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The observation of higher-order harmonic generation (HHG) from bulk crystals has stimulated significant efforts to understand the involved mechanisms and their analogue to the intuitive three-step recollision model of gas phase HHG. On the technological side, efficient solid-state HHG is anticipated to enable compact attosecond and ultraviolet light sources that could unveil electron dynamics in chemical reactions and provide sharper tomographic imaging of molecular orbitals. Here we explore the roles of electronic band structure and Coulomb interactions in solid-state HHG by studying the optical response of linear atomic chains to intense ultrashort pulses. Specifically, we simulate electron dynamics in monoatomic chains by solving the single-particle density matrix equation of motion, incorporating tight-binding electronic states and a self-consistent electron-electron interaction, in the presence of intense ultrafast optical fields. While linear atomic chains constitute an idealized system, our realistic 1D model readily provides insight related to the time-evolution of electronic states in reciprocal space, both in the absence or presence of electron interactions, which we demonstrate to play an important role in the HHG yield. Our findings apply directly to extreme nonlinear optical phenomena in atoms on surfaces, linear arrays of dopant atoms in semiconductors, and linear molecules, such as polycyclic aromatic hydrocarbon chains, and can be straightforwardly extended to optimize existing or identify new solid-state platforms for HHG.

Pyramidal quantum dots have been established as a promising source of single and entangled photons for quantum information applications. However, their small brightness calls for new strategies both to boost extraction efficiency and to plan for heterogeneous integration protocols in view of demanding quantum information processing applications. In this paper we show that a simple technique based on chemo-mechanical planarization (CMP) can effectively remove several obstacles to the further processing of this kind of system, and pave the way for the use of in-situ lithographic techniques to tag individual quantum dots.

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According to the demand for high-performance silver-based telescope mirrors, attempts are being made to develop surface coatings that protect the mirrors from corrosion. Aluminum nitride (AlN) is utilized for various optical coatings, and its high optical transparency and mechanical robustness make it potentially well-suited as a protective coating of silver-based mirrors. However according to our best knowledge, AlN with controlled oxygen content has never been used to protect silver mirrors. In this study, various protective coatings based on AlN were prepared by RF magnetron sputtering. Specific amounts of oxygen were deliberately introduced to obtain protective layers with refractive indices within a certain range (i.e., high ~2.1, medium ~1.8, and low ~1.6 at 400 nm). The designed protective layers were applied to two types of silver-based mirror test structures, and their performance was assessed in terms of optical reflectivity and structural integrity of the test structures that underwent environmental testing in a controlled atmosphere at 80C with ~80% relative humidity. Comprehensive analysis on the samples before and after the environmental testing indicates that AlN-based protective layers with medium refractive index outperform similar samples using AlN with higher or lower refractive index., We suggest that the benefits of the best AlN barrier with specific refractive index are likely associated with the unique optical, chemical, and structural characteristics based on a unique nitrogen/oxygen ratio.

Fluorescent carbon dots (CDs) are one class of carbon-based nanomaterials that exhibit special photoluminescence properties. The unique properties of CDs, such as biocompatibility, tunable emission wavelength, and cost-effective, synthesis, have aroused intense interest. Conventionally, in the same particle size, the emission wavelength of CDs can be controlled by the graphitization of the monomer precursors. To date, it is still challenging to produce long-wavelength emissive CDs because it requires a higher graphitization degree of precursors. Not many results have been reported for the CDs with the emission wavelength longer than 600 nm (red). In this paper, we report a new type of red emissive CDs with the emission peak at 660 nm under ultraviolet light excitation with 30% quantum yield. Different from the conventional CDs with short Stokes shift, the new CDs exhibit 255 nm Stokes shift. This property will benefit applications of biosensors, solid-state lighting, and electronic displays. Furthermore, the carbon dots can be embedded into UV-curable polymer. With the fast photocuring technology, red emissive polymer pattern can be produced immediately by printing, stamping, or plotting. A red emission microLED was fabricated using CD-embedded polymer to generate a color coordinate at (0.56, 0.42).

