Impact of UV wavelength and curing time on the properties of spin-coated low-k films

Advanced spin-on k 2.3 films with similar to 40% porosity were enabled by liquid phase self-assembly (LPSA) mechanism on Si substrates. UV-assisted thermal template removal is investigated as a faster alternative to the conventional thermal process. The as-deposited films were exposed to narrow-band UV light of 172 nm, 222 nm, 254 nm or 185/254 nm at 400 degrees C for different time. The optical, mechanical, chemical and electrical properties of the resulting films are discussed in this work. Photons with wavelength of about 172 nm from one side are detrimental to the electrical and chemical properties of the low-k films hut from the other side notably improve the porous low-k mechanical properties. Exposure to 222 nm light as short as 3 min, is more efficient in terms of template removal when compared to 2h thermal cure, while in both cases similar mechanical and electrical properties are reported. UV-cure using 254 nm or dual band 254/185 nm photons seem to have a minor contribution to the template removal efficiency for the applied doses. Higher doses are necessary in order to better understand the effective contribution of these photon energies. Finally, the HF etching mechanism is discussed

UV cure of oxycarbosilane low-k films

status: publishe

Nucleation Mechanism during WS2 Plasma Enhanced Atomic Layer Deposition on Amorphous Al2O3 and Sapphire Substrates

The structure, crystallinity and properties of as-deposited two-dimensional (2D) transition metal dichalcogenides are determined by nucleation mechanisms in the deposition process. 2D materials grown by atomic layer deposition (ALD) in absence of a template, are polycrystalline or amorphous. Little is known about their nucleation mechanisms. Therefore, we investigate the nucleation behavior of WS2 during plasma enhanced ALD from WF6, H2 plasma and H2S at 300 °C on amorphous ALD Al2O3 starting surface and on monocrystalline, bulk sapphire. Preferential interaction of the precursors with the Al2O3 starting surface promotes fast closure of the WS2 layer. The WS2 layers are fully continuous at WS2 content corresponding to only 1.2 WS2 monolayers. On amorphous Al2O3, (0002) textured and polycrystalline WS2 layers form with grain size of 5 nm to 20 nm due to high nucleation density (~1014 nuclei/cm2). The WS2 growth mode changes from 2D (layer-by-layer) growth on the initial Al2O3 surface to three-dimensional (Volmer-Weber) growth after WS2 layer closure. Further growth proceeds from both WS2 basal planes in register with the underlying WS2 grain, and from or over grain boundaries of the underlying WS2 layer with different in-plane orientation. In contrast, on monocrystalline sapphire, WS2 crystal grains can locally align along a preferred in-plane orientation. Epitaxial seeding occurs locally albeit a large portion of crystals remain randomly oriented, presumably due to the low deposition temperature. The WS2 sheet resistance is 168 MΩµm suggesting that charge transport in the WS2 layers is limited by grain boundaries.status: publishe

Efficient long-range conduction in cable bacteria through nickel protein wires

Filamentous cable bacteria display long-range electron transport, generating electrical currents over centimeter distances through a highly ordered network of fibers embedded in their cell envelope. The conductivity of these periplasmic wires is exceptionally high for a biological material, but their chemical structure and underlying electron transport mechanism remain unresolved. Here, we combine high-resolution microscopy, spectroscopy, and chemical imaging on individual cable bacterium filaments to demonstrate that the periplasmic wires consist of a conductive protein core surrounded by an insulating protein shell layer. The core proteins contain a sulfur-ligated nickel cofactor, and conductivity decreases when nickel is oxidized or selectively removed. The involvement of nickel as the active metal in biological conduction is remarkable, and suggests a hitherto unknown form of electron transport that enables efficient conduction in centimeter-long protein structures

