Manipulation of exciton and trion quasiparticles in monolayer WS2 via charge transfer

Charge doping in transition metal dichalcogenide is currently a subject of high importance for future electronic and optoelectronic applications. Here, we demonstrate chemical doping in the CVD-grown monolayer (1L) of WS2 by a few commonly used laboratory solvents by investigating the room temperature photoluminescence (PL). The appearance of distinct trionic emission in the PL spectra and quenched PL intensities suggests n-type doping in WS2. The temperature-dependent PL spectra of the doped 1L-WS2 reveal a significant enhancement of trions emission intensity over the excitonic emission at low temperature, indicating the stability of trion at low temperature. The temperature-dependent exciton-trion population dynamic has been modeled using the law of mass action of trion formation. These results shed light on the solution-based chemical doping in 1L-WS2 and its profound effect on the photoluminescence which is essential for the control of optical and electrical properties for optoelectronic applications

Analyses of Substrate-Dependent Broadband Microwave (1–40 GHz) Dielectric Properties of Pulsed Laser Deposited Ba0.5Sr0.5TiO3 Films

Ba0.5Sr0.5TiO3 (BST-0.5) thin films (600 nm) were deposited on single crystal MgO, SrTiO3 (STO), and LaAlO3 (LAO) substrates by pulsed laser deposition at an oxygen partial pressure of 80 mTorr and temperature of 720 °C. X-ray diffraction and in situ reflection high-energy electron diffraction routinely ascertained the epitaxial quality of the (100)-oriented nanocrystalline films. The broadband microwave (1–40 GHz) dielectric properties were measured using coplanar waveguide transmission line test structures. The out-of-plane relative permittivity (ε⏊/) exhibited strong substrate-dependent dielectric (relaxation) dispersions with their attendant peaks in loss tangent (tanδ), with the former dropping sharply from tens of thousands to ~1000 by 10 GHz. Although homogeneous in-plane strain (ϵǁ), enhances ε⏊/ with εMgOBST−0.5⏊/>εSTOBST−0.5⏊/>εLAOBST−0.5⏊/  at lower frequencies, two crossover points at 8.6 GHz and 18 GHz eventually change the trend to: εSTOBST−0.5⏊/>εLAOBST−0.5⏊/>εMgOBST−0.5⏊/. The dispersions are qualitatively interpreted using (a) theoretically calculated (T)−(ϵǁ) phase diagram for single crystal and single domain BST-0.5 film, (b) theoretically predicted ϵǁ-dependent, ε⏊/ anomaly that does not account for frequency dependence, and (c) literature reports on intrinsic and extrinsic microstructural effects, including defects-induced inhomogeneous strain and strain gradients. From the Vendik and Zubko model, the defect parameter metric, ξs, was estimated to be 0.51 at 40 GHz for BST-0.5 film on STO

Influence of space-charge on hysteresis loop characteristics of ferroelectric thin films

Hysteresis loops of Pb(Zr, Ti)O3 (PZT) thin films obtained by using a Sawyer-Tower (ST) circuit are affected by many factors. This paper investigated the influence of space charge on the hysteresis loop of thin-film ferroelectrics, based on the model that polarization consists of two parts: linear and switching polarization. It is found that the space charge affects both the shape and offset of the ideal hysteresis loop. Further investigation shows that the practical hysteresis loop has a close relationship with the equivalent ST circuit parameters: the leakage resistance of the FE film, the equivalent input impedance of the measurement equipment, the signal source, and other similar parameters. The normally assumed symmetric hysteresis loop without any offset is obtained with an ST circuit when the output becomes stable. The hysteresis loop obtained at the initial stage of applied signal depends on the initial status of the FE film, and remnant polarization causes an initial offset that gradually disappears