In this study, colloidal ternary Zn_xCd_1-xS (x=0.5 and 0.8, named as Zn_0.5 and Zn_0.8) white light quantum dots (WQDs) were prepared, which have the characteristics of band edge and surface state emissions, resulting in emitting white light. However, the low stability of device limits the application in solid state lighting (SSL). In order to solve the above problem, WQDs is coated with SiO₂ to protect and passivate the surface. The results show that emission intensity of powder-typed Zn_0.8 and Zn_0.5 WQDs reduces to 40 % after four months at room temperature. On the other hand, the emission intensity of silica coating samples increase twice times compared to as-prepared sample. The luminous efficacy of as-prepared Zn0.8- based and Zn_0.8@SiO₂-based white light emitting diode (WLED) are 4.1 and 0.2 lm/W, respectively. The luminous efficacy of as-prepared Zn_0.5-based and Zn_0.5@SiO₂-based white light emitting diode (WLED) are 8.1 and 6.2 lm/W, respectively. Moreover, the luminous efficacy of as-prepared Zn0.5-based WLED only maintains for one week, while the Zn_0.5@SiO₂- based devices can maintain for more than two weeks. These results confirm that coating SiO₂ on the surface enhances the stability of WQDs and white light devices.

At the limits of physical representation of bits, novel opportunities arise, in particular leveraging the granular nature of charges, photons and atoms. One interesting application is the generation of truly random numbers. The need of a true random sequence of numbers is strategic for a variety of applications, ranging from the game industry to cryptography. Physical sources that rely on natural phenomena spanning radioactive decay, chaotic oscillators, thermal and quantum noise have their own merit, but for the purposes of integration, attributes such as bandwidth and power consumption, need to be accounted for. Here we evaluate transition metal oxide two terminal devices, memristors operating near the quantum of conductance and negative differential resistance metal-insulator transition devices, as potential candidates for a solid state source. In particular, the caveats of each implementation will be covered, such as the necessity of postprocessing and scalability.

2D layered nanomaterials for semiconductor channel have recently been attracting great attentions from researchers in many possibilities of future applications such as high speed electronics, flexible electronics, and immunity of short channel effects in scale-down transistors. Among many 2D materials molybdenum disulfide (MoS2) is known as a pacesetting material, since it has displayed excellent carrier mobility, a high on/off current ratio, and a good subthreshold swing in a field-effect transistor (FET) form as a 2D n-type channel. In contrast to MoS2, MoTe2 is p-type 2D nanoflake and it has an appropriate bandgap for both visible and infrared light photodetection. Here, we have fabricated 2D WSe2/MoS2 and MoTe2/MoS2 multilayers van der Waals heterojunction PN diode and its application for visible-near infrared broadband multi-detection. The MoTe2/MoS2 PN diode shows excellent performance with an ideality factor of 1.7 and high rectification (ON/OFF) ratio of over 104. This PN diode exhibits spectral photo-responses from ultraviolet (405 nm) to near infrared (1310 nm) with obvious photovoltaic behaviors. In addition to the static behavior, photocurrent switching behaviors are clearly observed under periodic illuminations at up to 100 KHz. WSe2/MoS2 PN diode demonstrate excellent static and dynamic device performances at a low voltage of 3 V, with an ON/OFF current ratio higher than 106, ideality factors of 1.5, dynamic rectification at a high frequency of 1 kHz, high photoresponsivity of 180 mA W–1. The two types of devices show a linear response within optical power density range from 10-5 Wcm-2 to 1 Wcm-2.

