eﬃciency under the low bias voltage of 5 mV is about 2 × 10⁻² and the photocarrier generation rate is high of about 27%. This work has been published in JPCC 116, 14584 (2012)

Electronic devices based on nanoparticles

We have demonstrated that desirable monolayer and multilayer AuNP films can be achieved by using a simple centrifugal method combined with energy barrier control. The thickness of multilayer AuNP films can be tunable via the control of concentration of nanoparticles or the thickness of colloid solution. When the centrifugal method combines with conventional photo or electron-beam lithography methods and lift-off techniques, 2D and 3D designed complex AuNP assembled structures can be fabricated. The optical and electrical properties of the film can also be well controlled. For example, the electrical conduction exhibits Coulomb charging behavior, displaying that the assembled films have great potential for applications to nanoelectronic devices. This result has been published in The Journal of Physical Chemistry C 116, 8095 (2012).

Electronic devices based on nanoparticles

We also studied how the interparticle tunneling affects the charge conduction of self-assembled NPs by three means: to tune tunnel barrier width by modifying different molecules and bending the substrate, and to tune barrier height by applying high-dose electron beam exposure. All approaches indicate that the metal-Mott insulator transition is majorly governed by the interparticle coupling strength, which can be quantified by the room temperature sheet resistance. The Hubbard gap, following the prediction of quantum fluctuation theory, reduces to zero rapidly as the sheet resistance decreases to the quantum resistance. At very low temperature, the fate of devices near the Mott transition depends on strength of disorder. The charge conduction is from nearest-neighbor hopping to co-tunneling between NPs in Mott insulators whilst variable-range hopping through charge puddles in Anderson insulators. These results have been published in Nanoscale(2014).

Furthermore, we explored the charge transport properties of a two-dimensional network of self-assembled gold nanoparticles, which were prepared near the metal-insulator transition. The insulating devices demonstrated single-charge tunneling and resonant tunneling at mK temperatures. A magnetic field perpendicular to the substrate could suppress the Coulomb oscillations, suggesting that the charge interactions were due to dynamical charge inhomogeneities, rather than single-nanoparticle charging effects. This work has been published in Appl. Phys. Lett. 101, 083105 (2012).

Electronic devices based on nanoparticles

We report a class of stretchable devices fabricated from thin films of self-assembled NPs on transparent polyimide substrates. When the substrate is stretched or bended, the inter particle spacing of a gold nanoparticle assembly is altered and results in the device resistance change. Such phenomenon is similar similar to the piezoresistance effect, which describes a change in electrical conductivity resulted from the application of strain to a crystal. In our devices, the gauge factor could be as large as 100 when applied by a small strain of 0.5%. Such pressure and strain devices could find a wide range of applications in recreation, health care, and robotics. This work has been published in Scientific reports 5, 11939(2015)

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