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Light-induced metastabilities of Cu(In,Ga)Se2 (CIGS)-based thin film solar cells have been extensively researched for many years. It is commonly observed that junction capacitance and p-doping level in CIGS absorbers increase considerably after light soaking (LS). In this work, we focus on the LS behaviors of cells with different minority carrier lifetimes (τn). Experiments show that high efficiency cells with long τn lose open circuit voltage (Voc) and fill factor (FF) upon LS, whereas low efficiency cells with short τn lose less or even gain Voc and FF. The sodium content measured with glow discharge optical emission spectroscopy (GD-OES) increases in the region close to the CdS/CIGS interface with LS and may contribute to the observed LS behaviors. The change in electrical parameters is explained with simulations, which relate the Voc and FF changes to a reduced recombination rate in the space charge region due to the light-induced doping increase. The simulations also suggest that cells with higher n-doping in the CdS are less sensitive to changes in interface recombination rate and doping of CIGS, which agrees with the hypothesis that the CdS buffer deposition is important for the LS behavior.

The influence of the average Se-to-metal overpressure during three-stage co-evaporation of Cu(InxGa1−x)Se2 solar absorber layers has been investigated. Solar cell devices were fabricated using a baseline process consisting of chemical bath deposited CdS, magnetron sputtered intrinsic and Al-doped ZnO, and e-beam evaporated Ni/Al/Ni current collection grid. For the higher Se-to-metal rate ratios studied, an increased short-circuit current in combination with a decreased fill factor is observed, while the open-circuit voltage stays fairly constant. Based on quantum efficiency measurements, fitting of IV data to a one-diode model, and simulations, we suggest the observed effects to be due to a decreased effective doping in combination with a decreased bulk recombination with higher average Se-to-metal overpressures. This could e.g. be explained by a decreasing number of Se-vacancies or VSe–VCu divacancies with higher Se rate. For the range of lower average Se-to-metal rate ratios studied, device performance drops due to a decreased open-circuit voltage and, for the lowest Se rate investigated, fill factor. In addition to electrical characterization, the effects on absorber microstructure are discussed based on results obtained from X-ray diffraction and scanning electron microscopy.

Current available techniques for transmission electron microscopy (TEM) of tooth–biomaterial interfaces are mostly ineffective for brittle phases and impair integrated chemical and morphological characterization. Objectives The aims of this study were (1) to determine the applicability of new focused ion beam (FIB) and broad ion beam (BIB) techniques for TEM preparation of tooth–biomaterial interfaces; (2) to characterize the interfacial interaction with enamel and dentin of a conventional glass-ionomer (Chemfil Superior, DeTrey Dentsply, Germany), a 2-step self-etch (Clearfil SE, Kuraray, Japan) and a 3-step etch-and-rinse (OptiBond FL, Kerr, USA) adhesives; and (3) to characterize clinically relevant interfaces obtained from actual Class-I cavities. Methods After bonding to freshly extracted human third molars, non-demineralized and non-stained sections were obtained using the FIB/BIB techniques and examined under TEM. Results The main structures generally disclosed in conventional ultramicrotomy samples were recognized in FIB/BIB-based ones. There were not any major differences between FIB and BIB concerning the resulting ultrastructural morphology. FIB/BIB-sections enabled to clearly resolve sub-micron hydroxyapatite crystals on top of hard tissues and the interface between matrix and filler in all materials, even at nano-scale. Some investigated interfaces disclosed areas with a distinct “fog” or “melted look”, which is probably an artifact due to surface damage caused by the high-energy beam. Interfaces with enamel clearly disclosed the distinct “keyhole” shape of enamel rods sectioned at 90°, delimited by a thin electron-lucent layer of inter-rod enamel. At regions where enamel crystals ran parallel with the interface, we observed a lack of interaction and some de-bonding along with interfacial void formation. Significance The FIB/BIB methods are viable and reliable alternatives to conventional ultramicrotomy for preparation of thin sections of brittle and thus difficult to cut biomaterial–hard tissue interfaces. They disclose additional ultrastructural information about both substrates and are more suitable for advanced analytic procedures.

Calcium aluminate is the main constituent in calcium aluminate cements, used in a wide range of applications in construction and mining industries and recently also as biomedical implant. In applications that demand very precise reaction features, such as the biomedical ones, the phase purity is of very high importance. In this paper the formation of CaAl2O4 from CaCO3–Al2O3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 °C. Phase formation was studied in samples both quenched from the holding temperatures and in samples slowly cooled. Samples were characterized by X-ray powder diffraction (XRPD), using Guinier-Hagg film data and the Rietveld method, and scanning (SEM) and transmission (TEM) electron microscopy. Samples for TEM with very high site accuracy were produced using focused ion beam microscopy. In addition to CA (CaAl2O4) the samples contained major amounts of CA2 (CaAl4O7), C12A7 (Ca12Al14O33) and minor amounts of un-reacted A (Al2O3). Trace amounts of C3A (Ca3Al2O6) were observed only for samples heated to 1500 °C. The amount of the Ca-rich phase C12A7 was found to decrease with time as it reacts with A and, to a less degree, CA2 to form CA. In agreement with previous studies the amount of CA2 formed decreases comparatively slowly with time. Its un-reactivity is due to that it is concentrated in isolated porous regions of sizes up to 100 μm. The formation of the Ca aluminates is found to be in response to local equilibriums within small inhomogeneous regions, with no specific phase acting as an intermediate phase. Samples quenched from 1500 °C were found to contain smaller amounts of poorly crystallized phases. A reaction between C and A takes place already at 900 °C, forming a meta-stable orthorhombic modification of CA. The orthorhombic unit cell with a = 8.732(2) A, b = 8.078(2) A, c = √3·a = 15.124(4) A was verified by electron diffraction, revealing frequent twinning and disorder of the crystallites.

A method for producing ordered carbon nanopillar arrays is presented. The method is based on ion irradiation through a small anodic porous alumina membrane, resulting in carbon deposition within the centers of the pores on a gold covered SiO 2 / Si substrate. Samples were irradiated by 4 MeV Cl 2 + ions with fluences of 10 15 – 10 16 ions / cm 2 . The combined use of pick’n place positioning of the small porous alumina templates and ion beam irradiation is well suited for post-processing on silicon based integrated circuits. It provides fast local deposition at low temperature of high-density ordered carbon nanopillar arrays in larger silicon based systems, e.g., for field emitting or biosensors applications.

Electrical contacts of NiSi0.82Ge0.18 to p+-Si0.82Ge0.18 were fabricated and characterised. Lateral growth of the NiSi0.82Ge0.18 under SiO2 isolation was observed. A three-dimensional model was employed to extract the contact resistivity by considering both the lateral growth and the presence of a recessed NiSi0.82Ge0.18 step into the Si0.82Ge0.18. The contact resistivity extracted was 5.0 × 10− 8 and 1.4 × 10− 7 Ω cm2 for small contacts of circular geometry and large contacts of square shape, respectively. Possible causes responsible for this 3-fold difference in contact resistivity were discussed. An underestimate of the contact resistivity by 35% was found if a two-dimensional model was used without taking into account the complex interface morphology.