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 âˆ¼5%. 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.

Use of proteomics to identify biomarkers associated with chronic kidney disease and long-term outcomes in patients with myocardial infarction.

BACKGROUND: Patients with chronic kidney disease (CKD) have poor outcomes following myocardial infarction (MI). We performed an untargeted examination of 175 biomarkers to identify those with the strongest association with CKD and to examine the association of those biomarkers with long-term outcomes. METHODS: A total of 175 different biomarkers from MI patients enrolled in the Swedish Web-System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies (SWEDEHEART) registry were analysed either by a multiple reaction monitoring mass spectrometry assay or by a multiplex assay (proximity extension assay). Random forests statistical models were used to assess the predictor importance of biomarkers, CKD and outcomes. RESULTS: A total of 1098 MI patients with a median estimated glomerular filtration rate of 85 mL min-1 /1.73 m2 were followed for a median of 3.2 years. The random forests analyses, without and with adjustment for differences in demography, comorbidities and severity of disease, identified six biomarkers (adrenomedullin, TNF receptor-1, adipocyte fatty acid-binding protein-4, TNF-related apoptosis-inducing ligand receptor 2, growth differentiation factor-15 and TNF receptor-2) to be strongly associated with CKD. All six biomarkers were also amongst the 15 strongest predictors for death, and four of them were amongst the strongest predictors of subsequent MI and heart failure hospitalization. CONCLUSION: In patients with MI, a proteomic approach could identify six biomarkers that best predicted CKD. These biomarkers were also amongst the most important predictors of long-term outcomes. Thus, these biomarkers indicate underlying mechanisms that may contribute to the poor prognosis seen in patients with MI and CKD.

Kinetic study of hydrogen lateral diffusion at high temperature in a directly-bonded InP-SiO2/Si substrate.

Hybrid integration of III-V materials onto silicon by direct bonding technique is a mature and promising approaches to develop advanced photonic integrated devices into the silicon photonics platform. In this approach, the III-V material stack is grown on an InP wafer in a unique epitaxial step prior to the direct bonding process onto the silicon-on-insulator wafer. Currently, no additional epitaxial regrowth steps are implemented after bonding. This can be seen as a huge limitation as compared to the III-V on III-V wafer mature technology where multi-regrowth steps are most often implemented. In this work, we have studied the material behavior of an InP membrane on silicon (InPoSi) under epitaxial regrowth conditions by metal-organic vapor phase epitaxy (MOVPE). MOVPE requires high-temperature elevation, typically above 600 °C. We show for the first time the appearance of voids at 400 °C in an InP seed (100 nm) directly-bonded onto a thermally oxidized Si substrate despite the use of a thick SiO2 oxide (200 nm) at the bonding interface. This phenomenon is explained by a weakening of the bonding interface while high-pressurized hydrogen is present. A kinetic study of the hydrogen lateral diffusion is carried out, enabling the assessment of its lateral diffusion length. To overcome the void formation, highly efficient outgassing trenches after bonding are demonstrated. Finally, high-quality AlGaInAs-based multi-quantum well (MQW) heterostructure surrounded by two InP layers was grown by MOVPE on InPoSi template patterned with outgassing trenches. This process is not only compatible with MOVPE regrowth conditions (650 °C under PH3) but also with conventional fabrication processes used for photonic devices.

Morbidity and cause-specific mortality in first-time myocardial infarction with nonobstructive coronary arteries.

