Query: Quantum Energy and  at Two-Dimensional Interfaces

Candidate papers:

abstract: Energy and charge transfer processes in interacting donor acceptor systems are the bedrock of many fundamental studies and technological applications ranging from biosensing to energy storage and quantum optoelectronics. Central to the understanding and utilization of these transfer processes is having full control over the donor acceptor distance. With their atomic thickness and ease of integrability, two dimensional materials are naturally emerging as an ideal platform for the task. Here, we review how van der Waals semiconductors are shaping the field. We present a selection of some of the most significant demonstrations involving transfer processes in layered materials that deepen our understanding of transfer dynamics and are leading to intriguing practical realizations. Alongside current achievements, we discuss outstanding challenges and future opportunities.
author_names: Carlo Bradac

Zai-Quan Xu

Igor Aharonovich
title: Quantum Energy and Charge Transfer at Two Dimensional Interfaces.
venue: Nano letters
year: 2021

abstract: Increasing interest in using two dimensional transition metal dichalcogenides (2D TMDCs) in optical energy conversion technologies creates a demand for improving the yields and lifetimes of photogenerated charge carriers. Despite inherently fast photocarrier decay in neat 2D TMDCs, the unique photophysics in these quantum confined systems motivates continued effort to control the evolution of photoexcited states and create functional devices. An intriguing strategy to accomplish this goal is to employ TMDCs in heterojunctions with appropriate semiconductors, where energy level offsets drive photoinduced charge transfer (PCT) across material interfaces. PCT in TMDC based systems can be optimized for many different applications, such as driving free carriers to photocatalytic sites for redox reactions like water splitting, extracting charge to perform work in photovoltaics or photodetectors, and manipulating the spin and momentum valley electronic degrees of freedom for quantum computing systems. Here, we review recent strides in optimizing PCT for such applications through greater fundamental understanding of the photophysics that occurs at TMDC/semiconductor interfaces. After giving an overview of isolated TMDC properties, synthetic methods, and the basics of PCT, we discuss TMDCs in heterojunctions with several classes of materials, including other TMDCs, small molecule semiconductors, polymers, single walled carbon nanotubes, quantum dots, perovskites, and electrolytes. In addition to highlighting the unique benefits of each materials category, we also identify parallels across common themes, such as the roles of charge transfer states, spin, electronic coupling, delocalization, interfacial atomic morphology, and the precise design of energy landscapes to direct charge and energy motion. We hope to capture a broad range of the valuable work in this fast paced field to inspire new research directions for employing PCT in targeted TMDC based systems.
author_names: Dana B Sulas-Kern

Elisa M Miller

Jeffrey L Blackburn
title: Photoinduced charge transfer in transition metal dichalcogenide heterojunctions towards next generation energy technologies
year: 2020

abstract: Two dimensional transition metal dichalcogenide (2D TMD) semiconductors are new class of functional materials with a great promise for optoelectronics. Despite their atomic thickness, they strongly interact with light. This allows 2D TMDs to become suitable converters of photons into useful electric charges in heterostructures involving 2D TMDs and metallic nano plasmonics or semiconductor quantum dots (QDs) In this talk, I will illustrate how femtosecond pump probe spectroscopy can reveal a sub 45 fs charge transfer at a 2D/QDs heterostructure composed of tungsten disulfide monolayers (2D WS2) and a single layer of cadmium selenide (CdSe)/zinc sulfide (ZnS) core/shell 0D QDs. In another heterostructure involving 2D TMDs and plasmonics, I will describe how plasmons of an array of aluminum (Al) nanoantennas are excited indirectly via energy transfer from photoexcited exciton of 2D WS2 semiconductor. In particular, femtosecond spectroscopy measurements indicated that the lifetime of the resulting plasmon induced hot electrons in the Al array continue as long as that of the 2D WS2 excitons. Conversely, the presence of these excited plasmons almost triples the lifetime of the 2D WS2 excitons from ~15 to ~44 ps. This exciton plasmon coupling enabled by such hybrid nanostructures may open new opportunities for optoelectronic applications. This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Synthesis of the two dimensional materials was supported by the Materials Science and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy.
author_names: Abdelaziz Boulesbaa

Kai Wang

Viktoriia E Babicheva

Ivan I Kravchenko

Ming-Wei Lin

Masoud Mahjouri-Samani

Mengkun Tian

Alexander A Puretzky

Ilia N Ivanov

Christopher M Rouleau

Bobby G Sumpter

David B Geohegan
title: Ultrafast charge and energy exchanges at hybrid interfaces involving 2D semiconductors (Conference Presentation)
venue: LASE
year: 2017

abstract: In plane heterostructures of two dimensional transition metal dichalcogenides (TMDs) demonstrate the formation of one dimensional interfaces (or interlines) leading to new exciting properties and device functionalities. In this work, the interfacing effects have been studied in MoS2/WS2 quantum well and superlattice in plane heterostructures on the basis of first principles electronic calculations. In light of the orbital projected band structures, MoS2/WS2 in plane heterostructures illustrate type II band alignments with rather a small band offset for the valence band maximum and a relatively large band offset for the conduction band minimum. Upon increasing the width of TMD constituents, the band gap varies within a small range. In MoS2 and WS2, the surline energy and work function of zigzag edges with S terminations are obviously higher than those of metal terminations, and charge transfer from MoS2 to WS2 could be addressed due to the difference in the Fermi level. In gap levels induced by S vacancies in MoS2/WS2 in plane heterostructures are discrete and, interestingly, change to consecutive bands due to the built in electric field.
author_names: Wei Wei

