Optimisation of processing conditions during CVD growth of 2D WS2 films from a chloride precursor

Monolayer tungsten disulphide (WS2) is a direct band gap semiconductor which holds promise for a wide range of optoelectronic applications. The large-area growth of WS2 has previously been successfully achieved using a W(CO)6 precursor, however, this is flammable and a potent source of carbon monoxide (CO) upon decomposition. To address this issue, we have developed a process for the wafer-scale growth of monolayer WS2 from a tungsten hexachloride (WCl6) precursor in a commercial cold-wall CVD reactor. In comparison to W(CO)6, WCl6 is less toxic and less reactive and so lends itself better to the large-scale CVD growth of 2D layers. We demonstrate that a post-growth H2S anneal can lead to a dramatic improvement in the optical quality of our films as confirmed by photoluminescence (PL) and Raman measurements. Optimised films exhibit PL exciton emission peaks with full width at half maximum of 51 ± 2 meV, comparable to other state-of-the-art methods. We demonstrate that our WS2 films can be readily transferred from the sapphire growth substrate to a Si/SiO2 target substrate with no detectable degradation in quality using a polystyrene support layer. Our approach represents a promising step towards the industrial-scale fabrication of p-n junctions, photodetectors and transistors based on monolayer WS2.

"Non-stoichiometry and point native defects in non-oxide non-linear optical large single crystals: advantages and problems"

Advances and limitations in the field of growing large, a high optical quality single crystals of AgGaS2 (AGS), AgGaGeS4 (AGGS), ZnGeP2 (ZGP), LiInS2 (LIS), LiGaS2 (LGS), LiInSe2 (LISe), LiGaSe2 (LGSe)...

Dielectric spectroscopy of aluminum oxide (γ-Al2O3)

Aluminum oxide (Al2O3) are continuously demonstrating the functional characteristics in devices. The physiochemical properties of hydrothermally as-grown Aluminum oxide (Al2O3) have been investigated in this research article. The as-prepared material was confirmed as γ- phase formation of Al2O3. The average crystallite size was found ∼ 78 nm, whereas the particles were found in nano scale too. Moreover, the absence of impurity in EDS analysis, and the presence of the bending vibrations of Al-O-Al and Al-O band in FTIR characterization further confirmed the absence of impurity in the material. Evaluated dielectric properties such as a relatively high dielectric constant, and low dielectric loss indicated the good optical quality of γ- Al2O3. Impedance and modulus spectroscopic studies showed the non-Debye type relaxation in γ- Al2O3 with an average relaxation time of 5.8 μs. Overall, the dielectric spectroscopy analysis of γ- Al2O3 indicates the promising applications of γ- Al2O3 in devices as dielectrics.

Physiological Mechanisms Regulating Lens Transport

The transparency and refractive properties of the lens are maintained by the cellular physiology provided by an internal microcirculation system that utilizes spatial differences in ion channels, transporters and gap junctions to establish standing electrochemical and hydrostatic pressure gradients that drive the transport of ions, water and nutrients through this avascular tissue. Aging has negative effects on lens transport, degrading ion and water homeostasis, and producing changes in lens water content. This alters the properties of the lens, causing changes in optical quality and accommodative amplitude that initially result in presbyopia in middle age and ultimately manifest as cataract in the elderly. Recent advances have highlighted that the lens hydrostatic pressure gradient responds to tension transmitted to the lens through the Zonules of Zinn through a mechanism utilizing mechanosensitive channels, multiple sodium transporters respond to changes in hydrostatic pressure to restore equilibrium, and that connexin hemichannels and diverse intracellular signaling cascades play a critical role in these responses. The mechanistic insight gained from these studies has advanced our understanding of lens transport and how it responds and adapts to different inputs both from within the lens, and from surrounding ocular structures.

Comparative evaluation of a new frugal binocular indirect ophthalmoscope

Objectives We compare the optical quality and design characteristic a new low cost solar powered binocular indirect ophthalmoscope (BIO), Holo, to Keeler BIO. Methods Twenty-four participants each examined 10 simulation eyes using both the Holo and the Keeler BIO with a 30-diopter condensing lens. Number of Lea symbols printed on the retina of simulation eyes seen and time taken to identify them was recorded. Stereoacuity of 12 participants was tested while using the BIOs. Using 7-point Likert scale, participants gave feedback on design characteristic of both BIOs. Results There was no statistical difference in number of Lea symbols correctly identified (15.63/20 for Holo vs. 15/20 for Keeler BIO, p = 0.366, paired t test) or time taken to correctly identify each symbol (Holo 0.39 s faster; 95% confidence interval −2.24 to 3.03 s, p = 0.763) using each device. 12 out of 12 participants achieved stereoacuity of 60 arcsec using the Holo while with the Keeler BIO 11 achieved 60 arcsec and one 90 arcsec. There was no statistically significant difference in the scores for clarity of view, quality of illumination, field of view, binocularity, eye strain and robustness between the two devices. The Holo, scored higher for ease of use (6.5 vs. 6, p = 0.00488, Wilcoxon signed-rank test), comfort of wear (6 vs. 5, p = 0.000337) and portability (7 vs. 6, p = 0.000148). Conclusion The Holo has the potential to be a clinically useful yet affordable diagnostic tool suitable for the first time of equipping eye care workers in low resource settings with a BIO at volume.

