Uniformity study of wafer-scale InP-to-silicon hybrid integration

β-SiC nanowires were synthesized by a simple carbothermal reduction of carbonaceous silica xerogel. The morphology and structure of the nanowires were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results showed that the nanowires were hexagonal prism-shaped hierarchical nanostructures. The typical stacking faults and twin defects of SiC nanowires were also observed. Band-gap characterization and photoluminescence properties of SiC nanowires were investigated by UV-vis absorption spectroscopy and fluorescence photometry, respectively. The results showed the SiC nanowire was an indirect transition semiconductor and the band gap energy for the SiC nanowires was 2.85 eV. The photoluminescence peak value at 470 nm (2.64 eV) originating from the SiC nanowires was a little higher than the value of band-gap energy.     

Fabrication of two types of one-dimensional Si–C nanostructures by laser ablation

Two types of one-dimensional (1D) nanostructures—amorphous silicon carbide (SiC) nanowires, 5–30 nm thick and 0.5–2 μm long, and carbon nanotubes (CNTs) filled completely with crystalline SiC nanowires, 10–60 nm thick and 2–20 μm long—were synthesized by the laser ablation of carbon-silicon targets in the presence of high-pressure Ar gas up to 0.9 MPa. All the CNTs checked by transmission electron microscopy contained SiC, and no unfilled CNTs were produced. We discuss the growth of the two nanostructures based on the formation of molten Si–C composite particles and their instabilities leading to the precipitation of Si and C.     

Seed-mediated shape evolution of gold nanomaterials: from spherical nanoparticles to polycrystalline nanochains and single-crystalline nanowires

We studied the kinetics of the reduction of a gold precursor (HAuCl₄) and the effect of the molar ratio (R) of sodium citrate, which was introduced from a seed solution, and the gold precursor on the shape evolution of gold nanomaterials in the presence of preformed 13 nm gold nanoparticles as seeds. The reduction of the gold precursor by sodium citrate was accelerated due to the presence of gold seeds. Nearly single-crystalline gold nanowires were formed at a very low R value (R = 0.16) in the presence of the seeds as a result of the oriented attachment of the growing gold nanoparticles. At a higher R value (R = 0.33), gold nanochains were formed due to the non-oriented attachment of gold nanoparticles. At a much higher R value (R = 1.32), only larger spherical gold nanoparticles grown from the seeds were found. In the absence of gold seeds, no single-crystalline nanowires were formed at the same R value. Our results indicate that the formation of the 1D nanostructures (nanochains and nanowires) at low R values is due to the attachment of gold nanoparticles along one direction, which is driven by the surface energy reduction, nanoparticle attraction, and dipole–dipole interaction between adjacent nanoparticles.     

The characterization of electroplex generated from the interface between 2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole] zinc and N,N′-diphenyl-N,N′- bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine

The electroplex between (2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole) zinc [Zn(4-TfmBTZ)₂] as an electron-acceptor and N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) as an electron-donor was characterized by bilayer, blend, and multilayer quantum-well (MQW) device, respectively. The blend composition and quantum-well number are effective parameters for tuning electroluminescence color. White light with high color purity and color rendering index (CRI) was observed from these devices based on Zn(4-TfmBTZ)₂/NPB. Moreover, the blend and MQW devices all exhibit high operation stability, hence excellent color stability. For the device with 5 mol% NPB in blend layer, its Commission International Del’Eclairage (CIE) coordinate region is x=0.28–0.31, y=0.33–0.35 and CRI is 83.3–91.2 at 5–9 V. For MQW structure device with NPB of 60 nm thickness, its CIE coordinate region is x=0.29–0.32, y=0.31–0.34 and CRI=87.9–92.5 at 10–15 V. Such high color stability and purity and CRI, being close to ideal white light, are of current important for white OLED.     

