2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
The quality and temperature stability of surface passivation of silicon by a double layer consist... more The quality and temperature stability of surface passivation of silicon by a double layer consisting of a hydrogenated amorphous silicon thin film capped by a silicon nitride anti-reflection coating are studied. It is established that the passivation effect of the double layer can be significantly enhanced after short annealing for temperatures up to about 500 °C, whereas annealing at higher temperatures results in degradation of the passivation properties. It is found that the increased effective recombination lifetime after annealing at temperatures below 500 ºC results from hydrogen redistribution in the interface region. Furthermore, presence of interfacial structural defects formed due to hydrogen release at temperatures around 600 ºC, is believed to be the cause of the lifetime decrease after heat treatments at higher temperatures.
Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrate... more Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping.
The aim of this study was to explore further the preservation of tissues and the mineral distribu... more The aim of this study was to explore further the preservation of tissues and the mineral distribution in 1.6 million-year-old fossil hominin material from Koobi Fora, Kenya attributed to Paranthropus boisei (KNM-ER 1817). Bone, dentine and cementum microstructure were well preserved. Electron microprobe analysis of dentine and bone revealed an F-bearing apatite. Calcite now filled the original soft tissue spaces. The average Ca/P atomic ratio was 1.93, as compared to 1.67 in biological hydroxyapatite, indicating that the Ca-content had increased during fossilization. Analytical sums for mineral content were approximately 90 wt%. Some of the remaining 10 wt% may be preserved organic material. Demineralized dentine fragments showed irregularly distributed tubules encircled with a fibrous-like electron-dense material. A similar material was observed in demineralized dentine. Within this, structures resembling bacteria were seen. In demineralized bone an electron-dense material with a f...
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
The quality and temperature stability of surface passivation of silicon by a double layer consist... more The quality and temperature stability of surface passivation of silicon by a double layer consisting of a hydrogenated amorphous silicon thin film capped by a silicon nitride anti-reflection coating are studied. It is established that the passivation effect of the double layer can be significantly enhanced after short annealing for temperatures up to about 500 °C, whereas annealing at higher temperatures results in degradation of the passivation properties. It is found that the increased effective recombination lifetime after annealing at temperatures below 500 ºC results from hydrogen redistribution in the interface region. Furthermore, presence of interfacial structural defects formed due to hydrogen release at temperatures around 600 ºC, is believed to be the cause of the lifetime decrease after heat treatments at higher temperatures.
Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrate... more Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping.
A simple method for high-precision epitaxial semiconductor growth, using ex situ materials analys... more A simple method for high-precision epitaxial semiconductor growth, using ex situ materials analysis for frequent re-calibration, has been developed. The method is shown to allow reproducible growth of material for use in low-cost commercial heterostructure devices. Even tunnel devices, with their extreme sensitivity to growth parameters, show little variation in the electrical characteristics from wafers grown several months apart.
ABSTRACT In the expanding field of plasmonics, accurate control of the degree of plasmon localiza... more ABSTRACT In the expanding field of plasmonics, accurate control of the degree of plasmon localization is of crucial importance for tailoring optical properties at the nanoscale. In this paper, the degree of plasmon localization is directly probed by recording the momentum transfer dependence (i.e. the dispersion) of plasmon resonance energies using electron energy loss spectroscopy in the aberration-corrected scanning transmission electron microscope. Limited by the uncertainty principle, resolution in momentum space can easily be tuned by the beam convergence, and it is shown that localization is clearly identifiable, even at low-momentum resolution. In this proof-of-principle study, this technique was applied to multilayer graphene cones containing a varying number of topological defects at their apex. It is shown that a high degree of confinement of the π and π+σ volume plasmons is reached for five pentagonal defects at the cone apex. This effect was attributed to the presence of the topological defects themselves. Furthermore, slight negative refraction was observed for the five-pentagon cone, predominantly affecting the collective excitation of the π electrons.