BACKGROUND: Myocardial infarction (MI) with nonobstructive coronary arteries (MINOCA) is receiving increasing interest as a prognostically adverse entity distinct from myocardial infarction with significant coronary artery disease (MI-CAD). However, data are still limited regarding long-term cardiovascular morbidity and cause-specific mortality in MINOCA. METHODS: This is a registry-based cohort study using data from patients admitted to Swedish coronary care units. We investigated various nonfatal outcomes (recurrent MI, hospitalization for heart failure or stroke) and fatal outcomes (cardiovascular, respiratory or cancer-related mortality) in 4069 patients without apparent acute cardiovascular disease, used as non-MI controls, 7266 patients with first-time MINOCA and 69 267 patients with first-time MI-CAD. RESULTS: Almost all event rates (median follow-up 3.8 years) increased in a stepwise fashion across the three cohorts [rates of major adverse events (MAE; composite of all-cause mortality, recurrent MI, hospitalization for heart failure or stroke): n = 268 (6.6%), n = 1563 (21.5%), n = 17 777 (25.7%), respectively]. Compared to non-MI controls, MINOCA patients had an adjusted hazard ratio (HR) of 2.12 (95% confidence interval 1.84-2.43) regarding MAE. MINOCA patients had a substantial risk of cardiovascular mortality and the highest numerical risks of respiratory and cancer-related mortality. Male sex, previous heart failure and chronic obstructive pulmonary disease had a stronger prognostic impact in MINOCA than in MI-CAD. Female MINOCA patients with atrial fibrillation were at particular risk. CONCLUSIONS: Patients with first-time MINOCA have a considerable risk of adverse events. This stresses the need for a comprehensive search of the cause of MINOCA, thorough treatment of underlying disease triggers and close follow-up.

Growth dynamics of SiGe nanowires by the vapour-liquid-solid method and its impact on SiGe/Si axial heterojunction abruptness.

The vapour-liquid-solid (VLS) method is by far the most extended procedure for bottom-up nanowire growth. This method also allows for the manufacture of nanowire axial heterojunctions in a straightforward way. To do this, during the growth process, precursor gases are switched on/off to obtain the desired change in the nanowire composition. Using this technique, axially heterostructured nanowires can be grown, which are crucial for the fabrication of electronic and optoelectronic devices. SiGe/Si nanowires are compatible with complementary metal oxide semiconductor (CMOS) technology, which improves their versatility and the possibility of integration with current electronic technologies. Abrupt heterointerfaces are fundamental for the development and correct operation of electronic and optoelectronic devices. Unfortunately, the VLS growth of SiGe/Si heterojunctions does not provide abrupt transitions because of the high solubility of group IV semiconductors in Au, with the corresponding reservoir effect that precludes the growth of sharp interfaces. In this work, we studied the growth dynamics of SiGe/Si heterojunctions based on already developed models for VLS growth. A composition map of the Si-Ge-Au liquid alloy is proposed to better understand the impact of the growing conditions on the nanowire growth process and the heterojunction formation. The solution of our model provides heterojunction profiles that are in good agreement with the experimental measurements. Finally, an in-depth study of the composition map provides a practical approach to the drastic reduction of heterojunction abruptness by reducing the Si and Ge concentrations in the catalyst droplet. This converges with previous approaches, which use catalysts aiming to reduce the solubility of the atomic species. This analysis opens new paths to the reduction of heterojunction abruptness using Au catalysts, but the model can be naturally extended to other catalysts and semiconductors.

Flexible endosopic management of Zenker's diverticulum: characteristics and outcomes of 52 cases at a tertiary referral center.

Zenker's diverticulum causes substantial morbidity among affected elderly patients. In the United States, rigid endoscopic cricopharyngeal myotomy is the mainstay of management and the flexible endoscopic technique is reserved for those not deemed candidates for rigid endoscopy due to an inability to extend the neck and/or medical comorbidities. Short- and long-term outcomes following flexible endoscopic cricopharyngeal myotomy in the United States are limited. We reviewed the patient characteristics and outcomes of 58 consecutive flexible endoscopic cricopharyngeal myotomies performed at Mayo Clinic, Rochester, between March 2006 and November 2013. There were 58 procedures performed on 52 unique patients. The median age was 77 years, and 48% of patients were female. More than one third of patients had either failed previous rigid therapy or were deemed inoperable by the referring surgeon. Size of the diverticulum ranged from 1 cm to 5 cm with a mean of 2.8 cm. Most procedures (67%) were performed under general anesthesia. Initial procedural success was achieved in all patients. Of the patients, 77% reported complete symptom resolution at mean follow-up time of 26 months. Of the procedures, 71% were not associated with any adverse event, but esophageal microperforation occurred during 11 procedures (19%). Of these, nine resolved with conservative management, one required an endoscopic stent, and one developed a neck abscess that required drainage. Our data show in a group of elderly patients with preexisting comorbidities flexible endoscopy therapy for Zenker's diverticulum is feasible. Initial symptomatic improvement was universal, and long-term response appears durable. The most common adverse event was esophageal microperforation, and the majority (82%) of these resolved with conservative management. Direct comparison with outcomes of rigid endoscopic or open surgical techniques has not been performed, but these data suggest that a randomized trial is warranted to assess the efficacy and safety of a flexible endoscopic technique.

