The main challenge for light-emitting diodes is to increase the efficiency in the green part of the spectrum. Gallium phosphide (GaP) with the normal cubic crystal structure has an indirect band gap, ...which severely limits the green emission efficiency. Band structure calculations have predicted a direct band gap for wurtzite GaP. Here, we report the fabrication of GaP nanowires with pure hexagonal crystal structure and demonstrate the direct nature of the band gap. We observe strong photoluminescence at a wavelength of 594 nm with short lifetime, typical for a direct band gap. Furthermore, by incorporation of aluminum or arsenic in the GaP nanowires, the emitted wavelength is tuned across an important range of the visible light spectrum (555–690 nm). This approach of crystal structure engineering enables new pathways to tailor materials properties enhancing the functionality.
The ability of core–shell nanowires to overcome existing limitations of heterostructures is one of the key ingredients for the design of next generation devices. This requires a detailed ...understanding of the mechanism for strain relaxation in these systems in order to eliminate strain-induced defect formation and thus to boost important electronic properties such as carrier mobility. Here we demonstrate how the hole mobility of 110-oriented Ge–Si core–shell nanowires can be substantially enhanced thanks to the realization of large band offset and coherent strain in the system, reaching values as high as 4200 cm2/(Vs) at 4 K and 1600 cm2/(Vs) at room temperature for high hole densities of 1019 cm–3. We present a direct correlation of (i) mobility, (ii) crystal direction, (iii) diameter, and (iv) coherent strain, all of which are extracted in our work for individual nanowires. Our results imply 110-oriented Ge–Si core–shell nanowires as a promising candidate for future electronic and quantum transport devices.
Group IV semiconductor optoelectronic devices are now possible by using strain-free direct band gap GeSn alloys grown on a Ge/Si virtual substrate with Sn contents above 9%. Here, we demonstrate the ...growth of Ge/GeSn core/shell nanowire arrays with Sn incorporation up to 13% and without the formation of Sn clusters. The nanowire geometry promotes strain relaxation in the Ge0.87Sn0.13 shell and limits the formation of structural defects. This results in room-temperature photoluminescence centered at 0.465 eV and enhanced absorption above 98%. Therefore, direct band gap GeSn grown in a nanowire geometry holds promise as a low-cost and high-efficiency material for photodetectors operating in the short-wave infrared and thermal imaging devices.
Silicon crystallized in the usual cubic (diamond) lattice structure has dominated the electronics industry for more than half a century. However, cubic silicon (Si), germanium (Ge) and SiGe alloys ...are all indirect-bandgap semiconductors that cannot emit light efficiently. The goal
of achieving efficient light emission from group-IV materials in silicon technology has been elusive for decades
. Here we demonstrate efficient light emission from direct-bandgap hexagonal Ge and SiGe alloys. We measure a sub-nanosecond, temperature-insensitive radiative recombination lifetime and observe an emission yield similar to that of direct-bandgap group-III-V semiconductors. Moreover, we demonstrate that, by controlling the composition of the hexagonal SiGe alloy, the emission wavelength can be continuously tuned over a broad range, while preserving the direct bandgap. Our experimental findings are in excellent quantitative agreement with ab initio theory. Hexagonal SiGe embodies an ideal material system in which to combine electronic and optoelectronic functionalities on a single chip, opening the way towards integrated device concepts and information-processing technologies.
ldquoTrenchrdquo capacitors containing multiple metal-insulator-metal (MIM) layer stacks are realized by atomic-layer deposition (ALD), yielding an ultrahigh capacitance density of 440 at a breakdown ...voltage V DB > 6 V. This capacitance density on silicon is at least 10times higher than the values reported by other research groups. On a silicon substrate containing high-aspect-ratio macropore arrays, alternating MIM layer stacks comprising high- k Al 2 O 3 dielectrics and TiN electrodes are deposited using optimized ALD processing such that the conductivity of the TiN layers is not attacked. Ozone annealing subsequent to each Al 2 O 3 deposition step yields significant improvement of the dielectric isolation and breakdown properties.
The growth of wurtzite/zincblende (WZ and ZB, respectively) superstructures opens new avenues for band structure engineering and holds the promise of digitally controlling the energy spectrum of ...quantum confined systems. Here, we study growth kinetics of pure and thus defect-free WZ/ZB homostructures in GaP nanowires with the aim to obtain monolayer control of the ZB and WZ segment lengths. We find that the Ga concentration and the supersaturation in the catalyst particle are the key parameters determining growth kinetics. These parameters can be tuned by the gallium partial pressure and the temperature. The formation of WZ and ZB can be understood with a model based on nucleation either at the triple phase line for the WZ phase or in the center of the solid–liquid interface for the ZB phase. Furthermore, the observed delay/offset time needed to induce WZ and ZB growth after growth of the other phase can be explained within this framework.