Ying Dai

Baibiao Huang
title: In plane interfacing effects of two dimensional transition metal dichalcogenide heterostructures.
venue: Physical chemistry chemical physics PCCP
year: 2016

abstract: Abstract Polar discontinuities occurring at interfaces between two materials constitute both a challenge and an opportunity in the study and application of a variety of devices. In order to cure the large electric field occurring in such structures, a reconfiguration of the charge landscape sets in at the interface via chemical modifications, adsorbates, or charge transfer. In the latter case, one may expect a local electronic doping of one material: one example is the two dimensional electron liquid (2DEL) appearing in SrTiO3 once covered by a polar LaAlO3 layer. Here, it is shown that tuning the formal polarization of a (La,Al)1 x(Sr,Ti)xO3 (LASTO:x) overlayer modifies the quantum confinement of the 2DEL in SrTiO3 and its electronic band structure. The analysis of the behavior in magnetic field of superconducting field effect devices reveals, in agreement with ab initio calculations and self consistent Poisson Schrodinger modeling, that quantum confinement and energy splitting between electronic bands of different symmetries strongly depend on the interface total charge densities. These results strongly support the polar discontinuity mechanisms with a full charge transfer to explain the origin of the 2DEL at the celebrated LaAlO3/SrTiO3 interface and demonstrate an effective tool for tailoring the electronic structure at oxide interfaces.
author_names: Danfeng Li

S'ebastien Lemal

Stefano Gariglio

Zhenping Wu

Alexandre Fete

Margherita Boselli

Philippe Ghosez

J-M Triscone
title: Probing Quantum Confinement and Electronic Structure at Polar Oxide Interfaces
venue: Advanced science
year: 2018

abstract: Solar fuel generation mediated by semiconductor heterostructures represents a promising strategy for sustainable energy conversion and storage. The design of semiconductor heterostructures for photocatalytic energy conversion requires the separation of photogenerated charge carriers in real space and their delivery to active catalytic sites at the appropriate overpotentials to initiate redox reactions. Operation of the desired sequence of light harvesting, charge separation, and charge transport events within heterostructures is governed by the thermodynamic energy offsets of the two components and their photoexcited charge transfer reactivity, which determine the extent to which desirable processes can outcompete unproductive recombination channels. Here, we map energetic offsets and track the dynamics of electron transfer in MoS2/CdS architectures, prepared by interfacing two dimensional MoS2 nanosheets with CdS quantum dots (QDs) and correlate the observed charge separation to photocatalytic activity in the hydrogen evolution reaction. The energetic offsets between MoS2 and CdS have been determined using hard and soft X ray photoemission spectroscopy (XPS) in conjunction with density functional theory. A staggered type II interface is observed, which facilitates electron and hole separation across the interface. Transient absorption spectroscopy measurements demonstrate ultrafast electron injection occurring within sub 5 ps from CdS QDs to MoS2, allowing for creation of a long lived charge separated state. The increase of electron concentration in MoS2 is evidenced with the aid of spectroelectrochemical measurements and by identifying the distinctive signatures of electron phonon scattering in picosecond resolution transient absorption spectra. Ultrafast charge separation across the type II interface of MoS2/CdS heterostructures enables a high Faradaic efficiency of ca. 99.4 1.2% to be achieved in the hydrogen evolution reaction (HER) and provides a 40 fold increase in the photocatalytic activity of dispersed photocatalysts for H2 generation. The accurate mapping of thermodynamic driving forces and dynamics of charge transfer in these heterostructures suggests a means of engineering ultrafast electron transfer and effective charge separation in order to design viable photocatalytic architectures.
author_names: Junsang Cho

Nuwanthi Suwandaratne

Sara Abdel Razek

Yun-Hyuk Choi

Louis F J Piper

David F Watson

Sarbajit Banerjee
title: Elucidating the Mechanistic Origins of Photocatalytic Hydrogen Evolution Mediated by MoS2/CdS Quantum Dot Heterostructures.
venue: ACS applied materials interfaces
year: 2020

abstract: The problem of a bound state of two particles confined to parallel two dimensional layers and interacting via dipole dipole or dipole charge laws arises in connection with the study of bound states of charge transfer excitons at parallel interfaces or biexcitons and charged exciton complexes in double quantum wells. Binding energies of the dipole charge and the dipole dipole complexes are calculated as functions of the corresponding coupling constants. It is shown that for the dipole charge interaction the bound state exists at an arbitrary small coupling constant, though the binding energy decreases dramatically when the coupling constant falls below some critical value. On the contrary, it is shown for the dipole dipole interaction that the bound state exists only when the coupling constant exceeds a critical value. @S0163 1829~97!05408 8#
author_names: Vladimir I Yudson

