Enhancing the incorporation of Sn in vapor-liquid-solid GeSn nanowires by modulation of the droplet composition

We report on the influence of the liquid droplet composition on the Sn incorporation in GeSn nanowires (NWs) grown by the vapor-liquid-solid (VLS) mechanism with different catalysts. The variation of the NW growth rate and morphology with the growth temperature is investigated and 400 °C is identified as the best temperature to grow the longest untapered NWs with a growth rate of 520 nm min^-1. When GeSn NWs are grown with pure Au droplets, we observe a core-shell like structure with a low Sn concentration of less than 2% in the NW core regardless of the growth temperature. We then investigate the impact of adding different fractions of Ag, Al, Ga and Si to Au catalyst on the incorporation of Sn. A significant improvement of Sn incorporation up to 9% is obtained using 75:25 Au-Al catalyst, with a high degree of spatial homogeneity across the NW volume. Thermodynamic model based on the energy minimization at the solid-liquid interface is developed, showing a good correlation with the data. These results can be useful for obtaining technologically important GeSn material with a high Sn content and, more generally, for tuning the composition of VLS NWs in other material systems.

Functional Devices from Bottom-Up Silicon Nanowires: A Review

This paper summarizes some of the essential aspects for the fabrication of functional devices from bottom-up silicon nanowires. In a first part, the different ways of exploiting nanowires in functional devices, from single nanowires to large assemblies of nanowires such as nanonets (two-dimensional arrays of randomly oriented nanowires), are briefly reviewed. Subsequently, the main properties of nanowires are discussed followed by those of nanonets that benefit from the large numbers of nanowires involved. After describing the main techniques used for the growth of nanowires, in the context of functional device fabrication, the different techniques used for nanowire manipulation are largely presented as they constitute one of the first fundamental steps that allows the nanowire positioning necessary to start the integration process. The advantages and disadvantages of each of these manipulation techniques are discussed. Then, the main families of nanowire-based transistors are presented; their most common integration routes and the electrical performance of the resulting devices are also presented and compared in order to highlight the relevance of these different geometries. Because they can be bottlenecks, the key technological elements necessary for the integration of silicon nanowires are detailed: the sintering technique, the importance of surface and interface engineering, and the key role of silicidation for good device performance. Finally the main application areas for these silicon nanowire devices are reviewed.

Verifying the band gap narrowing in tensile strained Ge nanowires by electrical means

Group-IV based light sources are one of the missing links towards fully CMOS compatible photonic circuits. Combining both silicon process compatibility and a pseudo-direct band gap, germanium is one of the most viable candidates. To overcome the limitation of the indirect band gap and turning germanium in an efficient light emitting material, the application of strain has been proven as a promising approach. So far the experimental verification of strain induced bandgap modifications were based on optical measurements and restricted to moderate strain levels. In this work, we demonstrate a methodology enabling to apply tunable tensile strain to intrinsic germanium [Formula: see text] nanowires and simultaneously perform in situ optical as well as electrical characterization. Combining I/V measurements and μ-Raman spectroscopy at various strain levels, we determined a decrease of the resistivity by almost three orders of magnitude for strain levels of ∼5%. Thereof, we calculated the strain induced band gap narrowing in remarkable accordance to recently published simulation results for moderate strain levels up to 3.6%. Deviations for ultrahigh strain values are discussed with respect to surface reconfiguration and reduced charge carrier scattering time.

Chemical Bath Deposition of ZnO Nanowires Using Copper Nitrate as an Additive for Compensating Doping

The controlled incorporation of dopants like copper into ZnO nanowires (NWs) grown by chemical bath deposition (CBD) is still challenging despite its critical importance for the development of piezoelectric devices. In this context, the effects of the addition of copper nitrate during the CBD of ZnO NWs grown on Au seed layers are investigated in detail, where zinc nitrate and hexamethylenetetramine are used as standard chemical precursors and ammonia as an additive to tune the pH. By combining thermodynamic simulations with chemical and structural analyses, we show that copper oxide nanocrystals simultaneously form with ZnO NWs during the CBD process in the low-pH region associated with large supersaturation of Cu species. The Cu(II) and Zn(II) speciation diagrams reveal that both species show very similar behaviors, as they predominantly form either X²⁺ ions (with X = Cu or Zn) or X(NH₃)₄²⁺ ion complexes, depending on the pH value. Owing to their similar ionic structures, Cu²⁺ and Cu(NH₃)₄²⁺ ions preferentially formed in the low- and high-pH regions, respectively, are able to compete with the corresponding Zn²⁺ and Zn(NH₃)₄²⁺ ions to adsorb on the c-plane top facets of ZnO NWs despite repulsive electrostatic interactions, yielding the significant incorporation of Cu. At the highest pH value, additional attractive electrostatic interactions between the Cu(NH₃)₄²⁺ ion complexes and negatively charged c-plane top facets further enhance the incorporation of Cu into ZnO NWs. The present findings provide a deep insight into the physicochemical processes at work during the CBD of ZnO NWs following the addition of copper nitrate, as well as a detailed analysis of the incorporation mechanisms of Cu into ZnO NWs, which are considered beyond the only electrostatic forces usually driving the incorporation of dopants such as Al and Ga.

