Interactions among electrons and the topology of their energy bands can create novel quantum phases of matter. Most topological electronic phases appear in systems with weak electron-electron interactions. The instances where topological phases emerge only as a result of strong interactions are rare, and mostly limited to those realized in the presence of intense magnetic fields 1 . The discovery of flat electronic bands with topological character in magic-angle twisted bilayer graphene (MATBG) has created a unique opportunity to search for new strongly correlated topological phases 2-9 . Here we introduce a novel local spectroscopic technique using a scanning tunneling microscope (STM) to detect a sequence of topological insulators in MATBG with Chern numbers C = ±1, ±2, ±3, which form near 𝜈 = ±3, ±2, ±1 electrons per moiré unit cell respectively, and are stabilized by the application of modest magnetic fields. One of the phases detected here (C = +1) has been previously observed when the sublattice symmetry of MATBG was intentionally broken by hexagonal boron nitride (hBN) substrates, with interactions playing a secondary role 9 . We demonstrate that strong electron-electron interactions alone can produce not only the previously observed phase, but also new and unexpected Chern insulating phases in MATBG. The full sequence of phases we observed can be understood by postulating that strong correlations favor breaking time-reversal symmetry to form Chern insulators that are stabilized by weak magnetic fields. Our findings illustrate that many-body correlations can create topological phases in moiré systems beyond those anticipated from weakly interacting models. The role of topology in the electronic properties of moiré flat-band systems has been experimentally revealed by the discovery of a quantized anomalous Hall conductance 𝜎 𝑥𝑦 = 𝐶𝑒 2 /ℎ, with various integer Chern numbers C in different graphene-based heterostructures 9-12 .
We fabricated a high-performance pentacene organic thin-film transistor (OTFT) on plastic and passivated it with polyvinylalcohol and photosensitive acryl layers. The pentacene was grown on the thin-film transistor area using a self-organized process. The OTFT after the passivation exhibited the field-effect mobility of 0.80cm2∕Vs, threshold voltage of −9.2V, and on/off current ratio of 108. The field-effect mobility and threshold voltage change exponentially with time in air. The lifetime, defined as the time required to decrease the on current by one-half, was found to be ∼11000h in ambient air. The absolute value of threshold voltage of the unpassivated OTFT increases with time in air, but it decreases with time in the passivated OTFT. This indicates that the origins for the degradation in the performances of the two OTFTs are different. H2O in unpassivated and O2 in passivated OTFT appear to be the major origin for the degradation.
Organic thin-film transistors (OTFTs) based on pentacene semiconductor are elaborated on the plastic substrates through a four-level mask process without photolithographic patterning to yield a simple fabrication process. Octadecyltrimethoxysilane (OTMS) as an organic molecule for self-assembled monolayers is deposited on the surface of zirconium oxide dielectric layer. The effect of OTMS interlayer with gate dielectric surface modification on the field effect mobility of OTFTs has been examined and these prototype organic transistors showed excellent electrical characteristics with field effect mobility >0.66cm2∕Vs and Ion∕Ioff>10.5
Hydrogen-free diamond-like carbon (DLC) films were deposited by the layer-by-layer technique using plasma enhanced chemical vapor deposition (PECVD), i.e., the alternative deposition of thin DLC layer and subsequent CF4 plasma exposure on its surface. The hydrogen-free DLC could be grown on the Si wafer by repeated deposition of the 5 nm DLC layer and subsequent 200 s CF4 plasma exposure on its surface. On the other hand, the conventional DLC deposited by PECVD contains 25 at. % hydrogen inside. The CF4 plasma exposure on the thin DLC layer appears to etch weak C–C bonds and break hydrogen bonds, resulting in a widening optical band gap and increasing conductivity activation energy.
This paper presents a study of the anodic bonding technique using a hydrophilic surface. Our method differs from conventional processes in the pre-treatment of the wafer. Hydrophilic surfaces were achieved from dipping in H 2 O/H 2 O 2 /NH 4 OH solution. The hydrophilic surface has a large number of -OH groups, which can form hydrogen bonds when two wafers are in contact. This induces a higher electrostatic force, because of the decreasing gap between the glass and silicon wafer. We achieved improved properties, such as a wider bonded area and a higher bond strength than those of conventional methods. Also, the fabricated pressure sensors on the 5-inch silicon wafer were bonded to Pyrex #7740 glass of 3 mm thickness. In order to investigate the migration of the sodium ions, the depth profile at the glass surface by secondary-ion mass spectroscopy and the bonding current were compared with that of conventional methods.
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