We report waveguides in Ni-doped Li sub(2)O-Ga sub(2)O sub(3)-SiO sub(2 ) (Ni:LGS) glass and glass-ceramic (GC) fabricated with a femtosecond (fs) laser with repetition rate of 1 kHz. When the glass ...is annealed to form a GC, the waveguides are erased. However, in the GC the waveguides are not erased by annealing. In Ni:LGS GC a 415 nm absorption band was created by fs laser waveguide writing due to the creation of Ni nanoparticles with an estimated diameter of a few nm. Raman and photoluminescence spectra of the bulk and waveguide structures were indistinguishable; however, fluorescence decay profiles indicated more long lifetime components in the waveguide compared to the bulk.
Ion implantation and thermal annealing effects on composition and structure of Ni/Ti multilayer have been studied and reported in this paper. The thin films composed of five (Ni/Ti) bilayers were ...deposited by d.c. ion sputtering on (100) Si wafers to a total thickness of ∼180 nm. Ion irradiations were performed by 180 keV Ar+ ions with fluence of 6 × 1016 ions cm−2. After deposition and implantation, the samples were annealed at 400 °C for 30 min in an inert ambient. Composition and structural characterizations were performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Annealing of as-deposited samples at 400 °C induces a progressed interaction between Ni and Ti layers with the initial formation of NiTi alloy phase. Progressed alloying was achieved for the ion fluence of 6 × 1016 ions cm−2 and the formed structure is composed of NiTi compound, only at depth around the projected ion range. In the deeper layers, beyond the projected range of implanted ions, the diffusion of Ni atoms can lead to solid state amorphization. Subsequent annealing at 400 °C for 30 min enabled enhanced interaction between intermixed Ni and Ti layers, and in the layers close to the Si substrate the conditions for the formation of intermetallic compound are created.
► Ni/Ti multilayer system is modified by ion implantation and thermal annealing. ► Thermal annealing is induced initial formatiom of NiTi intermetallic compound. ► NiTi nanoalloy phase is formed at room temperature after Ar ion implantation. ► Subsequent annealing of implanted Ni/Ti multilayer is enhanced formation of NiTi nanoalloy.
Amorphous iron disilicide (a-FeSi2) shows potential as a photovoltaic material due to its bandgap of ∼0.9 eV and high absorption coefficient. We present a detailed characterization of a-FeSi2, with ...particular emphasis on the electrical properties of a-FeSi2 c-Si heterostructures, under both dark and illuminated conditions. The samples were prepared on quartz and silicon substrates using RF co-sputtering of an iron silicon target. Optical transmission spectroscopy was used to confirm the bandgap of the samples. Van der Pauw measurements and current-voltage analysis techniques were used to determine the carrier type and conduction mechanisms of the samples. The results show that a-FeSi2 forms a rectifying p-n heterojunction on p-type crystalline silicon. The silicide is characterized by very high carrier concentrations, resulting in the depletion region being almost entirely formed within the silicon substrate. Initial J-V results suggest carrier recombination within the silicide to be the dominant contribution to the conduction across the junction, with photovoltaic effects having been observed under AM1.5 conditions.
The effect of the temperature ranging from cryogenics to room temperature were investigated on the formation of the optically-active point defect called the G-centre. The G- centre as an emissive ...point defect gained a lot of attention recently due to its sharp zero phonon luminescence peak at a wavelength of 1.28 μm (0.97 eV) with the evidence of lasing occurred in the structure. The emission of the G-centre is attributed to the carbon substitutional-carbon interstitial (CsCi) complex which interacts with silicon interstitials during the damage event. This complex is generated by implantation of carbon and followed by proton irradiation. Prior to the carbon implantation, two of the samples were pre-amorphised by germanium. Photoluminescence (PL) measurements were carried out at temperature ranging from 80 K up to room temperature to observe the intensity of the main peaks. The results confirm that the main peaks of point-defect centre in all of the samples including the G-centre suffer from the temperature quenching. However, the peak intensity for some of the wavelength especially the ones with high FWHM, do perform better at high temperature. The temperature quenching phenomena observed in the point-defect technique is the main problem that needs to be addressed and solved before realizing the method in the all silicon photonic system.