Bilayered vanadium oxide, δ-V₂O₅·nH₂O, is a promising electrode material for Na-ion batteries due to its large interlayer spacing, 11.5 Å, that allows for insertion of many charge-carrying ions. Previously, δ-V₂O₅·nH₂O electrodes have shown high capacities in Na-ion batteries^1-3. However, capacity fade is common when synthesized via cost effective, sol-gel routes. Poor cycling stability is attributed to the loss of V-O layers’ stacking order upon cycling¹. Therefore, methods to improve the structural stability of the δ-V₂O₅·nH₂O phase are necessary for its utilization as Na-ion cathodes. A synthesis approach known as chemical pre-intercalation allows for the insertion of inorganic cations into the structure of electrode materials prior to electrochemical cycling. Previously, we have demonstrated that chemical pre-intercalation of Na-ions into the bilayered phase results in high initial capacities above 350 mAh g^-1 in Na-ion cells³. In this study, we focus on the incorporation of low-temperature annealing to increase structural and electrochemical stability of the bilayered phase in Na-ion batteries. We demonstrate that annealing can lead to increased crystallinity leading to increased cycling stability. This result shows how synthesis approaches affect the structure of the bilayered vanadium oxide phase and can lead to increased electrochemical stability in Na-ion cells.

Hybrid organic-inorganic semiconductors, such as hybrid perovskites, are crystalline materials with unique properties derived from the organic or inorganic components. Resonant infrared matrix-assisted pulsed laser evaporation (RIRMAPLE) is a gentle physical vapor deposition technique that can enable two-dimensional hybrid perovskite thin films that are difficult to realize by solution-based processing. This work describes the RIR-MAPLE deposition of a model twodimensional hybrid perovskite material system, namely phenethylammonium lead halide [(PEA)₂PbX₄] perovskites (n=1). Different schemes for delivery of precursor materials to the substrate, as well as different mixed halide compositions, are demonstrated using RIR-MAPLE, and the film morphology, crystal structure, and optical properties are characterized.

Perovskite Chalcogenides are a new class of semiconductors, which have large chemical and structural tunability that translates to tunable band gap in the visible to infrared part of the electromagnetic spectrum. Besides this band gap tunability, they offer a unique opportunity to realize large density of states semiconductors with high carrier mobility. In this talk, I will discuss some of the experimental advances made both in my research group and in the research community on the theory, synthesis of these materials and understanding their optoelectronic properties. Perovskite structure is composed of an octahedrally coordinated transition metal or main group element with anions such as oxygen, chalcogen or halogens. The octahedra is typically connected in the corners and the voids are filled by alkali, alkaline or rare earth elements. The valence and the size of the cations and anions can lead to different connectivity of these octahedra, which offers a knob to control both the chemical composition and the dimensionality of these materials. Moreover, the large number of elements in the periodic table can be accommodated in these extended perovskite and related structures, which allows us finer knobs to control the physical and chemical properties, in our case, we tailor light-matter interaction precisely over a broad energy range spanning the visible to infrared spectrum. We leverage this effect in early transition metal based perovskite chalcogenides and related phases to achieve properties such as highly anisotropic absorption and refraction (BaTiS3, Sr1+xTiS3), unconventional band gap evolution (BaZrS3 and Ban+1ZrnS3n+1 for n ≥ 1). Finally, I will provide a general outlook for future studies on these exciting new class of materials. References: 1. S. Niu et al. Nature Photonics, 12, 392-396 (2018). 2. S. Niu et al. Advanced Materials 29, 1604733 (2017). 3. S. Niu et al. Chemistry of Materials, 30 (15), 4897-4901 (2018). 4. S. Niu et al. Chemistry of Materials, 30 (15), 4882-4886 (2018).

We use the (Mo,W)Te₂ system to explore the potential of transition metal dichalcogenides (TMDs) as phase-change materials for integrated photonics. We measure the complex optical constant of MoTe₂ in both the 2H and 1T’ phases by spectroscopic ellipsometry. We find that both phases have large refractive index, which is good for confined lightmatter interaction volume. The change Δn between phases is of σ(1), which is large and comparable to established phase-change materials. However, both phases have large optical loss, which limits to figure of merit throughout the measured range. We further measure the NIR reflectivity of MoTe₂ and Mo_0.91W_0.09Te₂, in both the 2H and 1T’ phases. The data show that the strong optical contrast between the 2H and 1T’ structures persists even as the thermodynamic barrier between them is reduced by alloying. This bodes well for alloy design of phase-change materials.

