Enhanced broadband optical transmission in metallized woodpiles

We present an optimized isotropic metal deposition technique used for covering three-dimensional polymer structures with a 50 nm smooth silver layer. The technology allows fast and isotropic coating of complex 3D dielectric structures with thin silver layers. Transmission measurements of 3D metallized woodpiles reveal a new phenomenon of enhanced optical transmission in broadband range (up to 300 nm) in the near IR.     

10.6 μm Infrared light photoinduced insulator-to-metal transition in vanadium dioxide

Vanadium dioxide has excellent phase transition characteristic. Before or after phase transition, its optical, electrical, magnetic characteristic hangs hugely. It has a wide application prospect in many areas. Now, the light which can make vanadium dioxide come to pass photoinduced phase transition range from soft X-ray to medium infrared light (6.9 μm, 180 meV). However, whether 10.6 μm (117 meV) long wave infrared light can make vanadium dioxide generate photoinduced phase transition has been not studied. In this paper, we researched the response characteristic of vanadium dioxide excited by 10.6 μm infrared light. We prepared the vanadium dioxide and test the changes of vanadium dioxide thin film’s transmittance to 632.8 nm infrared light when the thin film is irradiate by CO₂ laser. We also test the resistivity of vanadium dioxide. Excluding the effect of thermal induced phase transition, we find that the transmittance of vanadium dioxide thin film to 632.8 nm light and resistivity both changes when irradiating by 10.6 μm laser. This indicates that 10.6 μm infrared light can make the vanadium dioxide come to pass photoinduced phase transition. The finding makes vanadium has a potential application in recording the long-wave infrared hologram and making infrared detector with high resolution.     

Electric-field mediated nickel-induced nanocrystallization of?amorphous silicon thin films in the complete absence of external heating

DC electric-field mediated nanocrystallization of thermally evaporated silicon thin films with nickel as seed/cap layer has been attempted in complete absence of any external heat input. When 60 nm Si thin film coated onto 5 nm Ni thin film was treated by a direct current (DC) electric field (up to 3.3 kV/cm up to 5 minutes) after the deposition, amorphous silicon thin films became nanocrystalline (6–10 nm). Silicon nanograins (average diameter 90 nm) grow to larger sizes (average diameter 240 nm) with sharpening of grain size distribution. Huge grain growth (4-fold increase) has been observed when nickel was used as cap layer (5 nm Ni/60 nm Si). XRD data show the signature of nickel silicide formation on the surface in nickel cap layer case. Field treatment has changed the optical absorption edge (shifts left in nm units) and the refractive index of silicon thin film when nickel was used as under layer, and an almost negligible effect on the optical properties has been observed when nickel was used as cap layer.     

Investigation on optical properties of Bi<Subscript>2.85</Subscript>La<Subscript>0.15</Subscript>TiNbO<Subscript>9</Subscript> thin films by prism coupling technique

Layered-perovskite ferroelectric Bi_2.85La_0.15TiNbO₉ (LBTN) optical waveguiding thin films were grown on fused silica substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) revealed that the film is highly (00l) textured. We observed sharp and distinct transverse electric (TE) and transverse magnetic (TM) multimodes and measured the refractive indices of LBTN thin films at 632.8 nm. The ordinary and extraordinary refractive indices were calculated to be n _TE=2.358 and n _TM=2.464, respectively. The film homogeneity and the film-substrate interface were analyzed using an improved version of the inverse Wentzel–Kramer–Brillouin (iWKB) method. The refractive index of the film remains constant at n ₀ within the waveguiding layer. The average transmittance of the film is 70% in the wavelength range of 400–1400 nm and the optical waveguiding properties were evaluated by the optical prism coupling method. Our results showed that the LBTN films are very good electro-optical active material.     

Design and fabrication of non-superparamagnetic high moment magnetic nanoparticles for bioapplications

We present a new type of magnetic nanoparticles for bioapplications. Multilayered nanodisks consisting of two magnetic layers separated by a non-magnetic layer with two capping layers were designed and fabricated. Two key magnetic requirements for bioapplications, a high saturation magnetic moment and a near-zero remanence, were achieved through the magnetostatic interlayer coupling between two magnetic layers. Capping layers provide functionalization sites for biomolecule attachment. A pillar-template-based synthesis method was employed for fabrication. Nanodisks with a diameter of 70 nm and a thickness of 60 nm were produced in large quantity. The magnetic characterization shows that each nanodisk possesses a magnetic moment equivalent to 100 10-nm Co nanoparticles and a near-zero remanent moment.     

