Jun Yuan

Jun Yuan
The University of York · Department of Physics

Professor

About

230
Publications
21,277
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
6,017
Citations
Introduction
My research interests spans from exotic such as beams with orbital angular momentum to practical such as nanoparticle synthesis and characterisation. The central themes linking them are the fundamental understanding of the science behind nature phenomena to understand the functionality of advanced materials.

Publications

Publications (230)
Article
Here, we describe a systematic derivation of the general form of the optical helicity density of ellipticaly polarized paraxial Laguerre–Gaussian modes LG`; p; . The treatment incorporates the contributions of the longitudinal field components for both the paraxial electric E and magnetic B fields, which satisfyMaxwell’s self-consistency condition...
Article
Full-text available
Controlled growth of far-from-equilibrium-shaped nanoparticles with size selection is essential for the exploration of their unique physical and chemical properties. Shape control by wet-chemistry preparation methods produces surfactant-covered surfaces with limited understanding due to the complexity of the processes involved. Here, we report the...
Article
The chirality and helicity of a linearly polarised Laguerre-Gaussian (LG) beam are examined. Such a type of light possesses a large longitudinal field amplitude when it is created with a sufficiently small beam waist and so gives rise to substantial magnitudes of chirality and helicity density distributions. In the simplest case of a doughnut beam...
Article
We consider the optical dipole potential energy, which arises from the interaction of a two-level atom with a circularly polarized Laguerre-Gaussian laser beam of small waist. The beam is characterized by the existence of a longitudinal electric field component which is responsible for the appearance of a chiral term in the optical dipole potential...
Article
Full-text available
We report the first preparation of small gold–nickel (AuNi) bimetallic nanoparticles (<5 nm) supported on titania by the method of galvanic replacement reaction (GRR), evidenced by the replacement of Ni atoms by Au atoms according to the stoichiometry of the reaction. We showed that this preparation method allowed not only the control of the gold a...
Chapter
The type of structured light focused on in this chapter is the one associated with twisted light, or optical vortices. We briefly outline the standard formalism of the optical angular momentum, emphasizing the formal division into spin angular momentum (SAM) and orbital angular momentum (OAM). The discrete integer nature of the winding number ℓ, as...
Preprint
Full-text available
We consider the optical dipole potential energy, which arises from the interaction of a two-level atom with a circularly polarized Laguerre-Gaussian laser beam of small waist. The beam is characterized by the existence of a longitudinal electric field component which is responsible for the appearance of a chiral term in the optical dipole potential...
Preprint
Full-text available
The chirality and helicity of linearly polarised Laguerre-Gaussian (LG) beams are examined. Such a type of light possesses a substantial longitudinal field when its beam waist is sufficiently small and so gives rise to non-zero chirality and helicity. In the simplest case of a doughnut beam of winding number $\ell=1$ and another identical to it but...
Article
We consider the interaction of atoms with two tightly focused and axially shifted counter-propagating optical beams. At sub-wavelength focusing, we find that the scattering force potential in the three-dimensional space between the shifted focal planes changes from a feature with a saddle-point to a three-dimensional trapping potential. Further ana...
Article
Counter-propagating co-axial Laguerre–Gaussian (LG) beams are considered, not in the familiar scenario where the focal planes coincide at z = 0, but when they are separated by a finite axial distance d. The simplest case is where both beams are doughnut beams which have the same linear polarisation. The total fields of this system are shown to disp...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
Coherent shaping of matter waves in temporal and spatial domains by photon-induced near fields opens up new possibilities for the quantum control of matter.
Article
Structured electron beams carrying orbital angular momentum are currently of considerable interest, both from a fundamental point of view and for application in electron microscopy and spectroscopy. Until recently, most studies have focused on the azimuthal structure of electron vortex beams with well-defined orbital angular momentum. To unambiguou...
