3 research outputs found
Redox Modifications of Carbon Dots Shape Their Optoelectronics
Carbon dots (CDs) are 1–10 nm scaled complex nanostructures with a wide range of applications and show unconventional photophysical behavior upon excitation. In this article, we have unveiled some of the underlying mechanisms and excited state dynamics of CDs by perturbing their interface with oxidizing and reducing agents. With no substantial alteration in size of surface-treated oxidized (^OCDs), reduced (^RCDs), and untreated CDs (^UCDs), we observe marked changes in their charge transport properties and diverse spectral signatures in singlet and triplet excited states. Fine tuning of the spectral behavior of nanomaterials is often treated as an outcome of quantum confinement of the excitons. Herein with different spectroscopic techniques along with conducting atomic force microscopy and triplet–triplet absorption, we elucidate that, not just confinement, the structural modification at the surface also dictates optoelectronic behavior by altering some properties such as energy band gap, quantum tunneling across the metal–CD–metal junction, and yield of triplet excitons
Effects of Mg Doping to a LiCoO<sub>2</sub> Channel on the Synaptic Plasticity of Li Ion-Gated Transistors
Artificial synapses with ideal functionalities are essential
in
hardware neural networks to allow for energy-efficient analog computing.
However, the realization of linear and symmetric weight updates in
real synaptic devices has proven challenging and ultimately limits
the online training capabilities of neural network systems. Herein,
we investigate the effect of Mg doping on a LiCoO2 (LCO)
channel in a Li ion-gated synaptic transistor, so as to improve long-term
and short-term plasticity. Two transistor structures, based on a lithium
phosphorus oxynitride electrolyte, were examined by using undoped
LCO and Mg-doped LCO as the channel material between the source and
drain electrodes. It was found that Mg doping increased the initial
channel conductance by 3 orders of magnitude, which is probably due
to the substitution of Co3+ by Mg2+ and the
compensation of hole creation. It was further found that the doped
channel transistor showed good retention characteristics and better
linearity of long-term potentiation and depression when voltage pulses
were applied to the gate electrode. The improved retention and linearity
are attributed to an extended range of the insulator-to-conductor
transition by Mg doping and Li-ion extraction/insertion cooperated
in the LCO channel. Using the obtained synaptic weight update, artificial
neural network simulations demonstrated that the doped channel transistor
shows an image recognition accuracy of ∼80% for handwritten
digits, which is higher than ∼65% exhibited by the undoped
channel transistor. Mg doping also improved short-term plasticity
such as paired-pulse facilitation/depression and Hebbian spike timing-dependent
plasticity. These results indicate that elemental doping to the channel
of Li ion-gated synaptic transistors could be a useful procedure for
realizing robust neuromorphic systems based on analog computing