The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth.

BackgroundThe purpose of this study was to explore the optimal cut-off point of calf circumference (CC) as a simple proxy marker of appendicular skeletal muscle mass (ASM) and sarcopenia in the Korean elderly and to test the criterion-related validity of CC by analyzing its relationships with the physical function.MethodsThe participants were 657 adults aged 70 to 84 years who had completed both dual energy X-ray absorptiometry (DXA) and physical function test in the first baseline year of the Korean Frailty and Aging Cohort Study.ResultsASM and skeletal muscle mass index (SMI) were correlated positively with CC (male, ASM, r = 0.55 and SMI, r = 0.54; female, ASM, r = 0.55 and SMI, r = 0.42; all P < 0.001). Testing the validity of CC as a proxy marker for low muscle mass, an area under the curve (AUC) of 0.81 for males and 0.72 for females were found and their optimal cut-off values of CC were 35 cm for males and 33 cm for females. In addition, CC-based low muscle groups were correlated with physical functions even after adjusting for age and body mass index. Also, the cut-off value of CC for sarcopenia was 32 cm (AUC; male, 0.82 and female, 0.72).ConclusionThe optimal cut-off values of CC for low MM are 35 cm for males and 33 cm for females. Lower CC based on these cut-off values is related with poor physical function. CC may be also a good indicator of sarcopenia in Korean elderly.

We report metal-free synthesis of high-density single-crystal elementary semiconductor nanowires with tunable electrical conductivities and systematic diameter control with narrow size distributions. Single-crystal silicon and germanium nanowires were synthesized by nucleation on nanocrystalline seeds and subsequent one-dimensional anisotropic growth without using external catalyst. Systematic control of the diameters with tight distribution and tunable doping concentration were realized by adjusting the growth conditions, such as growth temperature and ratio of precursor partial pressures. We also demonstrated both n-type and ambipolar field effect transistors using our undoped and phosphorus-doped metal-free silicon nanowires, respectively. This growth approach offers a method to eliminate potential metal catalyst contamination and thus could serve as an important point for further developing nanowire nanoelectronic devices for applications.

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Hybrid colloidal quantum dot (CQD) solar cells are fabricated from multilayer stacks of lead sulfide (PbS) CQD and single layer graphene (SG). The inclusion of graphene interlayers is shown to increase power conversion efficiency by 9.18%. It is shown that the inclusion of conductive graphene enhances charge extraction in devices. Photoluminescence shows that graphene quenches emission from the quantum dot suggesting spontaneous charge transfer to graphene. CQD photodetectors exhibit increased photoresponse and improved transport properties. We propose that the CQD/SG hybrid structure is a route to make CQD thin films with improved charge extraction, therefore resulting in improved solar cell efficiency.

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Colloidal metal chalcogenide quantum dots (QDs) have excellent quantum efficiency in light-matter interactions and good device stability. However, QDs have been brought to the forefront as viable building blocks in bottomup assembling semiconductor devices, the development of QD solar cell (QDSC) is still confronting considerable challenges compared to other QD technologies due to their low performance under natural sunlight, as a consequence of untapped potential from their quantized density-of-state and inorganic natures. This report is designed to address this long-standing challenge by accessing the feasibility of using QDSC for indoor and concentration PV (CPV) applications. This work finds that above bandgap photon energy irradiation of QD solids can generate high densities of excitons via multi-photon absorption (MPA), and these excitons are not limited to diffuse by Auger recombination up to 1.5 × 10 19 cm −3 densities. Based on these findings, a 19.5% (2000 lux indoor light) and an 11.6% efficiency (1.5 Suns) have been facilely realized from ordinary QDSCs (9.55% under 1 Sun). To further illustrate the potential of the MPA in QDSCs, 21.29% efficiency polymer lens CPVs (4.08 Suns) and viable sensor networks powered by indoor QDSCs matrix have been demonstrated.