Can We Rationally Design and Operate Spatial Atomic Layer Deposition Systems for Steering the Growth Regime of Thin Films?

Fine control over the growth of materials is required to precisely tailor their properties. Spatial atomic layer deposition (SALD) is a thin-film deposition technique that has recently attracted attention because it allows producing thin films with a precise number of deposited layers, while being vacuum-free and much faster than conventional atomic layer deposition. SALD can be used to grow films in the atomic layer deposition or chemical vapor deposition regimes, depending on the extent of precursor intermixing. Precursor intermixing is strongly influenced by the SALD head design and operating conditions, both of which affect film growth in complex ways, making it difficult to predict the growth regime prior to depositions. Here, we used numerical simulation to systematically study how to rationally design and operate SALD systems for growing thin films in different growth regimes. We developed design maps and a predictive equation allowing us to predict the growth regime as a function of the design parameters and operation conditions. The predicted growth regimes match those observed in depositions performed for various conditions. The developed design maps and predictive equation empower researchers in designing, operating, and optimizing SALD systems, while offering a convenient way to screen deposition parameters, prior to experimentation.

Atmospheric atomic layer deposition of SnO2 thin films with tin(II) acetylacetonate and water

Due to its unique optical, electrical, and chemical properties, tin dioxide (SnO₂) thin films attract enormous attention as a potential material for gas sensors, catalysis, low-emissivity coatings for smart windows, transparent electrodes for low-cost solar cells, etc. However, the low-cost and high-throughput fabrication of SnO₂ thin films without producing corrosive or toxic by-products remains challenging. One appealing deposition technique, particularly well-adapted to films presenting nanometric thickness is atomic layer deposition (ALD). In this work, several metalorganic tin-based complexes, namely, tin(IV) tert-butoxide, bis[bis(trimethylsilyl)amino] tin(II), dibutyltin diacetate, tin(II) acetylacetonate, tetrakis(dimethylamino) tin(IV), and dibutyltin bis(acetylacetonate), were explored thanks to DFT calculations. Our theoretical calculations suggest that the three last precursors are very appealing for ALD of SnO₂ thin films. The potential use of these precursors for atmospheric-pressure spatial atomic layer deposition (AP-SALD) is also discussed. For the first time, we experimentally demonstrate the AP-SALD growth of SnO₂ thin films using tin(II) acetylacetonate (Sn(acac)₂) and water. We observe that Sn(acac)₂ exhibits efficient ALD activity with a relatively large ALD temperature window (140-200 °C), resulting in a growth rate of 0.85 ± 0.03 Å per cyc. XPS analyses show a single Sn 3d_5/2 characteristic peak for Sn⁴⁺ at 486.8 ± 0.3 eV, indicating that a pure SnO₂ phase is obtained within the ALD temperature window. The as-deposited SnO₂ thin films are in all cases amorphous, and film conductivity increases with the deposition temperature. Hall effect measurements confirm the n-type nature of SnO₂ with a free electron density of about 8 × 10¹⁹ cm^-3, electron mobility up to 11.2 cm² V^-1 s^-1, and resistivity of 7 × 10^-3 Ω cm for samples deposited at 270 °C.

Silver Nanowire Networks: Ways to Enhance Their Physical Properties and Stability

Silver nanowire (AgNW) networks have been intensively investigated in recent years. Thanks to their attractive physical properties in terms of optical transparency and electrical conductivity, as well as their mechanical performance, AgNW networks are promising transparent electrodes (TE) for several devices, such as solar cells, transparent heaters, touch screens or light-emitting devices. However, morphological instabilities, low adhesion to the substrate, surface roughness and ageing issues may limit their broader use and need to be tackled for a successful performance and long working lifetime. The aim of the present work is to highlight efficient strategies to optimize the physical properties of AgNW networks. In order to situate our work in relation to existing literature, we briefly reported recent studies which investigated physical properties of AgNW networks. First, we investigated the optimization of optical transparency and electrical conductivity by comparing two types of AgNWs with different morphologies, including PVP layer and AgNW dimensions. In addition, their response to thermal treatment was deeply investigated. Then, zinc oxide (ZnO) and tin oxide (SnO2) protective films deposited by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) were compared for one type of AgNW. We clearly demonstrated that coating AgNW networks with these thin oxide layers is an efficient approach to enhance the morphological stability of AgNWs when subjected to thermal stress. Finally, we discussed the main future challenges linked with AgNW networks optimization processes.