The use of double lasso, fully covered self-expandable metal stents with new "anchoring flap" system in the treatment of benign biliary diseases.

BACKGROUND: Many benign biliary diseases (BBD) can be treated with fully covered, self-expandable metal stents (FCSEMS) but stent migration occurs in up to 35.7 %. The aim of this study was to prospectively assess the rate of, safety and effectiveness and stent migration of a new biliary FCSEMS with an anti-migration flap (FCSEMS-AF) in patients with BBD. PATIENTS AND METHODS: This was a prospective study from four Italian referral endoscopy centers of 32 consecutive patients (10 females and 22 males; mean age: 60.1 ± 14.8 years; range: 32-84 years) with BBD who were offered endoscopic placement of a FCSEMS-AF as first-line therapy. RESULTS: Were 24 strictures and 8 leaks. Stent placement was technically successful in 32/32 patients (100 %). Immediate clinical improvement was seen in all 32 patients (100 %). One late stent migration occurred (3.3 %). FCSEMS-AF were removed from 30 of the 32 patients (93.7 %) at a mean (± SD) of 124.4 ± 84.2 days (range: 10-386 days) after placement. All patients remained clinically and biochemically well at 1- and 3-month follow-up. One patient (3.3 %) with a post-laparoscopic cholecystectomy stricture developed distal stent migration at 125 days. CONCLUSION: This new FCSEMS with anti-migration flap seems to be a safe and effective first-line treatment option for patients with BBD.

Peroral cholangioscopy facilitates targeted tissue acquisition in patients with suspected cholangiocarcinoma.

AIM: Biliary strictures that are suspicious for cholangiocarcinoma (CCA) are commonly encountered in clinical practice in patients with and without primary sclerosing cholangitis (PSC). A definitive histologic diagnosis of CCA via endoscopic retrograde cholangiography (ERCP) is often not obtainable with standard biliary brush cytology. Peroral cholangioscopy is an additional tool to help provide a diagnosis of CCA in patients with suspicious biliary strictures. Aim of the study was to assess the use of peroral cholangioscopy in patients with and without PSC and indeterminate biliary strictures. METHODS: Retrospective study. RESULTS: 25 patients were included in the study. All patients underwent ERCP with peroral cholangioscopy. Tissue samples obtained included routine cytology, fluorescent in-situ hybridization, and cholangioscopic-directed forceps biopsies. The operating characteristics of cholangioscopy to detect malignancy in 18 PSC patients with suspected cholangiocarcinoma were a sensitivity of 75%, specificity of 55%, and a positive predictive value (PPV) of 23%, and a negative predictive value of 92%. In 7 non-PSC patients with suspected cholangiocarcinoma these values sensitivity=100%, 25%, 50%, and NPV=100%, respectively. The overall operating characteristics of cholangioscopy to detect malignancy in all 25 patients with suspected cholangiocarcinoma were: sensitivity of 86%, specificity of 50%, PPV of 32%, and NPV of 93%. CONCLUSION: Cholangioscopy helps identify sites for tissue acquisition in PSC and non-PSC patients with biliary strictures suspicious for malignancy.

[Catheter-related bladder discomfort after urological surgery: importance of the type of surgery and efficiency of treatment by clonazepam]. / Inconfort lié à la sonde vésicale en postopératoire: importance du type d'intervention et efficacité du traitement par clonazépam.