To further the present understanding of growth conditions on the quality of transition metal dichalcogenide (TMDC) thin films grown by molecular beam epitaxy (MBE), we study the effect of growth temperature and chalcogento- metal flux ratio on the chemical composition and surface morphology of synthesized WSe2 thin films. In-situ X-ray photoelectron spectroscopy (XPS) is performed to analyze the intrinsic chemical composition of the grown material prior to atmospheric exposure and ex-situ atomic force microscopy (AFM) is employed to study the surface morphology of grown, sub-monolayer films. We find that both low and high growth temperature ranges can be detrimental to the chemical homogeneity of the grown material and that these results are echoed in the resulting grain morphology. Growing at 375 °C resulted in the formation of metastable 1T’-WSe₂ alongside the thermodynamically stable 2H phase. Thin films grown at 750 °C resulted in the formation of highly Se deficient material. An intermediate growth temperature of 565 °C produced the most chemically homogeneous films above a critical chalcogen to metal flux ratio of 3250:1. Density functional theory calculations are used to rationalize the insights gained from the measured XPS data. Especially, the influence of Se-vacant WSe_2-x monolayers is explored and its impact on the coordination environment around the Se-atoms is used to interpret the measured XPS data.

Raman microscopy proved to be an extremely useful technique for characterization of 2D materials such as graphene, transition metal dichalcogenides (TMDs), black phosphorous, etc. Unfortunately, natural spatial resolution of confocal Raman microscopy, which is limited by the wavelength of the laser used (400-800 nm), is not sufficient for mapping heterogeneities and defects in these materials with characteristic dimensions of few – to few tens of nanometers. Tip Enhanced Raman Spectroscopy (TERS) provides dramatically improved spatial resolution of Raman maps, down to few nanometers, and in addition provides dramatic enhancement of the Raman signal. Since TERS is a relatively new technique, peculiarities of the near-field Raman response of many 2D materials still remain to be discovered and explained. Interesting unexpected effect was observed in the course of TERS characterization of WSe2 and MoSe2 exfoliated to gold and chromium. It is well known that TERS produces the strongest enhancement in so-called gap mode, when a thin sample is sandwiched between a plasmonic tip and a plasmonic substrate, usually silver or gold. To our surprise, TERS spectra of both WSe2 and MoSe2 crystals exfoliated to chromium showed very similar intensities of characteristic Raman bands compared to samples exfoliated to gold, although the background spectra obtained from the bare metal areas were much weaker for chromium compared to gold. Calculations of the optical field intensity of a TERS probe over gold and chromium surface confirmed that we indeed observed a gap mode TERS response on non-plasmonic chromium substrate. This important observation expands the choice of substrates suitable for high quality TERS characterization of 2D materials. Another interesting phenomenon discovered in the course of TERS imaging of WSe2 and MoSe2 deposited on metallic substrates was the appearance of new Raman peak in WSe2 deposited on silver at 295-297 cm-1 and an intense peak in TERS spectra of MoSe2 at 335cm-1, which is either absent or much less pronounced in conventional confocal Raman spectra of this material. We’ll discuss possible nature of these unexpected peaks.

Here we present electric field-controlled, two-dimensional (2D) exciton dynamics in transition metal dichalcogenide monolayers. We have experimentally investigated the spectral and temporal properties of the A-exciton in a molybdenum diselenide (MoSe₂) monolayer under controlled variation of a vertical, electric dc field at room temperature. By using steady-state and timeresolved photoluminescence spectroscopies, we have observed dc field-induced spectral shifts and linewidth broadenings that are consistent with the shortening of the exciton’s non-radiative lifetime due to field-induced dissociation. We discuss the implications of the results for future developments in nanoscale metrology and exploratory, optoelectronics technologies based on layered, 2D semiconductors.

The effects of the peculiar in-plane lattice vibrations in monolayer molybdenum disulfide (MoS₂) are oftentimes ignored in the analysis of the material’s lattice behaviors due to the lack of variation of polarization for the excitation light. In this work, we have observed variations in the relative intensity of the two most dominant Raman peaks of MoS₂ via polarized micro-Raman spectroscopy using elliptically polarized incident light. The asymmetry of the incident excitation light gives an additional degree of freedom affecting the relationship between the x- (E¹₂gx) and y- (E¹₂gy) components of the material’s in-plane lattice vibrations. Different ratio of the magnitudes for E¹₂gx and E¹₂gy in the lattice vibrations can be induced by changing the polarization state of the incident light. This work investigates the material’s unexplored fundamental phonon property which may enlighten past and future studies involving phonon behaviors.

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Zirconium oxide doped with rare earth elements (Y, Ce, etc.) is an important candidate material for incorporation in medical implants and prosthetics. Due to their mechanical properties, the doped compounds hold a unique place among the oxide ceramics since they can undergo phase transformations allowing a toughening mechanism. We aim to determine the influence of different types of thermal treatments for Zr_1-xCe_xO₂ (x=0.1; 0.15; 0.20) as well as the structural and mechanical properties of these materials using X-ray and Neutron Diffraction (ND) as well as high resolution of SEM imaging combined with Electron Backscattered Diffraction (EBSD). Our analyses have shown that, following the doping mechanism, the samples exhibit stable crystallographic structures but also improved material strengths, which can make these compounds suitable for a wide range of promising clinical applications.

The magnetic properties of nano-graphene monolayer were investigated in the framework of Ising ferromagnetic model with mixed spins by means of Monte Carlo technique based on Metropolis algorithm. A transition between ferromagnetic and paramagnetic phases of the monolayer was established. This makes such type of nanosystem promising for spintronics and sensor applications (as magnetic field sensors). Near absolute zero temperature a magnetic hysteresis was obtained, that strongly depends on the values of the interaction constant and temperature. Obtained results agree with available theoretical and experimental works of other authors.

The interest of 2D materials is constantly increasing because of their very attractive mechanical, electrical and optical parameters. They have been used in many applications, e.g. photodetectors, sensors, modulators, insulators. One of the recently discovered 2D materials is phosphorene. In contrast to graphene, phosphorene has a direct bandgap tuned by numbers of layers in the 2D structure. The phosphorene flakes are strongly anisotropic. This study presents the detailed optical properties of electrochemically obtained phosphorene flakes versus centrifugation speed. A layer of phosphorene on a silicon wafer changes with increased centrifuge speed. A relationship that combines the size of the phosphorene flakes and ellipsometric angles, as well as the transmittance data obtained on a spectrophotometer was received. Hence, such an approach could allow for non-contact comparing the size of phosphorene flakes.

It is known that heterogeneously coupled dot structure consisting of sub monolayer (SML) and Stranski Krastanov quantum dots (QDs) has less cumulative strain compared to that in the homogeneously coupled SK dots structure which leads to better carrier confinement in the heterogeneously coupled structure. Here we have theoretically analysed the two heterogeneously coupled dot structures having SML series deposited over SK QDs (Samples A, B, C) and SK QDs over the SML stacks (samples D, E, F). Samples A and D have 1 nm, samples B and E have 2 nm, and samples C and F have 3 nm of InGaAs capping layer thickness over the InAs QD. The optimized structure obtained from previous experimental study consists of six SML stacks with barrier thickness of 7.5 nm between SML and SK QDs. The simulated peaks were validated with experimental data for reliability. Our motivation is to compare hydrostatic and biaxial strains and to find the better structure for long wavelength detection along with high-temperature operation conditions. The result shows that magnitude of hydrostatic strain decreases with the capping layer thickness in both systems indicating carrier confinement of samples C and F are better than the others. Therefore, they can be operated at a slightly higher temperature compared to the other samples. Furthermore, in both systems, biaxial strain in the dot has a positive correlation with the capping layer thickness, showing maximum valence band splitting in samples C and F, thus having lower band gap which makes them a better choice for longer wavelength detection.

