Covalently Functionalized MXenes for Highly Sensitive Humidity Sensors.

Transition metal carbides and nitrides (MXenes) are an emerging class of 2D materials, which are attracting ever-growing attention due to their remarkable physicochemical properties. The presence of various surface functional groups on MXenes' surface, e.g., F, O, OH, Cl, opens the possibility to tune their properties through chemical functionalization approaches. However, only a few methods have been explored for the covalent functionalization of MXenes and include diazonium salt grafting and silylation reactions. Here, an unprecedented two-step functionalization of Ti3 C2 Tx MXenes is reported, where (3-aminopropyl)triethoxysilane is covalently tethered to Ti3 C2 Tx and serves as an anchoring unit for subsequent attachment of various organic bromides via the formation of CN bonds. Thin films of Ti3 C2 Tx functionalized with linear chains possessing increased hydrophilicity are employed for the fabrication of chemiresistive humidity sensors. The devices exhibit a broad operation range (0-100% relative humidity), high sensitivity (0.777 or 3.035), a fast response/recovery time (0.24/0.40 s ΔH-1 , respectively), and high selectivity to water in the presence of saturated vapors of organic compounds. Importantly, our Ti3 C2 Tx -based sensors display the largest operating range and a sensitivity beyond the state of the art of MXenes-based humidity sensors. Such outstanding performance makes the sensors suitable for real-time monitoring applications.

Unveiling Charge-Transport Mechanisms in Electronic Devices Based on Defect-Engineered MoS2 Covalent Networks.

Device performance of solution-processed 2D semiconductors in printed electronics has been limited so far by structural defects and high interflake junction resistance. Covalently interconnected networks of transition metal dichalcogenides potentially represent an efficient strategy to overcome both limitations simultaneously. Yet, the charge-transport properties in such systems have not been systematically researched. Here, the charge-transport mechanisms of printed devices based on covalent MoS2 networks are unveiled via multiscale analysis, comparing the effects of aromatic versus aliphatic dithiolated linkers. Temperature-dependent electrical measurements reveal hopping as the dominant transport mechanism: aliphatic systems lead to 3D variable range hopping, unlike the nearest neighbor hopping observed for aromatic linkers. The novel analysis based on percolation theory attributes the superior performance of devices functionalized with π-conjugated molecules to the improved interflake electronic connectivity and formation of additional percolation paths, as further corroborated by density functional calculations. Valuable guidelines for harnessing the charge-transport properties in MoS2 devices based on covalent networks are provided.

Intravitreal Injections during the COVID-19 Outbreak in Northern Italy: An Innovative Approach for a High Quality and Safe Treatment.

BACKGROUND: Intravitreal injection (IVI) is a standard procedure performed in ophthalmology to treat several conditions, and is performed in different settings across countries. The Italian guidelines recommend this intervention is performed in an operating room to minimize the risk of infections, while in other countries, including Canada, USA and the UK, IVIs are performed in the ophthalmologist's office. The 2020 COVID-19 outbreak caused a dramatic modification in outpatient care. Consequently, non-urgent surgical activities, like IVIs, were subjected to a drastic reduction. METHODS: We conducted observational study which investigated the outcomes of IVIs performed in an ophthalmologist's office using a mobile laminar flow unit, the Operio mobile (Toul Meditech, Operio®) versus an operating room setting. RESULTS: Use of the Operio mobile allowed the safety performance of 3838 IVIs during COVID-19 and significantly reduced the waiting time of the first visit. This results in a faster intervention without affecting the technical IVI procedure that remained unchanged comparing the two settings. Specifically, we observed a 26% reduction in operation costs for each IVI performed in the office, which can be translated to a higher impact when considering the total number of IVIs performed over one year. CONCLUSION: The use of the Operio mobile in an ophthalmologist's office provides flexibility to perform IVIs, assuring patient safety, reducing healthcare personnel employment times, and the waiting lists for the patients, increasing the number of surgeries and improving the cost-effectiveness of the procedure.

Electron Irradiation of Metal Contacts in Monolayer MoS2 Field-Effect Transistors.

Metal contacts play a fundamental role in nanoscale devices. In this work, Schottky metal contacts in monolayer molybdenum disulfide (MoS2) field-effect transistors are investigated under electron beam irradiation. It is shown that the exposure of Ti/Au source/drain electrodes to an electron beam reduces the contact resistance and improves the transistor performance. The electron beam conditioning of contacts is permanent, while the irradiation of the channel can produce transient effects. It is demonstrated that irradiation lowers the Schottky barrier at the contacts because of thermally induced atom diffusion and interfacial reactions. The simulation of electron paths in the device reveals that most of the beam energy is absorbed in the metal contacts. The study demonstrates that electron beam irradiation can be effectively used for contact improvement through local annealing.

