Magnetic properties of epitaxial single crystal ultrathin Fe\u3csub\u3e3\u3c/sub\u3eSi films on GaAs (001)

Magnetic properties of Fe3Si films with thickness from 2 to 210 monolayers (ML) epitaxially grown on GaAs (001) were studied using a superconducting quantum interference device and alternating gradient force magnetometers. Growth of these single-crystal intermetallic compound films were carried out in a multichamber molecular beam epitaxy (MBE) system. The samples were covered in situ with Au 50 Å thick to prevent oxidation when the samples were removed from the MBE chamber. All the films are ferromagnetic even for samples as thin as 2 ML. The easy magnetization direction of the films is parallel to the film surface. The magnetic coercivity forces (Hc) of the samples increase as the film thickness decreases to 10 ML, and then decrease when the film thickness decreases further to 2 ML

Understorey plant community and light availability in conifer plantations and natural hardwood forests in Taiwan

Questions: What are the effects of replacing mixed species natural forests with Cryptomeria japonica plantations on understorey plant functional and species diversity? What is the role of the understorey light environment in determining understorey diversity and community in the two types of forest? Location: Subtropical northeast Taiwan. Methods: We examined light environments using hemispherical photography, and diversity and composition of understorey plants of a 35‐yr C. japonica plantation and an adjacent natural hardwood forest. Results: Understorey plant species richness was similar in the two forests, but the communities were different; only 18 of the 91 recorded understorey plant species occurred in both forests. Relative abundance of plants among different functional groups differed between the two forests. Relative numbers of shade‐tolerant and shade‐intolerant seedling individuals were also different between the two forest types with only one shade‐intolerant seedling in the plantation compared to 23 seedlings belonging to two species in the natural forest. In the natural forest 11 species of tree seedling were found, while in the plantation only five were found, and the seedling density was only one third of that in the natural forest. Across plots in both forests, understorey plant richness and diversity were negatively correlated with direct sunlight but not indirect sunlight, possibly because direct light plays a more important role in understorey plant growth. Conclusions: We report lower species and functional diversity and higher light availability in a natural hardwood forest than an adjacent 30‐yr C. japonica plantation, possibly due to the increased dominance of shade‐intolerant species associated with higher light availability. To maintain plant diversity, management efforts must be made to prevent localized losses of shade‐adapted understorey plants

INFLUENCE OF STEEL ALLOY COMPOSITION ON THE PROCESS ROBUSTNESS OF AS-BUILT HARDNESS IN LASER-DIRECTED ENERGY DEPOSITION

To ensure consistent quality of additively manufactured parts, it is advantageous to identify alloys which can meet performance criteria while being robust to process variations. Toward such an end, this work studied the effect of steel alloy composition on the process robustness of as-built hardness in laser-directed energy deposition (L-DED). In-situ blending of ultra-high-strength lowalloy steel (UHSLA) and pure iron powders produced 10 alloys containing 10-100% UHSLA by mass. Thin-wall samples were deposited, and the hardness sensitivity of each alloy was evaluated with respect to laser power and interlayer delay time. The sensitivity peaked at 40-50% UHSLA, corresponding to phase fluctuations between lath martensite and upper bainite depending on the cooling rate. Lower (10-20%) or higher (70-100%) alloy contents transformed primarily to ferrite or martensite, respectively, with auto-tempering of martensite at lower cooling rates. By avoiding martensite/bainite fluctuations, the robustness was improved.Mechanical Engineerin

Noise measurement of YBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7-χ\u3c/sub\u3e and Ti\u3csub\u3e2\u3c/sub\u3eBa\u3csub\u3e2\u3c/sub\u3eCa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e10-χ\u3c/sub\u3e thin films

The noise of YBa2Cu3O7-χ and Ti2Ba2Ca2Cu2O10-χ thin films in the frequency range from 0.5 Hz to 100 kHz was studied. In the normal state, it was found that 1/f noise dominated, with a magnitude strongly dependent on temperature. In the superconducting state, the noise was only observable at frequencies below 5 Hz with our present setup. Equilibrium thermal fluctuation noise was not observed in these films

Magnetic properties of epitaxial single crystal ultrathin Fe\u3csub\u3e3\u3c/sub\u3eSi films on GaAs (001)

Magnetic properties of Fe3Si films with thickness from 2 to 210 monolayers (ML) epitaxially grown on GaAs (001) were studied using a superconducting quantum interference device and alternating gradient force magnetometers. Growth of these single-crystal intermetallic compound films were carried out in a multichamber molecular beam epitaxy (MBE) system. The samples were covered in situ with Au 50 Å thick to prevent oxidation when the samples were removed from the MBE chamber. All the films are ferromagnetic even for samples as thin as 2 ML. The easy magnetization direction of the films is parallel to the film surface. The magnetic coercivity forces (Hc) of the samples increase as the film thickness decreases to 10 ML, and then decrease when the film thickness decreases further to 2 ML

Structure of Sc\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e films epitaxially grown on α -Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e (0001)

The crystal structure of scandium oxide films epitaxially grown on α -Al2O3 (0001) under an ultrahigh-vacuum is studied by single-crystal x-ray diffraction. The Sc2O3 film grows in bixbyite phase on the basal (0001) surface of the sapphire substrate with its (111) axis aligned parallel to the substrate normal. In-plane orientation of the film, however, exhibits two distinct growth directions that are defined by the two possible surface orientations of the stepped α -Al2O3 substrate. The atomic structure of the high-quality epitaxial film is fully relaxed and the film has unusual thickness uniformity