The indentation method of nonlinear viscoelastic materials is investigated through combined numerical and experimental efforts to reveal the correlation between the viscoelastic kernel function and the indentation responses. It is shown that the viscoelastic kernel function of a nonlinear viscoelastic solid with viscous response characterized by a linear rate constitutive equation scales with the normalized relaxation load in an indentation relaxation test. This scaling relation does not depend on the geometry of the indented solid and the profile of the indenter. Therefore, it may serve as a fundamental relation for characterizing the viscoelastic properties of some biological soft tissues and artificial soft materials with regular/irregular surface morphology.

Three-dimensional (3D) chrysanthemum-like carbon nanofiber (CCNF) foam architectures were synthesized on highly porous nickel foam via a one-step ambient pressure chemical vapor deposition process by introducing a mixture of precursor gases (H2 and C2H2). The as-synthesized 3D foam architectures were characterized by scanning electron microscopy and transmission electron microscopy, which demonstrate high porosity and a densely packed nature of the hierarchical carbon nanostructures. Symmetrical electrochemical double-layer capacitors were fabricated using electrodes based on the CCNF foam architectures. Cyclic voltammetry, charge–discharge measurements, and electrochemical impedance spectroscopy were conducted to determine the performance metrics. The supercapacitors (SCs) demonstrate a high areal capacitance of 1.37 F/cm2 (gravimetric specific capacitance: 23.83 F/g), which leads to superior values for per area energy density (0.19 Wh/cm2) and power density (141.77 W/cm2). In addition, capacitance retention of ∼100% over 13,000 charge–discharge cycles demonstrates the high electrochemical stability of this type of carbon nanostructure foam for high areal capacitance SCs.

We report on the successful synthesis of a graphene–carbon nanotube (CNT) hybrid architecture by a parallel chemical vapor deposition (CVD) of the two carbon allotropes. The carbon hybrid is a three-dimensional (3D) nanostructure with tuneable architecture comprising vertically grown CNTs as pillars and a large-area graphene plane as the floor. The formation of CNTs and graphene occurs simultaneously in a single CVD growth that we describe as a synchronous synthesis method. Unique nature of the fabrication approach contributes significantly to the quality and composure of final nanohybrid. Detailed characterization elucidates the cohesive structure and robust contact between the graphene floor and the CNTs in the hybrid structure. The functionality of the synthesized graphene hybrid structure has been demonstrated by its incorporation into a supercapacitor cell. Our fabrication approach provides an attractive pathway for the fabrication of novel 3D hybrid nanostructures and efficient device integration.

Bulk-heterojunction organic photovoltaic (BHJ-OPV) technology promises high efficiency at ultralow cost and weight, with potential for nontraditional applications such as building-integrated photovoltaic (PV). There is a widespread presumption that the complexity of morphology makes carrier transport in OPV irreducibly complicated and, possibly, beyond predictive modeling. However, understanding the complex morphology is important because it not only dictates cell efficiency but also the panel performance and the operating lifetime. In this paper, we derive the fundamental thermodynamic as well as morphology-specific practical limits of BHJ-OPV efficiency and lifetime. We find that performance improvement relies not only on morphology engineering but also on increasing the effective mobility–lifetime (μτ) product, the cross-gap between donor/acceptors, and reducing the series resistance. Even if the OPV fails to achieve the highest efficiency anticipated by the thermodynamic limit, its novel form factor, lightweight, and transparency can make it a commercially viable option for many applications.

Much of the motivation for exploring nitrogen-vacancy (NV) centers in diamond in the past decade has been for their potential as a solid-state alternative to trapped ions for quantum computing. In this area, the NV center has exceeded expectations and even shown an unprecedented capability to perform certain quantum processing and storage operations at room temperature. The ability to operate in ambient conditions, combined with the atom-like magnetic Zeeman sensitivity, has also led to intensive investigation of NV centers as nanoscale magnetometers. Thus, aside from room-temperature solid-state quantum computers, the NV could also be used to image individual spins in biological systems, eventually leading to a new level of understanding of biomolecular interactions in living cells.

The use of the nitrogen-vacancy (NV) center in diamond as a single spin sensor or magnetometer has attracted considerable interest in recent years because of its unique combination of sensitivity, nanoscale resolution, and room temperature operation. These properties, together with long-term photostability of the NV fluorescence and the inherent biocompatibility of diamond, make the NV system ideal for applications in biology. This article focuses on the role of the NV center in biological applications from optical tracking to nanoscale sensing.

Structured lead zirconium titanate (PZT)–epoxy composites are prepared by dielectrophoresis. The piezoelectric and dielectric properties of the composites as a function of PZT volume fraction are investigated and compared with the corresponding unstructured composites. The effect of poling voltage on piezoelectric properties of the composites is studied for various volume fractions of PZT composites. The experimentally observed piezoelectric and dielectric properties have been compared with theoretical models. Dielectrophoretically structured composites exhibit higher piezoelectric voltage coefficients compared to 0–3 composites. Structured composites with 0.1 volume fraction of PZT have the highest piezoelectric voltage coefficient. The flexural strength and bending modulus of the structured and random composites were analyzed using three-point bending tests.