Effect of thickness on physical properties of electron beam vacuum evaporated CdZnTe thin films for tandem solar cells

The thickness and physical properties of electron beam vacuum evaporated CdZnTe thin films have been optimized in the present work. The films of thickness 300 nm and 400 nm were deposited on ITO coated glass substrates and subjected to different characterization tools like X-ray diffraction (XRD), UV‐Vis spectrophotometer, source meter and scanning electron microscopy (SEM) to investigate the structural, optical, electrical and surface morphological properties respectively. The XRD results show that the as-deposited CdZnTe thin films have zinc blende cubic structure and polycrystalline in nature with preferred orientation (111). Different structural parameters are also evaluated and discussed. The optical study reveals that the optical transition is found to be direct and energy band gap is decreased for higher thickness. The transmittance is found to increase with thickness and red shift observed which is suitable for CdZnTe films as an absorber layer in tandem solar cells. The current-voltage characteristics of deposited films show linear behavior in both forward and reverse directions as well as the conductivity is increased for higher film thickness. The SEM studies show that the as-deposited CdZnTe thin films are found to be homogeneous, uniform, small circle-shaped grains and free from crystal defects. The experimental results confirm that the film thickness plays an important role to optimize the physical properties of CdZnTe thin films for tandem solar cell applications as an absorber layer.     

Deposition of copper iodide thin films by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) methods

In this paper, we report structural, morphological, electrical studies of copper iodide (CuI) thin films deposited onto glass substrates by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) methods. CuI thin films were characterized for their structural, morphological and wettability studies by means of X-ray diffraction (XRD), FT-Raman spectroscopy, scanning electron microscopy (SEM), optical absorption, and contact angle measurement methods. Thickness of thin films was 1 ± 0.1 μm measured by gravimetric weight difference method. The CuI thin films were nanocrystalline, with average crystal size of ～60 nm. The FT-IR study confirmed the formation of CuI on the substrate surface. SEM images revealed the compact and cube like structure for CuI thin films deposited by CBD and SILAR methods, respectively. Optical absorption study revealed optical energy gaps as 2.3 and 3.0 eV for CBD and SILAR methods, respectively. Wettability study indicated that CuI thin films deposited by SILAR method are more hydrophobic as compared to CBD method.     

Surface ordering near the smectic-A-smectic-C transition in thin, free-standing, liquid-crystal films

Optical reflectivity measurements have been conducted near the smectic-A-smectic-C phase transition in free-standing films with thickness between two and eleven molecular layers. The temperature dependence of the reflectivity in thin film differs significantly from that in thick films. The optical thickness per layer increases in films with two to five layers as a result of cooling, in contrast with thick films. The average layer spacing was found to decrease with decreasing film thickness. Zh. éksp. Teor. Fiz. 111, 949–953 (March 1997) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Quantum dots of Cd0.5Mn0.5Te semimagnetic semiconductor formed by the cold isostatic pressure method

Cd_0.5Mn_0.5Te is a semimagnetic semiconductor, which crystallizes in the zinc-blende structure (ZB) and exhibits a magnetic spin glass like transition at 21 K. Under pressure it shows a first-order phase transition around 2.6 GPa to the NaCl like structure. In this work, the pressure cycled method using a Paris–Edinburgh cell up to 8 GPa has been applied to Cd_0.5Mn_0.5Te samples in order to obtain recovered nanocrystals. The nanoparticles have been characterized by EDX and electron microscopy. The X-ray and electron diffraction results confirmed the existence of nanocrystals in the ZB phase with an average size of 7 nm. Magnetization measurements made in the range of 2–300 K at low field show that the temperature of the magnetic transition decreases when the crystallites’ size is reduced.     

Effects of thin MnAl buffer layer on structural and magnetic properties of MnAl films

Thin Mn(2 nm)/Al(2 nm) bilayers serving as buffer layers have been prepared prior to the deposition of MnAl films. The ferromagnetic τ-phase forms in the buffer layers at an optimum substrate temperature. As a template it induces the growth of following MnAl film. Compared with the case of film without buffer layer, the growth of non-ferromagnetic phase is suppressed and the structural and magnetic properties of MnAl film are improved. Weak dipolar inter-grain coupling is revealed in the MnAl film, and the magnetic reversal process is dominated by magnetic moment rotation.     