M G Rozman

P Reineker
title: Bound states of two particles confined to parallel two dimensional layers and interacting via dipole dipole or dipole charge laws
year: 1997

abstract: Interfacial electron transfer (ET) constitutes the key step in conversion of solar energy into electricity and fuels. Required for fast and efficient charge separation, strong donor acceptor interaction is typically achieved through covalent chemical bonding and leads to fast, adiabatic ET. Focusing on interfaces of pyrene, coronene, and a graphene quantum dot (GQD) with TiO2, we demonstrate the opposite situation: covalent bonding leads to weak coupling and nonadiabatic (NA) ET, while through space p electron interaction produces adiabatic ET. Using real time time dependent density functional theory combined with NA molecular dynamics, we simulate photoinduced ET into TiO2 from flat and vertically placed molecules and GQD containing commonly used carboxylic acid linkers. Both arrangements can be achieved experimentally with GQDs and other two dimensional materials, such as MoS2. The weak through bond donor acceptor coupling is attributed to the p electron withdrawing properties of the carboxylic acid group. The calculated ET time scales are in excellent agreement with pump probe optical experiments. The simulations show that the ET proceeds faster than energy relaxation. The electron couples to a broad spectrum of vibrational modes, ranging from 100 cm 1 large scale motions to 1600 cm 1 C C stretches. Compared to graphene/TiO2 heterojunctions, the molecule/TiO2 and GQD/TiO2 systems exhibit energy gaps, allowing for longer lived excited states and hot electron injection, facilitating charge separation and higher voltage. The reported state of the art simulations generate a detailed time domain, atomistic description of the interfacial charge and energy transfer and relaxation processes, and demonstrate that the fundamental principles leading to efficient charge separation in nanoscale materials depend strongly and often unexpectedly on the type of donor acceptor interaction. Understanding these principles is critical to the development of highly efficient photovoltaic and photocatalytic cells.
author_names: Run Long

David Casanova

Wei-Hai Fang

Oleg V Prezhdo
title: Donor Acceptor Interaction Determines the Mechanism of Photoinduced Electron Injection from Graphene Quantum Dots into TiO2: p Stacking Supersedes Covalent Bonding.
venue: Journal of the American Chemical Society
year: 2017

abstract: Design and characterization of molecular adsorbates for solar energy conversion Charge and exciton dynamics in semiconductor quantum dots: a time domain, ab initio view Multiscale modelling of interfacial electron transfer Plasmon enhanced solar chemistry: electrodynamics and quantum mechanics Charge carrier generation, separation, recombination and transport in nanostructured materials Two dimensional photon echo spectroscopy and energy transfer Ultrafast imaging and microscopy of energy conversion materials Ultrafast multiphoton photoemission microscopy of solid surfaces in the real and reciprocal space Light at the tip: hybrid scanning tunnelling/optical spectroscopy microscopy Time resolved IR spectroscopy of metal oxides and interfaces Carrier dynamics in photovoltaic structures and materials studied with time resolved terahertz spectroscopy Time resolved x ray absorption spectroscopy for solar energy research.
author_names: Piotr Piotrowiak
title: Solar energy conversion dynamics of interfacial electron and excitation transfer
year: 2013

abstract: During the last decade our expertise in nanotechnology has advanced considerably. The possibility of incorporating in the same nanostructure different organic and inorganic materials has opened up a promising field of research, and has greatly increased the interest in the study of properties of excitations in organic materials. In this book not only the fundamentals of Frenkel exciton and polariton theory are described, but also the electronic excitations and electronic energy transfers in quantum wells, quantum wires and quantum dots, at surfaces, at interfaces, in thin films, in multilayers, and in microcavities. Among the new topics in the book are those devoted to the optics of hybrid Frenkel Wannier Mott excitons in nanostructures, polaritons in organic microcavities including hybrid organic inorganic microcavities, new concepts for organic light emitting devices, the mixing of Frenkel and charge transfer excitons in organic quasi one dimensional crystals, excitons and polaritons in one and two dimensional crystals, surface electronic excitations, optical biphonons, and Fermi resonances by polaritons. All new phenomena described in the book are illustrated by available experimental observations. The book will be useful for scientists working in the field of photophysics and photochemistry of organic solids (for example, organic light emitting devices and solar cells) and for students who are entering this field. It is partly based on a book by the author written in 1968 "Theory of Excitons" in Russian. However the new book includes only 5 chapters from this version, all of which have been updated. The 10 new chapters contain discussions of new phenomena, their theory and their experimental observations.
author_names: Vladimir M Agranovich
title: Excitations in organic solids
year: 2008