The Solution Growth of Copper Nanowires and Nanotubes is Driven by Screw Dislocations

Copper (Cu) nanowires (NWs) are inexpensive conducting nanomaterials intensively explored for transparent conducting electrodes and other applications. However, the mechanism for solution growth of Cu NWs remains elusive so far. Here we show that the one-dimensional anisotropic growth of Cu NWs and nanotubes (NTs) in solution is driven by axial screw dislocations. All three types of evidence for dislocation-driven growth have been conclusively observed using transmission electron microscopy (TEM) techniques: rigorous two-beam TEM analysis that conclusively characterizes the dislocations in the NWs to be pure screw dislocations along ⟨110⟩ direction, twist contour analysis that confirms the presence of Eshelby twist associated with the dislocation, and the observation of spontaneously formed hollow NTs. The reduction–oxidation (redox) electrochemical reaction forming the Cu NWs presents new chemistry for controlling supersaturation to promote dislocation-driven NW growth. Using this understanding to intentionally manipulate the supersaturation, we have further improved the NW growth by using a continuous flow reactor to yield longer Cu NWs under much milder chemical conditions. The rational synthesis of Cu NWs with control over size and geometry will facilitate their applications

Influence of Hole-Sequestering Ligands on the Photostability of CdSe Quantum Dots

Chalcogenide nanocrystals or quantum dots (QDs) such as CdSe and PbSe have great potential as absorbers for QD-sensitized solar cells, but their practical utility is limited by fast degradation when exposed to ambient environments. Here we present results showing that small organic molecules acting as hole-accepting ligands can be very effective in reducing photooxidation of CdSe QDs. The aromatic amine, 4-dimethylaminothiophenol (DMATP), is shown to be especially effective in enhancing stability of CdSe QDs when illuminated in air or in aqueous environments. Using photoluminescence and density functional theory (DFT) calculations, we show that the enhanced stability results from hole transfer from the QD to the ligand and delocalization of the resulting positive charge on the aromatic ring and amino group instead of the sulfur atom that links the molecule to the CdSe

A General Method To Measure the Hall Effect in Nanowires: Examples of FeS₂ and MnSi

We present a general methodology for measuring the Hall effect on nanostructures with one-dimensional (1D) nanowire morphology. Relying only on typical e-beam lithography, the methodology developed herein utilizes an angled electrode evaporation technique so that the nanowire itself is a shadow mask and an intimate sidewall contact can be formed for the Hall electrodes. A six-contact electrode scheme with offset transverse contacts is utilized that allows monitoring of both the longitudinal resistivity and the Hall resistivity which is extracted from the raw voltage from the transverse electrodes using an antisymmetrization procedure. Our method does not require the use of a highly engineered lithographic process to produce directly opposing Hall electrodes with a very small gap. Hall effect measurements on semiconducting iron pyrite (FeS₂) nanowire devices are validated by comparing to Hall effect measurements in the conventional Hall geometry using FeS₂ plate devices. This Hall effect measurement is further extended to MnSi nanowires, and the distinct anomalous Hall effect signature is identified for the first time in chiral magnetic MnSi nanowires, a significant step toward identifying the topological Hall effect due to skyrmions in chiral magnetic nanowires

Controlled Synthesis of Layered Double Hydroxide Nanoplates Driven by Screw Dislocations

Layered double hydroxides (LDHs) are a family of two-dimensional (2D) materials with layered crystal structures that have found many applications. Common strategies to synthesize LDHs lead to a wide variety of morphologies, from discrete 2D nanosheets to nanoflowers. Here, we report a study of carefully controlled LDH nanoplate syntheses using zinc aluminum (ZnAl) and cobalt aluminum (CoAl) LDHs as examples and reveal their crystal growth to be driven by screw dislocations. By controlling and maintaining a low precursor supersaturation using a continuous flow reactor, individual LDH nanoplates with well-defined morphologies were synthesized on alumina-coated substrates, instead of the nanoflowers that result from uncontrolled overgrowth. The dislocation-driven growth was further established for LDH nanoplates directly synthesized using the respective metal salt precursors. Atomic force microscopy revealed screw dislocation growth spirals, and under transmission electron microscopy, thin CoAl LDH nanoplates displayed complex contrast contours indicative of strong lattice strain caused by dislocations. These results suggest the dislocation-driven mechanism is generally responsible for the growth of 2D LDH nanostructures, and likely other materials with layered crystal structures, which could help the rational synthesis of well-defined 2D nanomaterials with improved properties

Chemical Pressure Stabilization of the Cubic B20 Structure in Skyrmion Hosting Fe_1–<i>x</i>Co_<i>x</i>Ge Alloys

