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Benefits for mothers and children can be achieved through the successful integration of an early childhood development programme into PMTCT Option B+ services in Malawi.Our study based on in-depth interviews with 62 mothers indicated that such an approach is feasible and acceptable.Participating mothers reported that the integration of the early childhood development component improved their confidence and they believed it improved their parenting;led to improved relationships with health care providers;increased the engagement of fathers and support from others in the family;helped mothers build a new social network and support system through the peer engagement components;reduced the risk of stigmatization in the health care setting.

The interaction of clean and partially oxidized Cu(110) with sulphur was studied by scanning tunneling microscopy and density functional theory calculations in the low-coverage range. On the clean Cu surface individual S atoms adsorb in the troughs between the Cu atom rows. Hollow sites are preferred, but long-bridge sites are occasionally occupied as well. The majority of adsorbed S, however, seems to be involved in the formation of highly mobile CuxSy clusters of various sizes. The clusters preferentially attach to steps thus changing the step morphology completely. Some of the clusters form aggregates on the terraces. On the partially oxidized surface similar clusters form and cause long-range mass transport to steps. Additionally, nanowires form in [001] direction on and along the surface oxide stress domains. These nanowires have a complex composition, exhibit different corrugations and appear sometimes as three-dimensional needles. Occasionally they flip their direction by 90°, but doing so they partially decompose. Finally, annealing of the S-O-Cu surface leads to consumption of the surface oxide stripes indicating loss of oxygen presumably via SO2 formation. Simultaneously, linear sulphur chains suspended between the [001] –O-Cu-O- chains form in [ 1 1 ¯ 0 ] direction. The surprising multitude of processes and products even at low-pressure, low-temperature conditions in the comparatively simple S-O-Cu system highlights the difficulty of controlling reactivity and selectivity on such convertible catalyst surfaces.

Author(s): Kameni Boumenou, C; Elizabeth, A; Babbe, F; Debot, A; Monig, H; Redinger, A | Abstract: In-depth understanding and subsequent optimization of the contact layers in thin film solar cells are of high importance in order to reduce the amount of nonradiative recombination and thereby improve device performance. In this work, the buried MoSe2/CuInSe2 interface of stoichiometric absorbers is investigated with scanning tunneling spectroscopy and Kelvin probe force microscopy combined with compositional measurements acquired via photo-electron spectroscopy after a mechanical lift-offnprocess. We find that the local density of states, as measured with scanning tunneling spectroscopy, is similar to the front-side of ultra-high vacuum annealed CISe absorbers. The grain boundaries exhibit a weak upward band bending, opposite to Cu-poor CuGaSe2, and we measure an increased Cu accumulation at the rear CISe surface compared to the bulk composition and a non-zero concentration of Cu on the Mo-side. Grazing incidence X-ray diffraction measurements corroborate that a small amount of a CuxSe secondary phase is present at the MoSe2/CuInSe2 interface in contrast to reports on Cu-poor material. Our findings shed new light into the complex interface formation of CuInSe2-based thin film solar cells grown under Cu-rich conditions.

The primary objective of this work was the fabrication and testing of a wireless LC resonator based on micro-patterned electroceramic materials for the monitoring of high-temperature systems. The two-dimensional planar LC resonator sensors were designed and simulated using ANSYS Maxwell software, and these sensors were then fabricated from electrically conductive La 2 NiO 4 /Al 2 O 3 particulate inks. The patterning and deposition of the ink were completed using a novel micro-casting process onto Al 2 O 3 ceramic substrates, and the final pattern was bonded onto the substrate at 1200 o C for 2 h. The final patterned materials were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and four-point conductivity to characterize the phase and microstructure development, and the resultant electrical conductivity (at 500-1200 o C), respectively. The frequency shift with respect to temperature was measured, which is directly related to changes in the sensor’s dielectric permittivity and pattern dimensions. The sensors were characterized at 500 – 1000 o C in an ambient atmosphere with an RF signal ranging from 10 – 80 MHz at 175 kHz·s -1 sweep rate. A new robust and adaptive signal processing approach was introduced to increase the degree of freedom for analyzing the wireless sensors.

Author(s): Boumenou, CK; Babbe, F; Elizabeth, A; Melchiorre, M; Spindler, C; Guillot, J; Monig, H; Siebentritt, S; Redinger, A | Abstract: Effective defect passivation of semiconductor surfaces and interfaces is indispensable for the development of high efficiency solar cells. In this study we systematically investigated the surface and grain boundary properties of CuInSe2 (CISe) with scanning tunneling microscopy (STM) and spectroscopy (STS) after different surface treatments such as potassium cyanide (KCN) etching, pre-electrolyte treatment with cadmium ions, and annealing in ultrahigh vacuum (UHV). We show that air exposed samples with a subsequent KCN etching step exhibits a highly defective surface. However, a Cd pre-electrolyte treatment passivates most of these defects, which manifests itself by a reduction of the high conductance in the STS measurements at positive sample biases. The origin of the improvement can be traced back to an increase in surface band bending, which leads to a type inversion, induced by a change in the concentration of Cu vacancies. We observe a defect passivation at the CISe surface and at the grain boundaries. Our results give a direct explanation of why the CdS buffer layer in CISe thin film solar cells is of utmost importance for high efficiency devices.

