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Unconventional chiral charge order in kagome superconductor KV3Sb5
Intertwining quantum order and non-trivial topology is at the frontier of condensed matter physics
1
–
4
. A charge-density-wave-like order with orbital currents has been proposed for achieving the quantum anomalous Hall effect
5
,
6
in topological materials and for the hidden phase in cuprate high-temperature superconductors
7
,
8
. However, the experimental realization of such an order is challenging. Here we use high-resolution scanning tunnelling microscopy to discover an unconventional chiral charge order in a kagome material, KV
3
Sb
5
, with both a topological band structure and a superconducting ground state. Through both topography and spectroscopic imaging, we observe a robust 2 × 2 superlattice. Spectroscopically, an energy gap opens at the Fermi level, across which the 2 × 2 charge modulation exhibits an intensity reversal in real space, signalling charge ordering. At the impurity-pinning-free region, the strength of intrinsic charge modulations further exhibits chiral anisotropy with unusual magnetic field response. Theoretical analysis of our experiments suggests a tantalizing unconventional chiral charge density wave in the frustrated kagome lattice, which can not only lead to a large anomalous Hall effect with orbital magnetism, but also be a precursor of unconventional superconductivity.
An unconventional chiral charge order is observed in a kagome superconductor by scanning tunnelling microscopy. This charge order has unusual magnetic tunability and intertwines with electronic topology.
Journal Article
Single-electron devices and circuits in silicon
\"This book reviews research on single-electron devices and circuits in silicon. These devices provide a means to control electronic charge at the one-electron level and are promising systems for the development of few-electron, nanoscale electronic circuits. The book considers the design, fabrication, and characterization of single-electron transistors, single-electron memories, few-electron transfer devices such as electron pumps and turnstiles, and single-electron logic devices. A review of the many different approaches used for the experimental realisation of these devices is provided and devices developed during the author's own research are used as detailed examples. An introduction to the physics of single-electron charging effects is included.\"--Jacket.
Book
Highly stretchable organic electrochemical transistors with strain-resistant performance
Realizing fully stretchable electronic materials is central to advancing new types of mechanically agile and skin-integrable optoelectronic device technologies. Here we demonstrate a materials design concept combining an organic semiconductor film with a honeycomb porous structure with biaxially prestretched platform that enables high-performance organic electrochemical transistors with a charge transport stability over 30–140% tensional strain, limited only by metal contact fatigue. The prestretched honeycomb semiconductor channel of donor–acceptor polymer poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-diketo-pyrrolopyrrole-alt-2,5-bis(3-triethyleneglycoloxy-thiophen-2-yl) exhibits high ion uptake and completely stable electrochemical and mechanical properties over 1,500 redox cycles with 10
4
stretching cycles under 30% strain. Invariant electrocardiogram recording cycles and synapse responses under varying strains, along with mechanical finite element analysis, underscore that the present stretchable organic electrochemical transistor design strategy is suitable for diverse applications requiring stable signal output under deformation with low power dissipation and mechanical robustness.
Highly stretchable organic electrochemical transistors with stable charge transport under severe tensional strains are demonstrated using a honeycomb semiconducting polymer morphology, thereby enabling controllable signal output for diverse stretchable bioelectronic applications.
Journal Article
The case for books : past, present, and future
\"The era of the printed book is at a crossroad. E-readers are flooding the market, books are available to read on cell phones, and companies such as Google, Amazon, and Apple are competing to command near monopolistic positions as sellers and dispensers of digital information. Is the printed book resilient enough to survive the digital revolution, or will it become obsolete? In this lasting collection of essays, Robert Darnton--an intellectual pioneer in the field of this history of the book--lends unique authority to the life, role, and legacy of the book in society.\"--P. 4 of cover.
Book
Topological spintronics and magnetoelectronics
Topological electronic materials, such as topological insulators, are distinct from trivial materials in the topology of their electronic band structures that lead to robust, unconventional topological states, which could bring revolutionary developments in electronics. This Perspective summarizes developments of topological insulators in various electronic applications including spintronics and magnetoelectronics. We group and analyse several important phenomena in spintronics using topological insulators, including spin–orbit torque, the magnetic proximity effect, interplay between antiferromagnetism and topology, and the formation of topological spin textures. We also outline recent developments in magnetoelectronics such as the axion insulator and the topological magnetoelectric effect observed using different topological insulators.