Hybrid coupled quantum dot (QD) structures have a high absorption coefficient along with the minimum cumulative strain in the heterostructure compared to that in the homogeneously coupled heterostructure of only Stranski-Krastanov (SK) QDs. Here, we are introducing a theoretical analysis of the hybrid heterostructure consisting of six submonolayer (SML) stacks above SK QDs with a various capping layer combinations. Sample A (InGaAs-InGaAs) has both SK and SML capping layers of InGaAs. Similarly, Sample B (InGaAsInAlGaAs), sample C (InAlGaAs-InGaAs), and sample D (InAlGaAs-InAlGaAs) have variations in the capping composition of SK and SML dots. The barrier thickness between SML stacks and SK dots is taken to be 7.5nm, and the capping layer thickness of the SK dot is 3nm. The number of SML stacks and barrier thickness has been optimized from our previous experimental work. Hydrostatic and biaxial strains of four samples are analyzed and compared. It has been found that sample D shows the lowest magnitude of hydrostatic strain in both SML and SK dots, suggesting better carrier confinement in both QDs. Moreover, Sample D has the highest biaxial strain in the SK dot indicating the maximum splitting of the valence band which leads to a lower band gap in the sample. Thus, after optimizing all the performance parameters, we found that Sample D could be the potential candidate for optoelectronic device applications.

InAs/GaAs Quantum Dots have piqued the interest of researchers owing to the advantages they offer in the fabrication of highly efficient optoelectronic devices. In this study, we aim to examine the consequence varying V-III ratio on optical and structural behavior of self-assembled InAs/GaAs Stranski-Krastanov (SK) Quantum Dots grown on GaAs substrate using Molecular Beam Epitaxy (MBE). Three samples consisting of three layers of vertically stacked Quantum Dots with three different V-III ratios (48, 60 and 80 respectively) grown at a substrate temperature of 490°C have been thoroughly examined using PL spectroscopy and HR-XRD. The best optical response is seen in the sample with 80 as VIII ratio. A higher As vapor pressure during growth seems to suppress the surface migration of Indium atoms leading to bigger dot size, increased PL intensity and more uniform distribution rendering better optical response. The absence of satellite peaks in HR-XRD measurements of sample with lower V-III ratio indicates significant density of point-defects. HRXRD analysis reveals an increase in perpendicular strain with greater V-III ratio. Reduced FWHM in sample with higher V-III ratio is in accordance with suppressed Indium diffusion and strain propagation across multi-layered nanostructure contributing to greater uniformity in dot-size. PL spectrum of sample with least V-III ratio shows sharp peaks around 900 nm indicating incomplete dot-formation at such low ratios leaving significant part of wetting layer exposed. Our investigation provides interesting insights into kinetics of nanostructure growth which will prove to be helpful in fabrication of optimized nanostructures.

In spite of numerous advantages offered by Quantum Dot (QD) based imaging systems in infrared photo-detection, the physical realization of such systems has always been a challenging task. In this study, we aim to analyze the effects of growth rate variation on the structural and optical properties of self-assembled InAs/GaAs Stranski-Krastanov (SK) QDs grown on semi-insulating GaAs substrate using MBE (Molecular Beam Epitaxy). Five samples grown at a substrate temperature of 490°C with varying growth rates (0.025ML/s, 0.05ML/s, 0.075ML/s, 0.1ML/s, 0.15ML/s) were investigated using PL spectroscopy, and AFM measurements. PL spectroscopy showed a blue shift in the ground state peak wavelength with an increase in growth rate which was further corroborated by AFM measurements, showing reduced dot-size with an increased growth rate. AFM measurements showed an increase in dot density with an increased growth rate suggesting increased tendency towards nucleation. Integrated PL intensity witnessed an initial increase with an increased growth rate before achieving its maxima for sample grown at 0.075ML/s, rendering the sample grown at 0.075ML/s best in terms of optical activity. These observations provided key insights into the growth kinetics operating during dot-formation through SK growth mode by evaluating the competition between the forces due to surface diffusion and nucleation.

