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We fabricated silicon nanowire/cadmium telluride quantum dots (CdTe QDs)/organic hybrid solar cells and investigated their structure and electrical properties. Transmission electron microscope revealed that CdTe QDs were uniformly distributed on the surface of the silicon nanowires, which made PEDOT:PSS easily filled the space between SiNWs. The current density–voltage ( J – V ) characteristics of hybrid solar cells were investigated both in dark and under illumination. The result shows that the performance of the hybrid solar cells with CdTe QDs layer has an obvious improvement. The optimal short-circuit current density ( J sc ) of solar cells with CdTe QDs layer can reach 33.5 mA/cm 2 . Compared with the solar cells without CdTe QDs, J sc has an increase of 15.1%. Power conversion efficiency of solar cells also increases by 28.8%. The enhanced performance of the hybrid solar cells with CdTe QDs layers are ascribed to down-shifting effect of CdTe QDs and the modification of the silicon nanowires surface with CdTe QDs. The result of our experiments suggests that hybrid solar cells with CdTe QDs modified are promising candidates for solar cell application.

In this letter, we investigated spectral and opto-electronic conversion properties of the inorganic/organic hybrid cells by using silver nanoparticles (AgNPs)/Si nanoholes (SiNHs) nanocomposite films, which were fabricated by the modified metal-assisted electroless etching (EE) method. It was found that the optical absorption spectra of the films with AgNPs demonstrate a clear peak and show the enhancement of total absorption at the short wavelength. The results of current–voltage ( I – V ) measurements show that solar cells with AgNPs exhibit an increase of the power conversion efficiency by a factor of 2–3, in comparison with those of the samples without AgNPs. Moreover, higher external quantum efficiency (EQE) values in AgNPs-decorated solar cells were confirmed in the short-wavelength spectral region (400–700 nm), which were essential to achieve high-performance photovoltaic cells. We thought these were mainly attributed to the localized surface plasmon resonance (LSPR) effects and increased light scattering of AgNPs.

With the research in the technology of AADL, we design and realize the parser for AADL and code generation tools which transform AADL model into C source code based on Spoofax/XL. This lays a good foundation for further realizing the AADL unified modeling, verification, implementation and code generation integrated environment.

Eu-doped ZnSe:/ZnS quantum dots (formed as ZnSe:Eu/ZnS QDs) were successfully synthesized by a two-step wet chemical method: nucleation doping and epitaxial shell growing. The sensitization characteristics of Eu-doped ZnSe and ZnSe/ZnS core/shell QD are studied in detail using photoluminescence (PL), PL excitation spectra (PLE) and time-resolved PL spectroscopy. The emission intensity of Eu ions is enhanced and that of ZnSe QDs is decreased, implying that energy was transferred from the excited ZnSe host materials (the donor) to the doped Eu ions (the acceptor). PLE reveals that the ZnSe QDs act as an antenna for the sensitization of Eu ions through an energy transfer process. The dynamics of ZnSe:Eu/ZnS core/shell quantum dots with different shell thicknesses and doping concentrations are studied via PL spectra and fluorescence lifetime spectra. The maximum phosphorescence efficiency is obtained when the doping concentration of Eu is approximately 6% and the sample showed strong white light under ultraviolet lamp illumination. By surface modification with ZnS shell layer, the intensity of Eu-related PL emission is increased approximately three times compared with that of pure ZnSe:Eu QDs. The emission intensity and wavelength of ZnSe:Eu/ZnS core/shell quantum dots can be modulated by different shell thickness and doping concentration. The results provide a valuable insight into the doping control for practical applications in laser, light-emitting diodes and in the field of biotechnology. Copyright © 2014 John Wiley & Sons, Ltd.

