photonics and electronics, ranging from the relatively simple nanoscale emitter and complementary logic that can be obtained from single nanorod p±n junctions. Moreover, the direct growth of modulation-doped nanorods eliminates the lithographic steps used to create doped nanotube p±n junctions. [18,19] Therefore, we believe that controlled growth of modulation-doped nanorod p±n junctions represents an advance over previous work. [9,11,18±20] Experimental GaN nanorods were grown in a horizontal HVPE system. In the growth process, the Ga precursor (7N) was synthesized in the lower region of the reactor, via the reaction of HCl gas (5N) (in an N 2 diluent gas) with Ga metal (at 750 C), to form GaCl. This precursor was then transported to the substrate area, where it was mixed with NH 3 (6N4) to form GaN at 478 C (substrate temperature). After the furnace was cooled to room temperature, a dark yellow layer was found on the surface of the substrate.Nanorods dispersed in methanol were deposited onto oxidized silicon substrates, and electrical contacts were fabricated using focused ion beam (FEI company, Strata DB 235) lithography. GaN nanorod LED contacts were fabricated by a two-step process in which the n-type contact (first step) was made using Ti/Al (100 nm/200 nm) by electron-beam evaporation and then was annealed at 950 C for 30 s to form an ohmic contact. In the second step, the p-type contact was made using Ni/Au (100 nm/200 nm) by electron-beam evaporation and then was annealed at 600 C for 30 s to form an ohmic contact. Electrical transport measurements were made using a home-made system under computer control. In order to investigate the optical properties of GaN nanorod p±n junctions, we carried out cathodoluminescence (CL) spectroscopy and imaging. The CL spectra of the nanorod at room temperature were taken in a high-resolution scanning electron microscope (SEM, FEI company, XL 30 SFEG) combined with a CL system (Gatan, MONOCL2) having a 1200 lines/mm grating blazed at 500 nm. The emission was detected using a Peltier-cooled photomultiplier. The maximum spectral resolution is 0.2 nm. The experimental conditions in CL spectroscopy were carefully established to minimize the undesired influence of electron-beam bombardment on the conditions of the specimens.

Boron nitride (BN) aerogels are porous materials with a continuous three-dimensional network structure. They are attracting increasing attention for a wide range of applications. Here, we report the template-assisted synthesis of BN aerogels by catalyst-free, low-pressure chemical vapor deposition on graphene-carbon nanotube composite aerogels using borazine as the B and N sources with a relatively low temperature of 900 °C. The three-dimensional structure of the BN aerogels was achieved through the structural design of carbon aerogel templates. The BN aerogels have an ultrahigh specific surface area, ultralow density, excellent oil absorbing ability, and high temperature oxidation resistance. The specific surface area of BN aerogels can reach up to 1051 m2 g−1, 2-3 times larger than the reported BN aerogels. The mass density can be as low as 0.6 mg cm−3, much lower than that of air. The BN aerogels exhibit high hydrophobic properties and can absorb up to 160 times their weight in oil. This is much higher than porous BN nanosheets reported previously. The BN aerogels can be restored for reuse after oil absorption simply by burning them in air. This is because of their high temperature oxidation resistance and suggests broad utility as water treatment tools.

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