ANALYSIS OF METHODS FOR SYNTHESIS OF A BORON-DOPED LITHIUM NIOBATE CHARGE USED FOR GROWING SINGLE CRYSTALS

Проведен анализ известных методов синтеза шихты ниобата лития, легированной бором, которая используется при выращивании монокристаллов высокого оптического качества методом Чохральского. Установлено, что способ гомогенного легирования (шихта получается из прекурсора NbO :B и LiCO) по сравнению с твердофазным (шихта получается из смеси LiCO: NbO : HBO ) позволяет выращивать кристаллы LiNbO: B с более однородным распределением в них примеси бора, а также в объеме расплава, при этом упрощаются технологические режимы, устанавливаемые при росте кристаллов. В работе впервые рассмотрен жидкофазный метод синтеза шихты, исключающий стадию прокалки гомогенизированной смеси пентаоксида ниобия и карбоната лития. Результаты имеют важное значение при выборе технологии выращивания легированных бором монокристаллов ниобата лития для конкретных областей техники. Known methods of a boron doped lithium niobate charge synthesis were analyzed. Such a charge is applied for the growth by Czochralski of single crystals with high optical quality. Homogeneous doping (the charge is obtained from precursor NbO:B and LiCO) was compared with solid phase doping (the charge is obtained from the mixture LiCO: NbO: HBO). Homogeneous doping was determined to help produce LiNbO: B crystals with a more uniform distribution of a boron dopant, boron distributes more uniform in the melt volume; technological regimes established during crystal growth become easier. For the first time the paper considers liquid-phase charge synthesis method; the method excludes the stage of annealing of homogenized mixture of niobium pentoxide and lithium carbonate. Results are crucial for the choice of technology at growing of boron doped lithium niobate crystals for exact areas of technics.

Towards Interband Cascade lasers on InP Substrate

In this study, we propose designs of an interband cascade laser (ICL) active region able to emit in the application-relevant mid infrared (MIR) spectral range and to be grown on an InP substrate. This is a long-sought solution as it promises a combination of ICL advantages with mature and cost-effective epitaxial technology of fabricating materials and devices with high structural and optical quality, when compared to standard approaches of growing ICLs on GaSb or InAs substrates. Therefore, we theoretically investigate a family of type II, “W”-shaped quantum wells made of InGaAs/InAs/GaAsSb with different barriers, for a range of compositions assuring the strain levels acceptable from the growth point of view. The calculated band structure within the 8-band k·p approximation showed that the inclusion of a thin InAs layer into such a type II system brings a useful additional tuning knob to tailor the electronic confined states, optical transitions’ energy and their intensity. Eventually, it allows achieving the emission wavelengths from below 3 to at least 4.6 μm, while still keeping reasonably high gain when compared to the state-of-the-art ICLs. We demonstrate a good tunability of both the emission wavelength and the optical transitions’ oscillator strength, which are competitive with other approaches in the MIR. This is an original solution which has not been demonstrated so far experimentally. Such InP-based interband cascade lasers are of crucial application importance, particularly for the optical gas sensing.

Effect of Substrate and Thickness on the Photoconductivity of Nanoparticle Titanium Dioxide Thin Film Vacuum Ultraviolet Photoconductive Detector

Vacuum ultraviolet radiation (VUV, from 100 nm to 200 nm wavelength) is indispensable in many applications, but its detection is still challenging. We report the development of a VUV photoconductive detector, based on titanium dioxide (TiO2) nanoparticle thin films. The effect of crystallinity, optical quality, and crystallite size due to film thickness (80 nm, 500 nm, 1000 nm) and type of substrate (silicon Si, quartz SiO2, soda lime glass SLG) was investigated to explore ways of enhancing the photoconductivity of the detector. The TiO2 film deposited on SiO2 substrate with a film thickness of 80 nm exhibited the best photoconductivity, with a photocurrent of 5.35 milli-Amperes and a photosensitivity of 99.99% for a bias voltage of 70 V. The wavelength response of the detector can be adjusted by changing the thickness of the film as the cut-off shifts to a longer wavelength, as the film becomes thicker. The response time of the TiO2 detector is about 5.8 μs and is comparable to the 5.4 μs response time of a diamond UV sensor. The development of the TiO2 nanoparticle thin film detector is expected to contribute to the enhancement of the use of VUV radiation in an increasing number of important technological and scientific applications.

Chemical Route Manufactured ZnO Nanoparticles And Their Biological Accumulation

ZnO nanocrystalline powder was successfully synthesized via co-precipitation method coupled with high annealing treatment. X-ray diffraction analysis revealed that the NPs have a pure hexagonal wurtzite structure with a mean crystallite size of approximately 59 nm. FESEM observations along with EDS analysis indicated the formation of fine particles in the nanoscale regime, with hexagonal shape and high purity. Both Raman and photoluminescence characterizations confirmed the high crystalline and the optical quality of the synthesized ZnO NPs. The assessment of the impact of ZnO-based nanoparticles and their effects on body and bioaccumulative bioindicators of pollution, Helix aspersa snails was performed in order to preserve the safe development of nanotechnology.