Structural modifications of low-energy heavy-ion irradiated germanium

Heavy-ion irradiation of crystalline germanium (c-Ge) results in the formation of a homogeneous amorphous germanium (a-Ge) layer at the surface. This a-Ge layer undergoes structural modification such as a strong volume expansion accompanied by drastic surface blackening with further ion irradiation. In the present paper we investigate the mechanism of this ion-induced structural modification in a-Ge basically for the irradiation with I ions (3 and 9 MeV) at room and low temperature as a function of ion fluence for the ion incidence angles of Θ=7 and Θ=45. For comparison, Ag- and Au-ion irradiations were performed at room temperature as a function of the ion fluence. At fluences two orders of magnitude above the amorphization threshold, morphological changes were observed for all irradiation conditions used. Over a wide range of ion fluences we demonstrate that the volume expansion is caused by the formation of voids at the surface and in the depth of the projected ion range. At high ion fluences the amorphous layer transforms into a porous structure as established by cross section and plan view electron microscopy investigations. However, the formation depth of the surface and buried voids as well as the shape and the dimension of the final porous structure depend on the ion fluence, ion species, and irradiation temperature and will be discussed in detail. The rate of the volume expansion (i.e., porous layer formation) depends linearly on the value of εn. This clearly demonstrates that the structural changes are determined solely by the nuclear energy deposited within the amorphous phase. In addition, at high ion fluences all perpendicular ion irradiations lead to a formation of a microstructure at the surface, whereas for nonperpendicular ion irradiations a nonsaturating irreversible plastic deformation (ion hammering) without a microstructure formation is observed. For the irradiation with ion energies of several MeV, the effect of plastic deformation shows a linear dependence on the ion fluence. Based on these results, we provide an explanation for the differences in surface morphology observed for different angles of incidence of the ion beam will be discussed in detail

Surface charge reversal method for high-resolution inkjet printing of functional water-based inks

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Printed electronics is a rapidly growing area of research being explored for the manufacture of large-area and cost-effective electronic devices by the patterned application of functional inks. There are challenges associated with processing the inks compatible with inkjet printing technology and developing effi cient methods to successfully obtain the desired features, particularly when it comes to metal and metal-organic complex inks. Here, a reliable method is developed to achieve a sophisticated microstructured pattern using the inkjet printing technique assisted by a surface charge reversal effect. In addition, a procedure is formulated to obtain good quality, stable metal-organic water-based inks compatible with salts of a variety of transition metals and rare earths, without the need for additional volatile solvents. A feasible and water-based ink formulation combined with a simple and noninvasive surface charge reversal treatment constitutes a major step toward the manufacture of high-resolution, inorganic patterned thin fi lms on hydrophobic substrates using inkjet printing. These outcomes lead to the path of effective fusion of inorganic and organic heterointerfaces by simples designing and printing.This work was supported by the University of New South Wales and Spanish MICINN (Consolider CSD2007-0041). A portion of this work was performed at the ACT node of the Australian National Fabrication Facility. The authors wish to acknowledge Dr. F. Kremer for the electron diffraction measurement.Peer Reviewe

Amorphization of embedded Cu nanocrystals by ion irradiation

While bulk crystalline elemental metals cannot be amorphized by ion irradiation in the absence of chemical impurities, the authors demonstrate that finite-size effects enable the amorphization of embedded Cu nanocrystals. The authors form and compare the atomic-scale structure of the polycrystalline, nanocrystalline, and amorphous phases, present an explanation for the extreme sensitivity to irradiation exhibited by nanocrystals, and show that low-temperature annealing is sufficient to return amorphized material to the crystalline form

Effects of Flooding on the Flora and Fauna of a Reconstructed Tallgrass Prairie

Prairie restoration for the purpose of biofuel production has the potential to be much more beneficial than using corn-based ethanol. These benefits include less damage to soil from fertilizers or pesticides, less management and greater suitability for native fauna. The current study of this restoration consists of surveying vegetation characteristics on four different soil types seeded with four different mixes, as well as observing bird and butterfly use of the restoration. In the fourth year of management of this particular prairie restoration a great deal of flooding occurred. The frequency and intensity of the flooding had a great affect on the vegetation in terms of what was able to survive long periods of saturation. Species abundance and richness for both butterflies and birds dropped significantly this year compared to the past three years of management. These factors lead to the conclusion that periodic flooding will alter flora and fauna composition of restored prairies and sets a basis for further observations of the effect on the ecosystem. As prairie restorations take several years to fully express, the full impact of the flood may take some time to determine

Swift-heavy-ion-induced damage formation in III-V binary and ternary semiconductors

Damage formation in InP, GaP, InAs, GaAs, and the related ternary alloys Ga0.50 In0.50 P and Ga0.47 In0.53 As irradiated at room temperature with 185 MeV Au ions was studied using Rutherford backscattering spectroscopy in channeling configuration, transmission electron microscopy, and small-angle x-ray scattering. Despite nearly identical ion-energy loss in these materials, their behavior under swift-heavy-ion irradiation is strikingly different: InP and Ga0.50 In0.50 P are readily amorphized, GaP and GaAs remain almost undamaged and InAs and Ga0.47 In0.53 As exhibit intermediate behavior. A material-dependent combination of irradiation-induced damage formation and annealing is proposed to describe the different responses of the III-V materials to electronic energy loss