Magnetotransport and magnetic properties of amorphous [Formula: see text] thin films.

[Formula: see text] is an intermetallic compound with a bulk Curie temperature ([Formula: see text]) of 6-13 K. While existing studies have focused on [Formula: see text] crystals, amorphous thin-films of [Formula: see text] are potentially important since they would be magnetically soft without magnetocrystalline anisotropy, meaning that small external magnetic fields could reverse the direction of their magnetization. Here, we report [Formula: see text] thin-films with a thickness in the 5-200 nm range, deposited by DC magnetron sputtering onto Si(100). Films are amorphous with a weak temperature-dependent resistivity with values ranging between 150 and 300 [Formula: see text] cm. By means of noise spectroscopy, by analyzing the time-dependence of fluctuation-induced voltages, it is found that at low temperatures the resistance fluctuations are due to the Kondo effect. Volume magnetometry indicates [Formula: see text] K with a magnetic coercive field of 30 mT at 5 K for a 125-nm-thick film. The results are promising for the development of Ferromagnet(F)/Superconductor(S)/Ferromagnet(F) pseudo spin-valve devices based on amorphous [Formula: see text] thin films.

Observation of 2D Conduction in Ultrathin Germanium Arsenide Field-Effect Transistors.

We report the fabrication and electrical characterization of germanium arsenide (GeAs) field-effect transistors with ultrathin channels. The electrical transport is investigated in the 20-280 K temperature range, revealing that the p-type electrical conductivity and the field-effect mobility are growing functions of temperature. An unexpected peak is observed in the temperature dependence of the carrier density per area at ∼75 K. Such a feature is explained considering that the increased carrier concentration at higher temperatures and the vertical band bending combined with the gate field lead to the formation of a two-dimensional (2D) conducting channel, limited to few interfacial GeAs layers, which dominates the channel conductance. The conductivity follows the variable-range hopping model at low temperatures and becomes the band-type at higher temperatures when the 2D channel is formed. The formation of the 2D channel is validated through a numerical simulation that shows excellent agreement with the experimental data.

Nanotip Contacts for Electric Transport and Field Emission Characterization of Ultrathin MoS2 Flakes.

We report a facile approach based on piezoelectric-driven nanotips inside a scanning electron microscope to contact and electrically characterize ultrathin MoS2 (molybdenum disulfide) flakes on a SiO2/Si (silicon dioxide/silicon) substrate. We apply such a method to analyze the electric transport and field emission properties of chemical vapor deposition-synthesized monolayer MoS2, used as the channel of back-gate field effect transistors. We study the effects of the gate-voltage range and sweeping time on the channel current and on its hysteretic behavior. We observe that the conduction of the MoS2 channel is affected by trap states. Moreover, we report a gate-controlled field emission current from the edge part of the MoS2 flake, evidencing a field enhancement factor of approximately 200 and a turn-on field of approximately   40   V / µ m at a cathode-anode separation distance of 900   nm .

Bias Tunable Photocurrent in Metal-Insulator-Semiconductor Heterostructures with Photoresponse Enhanced by Carbon Nanotubes.

Metal-insulator-semiconductor-insulator-metal (MISIM) heterostructures, with rectifying current-voltage characteristics and photosensitivity in the visible and near-infrared spectra, are fabricated and studied. It is shown that the photocurrent can be enhanced by adding a multi-walled carbon nanotube film in the contact region to achieve a responsivity higher than 100   mA   W - 1 under incandescent light of 0.1   mW   cm - 2 . The optoelectrical characteristics of the MISIM heterostructures are investigated at lower and higher biases and are explained by a band model based on two asymmetric back-to-back Schottky barriers. The forward current of the heterojunctions is due to majority-carrier injection over the lower barrier, while the reverse current exhibits two different conduction regimes corresponding to the diffusion of thermal/photo generated carriers and majority-carrier tunneling through the higher Schottky barrier. The two conduction regimes in reverse bias generate two plateaus, over which the photocurrent increases linearly with the light intensity that endows the detector with bias-controlled photocurrent.

Thermoresistive Properties of Graphite Platelet Films Supported by Different Substrates.

