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Climate change and other environmental hazards pose severe threat to agricultural production across the world. The developing countries like India are more vulnerable to climate change. This study aims to examine the impact of climate change on major crop yields in India using time series data over a period of 1980-2017. The estimated empirical outcomes show that climatic variables have substantial effect on major crop yields in general. An increase in rainfall has an adverse effect on rice and pulses. However, it has a positive relationship with wheat, cotton, groundnut and sugarcane crops during the study period. Further, except groundnut, the average maximum temperature has a positive influence on all crops. The average minimum temperature has an adverse impact on wheat and cotton crops but it has a positive association with rice, pulses, groundnut and sugarcane. Conclusively, this found that crop yields are impacted differently with different climatic variables in India. This study recommends taking adaptation activities to cope with the adverse impacts of climate change.

Spatially modulated biaxial tensile strain in a few-layers M0S2 on pre-patterned Si substrate is demonstrated. Using depth-controlled nanoindentation, localized strain on Si is achieved. Results are verified by observing shifts in the MoS2’s bandgap and phonon modes.

The efficient monolithic III-V integration on silicon (Si) substrates can leverage the excellent optoelectronic properties of III-V semiconductors and the Si microfabrication technology for electronic, optoelectronics, integrated photonics devices. However, the origin of the interfacial and material defects during III-V monolithic integration on Si poses the challenge to achieve efficient optical emitters, detectors. In this study, we investigated different surface treatment schemes before rapid melt growth (RMG) of GaSb on Si substrate to attain defect control. The deposition of an Sb layer (10 nm) on GaSb precursors surfaces resulted in achieving better structural and optical properties of GaSb post RMG. We achieved a reduction of 2.48 atomic % of unintentional incorporation of Si into the GaSb via Sb treatment compared to that of untreated GaSb analysed using transmission electron microscopy and energy-dispersive X-ray spectroscopy. Improved surface morphology with reduced root mean square roughness of 3.7 nm is obtained with Sb layer treatment compared to 5.6 nm for untreated GaSb precursor measured by atomic force microscopy. We obtained improved optical properties and low defect density with an in-situ Sb treatment scheme on GaSb precursor surface by µ-Photoluminescence and µ-Raman spectroscopy analysis.

We study the band discontinuity at the GaN/single-layer (SL) WSe2 heterointerface. The GaN thin layer is epitaxially grown by molecular beam epitaxy on chemically vapor deposited SL-WSe2/c-sapphire. We confirm that the WSe2 was formed as an SL from structural and optical analyses using atomic force microscopy, scanning transmission electron microscopy, micro-Raman, absorbance, and microphotoluminescence spectra. The determination of band offset parameters at the GaN/SL-WSe2 heterojunction is obtained by high-resolution X-ray photoelectron spectroscopy, electron affinities, and the electronic bandgap values of SL-WSe2 and GaN. The valence band and conduction band offset values are determined to be 2.25 ± 0.15 and 0.80 ± 0.15 eV, respectively, with type II band alignment. The band alignment parameters determined here provide a route toward the integration of group III nitride semiconducting materials with transition metal dichalcogenides (TMDs) for designing and modeling of their heterojunction-based electr...

At present, the demand of energy resources is increasing while their stocks are decreasing with high rate. Bio-diesel is an energy source which is renewable and would help in controlling the demand and supply of fuel but also in the reduction of pollution. Bio-diesel is simple to use and easy to transport. Different ratios of bio-diesel and diesel were mixed to prepare blends which showed viscosity, heat content, density, efficiency closer to diesel. The performance of various blends was tested on four stroke single cylinder compression ignition engine. Testing showed that partial substitution of diesel by bio-diesel can result in increase performance of engine. The results conclude that bio-diesel would be a better alternative to diesel in coming days.In this investigation we were planed to investigate fuel consumption, power in different loading condition, break specific fuel consumption, break mean effective pressure from bio-diesel (Blend of 5% Growdiesel + HSD, 2% Growdiesel + HSD,1% Growdiesel +HSD, .5% Growdiesel +HSD) with HSD. Planed to take 10 hr trials in cache combination and comparison of data and valuable findings related cost. The results that the performance of high percentage blends and pure bio-diesel doesn’t fit the engine due to their viscosity and low thermal efficiency.

Metal-semiconductor-metal (MSM) photodetectors made of gallium antimonide (GaSb) on silicon waveguides by the rapid melt growth method are investigated. By controlling the thermodynamics of crystal regrowth and optimizing the process condition, single-crystal GaSb stripes are monolithically integrated on the silicon substrate. The MSM GaSb waveguide photodetector shows a responsivity of 0.57 A/W at 1550 nm.

