Author Correction: Carbon nanotubes as emerging quantum-light sources.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Publisher Correction: Carbon nanotubes as emerging quantum-light sources.

In the version of this Perspective originally published, the x-axis label of Fig. 1d was missing; it should have read 'Wavelength (nm)'. The units of the y axis of Fig. 3b were incorrect; they should have been meV. And the citation of Fig. 3c in the main text was incorrect; it should have been to Fig. 3b. These issues have now been corrected.

Carbon nanotubes as emerging quantum-light sources.

Progress in quantum computing and quantum cryptography requires efficient, electrically triggered, single-photon sources at room temperature in the telecom wavelengths. It has been long known that semiconducting single-wall carbon nanotubes (SWCNTs) display strong excitonic binding and emit light over a broad range of wavelengths, but their use has been hampered by a low quantum yield and a high sensitivity to spectral diffusion and blinking. In this Perspective, we discuss recent advances in the mastering of SWCNT optical properties by chemistry, electrical contacting and resonator coupling towards advancing their use as quantum light sources. We describe the latest results in terms of single-photon purity, generation efficiency and indistinguishability. Finally, we consider the main fundamental challenges stemming from the unique properties of SWCNTs and the most promising roads for SWCNT-based chip integrated quantum photonic sources.

Diameter dependent thermoelectric properties of individual SnTe nanowires.

The lead-free compound tin telluride (SnTe) has recently been suggested to be a promising thermoelectric material. In this work, we report on the first thermoelectric study of individual single-crystalline SnTe nanowires with different diameters ranging from ∼218 to ∼913 nm. Measurements of thermopower S, electrical conductivity σ and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25-300 K. While the electrical conductivity does not show a strong diameter dependence, the thermopower increases by a factor of two when the nanowire diameter is decreased from ∼913 nm to ∼218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may arise from the enhanced phonon - surface boundary scattering and phonon-defect scattering. Temperature dependent figure of merit ZT was determined for individual nanowires and the achieved maximum value at room temperature is about three times higher than that in bulk samples of comparable carrier density.

Highly efficient charge separation and collection across in situ doped axial VLS-grown Si nanowire p-n junctions.

VLS-grown semiconductor nanowires have emerged as a viable prospect for future solar-based energy applications. In this paper, we report highly efficient charge separation and collection across in situ doped Si p-n junction nanowires with a diameter <100 nm grown in a cold wall CVD reactor. Our photoexcitation measurements indicate an internal quantum efficiency of ~50%, whereas scanning photocurrent microscopy measurements reveal effective minority carrier diffusion lengths of ~1.0 µm for electrons and 0.66 µm for holes for as-grown Si nanowires (d(NW) ≈ 65-80 nm), which are an order of magnitude larger than those previously reported for nanowires of similar diameter. Further analysis reveals that the strong suppression of surface recombination is mainly responsible for these relatively long diffusion lengths, with surface recombination velocities (S) calculated to be 2 orders of magnitude lower than found previously for as-grown nanowires, all of which used hot wall reactors. The degree of surface passivation achieved in our as-grown nanowires is comparable to or better than that achieved for nanowires in prior studies at significantly larger diameters. We suggest that the dramatically improved surface recombination velocities may result from the reduced sidewall reactions and deposition in our cold wall CVD reactor.

Near-unity quantum yields of biexciton emission from CdSe/CdS nanocrystals measured using single-particle spectroscopy.

Biexciton photoluminescence (PL) quantum yields (Q(2X)) of individual CdSe/CdS core-shell nanocrystal quantum dots with various shell thicknesses are derived from independent PL saturation and two-photon correlation measurements. We observe a near-unity Q(2X) for some nanocrystals with an ultrathick 19-monolayer shell. High Q(2X)'s are, however, not universal and vary widely among nominally identical nanocrystals indicating a significant dependence of Q(2X) upon subtle structural differences. Interestingly, our measurements indicate that high Q(2X)'s are not required to achieve complete suppression of PL intensity fluctuations in individual nanocrystals.

Awareness of blindness and other smoking-related diseases and its impact on motivation for smoking cessation in eye patients.