Background: Daily oral TDF/FTC is protective against HIV infection when used for pre-exposure prophylaxis (PrEP). However, daily adherence to oral PrEP is difficult for many; therefore, finding alternative PrEP strategies remains a priority. HPTN 076 evaluated the long-acting injectable form of rilpivirine (RPV), known as RPV LA for safety, pharmacokinetics and acceptability. Methods: HPTN 076 (NTC 02165202) was a phase 2, double-blind, 2:1 randomized trial comparing the safety of 1200mg RPV LA (LA) to placebo (P). The study included a 28-day oral run-in phase of daily, self- administered oral RPV (25 mg), with directly observed oral dosing about six times. Of 136 enrolled sexually active, HIV-uninfected, low HIV-risk African (100) and US (36) adult women, injectable product was administered in two gluteal, intramuscular (IM) injections once every eight weeks to 122 participants following the oral run-in phase. A maximum of six injection time points occurred over a 48-week period. Acceptability, safety, tolerability and pharmacokinetic (PK) data were collected throughout the study. This paper includes primary endpoint data collected up to the week 52 post enrollment. Findings: The median age of the enrolled population was 31 years (IQR: 25,38), median weight 75 kg (IQR: 64, 89), median body mass index (BMI) 30 (IQR: 27, 35), 46% married, 94% Black and 60% unemployed. A total of 122 (80 LA, 42 P) women received at least one injection and 98 (64 LA, 34 P) received all six injections. During the injection phase, three women withdrew from the study (2 LA, 1 P) and 16 women discontinued study product (10 LA, 6 P). Fourteen women (11 LA and 3 P) discontinued oral study product and did not enter the injection phase. Study product discontinuations were not significantly different between the two arms throughout. Of the product discontinuations in the injection phase, 8% in LA and 5% in P arm were due to adverse events (AEs), including one randomized to the P arm with prolonged QTc interval on EKG. The proportion of women who experienced Grade 2 or higher AEs during the injection phase as the primary outcome was not significantly different between the two arms [73.8%, 95% CI: (63.2%, 82.1%) for LA and 73.8%, 95% CI: (58.9%, 84.7%), p>0.99]. Transient Grade ≥2 liver abnormalities occurred in 14% of women in the LA arm compared with 12% in P arm. Three LA women (4%) developed Grade 3 injection site reactions compared with none in P arm. In participants who received at least 1 injection, the geometric mean of overall RPV trough concentrations (Ctrough) was 62.2 ng/mL. In participants who received all six injections, the geometric mean of CTrough through the injection phase and after the last injection were 72.8 ng/mL and 100.9 ng/mL, respectively. At week 52 (eight weeks after last injection), the geometric mean of RPV Ctrough was 75.0 ng/mL. At the last injection visit (Week 44), 80 % of women who answered acceptability questions strongly agreed that they would think about using- and 68% that they would definitely use a PrEP injectable in the future. Interpretation: RPV LA IM injections every eight weeks in African and US women were safe and acceptable. Overall, despite more injection site reactions and pain in the participants receiving RPV LA the injections were well tolerated. Data from this study support the further development of injectable PrEP agents. Keyword: RPV LA as Pre exposure prophylaxis

Alkali post-deposition treatments (PDTs) of Cu(In,Ga)Se 2 (CIGSe) absorbers are known to improve the power conversion efficiency of the thin-film solar cell devices. The PDTs are usually carried out via evaporation of alkali fluorides in a selenium atmosphere onto a hot substrate. In this work, an alkali metal dispenser was used to evaporate pure metallic potassium onto epitaxial CIGSe absorbers. Subsequently, the absorber layers were heated in-situ to monitor chemical reactions and diffusion into the bulk. Due to the absence of grain boundaries, fluorine, and selenium, the effect of K on CIGSe absorber properties can be directly monitored. We find that potassium effectively diffuses into the bulk of epitaxial CIGSe absorber layers. The diffusion depends on the Cu-content of the CIGSe absorbers, in which Cu-depleted films present higher diffusion rate of K. Photoluminescence (PL) imaging corroborates that K in the bulk of the CIGSe absorber increases the PL yield, suggesting a passivation of defects or an increase in doping. This work highlights that alkali PDTs are not limited by interface and grain boundary modifications but also changes the absorber bulk properties, which needs to be taken into account.

The p-type semiconductor Cu2SnS3 is alloyed with Ag to investigate its effect on absorber layer and solar cell properties. Ag replaces the Cu in (Cu1‐ x Ag x )2SnS3 (ACTS) up to x ≤ 6% at 550 °C. Above this percentage, Ag forms secondary phases. We find a significant increase in grain size, from hundreds of nanometers to several microns, and increased photoluminescence yield with increasing Ag concentration. Low-temperature photoluminescence measurements show that compensation is increased for the ACTS absorber layers, which could be beneficial for CTS, but also that the electrostatic band gap fluctuations are increased. The external quantum efficiency of the solar cells made from ACTS shows an increased carrier collection length from 320 nm for CTS to 700 nm and a thicker buffer layer. We attribute the increase in collection length to both increased depletion width (increased compensation) and diffusion length (larger grains). Overall the ACTS solar cells have a lower power conversion efficiency due to lower shunt resistance and open-circuit voltage, which are attributed to increase in pinholes, electrostatic fluctuation, and changes at the CdS/ACTS interface.

The selenization of metallic Cu-Zn-Sn-Ge precursors is a promising route for the fabrication of low-cost and efficient kesterite thin film solar cells. Nowadays, efficiencies of kesterite solar cells are still below 13 %. For Cu(In,Ga)Se2 solar cells, the formation of compositional gradients along the depth of the absorber layer has been demonstrated to be a key requirement for producing thin film solar cells with conversion efficiencies above the 22 % level. No clear understanding has been reached so far about how to produce these gradients in an efficient manner for kesterite compounds, but among the possible candidates, Ge arises as one of the most promising ones. In the present work, we evaluate the potential of incorporating Ge in Cu2ZnSnSe4 to produce compositional gradients in kesterites. Synchrotron-based in-situ energy-dispersive X-ray diffraction and X-ray fluorescence has been used to study the selenization of Cu-Zn-Sn-Ge metallic precursors. We propose a reaction mechanism for the incorporation of Ge atoms into the kesterite lattice after the formation of Cu2ZnSnSe4. Electron microscopy reveals that the annealing process leads to Cu2Zn(Sn,Ge)Se4 absorber layers with an increase of Ge content towards the back contact with independence of the original location of Ge in the precursor layer. The effect of the Ge gradient on the optoelectronic properties of the absorber layer has been evaluated with room temperature cathodoluminescence. The implications of the results for the development of kesterite solar cells are discussed, with the aim of encouraging new synthesis routes for compositionally graded absorbers.