O-Band Emitting InAs Quantum Dots Grown By MOCVD On A 300 mm Ge-Buffered Si (001) Substrate

The epitaxy of III-V semiconductors on silicon substrates remains challenging because of lattice parameter and material polarity differences. In this work, we report on the Metal Organic Chemical Vapor Deposition (MOCVD) and characterization of InAs/GaAs Quantum Dots (QDs) epitaxially grown on quasi-nominal 300 mm Ge/Si(001) and GaAs(001) substrates. QD properties were studied by Atomic Force Microscopy (AFM) and Photoluminescence (PL) spectroscopy. A wafer level µPL mapping of the entire 300 mm Ge/Si substrate shows the homogeneity of the three-stacked InAs QDs emitting at 1.30 ± 0.04 µm at room temperature. The correlation between PL spectroscopy and numerical modeling revealed, in accordance with transmission electron microscopy images, that buried QDs had a truncated pyramidal shape with base sides and heights around 29 and 4 nm, respectively. InAs QDs on Ge/Si substrate had the same shape as QDs on GaAs substrates, with a slightly increased size and reduced luminescence intensity. Our results suggest that 1.3 μm emitting InAs QDs quantum dots can be successfully grown on CMOS compatible Ge/Si substrates.

Reversible Al Propagation in Si x Ge1-x Nanowires: Implications for Electrical Contact Formation

While reversibility is a fundamental concept in thermodynamics, most reactions are not readily reversible, especially in solid-state physics. For example, thermal diffusion is a widely known concept, used among others to inject dopants into the substitutional positions in the matrix and improve device properties. Typically, such a diffusion process will create a concentration gradient extending over increasingly large regions, without possibility to reverse this effect. On the other hand, while the bottom-up growth of semiconducting nanowires is interesting, it can still be difficult to fabricate axial heterostructures with high control. In this paper, we report a thermally assisted partially reversible thermal diffusion process occurring in the solid-state reaction between an Al metal pad and a Si x Ge1-x alloy nanowire observed by in situ transmission electron microscopy. The thermally assisted reaction results in the creation of a Si-rich region sandwiched between the reacted Al and unreacted Si x Ge1-x part, forming an axial Al/Si/Si x Ge1-x heterostructure. Upon heating or (slow) cooling, the Al metal can repeatably move in and out of the Si x Ge1-x alloy nanowire while maintaining the rodlike geometry and crystallinity, allowing to fabricate and contact nanowire heterostructures in a reversible way in a single process step, compatible with current Si-based technology. This interesting system is promising for various applications, such as phase change memories in an all crystalline system with integrated contacts as well as Si/Si x Ge1-x /Si heterostructures for near-infrared sensing applications.

Impact of droplet composition on the nucleation rate and morphology of vapor-liquid-solid GeSn nanowires

It is well-known that the chemical potential which drives the vapor-liquid-solid growth of semiconductor nanowires is strongly affected by the liquid phase composition. Here, we investigate theoretically how the droplet composition influences the nucleation of Au-catalyzed GeSn nanowires on Ge(111) and Si(111) substrates. We compare the chemical potentials in an Au-Ge-Sn catalyst droplet before and after adding Ga and/or Si atoms. It is found that the presence of these atoms enhances the nucleation rate of nanowires on both substrates. Theoretical results are compared to experimental data on GeSn nanowires grown in a hot-wall reduced pressure chemical vapor deposition reactor. It is shown that the intentional addition of Ga in the de-wetting step improves the uniformity of the nanowire dimensions and yields higher density of nanowires over Ge(111) substrates. The nanowire growth on Si(111) substrate occurs only when Ga and/or Si are added to Au droplets. These results show that controlling the composition of the catalyst droplet is crucial for improving the quality of GeSn nanowires.

