D.J. Fu

The sensitivity of gas sensor based on single ZnO nanowire modulated by helium ion radiation

In this letter, we present a gas sensor using a single ZnO nanowire as a sensing unit. This ZnO nanowire-based sensor has quick and high sensitive response to H2S in air at room temperature. It has also been found that the gas sensitivity of the ZnO nanowires could be modulated and enhanced by He+ implantation at an appropriate dose. A possible explanation is given based on the modulation model of the depletion layer.

Room-temperature ferromagnetism in Cu+ implanted ZnO nanowires

We experimentally showed ferromagnetism at above 300?K for ZnO nanowires prepared by reactive vapour deposition and subsequently implanted with 2?at% of Cu. The magnetic moments of the samples annealed in oxygen and in argon at 600??C for 120?min are about 0.42??B and 0.33??B per Cu atom, respectively. No ferromagnetism-related secondary phase existed according to the results of x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy including HRTEM and EELS mapping. It can be concluded that the d9 configuration in the ground state of Cu2+ plays an important role in ferromagnetism. This controllable and shallow doped ion implantation technique may find potential applications in spintronic, especially nano-spintronic, devices.

Ferroelectric and magnetic properties of CdMnS films prepared by coevaporation

We report on impurity ferroelectricity and ferromagnetic properties in semiconductor-structured CdMnS films. We observed ferroelectric hysteresis in CdMnS. A remnant polarization of 1.72 μC/cm2 and a coercive field of 14.3 kV/cm were obtained in samples with Mn concentration below 2%. The coevaporated CdMnS samples become ferromagnetic when doped with Au, with a spontaneous magnetization of 1.39×10−6 emu and a coercive magnetic field of 75.4 gauss at 10 K, and the Curie point was found to be higher than room temperature. Through magnetic force microscopy, we observed clear magnetic clusters with sizes ranging from a few nanometers to 102 nm, and found the magnetization to be highly dependent on Au concentration. A combination of this ferroelectricity in CdMnS and ferromagnetism in Au-doped CdMnS may find use in ternary bit nonvolatile memory devices.

Room temperature ferroelectric and magnetic properties of (Co, Li) coimplanted ZnO films

Simultaneous room temperature ferroelectricity and magnetism was observed in (Co, Li) coimplanted ZnO films. The implantation were conducted for Li and Co at energies of 50 and 400 keV, respectively, to doses of 1×1016 and 5×1016 cm−2. Remnant dipole polarization of 10.2 μC/cm2 and coercive electric field of 24.8 kV/cm were recorded for coimplanted ZnO films annealed at 700 °C. The implanted samples annealed at 700 °C also exhibited a saturation magnetization over 11.4×10−5 emu and coercive magnetic field of 67 Oe. The ferroelectricity is interpreted by the ionic radius difference between the dopants and host cations, and the magnetism is explained by bound magnetic polarons mediated by electrons and defects.

Multilayer CNx/TiN composite films prepared by multi-arc assisted DC reactive magnetron sputtering

Abstract We incorporated the multi-arc discharge in a reactive magnetron sputtering system to produce alternating CN x /TiN coatings. X-ray photoelectron spectrometry (XPS) measurements showed that the carbon nitride was formed and the N content was between 12 and 40 at.% in the CN x films. The microstructure of the films was studied by atomic microscopy (AFM) and transmission electron diffraction (TED). There were β-C 3 N 4 and c-C 3 N 4 phases in the films. Under appropriate deposition conditions, alternating CN x /TiN coatings with high hardness, low friction coefficient and good adhesion were obtained on high-speed tool steel (HSS) substrates.

Raman Scattering Studies on Ag Nanocluster Composites Formed by Ion Implantation into Silica

Highly-pure amorphous silica slides were implanted by 200 keV Ag ions with doses ranged from 1×1016 to 2×1017 ions/cm2. Optical absorption spectra show that Ag nanoclusters with various sizes have been formed. Enhancement of surface enhanced Raman scattering signal by a factor up to about 103 was obtained by changing the Ag particle size. The silica was damaged by the implanted Ag ions, and the large compression stress on the silica leads to the shift of Raman peaks. New bands at 1368 and 1586 cm-1, which are attributed to the vibration of Ag–O bond and O2 molecules in silica, are observed in the samples with doses higher than 1×1017 ions/cm2.

Ion irradiation induced hollow and sandwiched nanoparticles

We report on the fabrication of hollow and sandwiched nanoparticles by ion irradiation. Ag nanoparticles embedded in silica were irradiated by N+, Si+, Ar+, and Cu+ ions at 300keV to a fluence of 5×1016ions∕cm2, by Cu+ ions at varying energies from 110to500keV to a fluence of 5×1016ions∕cm2, and by Cu+ ions at 400keV to fluences varied from 1×1016to1×1017ions∕cm2. The size of the irradiation-induced nanovoids increases with increasing ion mass and energy. The formation of nanovoids depends on the electronic and nuclear energy loss of the irradiation ions. The formation of irradiation-induced sandwiched nanoparticles is because of the capture of knocked-out Ag atoms from nanoshells by nanovoids. The size of the inner nanoparticles within the sandwiched structure increases with increasing fluence.

Effect of ferromagnetic properties in Al-doped Zn1−xCoxO nanowires synthesized by water-assistance reactive vapor deposition

The Zn1−xCoxO and Al-doped Zn1−xCoxO nanowires have been synthesized by the water-assistance reactive vapor deposition method. No Co precipitates appeared in the both kinds of ZnO nanowires according to the results observed by high-resolution transmission electron microscope, x-ray diffraction, and electron energy-loss spectroscopy, revealing that the magnetism of the ZnO nanowires was independent of the Co precipitates. The Al-doped Zn1−xCoxO nanowires show much stronger ferromagnetism than Zn1−xCoxO nanowires in the temperature range of 4–350 K. It is believed that the ferromagnetism in Zn1−xCoxO nanowires could be enhanced by Al doping to introduce donor carriers. Moreover, a multiple mechanism for the ferromagnetism of Al-doped Zn1−xCoxO nanowires is discussed.

AlN films deposited by middle-frequency magnetron sputtering with and without anode-layer ion source assistance

AlN films were deposited on Si (1 1 1) substrates by middle-frequency magnetron sputtering with and without anode-layer ion source assistance, and stoichiometric films were obtained. The structure and composition of the films were characterized by x-ray diffraction, atomic force microscopy and scanning electron microscopy. The films deposited under optimal conditions have strong diffraction of AlN (0 0 2) and a relatively weak diffraction of AlN (1 0 0), and the full width at half maximum of (0 0 2) peaks of these films falls in the range of 612–648 arcsec. The effect of the anode-layer ion source on the AlN film growth is discussed.