Zn-doped Ge2Sb2Te5 (GST) thin films are deposited on glass substrates by an electron-beam evaporation technique in an ultra-high vacuum. GST mixed with 5%, 10%, 20% Zn is used. Through in situ resistance measurements, an increase of crystalline temperature in Zn-doped GST was observed. From absorption spectra, the optical bandgap values of 10% Zn-doped GST in different structures are estimated to be 1.1, 0.9, and 0.7 eV, respectively, which are slightly wider than that of pure GST. A prototype phase-change memory (PCM) device using GST thin film doped with Zn was fabricated. The current–voltage test results of the devices show better switching performances in both SET and RESET processes than that of the device using pure GST film. The threshold voltage is greatly increased with the adding of Zn atom with fixed proportion, which can weaken the interaction during the read and write operation of PCM.

Pure Ge2Sb2Te5 thin films and Si-doped Ge2Sb2Te5 thin films were deposited by electron beam evaporation method. The property of Si-doped Ge2Sb2Te5 films are compared with that of pure Ge2Sb2Te5 films. Through in situ resistance measurement and I–V characteristic tests, an improvement of amorphous stability and an increase of crystalline resistivity are observed. The phase-separation phenomenon is observed in TEM pictures and a distinct decrease of crystal grain size in Si-doped Ge2Sb2Te5 thin film can be seen in HRTEM pictures. A blueshift and broadening of peaks after Si doping in Raman spectra are found and from absorption spectra, the broadening of crystalline optical bandgap in Si-doped Ge2Sb2Te5 thin film is proved. Finally, the behavior of doped Si atoms is proposed to explain the effect of Si doping in Ge2Sb2Te5 thin film.

GST (GeSbTe) thin films were deposited on glass substrates by electron beam evaporation; Ni was used as the top and bottom electrodes. The I–V (current–voltage) characteristic of the phase change memory (PCM) cell was measured; results showed an electrical threshold switching characteristic for the sample with a threshold voltage of 3.08 V. The threshold switching is attributed to the formation of conductive filaments in the amorphous matrix. Current-voltage spectra which were obtained by C-AFM show that the GST thin film switching from amorphous to the crystalline phase occurs at 1.51 V. C-AFM was used to fabricate crystalline nanoarrays on the sample surface and examine the electrical properties of arrays. In the I–V measurements by C-AFM, when the applied voltage is higher than threshold voltage, conducting nanofilaments with average sizes of 15–60 nm were formed and crystallized spots with current signals were observed. Different times of I–V spectroscopies were applied on thin films to investigate the electrical properties of films during the phase change process. C-AFM results show that as the times of I–V spectroscopies increased, the morphology of crystallized spots changed from bump to pit; the sizes of conductive nanofilaments and detected current signals increased. These results can be attributed to the energy induced by Joule heating dissipated to surrounding films increases with the increasing times of I–V spectroscopies.

GeSbTe (GST) thin films were deposited on quartz substrates using electron beam evaporation system and then annealed in nitrogen atmosphere at different temperatures, ranging from 20 °C to 300 °C. X-ray diffraction (XRD) and Atomic Force microscope (AFM) measurements were used to characterize the as-deposited and post-annealed thin films. Annealing treatment was found to induce changes on microstructure, surface roughness and grain size, indicating that with the increase of annealing temperature, the amorphous GST films first changed to face-centered-cubic (fcc) phase and then the stable hexagonal (hex) phase. Meanwhile, conductive-AFM (C-AFM) was used to produce crystallized GST dots on thin films. I–V spectroscopy results show that GST films can switch from amorphous state to crystalline state at threshold voltage. After switching, I–V curve exhibits ohmic characteristic, which is usually observed in crystallized GST films. By applying repeated I–V spectroscopies on the thin films, crystallized nuclei were observed. As the times of I–V spectroscopies increases, the area of written dots increases, and the center of the mark begin to ablate. The AFM images show that the shape of marks is an ablated center with a raised ring surrounding it.