An in-depth understanding of the electronic properties of grain boundaries (GBs) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very high and hence limit the solar cell device performance. Kelvin Probe Force Microscopy (KPFM) is the method of choice to investigate GB band bending on the nanometer scale and thereby helps to develop passivation strategies. Here, it is shown that the workfunction, measured with amplitude modulation (AM)-KPFM, which is by far the most common KPFM measurement mode, is prone to exhibit measurement artifacts at grain boundaries on typical solar cell absorbers such as Cu(In,Ga)Se 2 and CH 3 NH 3 PbI 3 . This is a direct consequence of a change in the cantilever–sample distance that varies on rough samples. Furthermore, we critically discuss the impact of different environments (air versus vacuum) and show that air exposure alters the GB and facet contrast, which leads to erroneous interpretations of the GB physics. Frequency modulation (FM)-KPFM measurements on non-air-exposed CIGSe and perovskite absorbers show that the amount of band bending measured at the GB is negligible and that the electronic landscape of the semiconductor surface is dominated by facet-related contrast due to the polycrystalline nature of the absorbers.

Kesterite Cu2ZnSnS4 (CZTS), having only earth abundant elements, is a promising solar cell material. Nevertheless, the impact of the SnS secondary phase, which often forms alongside CZTS synthesis at high annealing temperature, on CZTS solar cells is poorly studied. We confirm, by means of X-ray diffraction, Raman scattering, and energy dispersive X-ray spectroscopy mapping, that this phase tends to segregate at both the surface and the back side of annealed CZTS films with Cu-poor and Zn-rich composition. Using electron beam-induced current measurements, it is further demonstrated that the formation of SnS on the CZTS surface is harmful for solar cells, whereas the SnS phase can be beneficial for solar cells when it segregates on the CZTS rear. This positive contribution of SnS could stem from a passivation effect at the CZTS/SnS rear interface. This work opens new possibilities for an alternative interface development for kesterite-based photovoltaic technology.

In this atom probe tomography study of the composition of extended defects in Cu-poor Cu${}_{2}$ZnSnSe${}_{4}$ thin films, the authors detect Na segregation, Cu enrichment, and Zn, Sn, and Se depletion at grain boundaries in a precursor film. Stacking faults show Zn enrichment and Cu and Sn depletion in the same precursor. After an annealing step, the authors observe that the Na excess at grain boundaries is increased by one order of magnitude and that grain boundaries and dislocations in the annealed film exhibit, in general, significantly reduced chemical variations.

Halogens are used as modifiers in catalytic processes, notably including photocatalytic watersplitting; as redox-active species in dye-sensitized solar cells; and as etchants in device fabrication. Atomically resolved studies of the adsorption and reactivity of halogens on Pt and Pd surfaces are scarce in view of the prominent role these metals play in the mentioned applications. The present study reports phases of halogens on Pd(110) in the submonolayer coverage range as monitored by temperature-programmed desorption, low-energy electron diffraction, scanning tunneling microscopy, and density functional calculations. Domain wall and compression structures are observed, as is typical for halogens (except fluorine) on transition and noble metals, but not on Pt, where the bonding is much more site-specific and a different succession of phases is found. The reactivity of Br toward Pd(110) is greater than that of Cl, as judged by the corrosive attack and by the bond strength derived from the thermal desorption temperature. The results confirm that an ionic-bonding picture based on a large metal-to-halogen charge transfer is not valid for Pd and Pt. Rather, the bonding is predominantly covalent, and the reactivity does not obey simple intuitive rules.

We investigate the adsorption of cobalt phthalocyanine (CoPc) molecules on a thin layer of cobalt oxide grown on Ir(100). To that end we compare the results of low-temperature scanning tunneling microscopy (STM) with those of ab-initio density functional theory (DFT) calculations and reveal the adsorption geometry. We find that the CoPc molecules lie flat on the surface and that their central cobalt atom forms a chemical bond to a substrate oxygen ion. However, this bond contributes only modestly to the adsorption energy, while van-der-Waals forces dominate the potential landscape and determine to a large extend the geometry as well as the distortion of substrate and molecule. Furthermore they lead to attractive molecule-molecule interactions at higher molecular coverages. The DFT calculations predict energetic positions of the molecular orbitals which are compared to scanning tunneling spectroscopy (STS) measurements., 14 pages, 5 figures

We have studied the surface of pure and oxidized Pt$_3$Zr(0001) by scanning tunneling microscopy (STM), Auger electron microscopy, and density functional theory (DFT). The well-annealed alloy surface shows perfect long-range chemical order. Occasional domain boundaries are probably caused by nonstoichiometry. Pt$_3$Zr exhibits ABAC stacking along [0001]; only the A-terminated surfaces are seen by STM, in agreement with DFT results showing a lower surface energy for the A termination. DFT further predicts a stronger inward relaxation of the surface Zr than for Pt, in spite of the larger atomic size of Zr. A closed ZrO$_2$ film is obtained by oxidation in $10^{-7}$ mbar O$_2$ at 400 $^\circ$C and post-annealing at $\approx 800 ^\circ$C. The oxide consists of an O-Zr-O trilayer, equivalent to a (111) trilayer of the fluorite structure of cubic ZrO$_2$, but contracted laterally. The oxide forms a $(\sqrt{19} \times \sqrt{19})$R23$^\circ$ superstructure. The first monolayer of the substrate consists of Pt and contracts, similar to the metastable reconstruction of pure Pt(111). DFT calculations show that the oxide trilayer binds rather weakly to the substrate. In spite of the O-terminated oxide, bonding to the substrate mainly occurs via the Zr atoms in the oxide, which strongly buckle down towards the Pt substrate atoms, if near a Pt position. According to DFT, the oxide has a bandgap; STM indicates that the conduction band minimum lies $\approx 2.3$ eV above $E_\mathrm{F}$.