Given the lower specificity for high‐grade cervical lesions of high‐risk human papillomavirus (hrHPV) testing compared to cytology, additional triage testing for hrHPV test‐positive women is needed ...to detect high‐grade cervical lesions. Here, we tested whether combined methylation analysis for cell adhesion molecule 1 (CADM1) and T‐lymphocyte maturation associated protein (MAL), both functionally involved in cervical carcinogenesis, could serve as such a triage marker. Four quantitative methylation‐specific PCRs (qMSP), two for CADM1 (regions M12 and M18) and MAL (regions M1 and M2) each, were applied to 261 cervical tissue specimens ranging from no neoplasia to carcinoma. When qMSPs were combined and positivity for at least one of the qMSPs in the combination was taken into account, the highest positivity rates for cervical intraepithelial neoplasia grade 3 (CIN3) lesions (97%) and squamous cell‐ and adeno‐carcinomas (99%) were obtained by combining a single CADM1 marker with a single MAL marker. Subsequent qMSP analysis of 70 GP5+/6+‐PCR hrHPV‐positive scrapings revealed that a two‐marker panel consisting of CADM1‐M18 and MAL‐M1 was most discriminative, detecting 90% of women with CIN3 (n = 30), whereas it showed a positive result in only 13.5% of women without cervical disease (n = 40). Finally, we applied hrHPV GP5+/6+‐PCR testing followed by CADM1‐M18/MAL‐M1 methylation analysis to a cohort of 79 women visiting the outpatient colposcopy clinic. hrHPV testing revealed a sensitivity of 97% and a specificity of 33% for CIN3+. Additional CADM1‐M18/MAL‐M1 methylation analysis on the hrHPV‐positive women increased the specificity to 78% with a sensitivity of 70%. In conclusion, the methylation marker panel CADM1‐M18 and MAL‐M1 may serve as an alternative molecular triage tool for hrHPV‐positive women.
Despite the increasing interest for biochar as a soil amendment, a knowledge gap remains on its impacts on non-target soil and aquatic species. We hypothesised that biochar particle size and ...application rate can play a role in the toxicity to biota. Pine woodchip biochar was incorporated in a clean soil at three particle size classes: small (<0.5 mm), medium (1–2 mm), and large (<4 mm), and at two concentrations: 1% and 6% w/w. A laboratory screening with earthworm Eisenia andrei avoidance behaviour bioassay was carried out to test the most adequate application rates, particle sizes and soil-biochar pre-incubation period. Thereafter, a 28-day greenhouse microcosm experiment was conducted as an ecologically more representative approach. Survival, vertical distribution and weight changes of E. andrei, and bait-lamina consumption were recorded. Soil leachates from the microcosms were collected to evaluate their impact on Daphnia magna immobilisation and Vibrio fischeri (Microtox®) bioluminescence. A feeding experiment with E. andrei was also performed to address earthworm weight changes and to conduct a screening of PAH-type metabolites in their tissue. The 6% <0.5 mm treatment pre-incubated for 96 h induced significant avoidance of the earthworms. Significantly lower bait-lamina consumption was observed in microcosms for the 6% <0.5 mm treatment. Moreover, particle size was a statistically significant factor regarding the loss of weight in the feeding experiment and higher concentration of naphthalene-type metabolites detected in E. andrei tissue, when exposed to <0.5 mm biochar particles. The leachates had no adverse effects on the aquatic species. The results suggest that particles <0.5 mm of pine woodchip biochar can pose sub-lethal effects on soil biota.
•Integrative ecotoxicological assessment of biochar-amended soil was employed.•Bait-lamina consumption was particle size- and application rate-dependent.•Woodchip biochar particles <0.5 mm posed sub-lethal toxicity to earthworms.•Leachates did not induce any adverse effects on the aquatic species.
High-risk human papillomavirus (hrHPV)-positive women require triage to identify those with cervical high-grade intraepithelial neoplasia and cancer (⩾CIN3 (cervical intraepithelial neoplasia grade ...3)). FAM19A4 methylation analysis, which detects advanced CIN and cancer, is applicable to different sample types. However, studies comparing the performance of FAM19A4 methylation analysis in hrHPV-positive self-samples and paired physician-taken scrapes are lacking.
We compared the performance of FAM19A4 methylation analysis (and/or HPV16/18 genotyping) in self-samples and paired physician-taken scrapes for ⩾CIN3 detection in hrHPV-positive women (n=450,18-66 years).
Overall FAM19A4 methylation levels between sample types were significantly correlated, with strongest correlation in women with ⩾CIN3 (Spearman's ρ 0.697, P<0.001). The performance of FAM19A4 methylation analysis and/or HPV16/18 genotyping did not differ significantly between sample types. In women ⩾30 years, ⩾CIN3 sensitivity of FAM19A4 methylation analysis was 78.4% in self-samples and 88.2% in scrapes (ratio 0.89; CI: 0.75-1.05). In women <30 years, ⩾CIN3 sensitivities were 37.5% and 45.8%, respectively (ratio 0.82; CI: 0.55-1.21). In both groups, ⩾CIN3 specificity of FAM19A4 methylation analysis was significantly higher in self-samples compared with scrapes.
FAM19A4 methylation analysis in hrHPV-positive self-samples had a slightly lower sensitivity and a higher specificity for ⩾CIN3 compared with paired physician-taken scrapes. With a similarly good clinical performance in both sample types, combined FAM19A4 methylation analysis and HPV16/18 genotyping provides a feasible triage strategy for hrHPV-positive women, with direct applicability on self-samples.
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