We have investigated the thermoelectric material Zn 4 Sb 3 using transmission electron microscopy... more We have investigated the thermoelectric material Zn 4 Sb 3 using transmission electron microscopy (TEM). Nanoscale inclusions with a diameter of about 10 nm were observed, constituting on the order of 1% by volume of the material. Studies using energy filtered imaging, electron diffraction, and high-angle annular dark-field STEM indicate that the inclusions consist of Zn. These inclusions are expected to scatter the medium and long-wavelength phonons effectively, thus contributing to phonon glass behavior which results in the exceptionally low thermal conductivity for this thermoelectric material.
Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium ... more Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium alloys have been carried out. The Ga alloys were made by triturating a LU powder (Ag-Sn-Cu rich alloy powder) and a GF powder (Ag-Sn-Cu-Pd rich alloy powder) with a liquid Ga alloy containing Ga, In and Sn. The dental materials were found to be composites consisting of remaining, undissolved particles from the Ag-based alloy powders in a matrix of reaction products with the Ga alloy. SEM studies have been carried out to give an overview of the composites. The distribution of the elements was found by the X-ray mapping technique. The phases in the matrix and the remaining alloy particles have been identified by electron diffraction, high-resolution electron microscopy and energy-dispersive X-ray spectroscopy. The following phases were identified in the LU alloy: orthorhombic Ag3Sn, cubic Ag9In4, tetragonal beta-Sn and hexagonal Ag2Ga. In addition to these well-known phases Ga-rich regions were observed consisting of an intergrowth of tetragonal CuGa2 and one of the cubic gamma-Cu9Ga4 phases. In addition to these phases cubic Ga7Pd3 was found in the GF alloy. The anomalous setting expansion of the GF alloy may be explained by the presence of Ga7Pd3.
Nanocomposite Cr-B-N coatings were deposited from CrB 0.2 compound targets by reactive arc evapor... more Nanocomposite Cr-B-N coatings were deposited from CrB 0.2 compound targets by reactive arc evaporation using an Ar/N 2 discharge at 500°C and −20 V substrate bias. Elastic recoil detection (ERDA), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) were used to study the effect of the N 2 partial pressure on composition and microstructure of the coatings. Cross-sectional scanning electron microscopy (SEM) showed that the coating morphology changes from a glassy to a columnar structure with increasing N 2 partial pressure, which coincides with the transition from an amorphous to a crystalline growth mode. The saturation of N content in the coating confirms the formation of a thermodynamically stable CrN-BN dual-phase structure at higher N 2 fractions, exhibiting a maximum in hardness of approximately 29 GPa.
Nanocrystals embedded in SiO 2 films are the subject of a number of recent works, mainly because ... more Nanocrystals embedded in SiO 2 films are the subject of a number of recent works, mainly because of their potential usefulness in the fabrication of optoelectronic devices and nanocrystal memory structures. One interesting method for the fabrication of such nanocrystals is the ion implantation of segregating species into SiO 2 films followed by heat treatment in order to induce nanocrystal formation. This method is both relatively simple and also compatible with the current MOS (metal-oxide-semiconductor) device technology. An unintentional effect can occur during the fabrication of nanocrystals using this method, namely a significant diffusion of the implanted species during annealing, away from the regions with the highest concentration. The Si/ SiO 2 interface can be exposed to this diffusion flux. This can result in an altered interface and have a significant influence on electronic devices. Here, we report on ion implantation of Ge into SiO 2 on Si followed by annealing under conditions, resulting in Ge accumulation at the Si/ SiO 2 interface as determined by secondary-ion mass spectroscopy analysis, transmission electron microscopy with energy dispersive analysis of x-rays, and Rutherford backscattering spectrometry. The accumulation of Ge at the Si/ SiO 2 interface has also been reported before. The resulting effect on the electronic structure of the interface is a priori unknown. We have fabricated MOS capacitors on the sample structures and their capacitance-voltage characteristics were measured and analyzed. We measure an interface state density around 1 ϫ 10 12 cm −2 , which is high compared to standard Si MOS devices. We discuss the results in terms of the previous electrical measurements on Ge-oxide interfaces and SiGe interfaces, which also can yield a high interface state density. The specific conditions we report result in a sufficiently low Ge concentration that nanocrystals are not segregated in the SiO 2 film, while Ge still accumulates at the Si/ SiO 2 interface after annealing.