The adsorption of CO molecules at the Ca3Ru2O7(001) surface was studied using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). Ca3Ru2O7 can be easily cleaved along the (001) plane, yielding a smooth, CaO-terminated surface. The STM shows a characteristic pattern with alternating dark and bright stripes, resulting from the tilting of the RuO6 octahedra. At 78 K, CO adsorbs at an apical surface O at the channel edge with a predicted binding energy of E ads = − 0.85 eV. After annealing at room temperature, the CO forms a strong bond ( E ads = − 2.04 eV) with the apical O and the resulting carboxylate takes the place of the former surface O. This carboxylate can be decomposed by scanning the surface with a high sample bias voltage of +2.7 V, restoring the original surface.

The continuous improvement of Cu(In,Ga)Se2 (CIGSe) solar cells relies considerably on advanced characterization of individual layers in the solar-cell stacks as well as of completed CIGSe devices. The present contribution provides an overview of corresponding efforts performed by various research groups at Helmholtz-Zentrum Berlin fur Materialien und Energie GmbH. In-situ growth monitoring of CIGSe absorber layers by means of energy-dispersive X-ray spectrometry and light scattering is described, as well as structural analyses by means of X-ray and neutron diffraction. In addition, the characterization of surfaces and interfaces by soft X-ray and electron spectroscopy, the microscopic analysis by means of correlative electron microscopy, and optoelectronic characterization by optical spectroscopy are highlighted. The present contribution shows which substantial efforts in a research network are necessary in order to obtain deeper insight into materials properties and potentially limiting factors for the device performance, as well as to be able to control these factors during the solar-cell production.

We present a high-temperature Cu $_2$ ZnSnSe $_4$ coevaporation study, where solar cells with a power conversion efficiency of 7.1% have been achieved. The process is monitored with laser light scattering in order to follow the incorporation of the Sn into the film. We observe the segregation of ZnSe at the Mo/CZTSe interface. Optical analysis has been carried out with photoluminescence and spectrophotometry. We observe strong band tailing and a bandgap, which is significantly lower than in other reported efficient CZTSe absorbers. The photoluminescence at room temperature is lower than the bandgap due to the existence of a large quantity of tail states. Finally, we present effects of low-temperature postannealing of the absorbers on ordering of the Cu/Zn atoms in CZTSe and solar cell parameters. We observe strong changes in all solar cell parameters upon annealing. The efficiency of the annealed devices is significantly reduced, although ordering is improved compared with ones made from nonannealed absorbers.

Evaluating interfering capacitance steps in admittance spectroscopy for solar cell defect analysis is still a problem which needs to be solved. While the common analysis developed by Walter et al.[1] is capable of extracting defect distributions from the capacitance data, it results in erroneous defect densities in the presence of overlapping capacitance steps. We derive an expression for the capacitance step caused by defects with a density of states distributed in energy. By adding several of these defect distributions, interfering capacitance steps can be described. Thus, it is possible to fit the entire capacitance spectrum simultaneously for all temperatures. We apply the presented method to Cu 2 ZnSnSe 4 -based solar cells with power conversion efficiencies between 5% and 7%. Comparing the obtained defect parameters with the ones obtained by the method from Walter et al. reveals that the Walter method overestimates the defect densities in the case of overlapping capacitance steps.

In this study, we investigate the structural and chemical changes of monatomic ${\mathrm{CoO}}_{2}$ chains grown self-organized on the Ir(100) surface [P. Ferstl et al., Phys. Rev. Lett. 117, 046101 (2016)] and on Pt(100) under reducing and oxidizing conditions. By a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory we show that the cobalt oxide wires are completely reduced by ${\mathrm{H}}_{2}$ at temperatures above 320 K and a $3\ifmmode\times\else\texttimes\fi{}1$ ordered ${\mathrm{Ir}}_{2}\mathrm{Co}$ or ${\mathrm{Pt}}_{2}\mathrm{Co}$ surface alloy is formed. Depending on temperature, the surface alloy on Ir(100) is either hydrogen covered $(Tl400$ K) or clean and eventually undergoes an irreversible order-disorder transition at about 570 K. The ${\mathrm{Pt}}_{2}\mathrm{Co}$ surface alloy disorders with the desorption of hydrogen, whereby Co submerges into subsurface sites. Vice versa, applying stronger oxidants than ${\mathrm{O}}_{2}$ such as ${\mathrm{NO}}_{2}$ leads to the formation of ${\mathrm{CoO}}_{3}$ chains on Ir(100) in a $3\ifmmode\times\else\texttimes\fi{}1$ superstructure. On Pt(100), such a ${\mathrm{CoO}}_{3}$ phase could not be prepared so far, which, however, is due to the ultrahigh vacuum conditions of our experiments. As revealed by theory, this phase will become stable in a regime of higher pressure. In general, the structures can be reversibly switched on both surfaces using the respective agents ${\mathrm{O}}_{2},{\mathrm{NO}}_{2}$, and ${\mathrm{H}}_{2}$.