Ultrahigh-temperature microwave annealing of Al⁺- and P⁺-implanted 4H-SiC

In this work, an ultrafast solid-state microwaveannealing has been performed, in the temperature range of 1700–2120°C on Al⁺- and P⁺-implanted 4H-SiC. The solid-state microwave system used in this study is capable of raising the SiC sample temperatures to extremely high values, at heating rates of ∼600°C∕s. The samples were annealed for 5–60s in a pure nitrogen ambient. Atomic force microscopy performed on the annealed samples indicated a smooth surface with a rms roughness of 1.4nm for 5×5μm² scans even for microwaveannealing at 2050°C for 30s. Auger sputter profiling revealed a <7nm thick surface layer composed primarily of silicon, oxygen, and nitrogen for the samples annealed in N₂, at annealing temperatures up to 2100°C. X-ray photoelectron spectroscopy revealed that this surface layer is mainly composed of silicon oxide and silicon nitride. Secondary ion mass spectrometry depth profiling confirmed almost no dopant in diffusion after microwaveannealing at 2100°C for 15s. However, a sublimation of ∼100nm of the surface SiC layer was observed for 15sannealing at 2100°C. Rutherford backscattering spectra revealed a lattice damage-free SiC material after microwaveannealing at 2050°C for 15s, with scattering yields near the virgin SiC material. Van der Pauw–Hall measurements have revealed sheet resistance values as low as 2.4kΩ∕□ for Al⁺-implanted material annealed at 2100°C for 15s and 14Ω∕□ for the P+-implanted material annealed at 1950°C for 30s. The highest electron and hole mobilities measured in this work were 100 and 6.8cm2/Vs, respectively, for the P⁺- and Al⁺-implanted materials.The GMU work is supported by Army Research Of- fice Dr. Prater under Grant No. W911NF-04-1-0428 and a subcontract from LT Technologies under NSF SBIR Grant No. 0539321

The Evolution of the Stellar Hosts of Radio Galaxies

We present new near-infrared images of z>0.8 radio galaxies from the flux-limited 7C-III sample of radio sources for which we have recently obtained almost complete spectroscopic redshifts. The 7C objects have radio luminosities about 20 times fainter than 3C radio galaxies at a given redshift. The absolute magnitudes of the underlying host galaxies and their scale sizes are only weakly dependent on radio luminosity. Radio galaxy hosts at z~2 are significantly brighter than the hosts of radio-quiet quasars at similar redshifts and the model AGN hosts of Kauffmann & Haehnelt (2000). There is no evidence for strong evolution in scale size, which shows a large scatter at all redshifts. The hosts brighten significantly with redshift, consistent with the passive evolution of a stellar population that formed at z>~3. This scenario is consistent with studies of host galaxy morphology and submillimeter continuum emission, both of which show strong evolution at z>~2.5. The lack of a strong ``redshift cutoff'' in the radio luminosity function to z>4 suggests that the formation epoch of the radio galaxy host population lasts >~1Gyr from z>~5 to z~3. We suggest these facts are best explained by models in which the most massive galaxies and their associated AGN form early due to high baryon densities in the centres of their dark matter haloes.Comment: To appear in A

Athermal annealing of Si-implanted GaAs and InP

GaAs and InP crystals ion implanted with Si were athermally annealed by exposing each crystal at a spot of ~2 mm diameter to a high-intensity 1.06 μm wavelength pulsed laser radiation with ~4 J pulse energy for 35 ns in a vacuum chamber. As a result a crater is formed at the irradiated spot. The crater is surrounded by a dark-colored ring-shaped region which is annealed by mechanical energy generated by rapidly expanding hot plasma that formed on the exposed spot. The electrical characteristics of this annealed region are comparable to those of a halogen-lamp annealed sample. No redistribution of impurities due to transient diffusion is observed in the implant tail region. In x-ray diffraction measurements, a high angle side satellite peak due to lattice strain was observed in the crater and near crater regions of the athermally annealed sample in addition to the main Bragg peak that corresponds to the pristine sample. This high angle side satellite peak is not observed in regions away from the crater (≥5 mm from the center of the crater in GaAs)

Heat flow model for pulsed laser melting and rapid solidification of ion implanted GaAs

Some of the authors thank for the support of the Center for Nanoscale Systems (CNS) at Harvard University is acknowledged. Harvard-CNS is a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award No. ECS-0335765. K. M. Yu and J. W. Beeman were supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.Some of the authors thank for the support of the Center for Nanoscale Systems (CNS) at Harvard University is acknowledged. Harvard-CNS is a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award No. ECS-0335765. K. M. Yu and J. W. Beeman were supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231

Electrical and structural properties of In-implanted Si1−xGex alloys

We report on the effects of dopant concentration and substrate stoichiometry on the electrical and structural properties of In-implanted Si1−xGex alloys. Correlating the fraction of electrically active In atoms from Hall Effect measurements with the In atomic environment determined by X-ray absorption spectroscopy, we observed the transition from electrically active, substitutional In at low In concentration to electrically inactive metallic In at high In concentration. The In solid-solubility limit has been quantified and was dependent on the Si1−xGex alloy stoichiometry; the solid-solubility limit increased as the Ge fraction increased. This result was consistent with density functional theory calculations of two In atoms in a Si1−xGex supercell that demonstrated that In–In pairing was energetically favorable for x ≲ 0.7 and energetically unfavorable for x ≳ 0.7. Transmission electron microscopy imaging further complemented the results described earlier with the In concentration and Si1−xGex alloy stoichiometry dependencies readily visible. We have demonstrated that low resistivity values can be achieved with In implantation in Si1−xGex alloys, and this combination of dopant and substrate represents an effective doping protocol