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This work reports a comparative study of laser ion implantation mainly performed at the Nuclear Physics Institute in Rez (Czech Republic), National Institute of Nuclear Physics (Italy), and the Plasma Physics Laboratory at the University of Messina (Italy) using different approaches. Thick metallic targets were irradiated in vacuum by a focused laser beam to generate plasma-producing multi-energy and multi-species ions. A post-acceleration system was employed in order to increase the energy of the produced ions and to generate ion beams suitable to be implanted in different substrates. The ion dose was controlled by the laser repetition rate and the time of irradiation. Rutherford backscattering analysis was carried out to evaluate the integral amount of implanted ion species, the concentration–depth profiles, the ion penetration depth, and the uniformity of depth profiles for ions laser implanted into monocrystalline substrates. The laser implantation under normal conditions and in post-acceleration configuration will be discussed on the basis of the characterization of the implanted substrates.
Semiconducting and insulating polymers and copolymers/Au nanograins based hybrid multilayers (HyMLs) were fabricated on p-Si single-crystal substrate by an iterative method that involves, respectively, Langmuir-Blodgett and spin-coating techniques (for the deposition of organic film) and sputtering technique (for the deposition of metal nanograins) to prepare Au/HyMLs/p-Si Schottky device. The electrical properties of the Au/HyMLs/p-Si Schottky device were investigated by current-voltage (I–V) measurements in the thickness range of 1-5 bilayers (BL).
At different number of layers, current-voltage (I–V) measurements were performed. Results showed a rectifying behavior. Junction parameters, such as barrier height (BH), from the I–V measurements for example for the PMMA-b-PS based Au/HyMLs/p-Si structure were obtained as 0.72±0.02 eV at 1BL and 0.64±0.02eV at 5BL. It was observed that the BH value of 0.61 eV obtained for the 5 BL PS based Au/HyMLs/p-Si structure was lower than the value of 0.68 eV of conventional Au/p-Si Schottky diodes. Thus, modification of the interfacial potential barrier for Au/p-Si diodes has been achieved using a thin MLs of different polymers based HyMls semiconductor.
We report on the results concerning the characteristics and the
behavior of expanding plasma generated by a Laser Ion Source (LIS). The
LIS technique is an efficient means in producing of multi-charged ions
utilizing pulsed laser beams. In order to extract Cu ions, in this
experiment an XeCl excimer UV laser was employed, providing a power
density on the target surface up to 5 × 108
W/cm2. Two typologies of diagnostic systems were
developed in order to detect the plasma current and the ion energy. The
time-of-flight (TOF) measurements were performed exploiting either a
Faraday cup or an Ion Energy Analyzer (IEA). This latter allowed
getting quantitative information about the relative ion abundances,
their kinetic energy and their charge state. To study the plasma
characteristics we measured the total etched material per pulse at 70
mJ. It was 0.235 μg and the overall degree of ionization, 16%. The
angular distribution of the ablated material was monitored by optical
transmission analysis of the deposited film as a function of the angle
with respect to the normal to the target surface. Applying a high
voltage to an extraction gap a multi-charged ion beam was obtained;
different peaks could be distinguished in the TOF spectrum, resulting
from the separation of ions of hydrogen, adsorbed compounds in the
target and copper.
Colonization of roots by arbuscular mycorrhizal (AM) fungi in several annual crops in two consecutive seasons was
compared with, in the second season, the density of fungal propagules in the soil with the use of a bioassay. Root
density decreased down the soil profile in both years in all crops, and a high proportion of roots were mycorrhizal
throughout the profile. AM colonization decreased down the profile in cotton and lablab in the second season only.
The bioassay indicated that most propagules of AM fungi in soils under cotton were located near the surface, with
virtually no propagules at 1 m. The absence of propagules at depth indicates a lack of mycelium deep in the soil,
and suggests that mycorrhizas are primarily initiated in the surface soil and that the fungi colonize the root system
mostly through secondary spread down the profile. The use of AM colonization in the field as an indicator of
propagule density and symbiotic function should be qualified by an understanding of the depth in the soil from
which roots were extracted.
In an experiment to determine the influence of mycorrhizal colonization on root development, fertilized seedlings
of cotton were grown in long tubular pots. Inoculation of soil with an isolate of Glomus mosseae at 10, 25 or 40 cm
below the soil surface resulted in spread of arbuscular mycorrhizas up and down the root system, and localized
elongation of roots following colonization. Specific root length was not influenced by colonization. Increases in
local root density at the point of inoculation were observed, though total root mass in relation to shoot mass
declined following initiation of mycorrhizas.
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