PURPOSE: Cigarette smoking is a major cause of morbidity and mortality. The association between smoking and eye diseases is less widely recognised relative to other better-known smoking-related conditions. This study aims to assess the awareness and fear of known smoking-related diseases among current smokers attending an ophthalmology outpatient clinic and to evaluate their relative impact on the likelihood of smoking cessation. PATIENTS AND METHODS: A cross-sectional survey using a structured interview of randomly selected current smokers attending an eye clinic was conducted. The knowledge of six smoking-related diseases (lung cancer, heart attack, stroke, blindness, other cancers, and other lung diseases) was assessed. The fear of smoking-related conditions and the relative impact of each smoking-related condition on the smoker's motivation to quit smoking were evaluated. RESULTS: Out of 200 current smokers aged from 14 to 83 years, only 42.5% (85 patients) were aware that smoking causes blindness. Smokers' perception of harm caused by smoking was 6.53±3.21 (mean±SD) on a visual analogue scale of 0 to 10. Patients placed blindness as the second most important motivating factor to quit smoking immediately, within 1 year and 5 years, after lung cancer. CONCLUSION: The awareness of the risk of blindness from smoking was lowest compared with five other smoking-related diseases among eye patients who smoke. However, blindness remains a key motivational factor in smoking cessation and hence should be emphasised as an important negative health consequence of smoking in public health education and anti-smoking campaigns.

Nano-engineered electron-hole exchange interaction controls exciton dynamics in core-shell semiconductor nanocrystals.

A strong electron-hole exchange interaction (EI) in semiconductor nanocrystals (NCs) gives rise to a large (up to tens of meV) splitting between optically active ('bright') and optically passive ('dark') excitons. This dark-bright splitting has a significant effect on the optical properties of band-edge excitons and leads to a pronounced temperature and magnetic field dependence of radiative decay. Here we demonstrate a nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. We show that the dark-bright splitting can be widely tuned by controlling the electron-hole spatial overlap in core-shell CdSe/CdS NCs with a variable shell width. In thick-shell samples, the EI energy reduces to <250 µeV, which yields a material that emits with a nearly constant rate over temperatures from 1.5 to 300 K and magnetic fields up to 7 T. The EI-manipulation strategies demonstrated here are general and can be applied to other nanostructures with variable electron-hole overlap.

Imaging of blebs after phacotrabeculectomy with Ologen collagen matrix implants.

OBJECTIVE: To analyse blebs of phacotrabeculectomies performed with Ologen collagen implants (ProTop & MediKing, Taipei, Taiwan) and to compare these with blebs of mitomycin C (MMC)­augmented phacotrabeculectomies. METHODS: 33 participants underwent phacotrabeculectomy with Ologen implants, and 33 controls underwent phacotrabeculectomy with MMC. Blebs were analysed for height and area using anterior segment optical coherence tomography (ASOCT) at 30, 60 and 90 days after surgery and were also graded clinically with the Moorfields bleb grading system (MBGS) 60 days after surgery. RESULTS: With ASOCT, there was no difference in mean bleb height at 30 and 60 days, but at 90 days, bleb height was lower in the Ologen group (Ologen vs MMC, 0.74±0.20 vs 1.00±0.28 mm, p<0.001). There was no difference in mean bleb area at 30, 60 or 90 days. Mean reduction in intraocular pressure at 90 days was greater in the MMC group (Ologen vs MMC, 2.18±4.93 vs 8.00 ±7.60 mm Hg, p<0.001). At 90 days, the Ologen implants were visible in ASOCT images in 13 (39.4%) of 33 participants. With the Moorfields bleb grading system at 60 days, there was no difference in maximal bleb area score between the groups, but bleb height score was lower (Ologen vs MMC, 1.53±0.51 vs 1.81±0.59, p=0.05) and central bleb vascularity score was higher in the Ologen group (3.88±0.55 vs 2.91±0.59, p<0.001). CONCLUSIONS: Within 3 months of surgery, mean bleb height was lower in the Ologen blebs compared with the MMC blebs. The Ologen implants had not degraded in a third of eyes.

Visual acuity outcomes after deep anterior lamellar keratoplasty: a case-control study.

AIM: To compare visual outcomes between deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PK). Secondarily to compare refractive outcomes, complications and graft survival between the three cohorts. METHODS: Retrospective case-control study evaluating visual acuity outcomes (VA) following DALK with complete Descemet's baring (DALKa) (modified Anwar big bubble technique--51 eyes), pre-descemetic anterior lamellar keratoplasty (DALKm) (manual technique--52 eyes) and PK (103 eyes) with mean follow-up of 13.6, 19.3 and 18.6 months, respectively. RESULTS: The common indications for surgery were corneal scars (36.4%), keratoconus (28.6%) and corneal dystrophies (13.6%). A best-corrected VA of 6/7.5 or better was achieved in 19.4% (PK), 21.6% (DALKm) and 38.5% (DALKa) of cases (p=0.02), and eyes that underwent DALKa had significantly better visual outcomes than PK (p=0.03). Complications following PK were glaucoma (15%), endothelial rejection (12%) and epithelial problems (11%); in the lamellar group, glaucoma (9%), epithelial problems (5%) and Descemet's detachment (3%) were more common. The 2-year estimated probability of graft survival was 90% for PK, 98% for DALKm and 100.0% for DALKa (p=0.35). CONCLUSIONS: Lamellar keratoplasty with complete baring of the Descemet's membrane (DALKa) gave significantly better visual outcomes compared to PK or pre-descemetic ALK and should be the preferred from of corneal replacement in corneal disorders with healthy endothelium.