Atom probe tomography and transmission electron microscopy are used to study the formation of nano sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin -films. For a Cu -rich precursor, which was deposited at 320 degrees C under Cu- and Zn-rich growth conditions, Cu2-xSe grains at the surface are detected. During annealing the precursor at 500 degrees C in a SnSe + Se atmosphere most of the Cu2-xSe is transformed to Cu2ZnSnSe4 via the consumption of excessive ZnSe and incorporation of Sn. However, atom probe tomography studies also reveal the formation of various nanometer-sized Cu-Sn-Se particles close to the CdS/Cu(2)ZnSnSe4 interface. One of those particles has a composition close to the Cu2SnSe3 compound. This phase has a smaller band gap than Cu2ZnSnSe4 and is proposed to lead to a significant drop in the open -circuit voltage and could be the main cause for a detrimental p-n junction and the zero efficiency of the final device. Possible effects of the other phases on solar cell performance and formation mechanisms are discussed as well. (C)2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Nanotechnology for Next Generation High Efficiency Photovoltaics Spring International School and Workshop (NEXTGEN NANOPV), SPAIN, APR 20-24, 2015; International audience; Non-destructive characterization of both single layers and completed devices are important issues for the development of efficient and low cost Cu(In,Ga)(S,Se)(2) (CIGS) modules at high yields. This implies for the need of methodologies suitable for the assessment of optical, electrical, and physico-chemical parameters that are relevant for the final device efficiency and that can be used for quality control and process monitoring at different process steps. In these applications, detection of in-homogeneities in the different layers from large area modules is especially relevant, being the presence of these inhomogeneities responsible for the existing gap between the efficiencies achieved in these technologies at cell and module levels. In this context, this work reviews the different optical methodologies that have been developed in the framework of the SCALENANO European project for the advanced assessment of the different layers in high efficiency electrodeposited - based CIGS devices. This has includes different strategies as those based on Raman scattering, Photoluminescence/Electroluminescence (PL/EL) based techniques and new photoelectrochemical based tools and firstly Raman spectroscopy is very sensitive to both composition and crystal quality parameters that are determining for device efficiency. Use of resonant Raman excitation strategies allows achieving a high sensitivity of the Raman spectra to the analysed features in the different regions of the device. This involves selection of the suitable excitation wavelength (in the broad spectral region from UV to IR) for the resonant Raman excitation of the required layer in the device. The strong increase in the intensity of the Raman peaks related to the use of resonant excitation conditions allows also decreasing the measuring time to times compatible with the implementation of these techniques at online process monitoring level. Analysed parameters include the electrical conductivity of the Al-doped ZnO window layer, the thickness of the CdS buffer layer and the chemical composition (SAS+Se) relative content) and presence of relevant secondary phases as Cu-poor ordered vacancy compounds in the surface region of the absorbers. In addition PL/EL imaging are powerful techniques that provide direct access to the optoelectronic properties of the materials and devices. Whereas EL is performed using complete devices by injecting current in analogy to the operation of a light emitting diode, PL allows the characterization of bare absorber materials without the need for any functional or contacting layers. Moreover, semiconductor photo-electrochemistry (PEC) is a versatile technique that enables many opto-electronic properties of semiconductors to be determined. Essentially, a semiconductor on a conducting substrate placed in a solution containing redox species forms a Schottky barrier junction. The formation of such a diode enables basic semiconductor properties to be measured such as doping type, doping density, band gap and the flat band position versus the vacuum energy scale. In all these cases, quality control indicators suitable for the advanced assessment of these processes have been identified and validated for the electrodeposition-based processes developed at Nexcis Company. (C) 2016 Elsevier B.V. All rights reserved.

Cu2ZnSnSe4 (CZTSe) thin film solar cells have been produced via co-evaporation followed by a high-temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe2 capping layer has been evaporated onto the absorber prior to the high-temperature treatment. This eliminates the Sn losses due to SnSe evaporation. A solar cell efficiency of 5.1% could be achieved with this method. Moreover, the device does not suffer from high series resistance, and the dominant recombination pathway is situated in the absorber bulk. Finally, different illumination conditions (white light, red light, and yellow light) reveal a strong loss in fill factor if no carriers are generated in the CdS buffer layer. This effect, known as red-kink effect, has also been observed in the closely related Cu(In,Ga)Se2 thin film solar cells. Copyright © 2013 John Wiley & Sons, Ltd.

Photoluminescence imaging as well as quantitative photoluminescence spectroscopy has been successfully applied to different solar cell materials, such as crystalline silicon and polycrystalline Cu(In, Ga)Se 2 . These methods can be used to investigate spatial inhomogeneities, as well as for the contactless determination of quasi-Fermi level splittings, which are related to the open-circuit voltage in finished photovoltaic devices. The theory underlying the analysis of quantitative PL imaging is found to work reliably for more ideal semiconductors such as silicon, but can pose substantial problems for the more non-ideal semiconductors such as kesterite-type materials, where both the optical properties as well as the recombination process may vary widely from sample to sample. In this contribution we will evaluate different approaches to analyse quantitative PL imaging and discuss the potential pitfalls incurred, especially when the actual sample temperature during the measurement is not properly taken into account.

The structural evolution of graphene on Ni(111) is investigated as a function of growth temperature by scanning tunneling microscopy (STM). Low temperature (400–500 °C) growth results in a continuous but highly defective film with small ordered graphene domains and disordered domains composed of Stone–Wales (SW)-like defects. As the growth temperature is increased, the disordered domains shrink leaving small clusters of defects alongside epitaxially matched graphene. Density functional theory (DFT) calculations indicate the crucial role of the metallic support for the healing of SW defects, as the interaction with the substrate leads to a stabilization of the reaction intermediate. This work highlights the effect of the graphene–substrate interaction on the temperature dependence of the defect concentration in epitaxial graphene on Ni(111).

The field of low-cost flexible displays has attracted an enormous amount of interest in the past few years. This paper analyzes the challenges associated with designing a backplane for an electrophoretic front plane and develops a general model which relates semiconductor and lithographic performance metrics to display qualities such as speed, uniformity, and resolution. Specific examples are given for all ink-jet printed displays as well as for partially or all photolithographically patterned displays.