Acta Crystallographica Section B Structural Science, 2006
The crystal structure of Zr 2 NiD 4.5 has been determined by a combination of synchrotron radiati... more The crystal structure of Zr 2 NiD 4.5 has been determined by a combination of synchrotron radiation powder X-ray diffraction, electron diffraction and powder neutron diffraction data. Deuterium ordering results in a triclinic supercell given by a super = 6.81560 , b super = 8.85137 (9), c super = 8.88007 (10) Å , super = 79.8337 , super = 90.0987 (9), super = 90.3634 , which relates to the non-super unit cell as a super = Àa, b super = Àb À c, c super = Àb + c. The centrosymmetric and fully ordered deuterium sublattice was determined by simulated annealing and Rietveld refinement. Deuterium was found to occupy three types of tetrahedral sites: two that are coordinated by four Zr atoms and one that is coordinated by three Zr atoms and one Ni atom. All D-D distances are longer than 2 Å . The feasibility of the crystal structure was supported by density functional theory calculations.
Textured, thin films of BiFeO 3 (∼120 nm thickness) were synthesized by chemical solution deposit... more Textured, thin films of BiFeO 3 (∼120 nm thickness) were synthesized by chemical solution deposition from a mixture of iron-and bismuth-2-methoxyethoxides on Si(100)/SiO 2 /TiO 2 /Pt substrates. The use of alkoxides ensured good homogeneity and a low degree of organics that further facilitated low crystallization temperatures. Crystalline films were according to x-ray diffraction already obtained at 480°C. Precursor characteristics were investigated using thermogravimetry and differential scanning calorimetry, whereas phase purity, microstructure and film topography were examined by x-ray diffraction, transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. A small (10%) Bi excess was found necessary to obtain dense, pore-free films. Such additions also prevented decomposition of BiFeO 3 at high temperatures. The observed (012) texture is believed to originate from the growth mechanism as no relation to the substrate is found. This is also confirmed by observing (012) texture for films on glass substrates.
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
The quality and temperature stability of surface passivation of silicon by a double layer consist... more The quality and temperature stability of surface passivation of silicon by a double layer consisting of a hydrogenated amorphous silicon thin film capped by a silicon nitride anti-reflection coating are studied. It is established that the passivation effect of the double layer can be significantly enhanced after short annealing for temperatures up to about 500 °C, whereas annealing at higher temperatures results in degradation of the passivation properties. It is found that the increased effective recombination lifetime after annealing at temperatures below 500 ºC results from hydrogen redistribution in the interface region. Furthermore, presence of interfacial structural defects formed due to hydrogen release at temperatures around 600 ºC, is believed to be the cause of the lifetime decrease after heat treatments at higher temperatures.
Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrate... more Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping.
The aim of this study was to explore further the preservation of tissues and the mineral distribu... more The aim of this study was to explore further the preservation of tissues and the mineral distribution in 1.6 million-year-old fossil hominin material from Koobi Fora, Kenya attributed to Paranthropus boisei (KNM-ER 1817). Bone, dentine and cementum microstructure were well preserved. Electron microprobe analysis of dentine and bone revealed an F-bearing apatite. Calcite now filled the original soft tissue spaces. The average Ca/P atomic ratio was 1.93, as compared to 1.67 in biological hydroxyapatite, indicating that the Ca-content had increased during fossilization. Analytical sums for mineral content were approximately 90 wt%. Some of the remaining 10 wt% may be preserved organic material. Demineralized dentine fragments showed irregularly distributed tubules encircled with a fibrous-like electron-dense material. A similar material was observed in demineralized dentine. Within this, structures resembling bacteria were seen. In demineralized bone an electron-dense material with a f...
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
The quality and temperature stability of surface passivation of silicon by a double layer consist... more The quality and temperature stability of surface passivation of silicon by a double layer consisting of a hydrogenated amorphous silicon thin film capped by a silicon nitride anti-reflection coating are studied. It is established that the passivation effect of the double layer can be significantly enhanced after short annealing for temperatures up to about 500 °C, whereas annealing at higher temperatures results in degradation of the passivation properties. It is found that the increased effective recombination lifetime after annealing at temperatures below 500 ºC results from hydrogen redistribution in the interface region. Furthermore, presence of interfacial structural defects formed due to hydrogen release at temperatures around 600 ºC, is believed to be the cause of the lifetime decrease after heat treatments at higher temperatures.
Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrate... more Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping.
A simple method for high-precision epitaxial semiconductor growth, using ex situ materials analys... more A simple method for high-precision epitaxial semiconductor growth, using ex situ materials analysis for frequent re-calibration, has been developed. The method is shown to allow reproducible growth of material for use in low-cost commercial heterostructure devices. Even tunnel devices, with their extreme sensitivity to growth parameters, show little variation in the electrical characteristics from wafers grown several months apart.
ABSTRACT In the expanding field of plasmonics, accurate control of the degree of plasmon localiza... more ABSTRACT In the expanding field of plasmonics, accurate control of the degree of plasmon localization is of crucial importance for tailoring optical properties at the nanoscale. In this paper, the degree of plasmon localization is directly probed by recording the momentum transfer dependence (i.e. the dispersion) of plasmon resonance energies using electron energy loss spectroscopy in the aberration-corrected scanning transmission electron microscope. Limited by the uncertainty principle, resolution in momentum space can easily be tuned by the beam convergence, and it is shown that localization is clearly identifiable, even at low-momentum resolution. In this proof-of-principle study, this technique was applied to multilayer graphene cones containing a varying number of topological defects at their apex. It is shown that a high degree of confinement of the π and π+σ volume plasmons is reached for five pentagonal defects at the cone apex. This effect was attributed to the presence of the topological defects themselves. Furthermore, slight negative refraction was observed for the five-pentagon cone, predominantly affecting the collective excitation of the π electrons.
We have investigated the thermoelectric material Zn 4 Sb 3 using transmission electron microscopy... more We have investigated the thermoelectric material Zn 4 Sb 3 using transmission electron microscopy (TEM). Nanoscale inclusions with a diameter of about 10 nm were observed, constituting on the order of 1% by volume of the material. Studies using energy filtered imaging, electron diffraction, and high-angle annular dark-field STEM indicate that the inclusions consist of Zn. These inclusions are expected to scatter the medium and long-wavelength phonons effectively, thus contributing to phonon glass behavior which results in the exceptionally low thermal conductivity for this thermoelectric material.
Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium ... more Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium alloys have been carried out. The Ga alloys were made by triturating a LU powder (Ag-Sn-Cu rich alloy powder) and a GF powder (Ag-Sn-Cu-Pd rich alloy powder) with a liquid Ga alloy containing Ga, In and Sn. The dental materials were found to be composites consisting of remaining, undissolved particles from the Ag-based alloy powders in a matrix of reaction products with the Ga alloy. SEM studies have been carried out to give an overview of the composites. The distribution of the elements was found by the X-ray mapping technique. The phases in the matrix and the remaining alloy particles have been identified by electron diffraction, high-resolution electron microscopy and energy-dispersive X-ray spectroscopy. The following phases were identified in the LU alloy: orthorhombic Ag3Sn, cubic Ag9In4, tetragonal beta-Sn and hexagonal Ag2Ga. In addition to these well-known phases Ga-rich regions were observed consisting of an intergrowth of tetragonal CuGa2 and one of the cubic gamma-Cu9Ga4 phases. In addition to these phases cubic Ga7Pd3 was found in the GF alloy. The anomalous setting expansion of the GF alloy may be explained by the presence of Ga7Pd3.
Nanocomposite Cr-B-N coatings were deposited from CrB 0.2 compound targets by reactive arc evapor... more Nanocomposite Cr-B-N coatings were deposited from CrB 0.2 compound targets by reactive arc evaporation using an Ar/N 2 discharge at 500°C and −20 V substrate bias. Elastic recoil detection (ERDA), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) were used to study the effect of the N 2 partial pressure on composition and microstructure of the coatings. Cross-sectional scanning electron microscopy (SEM) showed that the coating morphology changes from a glassy to a columnar structure with increasing N 2 partial pressure, which coincides with the transition from an amorphous to a crystalline growth mode. The saturation of N content in the coating confirms the formation of a thermodynamically stable CrN-BN dual-phase structure at higher N 2 fractions, exhibiting a maximum in hardness of approximately 29 GPa.