Optimization of GOPS-Based Functionalization Process and Impact of Aptamer Grafting on the Si Nanonet FET Electrical Properties as First Steps towards Thrombin Electrical Detection

Field effect transistors (FETs) based on networks of randomly oriented Si nanowires (Si nanonets or Si NNs) were biomodified using Thrombin Binding Aptamer (TBA-15) probe with the final objective to sense thrombin by electrical detection. In this work, the impact of the biomodification on the electrical properties of the Si NN-FETs was studied. First, the results that were obtained for the optimization of the (3-Glycidyloxypropyl)trimethoxysilane (GOPS)-based biofunctionalization process by using UV radiation are reported. The biofunctionalized devices were analyzed by atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM), proving that TBA-15 probes were properly grafted on the surface of the devices, and by means of epifluorescence microscopy it was possible to demonstrate that the UV-assisted GOPS-based functionalization notably improves the homogeneity of the surface DNA distribution. Later, the electrical characteristics of 80 devices were analyzed before and after the biofunctionalization process, indicating that the results are highly dependent on the experimental protocol. We found that the TBA-15 hybridization capacity with its complementary strand is time dependent and that the transfer characteristics of the Si NN-FETs obtained after the TBA-15 probe grafting are also time dependent. These results help to elucidate and define the experimental precautions that must be taken into account to fabricate reproducible devices.

Improvement of AlN Film Quality Using Plasma Enhanced Atomic Layer Deposition with Substrate Biasing

In recent years, plasma enhanced atomic layer deposition (PEALD) has emerged as a key method for the growth of conformal and homogeneous aluminum nitride (AlN) films at the nanoscale. In this work, the utilized PEALD reactor was equipped not only with a traditional remote Inductively Coupled Plasma source but also with an innovative additional power supply connected to the substrate holder. Thus, we investigate here the substrate biasing effect on AlN film quality deposited on (100) silicon. We report that by adjusting the ion energy via substrate biasing, the AlN film quality can be significantly improved. Indeed, compared to films commonly deposited without bias, AlN deposited with a platen power of 5 W displays a 14% increase in the number of N-Al bonds according to X-ray spectroscopy analysis. Moreover, after having integrated them into Metal-AlN-Si capacitors, the 5 W AlN film exhibits a permittivity increase from 4.5 to 7.0 along with a drastic drop of leakage current density of more than 5 orders of magnitude. The use of substrate biasing during PEALD is thereby a promising strategy for the improvement of AlN film quality.

Morphology Transition of ZnO from Thin Film to Nanowires on Silicon and its Correlated Enhanced Zinc Polarity Uniformity and Piezoelectric Responses

ZnO thin films and nanostructures have received increasing interest in the field of piezoelectricity over the last decade, but their formation mechanisms on silicon when using pulsed-liquid injection metal-organic chemical vapor deposition (PLI-MOCVD) are still open to a large extent. Also, the effects of their morphology, dimensions, polarity, and electrical properties on their piezoelectric properties have not been completely decoupled yet. By only tuning the growth temperature from 400 to 750 °C while fixing the other growth conditions, the morphology transition of ZnO deposits on silicon from stacked thin films to nanowires through columnar thin films is shown. A detailed analysis of their formation mechanisms is further provided. The present transition is associated with strong enhancement of their crystallinity and growth texture along the c-axis together with a massive relaxation of the strain in nanowires. It is also related to a prevailed zinc polarity, for which its uniformity is strongly improved in nanowires. The nucleation of basal-plane stacking faults of I₁-type in nanowires is also revealed and related to an emission line at about 3.326 eV in cathodoluminescence spectra, further exhibiting fairly low phonon coupling. Interestingly, the transition is additionally associated with a significant improvement of the piezoelectric amplitude, as determined by piezoresponse force microscopy measurements. The Zn-polar domains exhibit a larger piezoelectric amplitude than the O-polar domains, showing the importance of controlling the polarity in these deposits as a prerequisite to enhance the performances of piezoelectric devices. The present findings demonstrate the high potential in using the PLI-MOCVD system to form ZnO with different morphologies and polarity uniformity on silicon. They further reveal unambiguously the superiority of nanowires over thin films for piezoelectric devices.

