STM Spectroscopy of ultra-flat graphene on hexagonal boron nitride

Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy-momentum dispersion relations which cross at the Dirac point. However, accessing the physics of the low density region at the Dirac point has been difficult because of the presence of disorder which leaves the graphene with local microscopic electron and hole puddles, resulting in a finite density of carriers even at the charge neutrality point. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance. In this letter, we use scanning tunneling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moire patterns in the topographic images. However, contrary to recent predictions, this conformation does not lead to a sizable band gap due to the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron-hole charge fluctuations are reduced by two orders of magnitude as compared to those on silicon oxide. This leads to charge fluctuations which are as small as in suspended graphene, opening up Dirac point physics to more diverse experiments than are possible on freestanding devices.Comment: Nature Materials advance online publication 13/02/201

Design and Optimization of Bicycle Frame for the Cyclist's Comfort

Bicycle plays an inherent role in our life. Bicycle riding is a globally popular sport and an economic transportation. The performance of frame is depends on the weight of the bicycle and frame design. Optimization of weight and structure of the bicycle frame is the best scope of optimizing the overall performance of the bicycle. When the rider ridding bicycle on rough surface, the induced vibrations will cause the fatigue of its rider and the fracture of its frame structure. This paper deals with the study of the structural design, modal analysis and optimization of bicycle frame by using composite material with help of FEA. Firstly structural analysis, numerical results obtained by applying dynamic loading condition. Secondly, the Modal analysis is used to identify modes of bicycle frame to calculate natural frequencies and mode shapes by using Finite Element Analysis. Finally, the analyzed frames are then optimized to reduce weight without affecting their capacity to be resistant to mechanical stresses

Probing the Relationship between Defects and Enhanced Mobility in MoS2 Monolayers Grown by Mo Foil

Atomic vacancies, such as chalcogen vacancies in 2D TMDs, are important in changing the host material's electronic structure and transport properties. We present a straightforward one-step method for growing monolayer MoS2 utilizing oxidized Molybdenum (Mo) foil using CVD and delve into the transport properties of as-grown samples. Devices fabricated from these MoS2 sheets exhibit excellent electrical responses, with the standout device achieving mobility exceeding 100 cm2V-1s-1. Structural analysis and optical signatures unveiled the presence of chalcogen defects within these samples. To decipher the influence of inherent defects on the electronic transport properties, we measured low-temperature transport on two distinct sets of devices exhibiting relatively high or low mobilities. Combining the thermally activated transport model with quantum capacitance calculations, we have shown the existence of shallow states near the conduction band, likely attributed to sulfur vacancies within MoS2. These vacancies are responsible for the hopping conduction of electrons in the device channel. Furthermore, our claims were substantiated through low-temperature scanning tunnelling microscopy measurements, which revealed an abundance of isolated and lateral double sulfur vacancies in Mo foil-grown samples. We found that these vacancies increase the density of states near the conduction band, inducing intrinsic n-type doping in the MoS2 channel. Consequently, this elevated conductivity enhances the field-effect mobility of MoS2 transistors. Our study offers insights into chalcogen vacancies in CVD-grown monolayer MoS2 and highlights their beneficial impact on electronic transport properties

Valorization of Sorghum Stalk Residues for Bioethanol Production: A Sustainable Pathway to Agricultural Waste-to-Energy Conversion

The renewable biomass waste from sorghum stalks, which farmers burn in open fields, results in environmental harm. Flexible approaches for waste energy conversion generate efficient second-generation bioethanol from sorghum stalks. This study explores the sustainable bioethanol production from sorghum stalk waste through optimized CaO alkali pretreatment. Scientists studied sorghum stalks, which constitute agricultural waste, as a raw material for lignocellulosic content determination to identify their high levels of cellulose (38.3%) and hemicellulose (27.4%). A pretreatment using 2% w/v CaO solution resulted in the greatest total sugar production of 465.2 mg/g, together with maximum reducing sugar level at 297.4 mg/g. The glucose yield from pretreated biomass increased to 318.7 mg/g after enzymatic hydrolysis was performed. After 72 hours of Saccharomyces cerevisiae fermentation of the hydrolysate, an ethanol concentration of 19.6 g/L was attained, reaching a theoretical yield of 78.4%. The total reducing sugar recovery rate throughout pretreatment came to 91.6%, and the reducing sugar recovery rate marked 86.5%, but during hydrolysis, the recovery reached 88.3% (total sugar) and 84.1% (reducing sugar). Scientists have determined the renewable energy potential of sorghum bioethanol by establishing that it provides 13.9 MJ of energy for every kilogram of dry biomass. Therefore, this studyindicates that the proposed process delivers both economical benefits and environmental advantages according to assessed technical-economic calculations. Also, the study establishes that transforming sorghum stalk waste into bioethanol is possible through this process, which benefits sustainable agricultural systems and the circular bioeconomy framework and contributes to worldwide renewable energy system development with low-carbon emissions goals