The influence of variation in InAs monolayer coverage on the formation of self-assembled quantum dots (QDs) grown by molecular beam epitaxy (MBE) was investigated by Photoluminescence (PL), Photoluminescence excitation (PLE), and High-resolution X-ray diffraction (HRXRD) measurements. Redshift in the PL spectra was observed with increase in monolayer (ML) coverage of InAs QD from 2 ML to 3.4 ML, as a consequence of an increase in dot size. However, the PL peak intensity initially enhanced from 2 ML to 2.7 ML followed by a drop in 3.4 ML, which promulgate the incoherent dot formation along with the facilitation of defects. The full width at half maxima (FWHM) of the lowtemperature ground state emission spectra was found to be around 48 meV for 2 ML and 3.4 ML InAs QD, but for 2.7 ML it was around 40 meV as a result of lower dispersion in dot size. PLE spectra and a prolonged double-peak feature in the power dependent PL spectra revealed that the transition of the size distribution of InAs QD from single-modal to bimodal occurred as the InAs QD coverage increased. Besides, HRXRD measurements explained the formation of compressively strained QDs with increased InAs coverage. The activation energy for all samples was calculated from the temperature-dependent photoluminescence spectra and the optimum value (~327 meV) obtained for 2.7 ML sample, which attributes deeper barrier potential. Thus, possessing efficient activation energy, relaxed strain and predominantly enhanced luminescence, InAs QD with 2.7 ML coverage is the optimized structure for various optoelectronic device applications.

The effect of substrate temperature variation on properties of InAs/GaAs Quantum Dots has been studied. Increase in substrate temperature during growth leads to blue-shift in the PL spectrum which becomes fairly evident after a threshold substrate temperature. Beyond the threshold substrate temperature (beyond 500°C), the effects due to Indium desorption cannot be neglected and hence they contribute to poor optical quality of dots as evident from reduced integrated PL intensity on increasing substrate temperature. AFM measurements also corroborate these findings showing reduced dot size and higher dot density after threshold substrate temperature. We suggest an optimum substrate temperature around 480 ″C for growth process.

In the present work, an eco-friendly and low-cost lithium-ion full cell assembled using Mn₃O₄-mesoporous (MnMC) composite anode and LiFePO₄ cathode (LFP) is investigated for energy storage applications. Hydrothermally synthesized Mn₃O₄ nanoflakes with a length of 40-50 nm are physically mixed with mesoporous carbon (MC) to obtain MnMC nanocomposite, and sol-gel method in the presence of citric acid is employed to synthesize the cathode material LiFePO₄. The structural and morphological details of LFP cathode are investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) techniques and the electrochemical performance is evaluated by assembling half cells with lithium metal as the counter electrode. The MnMC nanocomposite is pre-lithiated and combined with LFP cathode for the full lithium ion cell with a cathode limiting capacity. The LFP-MnMC full cells exhibit reversible capacity of the LFP cathode and show good cycling stability with a capacity retention of 66% and the average Coulombic efficiency is found to be 98% after 100 cycles.

Hybrid capacitive deionization (HCDI) is an emerging water desalination technology that integrates an intercalation electrode against a capacitive carbon counter electrode. The former electrode incorporates ions into the material volume unrestricted by surface area. Tunnel manganese oxide nanowires are a promising class of intercalation materials due to their low cost, small environmental footprint, stability in aqueous solutions, and high theoretical ion removal capacity. Previous HCDI studies reported high desalination performance of disordered Na-stabilized manganese oxide (Na_xMnO₂) tunnel phases known as 2xn-MnO₂ and hybrid-MnO₂. In contrast, this study focuses, for the first time on the synthesis and HCDI water desalination performance of highly ordered Na_xMnO₂ phases with uniform rectangular tunnels. These tunnels are formed by 2 MnO₆ octahedra on one side and 3 or 4 MnO₆ octahedra on the perpendicular side called Na-2x3 and Na-2x4, respectively. The analysis includes ion removal performance in NaCl solution to understand ion intercalation and surface adsorption processes into tunnel manganese oxides and the role of the stabilizing ions compared to the two previously reported disordered phases.