INTRODUCTION: Bladder catheter can induce a Catheter-Related Bladder Discomfort (CRBD). Antagonist of muscarinic receptor is the gold standard treatment. Clonazepam is an antimuscarinic, muscle relaxing oral drug. The aim of this study is to look for a correlation between the type of surgical procedure and the existence of CRBD and to evaluate the efficiency of clonazepam. METHODS: One hundred patients needing bladder catheter were evaluated. Sexe, age, BMI, presence of diabetes, surgical procedure and existence of CRBD were noted. Pain was evaluated with analogic visual scale. Timing of pain, need for specific treatment by clonazepam and its efficiency were noted. Correlation between preoperative data, type of surgical procedure, existence of CRBD and efficiency of treatment were evaluated. RESULTS: There were 79 men and 21 women (age: 65.9 years, BMI: 25.4). Twelve patients presented diabetes. Surgical procedure concerned prostate in 39 cases, bladder in 19 cases (tumor resections), endo-urology in 20 cases, upper urinary tract in 12 cases (nephrectomy…) and lower urinary tract in 10 cases (sphincter, sub-uretral tape). Forty patients presented CRBD, (pain 4.5 using VAS). This pain occurred 0.6 days after surgery. No correlation was found between preoperative data and CRBD. Bladder resection and endo-urological procedures were surgical procedures which procured CRBD. Clonazepam was efficient in 30 (75 %) out of 40 patients with CRBD. However, it was less efficient in case of bladder tumor resection. CONCLUSION: CRBD is frequent and occurred immediately after surgery. Bladder resection and endo-urology were the main surgical procedures which induced CRBD. Clonazepam is efficient in 75 %. Bladder resection is the surgical procedure which is the most refractory to treatment. LEVEL OF EVIDENCE: 5.

Virtual clinic for hearing loss and non-pulsatile tinnitus: initial experience of 210 cases.

OBJECTIVE: Patients with hearing loss and tinnitus face lengthy waits to be seen in the ENT clinic. SHOEBOX Audiometry is an iPad-based, audiometric screening tool. A virtual hearing loss and non-pulsatile tinnitus clinic involving an ENT specialist virtually assessing cases based on the SHOEBOX audiogram, a patient symptom questionnaire and the primary care referral letter were implemented. This service evaluation explored the outcomes of the virtual clinic in reducing the need for a face-to-face ENT appointment. METHOD: This was a retrospective service evaluation of the first six months of the virtual hearing loss and non-pulsatile tinnitus clinic. RESULTS: A total of 210 patients were included: 34.8 per cent (73) were discharged without requiring audiologist assessment or an ENT appointment, 51.9 per cent (109) required formal audiological assessment, 36.7 per cent (77) required imaging and only 13.8 per cent (29) required a face-to-face ENT appointment. CONCLUSION: A virtual hearing loss and non-pulsatile tinnitus clinic minimised the number of patients requiring a traditional face-to-face clinic appointment within ENT.

Surrogacy and Adoption: An Empirical Investigation of Public Moral Attitudes.

Surrogacy and adoption are both family-making measures subject to extensive domestic and international regulation. In this nationally representative survey study (N = 1552), we explore public attitudes to various forms of surrogacy and adoption in the United Kingdom, in response to an early proposal to allow "double donor" surrogacy as part of the ongoing legal reform project. We sought to both gauge public moral support for adoption and surrogacy generally, the effect that prospective parents' fertility had on this support, and the extent to which the public would find equivalencies between "double donor" surrogacy (DDS) and planned private adoption (PPA) to be morally significant. Our findings indicate that whilst there is broad baseline support for all forms of adoption and surrogacy, this support increases significantly when one or both prospective parents are infertile. These findings also suggest that the language in which a family-making arrangement is characterized has a greater influence on moral support for the arrangement than practical features such as the biological relationship (or absence thereof) between one/both parents and the child.

Esophageal self-expandable stent material and mesh grid density are the major determining factors of external beam radiation dose perturbation: results from a phantom model.

BACKGROUND: Self-expandable esophageal stents are increasingly used for palliation or as an adjunct to chemoradiation for esophageal neoplasia. The optimal esophageal stent design and material to minimize dose perturbation with external beam radiation are unknown. We sought to quantify the deviation from intended radiation dose as a function of stent material and mesh density design. METHODS: A laboratory dosimetric film model was used to quantify perturbation of intended radiation dose among 16 different esophageal stents with varying material and stent mesh density design. RESULTS: Radiation dose enhancement due to stent backscatter ranged from 0 % to 7.3 %, collectively representing a standard difference from the intended mean radiation dose of 1.9 (95 % confidence interval [CI] 1.5 - 2.2). This enhancement was negligible for polymer-based stents and approached 0 % for the biodegradable stents. In contrast, all metal alloy stents had significant radiation backscatter; this was largely determined by the density of mesh design and not by the type of alloy used. CONCLUSIONS: Stent characteristics should be considered when selecting the optimal stent for treatment and palliation of malignant esophageal strictures, especially when adjuvant or neo-adjuvant radiotherapy is planned.