Highly emissive multiexcitons in steady-state photoluminescence of individual "giant" CdSe/CdS Core/Shell nanocrystals.

The development of nanocrystal quantum dots (NQDs) with suppressed nonradiative Auger recombination has been an important goal in colloidal nanostructure research motivated by the needs of prospective applications in lasing devices, light-emitting diodes, and photovoltaic cells. Here, we conduct single-nanocrystal spectroscopic studies of recently developed core-shell NQDs (so-called "giant" NQDs) that comprise a small CdSe core surrounded by a 16-monolayer-thick CdS shell. Using both continuous-wave and pulsed excitation, we observe strong emission features due both to neutral and charged biexcitons, as well as multiexcitons of higher order. The development of pronounced multiexcitonic peaks in steady-state photoluminescence of individual nanocrystals, as well as continuous growth of the emission intensity in the range of high pump levels, point toward a significant suppression of nonradiative Auger decay that normally renders multiexcitons nonemissive. The unusually high multiexciton emission efficiencies in these systems open interesting opportunities for studies of multiexciton phenomena using well-established methods of single-dot spectroscopy, as well as new exciting prospects for applications, that have previously been hampered by nonradiative Auger decay.

Haemorrhagic pigment epithelial detachment as a predictive feature of polypoidal choroidal vasculopathy in a Chinese population.

PURPOSE: To determine the frequency of haemorrhagic pigment epithelial detachment (PED) among patients presenting with either polypoidal choroidal vasculopathy (PCV) or choroidal neovascularization (CNV) and calculate the degree to which the presence of a haemorrhagic PED can be used to predict the diagnosis of PCV. METHODS: A retrospective review of 290 eyes of 253 patients presenting to the Singapore National Eye Centre with serosanguineous maculopathy. Patients underwent ophthalmologic examination including digital colour fundus photography and stereoscopic fluorescein angiography and indocyanine green angiography (ICGA). Classification into PCV or CNV was based on ICGA findings, and presence or absence of haemorrhagic PED was documented. RESULTS: In total, 138 eyes of 123 patients were diagnosed with PCV and 152 eyes of 130 patients with CNV. A haemorrhagic PED was a significantly more common (P<0.001) presenting feature in PCV eyes (63, 45.7%) than CNV eyes (6, 3.9%) (odds ratio (OR) 20.4, 95% confidence interval (CI) 8.5-49.4). Age-related maculopathy was found significantly more frequently (P<0.001) in the unaffected fellow eye of CNV patients (57, 52.8%) than PCV patients (28, 22.8%) (OR 3.2, 95% CI 1.8-5.7). CONCLUSIONS: In patients of Chinese ethnicity, a haemorrhagic PED is significantly more likely to be the presenting feature of PCV than CNV. Patients presenting with this clinical feature should make the clinician suspicious of an underlying diagnosis of PCV.

Comparison of Visante and slit-lamp anterior segment optical coherence tomography in imaging the anterior chamber angle.

AIMS: To compare the diagnostic performance of two anterior segment optical coherence tomography (AS-OCT) devices in assessing the anterior chamber angle (ACA). METHODS: Visante-OCT and slit-lamp-OCT (SL-OCT) were performed on 101 patients by a single operator. The AS-OCT images were processed by customised 'dewarping' software and assessed by two glaucoma specialists masked to clinical findings. A closed ACA was defined by the presence of contact between the iris and angle anterior to the scleral spur. Measurements of the ACA, anterior chamber depth (ACD), and pupil diameter were analysed. Gonioscopy was performed by another examiner masked to AS-OCT findings. RESULTS: Qualitative analysis could be carried out in 83 (83%) eyes and quantitative analysis in 61 (60%) eyes. A closed angle in at least one quadrant of the eye was observed in 30 eyes with gonioscopy; Visante-OCT imaging identified 29 of 30 (97%) and SL-OCT imaging identified 27 of 30 (90%) of these eyes (P=0.50, McNemar test). Visante-OCT detected more eyes with at least one closed quadrant than SL-OCT (55 vs46 eyes, respectively, P=0.01). Overall, SL-OCT had better agreement with gonioscopy than with Visante-OCT. Both AS-OCTs showed good agreement for ACD measurements; however, SL-OCT tended to provide consistently higher ACA measurements and smaller pupil diameters than did Visante-OCT. CONCLUSIONS: Both AS-OCT devices detected most of the eyes with closed ACA on gonioscopy. However, Visante-OCT detected more closed ACAs than did SL-OCT. The better agreement between SL-OCT and gonioscopy is likely because of the use of visible light during both examinations. The ACA measurements obtained with each device are not interchangeable.

