Clement Lansalot-Matras

Layer-Controlled, Wafer-Scale, and Conformal Synthesis of Tungsten Disulfide Nanosheets Using Atomic Layer Deposition

The synthesis of atomically thin transition-metal disulfides (MS2) with layer controllability and large-area uniformity is an essential requirement for their application in electronic and optical devices. In this work, we describe a process for the synthesis of WS2 nanosheets through the sulfurization of an atomic layer deposition (ALD) WO3 film with systematic layer controllability and wafer-level uniformity. The X-ray photoemission spectroscopy, Raman, and photoluminescence measurements exhibit that the ALD-based WS2 nanosheets have good stoichiometry, clear Raman shift, and bandgap dependence as a function of the number of layers. The electron mobility of the monolayer WS2 measured using a field-effect transistor (FET) with a high-k dielectric gate insulator is shown to be better than that of CVD-grown WS2, and the subthreshold swing is comparable to that of an exfoliated MoS2 FET device. Moreover, by utilizing the high conformality of the ALD process, we have developed a process for the fabrication of WS2 nanotubes.

Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer

The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo1−xWxS2 alloy using sulfurization of super-cycle atomic layer deposition Mo1−xWxOy. Various spectroscopic and microscopic results indicate that the synthesized Mo1−xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo1−xWxS2 multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet–visible spectrophotometer results reveal that a VCC Mo1−xWxS2 multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo1−xWxS2 multilayer. Further, we demonstrate that a VCC Mo1−xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption.

Atomic layer deposition of Y2O3 films using heteroleptic liquid (iPrCp)2Y(iPr-amd) precursor

Y2O3 films grown with a new liquid Y precursor, (iPrCp)2Y(iPr-amd), have been investigated in terms of the chemical properties of the precursor, atomic layer deposition (ALD) process, and material characterization of the deposited film, as well as its non-volatile resistive switching behavior has been investigated. A heteroleptic (iPrCp)2Y(iPr-amd) has been synthesized because it exists in a liquid phase at room temperature. A vapor pressure of 1 Torr is obtained at 168 °C, and thermal evaporation and decomposition begins from 250 °C and 425 °C, respectively. The Y2O3 film is fabricated by ALD technique using (iPrCp)2Y(iPr-amd) and water as the precursors. The growth of the Y2O3 films is self-limited with an ALD window from 350 °C to 450 °C and a growth rate of 0.06 nm per cycle. The deposited Y2O3 film shows a polycrystalline cubic structure, higher refractive index of over 1.8 at 632.8 nm, and a high dielectric constant of 24. The as-deposited Y2O3 film is highly stoichiometric and constant in terms of Y and O through the depth, and it also includes small –OH bonds in the film without any additional processes. The Ru/Y2O3/Ru resistor shows resistance switching between the low and high resistance states with voltage sweeping, and the resistance ratio between the two states is more than 1000 times, which is preferable for non-volatile memory operation.

Comparison of the Atomic Layer Deposition of Tantalum Oxide Thin Films Using Ta(NtBu)(NEt2)3, Ta(NtBu)(NEt2)2Cp, and H2O

The growth characteristics of Ta2O5 thin films by atomic layer deposition (ALD) were examined using Ta(NtBu)(NEt2)3 (TBTDET) and Ta(NtBu)(NEt2)2Cp (TBDETCp) as Ta-precursors, where tBu, Et, and Cp represent tert-butyl, ethyl, and cyclopentadienyl groups, respectively, along with water vapor as oxygen source. The grown Ta2O5 films were amorphous with very smooth surface morphology for both the Ta-precursors. The saturated ALD growth rates of Ta2O5 films were 0.77 Å cycle-1 at 250 °C and 0.67 Å cycle-1 at 300 °C using TBTDET and TBDETCp precursors, respectively. The thermal decomposition of the amido ligand (NEt2) limited the ALD process temperature below 275 °C for TBTDET precursor. However, the ALD temperature window could be extended up to 325 °C due to a strong Ta-Cp bond for the TBDETCp precursor. Because of the improved thermal stability of TBDETCp precursor, excellent nonuniformity of ∼2% in 200 mm wafer could be achieved with a step coverage of ∼90% in a deep hole structure (aspect ratio 5:1) which is promising for 3-dimensional architecture to form high density memories. Nonetheless, a rather high concentration (∼7 at. %) of carbon impurities was incorporated into the Ta2O5 film using TBDETCp, which was possibly due to readsorption of dissociated ligands as small organic molecules in the growth of Ta2O5 film by ALD. Despite the presence of high carbon concentration which might be an origin of large leakage current under electric fields, the Ta2O5 film using TBDETCp showed a promising resistive switching performance with an endurance cycle as high as ∼17 500 for resistance switching random access memory application. The optical refractive index of the deposited Ta2O5 films was 2.1-2.2 at 632.8 nm using both the Ta-precursors, and indirect optical band gap was estimated to be ∼4.1 eV for both the cases.

Synthesis and PEALD evaluation of new Nickel precursors

A new family of oxygen and fluorine free Nickel (Ni) precursors, which are based on allyl and alkylpyrrolylimine ligands [Ni(allyl)(PCAI-R)], has been developed and evaluated for a Ni metal film with thermal and plasma enhanced ALD using H₂/NH₃ as a reducing agent. From Ni(allyl)(PCAI-iPr), pure Ni film with very low resistivity (5.3 μO·cm) was obtained at 400°C by PEALD, which is close to the resistivity value of bulk Nickel (5-10 μO·cm) [1].