SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Thin films

166

The coating of thin films is applied in numerous fields and many methods are employed for the deposition of these films. Some coating techniques may deposit films at high speed; for example, ordinary printing paper is coated with micrometre-thick layers of clay at a speed of tens of meters per second. However, to coat nanometre thin films at high speed, vacuum techniques are typically required, which increases the complexity of the process. Here, we report a simple wet chemical method for the high-speed coating of films with thicknesses at the nanometre level. This soap-film coating technique is based on forcing a substrate through a soap film that contains nanomaterials. Molecules and nanomaterials can be deposited at a thickness ranging from less than a monolayer to several layers at speeds up to meters per second. We believe that the soap-film coating method is potentially important for industrial-scale nanotechnology.

Concepts: Light, Coating, Thin film, Speed, Deposit account, Thin films, Miles per hour, Speed of light

29

In this article, we report only 10 atomic layer thick, high mobility, transparent thin film transistors (TFTs) with ambipolar device characteristics fabricated on both a conventional silicon platform as well as on a flexible substrate. Monolayer graphene was used as metal electrodes, 3-4 atomic layers of h-BN were used as the gate dielectric, and finally bilayers of WSe2 were used as the semiconducting channel material for the TFTs. The field effect carrier mobility was extracted to be 45 cm(2)/(V s), which exceeds the mobility values of state of the art amorphous silicon based TFTs by ∼100 times. The active device stack of WSe2-hBN-graphene was found to be more than 88% transparent over the entire visible spectrum and the device characteristics were unaltered for in-plane mechanical strain of up to 2%. The device demonstrated remarkable temperature stability over 77-400 K. Low contact resistance value of 1.4 kΩ-μm, subthreshold slope of 90 mv/decade, current ON-OFF ratio of 10(7), and presence of both electron and hole conduction were observed in our all two-dimensional (2D) TFTs, which are extremely desirable but rarely reported characteristics of most of the organic and inorganic TFTs. To the best of our knowledge, this is the first report of all 2D transparent TFT fabricated on flexible substrate along with the highest mobility and current ON-OFF ratio.

Concepts: Semiconductor, Silicon, Transistor, Field-effect transistor, Thin film, Thin-film transistor, Amorphous silicon, Thin films

9

The emerging field of plasmonic metamaterials has introduced new degree of freedom to manipulate optical field from nano to macroscopic scale, offering an attractive platform for sensing applications. So far, metamaterial sensor concepts, however, have focused on hot-spot engineering to improve the near-field enhancement, rather than fully exploiting tailored material properties. Here, we present a novel spectroscopic technique based on the metamaterial infrared (IR) absorber allowing for a low-background detection scheme as well as significant plasmonic enhancement. Specifically, we experimentally demonstrate the resonant coupling of plasmonic modes of a metamaterial absorber and IR vibrational modes of a molecular self-assembled monolayer. The metamaterial consisting of an array of Au/MgF2/Au structures exhibits an anomalous absorption at ~3000 cm(-1), which spectrally overlaps with C-H stretching vibrational modes. Symmetric/asymmetric C-H stretching modes of a 16-Mercaptohexadecanoic acid monolayer are clearly observed as Fano-like anti-resonance peaks within a broad plasmonic absorption of the metamaterial. Spectral analysis using Fano line-shape fitting reveals the underlying resonant interference in plasmon-molecular coupled systems. Our metamaterial approach achieves the attomole sensitivity with a large signal-to-noise ratio in the far-field measurement, thus may open up new avenues for realizing ultrasensitive IR inspection technologies.

Concepts: Spectroscopy, Optics, Electromagnetic radiation, Nanomaterials, Materials science, Infrared, Self-assembled monolayer, Thin films

3

Despite the need for molecularly smooth self-assembled monolayers (SAMs) on silicon dioxide surfaces (the most common dielectric surface), current techniques are limited to non-ideal silane grafting. Here, we show unique bio-inspired zwitterionic molecules forming a molecularly smooth and uniformly thin SAM in “water” in <1 min on various dielectric surfaces, which enables a dip-coating process that is essential for organic electronics to become reality. This monomolecular layer leads to high mobility of organic field-effect transistors (OFETs) based on various organic semiconductors and source/drain electrodes. A combination of experimental and computational techniques confirms strong adsorption (Wad>20 mJ m-2), uniform thickness (~0.5 or ~1 nm) and orientation (all catechol head groups facing the oxide surface) of the “monomolecular” layers. This robust (strong adsorption), rapid, and green SAM represents a promising advancement towards the next generation of nanofabrication compared to the current non-uniform and inconsistent polysiloxane-based SAM involving toxic chemicals, long processing time (>10 h), and/or heat (>80°C).

Concepts: Oxygen, Silicon, Transistor, Germanium, Self-assembled monolayer, Thin films, Monolayer, Organic semiconductor

3

The conversion of a biphenylthiol self-assembled monolayer (BPT SAM) on copper into graphene via electron irradiation and annealing is described by Andrey Turchanin and co-workers on page 4146. This 2D solid-state reaction can be tuned by temperature, allowing the crystallinity of the graphene layers to be adjusted. It is feasible to create graphene structures of any 3D shape as molecular self-assembly can be conducted on nonplanar suraces. Scanning tunneling microscopy of the PT SAM on Cu(111) is described.