We studied using rapid melt growth (RMG) method to make GaSb microdisks on Si substrate. By optimizing the process condition, we observe a strong photoluminescence.

Combined experimental and theoretical efforts are focused to study hexagonal In x Ga 1−x N/GaN[0001] multiple-quantum wells (MQWs). Plasma-assisted molecular-beam epitaxy (PA-MBE) is used to grow high-quality MQWs with multiplicity of 1, 3 and 5. Characterizations methods based on scanning tunneling electron microscopy (STEM) and photoluminescence (PL) indicated that each period is composed of 10 nm GaN barrier and 2.5 nm In x Ga 1−x N well with x ≤ 0.12. Usually, these MQWs have radiations with the blue region. However, in power (from 0.008 mW to 8 mW) dependent micro-photoluminescence (PL), measured at room temperature, blue shifts of about 11.11 nm, 11.94 nm and 14.94 nm were observed corresponding to the single-quantum well (1-QW), 3-MQW, and 5-MQW, respectively. While in literature such shift is speculated to be attributed to so-called “quantum-confined stark effect” (QCSE) in localized luminescent centers with the InGaN wells caused by inhomogeneity of alloy distribution, we extended a rigorous theoretical investigation based on 3D tight-binding method using simple sp3-basis set. The theoretical results show that the wells are isolated and the experimentally observed blue-shifts should be caused by alloying and interface fluctuations. Specifically, the larger blue-shift in 5-MQW sample should be attributed to higher bi-axial strain and interface-specific effects that cause further increase of the hole well's (h-Well) depth, V 0 J, and increase in number of localized hole states within the h-Well. Furthermore, this study reveals the role of bi-axial strain, well composition, and interface specific effects on the peculiar behaviors of valence-band offset (VBO) in In x Ga 1−x N/GaN MQWs.

We study the band discontinuity at the GaN/single-layer (SL) WSe

The lack of optical constants information for hybrid perovskite of CHsub3/subNHsub3/subPbBrsub3/subin thin films form can delay the progress of efficient LED or laser demonstration. Here, we report on the optical constants (complex refractive index and dielectric function) of CHsub3/subNHsub3/subPbBrsub3/subperovskite thin films using spectroscopic ellipsometry. Due to the existence of voids, the refractive index of the thin films is around 8% less than the single crystals counterpart. The energy bandgap is around 2.309 eV as obtained from photoluminescence and spectrophotometry spectra, and calculated from the SE analysis. The precise measurement of optical constants will be useful in designing optical devices using CHsub3/subNHsub3/subPbBrsub3/subthin films.

We study the impact of quantum-confined stark effect (QCSE) on bias dependent micro-photoluminescence emission of the quantum disk (Q-disk) based nanowires light emitting diodes (NWs-LED) exhibiting the amber colored emission. The NWs are found to be nitrogen polar (N-polar) verified using KOH wet chemical etching and valence band spectrum analysis of high-resolution X-ray photoelectron spectroscopy. The crystal structure and quality of the NWs were investigated by high-angle annular dark field - scanning transmission electron microscopy. The LEDs were fabricated to acquire the bias dependent micro-photoluminescence spectra. We observe a redshift and a blueshift of the μPL peak in the forward and reverse bias conditions, respectively, with reference to zero bias, which is in contrast to the metal-polar InGaN well-based LEDs in the literature. Such opposite shifts of μPL peak emission observed for N-polar NWs-LEDs, in our study, are due to the change in the direction of the internal piezoelectric field. The quenching of PL intensity, under the reverse bias conditions, is ascribed to the reduction of electron-hole overlap. Furthermore, the blueshift of μPL emission with increasing excitation power reveals the suppression of QCSE resulting from the photo-generated carriers. Thereby, our study confirms the presence of QCSE for NWs-LEDs from both bias and power dependent μPL measurements. Thus, this study serves to understand the QCSE in N-polar InGaN Q-disk NWs-LEDs and other related wide-bandgap nitride nanowires, in general.