This Perspective discusses the interplay between magnetism and topology in condensed matter.
Journal Article
Ultrasoft slip-mediated bending in few-layer graphene
Continuum scaling laws often break down when materials approach atomic length scales, reflecting changes in their underlying physics and the opportunities to access unconventional properties. These continuum limits are evident in two-dimensional materials, where there is no consensus on their bending stiffnesses or how they scale with thickness. Through combined computational and electron microscopy experiments, we measure the bending stiffness of graphene, obtaining 1.2–1.7 eV for a monolayer. Moreover, we find that the bending stiffness of few-layer graphene decreases sharply as a function of bending angle, tuning by almost 400% for trilayer graphene. This softening results from shear, slip and the onset of superlubricity between the atomic layers and corresponds with a gradual change in scaling power from cubic to linear. Our results provide a unified model for bending in two-dimensional materials and show that their multilayers can be orders of magnitude softer than previously thought, among the most flexible electronic materials currently known.
The bending stiffness of few-layer graphene is shown to decrease significantly with the bending angle due to shear and slip between the atomic layers, which culminate in superlubric behaviour as the bending angle further increases.
Journal Article
High-mobility band-like charge transport in a semiconducting two-dimensional metal–organic framework
Metal–organic frameworks (MOFs) are hybrid materials based on crystalline coordination polymers that consist of metal ions connected by organic ligands. In addition to the traditional applications in gas storage and separation or catalysis, the long-range crystalline order in MOFs, as well as the tunable coupling between the organic and inorganic constituents, has led to the recent development of electrically conductive MOFs as a new generation of electronic materials. However, to date, the nature of charge transport in the MOFs has remained elusive. Here we demonstrate, using high-frequency terahertz photoconductivity and Hall effect measurements, Drude-type band-like transport in a semiconducting, π–d conjugated porous Fe3(THT)2(NH4)3 (THT, 2,3,6,7,10,11-triphenylenehexathiol) two-dimensional MOF, with a room-temperature mobility up to ~ 220 cm2 V–1 s–1. The temperature-dependent conductivity reveals that this mobility represents a lower limit for the material, as mobility is limited by impurity scattering. These results illustrate the potential for high-mobility semiconducting MOFs as active materials in thin-film optoelectronic devices.
Journal Article
Double doping of conjugated polymers with monomer molecular dopants
Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.A monomer molecular dopant with high electron affinity is shown to accept up to two electrons from conjugated polymers with low ionization efficiency and then generate free charge carriers with an efficiency of up to 170%.
Journal Article
Multi-cation perovskites prevent carrier reflection from grain surfaces
The composition of perovskite has been optimized combinatorially such that it often contains six components (A
x
B
y
C
1−
x
−
y
PbX
z
Y
3−
z
) in state-of-art perovskite solar cells. Questions remain regarding the precise role of each component, and the lack of a mechanistic explanation limits the practical exploration of the large and growing chemical space. Here, aided by transient photoluminescence microscopy, we find that, in perovskite single crystals, carrier diffusivity is in fact independent of composition. In polycrystalline thin films, the different compositions play a crucial role in carrier diffusion. We report that methylammonium (MA)-based films show a high carrier diffusivity of 0.047 cm
2
s
−1
, while MA-free mixed caesium-formamidinium (CsFA) films exhibit an order of magnitude lower diffusivity. Elemental composition studies show that CsFA grains display a graded composition. This curtails electron diffusion in these films, as seen in both vertical carrier transport and surface potential studies. Incorporation of MA leads to a uniform grain core-to-edge composition, giving rise to a diffusivity of 0.034 cm
2
s
−1
in CsMAFA films. A model that invokes competing crystallization processes allows us to account for this finding, and suggests further strategies to achieve homogeneous crystallization for the benefit of perovskite optoelectronics.
Methylammonium is shown to influence the crystallization process in hybrid lead halide perovskites, leading to a more homogeneous chemical distribution of caesium and formamidinium and improved charge transport between grains in multi-cation systems.
Journal Article