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A strong influence of ion implantation flux on the accumulation of radiation damage, the so-called dose rate effect, is observed and systematically studied in SiC. 100 keV Si[sup +] ions were implanted into bulk 4H-SiC wafers using different ion fluxes (1.9×10[sup 10]–4.9×10[sup 13] ions/cm[sup 2] s) and keeping the implantation dose constant at 5×10[sup 14] Si[sup +]/cm[sup 2]. The implants were performed both at room and elevated temperatures, up to 220 °C. Rutherford backscattering spectrometry in the channelling mode using 2 MeV He[sup +] ions was employed to measure ion implantation damage profiles in the samples. For the flux interval used the most, pronounced dynamic annealing effect was detected at 80–160 °C, having an activation energy of 1.3 eV. For example, at 100 °C the amount of disordered Si atoms at the projected ion range is reduced by a factor of 4 by decreasing the ion flux from 4.9×10[sup 13] to 1.9×10[sup 10] ions/cm[sup 2] s. The results are discussed in terms of migration and annihilation of intrinsic type defects for both the Si- and C-sublattices. In addition, two regions for the damage accumulation – at the surface and at the damage peak for 100 keV Si[sup +] ions – are observed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Results concerning electronic, spatial, paramagnetic and optical properties of a self-trapped hole in NaCl are presented. The ab initio method of linear combinations of atomic orbitals (CRYSTAL code) is used. The maximum size of the supercell under consideration is 216 ions. Several types of exchange–correlation potentials (HF, B3LYP) are used. The optical transition energy is estimated from both the difference of total energies and the density of electron states. It is shown that the B3LYP40 functional provides a satisfactory description of the ground state of a defect. The energy of the πg →σu optical transition, which is unknown from experiments, is estimated theoretically. The obtained parameters of displacements of ions in the nearest neighborhood of a defect can be useful for description of magnetic characteristics of defects. [Copyright &y& Elsevier]

A method of simultaneous X-ray diffraction and electrical resistance measurements of materials in a diamond anvil cell has been developed. The experimental arrangement for the electrical measurements uses a gasket as a part of the electrode scheme. Application of the new methodology is demonstrated on the examples of the study of high-pressure high-temperature behavior of Pr and Fe-Ni alloys. Simultaneously obtained diffraction and resistance data provide the different, from earlier studies, interpretations of the topology of the dhcp-fcc phase transition in the phase diagram of Pr. Namely, the shape of a hysteretic region is mostly defined by kinetics of the dhcp phase growth rather than by thermodynamic driving force at the fcc to dhcp phase transformation. The results of combined X-ray diffraction and resistance measurements of Fe0.8Ni0.2 alloy up to 18 GPa and 425 K are reported along with the complementary resistance measurements of Fe0.9Ni0.1 alloy. [ABSTRACT FROM AUTHOR]

Abstract: We have studied phosphorus diffusion in strain relaxed Si1− x Ge x films (x=0.1 and 0.2) by secondary ion mass spectrometry (SIMS). The relaxed films were grown with low-pressure chemical vapor deposition (LPCVD) on a Si substrate followed by a graded SiGe layer. Two sets of samples were prepared under different growth conditions, and by transmission electron microscopy (TEM) it was shown that these conditions resulted in one set of samples containing a high density of threading dislocations in the relaxed films, and one set with a low dislocation density. The SIMS profiles of the phosphorus distributions in the samples, after annealing in N2-ambient in the temperature range of 700–950°C, show that the phosphorus diffusion is significantly faster in the films with the high dislocation density. Furthermore, the data suggests that the fast diffusion is due to a higher mobility of the diffusing complex rather than an increase in the point defect concentration mediating the diffusion, a result which indicates that the threading dislocations may act as channels for the rapid dopant diffusion in SiGe. [Copyright &y& Elsevier]

Abstract: Classical MD simulations have been applied to study the Frenkel pair accumulation in electron- and ion-irradiated SiC for a wide temperature range 20–1200K using different dose rates, so that ion flux affects significantly the resulting damage levels. Since the range of experimental dose rates is not accessible in MD simulations because of computational time limitations, an analytical model of amorphization accounting for different fractions of stable Frenkel pairs (FPs) was used to predict FPs generation/recombination behavior at experimental values of ion flux and study their role in crystalline-to-amorphous transition in SiC. Critical temperatures for amorphization using electron and ion irradiation as estimated with the formalism of our model are consistent with experimental data. FPs configurations responsible for damage annealing at different temperatures are discussed. For example, tetrahedral SiTC interstitials are shown to be dominating in the generation-recombination process for the temperature region 200–800K in electron-irradiated SiC. [Copyright &y& Elsevier]

