Effects of temperature and ammonia flow rate on the chemical vapour deposition growth of nitrogen-doped graphene.

We doped graphene in situ during synthesis from methane and ammonia on copper in a low-pressure chemical vapour deposition system, and investigated the effect of the synthesis temperature and ammonia concentration on the growth. Raman and X-ray photoelectron spectroscopy was used to investigate the quality and nitrogen content of the graphene and demonstrated that decreasing the synthesis temperature and increasing the ammonia flow rate results in an increase in the concentration of nitrogen dopants up to ca. 2.1% overall. However, concurrent scanning electron microscopy studies demonstrate that decreasing both the growth temperature from 1000 to 900 °C and increasing the N/C precursor ratio from 1/50 to 1/10 significantly decreased the growth rate by a factor of six overall. Using scanning tunnelling microscopy we show that the nitrogen was incorporated mainly in substitutional configuration, while current imaging tunnelling spectroscopy showed that the effect of the nitrogen on the density of states was visible only over a few atom distances.

Controlling the nanoscale rippling of graphene with SiO2 nanoparticles.

The electronic properties of graphene can be significantly influenced by mechanical strain. One practical approach to induce strain in graphene is to transfer atomically thin membranes onto pre-patterned substrates with specific corrugations. The possibility of using nanoparticles to impart extrinsic rippling to graphene has not been fully explored yet. Here we study the structure and elastic properties of graphene grown by chemical vapour deposition and transferred onto a continuous layer of SiO2 nanoparticles with diameters of around 25 nm, prepared on a Si substrate by the Langmuir-Blodgett technique. We show that the corrugation of the transferred graphene, and thus the membrane strain, can be modified by annealing at moderate temperatures. The membrane parts bridging the nanoparticles are suspended and can be reversibly lifted by the attractive forces between an atomic force microscope tip and graphene. This allows the dynamic control of the local morphology of graphene nanomembranes.

Detrimental effect of left varicocele on the reproductive capacity of the early haploid male gamete.

PURPOSE: We evaluated the fertilizing capacity of round spermatids recovered from varicocelized rabbits. MATERIALS AND METHODS: A left varicocele model was created in 5 rabbits (Group A). Four rabbits underwent a sham operation (Group B). After 3 months round spermatid nuclei were collected from the left testicle of each rabbit and injected into oocytes. Oocytes were cultured for 24 hours. RESULTS: The proportion of 2- to 4-cell stage embryos to the successfully injected oocytes was significantly lower in group A than in group B (p < 0.05). CONCLUSIONS: Our findings indicate a detrimental effect of varicocele on the fertilizing potential of round spermatid.

Retroperitoneal lymphadenectomy: the traditional treatment option.

Retroperitoneal lymphadenectomy (RPL) is the traditional treatment option for clinical stage II low-volume disease. There are several issues to consider when making this treatment decision, including an understanding of staging accuracy and an appreciation of the associated morbidity of surgery versus chemotherapy. The surgeon must also know what type of RPL is indicated and whether nerve-sparing surgery is feasible. We also present the results from our institution for stage II nonseminomas.