Nanopatterning Induced Si Doping in Amorphous Ga2O3 for Enhanced Electrical Properties and Ultra-Fast Photodetection.

Ga2O3 has emerged as a promising material for the wide-bandgap industry aiming at devices beyond the limits of conventional silicon. Amorphous Ga2O3 is widely being used for flexible electronics, but suffers from very high resistivity. Conventional methods of doping like ion implantation require high temperatures post-processing, thereby limiting their use. Herein, an unconventional method of doping Ga2O3 films with Si, thereby enhancing its electrical properties, is reported. Ion-beam sputtering (500 eV Ar+) is utilized to nanopattern SiO2-coated Si substrate leaving the topmost part rich in elemental Si. This helps in enhancing the carrier conduction by increasing n-type doping of the subsequently coated 5 nm amorphous Ga2O3 films, corroborated by room-temperature resistivity measurement and valence band spectra, respectively, while the nanopatterns formed help in better light management. Finally, as proof of concept, metal-semiconductor-metal (MSM) photoconductor devices fabricated on doped, rippled films show superior properties with responsivity increasing from 6 to 433 mA W-1 while having fast detection speeds of 861 µs/710 µs (rise/fall time) as opposed to non-rippled devices (377 ms/392 ms). The results demonstrate a facile, cost-effective, and large-area method to dope amorphous Ga2O3 films in a bottom-up approach which may be employed for increasing the electrical conductivity of other amorphous oxide semiconductors as well.

Superalkalis with Hydrogen as Central Electronegative Atom and their Possible Applications: Ab Initio and DFT Study.

Superalkalis are unusual species having ionization energies lower than that of the alkali metals. These species with various applications are of great importance in chemistry due to their low ionization energies and strong reducing property. A typical superalkali contains a central electronegative core decorated with excess metal ligands. In the quest for novel superalkalis, we have designed the superalkalis HLi2, HLiNa and HNa2 using hydrogen as central electronegative atom for the first time employing high level ab initio (CCSD(T), MP2) and density functional theory (ωB97X-D) methods. The superalkalis exhibit very low ionization energies, even lower than that of cesium. Stability of these species is verified from binding energy and dissociation energy values. The superalkalis are capable of reducing SO2, NO, CO2, CO and N2 molecules by forming stable ionic complexes and therefore can be used as catalysts for the reduction or activation of systems possessing very low electron affinities. The superalkalis form stable supersalts with tailored properties when interact with a superhalogen. They also show remarkably high non-linear optical responses, hence could have industrial applications. It is hoped that this work will enrich the superalkali family and spur further theoretical and experimental research in this direction.

A hybrid effective medium description for nanoporous gold films and thickness-mediated control of optical absorption.

With the increasing demand for sensing platforms operating across UV, visible, and near-infrared wavelengths, nanoporous gold has emerged as an ideal substrate for rapid, quantitative detection of analytes with excellent specificity and high sensitivity. This study investigates thickness-mediated compositional changes and their impact on scattering characteristics of thin nanoporous gold films fabricated using selective chemical etching. Specifically, we observe thickness-induced morphological and structural changes across different fabricated samples from 25-100nm in thickness. Upon their optical characterization across UV-VIS-NIR spectral regime, we notice that the constitutional differences among samples manifest distinctively \& deterministically in their total optical scattering response. In order to gain insights into these observed scattering responses and to fathom the subtle connections between structural properties of NPG films and their optical response, a hybrid theoretical model comprising Maxwell-Garnett \& Bruggeman effective medium approximations has been adopted. Our approach not only allows to appropriately account for the inhomogeneous nature of these films, but also corroborates well with the atomic force microscopy characterizations of the fabricated samples. Furthermore, tracing such a theoretical model is important as it helps in systematically ascertaining additional loss terms emerging in the complex dielectric function of films due to their nanoscale porosity \& roughness, permitting a good reproduction of measured optical spectra. We believe, our approach will not only facilitate accurate regulation of losses in NPG thin films but will also aid in deriving customized optical performance from them, thereby advancing their potential applications in sensing and beyond.

Dual Palladium-Photoredox-Mediated Regioselective Acylation of Carbazoles and Indolines.

We have described a dual palladium-photoredox-catalyzed highly regioselective acylation of carbazoles and indolines using molecular oxygen as the green oxidant. The reaction shows a broad substrate scope and good functional group tolerance. Late-stage functionalization of a carprofen drug derivative, further manipulation of products, and gram-scale synthesis of the acylated products were illustrated to show the versatility of the method.