Large-area graphitic films, produced by an advantageous technique based on spraying a graphite lacquer on glass and low-density polyethylene (LDPE) substrates were studied for their thermoresistive applications. The spray technique uniformly covered the surface of the substrate by graphite platelet (GP) unities, which have a tendency to align parallel to the interfacial plane. Transmission electron microscopy analysis showed that the deposited films were composed of overlapped graphite platelets of different thickness, ranging from a few tens to hundreds of graphene layers, and Raman measurements provided evidence for a good graphitic quality of the material. The GP films deposited on glass and LDPE substrates exhibited different thermoresistive properties during cooling-heating cycles in the -40 to +40 °C range. Indeed, negative values of the temperature coefficient of resistance, ranging from -4 × 10-4 to -7 × 10-4 °C-1 have been observed on glass substrates, while positive values varying between 4 × 10-3 and 8 × 10-3 °C-1 were measured when the films were supported by LDPE. These behaviors were attributed to the different thermal expansion coefficients of the substrates. The appreciable thermoresistive properties of the graphite platelet films on LDPE could be useful for plastic electronic applications.

Field Emission Characterization of MoS2 Nanoflowers.

Nanostructured materials have wide potential applicability as field emitters due to their high aspect ratio. We hydrothermally synthesized MoS2 nanoflowers on copper foil and characterized their field emission properties, by applying a tip-anode configuration in which a tungsten tip with curvature radius down to 30-100 nm has been used as the anode to measure local properties from small areas down to 1-100 µm2. We demonstrate that MoS2 nanoflowers can be competitive with other well-established field emitters. Indeed, we show that a stable field emission current can be measured with a turn-on field as low as 12 V/µm and a field enhancement factor up to 880 at 0.6 µm cathode-anode separation distance.

A WSe2 vertical field emission transistor.

We report the first observation of a gate-controlled field emission current from a tungsten diselenide (WSe2) monolayer, synthesized by chemical-vapour deposition on a SiO2/Si substrate. Ni contacted WSe2 monolayer back-gated transistors, under high vacuum, exhibit n-type conduction and drain-bias dependent transfer characteristics, which are attributed to oxygen/water desorption and drain induced Schottky barrier lowering, respectively. The gate-tuned n-type conduction enables field emission, i.e. the extraction of electrons by quantum tunnelling, even from the flat part of the WSe2 monolayers. Electron emission occurs under an electric field ∼100 V µm-1 and exhibits good time stability. Remarkably, the field emission current can be modulated by the back-gate voltage. The first field-emission vertical transistor based on the WSe2 monolayer is thus demonstrated and can pave the way to further optimize new WSe2 based devices for use in vacuum electronics.

Environmental Effects on the Electrical Characteristics of Back-Gated WSe2 Field-Effect Transistors.

We study the effect of polymer coating, pressure, temperature, and light on the electrical characteristics of monolayer WSe 2 back-gated transistors with Ni / Au contacts. Our investigation shows that the removal of a layer of poly(methyl methacrylate) (PMMA) or a decrease of the pressure change the device conductivity from p- to n-type. From the temperature behavior of the transistor transfer characteristics, a gate-tunable Schottky barrier at the contacts is demonstrated and a barrier height of ~ 70 meV in the flat-band condition is measured. We also report and discuss a temperature-driven change in the mobility and the subthreshold swing that is used to estimate the trap density at the WSe 2 / SiO 2 interface. Finally, from studying the spectral photoresponse of the WSe 2 , it is proven that the device can be used as a photodetector with a responsivity of ~ 0.5   AW - 1 at 700   nm and 0.37   mW / cm 2 optical power.

Transport and Field Emission Properties of MoS2 Bilayers.

We report the electrical characterization and field emission properties of MoS 2 bilayers deposited on a SiO 2 / Si substrate. Current-voltage characteristics are measured in the back-gate transistor configuration, with Ti contacts patterned by electron beam lithography. We confirm the n-type character of as-grown MoS 2 and we report normally-on field-effect transistors. Local characterization of field emission is performed inside a scanning electron microscope chamber with piezo-controlled tungsten tips working as the anode and the cathode. We demonstrate that an electric field of ~ 200 V / µ m is able to extract current from the flat part of MoS 2 bilayers, which can therefore be conveniently exploited for field emission applications even in low field enhancement configurations. We show that a Fowler-Nordheim model, modified to account for electron confinement in two-dimensional (2D) materials, fully describes the emission process.

The Nonmydriatic Fundus Camera in Diabetic Retinopathy Screening: A Cost-Effective Study with Evaluation for Future Large-Scale Application.

