Water (Non-)Interaction with MoO3

Spike rate dependent synaptic characteristics in lamellar, multilayered alpha-MoO3 based two-terminal devices - efficient way to control the synaptic amplification

Brain-inspired computing systems require a rich variety of neuromorphic devices using multi-functional materials operating at room temperature. Artificial synapses which can be operated using optical and electrical stimuli are in high demand. In this regard, layered materials have attracted a lot of attention due to their tunable energy gap and exotic properties. In the current study, we report the growth of layered MoO3 using the chemical vapor deposition (CVD) technique. MoO3 has an energy gap of 3.22 eV and grows with a large aspect ratio, as seen through optical and scanning electron microscopy. We used transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy for complete characterisation. The two-terminal devices using platinum (Pt/MoO3/Pt) exhibit superior memory with the high-resistance state (HRS) and low-resistance state (LRS) differing by a large resistance (∼MΩ). The devices also show excellent synaptic characteristics. Both optical and electrical pulses can be utilised to stimulate the synapse. Consistent learning (potentiation) and forgetting (depression) curves are measured. Transition from long term depression to long term potentiation can be achieved using the spike frequency dependent pulsing scheme. We have found that the amplification of postsynaptic current can be tuned using such frequency dependent spikes. This will help us to design neuromorphic devices with the required synaptic amplification.

Dopamine-Regulated Plasticity in MoO3 Synaptic Transistors

Field-effect transistor-based biosensors have gained increasing interest due to their reactive surface to external stimuli and the adaptive feedback required for advanced sensing platforms in biohybrid neural interfaces. However, complex probing methods for surface functionalization remain a challenge that limits the industrial implementation of such devices. Herein, a simple, label-free biosensor based on molybdenum oxide (MoO3) with dopamine-regulated plasticity is demonstrated. Dopamine oxidation facilitated locally at the channel surface initiates a charge transfer mechanism between the molecule and the oxide, altering the channel conductance and successfully emulating the tunable synaptic weight by neurotransmitter activity. The oxygen level of the channel is shown to heavily affect the device's electrochemical properties, shifting from a nonreactive metallic characteristic to highly responsive semiconducting behavior. Controllable responsivity is achieved by optimizing the channel's dimension, which allows the devices to operate in wide ranges of dopamine concentration, from 100 nM to sub-mM levels, with excellent selectivity compared with K+, Na+, and Ca2+.

Water Structures Reveal Local Hydrophobicity on the In2O3(111) Surface

Clean oxide surfaces are generally hydrophilic. Water molecules anchor at undercoordinated surface metal atoms that act as Lewis acid sites, and they are stabilized by H bonds to undercoordinated surface oxygens. The large unit cell of In₂O₃(111) provides surface atoms in various configurations, which leads to chemical heterogeneity and a local deviation from this general rule. Experiments (TPD, XPS, nc-AFM) agree quantitatively with DFT calculations and show a series of distinct phases. The first three water molecules dissociate at one specific area of the unit cell and desorb above room temperature. The next three adsorb as molecules in the adjacent region. Three more water molecules rearrange this structure and an additional nine pile up above the OH groups. Despite offering undercoordinated In and O sites, the rest of the unit cell is unfavorable for adsorption and remains water-free. The first water layer thus shows ordering into nanoscopic 3D water clusters separated by hydrophobic pockets.

Insights into the catalytic mechanism of 5-hydroxymethfurfural to phthalic anhydride with MoO3/Cu(NO3)2 in one-pot

A synthetic approach to obtain renewable phthalic anhydride (PA) from 5-hydroxymethfurfural (HMF) with a yield of 63.2% using MoO₃/Cu(NO₃)₂ as a catalyst in one pot.

A highly transparent humidity sensor with fast response speed based on α-MoO3 thin films

Metal oxide based humidity sensors are important indicators in environmental monitoring. However, most of them are non-transparent and have a long response time, which cannot meet the application of real-time humidity sensing in transparent electronics. Here, we report a metal oxide humidity sensor based on chemically synthesized molybdenum oxide (α-MoO₃) thin films. By a green reaction in an ice water bath, the stable precursor containing nanocrystalline colloids was obtained. Molybdenum oxide films with controllable morphology were fabricated through one-step spin coating. The α-MoO₃ based humidity sensor exhibits extremely high transparency (85%) in the visible region and has short response and recovery times (0.97 and 12.11 s). In addition, it also shows high sensitivity, good logarithmic linearity and selectivity in a wide relative humidity range of 11% to 95%. The mechanism of humidity sensing was further studied by complex impedance spectroscopy. This novel metal oxide humidity sensor combined with high transparency and fast response speed is expected to broaden the application ranges of humidity sensors.

A transparent and rapid humidity sensor based on α-MoO₃ thin films was fabricated by a facile chemical route.