We report an unusual thermal quenching of the micro-photoluminescence (µ-PL) intensity for a sandwiched single-layer (SL) MoS2. For this study, MoS2 layers were chemical vapor deposited on molecular beam epitaxial grown In0.15Al0.85N lattice matched templates. Later, to accomplish air-stable sandwiched SL-MoS2, a thin In0.15Al0.85N cap layer was deposited on the MoS2/In0.15Al0.85N heterostructure. We confirm that the sandwiched MoS2 is a single layer from optical and structural analyses using µ-Raman spectroscopy and scanning transmission electron microscopy, respectively. By using high-resolution X-ray photoelectron spectroscopy, no structural phase transition of MoS2 is noticed. The recombination processes of bound and free excitons were analyzed by the power-dependent µ-PL studies at 77 K and room temperature (RT). The temperature-dependent micro photoluminescence (TDPL) measurements were carried out in the temperature range of 77 – 400 K. As temperature increases, a significant red-shift is observed for the free-exciton PL peak, revealing the delocalization of carriers. Further, we observe unconventional negative thermal quenching behavior, the enhancement of the µ-PL intensity with increasing temperatures up to 300K, which is explained by carrier hopping transitions that take place between shallow localized states to the band-edges. Thus, this study renders a fundamental insight into understanding the anomalous thermal quenching of µ-PL intensity of sandwiched SL-MoS2.

The valence and conduction band offsets (VBO and CBO) at the semiconductor heterojunction are crucial parameters to design the active region of contemporary electronic and optoelectronic devices. In this report, to study the band alignment parameters at the In0.15Al0.85N/MoS2 lattice matched heterointerface, large area MoS2 single layers are chemical vapor deposited on molecular beam epitaxial grown In0.15Al0.85N films and vice versa. We grew InAlN having an in-plane lattice parameter closely matching with that of MoS2. We confirm that the grown MoS2 is a single layer from optical and structural analyses using micro-Raman spectroscopy and scanning transmission electron microscopy. The band offset parameters VBO and CBO at the In0.15Al0.85N/MoS2 heterojunction are determined to be 2.08 ± 0.15 and 0.60 ± 0.15 eV, respectively, with type-I band alignment using high-resolution x-ray photoelectron spectroscopy in conjunction with ultraviolet photoelectron spectroscopy. Furthermore, we design a MoS2 quantum well structure by growing an In0.15Al0.85N layer on MoS2/In0.15Al0.85N type-I heterostructure. By reducing the nitrogen plasma power and flow rate for the overgrown In0.15Al0.85N layers, we achieve unaltered structural properties and a reasonable preservation of photoluminescence intensity with a peak width of 70 meV for MoS2 quantum well (QW). The investigation provides a pathway towards realizing large area, air-stable, lattice matched, and eventual high efficiency In0.15Al0.85N/MoS2/In0.15Al0.85N QW-based light emitting devices.

Recent interest in two-dimensional materials has resulted in ultra-thin devices based on the transfer of transition metal dichalcogenides (TMDs) onto other TMDs or III-nitride materials. In this investigation, we realized p-type monolayer (ML) MoS2, and intrinsic GaN/p-type MoS2 heterojunction by the GaN overgrowth on ML-MoS2/c-sapphire using the plasma-assisted molecular beam epitaxy. A systematic nitrogen plasma ( N 2 *) and gallium (Ga) irradiation studies are employed to understand the individual effect on the doping levels of ML-MoS2, which is evaluated by micro-Raman and high-resolution X-Ray photoelectron spectroscopy (HRXPS) measurements. With both methods, p-type doping was attained and was verified by softening and strengthening of characteristics phonon modes E 2 g 1 and A 1 g from Raman spectroscopy. With adequate N 2 *-irradiation (3 min), respective shift of 1.79 cm−1 for A 1 g and 1.11 cm−1 for E 2 g 1 are obtained while short term Ga-irradiated (30 s) exhibits the shift of 1.51 cm−1 for A ...

Knowledge of materials' thermal-transport properties, conductivity and diffusivity, is crucial for several applications within areas of biology, material science and engineering. Specifically, a microsized, flexible, biologically integrated thermal transport sensor is beneficial to a plethora of applications, ranging across plants physiological ecology and thermal imaging and treatment of cancerous cells, to thermal dissipation in flexible semiconductors and thermoelectrics. Living cells pose extra challenges, due to their small volumes and irregular curvilinear shapes. Here a novel approach of simultaneously measuring thermal conductivity and diffusivity of different materials and its applicability to single cells is demonstrated. This technique is based on increasing phonon-boundary-scattering rate in nanomembranes, having extremely low flexural rigidities, to induce a considerable spectral dependence of the bandgap-emission over excitation-laser intensity. It is demonstrated that once in contact with organic or inorganic materials, the nanomembranes' emission spectrally shift based on the material's thermal diffusivity and conductivity. This NM-based technique is further applied to differentiate between different types and subtypes of cancer cells, based on their thermal-transport properties. It is anticipated that this novel technique to enable an efficient single-cell thermal targeting, allow better modeling of cellular thermal distribution and enable novel diagnostic techniques based on variations of single-cell thermal-transport properties.

