Force‐Driven Single‐Atom Manipulation on a Low‐Reactive Si Surface for Tip Sharpening

A single atomic manipulation on the delta‐doped B:Si(111)‐()R30° surface using a low temperature dynamic atomic force microscopy based on the Kolibri sensor is investigated. Through a controlled vertical displacement of the probe, a single Si adatom in order to open a vacancy is removed. It is shown that this process is completely reversible, by accurately placing a Si atom back into the vacancy site. In addition, density functional theory simulations are carried out to understand the underlying mechanism of the atomic manipulation in detail. This process also rearranges the atoms at the tip apex, which can be effectively sharpened in this way. Such sharper tips allow for a deeper look into the Si adatom vacancy site. Namely, high‐resolution images of the vacancy showing subsurface Si dangling bond triplets, which surround the substitutional B dopant atom in the first bilayer, are achieved.     

Atomic‐Level Sculpting of Crystalline Oxides: Toward Bulk Nanofabrication with Single Atomic Plane Precision

The atomic‐level sculpting of 3D crystalline oxide nanostructures from metastable amorphous films in a scanning transmission electron microscope (STEM) is demonstrated. Strontium titanate nanostructures grow epitaxially from the crystalline substrate following the beam path. This method can be used for fabricating crystalline structures as small as 1–2 nm and the process can be observed in situ with atomic resolution. The fabrication of arbitrary shape structures via control of the position and scan speed of the electron beam is further demonstrated. Combined with broad availability of the atomic resolved electron microscopy platforms, these observations suggest the feasibility of large scale implementation of bulk atomic‐level fabrication as a new enabling tool of nanoscience and technology, providing a bottom‐up, atomic‐level complement to 3D printing.     

Atom‐by‐Atom Fabrication of Monolayer Molybdenum Membranes

Fabrication of materials in the monolayer regime to acquire fascinating physical properties has attracted enormous interest during the past decade, and remarkable success has been achieved for layered materials adopting weak interlayer van der Waals forces. However, the fabrication of monolayer metal membranes possessing strong intralayer bonding remains elusive. Here, suspended monolayer Mo membranes are fabricated from monolayer MoSe₂ films via selective electron beam (e‐beam) ionization of Se atoms by scanning transmission electron microscopy (STEM). The nucleation and subsequent growth of the Mo membranes are triggered by the formation and aggregation of Se vacancies as seen by atomic resolution sequential STEM imaging. Various novel structural defects and intriguing self‐healing characteristics are unveiled during the growth. In addition, the monolayer Mo membrane is highly robust under the e‐beam irradiation. It is likely that other metal membranes can be fabricated in a similar manner, and these pure metal‐based 2D materials add to the diversity of 2D materials and introduce profound novel physical properties.     

A single-atom transistor

The ability to control matter at the atomic scale and build devices with atomic precision is central to nanotechnology. The scanning tunnelling microscope can manipulate individual atoms and molecules on surfaces, but the manipulation of silicon to make atomic-scale logic circuits has been hampered by the covalent nature of its bonds. Resist-based strategies have allowed the formation of atomic-scale structures on silicon surfaces, but the fabrication of working devices-such as transistors with extremely short gate lengths, spin-based quantum computers and solitary dopant optoelectronic devices-requires the ability to position individual atoms in a silicon crystal with atomic precision. Here, we use a combination of scanning tunnelling microscopy and hydrogen-resist lithography to demonstrate a single-atom transistor in which an individual phosphorus dopant atom has been deterministically placed within an epitaxial silicon device architecture with a spatial accuracy of one lattice site. The transistor operates at liquid helium temperatures, and millikelvin electron transport measurements confirm the presence of discrete quantum levels in the energy spectrum of the phosphorus atom. We find a charging energy that is close to the bulk value, previously only observed by optical spectroscopy.     

