Exploring the surface oxidation and environmental instability of 2H-/1T’-MoTe2 using field emission based scanning probe lithography. - In: Advanced materials, ISSN 1521-4095, Bd. 36 (2024), 4, 2310887, S. 1-14
An unconventional approach for the resistless nanopatterning 2H- and 1T’-MoTe2 by means of scanning probe lithography is presented. A Fowler-Nordheim tunneling current of low energetic electrons (E = 30-60 eV) emitted from the tip of an atomic force microscopy (AFM) cantilever is utilized to induce a nanoscale oxidation on a MoTe2 nanosheet surface under ambient conditions. Due to the water solubility of the generated oxide, a direct pattern transfer into the MoTe2 surface can be achieved by a simple immersion of the sample in deionized water. The tip-grown oxide was characterized using Auger electron and Raman spectroscopy, revealing it consists of amorphous MoO3/MoOx as well as TeO2/TeOx. With the presented technology in combination with subsequent AFM imaging it was possible to demonstrate a strong anisotropic sensitivity of 1T’-/(Td)-MoTe2 to aqueous environments. We finally used the discussed approach to structure a nanoribbon field effect transistor out of a few-layer 2H-MoTe2 nanosheet. This article is protected by copyright. All rights reserved
A universal design strategy based on NiPS3 nanosheets towards efficient photothermal conversion and solar desalination. - In: Advanced functional materials, ISSN 1616-3028, Bd. n/a (2023), n/a, 2310942, S. 1-11
2D nanomaterials are proposed as promising photothermal materials for interfacial photothermal water evaporation. However, low evaporation efficiency, the use of hazardous hydrofluoric solution, and poor stability severely limit their practical applications. Here, a mixed solvent exfoliation surface deposition (MSESD) strategy for the preparation of NiPS3 nanosheets and NiPS3/polyvinyl alcohol (PVA) converter is successfully developed. The converter is obtained by drop-casting the NiPS3/PVA nanosheets onto a sponge. The PVA is mainly deposited on the edge of NiPS3 nanosheets, which not only improves the stability of NiPS3 nanosheets, but also adheres to the sponge to prepare a 3D photothermal converter, which shows an evaporation rate of 1.48 kg m−2 h−1 and the average photothermal conversion efficiency (PTCE) of 93.5% under a light intensity of 1 kW m−2. The photothermal conversion mechanism reveals that the energy of absorbed photons in NiPS3 nanosheets can be effectively converted into heat through non-radiative photon transitions as well as multiple optical interactions. To the best of the knowledge, this is the first report on the application of 2D metal-phosphorus-chalcogen (MPChx) for solar desalination, which provides new insights and guidance for the development of high-performance 2D photothermal materials.
Gate-tunable hysteresis response of field effect transistor based on sulfurized Mo. - In: AIP Advances, ISSN 2158-3226, Bd. 13 (2023), 9, 095224, S. 095224-1-095224-7
Hysteresis effects and their tuning with electric fields and light were studied in thin film molybdenum disulfide transistors fabricated from sulfurized molybdenum films. The influence of the back-gate voltage bias, voltage sweep range, illumination, and AlOx encapsulation on the hysteresis effect of the back-gated field effect transistors was studied and quantified. This study revealed the distinctive contribution of MoS2 surface, MoS2/SiO2 interface defects and their associated traps as primary sources of of hysteresis.
Electrodeposition of reactive aluminum-nickel coatings in an AlCl3:[EMIm]Cl ionic liquid containing nickel nanoparticles. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Bd. 170 (2023), 7, 072504
The electrodeposition of aluminum-nickel coatings was performed by pulsed direct current in the ionic liquid (IL) 1.5:1 AlCl3:EMIm]Cl containing nickel nanoparticles (Ni NPs), for reactive dispersion coating application. Several electrochemical and characterization techniques were used to shed more light on the mechanism of Ni particle incorporation into the Al matrix. Thus, particle incorporation at the early stage of the deposition would mainly take place via particle adsorption at the substrate. However, as the thickness of the coating increases, it seems that the main mechanism for particle incorporation is via the reduction of ions adsorbed at the particles surface. Although a considerable high incorporation of Ni NPs has been achieved from the IL containing the highest concentration of Ni NPs (i.e. ∼33 wt% from a 20 g/L of Ni NPs bath), a high concentration of NPs in the IL resulted having a negative effect in terms of quality of the coatings, due to solidification of the electrolyte in a poorly conductive compound. Moreover, almost equivalent amounts of Ni and Al (Ni ∼45 wt.%and Al ∼44 wt.%) have been detected in some areas of the coatings. Such a layer composition would be desired for the targeted application.
Ruthenium and rhodium vertical interconnect formation using gas phase electrodeposition. - In: 2023 IEEE International Interconnect Technology Conference (IITC) and IEEE Materials for Advanced Metallization Conference (MAM) (IITC/MAM), (2023), insges. 3 S.
This paper presents localized gas phase electrodeposition of ruthenium (Ru) and rhodium (Rh) species into vertical interconnects. A spark discharge generates gas ions and charged species of the desired metal, which are transported by a gas flow and form a plasma jet. Prior lateral nano-bridge growth is further developed and enables the localized metal species deposition into vertical interconnect openings. This approach is additive and saves rare materials during processing. The process allows precise adjustment of the diameter, airgap size, and top finishing bump of the vertical interconnect.