We achieved considerable laser diode (LD) improvement after annealing InGaP/InAlGaP laser structure at 950°C for a total annealing time of 2 min. The photoluminescence intensity is increased by 10 folds and full-wave at half-maximum is reduced from ∼30 to 20 nm. The measured LDs exhibited significantly reduced threshold current (Ith), from 2 to 1.5 A for a 1-mm long LD, improved internal efficiency (ηi), from 63% to 68%, and increased internal losses αi, from 14.3 to 18.6 cm−1. Our work suggests that the use of strain-induced quantum well intermixing is a viable solution for high-efficiency AlGaInP devices at shorter wavelengths. The advent of laser-based solid-state lighting (SSL) and visible-light communications (VLC) highlighted the importance of the current findings, which are aimed at improving color quality and photodetector received power in SSL and VLC, respectively, via annealed red LDs.

The dislocation free InxAl1-xN nanowires (NWs) are grown on Si(111) by nitrogen plasma assisted molecular beam epitaxy in the temperature regime of 490 °C–610 °C yielding In composition ranges over 0.50 ≤ x ≤ 0.17. We study the optical properties of these NWs by spectroscopic ellipsometry (SE), photoluminescence, and Raman spectroscopies since they possesses minimal strain with reduced defects comparative to the planar films. The optical bandgap measurements of InxAl1-xN NWs are demonstrated by SE where the absorption edges of the NW samples are evaluated irrespective of substrate transparency. A systematic Stoke shift of 0.04–0.27 eV with increasing x was observed when comparing the micro-photoluminescence spectra with the Tauc plot derived from SE. The micro-Raman spectra in the NWs with x = 0.5 showed two-mode behavior for A1(LO) phonons and single mode behavior for E2H phonons. As for x = 0.17, i.e., high Al content, we observed a peculiar E2H phonon mode splitting. Further, we observe composition dep...

We report the band alignment parameters of the GaN/single-layer (SL) MoS2 heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS2/c-sapphire. We confirm that the MoS2 is an SL by measuring the separation and position of room temperature micro-Raman E12g and A1g modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS2 heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS2 and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electr...

The lack of optical constants information for hybrid perovskite of CH3NH3PbBr3 in thin films form can delay the progress of efficient LED or laser demonstration. Here, we report on the optical constants (complex refractive index and dielectric function) of CH3NH3PbBr3 perovskite thin films using spectroscopic ellipsometry. Due to the existence of voids, the refractive index of the thin films is around 8% less than the single crystals counterpart. The energy bandgap is around 2.309 eV as obtained from photoluminescence and spectrophotometry spectra, and calculated from the SE analysis. The precise measurement of optical constants will be useful in designing optical devices using CH3NH3PbBr3 thin films.

In this paper, c-plane stepped- and graded- InGaN/GaN multiple quantum wells (MQWs) are grown using plasma assisted molecular beam epitaxy (PAMBE) by in situ surface stoichiometry monitoring (i-SSM). Such a technique considerably reduces the strain build-up due to indium clustering within and across graded-MQWs; especially for QW closer to the top which results in mitigation of the quantum-confined Stark effect (QCSE). This is validated by a reduced power dependent photoluminescence blueshift of 10 meV in graded-MQWs as compared to a blueshift of 17 meV for stepped-MQWs. We further analyze microstrain within the MQWs, using Raman spectroscopy and geometrical phase analysis (GPA) on high-angle annular dark-field (HAADF)-scanning transmission electron microscope (STEM) images of stepped- and graded-MQWs, highlighting the reduction of ~1% strain in graded-MQWs over stepped-MQWs. Our analysis provides direct evidence of the advantage of graded-MQWs for the commercially viable c-plane light-emitting and laser diodes.

ZnO nanostructures were fabricated on copper substrates by hydrothermal method at an optimized growth temperature of -95 degrees C. Structural properties were investigated by field emission scanning electron and transmission electron microscopy. Distinct morphologies were found to be formed at different growth times. The formation of nanotubes mainly involved the initial nucleation followed by the growth of nanorods at 95 degrees C, and then with the increase of dissolution time at room temperature, the preferential chemical dissolution of the metastable Zn-rich [0001] polar surfaces resulted in removing the atoms from the surfaces, thus leading to the thinning of the wall of the nanostructures. Completely hollow ZnO nanotubes could be obtained at a high dissolution time. The room temperature photoluminescence and optical absorption properties of ZnO nanotubes have been studied as a function of dissolution time. The efficacy of ZnO nanotubes for glucose sensing applications has been studied.