Article
Structured electron beams carrying orbital angular momentum are currently of considerable interest, both from a fundamental point of view and for application in electron microscopy and spectroscopy. Until recently, most studies have focused on the azimuthal structure of electron vortex beams with well-defined orbital angular momentum. To unambiguou...
Preprint
Full-text available
Structured electron beams carrying orbital angular momentum are currently of considerable interest, both from a fundamental point of view and for application in electron microscopy and spectroscopy. Until recently, most studies have focused on the azimuthal structure of electron vortex beams with well-defined orbital angular momentum. To unambiguou...
Article
Full-text available
Bimetallic nanoparticles with tailored structure constitute a desirable model system for catalysts, as crucial factors such as geometric and electronic effects can be readily controlled by tailoring the structure and alloy bonding of the catalytic site. Herein, we report a facile colloidal method to prepare a series of platinum-gold (PtAu) nanopart...
Article
Full-text available
The relative stabilities of different chemical arrangements of Pd-Ir and Au-Rh nanoalloys (and their pure metal equivalents) are studied, for a range of compositions, for fcc truncated octahedral 38- and 79-atom nanoparticles (NPs). For the 38-atom NPs, comparisons are made of pure and alloy NPs supported on a TiO2(110) slab. The relative energies...
Article
Full-text available
Coherent x-ray diffraction investigations on Ag five-fold twinned nanowires (FTNWs) have drawn controversial conclusions concerning whether the intrinsic 7.35° angular gap could be compensated homogeneously through phase transformation or inhomogeneously by forming disclination strain field. In those studies, the x-ray techniques only provided an e...
Article
Full-text available
The preparation of inorganic nanomaterials with a desired structure and specific properties requires the ability to strictly control their size, shape and composition. A series of chemical reactions with platinum compounds carried out within the 1.5 nm wide channel of single-walled carbon nanotubes (SWNTs) have demonstrated the ability of SWNTs to...
Article
Full-text available
Coalescence dynamics of size-selected gold (Au) clusters (each with nominal 923 atoms), on amorphous Si3N4 substrate at room temperature, has been studied via time-resolved transmission electron microscopy (TEM). We found that the clusters approached each other in two stages. In the first stage, the drift velocity was independent of the particle se...
Article
The recent prediction and subsequent creation of electron vortex beams in a number of laboratories occurred after almost 20 years had elapsed since the recognition of the physical significance and potential for applications of the orbital angular momentum carried by optical vortex beams. A rapid growth in interest in electron vortex beams followed,...
Article
Full-text available
As a common type of structural defects, the grain boundary (GB) plays an important role in tailoring the physical and chemical properties of bulk crystals and their two-dimensional counterparts such as graphene and molybdenum disulfide (MoS2). In this study, we explore the atomic structures and dynamics of three high-symmetry GBs (α, β and γ) in mo...
Article
Full-text available
Wavefront engineering is an important quantum technology. Here, we demonstrate the design and production of a robust C-shaped and orbital angular momentum (OAM) carrying beam in which the doughnut shaped structure contains an adjustable gap. We find that the presence of the vortex line in the core of the beam is crucial for the robustness of the C-...
Article
Full-text available
Direct observation of atomic migration both on and below surfaces is a long-standing but important challenge in materials science as diffusion is one of the most elementary processes essential to many vital material behaviors. Probing the kinetic pathways, including metastable or even transition states involved down to atomic scale, holds the key t...
Article
Full-text available
Understanding the microscopic mechanism is fundamental for function-oriented controlled chemical vapor deposition growth of two-dimensional (2D) materials. In this work, we reveal the growth kinetics of 2D MoS 2 by capturing the nucleation seeds, evolving morphology, edge structure, and edge terminations at the atomic scale during chemical vapor de...
Article
A microscopic study of dissolution process of nanocrystals, an opposite while functioning cooperatively with growth in many cases, is an essential issues in variety aspects of research on nanocrystals. In this work, an in situ study of the dynamic dissolution process of palladium nanocrystals by liquid cell transmission electron microscope (TEM) is...