Inorganic Nanoparticles for Cancer Imaging and Therapy

Inorganic nanoparticles have received increased attention in the recent past as potential diagnostic and therapeutic systems in the field of oncology. Inorganic nanoparticles have demonstrated successes in imaging and treatment of tumors both ex vivo and in vivo, with some promise towards clinical trials. This review primarily discusses progress in applications of inorganic nanoparticles for cancer imaging and treatment, with an emphasis on in vivo studies. Advances in the use of semiconductor fluorescent quantum dots, carbon nanotubes, gold nanoparticles (spheres, shells, rods, cages), iron oxide magnetic nanoparticles and ceramic nanoparticles in tumor targeting, imaging, photothermal therapy and drug delivery applications are discussed. Limitations and toxicity issues associated with inorganic nanoparticles in living organisms are also discussed

Understanding the High Longitudinal Relaxivity of Gd(DTPA)-Intercalated (Zn,Al)-Layered Double Hydroxide Nanoparticles

In this study, biocompatible gadolinium diethylenetriaminepentaacetate (Gd(DTPA))-intercalated (Zn,Al)-layered double hydroxide (LDH) nanoparticles were synthesized, characterized for Gd(DTPA) loading percentage and nanostructure, and the spin−lattice relaxation times (T1) measured to determine their suitability as a potential T1-weighted contrast agent for magnetic resonance imaging (MRI). Compared to the most commonly used contrast agent in clinical MRI (i.e., molecular Gd(DTPA)), significant increases in longitudinal relaxivity (r1) were measured for all Gd(DTPA)-intercalated nanoparticles. For a specific Zn2Al(OH)6(Cl,0.5CO3)0.56Gd(DTPA)0.086·xH2O composition, r1 was found to be 28.38 s−1mM−1, which is over 6 times the r1 of molecular Gd(DTPA). This dramatic increase in r1 is attributed to (a) the much longer rotational correlation time (τR) of nanoparticles and (b) the inherent water of LDH that forms the second-/outer-sphere in the vicinity of intercalated Gd(DTPA)2−. The latter, with an extensive hydrogen bonding network and insignificant translational motion, results in a longer mean residence lifetime (τM), which makes the contribution of second-/outer-sphere significant. Therefore, when the Gd(DTPA)2− loading percentage increases from 8.6 to 55%, the diminution of the ratio of inherent water to Gd(DTPA)2− concomitantly diminishes the contributions by second-/outer-sphere water to r1. Additionally, the modest increase in r1 with decreasing particle size (∼315−540 nm) is perhaps due to the shortening of τM. Finally, the spin−spin relaxation times (T2) of 17O, determined at various temperatures, show a negligible exchange of water molecules at room temperature. Therefore, the very high r1 of nanoparticles indicate that protons of the bulk water are still accessible to the Gd3+ centers, possibly dominated by prototropic exchange through the hydrogen bonding network

Synthesis, Characterization, and In Vitro Drug Delivery Capabilities of (Zn, Al)-Based Layered Double Hydroxide Nanoparticles

There is an urgent need for the development of alternative strategies for effective drug delivery to improve the outcome of patients suffering from deadly diseases such as cancer. Nanoparticles, in particular layered double hydroxide (LDH) nanoparticles, have great potential as nanocarriers of chemotherapeutic molecules. In this study, we synthesized (Zn, Al)-LDH nanoparticles and report their enhanced pH-dependent stability in comparison to the commonly used (Mg, Al)-LDH nanoparticles. Fluorescein isothiocyanate (FITC) and valproate (VP) were intercalated into (Zn, Al)-LDH nanoparticles to study cellular uptake, biocompatibility, and drug delivery capabilities using cultured pancreatic adenocarcinoma BxPC3 cells. Fluorescence measurements indicated that FITC-intercalated LDH nanoparticles showed a greater degree of energy-dependent uptake rather than passive uptake by BxPC3 cells, especially at high concentrations of nanoparticles. Tetrazolium-based colorimetric assays indicated that BxPC3 cells treated with VP-intercalated LDH nanoparticles showed a significant reduction in cell viability along with about 30-fold reduction in IC50 compared to the drug alone. In contrast, the non-drug-intercalated LDH nanoparticles did not affect the cell viability indicating very low innate cytotoxicity. Our research indicates that the superior properties of (Zn, Al)-LDH nanoparticles make them ideal candidates for further development as in vivo chemotherapy drug delivery agents