Effects of Cs+ and Arn+ ion bombardment on the damage of graphite crystals

Intercalation mechanisms and diffusion or segregation phenomena in graphitic materials play a crucial role in different applied science fields. The investigation of such phenomena is usually accomplished through depth profiling experiments. Ar-GCIBs (Argon- Gas Cluster Ion Beams) are commonly adopted for in-depth concentration profiling of organic or soft materials; on the other hand, cesium ions are in general more suitable for the sputtering of inorganics. During such experiments, the beam-target interaction could alter chemistry and structure of the material. In this work, we define the optimal conditions in terms of both sputtering ion source and energy to preserve the crystal features. HOPG was used as a model system to compare morphological, physical, and chemical effects induced by different Arn+ clusters, and ultra-low energy Cs+ beam during ToF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) depth profiling experiments. We demonstrated, through in-situ AFM (Atomic Force Microscopy) analysis, that the monoatomic Cs+ beam alters to a lower extent the HOPG structure. On the contrary, Ar-GCIBs strongly modify the graphite surface basal plane and underlying layers. However, HOPG crystals treated with the cesium monoatomic source undergo a chemistry modification leading to the formation of graphite oxide (GOx) together with the presence of hydrogen, and cesium adducts

A flexible organic memory device with a clearly disclosed resistive switching mechanism

Flexible electronics is one of the main challenges for future hi-tech electronics. Since information storage elements are essential in any electronic system, the development of high-performance and flexible organic memories is a key requirement. Organic resistive switching memories represent a viable and promising technology ensuring scalability, flexibility, low cost and easy processing. However, despite of the remarkable progress, organic memory reliability, long term stability, ambient operation and large-area processing still need to be improved. Moreover, the rational device implementation lacks of a clear understanding of resistive switching mechanisms. In this work, high-performance cross-bar resistive memories based on a Parylene-C resistive layer sandwiched between silver electrodes are fabricated by means of large-area and high-throughput procedure. Parylene-C is a biocompatible, thermoplastic polymer, which can be deposited at room temperature. Memory elements show a reliable and reproducible switching behavior with low operating voltages, high ION/IOFF current ratio and record retention time in ambient conditions as well as high mechanical stability under bending conditions. The 3D molecular distribution of pristine and programmed devices is determined by state-of-the-art time-of-flight secondary ion mass spectrometer combined with an in-situ scanning probe microscopy (TOF-SIMS/SPM). The depth profile analysis indicates that resistive switching is driven by the formation of few localized nanometer scale conductive filaments formed by the diffusion of silver and oxygen across the organic layer which are activated, locally interrupted and re-activated during the memory cycling. The SPM images allow separating surface morphology related effects from the 3D molecular analysis and to identify some typical artefacts in TOF-SIMS image reconstructions due to preferential sputtering

Surface contamination and electrical damage by focused ion beam: conditions applicable to the extraction of TEM lamellae from nano-electronic devices

status: publishe

A flexible organic memory device with a clearly disclosed resistive switching mechanism

Flexible electronics is one of the main challenges for future hi-tech electronics. Since information storage elements are essential in any electronic system, the development of high-performance and flexible organic memories is a key requirement. Organic resistive switching memories represent a viable and promising technology ensuring scalability, flexibility, low cost and easy processing. However, despite of the remarkable progress, organic memory reliability, long term stability, ambient operation and large-area processing still need to be improved. Moreover, the rational device implementation lacks of a clear understanding of resistive switching mechanisms. In this work, high-performance cross-bar resistive memories based on a Parylene-C resistive layer sandwiched between silver electrodes are fabricated by means of large-area and high-throughput procedure. Parylene-C is a biocompatible, thermoplastic polymer, which can be deposited at room temperature. Memory elements show a reliable and reproducible switching behavior with low operating voltages, high ION/IOFF current ratio and record retention time in ambient conditions as well as high mechanical stability under bending conditions. The 3D molecular distribution of pristine and programmed devices is determined by state-of-the-art time-of-flight secondary ion mass spectrometer combined with an in-situ scanning probe microscopy (TOF-SIMS/SPM). The depth profile analysis indicates that resistive switching is driven by the formation of few localized nanometer scale conductive filaments formed by the diffusion of silver and oxygen across the organic layer which are activated, locally interrupted and re-activated during the memory cycling. The SPM images allow separating surface morphology related effects from the 3D molecular analysis and to identify some typical artefacts in TOF-SIMS image reconstructions due to preferential sputtering