Concepts: Electron, Nanotechnology, Self-organization, Microscopy, Scanning tunneling microscope, Scanning probe microscopy, Self-assembled monolayer, Thin films

1

The fabrication of porous coordination frameworks in thin-film forms has been investigated intensively with a view to using their structural response to external stimuli and guests for potential nanotechnological applications, for example as membranes for gas separation. Here we report a coordination framework that exhibits a dynamic guest-sorption behaviour in a nanometre-sized thin-film form (16 nm thick), yet shows no guest uptake in the bulk. Highly oriented crystalline thin films of this coordination framework-which consists of interdigitated two-dimensional layers of {Fe(py)2[Pt(CN)4]} (py, pyridine)-were fabricated through liquid-phase layer-by-layer synthesis. The resulting thin film exhibited a clear guest uptake with a structural transformation of the gate-opening type as characterized by in situ X-ray diffraction. Increasing the film’s thickness markedly suppressed this behaviour. We envisage that such a crystal-downsizing effect may be observed with other coordination frameworks, and may be of use to develop functional materials, for example, for switching or sensing devices.

Concepts: Diffraction, X-ray, Semiconductor, Chemical vapor deposition, Thin film, Thin films

1

Multilayer thin films have garnered intense scientific interest due to their potential application in diverse fields such as catalysis, optics, energy, membranes, and biomedicine. Here we review the current technologies for multilayer thin-film deposition using layer-by-layer assembly, and we discuss the different properties and applications arising from the technologies. We highlight five distinct routes of assembly—immersive, spin, spray, electromagnetic, and fluidic assembly—each of which offers material and processing advantages for assembling layer-by-layer films. Each technology encompasses numerous innovations for automating and improving layering, which is important for research and industrial applications. Furthermore, we discuss how judicious choice of the assembly technology enables the engineering of thin films with tailor-made physicochemical properties, such as distinct-layer stratification, controlled roughness, and highly ordered packing.

Concepts: Engineering, Technology, Thin film, Thin films

0

Recently surface engineering of the indium-tin oxide (ITO) electrode of sandwich-like organic electric memory is found to effectively improve their memory performances. However, there are few methods to modify ITO substrates. In this paper, we have successfully prepared alkyltrichlorosicane self-assembled monolayers (SAMs) on ITO substrates, and resistive random access memory devices are fabricated on these surfaces. Compared to the unmodified ITO substrates, organic molecules SA-Bu grown on these SAM-modified ITO substrates have rougher surface morphologies but smaller mosaicity. The organic layer on SAM-modified ITO further aged to eliminate the crystalline phase diversity. In consequence, the ternary memory yield are effetively improved to 40~47%. Our results suggest that insertion of alkyltrichlorosicanes self-assembled monolayer could be an efficient method to improve the performance of organic memory.

Concepts: Better, Oxygen, Indium tin oxide, Indium(III) oxide, Indium, Self-assembled monolayer, Thin films, Touchscreen

0

The synthesis of high-purity BiFeO3 (BFO) ceramic by solid-state reaction is known to be very difficult due to inevitable formation of the secondary phases, mostly mullite-type Bi2Fe4O9 and sillenite-type Bi25FeO39. In particular, it is very difficult to completely remove the Bi-deficient Bi2Fe4O9 phase from sintered ceramic BFO targets. This problem consequently leads to the difficulty of fabricating high-quality BFO thin films using these sintered targets. Herein, we introduce a simple but effective low-temperature processing scheme for removing impurity phases in which optimized processing conditions are obtained by chemically correlating the first calcination step with the subsequent leaching and sintering steps. More specifically, we suitably avoid the formation of the high-temperature-stable Bi2Fe4O9 phase by performing the calcination at significantly low temperatures (between 650 and 675 °C) with Bi-excess starting powders. We have then fabricated epitaxially grown BFO thin films using these phase-pure ceramic targets and consequently achieved high-quality ferroelectricity and switchable photovoltaic responses. On the basis of the present experimental observations, we suggest that a low impurity concentration in the sintered BFO ceramic target, even with a low relative density, is advantageous for high-quality thin-film fabrication.

Concepts: Chemical reaction, Ice, Semiconductor, Chemical vapor deposition, Thin film, Relative density, Sintering, Thin films

0

Controlled alignment of long DNA nanofibers is challenging. This communication reports a method to align human genomic DNA with nearly unlimited length using lithographically produced micro-patterns of self-assembled monolayers (SAMs) with positively charged terminal groups. The micro-patterns act as local DNA reservoirs to supply DNAs for nanofiber formation, and can also stretch and align DNA nanofibers to form an ordered array by controlling the dewetting profile. By reducing the size and inter-patch distance of a micro-patch, a nearly uniform array of long DNA nanofibers can be patterned over a large area. A controlled motion of a DNA containing droplet allows for free patterning of DNA nanofibers and production of complex structures without a transfer process. Bending of DNA nanofibers due to local distortion of the contact line bridges more adjacent micro-patches and increases the chance of producing continuous nanofibers. The interplay between surface tension and electrostatic attraction of positively charged micro-patterns allows the production of long DNA nanofibers in a simple yet powerful way.

Concepts: DNA, Electric charge, Electrostatics, Electric field, Surface tension, Coulomb's law, Self-assembled monolayer, Thin films