The formation of a Sn monolayer on Ge(1 0 0) studied at the atomic scale

The growth of multi-layer germanium-tin (GeSn) quantum wells offers an intriguing pathway towards the integration of lasers in a CMOS platform. An important step in growing high quality quantum well interfaces is the formation of an initial wetting layer. However, key atomic-scale details of this process have not previously been discussed. We use scanning tunneling microscopy combined with density functional theory to study the deposition of Sn on Ge(1 0 0) at room temperature over a coverage range of 0.01 to 1.24 monolayers. We demonstrate the formation of a sub-2% Ge content GeSn wetting layer from three atomic-scale characteristic ad-dimer structural components, and show that small quantities of Sn incorporate into the Ge surface forming two atomic configurations. The ratio of the ad-dimer structures changes with increasing Sn coverage, indicating a change in growth kinetics. At sub-monolayer coverage, the least densely packing ad-dimer structure is most abundant. As the layer closes, forming a two-dimensional wetting layer, the more densely packing ad-dimer structure become dominant. These results demonstrate the capability to form an atomically smooth wetting layer at room temperature, and provide critical atomic-scale insights for the optimization of growth processes of GeSn multi-quantum-wells to meet the quality requirements of optical GeSn-based devices

Responses of Arabica coffee (Coffea arabica L. var. Catuaí) cell suspensions to chemically induced mutagenesis and salinity stress under in vitro culture conditions

Crop improvement of Coffea arabica L. (coffee) via mutagenesis could accelerate breeding programs; thus, the present study aimed to develop an in vitro protocol using the chemical mutagens sodium azide (NaN3) and ethyl methanesulfonate (EMS) on embryogenic cell suspensions of Arabica coffee variety Catuaí and, subsequently, to evaluate the responses of the resulting mutagenized tissues to salinity stress. Embryogenic suspension cultures were incubated with 0.0, 2.5, 5.0, or 10.0 mM NaN3 or 0.0, 185.2, 370.5, or 741.0 mM EMS. As the concentration of NaN3 or EMS increased, the survival of embryogenic suspension cultures decreased compared to controls. The median lethal dose (LD50) for NaN3 was 5 mM for 15 min and for EMS it was 185.2 mM for 120 min. Embryogenic suspension cultures treated with NaN3 or EMS were cultured on selective medium supplemented with 0, 50, 100, 150, 250, or 300 mM NaCl showed that 50 mM NaCl could be used as selection pressure. Plantlet growth and total amino acid content were affected by NaCl stress; some mutants had longer shoots and higher amino acid content than controls. Random amplified polymorphic DNA (RAPD) analysis was performed to determine whether the NaN3 or EMS treatments could induce genetic variability and resulted in identifiable polymorphic markers. A total of 18 10-mer primers were used to amplify genomic DNA of putative mutant and non-mutant arabica coffee embryogenic cultures and produced 50 scorable bands, of which 22% were polymorphic.Universidad de Costa Rica/[111-B5-140]/UCR/Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí