J.Z. Jiang

Electrical and optical properties of phosphorus-doped p-type ZnO films grown by metalorganic chemical vapor deposition

P-doped p-type ZnO thin films have been grown by metalorganic chemical vapor deposition. By modulating the P evaporating temperature, p-type conductivity can be controlled due to the different P content incorporated into the ZnO films. The P-doped p-type ZnO thin films are of high optical quality, as indicated by low-temperature photoluminescence. P-related acceptor state with an energy level of 163 meV is identified from free-to-neutral-acceptor transitions. In addition, x-ray photoelectron spectroscopy confirms that only one chemical bonding state of P exists in the P-doped ZnO thin films.

Atomic structure of Al88Y7Fe5 metallic glass

The structure of Al88Y7Fe5 metallic glass has been investigated by differential scanning calorimetry, x-ray powder diffraction, and x-ray absorption fine structure (XAFS) techniques. The amorphous alloy crystallizes according to the following scheme: amorphous→α‐Al+residual amorphous→α‐Al+Al3Y+AlFeY. The atomic structure of the amorphous alloy was modeled by reverse Monte Carlo methods. The resulting structure indicates that the prepeak (at 1.42A−1) in the static structure factor S(Q) is caused by contributions of distinct Y-Y, Y-Fe pairs. From the analysis of our XAFS spectra at the Fe and Y K edge the following characteristics of the local structure are found: The interatomic distance between Fe and coordinated Al atoms in the amorphous state is significantly (8.9%) shorter than the sum of the nominal metallic-state radii. The average coordination number is anomalously 36% reduced compared to the value derived from the dense-random-packing (DRP) model, using again the nominal metallic-state radii. On th...

Magnetic stability of SnO2 nanosheets

Room temperature ferromagnetism has been observed in freshly synthesized and post-annealed SnO₂ nanosheets. The results of x-ray diffraction and x-ray photoelectron spectroscopy reveal that the newly synthesized samples and those annealed at 400 °C under either an O₂ or Ar atmosphere possess rutile structure and no other impurity phases are observed. The fitting results of the O 1s and Sn 3d spectra from SnO₂ samples annealed at 400 °C under an O₂ or Ar atmosphere both indicate that oxygen vacancies inevitably exist in these samples. It is found that the saturation magnetization of all the annealed samples does not feature mono-dependence on oxygen vacancies, whereas an Sn vacancy related origin seems more plausible to account for variations in the magnetization of samples studied. This finding corresponds to first-principle calculation results from our previous work. Furthermore, the Curie temperature of SnO₂ nanosheets was estimated to be around 300 °C, rendering it a very good option for the next generation of spintronics.

Free-volume evolution and its temperature dependence during rolling of Cu60Zr20Ti20 bulk metallic glass

The free-volume evolution during rolling Cu60Zr20Ti20 bulk metallic glass at room and cryogenic temperatures has been investigated by differential scanning calorimetry. When the specimen is rolled at cryogenic temperature, the free-volume content increases as the rolling proceeds first, and then saturates accompanied by the occurrence of phase separation as the thickness reduction exceeds 89%. If the rolling is performed at room temperature, although the free-volume content also rises in the earlier stage, it tends to decrease rather than saturate when the thickness reduction exceeds 87%, accompanied by partial crystallization. Phase separation does not change the annihilation rate of free volume, while the appearance of crystal/amorphous boundaries can enhance the annihilation.

Atomic structure in Zr70Ni30 metallic glass

Atomic structure of Zr70Ni30 metallic glass (MG) was investigated by reverse Monte Carlo simulation combining with x-ray diffraction and Ni and Zr K-edge extended x-ray absorption of fine structure measurements. Distributions of coordination number (CN) and Voronoi clusters were analyzed by Voronoi tessellation method. The average CN of atoms was obtained to be 11.4 together with the average CN of Zr and Ni atoms of about 11.8 and 10.6, respectively. It is found that Z11 Kasper polyhedron and distorted icosahedra are mainly favored structural units in Zr70Ni30 MG. The discrepancy in atomic structure between Zr70Ni30 MG and its corresponding crystalline (or quasicrystalline) phases can explain the fact that Zr70Ni30 MG does not transform to neither icosahedral nor fcc Zr2Ni phase during crystallization process.