A novel method of predicting the lifetime of polycrystalline metal-oxide thin-film transistors (TFTs) is presented. The measured threshold-voltage shift is correlated to the creation of defect (trap) states within the semiconductor grain boundaries. Once this relationship is established, conventional threshold-voltage shift and polycrystalline transport models can be used to predict the TFT current with time. Measured bias-stress data taken from ZnO TFTs fabricated on flexible polyethylene naphthalate substrates are accurately fit using this model.

To investigate the effect of steps on H2O binding on a nominal Pt(111) surface, we used thermal desorption spectroscopy of water adsorbed on purposefully nanostructured surfaces: a rippled surface containing densely packed (100)-microfaceted and (111)-microfaceted steps was created using grazing incidence ion bombardment, and a surface with triangular mounds mainly consisting of (111)-microfaceted steps was fabricated through homoepitaxial growth. These morphologies are determined by scanning tunneling microscopy. We find two additional high-temperature H2O desorption peaks using the rippled surface, whereas only the peak with the highest desorption temperature is present on the (111)-microfaceted mound. Thus, water preferentially binds to steps and especially favors (111)-microfaceted ones. Furthermore, the large step concentration on our nanostructured surfaces precludes the coexistence of a condensed and a diluted phase in a monolayer of water and suppresses the formation of crystalline ice multilayers...

In this work we examined the electronic structure of well-defined TiN/VN bilayers grown on a MgO(100) substrate by both experimentation and calculation. The electron energy-loss spectra were taken in transmission electron microscopes equipped with and without a monochromator. The experimental studies reveal nearly stoichiometric phases with atomic ratios Ti/N of 1.1 ± 0.1 and V/N of 1.2 ± 0.1. The comparison of the electron energy-loss near-edge structures of the N-K, Ti-L2,3, and V-L2,3 spectra with the theoretically calculated partial density of states using density functional theory revealed that core hole effects must be included. The calculations indicate that the N-K edge is sensitive to vacancies in the sublattice of VN. Thus, the N-K edge may be used as a fingerprint when studying non-stoichiometric or diffusional phenomena.

Solution-processed transparent zinc oxide (ZnO) transistors are demonstrated using a chemical bath deposition process for ZnO deposition. The process is glass compatible and amenable to producing fully transparent electronics. Mobility as high as 3.5 cm2/V ldr s with on-off ratios of ~105 is realized. The transparency of ZnO allows for complete coverage of the pixel by the pixel drive transistors; analysis shows that the performance achieved herein is sufficient even to drive high-brightness organic light-emitting diode (OLED) displays by exploiting the high mobility and optical transparency of these devices. This makes this technology extremely attractive for use in active-matrix OLED display applications.

Printed electronics provides a promising potential pathway toward the realization of ultralow-cost RFID tags for item-level tracking of consumer goods. Here, we report on our progress in developing materials, processes, and devices for the realization of ultralow-cost printed RFID tags. Using printed nanoparticle patterns that are subsequently sintered at plastic-compatible temperatures, low-resistance interconnects and passive components have been realized. Simultaneously, printed transistors with mobilities >10/sup -1/ cm/sup 2//V-s have been realized using novel pentacene and oligothiophene precursors for pMOS and ZnO nanoparticles for nMOS. AC performance of these devices is adequate for 135-kHz RFID, though significant work remains to be done to achieve 13.56-MHz operation.

An all ink-jet-deposited process capable of creating high-quality passive devices suitable for an RFID front-end is described. Gold nanocrystals are printed to create conductive lines with sheet resistance as low as 23 m/spl Omega/ per square. Optimal printing conditions are found for polyimide dielectric layers and films as thin as 340 nm are produced. These results are used to create spiral inductors, interconnect, and parallel plate capacitors.

Scanning tunneling spectroscopy measurements on clean V(0 0 1), carbon-covered V(0 0 1) and the oxygen-induced V(0 0 1) (1×5) reconstruction are reported. The clean V(0 0 1) surface shows a strong surface state 0.03 eV below the Fermi level. Isolated impurities shift the surface state 0.05 eV upwards in energy and broaden the peak observed in dI/dV. No significant influence of monoatomic steps on the surface state could be observed. For tunneling resistances down to about 1 M Ω the surface state is unaffected by the tip of the scanning tunneling microscope. A surface state is detected around +0.75 eV in small c(2×2) patches which are observed at higher carbon (and oxygen) coverages. The oxygen induced (1×5) reconstruction of V(0 0 1) shows a peak at similar energy (+0.63 eV) in the areas with O and C atoms in fourfold hollow sites and a peak around +0.91 eV above the rows of bridge-site oxygen. Ab initio band structure calculations confirm the existence of a surface state of dz2 symmetry with an energy close to that observed experimentally on clean V(0 0 1). This agreement provides strong evidence that the V(0 0 1) surface is not magnetic (at least at room temperature) as predicted by the calculations. We also compare the experimentally observed peak shifts on the carbon and oxygen covered surfaces with calculational results for carbon-covered geometries.

Carbon adsorption on V(1 0 0) was studied by both experimental methods and density functional theory. At low carbon coverages of ΘC=0.18 ML and oxygen below the experimental detection limit, measured scanning tunneling microscopy (STM) images show both areas of local c(2×2) structure and 〈0 1 0〉 oriented rows of C atoms. At higher coverages of ΘC=0.41 ML, mainly 〈0 1 0〉 oriented C rows with some local p(1×2) patterns are formed. The observed c(2×2) pattern is attributed to the presence of oxygen, since a mixture of carbon and oxygen favors the c(2×2) superstructure according to both the STM and the ab initio results. The calculations show that for ΘC=0.50 ML the p(1×2) structure is more stable than c(2×2) by 0.13 eV per adsorbed atom. From the ab initio results it is predicted that p(1×2) changes into c(2×2) at a mixed coverage of about ΘC≈0.37 ML and ΘO≈0.13 ML. The geometry of the c(2×2) structure was determined using quantitative low energy electron diffraction showing good agreement with the ab initio data. Also the simulated STM images agree well with the experimental STM data.