Iron monogermanide (FeGe) with the noncentrosymmetric cubic B20 structure is a well-known helimagnet and a magnetic skyrmion host with a relatively high ordering temperature (∼280 K). FeGe and related metal monogermanide compounds, such as CoGe and MnGe, have several structural polymorphs and typically require high pressure (∼4 GPa) and high temperature (∼1000 °C) to synthesize in the cubic B20 structure. Here, we report that the cubic B20 phase of both FeGe and alloys of Fe_1–<i>x</i>Co_<i>x</i>Ge could in fact be formed without the application of high pressure by simply reacting elemental powders at modest temperatures (550 °C). Furthermore, the incorporation of Co into Fe_1–<i>x</i>Co_<i>x</i>Ge (0.05 ≤ <i>x</i> ≤ 0.1) stabilizes the cubic B20 structure up to 650 °C, which we propose is caused by chemical pressure induced by the incorporation of Co into the lattice. Interestingly, chemical vapor transport reactions using the Fe_1–<i>x</i>Co_<i>x</i>Ge alloys as precursors yield plentiful growth of large (0.1 to 1 mm) single crystals of pure FeGe. Magnetic susceptibility measurements of the Fe_0.95Co_0.05Ge alloy show evidence of a skyrmion phase not previously reported in the Fe_1–<i>x</i>Co_<i>x</i>Ge system

Effectiveness of GnRH Antagonist in the Management of Subfertile Couples Undergoing Controlled Ovarian Stimulation and Intrauterine Insemination: A Meta-Analysis

<div><p>Background</p><p>Recent studies have indicated the use of gonadotropin-releasing hormone antagonists (GnRH-ant) as an adjuvant treatment to prevent premature luteinization (PL) and improve the clinical outcomes in patients undergoing controlled ovarian stimulation (COS) with intrauterine insemination (IUI). However, the results of these studies are conflicting.</p><p>Methods</p><p>We conducted a systematic review and meta-analysis of randomized trials aiming to compare the clinical efficacy of GnRH-ant in COS/IUI cycles. Twelve studies were identified that met inclusion criteria and comprised 2,577 cycles assigned to COS/IUI combined GnRH-ant or COS/IUI alone.</p><p>Results</p><p>Meta-analysis results suggested that GnRH-ant can significantly increase the clinical pregnancy rate (CPR) (OR = 1.42; 95% CI, 1.13–1.78) and decrease the PL rate (OR = 0.22, 95% CI, 0.16–0.30) in COS/IUI cycles. Subgroup analysis results suggested statistically significant improvement in the CPR in non-PCOS patients (OR = 1.54; 95% CI, 1.03–2.31) but not in the PCOS population (OR = 1.65; 95% CI, 0.93–2.94) and multiple mature follicle cycles (OR = 1.87; 95% CI, 0.27–12.66). There were no difference in the miscarriage and multiple pregnancy rates between the groups.</p><p>Conclusion</p><p>This meta-analysis suggested that GnRH-ant can reduce the incidence of PL and increase the CPR when used in COS/IUI cycles, and it was especially useful for non-PCOS patients. However, evidence to support its use in PCOS patients is still insufficient</p></div

Gated Hall Effect of Nanoplate Devices Reveals Surface-State-Induced Surface Inversion in Iron Pyrite Semiconductor

Understanding semiconductor surface states is critical for their applications, but fully characterizing surface electrical properties is challenging. Such a challenge is especially crippling for semiconducting iron pyrite (FeS₂), whose potential for solar energy conversion has been suggested to be held back by rich surface states. Here, by taking advantage of the high surface-to-bulk ratio in nanostructures and effective electrolyte gating, we develop a general method to fully characterize both the surface inversion and bulk electrical transport properties for the first time through electrolyte-gated Hall measurements of pyrite nanoplate devices. Our study shows that pyrite is n-type in the bulk and p-type near the surface due to strong inversion and yields the concentrations and mobilities of both bulk electrons and surface holes. Further, solutions of the Poisson equation reveal a high-density of surface holes accumulated in a 1.3 nm thick strong inversion layer and an upward band bending of 0.9–1.0 eV. This work presents a general methodology for using transport measurements of nanostructures to study both bulk and surface transport properties of semiconductors. It also suggests that high-density of surface states are present on surface of pyrite, which partially explains the universal p-type conductivity and lack of photovoltage in polycrystalline pyrite

Flowchart of the study selection.

<p>Flowchart of the study selection.</p

Forest plot of odds ratios (ORs) and 95% confidence interval (CI) of pooled trials comparing GnRH antagonist and control for clinical pregnancy rate.

<p>Forest plot of odds ratios (ORs) and 95% confidence interval (CI) of pooled trials comparing GnRH antagonist and control for clinical pregnancy rate.</p

Forest plot of ORs and 95% CI of pooled trials comparing the GnRH antagonist and control for the premature luteinization rate.

<p>Forest plot of ORs and 95% CI of pooled trials comparing the GnRH antagonist and control for the premature luteinization rate.</p