Large-scale synthesis of crystalline β-SiC nanowires

Large quantities of high-purity crystalline β-SiC nanowires have been synthesized at relatively low temperature via a new simple method, the chemical-vapor-reaction approach, in a home-made graphite reaction cell. A mixture of milled Si and SiC powders and C₃H₆ were employed as the starting materials. The results show that the nanowires with diameters of about 10–35 nm are single crystalline β-SiCwithout any wrapping of amorphous material, and the nanowire axes lie along the 〈111〉 direction. Some unique properties are found in the Raman scattering from the β-SiC nanowires, which are different from previous observations of β-SiC materials. A possible growth mechanism for the β-SiC nanowires is proposed. Received: 27 August 2002 / Accepted: 28 August 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-29/8491-000, E-mail: zjli-sohu@sohu.com     

Electronic structures,magnetic properties and half-metallicity in Heusler alloys Zr2IrZ (Z = Al,Ga, In)

The electronic structures, magnetic properties and half-metallicity in Zr₂IrZ (Z = Al, Ga, In) alloys with the Hg₂CuTi-type structure were systematically investigated by using the first-principle calculations. Zr₂IrZ (Z = Al, Ga, In) alloys are predicted to be half-metallic ferrimagnets which are quite robust against hydrostatic strain and tetragonal deformation. The total magnetic moment of Zr₂IrZ (Z = Al, Ga, In) alloys mainly originates from the 4d electrons of Zr atoms and follows the conventional Slater-Pauling rule: M_t = Z_t−18. (M_t is the total magnetic moment per unit cell and Z_t is the valence concentration). The origin of the band gap for Zr₂IrZ (Z = Al, Ga, In) alloys is also well studied. Unconventionally, Zr₂Ir-based alloys contain element with 5d valence electrons, which implies a wider field to search for new half-metallic materials.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Testing of QED-Theory and Precise Measurements of the Rydberg Series for the He-Like Multicharged Ions

The wavelengths of the 1snp ¹ P ₁−1s ^{2 1} S ₀ transitions in He-like Mg XI, F VIII (n= 4–8) and Al XII (n=6,9) have been calculated in the framework of the 1/Z expansion method including relativistic effects and QED contributions. It is found that QED corrections to the ground-state ionization energy are significant at the present level of experimental accuracy. This revised version was published online in July 2006 with corrections to the Cover Date.     

X-ray converters for radiation treatment of thin films

The energy absorbed in thin films of selected materials bombarded by x rays emitted in the braking of low-energy electrons (E ₀<500 keV) in converters with various atomic numbers (Z=29–73) is calculated by the Monte Carlo method. The program takes into account both of the K-shell ionization mechanisms that lead to emission of characteristic photons as a result of electron impact and as a result of the photoelectric effect, and the characteristic radiation is shown to make a large contribution to the absorbed energy in thin films. Calculations show that the proper choice of material and thickness of the converter affords a two-to fivefold increase in the energy of the x radiation absorbed in thin films of semiconductor materials. Zh. Tekh. Fiz. 68, 99–101 (November 1998)     

Long SiC nanowires synthesized from off-gases of the polycarbosilane-derived SiC preparation

In this communication, we report on the attempt to make full use of the off-gases from polycarbosilane-derived SiC preparation, and we successfully synthesized long SiC nanowires in large areas with Fe(NO₃)₃ as catalyst. The nanowires have diameters of about 80–300 nm and lengths of millimeters, and they are identified as single crystals β-SiC along the 〈111〉 direction. The VLS mechanism was employed to interpret the nanowire growth.     

Viscous modified gravity on a RS brane embedded in AdS<Subscript>5</Subscript>

We consider a modified gravity fluid on a Randall–Sundrum II brane situated at y=0, the action containing a power α of the scalar curvature. As is known from 4D spatially flat modified gravity, the presence of bulk viscosity may drive the cosmic fluid into the phantom region (w<−1) and thereafter inevitably into the Big Rip singularity, even if it is initially nonviscous and lies in the quintessence region (w>−1). The condition for this to occur is that the bulk viscosity contains the power (2α−1) of the scalar expansion. We combine this with the 5D RS II model, and we find that the Big Rip, occurring for α>1/2, carries over to the metric for the bulk metric, |y|>0. Actually, the scale factors on the brane and in the bulk become simply proportional to each other.     

