Green synthesis of nanocomposites consisting of silver and protease alpha chymotrypsin

The synergy of ultrasonication and the exposure to light radiation was found to be necessary in the formation of nanocomposites of silver and a protease alpha chymotrypsin. The reaction was carried out in aqueous medium and the process took just less than 35 min. Ultrasonication alone formed very negligible number of nanoparticles of <100 nm size whereas light alone produced enough number but the size of the particles was >100 nm.The effects of pH (in the range of 3–5, 9–10), ultrasonication time periods (0–30 min), ultrasonication intensity (33–83 W cm^?2), energy of light radiation (short UV, long UV and Fluorescent light) and time period of exposure (5–60 min) to different light radiations were studied.The formation of nanocomposites under these effects was followed by surface plasmon resonance (SPR) spectra, dynamic light scattering (DLS), transmission electron microscopy (TEM). Ag–chymotrypsin nanocomposites of sizes ranging from 13 to 72 nm were formed using the synergy of ultrasonication and exposure to short UV radiation. Results show that ultrasonication promoted nuclei formation, growth and reduction of polydispersity by Ostwald ripening.     

Investigating gate metal induced reduction of surface donor density in GaN/AlGaN/GaN heterostructure by electroreflectance spectroscopy

The internal field of GaN/AlGaN/GaN heterostructure on Si-substrate was investigated by varying the thickness of an undoped-GaN capping layer using electroreflectance spectroscopy. The four samples investigated are AlGaN/GaN heterostructure without a GaN cap layer (reference sample) and three other samples with GaN/AlGaN/GaN heterostructures in which the different thickness of GaN cap layer (2.7 nm, 7.5 nm, and 12.4 nm) has been considered. The sheet carrier density (n_s) of a two-dimensional electron gas has decreased significantly from 4.66 × 10¹² cm⁻² to 2.15 × 10¹² cm⁻² upon deposition of a GaN capping layer (12.4 nm) over the reference structure. Through the analysis of internal fields in each GaN capping and AlGaN barrier layers, it has been concluded that the undiminished surface donor states (n_s) of a reference structure and the reduced n_s caused by the Au gate metal are approximately 5.66 × 10¹² cm⁻² and 1.08 × 10¹² cm⁻², respectively.     

Photovoltaic effect in BiFeO3/BaTiO3 multilayer structure fabricated by chemical solution deposition technique

Photovoltaic (PV) properties of bismuth ferrite (BFO) and barium titanate (BTO) multilayered ferroelectric BFO/BTO/BFO/BTO thin film structure deposited on Pt/Ti/SiO₂/Si substrates using chemical solution deposition technique are presented. X-ray diffraction analysis confirms pure phase polycrystalline nature of deposited perovskite multilayered structures. Simultaneously both distorted rhombohedral (R3c) and tetragonal phases (P4mm) of the respective BFO and BTO components are also well retained. The ferroelectric sandwiched structures grown on fused quartz substrates exhibit high optical transmittance (~70%) with an energy band gap 2.62 eV. Current–voltage characteristics and PV response of multilayered structures is determined in metal-ferroelectric-metal (MFM) capacitor configuration. Considerably low magnitude of dark current density 1.53×10⁻⁷ A at applied bias of 5 V establish the resistive nature of semi-transparent multilayered structure. Enhanced PV response with 40 nm thin semitransparent Au as top electrode is observed under solid-state violet laser illumination (λ – 405 nm, 160 mW/cm²). The short circuit current density and open circuit voltage are measured to be 12.65 µA/cm² and 1.43 V respectively with a high retentivity. The results obtained are highly encouraging for employing artificial multilayered engineering to improve PV characteristics.     

Laser spectroscopic study of ozone in the 100←000 band for the SWIFT instrument

A complete spectroscopic study of 15 strong ozone lines in the 1132.5–1134.5 cm^?1 spectral range has been undertaken in the framework of the development of the stratospheric wind interferometer for transport studies (SWIFT), led by the Canadian Space Agency. Measurements have been performed with an interferometrically stabilized tunable diode laser spectrometer. Absolute line positions and intensities have been determined with high accuracy (4×10^?5 cm^?1 and 1–2% respectively). Self- and air-broadening coefficients at 296 K have been obtained with an accuracy of 1%. The air-shifting coefficient and its temperature dependence have also been measured for unblended lines together with the temperature dependence of the air-broadening. Line intensities have been calibrated by simultaneously performed UV absorption measurements at 253.7 nm. Our IR/UV comparison supports a previously reported inconsistency between recommended IR intensities (HITRAN08) and UV absorption cross-sections and indicates that current IR intensities are too small by ～3%.     

Two photon absorption characteristics of bulk GaTe crystal

We have investigated the structural and optical properties of bulk GaTe crystal grown by vertical Bridgman method. Two photon absorption (TPA) properties of GaTe crystal have been investigated by the open aperture Z-scan technique under 1064 nm wavelength with 4 ns or 65 ps pulse durations. The TPA coefficients are greater in ns regime than that of ps regime. Upon increasing intensity of incident light from 5.02×10⁷ W/cm² to 1.07×10⁸ W/cm², the TPA coefficients increased from 3.47×10^?6 cm/W to 8.53×10^?6 cm/W for nanosecond excitation. Similarly, when intensity of incident light was increased from 6.81×10⁸ W/cm² to 9.94×10⁸ W/cm² the TPA coefficients increased from 3.53×10^?7 cm/W to 6.83×10^?7 cm/W for picosecond excitation. Measured TPA coefficient of GaTe crystal is larger than that of GaSe and GaS layered crystals.     

Competing nucleation mechanisms and growth of InAsSbP quantum dots and nano-pits on the InAs(100) surface

InAsSbP quantum dots (QDs) and nano-pits (NPs) are grown on a InAs(100) surface by liquid phase epitaxy (LPE). Their morphology, dimensions and distribution density are investigated by high resolution scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and total energy calculations. QDs average density ranges from 5 to 7 × 10⁹ cm^?2, with heights and widths having a Gaussian distribution with sizes from 5 nm to 15 nm and 10 nm to 40 nm respectively. The average pits density is (2–6) × 10¹⁰ cm^?2 with dimensions ranging from 5–30 nm in width and depth. We also find a shift in the absorption edge towards the longer wavelengths together with broadening towards shorter wavelengths indicating that these QDs and lateral overgrown nano-pits are grown at the n-InAs/p-InAsSbP heterojunction interface. Together with total energy calculations, the results indicate that lattice mismatch ratio plays a central role in the growth of these strain-induced nano-objects.     

Searching of new,cheap, air- and thermally stable hole transporting materials for perovskite solar cells

In this work, two thermal- and air-stable, hole transporting materials (HTM) in perovskite solar cells are analyzed. Those obtained and investigated materials were two polyazomethines: the first one with three thiophene rings and 3,3′-dimethoxybenzidine moieties (S9) and the second one with three thiophene rings and fluorene moieties (S7). Furthermore, presented polyazomethines were characterized by Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy, atomic force microscopy (AFM) and thermogravimetric analysis (TGA) experiments. Both polyazomethines (S7 and S9) possessed good thermal stability with a 5% weight loss at 406 and 377 °C, respectively. The conductivity of S7 was two orders of magnitude higher than for S9 polymer (2.7 × 10^?8 S/cm, and 2.6 × 10^?10 S/cm, respectively). Moreover, polyazomethine S9 exhibited 31 nm bathochromic shift of the absorption band maximum compared to S7.Obtained perovskite was investigated by UV–vis and XRD. Electrical parameters of perovskite solar cells (PSC) were investigated at Standard Test Conditions (STC). It was found that both polyazomethines protect perovskite which is confirmed by ageing test where V_oc did not decrease significantly for solar cells with HTM in contrast to solar cell without hole conductor, where V_oc decrease was substantial. The best photoconversion efficiency (PCE = 6.9%), among two investigated in this work polyazomethines, was obtained for device with the following architectures FTO/TiO₂/TiO₂ + perovskite/S7/Au. Stability test proved the procreative effects of polyazomethines on perovskite absorber.     

