Metal semiconductor metal photodiodes based on all-epitaxial Ge-on-insulator-on-Si(111), grown by molecular beam epitaxy

We report on the fabrication and characterisation of an all-epitaxial Germanium-on-Insulator (GOI) Metal-Semiconductor-Metal (MSM) photodetector. The MSM photodetector is fabricated on a (111)-oriented epitaxial Ge layer, grown on an epitaxial Gd 2 O 3 /Si(111) substrate, by molecular beam epitaxy (MBE). The first step is the growth of the 15-nm thick Gd 2 O 3 epitaxial layer over CMOS-grade silicon, atop which an epitaxial layer of Ge is grown. Near infrared (NIR) MSM photodetectors have been fabricated over the Ge epitaxial layer with an inter-digitated (IDT) contact structure, with an active area of 100 μm x 124 μm. For the particular IDT dimensions, the dark current has been measured to be 475 μA. A responsivity of ∼ 2 mA/W is observed at a-5V bias, when excited at 1550 nm. © 2019 SPIE

Molecular beam epitaxy and defect structure of Ge (111)/epi-Gd2O3 (111) /Si (111) heterostructures

Molecular beam epitaxy of Ge (111) thin films on epitaxial-Gd2O3/Si(111) substrates is reported, along with a systematic investigation of the evolution of Ge growth, and structural defects in the grown epilayer. While Ge growth begins in the Volmer-Weber growth mode, the resultant islands coalesce within the first 10 nm of growth, beyond which a smooth two-dimensional surface evolves. Coalescence of the initially formed islands results in formation of rotation and reflection microtwins, which constitute a volume fraction of less than 1 %. It is also observed that while the stacking sequence of the (111) planes in the Ge epilayer is similar to that of the Si substrate, the (111) planes of the Gd2O3 epilayer are rotated by 180 degree about the [111] direction. In metal-semiconductor-metal schottky photodiodes fabricated with these all-epitaxial Ge-on-insulator (GeOI) samples, significant suppression of dark current is observed due to the presence of the Gd2O3 epilayer. These results are promising for application of these GeOI structures as virtual substrates, or for realization of high-speed group-IV photonic components.Comment: 15 pages, 6 figure

Barnyard grasses were processed with rice around 10000 years ago

Rice (Oryza sativa) is regarded as the only grass that was selected for cultivation and eventual domestication in the Yangtze basin of China. Although both macro-fossils and micro-fossils of rice have been recovered from the Early Neolithic site of Shangshan, dating to more than 10,000 years before present (BP), we report evidence of phytolith and starch microfossils taken from stone tools, both for grinding and cutting, and cultural layers, that indicating barnyard grass (Echinochloa spp.) was a major subsistence resource, alongside smaller quantities of acorn starches (Lithocarpus/Quercus sensu lato) and water chestnuts (Trapa). This evidence suggests that early managed wetland environments were initially harvested for multiple grain species including barnyard grasses as well as rice, and indicate that the emergence of rice as the favoured cultivated grass and ultimately the key domesticate of the Yangtze basin was a protracted process

Journey to the east: Diverse routes and variable flowering times for wheat and barley en route to prehistoric China.

Today, farmers in many regions of eastern Asia sow their barley grains in the spring and harvest them in the autumn of the same year (spring barley). However, when it was first domesticated in southwest Asia, barley was grown between the autumn and subsequent spring (winter barley), to complete their life cycles before the summer drought. The question of when the eastern barley shifted from the original winter habit to flexible growing schedules is of significance in terms of understanding its spread. This article investigates when barley cultivation dispersed from southwest Asia to regions of eastern Asia and how the eastern spring barley evolved in this context. We report 70 new radiocarbon measurements obtained directly from barley grains recovered from archaeological sites in eastern Eurasia. Our results indicate that the eastern dispersals of wheat and barley were distinct in both space and time. We infer that barley had been cultivated in a range of markedly contrasting environments by the second millennium BC. In this context, we consider the distribution of known haplotypes of a flowering-time gene in barley, Ppd-H1, and infer that the distributions of those haplotypes may reflect the early dispersal of barley. These patterns of dispersal resonate with the second and first millennia BC textual records documenting sowing and harvesting times for barley in central/eastern China

The virtues of small grain size: Potential pathways to a distinguishing feature of Asian wheats

Increase in grain/seed size recurrently features as a key element in the ‘domestication syndrome’ of plants (cf. Zohary and Hopf 2000; Fuller et al. 2014). In the context of its spread across Eurasia, however, the grain size of one of the world's major crop species underwent a substantial reduction. Between the fifth and second millennia BC, the grain length in a number of species of Triticum, collectively known as free-threshing wheat, decreased by around 30%. In order to understand and help account for this trend, we have obtained direct radiocarbon measurements from 51 charred wheat grains and measured the dimensions of several hundred grains from Asia to establish when and where that size diminution occurred. Our results indicate that the pace of a eastward/southward spread was interrupted around 1800 BC on the borders of the distinct culinary zone recognized by Fuller and Rowlands (2011), but regained pace around 200–300 years later in central-east China with a diminished grain size. We interpret this as evidence of a period of active crop selection to suit culinary needs, and consider whether it constitutes a distinct episode in the general character of genetic intervention in domesticated species.Financial support was provided by the European Research Council, under grant 249642 (FOGLIP), UKIERI – UK & India Collaborative Educational Research Initiative, and the International Center for Advanced Renewable Energy and Sustainability, Washington University in St. Louis