Article
Full-text available
Two-dimensional layered graphene-like crystals including transition-metal dichalcogenides (TMDs) have received extensive research interest due to their diverse electronic, valleytronic, and chemical properties, with the corresponding optoelectronics and catalysis application being actively explored. However, the recent surge in two-dimensional mate...
Article
Electron vortex beams constitute the first class of matter vortex beams which are currently routinely produced in the laboratory. Here, we briefly review the progress of this nascent field and put forward a natural quantum basis set which we show is suitable for the description of electron vortex beams. The normal modes are truncated Bessel beams (...
Article
A general orbital angular momentum (OAM) mode selection principle is put forward involving the rotationally symmetric superposition of chiral states. This principle is not only capable of explaining the operation of spiral zone plate holograms and suggesting that naturally occurring rotationally symmetric patterns could be inadvertent sources of vo...
Article
Full-text available
Understanding the microscopic mechanism is fundamental for function-oriented controlled chemical vapor deposition growth of two-dimensional (2D) materials. In this work, we reveal the growth kinetics of 2D MoS 2 by capturing the nucleation seeds, evolving morphology, edge structure, and edge terminations at the atomic scale during chemical vapor de...
Article
In the current extensive studies of layered two-dimensional (2D) materials, compared to hexagonal structures such as graphene, hBN, and MoS2, low-symmetry 2D materials have shown great potential for applications in anisotropic devices. Rhenium diselenide (ReSe2) possesses the bulk space group xxxx and belongs to the triclinic crystal system with a...
Chapter
The recent discovery of vortex electron beams [1–3] has generated many interests and the new understanding may lead to applications in material characterization [4]. The method of creating vortex electron beams using a forked aperture [2] is popular but has a drawback that electron vortex beams with different orders are produced side-by-side in the...
Chapter
The transition metal dichalcogenides (MoS2 etc.) are a new class of layered materials that can be prepared in variable layer thickness down to single molecular layer. Compared with the more well-known graphene, the monolayer version of graphite, the transition metal dichalcogenides are semiconductors and hence can be more useful in applications suc...
Article
Full-text available
Heterogeneous catalysis, which is widely used in the chemical industry, makes a great use of supported late-transition-metal nanoparticles, and bimetallic catalysts often show superior catalytic performances as compared to their single metal counterparts. In order to optimize catalyst efficiency and discover new active combinations, an atomic-level...
Article
The anisotropy of the electronic transition is a well-known characteristic of low-dimensional transition-metal dichalcogenides, but their layer-thickness dependence has not been properly investigated experimentally until now. Yet, it not only determines the optical properties of these low-dimensional materials, but also holds the key in revealing t...
Article
Full-text available
A systematic study of simulated atomic-resolution electronic energy-loss spectroscopy (EELS) for different graphene nanoribbons (GNRs) is presented. The results of ab initio studies of carbon [Formula: see text] core-loss EELS on GNRs with different ribbon edge structures and different hydrogen terminations show that theoretical core-loss EELS can...
Article
Full-text available
The high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) has been widely used in nanoparticle characterization due to its relatively straightforward interpretability, although multislice simulation is often required in order to take into account the strong dynamical screening effect if quantitative structure informat...
Article
Au, Rh, Pd, Au–Rh and Au–Pd nanoparticles (NPs) were synthesized by colloidal chemical reduction and immobilized on hydrothermally-prepared rutile titania nanorods. The catalysts were characterized by aberration-corrected TEM/STEM, XPS, and FTIR, and were evaluated in the hydrogenation of tetralin in the presence of H2S. Oxidizing and reducing ther...
Conference Paper
Objectives: To develop and evaluate an automated registration and segmentation pipeline for regional lobar pulmonary structure-function measurements, using volume-matched thoracic CT and MRI in order to guide therapy. Methods: Ten subjects underwent pulmonary function tests and volume-matched ¹H and ³He MRI and thoracic CT during a single 2-hr visi...