In this report, the performance of Quantum Dot Infrared Photodetector (QDIP) is examined in which the active layer consists of 10 layers of uncoupled InAs quantum dots (QDs) with quaternary In0.21Al0.21Ga0.58As capping. The optical, structural, and electrical properties of the QDIP is observed and compared with a sample in which the QDs are capped with binary GaAs layer. The observation of full width half maximum (FWHM) in the low-temperature photoluminescence (PL) of both sample shows a change in dot size distribution. Variation in the dot size distribution is also observed from the low temperature power dependent PL. Activation energy calculated from the temperature dependent PL indicates better carrier confinement in the structure with In_0.21Al_0.21Ga_0.58As capped QDs. This can be explained by the formation of higher barrier potential. Stain introduced due to lattice mismatch in the heterostructure is calculated from the high resolution X-ray diffraction (HRXRD) Rocking curves, which shows a relatively low value of strain in the QDIP heterostructure with In_0.21Al_0.21Ga_0.58As capping with respect to the QDIP with GaAs capping layer. A five order reduction in the dark current density is also observed form the QDIP with In_0.21Al_0.21Ga_0.58As capping due to insertion of Al in the capping layer. The dark current obtained for the In_0.21Al_0.21Ga_0.58As capped QDIP is 1.9E-5 A/cm², whereas the same for the GaAs capped QDIP is 4.91 A/cm². This attributes to the confinement enhancement in the prior QDIP heterostructure.

Uncapped In(Ga)As quantum dots (QDs) have got very little attention in comparison with its enfolded counterpart. The existence of surface states makes it less attractive to the research community. On the other hand, colloidal QDs have immense recognition in the field of bio-sensing and bio-imaging. Various surface passivated stable colloidal QDs are now commercially available, but only in solution form. Stable solid-state QDs are still a virtue. So, there is a huge demand for stable solid-state surface QDs which can be easily coupled with an electronic device for sensing application. Simply we need to change the ligand, corresponding to a particular target molecule, and we can detect various chemical and biological elements from low molar solution (Nano bio-sensor regime). With this motivation, we have epitaxially grown a simple vertically coupled InAs QD structure, where both seed and top dot layers are of 2.7 ML InAs. In addition, the top QDs are left uncapped to form a surface quantum dot layer. The as-grown sample is acid-etched (to remove the native oxides) and passivated in 0.5 M Thiourea solution for one hour. Significant enhancement of ground state photoluminescence peak has been observed after the passivation for both surface and buried QDs. Atomic force microscopic (AFM) images confirm the modulation of the surface before and after the ex-situ treatment.

Epitaxially grown III-As nanostructures, like quantum well (QW)/ quantum dot (QD) have already been scrutinized rigorously and incorporated into various devices, like light-emitting diode (LED), laser, Photodetector, solar cell, etc. Most of them use buried QW/QD heterostructure, where the as-grown nanostructures are capped with various combination of thick (In/Ga/Al)As matrix. In contrary, near-surface nanostructures have very less attention owing to additional surface states. However, these near-surface nanostructures have the potential to communicate with the external world. Therefore, it might act as a confined channel, which can be probed externally. Assertively, these near -surface nanostructures have immense potential to act as sensors. Before that, we need to passivate the surface states to hold the best communication with the outer environment. In the present study, we have used Thiourea as a source of sulfur and show the effect of passivation in terms of improved luminescence behavior. Near-surface GaAs/In_0.15Ga_0.85As/GaAs quantum well and self-assembled GaAs/InAs/GaAs SK quantum dots are grown on GaAs wafer through molecular beam epitaxy. The effective thickness of the top GaAs capping layer has been kept around eight nanometers and twelve nanometers to keep the nanostructure (QW/QD) very close to the surface. As grown samples have shown very poor photoluminescence peaks and increased by few orders after passivation. Pre-etching followed by sulfur passivation has shown the best enhancement of luminescence intensity.