Effects of non-homogeneity and oxide coating on silver nanowire networks under electrical stress: comparison between experiment and modeling

Silver nanowire (AgNW) networks are among the most promising indium-free, flexible transparent electrodes for energy, lighting and heating devices. However, the lack of stability of such networks is a key factor that limits their industrial application. While applications require homogeneous networks, non-homogeneous AgNW networks are intentionally prepared in the present work to probe the mechanisms leading to failure under electrical stress. We show that induced non-homogeneities have a strong impact both on the spatial distribution of temperature (measured by IR imaging) and the current density throughout the electrode (as deduced from modeling). Regions with higher current density under elevated electrical stress are correlated to the origin of degradation. Furthermore, the influence of a zinc oxide (ZnO) layer on electrical performances of non-homogeneous specimens is studied. Thanks to ZnO coating, the tortuosity of electrical potential lines measured by the one-probe mapping technique is much lower than for bare networks. Additionally, coated network electrical failure occurs at 40% higher voltage compared to bare network, over 18 V, while reaching superior power-induced heating of 360 °C. The results presented here will contribute to the design and fabrication of more robust nanowire networks, particularly for application in transparent heaters.

Planar and Transparent Memristive Devices Based on Titanium Oxide Coated Silver Nanowire Networks with Tunable Switching Voltage

Threshold switching devices are fundamental active elements in more than Moore approaches, integrating the new generation of non-volatile memory devices. Here, the authors report an in-plane threshold resistive switching device with an on/off ratio above 10⁶ , a low resistance state of 10 to 100 kΩ and a high resistance state of 10 to 100 GΩ. Our devices are based on nanocomposites of silver nanowire networks and titanium oxide, where volatile unipolar threshold switching takes place across the gap left by partially spheroidized nanowires. Device reversibility depends on the titanium oxide thickness, while nanowire network density determines the threshold voltage, which can reach as low as 0.16 V. The switching mechanism is explained through percolation between metal-semiconductor islands, in a combined tunneling conduction mechanism, followed by a Schottky emission generated via Joule heating. The devices are prepared by low-cost, atmospheric pressure, and scalable techniques, enabling their application in printable, flexible, and transparent electronics.

[Urethral discharge in Morocco: prevalence of microorganisms and susceptibility of gonococcos]

We studied 422 patients with urethral discharge recruited from 4 sentinel sites in Morocco to determine sociodemographic characteristics, history of STI infection, infecting organism and antibiotic susceptibility of Neisseria gonorrhoeae. The mean age of the sample was 28 years (range 16-67 years), and most were single, had multiple sex partners without taking protective measures and came from all social backgrounds; 59.9% had a history of a previous STI. The majority (87%) of the infections were the acute form. By polymerase chain reaction of urine samples of 399 patients, 41.6% had N. gonorrhoeae infection, 6.3% Chlamidia trachomatis and 10.8% both organisms; in 41.4% no organism was identified. N. gonorrhoeae was strongly susceptible to ciprofloxacin.

[Cutaneous blastomycosis revealing a corticoadenoma]

BACKGROUND

Blastomycosis is an uncommon chronic granulomatosis caused by Blastomyces dermatitidis. We present a case with a skin localization that disclosed malignant corticoadenoma.

CASE REPORT

A 32-year-old man consulted for inflammatory nodules of the face and lower limbs. The histological examination of a nodule biopsy was in favour of blastomycosis. Ketoconazole treatment was ineffective. Amphotericin B provided cure of the skin lesions. Search for extension disclosed a malignant corticoadrenoma.

DISCUSSION

Blastomycosis is very rare in Morocco. The portal is usually the lung. Unique skin involvement is very exceptional. To our knowledge this is the first report of a blastomycosis-corticoadenoma association. The clinical situation may be alarming in immunodepressed subjects. Amphotericin B treatment is indicated.

[Articular manifestations of Behçet's disease. Apropos of 65 cases]

The authors, in a series of 65 cases of Behçet's disease, notice 53% of rheumatological manifestations which are third in line after aphthosis and ocular disease. In order of decreasing frequency, it concerns arthritis (mono, oligo or poly-arthritis), arthralgias with an almost identical frequency, sacroiliitis, extraarticular involvement. These rheumatological manifestations are readily associated with necrotic pseudo-folliculitis and cutaneous aphthosis.

[Cowden's disease. Syndrome of multiple hamartomas]

Cowden's disease is a phacomatosis (multiple hamartomas), which is a familial, hereditary, dominant autosomal affection presenting as typical buccolabial mucocutaneous lesions associated with digestive tract polyps. Differential diagnosis of the predominantly digestive form of the disease is polyposis. A new case of this rare disorder is reported, only 62 cases being documented in literature.