Drying behaviour of nanofluid sessile droplets on self-affine vis-à-vis corrugated nanorough surfaces.

In recent years, evaporative self-assembly of sessile droplets has gained considerable attention owing to its wide applicability in many areas. While the phenomenon is well studied for smooth and isotropically rough (self-affine) surfaces, investigations comparing the outcomes on self-affine vis-à-vis corrugated surfaces remains to be done. In this experimental work, we compare the wetting and evaporation dynamics of nano-colloidal microlitre droplets on self-affine and corrugated nanorough surfaces having identical roughnesses and interface properties. The coupled influence of particle size, concentration, and surface structuring has been explored. Differences in wettability and evaporation dynamics are observed, which are explained via the interaction between wetting fluid and anisotropic surface roughness. Our findings exhibit different temporal behaviour of contact radius and angle in the evaporation process of the droplets. Further, the corrugated surface exhibits anisotropic wettability with a monotonic change in droplet shape as evaporation proceeds, finally giving rise to irregular dried patterns. The scaled rim width and crack spacing of the particulate deposits are examined. Our results can inspire fabrication of surfaces that can facilitate direction-dependent droplet motion for specific applications.

Surface Nanopatterning of Amorphous Gallium Oxide Thin Film for Enhanced Solar-blind Photodetection.

Gallium oxide is an ultra-wide band gap semiconductor (Eg > 4.4 eV), best suited intrinsically for the fabrication of solar-blind photodetectors. Apart from its crystalline phases, amorphous Ga2O3 based solar-blind photodetector offer simple and facile growth without the hassle of lattice matching and high temperatures for growth and annealing. However, they often suffer from long response times which hinders any practical use. Herein, we report a simple and cost-effective method to enhance the device performance of amorphous gallium oxide thin film photodetector by nanopatterning the surface using a broad and low energy Ar+ ion beam. The ripples formed on the surface of gallium oxide thin film lead to the formation of anisotropic conduction channels along with an increase in the surface defects. The defects introduced in the system act as recombination centers for the charge carriers bringing about a reduction in the decay time of the devices, even at zero-bias. The fall time of the rippled devices, therefore, reduces, making the devices faster by more than 15 times. This approach of surface modification of gallium oxide provides a one-step, low cost method to enhance the device performance of amorphous thin films which can help in the realization of next-generation optoelectronics.

Interconnected drying phenomena in nanoparticle laden water-ethanol binary droplets.

Understanding the evaporation of a multi-component droplet has found immense importance in various technological applications. This study investigates the evaporation behaviour of a colloidal binary droplet system comprising of the ethanol-water mixture and polystyrene nanoparticles. The wetting and evaporation dynamics were studied with an emphasis on the collective influence of ethanol and nanoparticle concentrations. The temporal behaviour of the contact angles, shapes and volumes of the droplets was monitored in order to analyse the evaporative behaviour. With increase of ethanol concentrations, the binary droplet volumes were found to decrease nonlinearly with time. Ethanol being more volatile evaporated in the initial stage. Towards the end of the evaporation process, the evaporation characteristics mimics the behaviour of pure water. Our study shows that the initial contact angle decreases monotonically with increased concentration of ethanol in the mixture. The contact angle is maximum for a particular nanoparticle concentration. Droplets with higher ethanol concentration show higher wettability which in its turn is maximum for low nanoparticle concentrations. This trend shows the interconnected effect of ethanol and nanoparticle concentrations on evaporation. Rim width of the final deposition pattern increases with nanoparticle concentration although it is almost independent of ethanol concentration. Finally, it is noticed that fast evaporation of a relatively more volatile component in a binary mixture droplet leads to nanoparticle segregation for low nanoparticle concentrations. Thus for binary mixtures, the evaporation of the more volatile component, ethanol for our case, offers characteristic differences in the resulting evaporation dynamics from that of pure water which finds applicability for multi-component evaporation processes.

Tuning the topographical parameters of Si pyramids for a better surface enhanced Raman response.