Core/shell quantum dots (QDs) show novel properties compared to conventional single QDs, such as high quantum yields, excellent photostability, good monodispersity. In aqueous solution, monodisperse and highly luminescent ZnSe:Eu3 +/ZnS core/shell nanocrystals were synthesized by the two-step wet chemical method. Transmission electron microscopy (TEM) images of ZnSe:Eu3 +QDs and ZnSe:Eu3 +/ZnS core/shell QDs showed nearly monodisperse particles with size of around 2.9 nm ± 0.3 and 4.5 nm ± 0.3. X-ray powder diffraction (XRD) results show that ZnSe:Eu3 +/ZnS QDs possess cubic zinc blende structure. The effects of the reaction time on the luminescence properties were systematically studied. From the photoluminescence (PL) spectra, it was found that the ZnSe:Eu3 +/ZnS nanocrystals with 3-mercaptopropionic acid (MPA) capping exhibited the Eu3 + ion related characteristic luminescence. When a larger band gap ZnS shell was deposited at the surface of the ZnSe:Eu3 +core, luminescence of Eu3 + ion related emission was enhanced nearly two times.

Co and Nd co-substituted Bi 5 Ti 3 FeO 15 thin films were prepared on Pt/Ti/SiO 2 /Si substrates via metal organic decomposition method. The structural and multiferroic properties of the films were investigated. It was found that Co ions enter into the lattice and occupy the Fe site. The Bi 4.15 Nd 0.85 Ti 3 Fe 0.5 Co 0.5 O 15 films simultaneously exhibit ferroelectric and ferromagnetic properties at room temperature, and its 2 P r and 2 M r are 38 μC/cm 2 and 3 kA/m, respectively. Moreover, substitutions create local ferromagnetic order and antiferromagnetic order depending on whether the local bonding is Fe O Co or Fe O Fe/Co O Co, respectively. The competing interaction of the ferromagnetic and antiferromagnetic phases results in an interesting magnetic behavior of the films.

Highly ordered CuInSe2 films with hollow nanocones were fabricated by electron beam evaporation and nanospheres lithograph. From the AFM analyses, polystyrene nanospheres with diameter of 220 nm are assembled regularly on glass substrates. After reaction ion etching under different powers and residues removal, different and new surface morphologies of substrates have been obtained, such as smooth nanocones and hollow nanocones. The diffuse reflection spectra demonstrate that films on the substrates with periodic nanopatterned structure have less reflection over wavelengths ranged from 200 nm to 2500 nm due to light trapping. Especially, reflection for hollow nanocone arrays has the larger suppression value than nanocone-patterned films, which proves that surface pattern of hollow nanocones has better anti-reflection effect. Furthermore, while hollow depth increases from 6 nm to 9 nm, its optical antireflective effect becomes remarkable. These results could yield new options for solar-cell design with higher energy conversion efficiency.

Highly-pure iron powder was covered on porous silicon for fabricating semiconducting β-FeSi2 structures. X-ray diffraction and Raman scattering results confirm the formation of pure-phase β-FeSi2 after high-temperature annealing at 1100°C and then long-time persistence at 900°C. Scanning electron microscope observations reveal that large-size (>μm) β-FeSi2 grains mainly form in the pores of porous silicon and some nanocrystals grow on local surfaces. The temperature-dependent photoluminescence spectra disclose that the observed ∼1.54 μm emission arises from free exciton recombination, which is confirmed via the activation energy (0.25 eV) measurement. Our method provides a way to synthesize single-phase β-FeSi2 materials.

The correctness of kernel is the key to the safety critical embedded application, and only by formal verification it can prove the kernel does not exist some defects or meet certain attributes. In this paper, we introduce SAFEBOX, a microkernel based on spatial-temporal isolation, give the formal description of SAFEBOX, and use theorem proverb Isabelle/HOL to verify the functional and non-functional properties of SAFEBOX.

The phase-change characteristics of silicon doped Ge 2 Sb 2 Te 5 (Si-GST) film were investigated and compared with pure Ge 2 Sb 2 Te 5 (GST) film. The results of in situ temperature dependence of the sheet resistance demonstrate that the crystalline resistivity of GST film increased by the silicon doping, but the phase transition temperature T c was almost unchanged. The minimum on/off ratio for Si-doped GST is around 240, which is high enough to be used for device application. Both of the GST and Si-doped GST prototype memory devices can perform SET and RESET cycles. The threshold voltage V th increased while the RESET current decreased with silicon doping. Applying the Kissinger method the activation energy for crystallization of Si-doped GST film (300 nm) is determined to be 2.30 ± 0.05 eV.