Formation mechanisms of ZnO nanowires on polycrystalline Au seed layers for piezoelectric applications

ZnO nanowires are considered as attractive building blocks for piezoelectric devices, including nano-generators and stress/strain sensors. However, their integration requires the use of metallic seed layers, on top of which the formation mechanisms of ZnO nanowires by chemical bath deposition are still largely open. In order to tackle that issue, the nucleation and growth mechanisms of ZnO nanowires on top of Au seed layers with a thickness in the range of 5-100 nm are thoroughly investigated. We show that the ZnO nanowires present two different populations of nano-objects with a given morphology. The majority primary population is made of vertically aligned ZnO nanowires, which are heteroepitaxially formed on top of the Au (111) grains. The resulting epitaxial strain is found to be completely relieved at the Au/ZnO interface. In contrast, the minority secondary population is composed of ZnO nanowires with a significant mean tilt angle around 20° with respect to the normal to the substrate surface, which are presumably formed on the (211) facets of the Au (111) grains. The elongation of ZnO nanowires is further found to be limited by the surface reaction at the c-plane top facet in the investigated conditions. By implementing the selective area growth using electron beam lithography, the position of ZnO nanowires is controlled, but the two populations still co-exist in the ensemble. These findings provide an in-depth understanding of the formation mechanisms of ZnO nanowires on metallic seed layers, which should be taken into account for their more efficient integration into piezoelectric devices.

Intersubband Optical Nonlinearity of GeSn Quantum Dots under Vertical Electric Field

The impact of vertical electrical field on the electron related linear and 3rd order nonlinear optical properties are evaluated numerically for pyramidal GeSn quantum dots with different sizes. The electric field induced electron confining potential profile’s modification is found to alter the transition energies and the transition dipole moment, particularly for larger dot sizes. These variations strongly influence the intersubband photoabsorption coefficients and changes in the refractive index with an increasing tendency of the 3rd order nonlinear component with increasing both quantum dot (QD) size and applied electric field. The results show that intersubband optical properties of GeSn quantum dots can be successively tuned by external polarization.

Design of Strain-Engineered GeSn/GeSiSn Quantum Dots for Mid-IR Direct Bandgap Emission on Si Substrate

Strain-engineered self-assembled GeSn/GeSiSn quantum dots in Ge matrix have been numerically investigated aiming to study their potentiality towards direct bandgap emission in the mid-IR range. The use of GeSiSn alloy as surrounding media for GeSn quantum dots (QD) allows adjusting the strain around the QD through the variation of Si and/or Sn composition. Accordingly, the lattice mismatch between the GeSn quantum dots and the GeSiSn surrounding layer has been tuned between - 2.3 and - 4.5% through the variation of the Sn barrier composition for different dome-shaped QD sizes. The obtained results show that the emission wavelength, fulfilling the specific QD directness criteria, can be successively tuned over a broad mid-IR range from 3 up to7 μm opening new perspectives for group IV laser sources fully integrated in Si photonic systems for sensing applications.

Microfluidic self-assembly of folate-targeted monomolecular siRNA-lipid nanoparticles

Non-viral delivery of nucleic acids for therapies based on RNA interference requires a rational design and optimal self-assembly strategies. Nucleic acid particles need to be small, stable and functional in terms of selective cell uptake and controlled release of encapsulated nucleic acids. Here we report on small (∼38 nm) monomolecular nucleic acid/lipid particles (mNALPs) that contain single molecules of short double-stranded oligonucleotides covered by a tight, highly curved lipid bilayer. The particles consist of DOPE, DOTAP, DOPC and DSPE-PEG(2000) and are assembled with 21 bp double-stranded DNA or small interfering RNA by solvent exchange on a hydrodynamic-focusing microfluidic chip. In comparison to vortex mixing by hand this method increases the encapsulation efficiency by 20%, and yields particles with a narrower size distribution, negligible aggregate formation and high stability in blood plasma and serum. Modification of mNALPs with folate-conjugated PEG-lipids results in specific binding and uptake by epithelial carcinoma KB cells overexpressing folate receptors. Binding is significantly reduced by competitive inhibition using free folate and is not observed with non-targeted mNALPs, revealing high specificity. The functionalized mNALPs show gene silencing in the presence of chloroquine, an endosome-destabilizing agent. Together, the robust self-assembly of small-sized mNALPs with their high stability and receptor-specific cell uptake demonstrate that the tight, PEG-grafted lipid-bilayer encapsulation may offer a promising approach towards the delivery of short double-stranded oligonucleotides.