Development of facile routes for the fabrication of surface enhanced Raman substrates (SERS) along with optimal conditions for a high enhancement factor are significant from an application perspective of SERS. Despite steady efforts to establish high SERS signals, cost effectiveness without compromising the enhanced and robust Raman signal remains a major challenge. To address this aspect, herein, we try to tune the topographical aspects of Si pyramidal textures in pursuit of efficient SERS substrates. These pyramidal surfaces are deployed as a pre-template for adopting a SERS substrate using a cost-effective wet chemical etching method. By controlling the etching time, various topographical parameters namely base size, height, pyramidal number density and uniformity of pyramidal textures are modulated. To make all the surfaces SERS active, a Au (50%)-Ag (50%) alloy nanolayer is post-deposited over them. Furthermore, SERS behavior of all the surfaces is investigated by using Rh6G dye as an analyte molecule. In addition to the high density of hot spots in terms of pyramidal number density, base size and uniformity shows a strong correlation in deciding the substantial SERS response. Furthermore, we find a high enhancement factor (∼1.42 × 108) for the substrate consisting of dense, small and uniformly sized pyramids. Finite Difference Time Domain (FDTD) simulations done on similar structures corroborate our results. Additionally, universal applicability of the proposed substrate is also verified by detecting methylene blue and methyl parathion analyte molecules. These substrates are much cheaper (∼5 USD for 1 × 1 cm2) in comparison with commercially available Klarite SERS substrates (∼100 USD for 2 × 2 mm2). We believe this work provides a critical insight into the design of potential SERS substrates using a significantly cost-effective wet chemical etching process.

Solution-processed MoS2 quantum dot/GaAs vertical heterostructure based self-powered photodetectors with superior detectivity.

The characteristics of a novel 0D/3D heterojunction photodetector fabricated using solution-processed colloidal MoS2 quantum dots (QDs) on GaAs is presented. MoS2 QDs with a dimension of ∼2 nm, synthesized by a standard sono-chemical exfoliation process with 2D layers have been used for the purpose. The microscopic and spectroscopic studies confirmed the formation of semiconducting (2H phase) MoS2 QDs. The photodetectors were fabricated using n-GaAs substrates with two different doping concentrations resulting in n-n heterojunctions between n-type 0D MoS2 QDs and bulk n-GaAs. The devices fabricated using GaAs with a higher doping concentration, showed an increase in the reverse current of the order of ∼102 upon illumination, while the same with a lower doping concentration showed an increase of the order of ∼103. All the heterojunction photodetector devices show a broadband operation over the visible wavelength range of 400-950 nm, with a peak responsivity of the devices being observed at 500 nm. The peak responsivity and detectivity are found to be ∼400 mA W-1 and ∼4 × 1012 Jones, respectively, even without any external applied bias, which are useful for self-powered photodetection. The results indicate that colloidal MoS2/GaAs based hybrid heterostructures provide a platform for fabricating broadband photodetectors by using highly absorbing MoS2 QDs, which may show the pathway towards next-generation optoelectronic devices with superior detection properties.

Epithelial to mesenchymal transition induces stem cell like phenotype in renal cell carcinoma cells.

BACKGROUND: Metastatic dissemination of solid tumors is often initiated by reactivation of an embryonic development program, epithelial-to-mesenchymal-transition (EMT). EMT has been associated with acquiring invasiveness and resistance to conventional therapies. However, the precise role of EMT during renal cell carcinoma is still debatable and is under investigation. In this context, our study is designed to evaluate the role of cyclosporine (CsA) and transforming growth factor-ß (TGFß) administration in inducing EMT-like state in renal carcinoma cells. We also studied the associated phenotypic changes which may lead to tumor metastasis. METHODS: The morphological changes in renal cell carcinoma cells (A498) treated with TGF-ß/CsA were observed by microscopy. Atomic force microscope was used to evaluate the changes in elasticity of cells treated with TGF-ß/CsA. The expression of mesenchymal and chemoresistance genes were checked by RT-PCR. Assays for migration, invasion, sphere formation ability and expression of cancer stem cell-like phenotypes were done to evaluate the metastatic potential of these cells. Lineage specific differentiations were also done to determine the acquisition of stem-cell like phenotype. RESULTS: Our results showed that treatment with TGF-ß/CsA led to loss of epithelial characteristics and gain of mesenchymal phenotype in vitro. Changes in shape and elastic properties of the cancer cells favoured metastatic progression, increased tumorisphere formation and invasiveness post treatment. We also observed higher expression of chemoresistance and stemness markers in EMT-induced cells. These cells also differentiated to various lineages like osteoblasts, adipocytes, neural and hepatic cells when induced with the respective differentiation media. CONCLUSION: We concluded that TGF-ß/CsA treatment led to acquisition of EMT-like cancer stem cells phenotype that enhanced local invasion and dissemination of renal carcinoma cells. This subpopulation of cells with EMT-like phenotype a can provide a better perception of the metastatic process. This can provide an in vitro system for testing pharmaceuticals for modulating EMT as a viable strategy within the therapeutic armamentarium for RCC patients. The results of our findings also suggest that CsA directly induced EMT like changes in epithelial cell which may be responsible for the potential risk of malignancy in transplant patients.