Eu-doped ZnSe:/ZnS quantum dots (formed as ZnSe:Eu/ZnS QDs) were successfully synthesized by a two-step wet chemical method: nucleation doping and epitaxial shell growing. The sensitization characteristics of Eu-doped ZnSe and ZnSe/ZnS core/shell QD are studied in detail using photoluminescence (PL), PL excitation spectra (PLE) and time-resolved PL spectroscopy. The emission intensity of Eu ions is enhanced and that of ZnSe QDs is decreased, implying that energy was transferred from the excited ZnSe host materials (the donor) to the doped Eu ions (the acceptor). PLE reveals that the ZnSe QDs act as an antenna for the sensitization of Eu ions through an energy transfer process. The dynamics of ZnSe:Eu/ZnS core/shell quantum dots with different shell thicknesses and doping concentrations are studied via PL spectra and fluorescence lifetime spectra. The maximum phosphorescence efficiency is obtained when the doping concentration of Eu is approximately 6% and the sample showed strong white light under ultraviolet lamp illumination. By surface modification with ZnS shell layer, the intensity of Eu-related PL emission is increased approximately three times compared with that of pure ZnSe:Eu QDs. The emission intensity and wavelength of ZnSe:Eu/ZnS core/shell quantum dots can be modulated by different shell thickness and doping concentration. The results provide a valuable insight into the doping control for practical applications in laser, light-emitting diodes and in the field of biotechnology.

Cadmium sulphide (CdS) and cadmium telluride (CdTe) thin films are deposited by electron beam evaporation. Atomic force microscopy (AFM) reveals that the root mean square (RMS) roughness values of the CdS films increase as substrate temperature increases. The optical band gap values of CdS films increase slightly with the increase in the substrate temperature, in a range of 2.42–2.48 eV. The result of Hall effect measurement suggests that the carrier concentration decreases as the substrate temperature increases, making the resistivity of the CdS films increase. CdTe films annealed at 300°C show that their lowest transmittances are due to their largest packing densities. The electrical characteristics of CdS/CdTe thin film solar cells are investigated in dark conditions and under illumination. Typical rectifying and photovoltaic properties are obtained.

Cadmium sulphide (CdS) thin films were deposited by electron beam evaporation at different substrate temperatures. The structural characteristics were studied by the x-ray diffraction pattern. The CdS films are polycrystalline, exhibiting a preferred orientation along the (002) plane. Atomic force microscopy reveals that the root mean square roughness of the films increases as the substrate temperature increases. The optical band gap values of CdS films increase slightly with the increasing substrate temperature, in the range of 2.42–2.48 eV. The electrical characteristics of CdS/p-Si heterojunctions were investigated in dark condition and under the illumination intensity of 100 mW/cm2. Excellent rectifying and photovoltaic properties were observed.

We have investigated the electrical properties of Ge1Sb2Te4 and Ge2Sb2Te5 thin films in the temperature range of 27 to 200 °C. The optical bandgap values obtained from the measured absorption spectra for amorphous Ge1Sb2Te4 and Ge2Sb2Te5 are 0.70 and 0.90 eV, respectively. The results of the in situ temperature dependence of the sheet resistance demonstrate that both Ge1Sb2Te4 and Ge2Sb2Te5 thin films in the amorphous phase exhibit a temperature-activated electrical conductivity with activation energy values of 0.42 and 0.45 eV, respectively. These results show that our experimental results agree well with the predictions of Mott’s model. The temperature dependent carrier mobility was measured accurately using the surface acoustic wave method, which is an appropriate method for materials with low conductivities and low mobility. Typical values of drift mobility for amorphous Ge1Sb2Te4 and Ge2Sb2Te5 thin films at room temperature are round 10−3 cm2/(Vs) and 10−2 cm2/(Vs), respectively. The values of drift ...