Composition-dependent interfacial abruptness in Au-catalyzed Si(1-x)Ge(x)/Si/Si(1-x)Ge(x) nanowire heterostructures

As MOSFETs are scaled down, power dissipation remains the most challenging bottleneck for nanoelectronic devices. To circumvent this challenge, alternative devices such as tunnel field effect transistors are potential candidates, where the carriers are injected by a much less energetically costly quantum band to band tunneling mechanism. In this context, axial nanowire heterointerfaces with well-controlled interfacial abruptness offer an ideal structure. We demonstrate here the effect of tuning the Ge concentration in a Si1-xGex part of the nanowire on the Si/Si1-xGex and Si1-xGex/Si interfacial abruptness in axial Si-Si1-xGex nanowire heterostructures grown by the Au-catalyzed vapor-liquid-solid method. The two heterointerfaces are always asymmetric irrespective of the Ge concentration or nanowire diameter. For a fixed diameter, the value of interface abruptness decreases with increasing the Ge content for the Si/Si1-xGex interface but shows no strong Ge dependence at the Si1-xGex/Si interface where it features a linear correlation with the nanowire diameter. To rationalize these findings, a kinetic model for the layer-by-layer growth of nanowire heterostructures from a ternary Au-Ge-Si alloy is established that predicts a discrepancy in Ge concentration in the layer and the catalyst droplet. The Ge concentration in each layer is predicted to be dependent on the composition of the preceding layer. The most abrupt heterointerface (∼5 nm) is achieved by growing Si1-xGex with x = 0.85 on Si in a 25 nm diameter nanowire.

Effect of HCl on the doping and shape control of silicon nanowires

The introduction of hydrogen chloride during the in situ doping of silicon nanowires (SiNWs) grown using the vapor-liquid-solid (VLS) mechanism was investigated. Compared with non-chlorinated atmospheres, the use of HCl with dopant gases considerably improves the surface morphology of the SiNWs, leading to extremely smooth surfaces and a greatly reduced tapering. Variations in the wire diameter are massively reduced for boron doping, and cannot be measured at 600 °C for phosphorous over several tens of micrometers. This remarkable feature is accompanied by a frozen gold migration from the catalyst, with no noticeable levels of gold clusters observed using scanning electron microscopy. A detailed study of the apparent resistivity of the NWs reveals that the dopant incorporation is effective for both types of doping. A graph linking the apparent resistivity to the dopant to silane dilution ratio is built for both types of doping and discussed in the frame of the previous results.

Temperature dependent photoluminescence properties of InAs/InP quantum dashes subjected to low energy phosphorous ion implantation and subsequent annealing

We report on the impact of phosphorous ion-implantation-induced band gap tuning on the temperature dependent photoluminescence (PL) properties of InAs/InP quantum dashes (QDas). The high temperature range carriers' activation energy, extracted from Arrhenius plots, is found to decrease from 238 to 42 meV when the ion implantation dose increases from 10(11) cm(-2) to 5 x 10(14) cm(-2) which is consistent with the observed emission energy blueshift increase with increasing the ion implantation doses. This effect is attributed to the As/P exchange which reduces the carrier confining potential depth. For intermediate ion implantation doses the reduced carrier confining potential barrier combined with the non-uniform intermixing process, that causes an increased QDas size dispersion, result in anomalous temperature-dependent PL properties. Indeed, the temperature induced PL emission energy redshift measured between 10 K and 300 K is found to be strongly affected by the carrier redistribution within the broadened localized QDas states.

InGaAs quantum dots grown by molecular beam epitaxy for light emission on Si substrates