Effect of Ta buffer layer and TaO x barrier thickness on the evolution of the structural and magnetic properties of the Fe/TaO x /Co trilayers

Fe/TaO _x /Co trilayers were grown on Si(100)/SiO₂ substrates and on tantalum buffer layers by a high vacuum magnetron sputtering system. The effects of both Ta buffer layer and tantalum-oxide barrier layer thickness on the structural and magnetic properties and the coupling of the ferromagnetic layers have been studied. It was observed that Ta improves the structural properties of the Fe layer resulting in an increased coercive field. For a barrier thickness of 4 nm a weak decoupling starts to appear between the ferromagnetic layers and a clear step formation is observed with increasing thickness. The minor hysteresis loops predict an interlayer coupling for thin barriers. The annealing of trilayers up to 250°C shows an increased coercivity for only the Fe layer. Annealing further at 400°C has the opposite effect of decreasing the coercivity, indicating intermixing at the interfaces of the Fe. The refractive index of the insulator barrier shows that the barrier layer is not totally in the form of tantalum-pentoxide.     

Degradation of the second critical magnetic field in multilayered composites with nanodimensional layers of niobium and Nb-Ti superconducting alloy

Multilayered tapes containing layers of superconducting niobium alloys with 30 and 31 wt % Ti and separated by niobium layers were investigated. The layers were ∼140 to ∼10 nm thick. Effective pinning of superconducting vortex filaments was observed on the interlayer Nb-NbTi interfaces. It was established that second critical magnetic field H _c2 decreased as the layer thickness decreased. With thin layers, its magnitude depended on the orientation of rolling the tape with respect to the external magnetic field. Results are explained by the proximity effect.     

Superlattice CoCrPt/Ru/CoFe structure fabricated by pulsed laser deposition

The synthetic antiferromagnets (SAF) have been used in spin-valve sensor in data storage industry [1]. We report a new hard/Ru/soft sandwich structure (SHBL) fabricated by pulsed lased deposition to replace current single layer structure for information recording application. SHBL consists of two magnetic layers separated by thin nonmagnetic layers, typically with Ru layers of 0.7-1.2 nm, through which antiferromagnetic coupling is induced. Varying the relative thickness of the magnetic layers, the spacer layers, and the type of magnetic materials can alter magnetic properties of CoCrPt/Ru/CoFe superlattice. The coercivity H_c and grain size of magnetic layer is also dependent on the laser fluence. High laser fluence results in both small grain size and high H_c. The observed phenomena are related to high quenching and deposition rates during PLD at high fluence, resulting in more pronounced phase segregation.     

Design of multi-layer mirrors for measuring optical phase modulation at 1300 nm

A theoretical design and experimental realization of multi-layer mirrors for Fabry–Perot interferometry and optical telecommunications is described in this work. The mirrors were designed and fabricated by 13 successive thin layers to achieve very high reflectance at optical wavelengths around 1300 nm. Thin layers are ZnS and MgF₂ presenting high and low refractive index, respectively. Layer thickness λ_o/2 at λ_o=656 nm. Experimental results include characterization of transmittance of mirrors around 1300 nm. Additionally, the mirrors were integrated in a Fabry–Perot interferometer to characterize optical sources emitting at 1300 nm. Finally to show a practical application, optical phase modulation was analyzed, using the fabricated mirrors through a scanning Fabry–Perot interferometer acting as high-resolution optical spectrum analyzer (OSA).     

Transparence and electrical properties of ZnO-based multilayer electrode

Three-layered ZnO/Ag–Ti/ZnO structures were prepared using both the sol-gel technique and DC magnetron sputtering. This study focuses on the electrical and optical properties of the ZnO/Ag–Ti/ZnO multilayers with various thicknesses of the Ag–Ti layer. The ZnO thin film prepared by the sol–gel method was dried at 300°C for 3 minutes, and a fixed thickness of 20 nm was obtained. The thickness of the Ag–Ti thin film was controlled by varying the sputtering time. The Ag–Ti layer substantially reduced the electrical resistivity of the sol–gel-sprayed ZnO thin films. The sheet resistance of the Ag–Ti layer decreased dramatically and then became steady beyond a sputtering time of 60 s. The sputtering time of Ag–Ti thin film deposition was determined to be 60 s, taking into account the optical transmittance. Consequently, the transmittance of the ZnO/Ag–Ti/ZnO multilayer films was 71% at 550 nm and 60% at 350 nm. The sheet resistance was 4.2 Ω/sq.     

Study on solid structure of pentacene thin films using Raman imaging

We present a 532‐nm excited Raman imaging study of pentacene thin films (thickness, 2, 5, 10, 20, 50, 100, and 150 nm) prepared on an SiO₂ surface. The structure of the pentacene films has been investigated by images and histograms of the ratio (R) of intensity of the 1596‐cm⁻¹ band (b_3g) to that of the 1533‐cm⁻¹ band (a_g), which can be used as a marker of solid‐state phases: 1.54‐nm and 1.44‐nm phases. The Raman images showed that island‐like 1.44‐nm phase domains are grown on the 1.54‐nm phase layer from 50 nm, and all the surface of the 1.54‐nm phase layer is covered with the 1.44‐nm phase layer from 100 nm. The structural disorders have been discussed on the basis of the full width at half maximum of a band in the histogram of the R values for each film. Copyright © 2012 John Wiley & Sons, Ltd.     

Direct monitoring of broadband light absorbers

The final performances of manufactured thin film filters usually depend on to the monitoring strategy. Some optical monitoring systems provide transmittance measurements while others measure the reflectance. With our system, we are able to simultaneously measure both transmittance and reflectance over an extended spectral range [400 nm; 1000 nm]. This reflectance channel is necessary for direct monitoring of some kinds of filters like light absorbers. Indeed, in this case, transmittance is cancelled after the first metallic layer deposition. The optical system is also very useful for in situ characterization especially for metallic absorbing materials.     

Metal oxide buffer layer for improving performance of polymer solar cells

We report the application of aluminum doped ZnO (ZnO:Al) layer as a buffer on ITO glass for fabrication of non-inverted polymer solar cells. The ZnO:Al thin film was deposited using DC magnetron sputtering, with the thickness being varied from 23 to 100 nm. The devices showed most discernible improvements in their efficiencies when a thin layer of ZnO:Al film of thickness ∼40 nm was introduced. The observed enhancement in short circuit current density and open circuit voltage is likely attributed to the role of the ZnO:Al film as an optical tuner and an interfacial diffusion barrier. The result suggests that a metal oxide layer inserted between ITO and polymer layers can be a route for improving both efficiency and stability of polymer solar cells.     

Investigation of thermal annealing effects on microstructural and optical properties of HfO2 thin films

In the present paper, we investigate the effect of thermal annealing on optical and microstructural properties of HfO₂ thin films (from 20 to 190 nm) obtained by plasma ion assisted deposition (PIAD). After deposition, the HfO₂ films were annealed in N₂ ambient for 3 h at 300, 350, 450, 500 and 750 °C. Several characterisation techniques including X-ray reflectometry (XRR), X-ray diffraction (XRD), spectroscopic ellipsometry (SE), UV Raman and FTIR were used for the physical characterisation of the as-deposited and annealed HfO₂ thin films. The results indicate that as-deposited PIAD HfO₂ films are mainly amorphous and a transition to a crystalline phase occurs at a temperature higher than 450 °C depending on the layer thickness. The crystalline grains consist of cubic and monoclinic phases already classified in literature but this work provides the first evidence of amorphous-cubic phase transition at a temperature as low as 500 °C. According to SE, XRR and FTIR results, an increase in the interfacial layer thickness can be observed only for high temperature annealing. The SE results show that the amorphous phase of HfO₂ (in 20 nm thick samples) has an optical bandgap of 5.51 eV. Following its transition to a crystalline phase upon annealing at 750 °C, the optical bandgap increases to 5.85 eV.     

Diamond-DLC double layer used in corrosive protective coating

Pinhole-free diamond layers can widely be used in sensor technology as resistive coating against electrolyte solutions. The diamond layers created with chemical vapour deposition technique (CVD) are pinhole-free only above a certain thickness (at least 2.4 μm). Such layer thicknesses reduce the application possibilities. On the other hand, thin (∼200 nm) diamond like carbon (DLC) layers deposited by pulsed laser deposition technique (PLD) are pinhole free but have adhesion or contiguity problems depending on layer thickness. Utilizing the advantages of these two techniques a combined method was developed in order to prepare a pinhole free thin diamond-DLC double layer, for corrosion protection coating. The effects of various deposition parameters (such as background gas, temperature, bias, layer thickness) on the protective properties of the layers have been studied.