Low voltage red phosphorescent organic light-emitting devices with triphenylphosphine oxide and 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl electron transport layers

We have developed red phosphorescent organic light-emitting devices operating at low voltages by using triphenylphosphine oxide (Ph₃PO) and 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) electron transport layers. 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) and tris-(1-phenylisoquinolinolato-C²,N) iridium(III) [Ir(piq)₃] were used as host and guest materials, respectively. Small voltage drops across the electron transport layers and direct injection of holes from 4,4′,4″-tris[N-(2-naphthyl)-N-phenyl-amino]-triphenylamine (2-TNATA) hole transport layer into the Ir(piq)₃ guests are responsible for the high current density at low voltage, resulting in a high luminance of 1000 cd/m² at low voltages of 2.8–3.0 V in devices with a structure of ITO/2-TNATA/CBP:Ir(piq)₃/DPVBi/Ph₃PO/LiF/Al.     

Nanostructures on GaAs surfaces due to 60 keV Ar+-ion beam sputtering

The effect of 60 keV Ar⁺-ion beam sputtering on the surface topography of p-type GaAs(1 0 0) was investigated by varying angle of incidence of the ion (0–60°) with respect to substrate normal and the ion fluence (2 × 10¹⁷–3 × 10¹⁸ ions/cm²) at an ion flux of 3.75 × 10¹³ ions/cm²-s. For normal incidence and at a fluence of 2 × 10¹⁷ ions/cm², holes and islands are observed with the former having an average size and density of 31 nm and 4.9 × 10⁹ holes/cm², respectively. For 30° and 45° off-normal incidence, in general, a smooth surface appears which is unaffected by increase of fluence. At 60° off-normal incidence dots are observed while for the highest fluence of 3 × 10¹⁸ ions/cm² early stage of ripple formation along with dots is observed with amplitude of 4 nm. The applicability and limitations of the existing theories of ion induced pattern formation to account for the observed surface topographies are discussed.     

Utilization of surface plasmon resonance of Au/Pt nanoparticles for highly photosensitive ZnO nanorods network based plasmon field effect transistor

Hydrothermally processed highly photosensitive ZnO nanorods based plasmon field effect transistors (PFETs) have been demonstrated utilizing the surface plasmon resonance coupling of Au and Pt nanoparticles at Au/Pt and ZnO interface. A significantly enhanced photocurrent was observed due to the plasmonic effect of the metal nanoparticles (NPs). The Pt coated PFETs showed I_on/I_off ratio more than 3 × 10⁴ under the dark condition, with field-effect mobility of 26 cm² V⁻¹ s⁻¹ and threshold voltage of −2.7 V. Moreover, under the illumination of UV light (λ = 350 nm) the PFET revealed photocurrent gain of 10⁵ under off-state (−5 V) of operation. Additionally, the electrical performance of PFETs was investigated in detail on the basis of charge transfer at metal/ZnO interface. The ZnO nanorods growth temperature was preserved at 110 °C which allowed a low temperature, economical and simple method to develop highly photosensitive ZnO nanorods network based PFETs for large scale production.     

Charged surface states scattering in AlGaN/GaN heterostructures

The electron mobility limited by charged surface states scattering was calculated accurately based on a self-consistent Schrödinger and Poisson equations solver. For a AlGaN thickness less than 5 nm, this new scattering mechanism is the dominated scattering for electron mobility. Moreover, there is a “high electron mobility window” for a certain AlGaN thickness range from 4 to 7 nm, where the electron mobility can be as high as 3000 cm²/Vs at a low temperature, which is consistent with reported experimental data [1] (Cao and Jena, 2007).     