The aim of this study is to achieve homogeneous, high density and dislocation free InGaAs quantum dots grown by molecular beam epitaxy for light emission on silicon substrates. This work is part of a project which aims at overcoming the severe limitation suffered by silicon regarding its optoelectronic applications, especially efficient light emission device. For this study, one of the key points is to overcome the expected type II InGaAs/Si interface by inserting the InGaAs quantum dots inside a thin silicon quantum well in SiO2 fabricated on a SOI substrate. Confinement effects of the Si/SiO2 quantum well are expected to heighten the indirect silicon bandgap and then give rise to a type I interface with the InGaAs quantum dots. Band structure and optical properties are modeled within the tight binding approximation: direct energy bandgap is demonstrated in SiO2/Si/InAs/Si/SiO2 heterostructures for very thin Si layers and absorption coefficient is calculated. Thinned SOI substrates are successfully prepared using successive etching process resulting in a 2 nm-thick Si layer on top of silica. Another key point to get light emission from InGaAs quantum dots is to avoid any dislocations or defects in the quantum dots. We investigate the quantum dot size distribution, density and structural quality at different V/III beam equivalent pressure ratios, different growth temperatures and as a function of the amount of deposited material. This study was performed for InGaAs quantum dots grown on Si(001) substrates. The capping of InGaAs quantum dots by a silicon epilayer is performed in order to get efficient photoluminescence emission from quantum dots. Scanning transmission electronic microscopy images are used to study the structural quality of the quantum dots. Dislocation free In50Ga50As QDs are successfully obtained on a (001) silicon substrate. The analysis of QDs capped with silicon by Rutherford Backscattering Spectrometry in a channeling geometry is also presented.

An improved AFM cross-sectional method for piezoelectric nanostructures properties investigation: application to GaN nanowires

We present an improved atomic force microscopy (AFM) method to study the piezoelectric properties of nanostructures. An AFM tip is used to deform a free-standing piezoelectric nanowire. The deflection of the nanowire induces an electric potential via the piezoelectric effect, which is measured by the AFM coating tip. During the manipulation, the applied force, the forcing location and the nanowire's deflection are precisely known and under strict control. We show the measurements carried out on intrinsic GaN and n-doped GaN-AlN-GaN nanowires by using our method. The measured electric potential, as high as 200 mV for n-doped GaN-AlN-GaN nanowire and 150 mV for intrinsic GaN nanowire, have been obtained, these values are higher than theoretical calculations. Our investigation method is exceptionally useful to thoroughly examine and completely understand the piezoelectric phenomena of nanostructures. Our experimental observations intuitively reveal the great potential of piezoelectric nanostructures for converting mechanical energy into electricity. The piezoelectric properties of nanostructures, which are demonstrated in detail in this paper, represent a promising approach to fabricating cost-effective nano-generators and highly sensitive self-powered NEMS sensors.

Growth and characterization of gold catalyzed SiGe nanowires and alternative metal-catalyzed Si nanowires

The growth of semiconductor (SC) nanowires (NW) by CVD using Au-catalyzed VLS process has been widely studied over the past few years. Among others SC, it is possible to grow pure Si or SiGe NW thanks to these techniques. Nevertheless, Au could deteriorate the electric properties of SC and the use of other metal catalysts will be mandatory if NW are to be designed for innovating electronic. First, this article's focus will be on SiGe NW's growth using Au catalyst. The authors managed to grow SiGe NW between 350 and 400°C. Ge concentration (x) in Si1-xGex NW has been successfully varied by modifying the gas flow ratio: R = GeH4/(SiH4 + GeH4). Characterization (by Raman spectroscopy and XRD) revealed concentrations varying from 0.2 to 0.46 on NW grown at 375°C, with R varying from 0.05 to 0.15. Second, the results of Si NW growths by CVD using alternatives catalysts such as platinum-, palladium- and nickel-silicides are presented. This study, carried out on a LPCVD furnace, aimed at defining Si NW growth conditions when using such catalysts. Since the growth temperatures investigated are lower than the eutectic temperatures of these Si-metal alloys, VSS growth is expected and observed. Different temperatures and HCl flow rates have been tested with the aim of minimizing 2D growth which induces an important tapering of the NW. Finally, mechanical characterization of single NW has been carried out using an AFM method developed at the LTM. It consists in measuring the deflection of an AFM tip while performing approach-retract curves at various positions along the length of a cantilevered NW. This approach allows the measurement of as-grown single NW's Young modulus and spring constant, and alleviates uncertainties inherent in single point measurement.

Surface recombination velocity measurements of efficiently passivated gold-catalyzed silicon nanowires by a new optical method

The past decade has seen the explosion of experimental results on nanowires grown by catalyzed mechanisms. However, few are known on their electronic properties especially the influence of surfaces and catalysts. We demonstrate by an optical method how a curious electron-hole thermodynamic phase can help to characterize volume and surface recombination rates of silicon nanowires (SiNWs). By studying the electron-hole liquid dynamics as a function of the spatial confinement, we directly measured these two key parameters. We measured a surface recombination velocity of passivated SiNWs of 20 cm s(-1), 100 times lower than previous values reported. Furthermore, the volume recombination rate of gold-catalyzed SiNWs is found to be similar to that of a high-quality three-dimensional silicon crystal; the influence of the catalyst is negligible. These results advance the knowledge of SiNW surface passivation and provide essential guidance to the development of efficient nanowire-based devices.