Nanoscale Topographical Fluctuations: A Key Factor for Evaporative Colloidal Self-Assembly.

This work investigates the role of surface parameters such as the nanoscale roughness, topography, and skewness of smooth and rough Si surfaces in the shape of patterns left by evaporating colloidal droplets of spherical polystyrene particles. The droplet contact angle, colloidal deposition pattern, crack density, and rim growth velocities are experimentally evaluated for varying roughness. The contact angle and rim growth rate are found to be more for rough surfaces in comparison to smooth ones. Roughness also helps in reducing stress in the drying droplets, thereby impeding the process of crack formation as exemplified by the experimental results. The altered Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions emerging from the contribution of nanoscale roughness are theoretically evaluated for each differently rough substrate-particle combination. The forces have been calculated by considering large- and small-scale roughness parameters of the experimental surfaces. The experimental findings have been duly corroborated by theoretical estimates. Finally, it is observed that the skewness of the surface and the small-scale asperity radius bear a correlation with the DLVO forces and subsequently with the ring deposit pattern. The present understanding of the influence of surface fluctuations on evaporative self-assembly would enable one to choose the right topographic surface for particular applications.

Exploration of M(100)-2×1 (M=Si, Ge) surface termination through hydrogen passivation using ethane and ammonia-borane derivatives: A theoretical approach.

Termination process of Si(100)-2 × 1 as well as Ge(100)-2 × 1 reconstructed surfaces have been explored comprehensively through the dehydrogenation of ethane and ammonia-borane and their several analogues by employing density functional theory (DFT). From our study, it is evident that the termination of Si-surface via the dehydrogenation of aforementioned ethane and NH3BH3 derivatives is more feasible compared to Ge-surface. For ethane, the investigation shows that the substitution of non-participating hydrogens with +I group (electron donating) causes an enhancement in the kinetic and thermodynamic feasibility of the termination process, whereas the implementation of -I substituent (electron withdrawing) makes an adverse effect. While exploring the termination of Si- as well as Ge-surfaces through the dehydrogenation of NH3BH3 and its derivatives, it is noticed that from both the kinetic as well as thermodynamic perspectives, the termination processes are more feasible than that of ethane and its derivatives. We have further examined the detailed mechanism of each termination process by analyzing the geometrical parameters and NPA charges. From bonding evaluation, it is evident that the hydrogen abstraction from ethane by both the surfaces is symmetric in nature, where both the hydrogens show slightly positive charge. But for NH3BH3 the hydrogen abstraction process becomes asymmetric, where the boron associated hydrogen is abstracted as hydride by the electrophilic surface Si (Ge) and the hydrogen bonded with the N-centre is abstracted as proton by the nucleophilic surface Si (Ge). Overall, the present theoretical work reveals one of the efficient chemical processes for terminating Si as well as Ge(100)-2 × 1 reconstructed surfaces through the formation of non-polar SiH bonds.

Towards a comprehensive understanding of the Si(100)-2×1 surface termination through hydrogen passivation using methylamine and methanol: a theoretical approach.

Using density functional theory, we explored the termination process of Si (100)-2 × 1 reconstructed surface mechanistically through the dehydrogenation of small molecules, considering methyl amine and methanol as terminating reagents. At first, both the terminating reagents form two types of adduct through adsorption on the Si (100)-2 × 1 surface, one in chemisorption mode and the other via physisorption, from which the dehydrogenation process is initiated. By analyzing the activation barriers, it was observed that termination of the Si-surface through the dehydrogenation is kinetically almost equally feasible using either reagent. We further examined in detail the mechanism for each termination process by analyzing geometrical parameters and natural population analysis charges. From bonding evaluation, it is evident that hydrogen abstraction from adsorbates on the Si-surface is asymmetric in nature, where one hydrogen is abstracted as hydride by the electrophilic surface Si and the other hydrogen is abstracted as proton by the neucleophilic surface Si. Moreover, it was also observed that hydride transfer from adsorbate to the Si-surface occurs first followed by proton transfer. Overall, our theoretical interpretation provides a mechanistic understanding of the Si (100)-2 × 1 reconstructed surface termination by amine and alcohol that will further motivate researchers to design different types of decorated semiconductor devices. Graphical Abstract Surface termination process of Si(100)-2×1 through formation of non-polar Si-H bonds via dehydrogenation of methylamine and methanol as terminating reagents.

Identification and characterization of intramolecular γ-halo interaction in d0 complexes: a theoretical approach.

