Influence of a urea–formaldehyde resin adhesive on pyrolysis characteristics and volatiles emission of poplar particleboard

To investigate the influence of urea–formaldehyde resin (UF resin) adhesive on the thermal utilization of wood waste, the pyrolysis of particleboard and its main components (poplar and UF resin) are studied in this paper.

Tunable electrical properties of silicon nanowires via surface-ambient chemistry

p-Type surface conductivity is a uniquely important property of hydrogen-terminated diamond surfaces. In this work, we report similar surface-dominated electrical properties in silicon nanowires (SiNWs). Significantly, we demonstrate tunable and reversible transition of p(+)-p-i-n-n(+) conductance in nominally intrinsic SiNWs via changing surface conditions, in sharp contrast to the only p-type conduction observed on diamond surfaces. On the basis of Si band energies and the electrochemical potentials of the ambient (pH value)-determined adsorbed aqueous layer, we propose an electron-transfer-dominated surface doping model, which can satisfactorily explain both diamond and silicon surface conductivity. The totality of our observations suggests that nanomaterials can be described as a core-shell structure due to their large surface-to-volume ratio. Consequently, controlling the surface or shell in the core-shell model represents a universal way to tune the properties of nanostructures, such as via surface-transfer doping, and is crucial for the development of nanostructure-based devices.

Field electron emission of ZnO nanowire pyramidal bundle arrays

A facile hydrothermal method was adopted to in situ grow ZnO nanowire pyramidal bundle arrays on zinc substrates at low growth temperature without the assistance of catalysts and templates. The bundle arrays were shown to form by sticking of nanowires at their tips. Field electron emission characterization of nanowires bundle arrays revealed a very low turn-on electric field of about 2.3 V/microm and a threshold electric field (corresponding to the field electron emission current density of 10 mA/cm2) of 6.8 V/microm, which are comparable to those observed in carbon nanotube arrays. The bundle arrays also show pronounced long-term field electron emission stability at a high current density. In addition, the formation mechanism of the pyramidal bundled arrays and the origin of the peculiar field electron emission properties were discussed.

Coaxial nanocables of p-type zinc telluride nanowires sheathed with silicon oxide: synthesis, characterization and properties

Coaxial nanocables with a single-crystalline zinc telluride (ZnTe) nanowire core and an amorphous silicon oxide (SiO(x)) shell have been synthesized via a simple one-step chemical vapor deposition (CVD) method on gold-decorated silicon substrates. The single-crystal ZnTe nanowire core is in zinc-blende structure along the [111] direction, while the uniform SiO(x) shell fully covers the core with no observable pin-hole or crack. Formation mechanisms of the ZnTe-SiO(x) nanocables are discussed. The ZnTe nanowire core shows p-type electrical properties while the SiO(x) shell acts as an effective insulating layer. The ZnTe-SiO(x) nanocables may have potential applications in nanoscale devices, such as p-type FETs and nanosensors.

Photoconductive properties of selenium nanowire photodetectors

Selenium nanowires with a diameter of about 70 nm and a growth direction along [001] were fabricated via a facile solution method. Photoconductive properties of Se wires were systematically characterized via photodetectors made of single Se nanowire. The photodetectors exhibited a high light on-off current ratio (Ilight/ Idark) of 450, and a fast light response speed of millisecond rise/fall time with excellent stability and reproducibility. It was also observed that the response time strongly depend on the intensity of the illumination light: the rise time and fall time for a typical photodetector is 0.68/1.85, 0.53/1.70, 0.54/1.65, 0.51/1.59, and 0.49/1.58 ms for light intensity of 0.18, 0.26, 0.43, 0.96, and 1.89 mW/cm2, respectively, and the relationship between the light intensity and the photocurrent can be fitted by using a simple power law. The diameters of the nanowire were found to have a significant influence on the response speed with smaller Se nanowires showing higher response speed. Finally, the mechanisms of photoconduction and factors affecting the performance of the photodetectors were elucidated.

High-quality Graphenes via a facile quenching method for field-effect transistors

Single- and few-layer graphene sheets with sizes up to 0.1 mm were fabricated by simply quenching hot graphite in an ammonium hydrogen carbonate aqueous solution. The identity and thickness of graphene sheets were characterized with transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. In addition to its simplicity and scalability, the present synthesis can produce graphene sheets with excellent qualities in terms of sizes, purity, and crystal quality. The as-produced graphene sheets can be easily transferred to solid substrates for further processing. Field-effect transistors based on individual graphenes were fabricated and shown to have high ambipolar carrier mobilities.

Structure determination of the hexagonal quasicrystal approximant μ′-(Al,Si)4Cr by the strong reflections approach

A number of different crystalline phases have been found in Al-rich Al-Cr-Si alloys by transmission electron microscopy (TEM). Among these, the new hexagonal phase micro'-(Al,Si)(4)Cr (a=2.01 and c=1.24 nm) often found coexisting with the hexagonal micro-(Al,Si)(4)Cr (a=1.998 and c=2.4673 nm, isostructural with micro-Al(4)Mn) and also with the hexagonal lambda-(Al,Si)(4)Cr (a=2.839 and c=1.239 nm, isostructural with lambda-Al(4)Mn). It is evident from their electron diffraction patterns that the structures of these three phases are related. The strong reflections in all three are distributed in a similar way. They all exhibit a pseudo-icosahedral symmetry. The structure factor amplitudes and phases for the strong reflections of the micro' phase could therefore be adopted from those of the lambda phase, according to the strong reflections approach. A structure model of the micro' phase is thus deduced from the known lambda-Al(4)Mn. micro' consists of chains of 3+3 or 4+2 interpenetrated icosahedra along the 100 directions. Similar to the lambda phase, there are two flat layers (F) and four puckered layers (P) in each unit cell of micro', stacked along the c-axis in a sequence of PFP(PFP)' where the (PFP)' block is related to the PFP block by a 6(3) screw.

Structure model for the τ(μ) phase in Al–Cr–Si alloys deduced from the λ phase by the strong-reflections approach

There are very obvious common features in the electron diffraction patterns of the λ and τ(μ) phases in the Al–Cr–Si system. The positions of the strong reflections and their intensity distributions are similar for the two structures. The relation of the reciprocal lattices of the λ and τ(μ) phases is studied. By applying the strong-reflections approach, the structure factors of τ(μ) are deduced from the corresponding structure factors of the known λ phase. Rules for selecting reflections for the strong-reflections approach are described. Similar to that of λ, the structure of τ(μ) contains six layers stacked along the c axis in each unit cell. There are 752 atoms in each unit cell, 53 of them are unique. The corresponding composition of the τ(μ) model is Al3.82 − x CrSi x . Simulated electron diffraction patterns from the structure model are in good agreement with the experimental ones. The arrangement of interpenetrated icosahedral clusters in the τ(μ) phase is discussed.