Silver/(sub-10 nm)hafnium-oxide-based resistive switching devices on silicon: characteristics and switching mechanism.

This study investigates the resistive switching (RS) behavior of Ag/HfO2(3 nm-thick)/SiO x (interfacial-layer)/Si devices. The findings are drawn from a systematic electrical and material characterization of the fabricated devices. Based on the current-time (I-t) and current-voltage (I-V) measurements, it is inferred that both metal and oxygen ion migration play a significant role in the switching events, leading to bipolar and unipolar switching modes depending on the biasing scheme. The results demonstrate two competing switching mechanisms taking place when the biasing voltage is increased beyond the RESET voltage in the bipolar mode. The devices are also shown to exhibit self-rectifying characteristics when the bias is applied to the Ag electrode. The proposed method of investigating the total charge passed through the device within the time to SET, during the I-t characterization, is particularly useful for identifying the current transport models governing the high-resistance state. The results reported in this manuscript provide useful insights into the control of RS behavior in this scientifically and technologically important material system. Developing a thorough understanding of the fundamental physics governing the observed RS behavior is a substantial step for the growing progress in the memristor device research, as well as for its potential exploitation in diverse CMOS-compatible applications.

Large area growth of vertically aligned luminescent MoS2 nanosheets.

Vertically aligned MoS2 nanosheets (NSs) with exposed edges were successfully synthesized over a large area (∼2 cm2). The NSs were grown using an ambient pressure chemical vapor deposition technique via rapid sulfurization of sputter deposited thick molybdenum films. Extensive characterization of the grown MoS2 NSs has been carried out using high resolution scanning and transmission electron microscopy (SEM & TEM). A special care was given to the TEM lamella preparation process by means of a focused ion beam to preserve the NS growth direction. The cross-section TEM measurements revealed the growth of densely packed, vertically aligned and straight MoS2 NSs. Additional characterization techniques such as atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL) were used to evaluate the MoS2 NSs. These studies revealed the high crystallinity and quality of the synthesized NSs. The MoS2 NSs show visible light emission similar to mechanically exfoliated monolayer MoS2 NSs. The striking PL signal comes from the exposed edges as shown by experimental and theoretical calculations. The vertical MoS2 NSs also exhibit a hydrophobic character with a contact angle of 114°. The as-grown MoS2 NSs would be highly useful in the development of catalysis, nano-optoelectronics, gas-sensing and bio-sensing device applications.

Synthesis of silver nanoparticles for the dual delivery of doxorubicin and alendronate to cancer cells.

We present the synthesis of a silver nanoparticle (AgNP) based drug-delivery system that achieves the simultaneous intracellular delivery of doxorubicin (Dox) and alendronate (Ald) and improves the anticancer therapeutic indices of both drugs. Water, under microwave irradiation, was used as the sole reducing agent in the size-controlled, bisphosphonate-mediated synthesis of stabilized AgNPs. AgNPs were coated with the bisphosphonate Ald, which templated nanoparticle formation and served as a site for drug attachment. The unreacted primary ammonium group of Ald remained free and was subsequently functionalized with either Rhodamine B (RhB), through amide formation, or Dox, through imine formation. The RhB-conjugated NPs (RhB-Ald@AgNPs) were studied in HeLa cell culture. Experiments involving the selective inhibition of cell membrane receptors were monitored by confocal fluorescence microscopy and established that macropinocytosis and clathrin-mediated endocytosis were the main mechanisms of cellular uptake. The imine linker of the Dox-modified nanoparticles (Dox-Ald@AgNPs) was exploited for acid-mediated intracellular release of Dox. We found that Dox-Ald@AgNPs had significantly greater anti-cancer activity in vitro than either Ald or Dox alone. Ald@AgNPs can accommodate the attachment of other drugs as well as targeting agents and therefore constitute a general platform for drug delivery.