Early agriculture in Sri Lanka:New Archaeobotanical analyses and radiocarbon dates from the early historic sites of Kirinda and Kantharodai (Kandarodai)

Archaeobotanical evidence from two Early Historic sites in Sri Lanka, Kantharodai and Kirinda, is reported, providing significant evidence for agricultural diversity beyond the cultivation of rice. These data highlight the potential of systematic archaeobotanical sampling for macro-remains in tropical environments to contribute to the understanding of subsistence history in the tropics. Direct AMS radiocarbon dating confirms both the antiquity of crops and refines site chronologies. Both sites have Oryza sativa subsp. indica rice and evidence of rice crop-processing and millet farming. In addition, phytolith data provide complementary evidence on the nature of early rice cultivation in Sri Lanka. Both Kantharodai and Kirinda possess rice agriculture and a diverse range of cultivated millets (Brachiaria ramosa, Echinochloa frumentacea, Panicum sumatrense, and Setaria verticillata). Pulses of Indian origin were also cultivated, especially Vigna radiata and Macrotyloma uniflorum. Cotton (Gossypium sp.) cultivation is evident from Kirinda. Both sites, but in particular Kirinda, provide evidence for use of the seeds of Alpinia sp., in the cardamom/ginger family (Zingiberaceae), a plausible wild spice, while coconuts (Cocos nucifera) were also found at Kirinda

Correction: Journey to the east: Diverse routes and variable flowering times for wheat and barley en route to prehistoric China.

[This corrects the article DOI: 10.1371/journal.pone.0187405.]

Between China and South Asia: A Middle Asian corridor of crop dispersal and agricultural innovation in the Bronze Age

© The Author(s) 2016. The period from the late third millennium BC to the start of the first millennium AD witnesses the first steps towards food globalization in which a significant number of important crops and animals, independently domesticated within China, India, Africa and West Asia, traversed Central Asia greatly increasing Eurasian agricultural diversity. This paper utilizes an archaeobotanical database (AsCAD), to explore evidence for these crop translocations along southern and northern routes of interaction between east and west. To begin, crop translocations from the Near East across India and Central Asia are examined for wheat (Triticum aestivum) and barley (Hordeum vulgare) from the eighth to the second millennia BC when they reach China. The case of pulses and flax (Linum usitatissimum) that only complete this journey in Han times (206 BC–AD 220), often never fully adopted, is also addressed. The discussion then turns to the Chinese millets, Panicum miliaceum and Setaria italica, peaches (Amygdalus persica) and apricots (Armeniaca vulgaris), tracing their movement from the fifth millennium to the second millennium BC when the Panicum miliaceum reaches Europe and Setaria italica Northern India, with peaches and apricots present in Kashmir and Swat. Finally, the translocation of japonica rice from China to India that gave rise to indica rice is considered, possibly dating to the second millennium BC. The routes these crops travelled include those to the north via the Inner Asia Mountain Corridor, across Middle Asia, where there is good evidence for wheat, barley and the Chinese millets. The case for japonica rice, apricots and peaches is less clear, and the northern route is contrasted with that through northeast India, Tibet and west China. Not all these journeys were synchronous, and this paper highlights the selective long-distance transport of crops as an alternative to demic-diffusion of farmers with a defined crop package

Structure and reactivity of di-<i>n</i>-butyltin(IV) derivative of chlordiazepoxide based on electronic structure calculations

938-949Density functional theory calculations in electronic structure studies of n-Bu2SnL2 (where L is the monoanion of chlordiazepoxide (LH), a benzodiazepine derivative with hypnotic action) have been reported using the Gaussian09 software. The molecular geometries of LH and tetrahedral n-Bu2SnL2 have been optimized at B3LYP/6-31G(d,p) and B3LYP/6-31G(d,p)/Def2-SVP(Sn) level of theory, respectively. Harmonic vibrational frequencies are computed at the same level of theory to find the true potential energy surface minima. The effect of functional, basis set and computational cost is analyzed. The various geometrical and thermochemical parameters have been obtained in gas phase and in the solvent. The atomic charges at all the atoms are calculated using Mulliken population analysis, Hirshfeld population analysis and natural population analysis. The charge distribution within the studied complex is explained on the basis of molecular electrostatic potential maps, and conceptual-DFT based global reactivity descriptors using the finite difference approximation method. The calculated parameters suggest a distorted tetrahedral geometry around the central Sn atom. The calculated Sn-O bond lengths reveals different degree of interaction of two chlordiazepoxide units with the di-n-butyltin(IV) moiety. Among the atoms coordinated to the central Sn atom, oxygen from one LH unit is nucleophilic, whereas the second oxygen atom from the other LH unit is electrophilic in nature. The results provide an insight into the efficacy of computational methods in understanding the structure and reactivity of organotin(IV) derivatives of hetero donor atoms