The interaction of Cl with Pt(110) was studied in UHV by scanning tunneling microscopy, low-energy electron diffraction, temperature- programmed desorption, and DFT calculations. Up to half a monolayer (ML) of Cl forms an adsorbate structure. Compression to higher local coverages leads to erosion of Pt atoms from the top layer and formation of PtCl(4) pentamers. Anneating results in heating of the Pt defects and formation of a long- range-ordered PtCl(4)/Cl/Pt(110) adlayer that is remarkably simitar to the adtayer structure found after deposition of [PtCl(4)](2-) from an electrolyte onto Au(100). Coadsorption of 0.5 ML of Cl with CO initiates PtCl(4) formation, but no volatile compounds are formed under these conditions. In similar experiments with Br, the original Pt surface is left intact, even if Br is compressed to local coverages of 0.75 ML, in agreement with the expected tower corrosion activity of Br.

The (001) surfaces of cleaved ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ samples were investigated using low-temperature scanning tunneling microscopy and density functional theory calculations. Intrinsic defects are not created during cleaving. This experimental observation is consistent with calculations, where the formation energy for a Sr and O vacancy, 4.19 eV and 3.81 eV, respectively, is significantly larger than that required to cleave the crystal, 1.11 eV/(1 \ifmmode\times\else\texttimes\fi{} 1) unit cell. Surface oxygen vacancies can be created through electron bombardment, however, and their appearance is shown to vary strongly with the imaging conditions. Point defects observed on as-cleaved surfaces result from bulk impurities and adsorption from the residual gas.

Adsorption of CO at the ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}(001)$ surface was studied with low-temperature scanning tunneling microscopy (STM) and density functional theory. In situ cleaved single crystals terminate in an almost perfect SrO surface. At 78 K, CO first populates impurities and then adsorbs above the apical surface O with a binding energy ${E}_{\mathrm{ads}}=\ensuremath{-}0.7\text{ }\text{ }\mathrm{eV}$. Above 100 K, this physisorbed CO replaces the surface O, forming a bent ${\mathrm{CO}}_{2}$ with the C end bound to the Ru underneath. The resulting metal carboxylate (Ru-COO) can be desorbed by STM manipulation. A low activation (0.2 eV) and high binding ($\ensuremath{-}2.2\text{ }\text{ }\mathrm{eV}$) energy confirm a strong reaction between CO and regular surface sites of ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$; likely, this reaction causes the ``UHV aging effect'' reported for this and other perovskite oxides.

During the reconstruction of the Ohio Turnpike, data were collected from construction sites using non-destructive tools. This study was done in two phases: the first one included using the Light Weight Deflectometer (LWD) and Automatic Dynamic Cone Penetrometer (ADCP) to evaluate the subgrade, which was recommended to be stabilized. The second phase included using the Falling Weight Deflectometer (FWD) and Ground Penetration Radar (GPR) to evaluate the structural capacity of the entire pavement. The data generated from these tests were statistically analyzed and compared with traditional measurements to develop QA/QC procedures that optimize risk and cost. This article sheds lights on the first phase of the study, which was mainly concerned with subgrade characterization using LWD and ADCP. The ADCP and LWD data correlated fairly well. Both the ADCP and LWD provide a measure of stiffness, whereby the nuclear density gauge provides a measure of density. In comparison, the LWD seems to be the most promising QA/QC candidate. It was the most cost-effective among the three tests, had the highest rate of production, and was the most reliable.

We have investigated the electronic structure of graphene supported on Re(0001) before and after the intercalation of one monolayer of Ag by means of angle-resolved photoemission spectroscopy measurements and density functional theory calculations. The intercalation of Ag reduces the graphene-Re interaction and modifies the electronic band structure of graphene. Although the linear dispersion of the {\pi} state of graphene in proximity of the Fermi level highlights a rather weak graphene-noble metal layer interaction, we still observe a significant hybridization between the Ag bands and the {\pi} state in lower energy regions. These results demonstrate that covering a surface with a noble metal layer does decouple the electronic states, but still leads to a noticeable change in the electronic structure of graphene., Comment: 5 pages, 3 figures

We present results, obtained by first principles density functional calculations, simulating scanning tunneling microscopy (STM) images for 1.5 monolayer of Co deposited on a p(1×2) Pt(1 1 0) surface. Two different surface structures are investigated theoretically: a CoPt/Pt(1 1 0) film covered by a Co monolayer, and Co/Pt(1 1 0) covered by an ordered CoPt layer. The surface geometry has been fully relaxed minimizing forces on ions. Covering with a cobalt monolayer reveals a tendency to form double-rows, the CoPt covered film features surface rumpling. STM scans were simulated using perturbation theory, the influence of different tip compositions is analyzed. The results obtained are in reasonable agreement with experimental findings.

The first scanning tunneling spectroscopy measurements on V(001) are reported. A strong surface state is detected which is very sensitive to the presence of segregated carbon impurities. The surface state energy shifts from 0.03 eV below the Fermi level at clean areas towards higher energies (up to approximately 0.2 eV) at contaminated areas. Because of the negative dispersion of this state, the upward shift cannot be described in a simple confinement picture. Rather, the surface state energy is governed by vanadium surface s- d interactions which are altered by carbon coverage.

Scanning tunneling microscopy (STM) scans on Fe(100) are compared with first principles calculations of the tunneling current based on the transfer Hamiltonian method. Experimentally, we find a reversal of corrugation for separations between sample and tip below 400 pm. In the simulations we can reproduce these topographies only in a distance range above 400 pm. The approach therefore fails to describe the observed corrugation reversal. We suggest that this failure is due to the quenching of surface states by the approaching STM tip.