Anomalous circular polarization of photoluminescence spectra of individual CdSe nanocrystals in an applied magnetic field.

We study the low-temperature magnetophotoluminescence from individual CdSe nanocrystals. Nanocrystals having a small "bright" exciton fine structure splitting (Delta_{XY}<0.5 meV) exhibit a conventional left and right circularly polarized Zeeman photoluminescence doublet in applied magnetic fields. In contrast, nanocrystals with large Delta_{XY} (>1 meV) show an anomalous magnetophotoluminescence polarization, wherein the lower-energy peak becomes circularly polarized with increasing field, while the higher-energy peak remains linearly polarized. This unusual behavior arises from strong mixing between the absorbing and emitting bright exciton levels due to strong anisotropic exchange interactions.

Time-resolved photoluminescence of type-II Ga(As)Sb/GaAs quantum dots embedded in an InGaAs quantum well.

Optical properties and carrier dynamics in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) are reported. A large blueshift of the photoluminescence (PL) peak is observed with increased excitation densities. This blueshift is due to the Coulomb interaction between physically separated electrons and holes characteristic of the type-II band alignment, along with a band-filling effect of electrons in the QW. Low-temperature (4 K) time-resolved PL measurements show a decay time of [Formula: see text] ns from the transition between Ga(As)Sb QDs and InGaAs QW which is longer than that of the transition between Ga(As)Sb QDs and GaAs two-dimensional electron gas ([Formula: see text] ns).

Single carbon nanotubes probed by photoluminescence excitation spectroscopy: the role of phonon-assisted transitions.

We study light absorption mechanisms in semiconducting carbon nanotubes using low-temperature, single-nanotube photoluminescence excitation spectroscopy. In addition to purely electronic transitions, we observe several strong phonon-assisted bands due to excitation of one or more phonon modes together with the first electronic state. In contrast with a small width of emission lines (sub-meV to a few meV), most of the photoluminescence excitation features have significant linewidths of tens of meV. All of these observations indicate very strong electron-phonon coupling that allows efficient excitation of electronic states via phonon-assisted processes and leads to ultrafast intraband relaxation due to inelastic electron-phonon scattering.

Low temperature emission spectra of individual single-walled carbon nanotubes: multiplicity of subspecies within single-species nanotube ensembles.

Low-temperature photoluminescence (PL) studies of individual semiconducting single-walled carbon nanotubes reveal ultranarrow peaks (down to 0.25 meV linewidths) that exhibit blinking and spectral wandering. Multiple peaks appear within bands previously assigned to nanotubes of certain chiralities, indicating the existence of numerous subspecies within single-chirality specimens. The sharp PL features show two types of distinctly different shapes (symmetric versus asymmetric) and temperature dependences (weak versus strong), which we attribute to the presence of unintentionally doped nanotubes along with undoped species.

Effect of zero- to one-dimensional transformation on multiparticle Auger recombination in semiconductor quantum rods.

We study the effect of the zero- to one-dimensional (1D) transformation on multiparticle Auger recombination using a series of elongated semiconductor nanocrystals (quantum rods). We observe a transition from the three- to two-particle recombination process as the nanocrystal aspect ratio is increased. This transition indicates that in the 1D confinement limit, Auger decay is dominated by Coulomb interactions between 1D excitons that recombine in a bimolecular fashion. One consequence of this effect is strongly reduced decay rates of higher multiparticle states that lead to increased optical-gain lifetimes and efficient light amplification due to involvement of excited electronic states.

Interplay of Rabi oscillations and quantum interference in semiconductor quantum dots.

We investigated the manifestation of Rabi oscillation in the coherent dynamics of excitons in self-assembled semiconductor quantum dots. The Rabi oscillation phenomenon was directly observed as a function of the input pulse area. Furthermore, by performing wave packet interferometry in the nonlinear excitation regime, we discover a new type of quantum interference phenomenon, resulting from the interplay between Rabi oscillation and quantum interference.