Hierarchical tree-shaped nanostructures, nanobelts, and nanowires of Zn 3 P 2 were synthesized in a thermal assisted laser ablation process. All nanostructures are tetragonal phased Zn 3 P 2 with excellent crystallinity and are free from an oxidization layer according to electron microscopy and X-ray diffraction analyses. Optical measurement revealed a strong absorption from the ultraviolet to near-infrared regions. Optoelectronic devices fabricated using individual nanowires demonstrate a high sensitivity and rapid response to impinging light. A crossed heterojunction of an n-type ZnO nanowire and a p-type Zn 3 P 2 nanowire has been characterized, and it offers a great potential for a high efficient spatial resolved photon detector.Being a novel optoelectronic material, Zn 3 P 2 has the following advantages over some other materials. It has a direct band gap in the range of 1.4-1.6 eV, which is the optimum range for solar energy conversion. The large optical absorption coefficient (>10 4 cm -1 ) and a long minority diffusion length (∼13 µm) of Zn 3 P 2 permit high current collection efficiency. 1 In addition, the constituent materials are abundant and cheap and would allow the large scale deployment of such devices as solar cells, infrared (IR) and ultraviolet (UV) sensors, lasers, and light polarization step indicators. 2,3 In order to investigate the potential applications of Zn 3 P 2 , several kinds of heterojunctions have been designed, such as InP/Zn 3 P 2 , 4 Mg/Zn 3 P 2 , 5 Zn 3 P 2 /ZnSe, 2,6 ITO/ Zn 3 P 2 , 7 and ZnO/Zn 3 P 2 . 8 However, the majority of research on Zn 3 P 2 has been limited to thin films, and very little work has been done in the nanoscale range except for very few reports on the synthesis of Zn 3 P 2 nanoparticles 9-11 and on the synthesis of nanotrumpets with an unavoidable ZnO layer coated on the surface. 12 Because of the large excitonic radii, Zn 3 P 2 is expected to exhibit pronounced quantum size effect, which has been observed for Zn 3 P 2 nanoparticles. 10 To the best of our knowledge, the electric property and photoresponse of Zn 3 P 2 nanostructures, and heterojunctions made from Zn 3 P 2 nanostructures, have not been reported thus far.In this paper we report for the first time the synthesis of single crystalline tree-shape Zn 3 P 2 structure arrays, nanowires, and nanobelts. The morphology and crystal structure were determined by electron microscopy and analytical techniques. In addition, the optical property of the synthesized nanostructures has been measured through photoluminescence (PL). Furthermore, we also present the crossed heterojunction made using a ZnO nanowire and a Zn 3 P 2 nanowire. Optoelectronic measurements of single Zn 3 P 2 nanowire and the crossed heterojunction indicate that Zn 3 P 2 was very sensitive to light and the heterojunction exhibits enhanced performance, which implies that the Zn 3 P 2 nanostructures have promising applications in optoelectronics.
We report here a systematic synthesis and characterization of aligned alpha-Fe2O3 (hematite), epsilon-Fe2O3, and Fe3O4 (magnetite) nanorods, nanobelts, and nanowires on alumina substrates using a pulsed laser deposition (PLD) method. The presence of spherical gold catalyst particles at the tips of the nanostructures indicates selective growth via the vapor-liquid-solid (VLS) mechanism. Through a series of experiments, we have produced a primitive "phase diagram" for growing these structures based on several designed pressure and temperature parameters. Transmission electron microscopy (TEM) analysis has shown that the rods, wires, and belts are single-crystalline and grow along <111>m or <110>h directions. X-ray diffraction (XRD) measurements confirm phase and structural analysis. Superconducting quantum interference device (SQUID) measurements show that the iron oxide structures exhibit interesting magnetic behavior, particularly at room temperature. This work is the first known report of magnetite 1D nanostructure growth via the vapor-liquid-solid (VLS) mechanism without using a template, as well as the first known synthesis of long epsilon-Fe2O3 nanobelts and nanowires.
A novel technique for fabrication of patterned and aligned polymer‐nanowire/micro‐and nanotube (PNW/PNT) arrays on a wafer‐level substrate of any material is reported. By creating a designed pattern on a spin‐coated polymer film using techniques, such as stamping or micro‐tip writing, plasma etching results in the formation of aligned PNW arrays distributed according to the pattern.
The ϵ‐Fe2O3 phase is commonly considered an intermediate phase during thermal treatment of maghemite (γ‐Fe2O3) to hematite (α‐Fe2O3). The routine method of synthesis for ϵ‐Fe2O3 crystals uses γ‐Fe2O3 as the source material and requires dispersion of γ‐Fe2O3 into silica, and the obtained ϵ‐Fe2O3 particle size is rather limited, typically under 200 nm. In this paper, by using a pulsed laser deposition method and Fe3O4 powder as a source material, the synthesis of not only one‐dimensional Fe3O4 nanowires but also high‐yield ϵ‐Fe2O3 nanowires is reported for the first time. A detailed transmission electron microscopy (TEM) study shows that the nanowires of pure magnetite grow along [111] and <211> directions, although some stacking faults and twins exist. However, magnetite nanowires growing along the <110> direction are found in every instance to accompany a new phase, ϵ‐Fe2O3, with some micrometer‐sized wires even fully transferring to ϵ‐Fe2O3 along the fixed structural orientation relationship, (001) ϵ‐Fe 2 O 3 ∥ (111) Fe 3 O 4, [010] ϵ‐Fe 2 O 3 ∥ <110> Fe 3 O 4. Contrary to generally accepted ideas regarding epsilon phase formation, there is no indication of γ‐Fe2O3 formation during the synthesis process; the phase transition may be described as being from Fe3O4 to ϵ‐Fe2O3, then to α‐Fe2O3. The detailed structural evolution process has been revealed by using TEM. 120° rotation domain boundaries and antiphase boundaries are also frequently observed in the ϵ‐Fe2O3 nanowires. The observed ϵ‐Fe2O3 is fundamentally important for understanding the magnetic properties of the nanowires.
Nanowires of up to 1 cm in length and approximately 30 nm in diameter were synthesized through a simple chemical vapor deposition process. Scanning electron microscopy (SEM) data showed that these nanowires were well-aligned and grew in the direction along the flow of the carrier gas. Through transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis, the nanowires were found to be composed of a single-crystalline ZnS core and amorphous SiO 2 shell. Gold catalyst particles were found at the tips of the nanowires and completely encased by a silica shell. Photoluminescence (PL) measurements were performed on nanowire samples in which the synthesis time was systematically varied to provide information regarding growth dynamics. After a systematic study on the structure, we propose that the core-shell nanowires were formed via a distinct volume and surface diffusion process occurring simultaneously for different chemical species in and on the gold catalyst particle.
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