Novel gas phase route toward patterned deposition of sputter-free Pt/Al nanofoils. - In: Advanced Materials Technologies, ISSN 2365-709X, Bd. 8 (2023), 18, 2300448, S. 1-8
This article reports a new approach toward fabrication and directed assembly of nanoparticulate reactive system (Nanofoils) on patterned substrates. Different from current state-of-the-art, gas phase electrodeposition uses nanoparticles instead of atoms to form densely packed multilayered thin films at room temperature-pressure. On ignition, the multilayer system undergoes an exothermic self-propagating reaction. The numerous contact points between two metallic nanoparticulate layers aid in high heat release. Sub-10-nm Platinum (Pt) and Aluminum (Al) particles are synthesized through cathode erosion of metal electrodes in a flow of pure nitrogen gas (spark ablation). Pt/Al bilayer stacks with total thickness of 3–8 µm undergo self-propagating reaction with a 10.3 mm s−1 wavefront velocity on local ignition. The reaction wavefront is captured using high speed videography. Calorimetry studies reveal two exothermic peaks suggesting Pt/Al alloy formation. The peak at 135 ˚C has a higher calorific value of 150 mW g−1 while the peak at 400 ˚C has a 12 mW g−1 exothermic peak. X-ray diffraction study shows reaction-products are cubic Al2Pt with small quantities of orthorhombic Al6Pt and orthorhombic AlPt2. Electron microscopy studies help draw a correlation between film morphology, bimetallic interface, nanoparticle oxidation, and self-propagating reaction kinetics that is significant in broadening our understanding towards nanoparticulate reactive systems.
Evaluation of hysteresis response in achiral edges of graphene nanoribbons on semi-insulating SiC. - In: Materials science forum, ISSN 1662-9752, Bd. 1089 (2023), S. 15-22
Hysteresis response of epitaxially grown graphene nanoribbons devices on semi-insulating 4H-SiC in the armchair and zigzag directions is evaluated and studied. The influence of the orientation of fabrication and dimensions of graphene nanoribbons on the hysteresis effect reveals the metallic and semiconducting nature graphene nanoribbons. The hysteresis response of armchair based graphene nanoribbon side gate and top gated devices implies the influence of gate field electric strength and the contribution of surface traps, adsorbents, and initial defects on graphene as the primary sources of hysteresis. Additionally, passivation with AlOx and top gate modulation decreased the hysteresis and improved the current-voltage characteristics.
Three-dimensional MoS2 nanosheet structures: CVD synthesis, characterization, and electrical properties. - In: Crystals, ISSN 2073-4352, Bd. 13 (2023), 3, 448, S. 1-14
The proposed study demonstrates a single-step CVD method for synthesizing three-dimensional vertical MoS2 nanosheets. The postulated synthesizing approach employs a temperature ramp with a continuous N2 gas flow during the deposition process. The distinctive signals of MoS2 were revealed via Raman spectroscopy study, and the substantial frequency difference in the characteristic signals supported the bulk nature of the synthesized material. Additionally, XRD measurements sustained the material’s crystallinity and its 2H-MoS2 nature. The FIB cross-sectional analysis provided information on the origin and evolution of the vertical MoS2 structures and their growth mechanisms. The strain energy produced by the compression between MoS2 islands is assumed to primarily drive the formation of vertical MoS2 nanosheets. In addition, vertical MoS2 structures that emerge from micro fissures (cracks) on individual MoS2 islands were observed and examined. For the evaluation of electrical properties, field-effect transistor structures were fabricated on the synthesized material employing standard semiconductor technology. The lateral back-gated field-effect transistors fabricated on the synthesized material showed an n-type behavior with field-effect mobility of 1.46 cm2 V^-1 s^-1 and an estimated carrier concentration of 4.5 × 10^12 cm^-2. Furthermore, the effects of a back-gate voltage bias and channel dimensions on the hysteresis effect of FET devices were investigated and quantified.
Phase formation of cubic silicon carbide from reactive silicon-carbon multilayers. - In: MRS advances, ISSN 2059-8521, Bd. 8 (2023), 9, S. 494-498
Silicon carbide layers were fabricated using self-propagating high-temperature synthesis of binary silicon-carbon based reactive multilayers. The silicon and carbon bilayers were fabricated with two different bilayer thicknesses. They are deposited by magnetron sputtering in an alternating layer system with a total thickness of 1 μm. The entire system is annealed by rapid thermal annealing at different temperatures ranging from 500 to 1100 ˚C. From XRD analysis we could find that the formation of the silicon carbide phase was initiated from 700 ˚C. With increasing bilayer thickness the silicon carbide phase formation was partially suppressed by the silicon recrystallization due to resulting lower carbon diffusion into silicon. The transformation process proceeds in a four-step process: densification/recrystallization, interdiffusion, nucleation and transformation. From this, it was noted that when compared to low bilayer thickness samples, the formation of the silicon carbide phase is delayed with increasing bilayer thickness and needs higher reaction initiation temperatures.
Energy-efficient operation conditions of MoS2-based memristors. - In: Physica status solidi, ISSN 1862-6319, Bd. 220 (2023), 13, 2200893, S. 1-12
Sufficient energy consumption for conventional information processing makes it necessary to look for new computational methods. One of the possible solutions to this problem is neuromorphic computations using memristive devices. Memristors based on molybdenum disulfide (MoS2) are a promising way to provide a sizeable amount of hysteresis at low energy costs. Herein, different configurations of MoS2 memristors as well as the mechanisms involved in hysteresis formation are shown. Bottom gated configuration is beneficial in terms of hysteresis area and energy efficiency. The impact of device channel dimensions on the hysteresis area and energy consumption is discussed. Different operation conditions with triangular, rectangular, sinusoidal, and sawtooth drain-to-source pulses are simulated, and rectangular pulses demonstrate the highest energy efficiency. The study shows the potential to realize low-power neuromorphic systems using MoS2 memristive devices.