Nanocrystals embedded in SiO 2 films are the subject of a number of recent works, mainly because ... more Nanocrystals embedded in SiO 2 films are the subject of a number of recent works, mainly because of their potential usefulness in the fabrication of optoelectronic devices and nanocrystal memory structures. One interesting method for the fabrication of such nanocrystals is the ion implantation of segregating species into SiO 2 films followed by heat treatment in order to induce nanocrystal formation. This method is both relatively simple and also compatible with the current MOS (metal-oxide-semiconductor) device technology. An unintentional effect can occur during the fabrication of nanocrystals using this method, namely a significant diffusion of the implanted species during annealing, away from the regions with the highest concentration. The Si/ SiO 2 interface can be exposed to this diffusion flux. This can result in an altered interface and have a significant influence on electronic devices. Here, we report on ion implantation of Ge into SiO 2 on Si followed by annealing under conditions, resulting in Ge accumulation at the Si/ SiO 2 interface as determined by secondary-ion mass spectroscopy analysis, transmission electron microscopy with energy dispersive analysis of x-rays, and Rutherford backscattering spectrometry. The accumulation of Ge at the Si/ SiO 2 interface has also been reported before. The resulting effect on the electronic structure of the interface is a priori unknown. We have fabricated MOS capacitors on the sample structures and their capacitance-voltage characteristics were measured and analyzed. We measure an interface state density around 1 ϫ 10 12 cm −2 , which is high compared to standard Si MOS devices. We discuss the results in terms of the previous electrical measurements on Ge-oxide interfaces and SiGe interfaces, which also can yield a high interface state density. The specific conditions we report result in a sufficiently low Ge concentration that nanocrystals are not segregated in the SiO 2 film, while Ge still accumulates at the Si/ SiO 2 interface after annealing.
Acta Crystallographica Section B Structural Science, 2006
The crystal structure of Zr 2 NiD 4.5 has been determined by a combination of synchrotron radiati... more The crystal structure of Zr 2 NiD 4.5 has been determined by a combination of synchrotron radiation powder X-ray diffraction, electron diffraction and powder neutron diffraction data. Deuterium ordering results in a triclinic supercell given by a super = 6.81560 , b super = 8.85137 (9), c super = 8.88007 (10) Å , super = 79.8337 , super = 90.0987 (9), super = 90.3634 , which relates to the non-super unit cell as a super = Àa, b super = Àb À c, c super = Àb + c. The centrosymmetric and fully ordered deuterium sublattice was determined by simulated annealing and Rietveld refinement. Deuterium was found to occupy three types of tetrahedral sites: two that are coordinated by four Zr atoms and one that is coordinated by three Zr atoms and one Ni atom. All D-D distances are longer than 2 Å . The feasibility of the crystal structure was supported by density functional theory calculations.
Textured, thin films of BiFeO 3 (∼120 nm thickness) were synthesized by chemical solution deposit... more Textured, thin films of BiFeO 3 (∼120 nm thickness) were synthesized by chemical solution deposition from a mixture of iron-and bismuth-2-methoxyethoxides on Si(100)/SiO 2 /TiO 2 /Pt substrates. The use of alkoxides ensured good homogeneity and a low degree of organics that further facilitated low crystallization temperatures. Crystalline films were according to x-ray diffraction already obtained at 480°C. Precursor characteristics were investigated using thermogravimetry and differential scanning calorimetry, whereas phase purity, microstructure and film topography were examined by x-ray diffraction, transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. A small (10%) Bi excess was found necessary to obtain dense, pore-free films. Such additions also prevented decomposition of BiFeO 3 at high temperatures. The observed (012) texture is believed to originate from the growth mechanism as no relation to the substrate is found. This is also confirmed by observing (012) texture for films on glass substrates.
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Papers by A. Gunnaes