To probe the influence of realistic tip models on the tunnel current and the corrugation of binary alloy surfaces we have calculated the electronic structure of PtX (100) sample surfaces and realistic STM tips with different tip atoms. We then used the Bardeen integral to calculate the tunnel current from the electronic structure of sample and tip numerically. Apart from the usual approximations of the perturbation approach the method developed is therefore fully ab initio. It can be shown that the currents obtained in the limit of low bias voltage are within the range of measurements, and equally, that including a realistic tip improves the agreement between measurements and calculations.

Atomically resolved scanning tunneling microscopy (STM) of ultra-thin NaCl films on Al(111) and Al(100) demonstrates that only one atomic species of NaCl is imaged as a protrusion. By comparison of the constant current STM images with ab initio calculations of the local density of states by means of the full-potential linearized augmented plane wave method, the protrusions could be attributed to the anion Cl – . The calculations shows that a higher density of occupied states at the Cl-sites than for the Na-sites around the Fermi level causes the STM contrast between Cl and Na. With increasing number of NaCl layers the density of states in the band gap is reduced and the apparent height of additional NaCl layers decreases. The maximum film thickness allowing successful imaging by STM was found to be three layers.

Recent STM studies achieved chemical resolution on PtRh and PtNi alloy surfaces. By a first-principles method employing the Tersoff–Hamann model, we have simulated STM scans on PtRh and PtNi(100) surfaces by calculating the apparent heights of individual surface atoms. The difference in apparent heights between Pt and Rh atoms is caused by changes in the density of states due to alloying. The simulations for the PtNi(100) surface, however, yield apparent heights of Pt and Ni atoms below atomic resolution, indicating that in the experiment, tip–sample interactions are responsible for chemical and atomic resolution.

Secondary phases, such as ZnSe, occur in Cu2ZnSnSe4 and can be detrimental to the resulting solar cell performance. Therefore, it is important to have simple tools to detect them. We introduce subband gap defect excitation room temperature photoluminescence of ZnSe as a practical and non-destructive method to discern the ZnSe secondary phase in the solar cell absorber. The PL is excited by the green emission of an Ar ion laser and is detected in the energy range of 1.2–1.3 eV. A clear spatial correlation with the ZnSe Raman signal confirms this attribution.

Scanning tunneling spectroscopy permits real-space observation of one-dimensional electronic states on a Fe(100) surface alloyed with Si. These states are localized along chains of Fe atoms in domain boundaries of the Fe(100) cs2 3 2dSi surface alloy, as confirmed by first-principles spinpolarized calculations. The calculated charge densities illustrate the d-like orbital character of the one-dimensional state and show its relationship to a two-dimensional state existing on the pure Fe(100) surface. [S0031-9007(96)00335-3]

Incommensurate relaxed overlayer Moir\'e structures are often interpreted as systems with weak lateral variations of the binding potential and thus no structural modulations in the overlayer material. We discuss here the example of a CoO(111) bilayer on Ir(100), which is a relaxed overlayer with strong structural response to the lateral modulation of interface properties but nevertheless is incommensurate. By means of density functional theory (DFT) calculations, we quantitatively reproduce all the structural parameters of the CoO(111) bilayer on Ir(100) as proposed by a recent low-energy electron diffraction analysis [Ebensperger et al., Phys. Rev. B 81, 235405 (2010)]. The calculations predict energetic degeneracies with respect to registry shifts of the CoO(111) film along [01$\overline{1}$]. Large-scale, low-temperature scanning tunneling microscopy topographies reveal that the true structure of the film is incommensurate in this direction, exhibiting a one-dimensional Moir\'e pattern with a period of about 9.4 ${a}_{\mathrm{Ir}}$. From DFT calculations for limiting (periodic) models, we can sample the potential landscape of the cobalt and oxygen atoms in the Moir\'e structure across the Ir(100) unit cell. We find that despite the non-commensurability of the film, the binding to the substrate is site specific with strong attraction and repulsion points for both cobalt and oxygen atoms, leading to severe local distortions in the film. The lateral modulation of the structural elements within the oxide film can be understood as a combination of the lateral variation in the Co-Ir binding potential and additional O-Ir binding.

Epitaxial Cu2ZnSnSe4 (CZTSe) thin films were grown by molecular beam epitaxy on GaAs(001) using two different growth processes, one containing an in-situ annealing stage as used for solar cell absorbers and one for which this step was omitted. Photoluminescences (PL) measurements carried out on these samples show no dependence of the emission shape on the excitation intensity at different temperatures ranging from 4 K to 300 K. To describe the PL measurements, we employ a model with fluctuating band edges in which the density of states of the resulting tail states does not seem to depend on the excited charge carrier density. In this interpretation, the PL measurements show that the annealing stage removes a defect level, which is present in the samples without this annealing.

Graphene has a close lattice match to the Ni(111) surface, resulting in a preference for 1 × 1 configurations. We have investigated graphene grown by chemical vapor deposition (CVD) on the nickel carbide (Ni(2)C) reconstruction of Ni(111) with scanning tunneling microscopy (STM). The presence of excess carbon, in the form of Ni(2)C, prevents graphene from adopting the preferred 1 × 1 configuration and leads to grain rotation. STM measurements show that residual Ni(2)C domains are present under rotated graphene. Nickel vacancy islands are observed at the periphery of rotated grains and indicate Ni(2)C dissolution after graphene growth. Density functional theory (DFT) calculations predict a very weak (van der Waals type) interaction of graphene with the underlying Ni(2)C, which should facilitate a phase separation of the carbide into metal-supported graphene. These results demonstrate that surface phases such as Ni(2)C can play a major role in the quality of epitaxial graphene.