Abstract: We have investigated evolution of implanted H in single crystalline ZnO in the temperature range from room temperature (RT) to 600 ∘C. H was implanted at RT with an energy of 100 keV and a dose of 2×1017 cm−2. Secondary Ion Mass Spectrometry (SIMS) was used for the study of H distribution. The effect of the implanted H on electrical properties of ZnO as a function of depth was investigated by Scanning Spreading Resistance Microscopy (SSRM) and Scanning Capacitance Microscopy (SCM). After the implantation, the SIMS measurements reveal a H profile with a peak concentration of ∼1022 cm−3 at a depth of 0.7 μm. An increased carrier concentration is observed by SSRM and SCM in the as-implanted sample in the H implanted region. After heat treatment for 2 h at 200 ∘C, no change in either H or carrier concentration profiles is detected. Annealing for 2 h at 400 ∘C leads to a decrease in the peak H concentration down to 2×1021 cm−3. However, no diffusion-like broadening of the H profile is revealed. Heat treatment at 600 ∘C results in a further decrease of the H concentration to 2×1020 cm−3 and, similarly to the 400 ∘C annealing, no broadening of the H profile is observed. This suggests that the implanted H is trapped in immobile complexes which dissociate during annealing with subsequent out-diffusion of H from the implanted region. The correlation between electrical activity of H and presence of radiation damage is discussed. [Copyright &y& Elsevier]

A method for accurate determination of the neutron yield or flux emitted by targets of neutron generators with complex surface configurations is presented. The method is based on the calculation of the neutron brightness distribution (number of neutrons irradiated from the unit of target surface in the unit of time) over the target, surface, by making several measurements at different points around the target. This distribution is obtained by solving an algebraic system of equations by means of the least squares method. [Copyright &y& Elsevier]

We present the results of an investigation of the electron structures of BaF2, LaF3 and BaF2:La crystals. The effects of lattice polarization and relaxation were considered. The calculations were performed using the Crystal98 code, the molecular statics method and the embedded cluster technique based on the Johnson''s scattered wave method. [Copyright &y& Elsevier]

Graphene oxide (GO) has become one of the emerging and important sole photocatalyst nanomaterials in recent years due to its exceptional/tunable optoelectronic properties, multifunctionality, and eco‐friendly nature. However, challenges remain in tuning surface chemistry, tailoring the band gap, developing doping strategies, and understanding the sole photocatalytic mechanism. This contribution investigated the synthesis of GO via the improved Hummers method by varying the ratio of the oxidizing agents (K2Cr2O7:KMnO4), as well as modifications by nitrogen (N) and boron (B) doping in view of its applications in photocatalytic degradation of organic dye pollutants. Furthermore, changes in surface chemistry, optical, compositional, morphological, and structural properties are investigated to understand the photocatalytic mechanism. The synthesized GO showed a broad spectrum of light absorption with a tunable band gap of 2.4–4.3 eV and exhibited more than 91% degradation of methylene blue dye under direct sunlight. However, the photocatalytic activity decreased after N and B doping attributed to reduced oxygen‐containing functional groups, low surface area, and dopants‐induced bonding configurations within the GO structure. This study provides a new insight into replacing metallic semiconductor photocatalysts with highly affordable, environmentally friendly, and potent metal‐free GO photocatalysts. [ABSTRACT FROM AUTHOR]

Measures the diffusion coefficient for nickel atom im unrelaxed amorphous silicon. Use of secondary ion mass spectrometry; Differentiation between the diffusion coefficients in amorphous-silicon and crystalline silicon; Description of the diffusion process by a model invoking trap-retarded interstitial migration; Presence of intrinsic traps in the amorphous traps.

The defect distributions in [sup 11]B-, [sup 14]N-, and [sup 27]Al-implanted epitaxial 4H–SiC are studied using monoenergetic positron beams. At least three types of defects are needed to account for the Doppler broadening annihilation spectra and two of the defects are tentatively identified as V[sub Si], and V[sub Si]V[sub C]. By comparing the defect profiles extracted from the annihilation spectra to the chemical profiles determined by secondary ion mass spectrometry, and to the primary defect profiles obtained from binary collision approximation simulations, it is concluded that the defects found at depths considerably deeper than the projected range of the implanted ions mainly originate from deeply channeled ions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Optical detection of magnetic resonance (ODMR) was used to study defects in electron-irradiated ZnO substrates. In addition to the shallow donor and the Zn vacancy, several ODMR centers with an effective electron spin were detected. Among these, the axial LU3 and non-axial LU4 centers are shown to be dominating recombination centers. The annealing behavior of radiation-induced defects was studied and possible defect models are discussed. [Copyright &y& Elsevier]

Electrical resistivity and Hall coefficient measurements have been realized on strained highly doped single n-Si1 - xGex epilayers grown on Si substrates in the temperature range 80–350 K. Free electron concentration and Hall mobility were determined. Conduction band parameters and high mobility results were discussed taking into account the strain induced conduction band modification. [Copyright &y& Elsevier]

[Display omitted] Ruby is a mineral in the corundum (Al 2 O 3) family and it is remarkably valuable as a gemstone. From the physics point of view, the ruby coloration depends on the balance of trace or chromophore impurities and defect complexes in the Al 2 O 3 lattice. Shifting this balance into right direction is of paramount importance for the ruby value as the gemstone and ion implantation can be applied for this purpose. Thus, in the present study, we explored the influence of high dose oxygen ion implants on the natural ruby coloration. By performing quantitative colorimetry analysis, we detected prominent coloration changes unambiguously attributed to the effect of the implants, even though the implanted oxygen profile was located at the near surface region of the sample. Moreover, applying near surface sensitive cathodoluminescence measurements we observed spectacular changes in the spectra correlated with the implants. Importantly, the trends observed in the colorimetry and cathodoluminescence as a function of the implantation parameters were consistent. As such, the present paper provides both the scientific perspective and quantitative interpretations potentially paving the way for the ion beams applications in the gemstone industry. [ABSTRACT FROM AUTHOR]

Abstract: A route for realizing non-polar ZnO (112̄0) films with atomically smooth surface is demonstrated by employing rf-plasma assisted molecular beam epitaxy on ZnO bulk substrates. It is found that high growth temperature plays an important role in suppressing the typical striped structure along ZnO [0001] direction on non-polar planes. An atomically smooth surface with a root mean square roughness of 0.51nm that is suitable for fabrication of quantum wells is achieved after solving the growth anisotropy problem, as confirmed by the combined studies of reflection high-energy electron diffraction and atomic force microscopy. [Copyright &y& Elsevier]

Successful implementation of ion beams for modification of ternary ZnO-based oxides requires understanding and control of radiation-induced defects. Here, we study structural disorder in wurtzite ZnO and Mg x Zn 1 − x O ( x ⩽ 0.3) samples implanted at room and 15 K temperatures with Ar ions in a wide fluence range (5 × 10 12 –3 × 10 16 cm −2 ). The samples were characterized by Rutherford backscattering/channeling spectrometry performed in-situ without changing the sample temperature. The results show that all the samples exhibit high radiation resistance and cannot be rendered amorphous even for high ion fluences. Increasing the Mg content leads to some damage enhancement near the surface region; however, irrespective of the Mg content, the fluence dependence of bulk damage in the samples displays the so-called IV-stage evolution with a reverse temperature effect for high ion fluences. [ABSTRACT FROM AUTHOR]

Abstract: Molecular beam epitaxy grown MgxZn1−xO (x ⩽0.3) layers were implanted at room temperature with 150keV 166Er+ ions in a fluence range of 5×1015–3×1016 cm−2. Evolution of ion-induced damage and structural changes were studied by a combination of Rutherford backscattering spectrometry, nuclear reaction analysis and time-of-flight elastic recoil detection analysis. Results show that damage production enhances in both Zn- and O-sublattices with increasing the Mg content in the MgZnO. However, MgZnO as well as pure ZnO exhibits a high degree of dynamic annealing and MgZnO can not be amorphized even at the highest ion fluence used. Annealing of heavily damaged ZnO leads to a strong surface erosion and thinning of the film. Increasing the Mg content suppresses the surface evaporation in high fluence implanted MgZnO but leads to a strong surface decomposition accompanied with a Mg-rich surface layer formation during post-implantation annealing. [Copyright &y& Elsevier]

