Nonvolatile memory with molecule-engineered tunneling barriers

We report a novel field-sensitive tunneling barrier by embedding C60 in SiO2 for nonvolatile memory applications. C60 is a better choice than ultra-small nanocrystals due to its monodispersion. Moreover, C60 provides accessible energy levels to prompt resonant tunneling through SiO2 at high fields. However, this process is quenched at low fields due to HOMO-LUMO gap and large charging energy of C60. Furthermore, we demonstrate an improvement of more than an order of magnitude in retention to program/erase time ratio for a metal nanocrystal memory. This shows promise of engineering tunnel dielectrics by integrating molecules in the future hybrid molecular-silicon electronics.Comment: to appear in Applied Physics Letter

50 mm diameter Sn-doped (001) beta-Ga2O3 crystal growth using the vertical Bridgeman technique in ambient air

Available online 3 July 202050 mm-diameter Sn-doped beta-Ga2O3 crystals with growth orientation perpendicular to (001) plane were grown with the newly-developed resistance heating vertical Bridgeman furnace using platinum-rhodium alloy crucibles in ambient air. Weak low angle grain boundaries and several small grains were detected on the both-side mirror polished 50 mm-diameter (001) wafer, using high resolution refraction x-ray topography. However, no imperfections were observed over the whole wafer area when using crossed polarizer analysis. Measured values of both the full width at half maximum and the dislocation densities were widely distributed in the wafer, ranging from 10 to 50 arcsec and 100 to 2000/cm(2) respectively with no distinctive correlations among them. The Sndoped crystals with concentrations ranging from 5 x 10(17) to 5 x 10(18) atom/cm(3) could be grown by Sn-doping in a range from 0.05 to 0.1 mol%, and (001) oriented, 50 mm-diameter n-type oxide semiconductor wafers with a carrier density of 3.6 x 10(18)/cm(3), a mobility of 60 cm(2)/Vsec and a resistivity of 0.03 Omega.cm, were obtained from a 0.1 mol% Sn-doped crystal.ArticleJOURNAL OF CRYSTAL GROWTH.546:125778(2020)journal articl

2-inch diameter (100) β-Ga2O3 crystal growth by the vertical Bridgman technique in a resistance heating furnace in ambient air

Available online 20 May 2020ArticleJOURNAL OF CRYSTAL GROWTH.545:125724(2020)journal articl

Morphology and formation mechanism of metallic inclusions in VB-grown sapphire crystals

Morphologies of metallic inclusions observed in sapphire crystals grown by the vertical Bridgman (VB) technique using a tungsten (W) crucible were investigated. Square- or hexagonal-shaped inclusions 2-5 mu m in size were observed in sapphire crystals around the interface between the seed and the grown crystal. It was found that such inclusions consisted of W metal used for the crucible. The morphology of some of the inclusions reflects a rhombic dodecahedron which is based on the cubic structure of W and is surrounded by {110} faces. It is probable that inclusions form in the sapphire melt during the crystal growth process, and then sink in the melt to the growth interface due to the high density of W. (C) 2013 Elsevier B.V. All rights reserved.JOURNAL OF CRYSTAL GROWTH. 401:388-391 (2014)journal articl

Hydrogeochemical and anthropogenic influence on the quality of water sources in the Rio del Rey Basin, South Western, Cameroon, Gulf of Guinea

This study which focuses on the hydrogeochemical and anthropogenic influence on water sources in the Rio del Rey Basin has provided an insight into the sources of major ions, water mineralisation processes, and the suitability of the water sources for drinking and agricultural purposes. Fifty-one (51) samples (38 groundwater, 9 surface water, 1 tap, 1 reservoir and 2 rainfall events) were analysed for physico-chemical and microbial quality. The pH of groundwater samples ranged from 5.5 to 8. Sixty percent (60%) of the groundwater samples were slightly acidic (5.5-6.4) and were different from the WHO (2004) standard for drinking water. Electrical conductivity values (3-274 μS/cm) and total dissolved solids (7.66 to 248.30 mg/l) for groundwater sources were low and signified low mineralisation and freshwater conditions. The relative abundance of major ions (meq/l) was Na+>K+>Mg2+>Ca2+ for cations and HCO3->NO3->SO42->Cl- for anions. The main water types were: Na-HCO3 (45%), Ca-HCO3 (35%), Na- Ca-HCO3 (15%), Ca-Mg-Cl (2%) and NaCl (2%). The processes that influenced the water chemistry were incongruent silicate dissolution and cation exchange. The chemical constituents were low and within the WHO (2004) guidelines for drinking water except for high concentrations of NO3- (77.28 mg/l) and Br- (0.08 mg/l) in one open well. Water quality index calculated using the adjusted form of CCME (2001) based on the major and chemical parameters (TDS, pH, F- and Br-) for groundwater and surface water data indicated that 90, 6, 2 and 2% provided excellent, good, marginal and poor water quality, respectively for drinking purposes. The evaluation of results showed that 90% of groundwater sources were suitable for agricultural purposes. Total coliform counts indicated that 97% of the groundwater sources were polluted.Key words: Groundwater chemistry, microbial quality, anthropogenic influence, Rio del Rey Basin

Estimation of Buttiker-Landauer traversal time based on the visibility of transmission current

We present a proposal for the estimation of B\"uttiker-Landauer traversal time based on the visibility of transmission current. We analyze the tunneling phenomena with a time-dependent potential and obtain the time-dependent transmission current. We found that the visibility is directly connected to the traversal time. Furthermore, this result is valid not only for rectangular potential barrier but also for general form of potential to which the WKB approximation is applicable . We compared these results with the numerical values obtained from the simulation of Nelson's quantum mechanics. Both of them fit together and it shows our method is very effective to measure experimentally the traversal time.Comment: 12 pages, REVTeX, including 7 eps figure

Vertical Bridgman growth of sapphire crystals, with thin-neck formation process

A new technique is proposed in the traditional vertical Bridgman growth of sapphire crystals, in which thin-neck formation follows the initial seeding. Low-angle grain boundaries generated at the periphery of the seeding interface were eliminated at the thin neck, and the c-axis sapphire crystals with main bodies free from low-angle grain boundaries were grown.ArticleJOURNAL OF CRYSTAL GROWTH. 401:146-149 (2014)journal articl

Growth of β-Ga2O3 single crystals using vertical Bridgman method in ambient air

A new approach to beta-Ga2O3 single crystal growth was studied, using the vertical Bridgman (VB) method in ambient air, while measuring the beta-Ga2O3 melting temperature and investigating the effects of crucible composition and shape. beta-Ga2O3 single crystals 25 mm in diameter were grown in platinum rhodium alloy crucibles in ambient air, with no adhesion of the crystals to the crucible wall. Single crystal growth without a crystal seed was realized by (100) faceted growth with a growth direction perpendicular to the (100) faceted plane. (C) 2016 Elsevier B.V. All rights reserved.ArticleJOURNAL OF CRYSTAL GROWTH.447:36-41(2016)journal articl

Water as a potential molecular probe for functional groups on carbon surfaces

A new and simple method, using water as a potential molecular probe, is proposed for the determination of the concentration of surface oxygen groups on carbon adsorbents. The procedure is based on a determination of the Henry constant between a water molecule and a functional group from the volume integration of the Boltzmann factor over the accessible space around the functional group. Three porous carbons are used in this study to test the new method: A-5, RF-100 and RF-200. The results obtained are in good agreement with those measured by Boehm titration. This new method can be applied to adsorbents containing small concentrations of oxygen groups where the Boehm titration method may give unreliable results