Erbium-doped lead silicate glass for near-infrared emission and temperature-dependent up-conversion applications

Erbium-doped lead silicate glass has been investigated for near-infrared emission and up-conversion applications. Near-infrared emission due to ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ is relatively broad (70.5 nm) and long-lived (3.7 ms). Also, up-conversion luminescence spectra of Er³⁺ ions in lead silicate glass have been examined as a function of temperature. The relative intensities of luminescence bands corresponding to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ were determined with temperature. The fluorescence intensity ratio and temperature sensitivity were calculated. The maximum sensitivity for Er³⁺ doped lead silicate glass is close to 26.4 × 10^?4 K^?1 at T = 590 K.     

Effect of temperature on the current–voltage characteristics of GaAs/AlGaAs quantum cascade photodetectors

Transport of electrons within a quantum cascade photodetector structure takes place with the help of the scattering of electrons by phonons. By calculating scattering rates of the electrons mediated by longitudinal optical phonons (the dominant scattering mechanism), current–voltage characteristic of a quantum cascade photodetector is calculated. The results indicate that with the increase of bias voltage dark current increases rapidly, then the increase becomes slow at higher voltages, whilst photocurrent remains approximately constant with only slight variations in its magnitude. With the increase of temperature from 80 K to 160 K dark current increases by about two orders of magnitude while photocurrent varies slightly, so that at the illuminating power of 1 mW/m² photocurrent density increases in mean from 1.10×10⁻⁹ A/cm² at 80 K to 1.14×10⁻⁹ A/cm² at 160 K and then decreases to 1.03×10⁻⁹ A/cm² at 240 K. Thus the responsivity of the detector varies only slightly with temperature. However owing to the decrease in the resistivity of the photodetector with the increase of temperature, Johnson noise limited detectivity decreases considerably.     

Laser-ablation-induced refractive index fields studied using pulsed digital holographic interferometry

Pulsed digital holographic interferometry has been used to investigate the plume and the shock wave generated in the ablation process of a Q-switched Nd-YAG (λ=1064 nm and pulse duration=12 ns) laser pulse on a polycrystalline boron nitride (PCBN) target under atmospheric air pressure. A special setup based on two synchronised wavelengths from the same laser for simultaneous processing and measurement has been used. Digital holograms were recorded for different time delays using collimated laser light (λ=532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave and the plume generated by the process. Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. The shock wave density has been calculated using the point explosion model and the shock wave condition equation and its behaviour with time at different power densities ranging from 1.4 to 9.1 GW/cm² is presented. Shock front densities have been calculated from the reconstructed refractive index fields using the Gladstone–Dale equation. A comparison of the shock front density calculated from the reconstructed data and that calculated using the point explosion model at different time delays has been done. The comparison shows quite good agreement between the model and the experimental data. Finally the reconstructed refractive index field has been used to estimate the electron number density distribution within the laser-induced plasma. The electron number density behaviour with distance from the target at different power densities and its behaviour with time are shown. The electron number densities are found to be in the order of 10¹⁸ cm^?3 and decay at a rate of 3×10¹⁵ electrons/cm³ ns.     

Diffraction patterns and nonlinear optical properties of gold nanoparticles

Stable gold nanoparticles have been prepared by using soluble starch as both the reducing and stabilizing agents; this reaction was carried out at 40 °C for 5 h. The obtained gold nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM) and z-scan technique. The size of these nanoparticles was found to be in the range of 12–22 nm as analyzed using transmission electron micrographs. The optical properties of gold nanoparticles have been measured showing the surface plasmon resonance. The second-order nonlinear optical (NLO) properties were investigated by using a continuous-wave (CW) He–Ne laser beam with a wavelength of 632.8 nm at three different incident intensities by means of single beam techniques. The nonlinear refractive indices of gold nanoparticles were obtained from close aperture z-scan in order of 10^?7 cm²/W. Then, they were compared with diffraction patterns observed in far-field. The nonlinear absorption of these nanoparticles was obtained from open aperture z-scan technique. The values of nonlinear absorption coefficient are obtained in order of 10^?1 cm/W.     