Appropriateness of hospital admissions in general hospitals in Egypt

We measured the rate of inappropriate admissions, and associated factors, in 3 general hospitals in Egypt. A total of 1191 admissions were reviewed using the Appropriateness Evaluation Protocol for adult patients and the Pediatric Appropriateness Evaluation Protocol for paediatric patients. Inappropriate admissions were 66.3% and 78.9% of admissions in the surgery departments of 2 hospitals compared with 1.9% in the 3rd hospital that followed a specific admission protocol for elective surgery. The paediatrics department had the lowest rates of inappropriate admissions in all hospitals (0%, 1.0% and 1.9%). On logistic regression analysis, the route of admission was the only factor significantly associated with inappropriate admissions in the departments of surgery, obstetrics/gynaecology and internal medicine.

Inhomogeneous broadening and alloy intermixing in low proton dose implanted InAs/GaAs self-assembled quantum dots

In this work, low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) experiments have been carried out to investigate the optical and electronic properties of InAs/GaAs quantum dots (QDs) subjected to room-temperature proton implantation at various doses (5 × 10(10)-10(14) ions cm(-2)) and subsequent thermal annealing. The energy shift of the main QD emission band is found to increase with increasing implantation dose. Our measurements show clear evidence of an inhomogeneous In/Ga intermixing at low proton implantation doses (≤5 × 10(11) ions cm(-2)), giving rise to the coexistence of intermixed and non-intermixed QDs. For higher implantation doses, a decrease of both the PL linewidth and the intersublevel spacing energy have been found to occur, suggesting that the dot-size, dot-composition and dot-strain distributions evolve towards more uniform ones.

Patient and surgeon correlates of shared decision making for surgical breast cancer treatment

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Background: The choice of surgical breast cancer treatment represents an opportunity for shared decision making (SDM), since both mastectomy and breast conserving surgery are viable options. Yet women vary in their desire for involvement in this decision. Correlates of SDM and/or the level of involvement in breast cancer surgical treatment decision-making are not known. Methods: Breast cancer patients of Detroit and Los Angeles SEER registries were mailed a questionnaire shortly after diagnosis in 2002 (N = 1,800, RR: 77%). Their responses were merged with a surgeon survey (N = 456, RR: 80%) for a dataset of 1,547 patients of 318 surgeons. Surgical treatment decision making was categorized into: 1) surgeon-based; 2) shared; or 3) patient-based. The concordance between a woman’s self-reported actual and desired decisional involvement was categorized as having more, less, or the right amount of involvement. Decision making and concordance were each analyzed as three-level dependent variables using multinomial logistic regression controlling for clustering within surgeons. Independent variables included patient clinical, treatment and demographic factors, surgeon demographic and practice-related factors, and a measure of surgeon-patient communication. Results: 37% of women reported the surgery decision was shared, 25% that it was surgeon-based, and 38% that it was patient-based. Two-thirds experienced the right amount of involvement, while 13% had less and 19% had more. Compared to women who reported a shared decision, those with surgeon-based decision were significantly (p < 0.05) more likely to have male surgeons, and those reporting a patient-based decision were more likely to have received mastectomy vs. breast conserving surgery. Women who were less involved in the surgery decision than they wanted were younger and had less education, while those with more involvement (vs. the right amount) more often had male surgeons. Patient-surgeon communication was associated with decisional involvement. Conclusions: Correlates of SDM and decisional involvement relating to surgical breast cancer treatment differ. Determining patients’ desired role in decision making may as important as achieving a shared decision for evaluating perceived quality of care.

No significant financial relationships to disclose.

[Vesico-uterine fistulas. Apropos of 2 cases]

Vesico-uterine fistulas (VUF) are an increasingly rare entity (5% of all urogenital fistulas). The authors report two cases of VUF following cesarean section. The literature is reviewed briefly, indicating that Youssef syndrome is the commonest presentation. This lesion is certainly benign but is a source of discomfort for sexually active women. Treatment is above all preventive. It is based per-partum on perfect management of all cases of difficult labour. Peroperatively, the technique used during each cesarean section must be carefully defined and followed. Treatment of a confirmed VUF is essentially surgical.