Abstract: Single-phase rock-salt Mg0.3Zn0.7O film was fabricated on MgO (100) substrate by radio-frequency plasma assisted molecular beam epitaxy. A smooth surface was observed by in-situ reflection high-energy electron diffraction and ex-situ atomic force microscopy. X-ray diffraction characterization demonstrated a high-quality single-phase structure with highly (200) orientation and cube-on-cube epitaxial relationship. Zn fraction in the single-phase rock-salt Mg0.3Zn0.7O film was determined by Rutherford backscattering spectrometry. Optical property of the film was investigated by reflectance spectroscopy, which indicated a solar-blind band gap of 255.5nm. The reason why Zn solubility limit is greatly enhanced in non-polar (100) film compared with (111) polar epilayer is tentatively discussed in this work, suggesting MgO (100) is more suitable for the synthesis of single-phase rock-salt MgZnO with high Zn content towards solar-blind opto-device applications. [Copyright &y& Elsevier]

Abstract: MgZnO films with different Mg contents were synthesized on c-plane sapphire by metal organic chemical vapor deposition, using diethyl zinc (DEZn) and bis(cyclopentadienyl) magnesium (Cp2Mg) as Zn and Mg precursors, respectively. Tertiary butanol (t-BuOH) was used as a weak oxidant in order to enhance the accuracy of Mg incorporation when varying DEZn/Cp2Mg flow rates. As a result the Mg contents in the range of 1–9% were confirmed by time-of-flight elastic recoil detection analysis, which is known to be specifically sensitive to detect light elements. Thus, independently and accurately determined composition in the samples was correlated with structural and optical properties as measured by x-ray diffraction and photoluminescence. [Copyright &y& Elsevier]

Abstract: The effect of implantation parameters on damage build-up in ZnO bombarded with Bi and Er ions is studied by Rutherford backscattering/channelling spectrometry. The results show that the damage accumulation behaviour in ZnO is different dramatically from that in other semiconductors. In particular, a variation of implantation parameters, such as collision cascade density, sample temperature and ion flux, has only a minor influence on the damage accumulation in the crystal bulk for the case of such heavy ions. Moreover, an intermediate damage peak, between the surface and bulk defect peaks, is observed for all the irradiation conditions studied. The cascade density affects the behaviour of this intermediate peak with increasing ion dose. [Copyright &y& Elsevier]

Abstract: The effect of tensile strain on Sb incorporation in Si and its activation during post-implantation annealing has been studied by a combination of Rutherford backscattering/channeling spectrometry, secondary ion mass spectrometry, X-ray diffraction and 4-point probe measurements. Our results show that, for Sb implanted samples a tensile strain has an important role for dopant behavior. Particularly, increasing the tensile strain in the Si layer from 0 to 0.8% leads to an enhancement of the fraction of incorporated Sb atoms in substitutional sites already during implantation from ~7 to 30%. Furthermore, 0.8% strain in antimony doped Si gives ~20% reduction in the sheet resistance in comparison to the unstrained sample. [Copyright &y& Elsevier]

Abstract: A route for synthesizing high Mg content single-phase wurtzite MgZnO films having band gaps in the solar-blind region is demonstrated by employing molecular beam epitaxy on Al2O3 substrates. Importantly, a low Mg content “quasi-homo” buffer, Mg0.17Zn0.83O, was applied to accommodate a host of structural discrepancies and therefore, avoiding phase separation in a high Mg content film, Mg0.55Zn0.45O, as proved by X-ray diffraction. The Mg fraction in the overgrown single-phase epilayer, Mg0.55Zn0.45O, was confirmed by Rutherford backscattering spectrometry. [Copyright &y& Elsevier]

Abstract: Samples of epitaxially grown n-type Si have been implanted with low doses (<1×109 cm−2) of He, C, Si, and I ions using energies from 2.75 to 48MeV. Deep level transient spectroscopy (DLTS) analysis of the implanted samples reveals a stronger signal for the signature of the singly negative charge state of the divacancy (V2(–/0)) as compared to that of the doubly negative charge state of the divacancy (V2(=/–)). Isochronal annealing for 20min ranging from 150 to 400°C results in a gradual decrease in the DLTS peak amplitude of the V2(–/0) signature, accompanied by an increase in the peak amplitudes of both the vacancy oxygen pair (VO) and the V2(=/–) levels, as well as an increase in the carrier capture rates for the levels. A model based on local compensation of charge carriers from individual ion tracks is proposed in order to explain the results, involving two fractions of V2: (1) V2 centers localized in regions with high defect density around the ion track and (2) V2 centers located in regions with a low defect density . [Copyright &y& Elsevier]