We have measured the near-infrared photoluminescence spectrum of phosphorus doped silicon (Si:P) and extracted the donor-bound exciton (D0X) energy at magnetic fields up to 28 T. At high field the ...Zeeman effect is strongly nonlinear because of the diamagnetic shift, also known as the quadratic Zeeman effect (QZE). The magnitude of the QZE is determined by the spatial extent of the wave-function. High field data allows us to extract values for the radius of the neutral donor (D0) ground state, and the light and heavy hole D0X states, all with more than an order of magnitude better precision than previous work. Good agreement was found between the experimental state radius and an effective mass model for D0. The D0X results are much more surprising, and the radius of the mJ = 3 2 heavy hole is found to be larger than that of the mJ = 1 2 light hole.
Environmental policies in African rangelands affect development and welfare as well as environmental measures. Biodiversity is widely perceived as declining, and environments as undergoing ...degradation, through rural population growth and resource use. These assumptions are often underpinned by environmental discourses contesting control of natural resources, rather than by objectively measured trends and causalities. Orthodox biodiversity conservation policy advocates fortress conservation. Savanna species do better where they can disperse across wider landscapes with conservation-compatible rural land uses, rather than isolated in protected areas, but community-based conservation initiatives have been disappointing. Policies addressing land degradation, and their underlying assumptions, are subject to similar challenges. The paper outlines a natural experiment investigating biodiversity and land cover changes 1975–1995 for 100,000
km
2 cross-border rangeland including the Serengeti–Mara conservation areas and their buffer zones. Ecological, ethnic and micro-economic continuities make it possible to control for confounding factors and identify main drivers of change. Privatisation of formerly communal rangeland, and its conversion to commercial monoculture, have driven drastic land cover and wildlife declines in Kenya. Population growth and agropastoral land use were not significant factors. The gap between natural and social science, and western versus local understandings, needs bridging to achieve more effective environmental policy.
Photoluminescence in the 1.2–1.35
μm range has been observed in silicon substrates incorporating thulium in the trivalent Tm
3+ state and co-doped with boron. The results showed eight sharp lines at ...1211.5, 1231.0, 1250.8, 1269.3, 1283.8, 1290.6, 1311.3 and 1326.0
nm, corresponding to known internal Tm
3+ transitions in the manifold from the
3H
5 to the
3H
6 ground states. The luminescence was strongly dependent on the sample fabrication processes. In this paper we will discuss the influence of Tm implantation parameters and post-implant annealing conditions on the photoluminescence response of silicon doped with Tm
3+.
Stability of nano-scaled Ta/Ti multilayers upon argon ion irradiation Milosavljević, M.; Milinović, V.; Peruško, D. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
10/2011, Letnik:
269, Številka:
19
Journal Article
Recenzirano
► The effects of argon ion irradiation on Ta/Ti multilayers were investigated. ► Despite of relatively heavy ion irradiation, Ta and Ti layers remain unmixed. ► Individual nanocrystalline layers keep ...the same level of interface planarity. ► Such behavior is assigned to dynamic demixing due to chemical driving forces. ► The results can be interesting towards developing radiation tolerant materials.
The effects of argon ion irradiation on structural changes in Ta/Ti multilayers deposited on Si wafers were investigated. The starting structures consisted of sputter deposited 10 alternate Ta (∼23
nm) and Ti (∼17
nm) layers of a total thickness ∼200
nm. They were irradiated at room temperature with 200
keV Ar
+, to the fluences from 5
×
10
15 to 2
×
10
16
ions/cm
2. The projected ion range was around mid-depth of the multilayered structure, and maximum displacements per atom ∼130. It was found that, despite of the relatively heavy ion irradiation, individual nanocrystalline Ta and Ti layers remain unmixed, keeping the same level of interface planarity. The changes observed in the mostly affected region are increase in lateral dimensions of crystal grains in individual layers, and incorporation of bubbles and defects that cause some stretching of the crystal lattice. Absence of interlayer mixing is assigned to Ta–Ti immiscibility (reaction enthalpy Δ
H
f
=
+2
kJ/mol). It is estimated that up to ∼5
at.% interface mixing induced directly by collision cascades could be compensated by dynamic demixing due to chemical driving forces in the temperature relaxation regime. The results can be interesting towards developing radiation tolerant materials based on multilayered structures.
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