In this work, we demonstrate the facile fabrication of 3-dimensional (3D) hierarchical porous flower-like NiCo 2 O 4 and its application as an anode material in high-performance lithium ion batteries (LIBs). The uniform flower-like NiCo 2 O 4 is built from porous nanoplates with thicknesses of approximately 25 nm.A detailed investigation reveals that PVP plays an important role, not only in controlling the formation of the delicate hierarchical flower-like structure, but also in creating the uniform pores of each nanoplate. Furthermore, a possible formation mechanism for this unique structure is proposed based on the experimental results. As a virtue of its beneficial structural features, the as-prepared NiCo 2 O 4 exhibits an enhanced lithium storage capacity and excellent cycling stability ($939 mA h g À1 at 100 mA g À1 after 60 cycles). This remarkable electrochemical performance can be attributed to the hierarchical structure and sufficient void space within the surface of the nanoplates, which effectively increases the contact area between the active materials and the electrolyte, reducing the Li + diffusion pathway and buffering the volume change during cycling.

Charged impurity (CI) scattering is one of the dominant factors that affect the carrier mobility in graphene. In this paper, we use Raman spectroscopy to probe the charged impurities in suspended graphene. We find that the 2D band intensity is very sensitive to the CI concentration in graphene, while the G band intensity is not affected.The intensity ratio between the 2D and G bands, I 2D /I G , of suspended graphene is much stronger compared to that of non-suspended graphene, due to the extremely low CI concentration in the former. This finding is consistent with the ultra-high carrier mobility in suspended graphene observed in recent transport measurements. Our results also suggest that at low CI concentrations that are critical for device applications, the I 2D /I G ratio is a better criterion in selecting high quality single layer graphene samples than is the G band blue shift.

Herein we demonstrate giant piezoresistance in silicon nanowires (NWs) by the modulation of an electric field-induced with an external electrical bias. Positive bias for a p-type device (negative for an n-type) partially depleted the NWs forming a pinch-off region, which resembled a funnel through which the electrical current squeezed. This region determined the total current flowing through the NWs. In this report, we combined the electrical biasing with the application of mechanical stress, which impacts the charge carriers' concentration, to achieve an electrically controlled giant piezoresistance in nanowires. This phenomenon was used to create a stress-gated field-effect transistor, exhibiting a maximum gauge factor of 5000, 2 orders of magnitude increase over bulk value. Giant piezoresistance can be tailored to create highly sensitive mechanical sensors operating in a discrete mode such as nanoelectromechanical switches.

In this paper, we report our study on gold (Au) films with different thicknesses deposited on single layer graphene (SLG) as surface enhanced Raman scattering (SERS) substrates for the characterization of rhodamine (R6G) molecules. We find that an Au film with a thickness of ∼7 nm deposited on SLG is an ideal substrate for SERS, giving the strongest Raman signals for the molecules and the weakest photoluminescence (PL) background. While Au films effectively enhance both the Raman and PL signals of molecules, SLG effectively quenches the PL signals from the Au film and molecules. The former is due to the electromagnetic mechanism involved while the latter is due to the strong resonance energy transfer from Au to SLG. Hence, the combination of Au films and SLG can be widely used in the characterization of low concentration molecules with relatively weak Raman signals.

No abstract

No abstract

Negative enrichment is the preferred approach for tumor cell isolation as it does not rely on biomarker expression. However, size-based negative enrichment methods suffer from well-known recovery/purity trade-off. Non-size based methods have a number of processing steps that lead to compounded cell loss due to extensive sample processing and handling which result in a low recovery efficiency. We present a method that performs negative enrichment in two steps from 2 ml of whole blood in a total assay processing time of 60 min. This negative enrichment method employs upstream immunomagnetic depletion to deplete CD45-positive WBCs followed by a microfabricated filter membrane to perform chemical-free RBC depletion and target cells isolation. Experiments of spiking two cell lines, MCF-7 and NCI-H1975, in the whole blood show an average of >90 % cell recovery over a range of spiked cell numbers. We also successfully recovered circulating tumor cells from 15 cancer patient samples.

No abstract