Abstract: Atomic force microscopy (AFM), scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) were used for the analysis of the morphology and electrical properties of heterojunction (HJ) solar cell structures made of Indium Tin Oxides (ITO) layers deposited on p-type polished Si substrates with a buffer layer of n-type hydrogenated amorphous Si (a-Si:H). By means of AFM measurements it is shown that the a-Si:H layer can be deposited on a Si substrate quite homogeneously with a roughness of only a few nanometers. In contrast, the morphology of the ITO layers depends on the deposition temperature and can be varied during the HJ solar cell processing. Cross section analysis of the HJ structures by SCM shows penetration of n-type carriers into the (p)Si bulk substrate and the formation of the resulting n–p electrical junction depends strongly on the ITO deposition temperature and the presence of the (n)a-Si:H layer. Complementary cross section SSRM measurements show only a highly n-type doped region confined to the ITO layer. Finally it is concluded that the properties of the HJ solar cell structures depend dramatically on the properties of the ITO layers and can be modified by variation of the ITO deposition temperature. [Copyright &y& Elsevier]

Abstract: Secondary ion mass spectrometry (SIMS) analysis of In, O, Si, and H concentrations versus depth distributions in ITO(In-Sn-O)/(n,p)a-Si:H/(p,n)-Si and ITO/(p)-Si heterojunction (HJ) solar cell structures was performed. SIMS measurements show some peculiarities of the element profiles in the interface of ITO/a-Si:H and a-Si:H/Si regions. These peculiarities can be attributed to the non-homogeneities (In-rich nanostructures, small dents or mounds) of the ITO layer. It is shown that the formation of In-rich nanostructures is more pronounced in case of ITO growth on a (p)a-Si:H/(n) Si substrate at 230 °C. SIMS profiles obtained from such non-homogeneous areas can show a penetration of In into the Si bulk, which is not a real distribution. A hydrogen redistribution from the a-Si:H layer into the neighboring ITO and Si layers in case of ITO/(n,p)a-Si:H/(p,n)-Si structures as well as hydrogen gettering to the ITO/(p)-Si interface was detected. It is concluded that the final heterojunction structure of ITO/(n,p)a-Si:H/(p,n)c-Si is rather complex and includes in addition to the individual ITO, a-Si:H and Si layers also intermediate ones with different composition. [Copyright &y& Elsevier]

Abstract: Positron annihilation spectroscopy was applied to study relaxed P-doped n-type layers with Ge concentrations up to 30%. As-grown SiGe layers were defect-free and annihilations are superpositions from bulk Si and Ge. Proton irradiation at 2MeV energy with a fluence was used to produce saturated positron trapping in monovacancy related defects. The defects were identified as V–P pairs, the E-center. The distribution of Si and Ge atoms surrounding the E-center is the same as in the host lattice. The vacancy migration process leading to the formation of V–P pairs therefore does not seem to have a preference for either Si or Ge atoms. [Copyright &y& Elsevier]

Abstract: In this work we have studied diffusion and electrical activation in Al+ and Sb+ implanted ZnO samples using secondary ion mass spectrometry (SIMS), scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM). The samples were hydrothermally grown and post-implant annealing was performed at 800, 900 and 1000 ∘C in pure oxygen atmosphere. After each annealing step the samples were characterized with SSRM/SCM and SIMS. The thermal treatments did not induce any significant impurity redistribution as measured by SIMS, while electrical compensation is observed by SSRM/SCM for the Sb-implanted sample yielding less n-doping than in the as-grown samples. In the Al-implanted samples, an increase in carrier concentration is observed; we ascribe this to Al-related donors and possibly interstitial lithium, a common residual impurity in the samples that have been shown to be very mobile by SIMS. [Copyright &y& Elsevier]

We have used positron annihilation spectroscopy to study vacancy type defects in strained P doped Si1−xGex layers grown on Si substrates and irradiated with 2 MeV protons. The results show that the dominant defect in the SiGe layer after irradiation is the E-center, the V–P pair. When the sample is annealed at 150–175°C the dominant defect species in the SiGe layer changes into a complex consisting of a vacancy, a P dopant and a Ge atom (V–P–Ge complex). The V–P–Ge complex anneals out at 200°C. The 50°C higher annealing temperature of the V–P–Ge complex corresponds to about 0.1–0.2 eV larger binding energy than that of the V–P pair. [Copyright &y& Elsevier]