Aims. The study aimed to present the experience of a screening programme for early detection of diabetic retinopathy (DR) using a nonmydriatic fundus camera, evaluating the feasibility in terms of validity, resources absorption, and future advantages of a potential application, in an Italian local health authority. Methods. Diabetic patients living in the town of Ponzano, Veneto Region (Northern Italy), were invited to be enrolled in the screening programme. The "no prevention strategy" with the inclusion of the estimation of blindness related costs was compared with screening costs in order to evaluate a future extensive and feasible implementation of the procedure, through a budget impact approach. Results. Out of 498 diabetic patients eligible, 80% was enrolled in the screening programme. 115 patients (34%) were referred to an ophthalmologist and 9 cases required prompt treatment for either proliferative DR or macular edema. Based on the pilot data, it emerged that an extensive use of the investigated screening programme, within the Greater Treviso area, could prevent 6 cases of blindness every year, resulting in a saving of €271,543.32 (-13.71%). Conclusions. Fundus images obtained with a nonmydriatic fundus camera could be considered an effective, cost-sparing, and feasible screening tool for the early detection of DR, preventing blindness as a result of diabetes.

Epithelial downgrowth after cataract surgery: an atypical presentation with scleral thinning and massive seeding in anterior chamber.

PURPOSE: To report an atypical presentation of epithelial downgrowth (ED) after clear cornea cataract extraction, characterized by mixed clinical expression of both cystic and diffuse form and massive epithelial debris seeding in anterior chamber, associated with scleral involvement. METHODS: In this case report, fine needle anterior chamber aspiration cytology was performed to identify pathologic tissue invading iris, cornea, and angular structures. The patient was treated with anterior chamber membrane surgical excision. RESULTS: Epithelial downgrowth was identified by cytologic assessment. The patient was treated with epithelial membrane peeling and scleral defect conjunctival covering. This conservative surgical approach led to a significant reduction of ocular pain. During follow-up, residual epithelial tissue was present in anterior chamber without tendency to regrowth. CONCLUSIONS: In doubtful cases of ED, histocytopathologic analysis should be performed without hesitation. Avoiding more invasive procedures, early detection and prompt surgical approach can result in improved outcome even in case of extensive intraocular involvement.

Late vitreomacular traction in toxoplasma retinochoroiditis resolved by vitrectomy.

This paper reports a case of late vitreomacular traction in a young patient secondary to toxoplasma retinochoroiditis resolved by vitrectomy. A 17-year-old female with chronic inflammatory bowel disease developed severe vitreomacular traction 8 months after resolution of ocular toxoplasmosis with medical therapy. Best-corrected visual acuity, full ophthalmic slit-lamp examination, colour fundus photography, spectral domain optical coherence tomography, and fluorescein angiography were performed. The patient underwent vitrectomy with removal of the clinically evident posterior hyaloid. Vitrectomy was rapidly successful in resolving the vitreomacular traction, with full recovery in best-corrected visual acuity of 20/20. Vitreoretinal traction in patients with previous toxoplasma retinochoroiditis may appear several months after resolution of the inflammatory condition. We suggest observing carefully for possible development of late vitreoretinal traction during follow-up of such patients.

Scanning laser ophthalmoscopy in the retromode in diabetic macular oedema.

PURPOSE: To determine the validity of scanning laser ophthalmoscopy in the retromode (RM-SLO) versus other imaging modalities in the diagnosis of diabetic macular oedema (DME). METHODS: Two hundred and sixty-three eyes were examined. Inclusion criteria were any stage of untreated or treated diabetic retinopathy and four imaging modalities of the macula carried out on the same day: time domain optical coherence tomography (OCT), fundus autofluorescence (FAF), RM-SLO and fluorescein angiography (FA). Two masked retinal specialists independently graded all images. Agreement between RM-SLO and OCT, FA and FAF in evaluating the presence and patterns of DME was evaluated by kappa statistics, sensitivity, specificity, observed proportional agreement, and proportional agreement in positive and negative cases. RESULTS: The agreement in evaluating the presence/absence of DME between RM-SLO and OCT, FA and FAF was good: κ = 0.73 (confidence interval; CI, 0.64-0.83), κ = 0.71 (CI, 0.61-0.81) and κ = 0.73 (CI, 0.63-0.83), respectively. The agreement in evaluating cystoid pattern of DME was almost perfect between RM-SLO and OCT, RM-SLO and FA, κ > 0.8; and good between RM-SLO and FAF, κ > 0.7. The agreement in evaluating the presence/absence of subfoveal neuroretinal was almost perfect between RM-SLO and OCT (κ = 0.83; 95% CI, 0.70-0.96). Subfoveal neuroretinal detachment did not show any specific pattern on FA or FAF. Sensitivity and specificity of RM-SLO in evaluating DME was 97.7% and 71.9% versus OCT, 97.4% and 68.1% versus FA and 96.1% and 73.3% versus FAF. Retinal thickness of 233 µm represented the cut-off value to define DME by RM-SLO. CONCLUSIONS: The combined use of non-invasive imaging techniques can improve the diagnostic interpretation of different aspects of DME.