Surface magnetism in amine-capped ZnO nanoparticles

Magnetic behaviors of pure ZnO nanoparticles have been investigated both experimentally and theoretically. It is found that monodisperse ZnO nanoparticles wrapped with oleylamine with an average particle size of about 9.6 nm prepared by thermal decomposition do show ferromagnetic behavior with a saturation magnetization of about 34 memu g(-1) and coercive force of about 22 Oe, whereas ZnO nanoparticles with an average particle size of 5.2 nm prepared by ultrasonic irradiation without solvents show a weak ferromagnetic property with a saturation magnetization of about 0.12 memu g(-1) and coercive force of about 150 Oe at ambient temperature. First-principles calculations reveal that the 2p holes on the atoms at the surface (dangling bond of O atoms at ZnO(0001) or 2p electrons of N atom in NH(3) adsorbed on Zn(0001)) could be the source for the magnetic behavior of oxide nanoparticles.

Thermal expansion of a La-based bulk metallic glass: insight from in situ high-energy x-ray diffraction

Constant-rate heating experiments using a fast x-ray camera (time resolution of 2.7 s) reveal detailed information about the thermal stability of La62Al14(Cu5/6Ag1/6)14Ni5Co5 (at.%) bulk metallic glass. Analyzing diffraction patterns in reciprocal space yields the thermal expansion of the amorphous alloy providing insight into the thermally activated relaxation effects and kinetics of the glass transition. The glass transition appears as a break in the value of the coefficient of volume thermal expansion. Furthermore, real space analysis based on the reduced pair distribution function G(r ) allows one to follow in situ the changes in the local atomic structure of the amorphous material during constant-rate heating. (Some figures in this article are in colour only in the electronic version)

Blue emission of Ge nanocrystals prepared by thermal decomposition

We report here a simple synthesis method for monodisperse Ge nanocrystals by thermal decomposition of precursor TOG at 360 °C, which is obtained by a reaction of GeCl4 with oleylamine at room temperature. The effect of refluxing time on the average dimension of Ge nanocrystals is discussed. Fundamental characterizations including HRTEM and XRD were performed on these Ge nanocrystals. FTIR, DSC and TG were used to explain the mechanism of formation of Ge nanocrystals by thermal decomposition of TOG. Ge nanocrystals with average grain sizes clearly exhibit blue emission, which might result from the hydrocarbon absorbed on the surface Ge nanocrystals, the amorphous oxide layer on the surface of Ge nanocrystals and/or defects in Ge nanocrystals.

Lateral buckling and mechanical stretchability of fractal interconnects partially bonded onto an elastomeric substrate

Fractal-inspired designs for interconnects that join rigid, functional devices can ensure mechanical integrity in stretchable electronic systems under extreme deformations. The bonding configuration of such interconnects with the elastomer substrate is crucial to the resulting deformation modes, and therefore the stretchability of the entire system. In this study, both theoretical and experimental analyses are performed for postbuckling of fractal serpentine interconnects partially bonded to the substrate. The deformation behaviors and the elastic stretchability of such systems are systematically explored, and compared to counterparts that are not bonded at all to the substrate.

Local strain behavior of bulk metallic glasses under tension studied by in situ x-ray diffraction

The uniaxial tensile behavior of Zr62Al8Ni13Cu17, Cu46Zr46Al8, Zr48Cu43Al7Ag2, and La62Al14(Cu5/6Ag1/6)14Co5Ni5 bulk metallic glasses (BMGs) has been investigated by using in situ synchrotron radiation diffraction technique. It is found that the local strain is basically homogeneously distributed at low stress. However, heterogeneity appears obviously when the stress is close to the fracture strength. The amplitude of fluctuation in local strain for four BMGs could relate to the distribution of excess free volume within the medium range order.