Azobenzene-functionalized alkanethiols in self-assembled monolayers on gold

Self-assembled monolayers (SAMs) of 4-trifluoromethyl-azobenzene-4′-methyleneoxy-alkanethiols (CF₃– C₆H₄–N=N–C₆H₄–O–(CH₂) _n –SH on (111)-oriented poly-crystalline gold films on mica were examined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The spectra are analyzed with the help of density-functional-theory calculations of the isolated molecule. Only one doublet is detected in the sulphur 2p spectra of the investigated SAMs, consistent with a thiolate bond of the molecule to the gold surface. The C 1s XP spectra and the corresponding XAS π ^* resonance exhibit a rich structure which is assigned to the carbon atoms in the different chemical surroundings. Comparing XPS binding energies of the azobenzene moiety and calculated initial-state shifts reveals comparable screening of all C 1s core holes. While the carbon 1s XPS binding energy lies below the π ^*-resonance excitation-energy, the reversed order is found comparing core ionization and neutral core excitation of the nitrogen 1s core-hole of the azo group. This surprising difference in core-hole binding energies is interpreted as site-dependent polarization screening and charge transfer among the densely packed aromatic moieties. We propose that a quenching of the optical excitation within the molecular layer is thus one major reason for the low trans to cis photo-isomerization rate of azobenzene in aromatic-aliphatic SAMs.     

Calculated optical properties of GaX (X=P,As, Sb) under hydrostatic pressure

The hydrostatic pressure dependence of the principal energy gaps and of the optical properties of GaX (X = P, As and Sb) has been calculated using the full potential-linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) for the exchange and correlation potential is applied. Also, we have used the Engel–Vosko GGA formalism, which optimizes the corresponding potential for band-structure and the optical properties calculations. Structural properties such as equilibrium lattice constants, the bulk modulus, and its pressure derivatives were calculated for GaP, GaAs, and GaSb in the zinc-blende structure (ZB). We have found that the results of the structural properties calculations are in agreement with those of ab initio and experimental data. In general, the pressure dependence of the principal energy gaps is compared to other values. The same is for the pressure coefficient. However, for the same structure, the comparison of our results with those of experimental and theoretical calculations shows good agreement. On the other hand, the effect of the applied pressure is clearly seen in the optical properties especially near the energy transition regions.     

Photoluminescence of CuInS<Subscript>2</Subscript> single crystals grown by traveling heater and chemical vapor transport methods

Photoluminescence of CuInS₂ single crystals grown by both the traveling heater method (THM) and chemical vapor transport (CVT) has been investigated at 4.2, 78, and 300 K. Intense emission in the near-band-edge region caused by free and bound excitons has been detected for both types of crystals. Taking into account the energy position of the luminescence line of the ground (n = 1) and first excited (n = 2) states, the binding energy for free A excitons has been estimated to be about 19.7 and 18.5 meV for CuInS₂ grown by CVT and THM, respectively. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 232–236, March–April, 2009.     

Double atomic photoeffect in the relativistic domain: Angular and energy distributions of photoelectrons

We study the double ionization of the atomic K-shell by a single photon in the relativistic energy domain. The differential and total cross sections of the process are calculated. It is shown that the ratio of the cross sections of double and single ionization increases with the photon energy, tending to the limit 0.34/Z ², where Z is the atomic number or the nuclear charge. The formulas are found to be valid for Z≫1 and αZ≪1, where α=1/137 is the fine-structure constant. Zh. éksp. Teor. Fiz. 114, 1537–1554 (November 1998)     

Anilinolysis of O‐butyl phenyl phosphonochloridothioate in acetonitrile: Synthesis,characterization, kinetic study,and reaction mechanism