Single-session ERCP in patients with previous Roux-en-Y gastric bypass using percutaneous-assisted transprosthetic endoscopic therapy: a case series.

Endoscopic retrograde cholangiopancreatography (ERCP) remains technically challenging following Roux-en-Y gastric bypass (RYGB). Various techniques have been described to access the excluded stomach. We describe our experience using percutaneous-assisted transprosthetic endoscopic therapy (PATENT) to perform antegrade ERCP. Balloon enteroscopy was used to access the excluded stomach. Direct retrograde percutaneous endoscopic gastrostomy (RPEG) was performed and an esophageal self-expandable metal stent (SEMS) was deployed within the gastrostomy tract. A duodenoscope was advanced through the SEMS and antegrade ERCP was performed. Following ERCP, a gastrostomy tube was placed through the SEMS to maintain patency. Five patients underwent successful antegrade ERCP using PATENT. All patients had a diagnosis of sphincter of Oddi dysfunction. Biliary sphincterotomy was performed in all patients and liver enzymes normalized in four patients with preprocedural elevations. In conclusion, antegrade ERCP employing PATENT is feasible and can be performed during a single endoscopic session in patients with previous RYGB.

Management and outcome trends in type 2 myocardial infarction: an investigation from the SWEDEHEART registry.

Despite poor prognosis, patients with type 2 myocardial infarction (MI) tend to be underdiagnosed and undertreated compared to those with type 1 MI. Whether this discrepancy has improved over time is uncertain. We conducted a registry-based cohort study investigating type 2 MI patients managed at Swedish coronary care units (n = 14,833) during 2010-2022. Multivariable-adjusted changes (first three vs last three calendar years of the observation period) were assessed regarding diagnostic examinations (echocardiography, coronary assessment), provision of cardioprotective medications (betablockers, renin-angiotensin-aldosterone-system inhibitors, statins) and 1-year all-cause mortality. Compared to type 1 MI patients (n = 184,329), those with type 2 MI less often had diagnostic examinations and cardioprotective medications. Increases in the use of echocardiography (OR 1.08 [95% confidence interval 1.06-1.09]) and coronary assessment (OR 1.06 [95% confidence interval 1.04-1.08]) were smaller compared to type 1 MI (pinteraction < 0.001). The provision of medications did not increase in type 2 MI. All-cause mortality rate in type 2 MI was 25.4% without temporal change (OR 1.03 [95% confidence interval 0.98-1.07]). Taken together, the provision of medications and all-cause mortality did ot improve in type 2 MI despite modest increases in diagnostic procedures. This emphasizes the need of defining optimal care pathways in these patients.

Covered self-expanding metal stent use in the pancreatic duct: a case series.

Plastic stents have been used in the pancreatic duct for a variety of indications. However, unlike in the bile duct, the use of covered self-expanding metal stents (CSEMSs) has been discouraged because multiple side branches drain into main pancreatic duct (MPD) and the ductal diameter is relatively small. This report aims to describe our experience using CSEMSs in the pancreatic duct in a series of nine patients, with special focus on adverse events. Indications were strictures (n = 5), intraductal mucinous neoplasm (IMPN; n = 1), pancreatic duct leak (n = 1), disconnected duct syndrome (n = 1), and severe acute pancreatitis/necrosis with disrupted duct (n = 1). Eight patients had symptomatic improvement, or radiological resolution of or improvement in their strictures, leaks, perforation, and necrosis. Two of these have indwelling CSEMSs for ongoing treatment. One patient (disconnected duct syndrome) was considered a treatment failure as the stent migrated and the patient underwent distal pancreatectomy for refractory pain. Two patients underwent pancreaticoduodenectomy for their malignancies after their CSEMSs had been in place for 43 and 49 days, respectively. Importantly no patients, including those with indwelling CSEMSs, developed stent-related acute pancreatitis with a median follow-up of 4 months. One patient developed post-procedure pain requiring hospitalization for 1 day. Median stent duration was 77 days. These observations suggest there is a potential role for the use of CSEMSs in the MPD in selected patients with pancreatic pathology.