A mechanistic investigation to detect intramolecular M⋯X-C type interactions in d0 neutral and cationic complexes was carried out through a benchmark study employing different density functional methods. As γ-halogen is involved in M⋯X-C type interactions, it is denoted as a γ-halo interaction and the respective conformers are designated as halo-conformers. By analyzing the geometrical parameters of halo-conformers, it was observed that, irrespective of the nature of the metal and the halogen, the Cγ-X bond distance increases compared to the usual C-X bond, which brings the M and X centers close enough to generate a weak interaction. Generation of the M⋯X-C interaction was confirmed by performing NBO, AIM and Wiberg bond index analyses, from which the persistence of γ-halo interaction was seen to be prominent. Moreover, for each neutral and cationic complex, the values of Wiberg bond order are in good agreement with the AIM results. The effect of the metal center, as well as γ-halogen substitution, on γ-halo interaction was also studied in the present work. To justify the practical subsistence of the halo-conformers, we checked the stability of the conformers with respect to their ß-conformers by comparing the zero-point-corrected electronic energies. Therefore, the entire study was designed in such a way that it can provide evidence in support of intramolecular M⋯X-C interactions, where, instead of the C-H bond, the Cγ-X bond will interact with the central transition metal.

Cardiac surgery in octogenarians.

The incidence of cardiac surgery in elderly patients has been increasing. Recent studies have shown that cardiac surgical procedures performed in octogenarians, in otherwise good physical and mental health, can improve mortality, morbidity, and quality of life. This study aimed to describe the preoperative clinical and demographic characteristics associated with immediate postoperative outcomes and determine whether intra-operative factors related to surgical and cardiopulmonary by-pass techniques impacted upon these. The results of cardiac surgeries performed at BM Birla Heart Research Centre, Kolkata for patients older than 80 years were retrospectively analysed between January 2009 and September 2011. Out of 61 cases, rate of hospital death, prolonged stay (length of stay > 14 days), return to intensive care unit were as follows: 2 (3.2%), 30 (49.1%), 3 (4.9%). Eight patients (13.1%) developed pulmonary, 5 (8.1%) renal and 1 (1.6%) gastro-intestinal complications. Two patients (3.2%) developed neurological defecit. Thus, newer techniques in cardiac surgical procedures are successful in most octogenarians with increased hospital morbidity, and longer hospital stay.

Echocardiographic evaluation and comparison of the effects of isoflurane, sevoflurane and desflurane on left ventricular relaxation indices in patients with diastolic dysfunction.

This prospective randomized study aims to evaluate and compare the effects of isoflurane, sevoflurane and desflurane (study drugs) on left ventricular (LV) diastolic function in patients with impaired LV relaxation due to ischemic heart disease using transesophageal Doppler echocardiography. After approval of the local ethics committee and informed consent, 45 patients scheduled for coronary artery bypass grafting surgery were enrolled in the study. Patients were selected by a preoperative Transthoracic Echocardiographic diagnosis of impaired relaxation or Grade 1 Diastolic Dysfunction. They randomly received fentanyl and midazolam anesthesia with 1 MAC of isoflurane (n=16), sevoflurane (n=14) or desflurane (n=15). Hemodynamic parameters and TEE derived ventricular diastolic relaxation indices before and after the study drug administration were compared. LV filling pressures were kept constant throughout the study period to exclude the effect of the loading conditions on diastolic function. Four patients in the sevoflurane group and three in the desflurane group were excluded from the study, after baseline TEE examination revealed normal diastolic filling pattern. All the three study drugs significantly reduced the systemic vascular resistance index with a significant increase in cardiac index. Mean arterial pressure was reduced by all the drugs, although the decrease was not statistically significant. Hemodynamic changes were comparable between all the three groups. In terms of LV relaxation indices, all three agents led to a significant improvement in diastolic function. Transmitral and Tissue Doppler E/A and Em/Am ratios improved significantly Transmitral and Tissue Doppler E/A and Em/Am ratios improved significantly accompanied by a significant decrease in deceleration time and isovolumetric relaxation time. The effect of all three agents on diastolic relaxation parameters was comparable. In conclusion , Isoflurane, sevoflurane and desflurane, do not appear to have a detrimental effect in patients with early diastolic dysfunction. On the contrary, these inhalational agents actually improve the LV relaxation. A significant reduction in afterload produced by these vapors can be a possible reason for these findings. The positive effect of these inhalational agents on LV relaxation can have a profound effect on the perioperative anesthetic management of patients with diastolic dysfunction.