This paper describes a simple optimized method for the synthesis of O‐butyl phenyl phosphonochloridothioate ( 4 ) under mild conditions. The target compounds were characterized by ¹H‐nuclear magnetic resonance (NMR), ¹³C‐NMR, and ³¹P‐NMR spectroscopy, as well as mass spectroscopy. The apparent structure of 4 was confirmed by optimization using the B3LYP/6‐311 + G(d,p) level in the Gaussian 09 program in acetonitrile. The nucleophilic substitution reactions of 4 with X‐anilines (XC₆H₄NH₂) and deuterated X‐anilines (XC₆H₄ND₂) were investigated kinetically in acetonitrile at 55.0°C. The free energy relationship with X in the anilines looked biphasic concave upwards with a break region between X = H and X = 3‐MeO, giving large negative ρ_X and small positive β_X values. The deuterium kinetic isotope effects were secondary inverse (k_H/k_D < 1: 0.789‐0.995) and the magnitudes, (k_H/k_D), increased when the nucleophiles were changed from weakly basic to strongly basic anilines. A concerted S_N2 mechanism is proposed on the basis of the selectivity parameters and the variation trend of the deuterium kinetic isotope effects with X.     

Femtosecond energy relaxation in suspended graphene: phonon-assisted spreading of quasiparticle distribution

Ultra-fast optical measurements of few-layer suspended graphene films grown by chemical vapor deposition were performed with femtosecond pump–probe spectroscopy. The relaxation processes were monitored in transient differential transmission (ΔT/T) after excitation at two different wavelengths of 350 and 680 nm. Intraband electron–electron scattering, electron–phonon scattering, interband Auger recombination and impact ionization were considered to contribute to ΔT/T. All these processes may play important roles in spreading the quasiparticle distribution in time scales up to 100 fs. Optical phonon emission and absorption by highly excited non-equilibrium electrons were identified from ΔT/T peaks in the wide spectral range. When the probe energy region was far from the pump energy, the energy dependence of the quasiparticle decay rate was found to be linear. Longer lifetimes were observed when the quasiparticle population was localized due to optical phonon emission or absorption.     

Electrochemical studies on polymer electrolytes based on poly(methyl methacrylate)-grafted natural rubber for lithium polymer battery

MG30 is natural rubber grafted with 30% poly(methyl methacrylate). Gel polymer electrolytes containing MG30–LiCF₃SO₃–X (X = propylene carbonate, ethylene carbonate) are prepared by solution casting technique. The polymer–salt complexes were investigated using Fourier-transformed infrared. The ionic conductivity of the electrolytes are determined by the ac impedance studies over the temperature range of 303–383 K and is observed to obey the Vogel–Tamman–Fulcher (VTF) rule. The Li⁺ transference number obtained using the Bruce and Vincent method is <0.3. The Li/Li⁺ interface stability is established and the electrolytes were found to be able to withstand a voltage of more than 4.2 V.     

The sensitivity and dynamic response of field ionization gas sensor based on ZnO nanorods

Field ionization gas sensors based on ZnO nanorods (50–300 nm in diameter, and 3–8 μm in length) with and without a buffer layer were fabricated, and the influence of the orientation of nano-ZnO on the ionization response of devices was discussed, including the sensitivity and dynamic response of the ZnO nanorods with preferential orientation. The results indicated that ZnO nanorods as sensor anode could dramatically decrease the breakdown voltage. The XRD and SEM images illustrated that nano-ZnO with a ZnO buffer layer displayed high c-axis orientation, which helps to significantly reduce the breakdown voltage. Device A based on ZnO nanorods with a ZnO buffer layer could distinguish toluene and acetone. The dynamic responses of device A to the NO _x compounds presented the sensitivity of 0.045 ± 0.007 ppm/pA and the response speed within 17–40 s, and indicated a linear relationship between NO _x concentration and current response at low NO _x concentrations. In addition, the dynamic responses to benzene, isopropyl alcohol, ethanol, and methanol reveals that the device has higher sensitivity to gas with larger static polarizability and lower ionization energy.