Outcome of access sphincterotomy using a needle knife converted from a standard biliary sphincterotome.

Cannulation fails in up to 10 % of all endoscopic retrograde cholangiopancreatographies (ERCPs). A standard sphincterotome can be converted to a needle knife to perform precut sphincterotomy (PCS). In this retrospective study, we analyzed cannulation rates, adverse events, and the percentage of patients requiring a second sphincterotome using a converted needle knife. Over a 7-year period, 3322 ERCPs were performed by one experienced therapeutic endoscopist; 1487 sphincterotomies were performed, 78 precut sphincterotomies using a converted needle knife. Successful cannulation using the converted needle knife was achieved in 96 % of cases at the initial procedure. Adverse events occurred in 17 % and post-ERCP pancreatitis was reported in 10 % of patients. A second sphincterotome was needed in 13 % of cases. This study shows a converted needle knife can be used for successful cannulation of either the biliary or the pancreatic duct after a failed cannulation with a standard sphincterotome, with a low percentage of adverse events anda reduction in the need for accessories.

Endoscopic treatment of intraluminal duodenal ("windsock") diverticulum: varying techniques from five cases.

The optimal endoscopic approach to intraluminal duodenal diverticulum (IDD) has not been established. We report on our experience of endoscopic resection of symptomatic IDD in five patients (three men, two women; mean age 37 years) who were treated between August 2004 and April 2012. Four patients underwent endoscopic diverticulectomy using a standard polypectomy snare. Following diverticulectomy, the remaining duodenal septum was incised using a needle-knife in two patients. The fifth patient underwent endoscopic diverticulotomy using a needle-knife. In four cases the IDD was resected and reviewed histologically and demonstrated substantial vascularity. All patients developed clinically significant, post-procedural bleeding, which was managed endoscopically. Endoscopic management of symptomatic IDD can be achieved using various approaches. Post-procedural bleeding appears to be a common adverse event, but this complication can be managed endoscopically.

Photodynamic therapy of intraductal papillary mucinous neoplasm.

Intraductal papillary mucinous neoplasm (IPMN) of the main pancreatic duct is usually treated by surgical excision of the affected pancreas. Nonoperative ablative therapies have not been described. We treated IPMN of the pancreatic duct with photodynamic therapy (PDT) in a patient who was a poor operative candidate. Porfimer sodium was administered intravenously, and laser light was delivered by a diffusing catheter placed in the pancreatic duct during endoscopic retrograde cholangiopancreatography (ERCP). Imaging and biopsy findings of IPMN resolved after PDT, and symptoms also resolved. Metastatic cancer was diagnosed 2 years after PDT had been initiated. Pancreatic PDT was well tolerated in this case, and may be a therapeutic option for selected patients with IPMN of the main pancreatic duct.

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.

Hidden defects in silicon nanowires.

Recent publications have reported the presence of hexagonal phases in Si nanowires. Most of these reports were based on 'odd' diffraction patterns and HRTEM images­'odd' means that these images and diffraction patterns could not be obtained on perfect silicon crystals in the classical diamond cubic structure. We analyze the origin of these 'odd' patterns and images by studying the case of various Si nanowires grown using either Ni or Au as catalysts in combination with P or Al doping. Two models could explain the experimental results: (i) the presence of a hexagonal phase or (ii) the presence of defects that we call 'hidden' defects because they cannot be directly observed in most images. We show that in many cases one direction of observation is not sufficient to distinguish between the two models. Several directions of observations have to be used. Secondly, conventional TEM images, i.e. bright-field two-beam and dark-field images, are of great value in the identification of 'hidden' defects. In addition, slices of nanowires perpendicular to the growth axis can be very useful. In the studied nanowires no hexagonal phase with long range order is found and the 'odd' images and diffraction patterns are mostly due to planar defects causing superposition of different crystal grains. Finally, we show that in Raman experiments the defect-rich NWs can give rise to a Raman peak shifted to 504­511 cm⁻¹ with respect to the Si bulk peak at 520 cm⁻¹, indicating that Raman cannot be used to identify a hexagonal phase.