Article
Full-text available
Au, Rh, Pd, Au–Rh and Au–Pd nanoparticles (NPs) were synthesized by colloidal chemical reduction and immobilized on hydrothermally-prepared rutile titania nanorods. The catalysts were characterized by aberration-corrected TEM/STEM, XPS, and FTIR, and were evaluated in the hydrogenation of tetralin in the presence of H2S. Oxidizing and reducing ther...
Article
Full-text available
Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment-theory investigation of point defects in monolayer molybdenum disu...
Article
Measuring magnetocrystalline anisotropy field distribution of patterned magnetic nanodots using a microscopically visualizing way is important for understanding some important magnetic behaviors such as switching field distribution (SFD) of patterned recording media. We present a detailed analysis of the remanent domain structures of L10-FePt trian...
Article
Full-text available
The properties of electron vortex beams are examined when subject to static magnetic fields. The fields are assumed to be applied after the electron vortex beam carrying a well-defined orbital angular momentum has been created as a result of using a holographic mask. The shifts in the electron vortex beam energy momentum as well as its angular mome...
Article
Full-text available
The anisotropy of the electronic transition is an important physical property not only determining the materials' optical property, but also revealing the underlying character of the electronic states involved. Here we used momentum-resolved electron energy-loss spectroscopy to study the evolution of the anisotropy of the electronic transition invo...
Article
High-angle annular dark-field scanning transmission electron microscopy in conjunction with image simulation is an important tool to determine the structure of nanomaterials. We show that molecular dynamics calculations can be combined with multislice image simulations to account for the large effects of surface-enhanced thermal vibrations and stru...
Article
We investigated the growth of two-dimensional (2D) palladium dendritic nanostructures (DNSs) using in situ liquid-cell transmission electron microscopy (TEM). Detailed in situ and ex situ high-resolution scanning TEM (S/TEM) characterization and fractal dimension analyses reveal that the diffusion-limited aggregation and direct atomic deposition ar...
Article
Oxidative etching has widely prevailed in the growth of a crystal and played a critical role in determining the growth behavior. In this letter, we report an in situ microscopic study on the oxidative etching of palladium cubic nanocrystals by liquid-cell scanning transmission electron microscopy. The etching was realized with oxidative radiation r...
Article
Full-text available
In recent years, the information retrieval of three-dimensional (3D) intensity distribution in reciprocal space has attracted much attention in nanometrology research. However, the development of 3D analysis of electron diffraction intensity including crystal structural identification and morphology determination of nanocrystals have so far focused...
Article
It is shown how the quantum mechanical mass flux and the electromagnetic fields of an electron Bessel vortex mode generate its intrinsic linear momentum and angular momentum properties. Although the corresponding volume density vectors due to the mass flux contain transverse vector components, their volume integrals are shown by explicit analysis t...
Article
Full-text available
Chiral electron-vortex beams, carrying a well-defined orbital angular momentum (OAM) about the propagation axis, are potentially useful as probes of magnetic and other chiral materials. We present an effective operator, expressible in a multipolar form, describing the inelastic processes in which electron-vortex beams interact with atoms, including...
Article
Full-text available
Structural characterization of individual nanosized boron-rich nanowires has been carried out through analysing the three-dimensional (3D) electron diffraction intensity distribution. Not only can the cyclic twinning structure of these nanowires be easily determined, the new approach also reveals the heterogeneous strain relaxation within the intac...
Article
A Reply to the Comment by P. Schattschneider, S. Löffler, J. Verbeeck.
Article
Boron carbide and boron suboxide low-dimensional materials with α-rhombohedral symmetry, here simply referred to as boron-rich nanomaterials, exhibit a variety of growth habits, including rodlike fibers, slablike platelets, and some intermediary structures, as confirmed by scanning electron microscopy (SEM) observation. The defect structures of the...