Terahertz emission dependence on the intensity ratio of 400–800 nm in generating terahertz waves from two-color laser-induced gas plasma

A transient photocurrent model is used to explain terahertz emission from gas plasma irradiated by a laser pulse and the second harmonic. By introducing the second harmonic, 400 nm, the corresponding terahertz emission is greatly enhanced. The exact dependence of terahertz emission on the intensity ratio of 400–800 nm is studied for the case with total intensity of 5.00 × 10¹⁴ W/cm². Results show the emission reaches the maximum at about the case for energy distribution of I_ω = 4.00 × 10¹⁴ W/cm², I_2ω = 1.00 × 10¹⁴ W/cm².     

Electrical and optical characteristics of a Si-doped (Al)GaInAs digital alloy/AlInAs-distributed Bragg mirrors on InP

We report electrical and optical characteristics of a Si-doped (Al)GaInAs digital alloy/AlInAs Bragg mirror lattice matched to InP grown by molecular beam epitaxy. A 98.2% reflectivity with a 107 nm stop band width centred at 1.54 μ m is obtained. An average voltage drop of 16 mV per period at a current density of 1 KA cm ^− 2is observed for a mean electron concentration of about 5.5  ×  10¹⁸cm ^− 3. The influence of structural and intrinsic properties of the heterostructure on the electrical resistivity and optical reflectivity is analysed.     

Ohmic contact and space-charge-limited current in molybdenum oxide modified devices

The effect of indium-tin oxide (ITO) surface treatment on hole injection of devices with molybdenum oxide (MoO₃) as a buffer layer on ITO was studied. The Ohmic contact is formed at the metal/organic interface due to high work function of MoO₃. Hence, the current is due to space charge limited when ITO is positively biased. The hole mobility of N, N′-bis-(1-napthyl)-N, N′-diphenyl-1, 1′biphenyl-4, 4′-diamine (NPB) at various thicknesses (100–400 nm) has been estimated by using space-charge-limited current measurements. The hole mobility of NPB, 1.09×10⁻⁵ cm²/V s at 100 nm is smaller than the value of 1.52×10⁻⁴ cm²/V s at 400 nm at 0.8 MV/cm, which is caused by the interfacial trap states restricted by the surface interaction. The mobility is hardly changed with NPB thickness for the effect of interfacial trap states on mobility which can be negligible when the thickness is more than 300 nm.     

Part 2: Ultra-short pulse laser patterning of very thin indium tin oxide on glass substrates

We investigate selective patterning of ultra-thin 20 nm Indium Tin Oxide (ITO) thin films on glass substrates, using 343, 515, and 1030 nm femtosecond (fs), and 1030 nm picoseconds (ps) laser pulses. An ablative removal mechanism is observed for all wavelengths at both femtosecond and picoseconds time-scales. The absorbed threshold fluence values were determined to be 12.5 mJ cm⁻² at 343 nm, 9.68 mJ cm⁻² at 515 nm, and 7.50 mJ cm⁻² at 1030 nm for femtosecond and 9.14 mJ cm⁻² at 1030 nm for picosecond laser exposure. Surface analysis of ablated craters using atomic force microscopy confirms that the selective removal of the film from the glass substrate is dependent on the applied fluence. Film removal is shown to be primarily through ultrafast lattice deformation generated by an electron blast force. The laser absorption and heating process was simulated using a two temperature model (TTM). The predicted surface temperatures confirm that film removal below 1 J cm⁻² to be predominately by a non-thermal mechanism.     

The study on the nonlinear optical response of Sudan I

The nonlinear optical properties of Sudan I were investigated by a single beam Z-scan technique. The Sudan I ethanol solution exhibited large nonlinear refractive indices under both CW and pulse laser excitations. The nonlinear refractive indices of Sudan I were in the order of ?10^?8 cm²/W under CW 633 nm excitation and ?10^?6 cm²/W under CW 488 nm excitation, respectively. Under the excitation of a pulse 532 nm laser, the nonlinear refractive index n₂ was calculated to be 1.19 × 10^?14 cm²/W. It was discussed that the mechanism accounting for the process of nonlinear refraction was attributed to the laser heating for the CW laser excitation and the electronic effect for the pulse excitation. Moreover, the second hyperpolarizability of Sudan I was also estimated in this paper.