Standard versus bolus photodynamic therapy in circumscribed choroidal hemangioma: functional outcomes.

PURPOSE: To compare standard versus bolus photodynamic therapy (PDT) in the treatment of symptomatic circumscribed choroidal hemangioma (CCH). METHODS: Twenty consecutive cases of CCH were included in this prospective randomized study. Each patient was randomly assigned to receive either standard PDT (10-minute 6 mg/mq2 verteporfin infusion; treatment at 15 min; 50 J/cm2; 83 s) or bolus PDT (6 mg/mq2 verteporfin infusion bolus in 1 min; treatment at 5 min; 100 J/cm2; 166 s). Best-corrected visual acuity (BCVA), fundus photography, optical coherence tomography, fluorescein, and indocyanine green angiography were performed at baseline and during follow-up. Retinal sensitivity was tested with microperimetry before and after treatment. Follow-up was longer than 32 months. RESULTS: Mean follow-up was 58±11 months. All cases (100%) showed clinical regression of the treated lesion. Neuroretinal and retinal pigment epithelium (RPE) changes were found in 9 (90%) bolus PDT over treated area. No similar RPE changes were found in patients treated with standard PDT. There was a no statistically significant difference in BCVA outcome between the 2 groups (p=0.078). Microperimetry revealed reduced sensitivity over the treated area in 7 bolus PDT vs 1 in standard treated eyes (p=0.008). CONCLUSIONS: Both standard and bolus PDT induce regression of symptomatic CCH. Bolus PDT may cause RPE and retinal changes associated with reduced retinal sensitivity.

Topical 1% 5-fluorouracil in ocular surface squamous neoplasia: a long-term safety study.

BACKGROUND/AIMS: The aim of this study was to evaluate the long-term corneal toxicity of topical chemotherapy with 1% 5-fluorouracil (5-FU) as a sole or adjuvant treatment of ocular surface squamous neoplasia (OSSN). METHODS: Forty-one consecutive cases of OSSN were included in this prospective study. Patients underwent topical chemotherapy with 1% 5-FU four times/day for 4 weeks (one course). Adjunctive courses were repeated until clinical and cytological tumour regression. Clinical confocal microscopy was used to check for 5-FU long-term corneal toxicity. RESULTS: Mean follow-up was 89.7±14.4 months (range 63-122 months). Twenty-two patients (53.7%) underwent topical 5-FU as a sole treatment, and 19 patients (46.3%) as adjuvant and/or debulking therapy. The mean number of 5-FU cycles was 1.9 (range 1-5 cycles). Three tumours (7.3%) treated with 5-FU alone recurred during follow-up. Recurrences were successfully treated with additional 5-FU courses. Clinical confocal microscopy showed no long-term difference between the treated eye and fellow (control) eye in: endothelial cells count, pleomorphism and polymegatism, anterior stromal keratocyte density, sub-basal nerve plexus fibre number, density, and beadings and central cornea epithelium thickness (p=NS). CONCLUSION: Topical 5-FU, as a sole or combined therapy, must be considered a long-term safe and effective treatment for patients affected by OSSN.

Modified enucleation for choroidal melanoma with large extrascleral extension.

PURPOSE: To report the technique and the outcome of modified (enlarged) enucleation via lateral orbitotomy for choroidal melanomas with massive extrascleral extension. METHODS: 5 patients with choroidal malanoma with massive, circumscribed perioptic/posterior extrascleral extension underwent modified enucleation via lateral orbitotomy. After lateral orbitotomy and orbital mass exposure with direct tumor visualization, a long optic nerve stump was cut and the orbital component of the tumor was completely (macroscopically) removed along with the globe in all cases. After haemostasis and orbital reconstruction an orbital implant was then placed. Follow-up was longer than 12 months. RESULTS: Excellent cosmetic outcome was acheived in all patients (100%) without operative or postoperative complications. At pathologic examination, tumors were completely removed in all cases (100%). CONCLUSIONS: Modified (enlarged) enucleation via lateral orbitotomy for selectd choroidal melanomas with massive, circumscribed perioptic/posterior extrascleral extension allows complete tumor removal and placement of an orbital implant, avoiding the long healing process of orbital exenteration with excellent clinical and cosmetic outcome.