Trapping and moving metal atoms with a six-leg molecule

Putting to work a molecule able to collect and carry adatoms in a controlled way on a surface is a solution for fabricating atomic structures atom by atom. Investigations have shown that the interaction of an organic molecule with the surface of a metal can induce surface reconstruction down to the atomic scale. In this way, well-defined nanostructures such as chains of adatoms, atomic trenches and metal-ligand compounds have been formed. Moreover, the progress in manipulation techniques induced by a scanning tunnelling microscope (STM) has opened up the possibility of studying artificially built molecular-metal atomic scale structures, and allowed the atom-by-atom doping of a single C(60) molecule by picking up K atoms. The present work goes a step further and combines STM manipulation techniques with the ability of a molecule to assemble an atomic nanostructure. We present a well-designed six-leg single hexa-t-butyl-hexaphenylbenzene (HB-HPB) molecule, which collects and carries up to six copper adatoms on a Cu(111) surface when manipulated with a STM tip. The 'HB-HPB-Cu atoms' complex can be further manipulated, bringing its Cu freight to a predetermined position on the surface where the metal atoms can finally be released.     

In Situ Repair of 2D Chalcogenides under Electron Beam Irradiation

Molybdenum disulfide (MoS₂) and bismuth telluride (Bi₂Te₃) are the two most common types of structures adopted by 2D chalcogenides. In view of their unique physical properties and structure, 2D chalcogenides have potential applications in various fields. However, the excellent properties of these 2D crystals depend critically on their crystal structures, where defects, cracks, holes, or even greater damage can be inevitably introduced during the preparation and transferring processes. Such defects adversely impact the performance of devices made from 2D chalcogenides and, hence, it is important to develop ways to intuitively and precisely repair these 2D crystals on the atomic scale, so as to realize high‐reliability devices from these structures. Here, an in situ study of the repair of the nanopores in MoS₂ and Bi₂Te₃ is carried out under electron beam irradiation by transmission electron microscopy. The experimental conditions allow visualization of the structural dynamics of MoS₂ and Bi₂Te₃ crystals with unprecedented resolution. Real‐time observation of the healing of defects at atomic resolution can potentially help to reproducibly fabricate and simultaneously image single‐crystalline free‐standing 2D chalcogenides. Thus, these findings demonstrate the viability of using an electron beam as an effective tool to precisely engineer materials to suit desired applications in the future.     

Atom inlays performed at room temperature using atomic force microscopy

The ability to manipulate single atoms and molecules laterally for creating artificial structures on surfaces is driving us closer to the ultimate limit of two-dimensional nanoengineering. However, experiments involving this level of manipulation have been performed only at cryogenic temperatures. Scanning tunnelling microscopy has proved, so far, to be a unique tool with all the necessary capabilities for laterally pushing, pulling or sliding single atoms and molecules, and arranging them on a surface at will. Here we demonstrate, for the first time, that it is possible to perform well-controlled lateral manipulations of single atoms using near-contact atomic force microscopy even at room temperature. We report the creation of 'atom inlays', that is, artificial atomic patterns formed from a few embedded atoms in the plane of a surface. At room temperature, such atomic structures remain stable on the surface for relatively long periods of time.     

Programmable Atom Equivalents: Atomic Crystallization as a Framework for Synthesizing Nanoparticle Superlattices

Decades of research efforts into atomic crystallization phenomenon have led to a comprehensive understanding of the pathways through which atoms form different crystal structures. With the onset of nanotechnology, methods that use colloidal nanoparticles (NPs) as nanoscale “artificial atoms” to generate hierarchically ordered materials are being developed as an alternative strategy for materials synthesis. However, the assembly mechanisms of NP‐based crystals are not always as well‐understood as their atomic counterparts. The creation of a tunable nanoscale synthon whose assembly can be explained using the context of extensively examined atomic crystallization will therefore provide significant advancement in nanomaterials synthesis. DNA‐grafted NPs have emerged as a strong candidate for such a “programmable atom equivalent” (PAE), because the predictable nature of DNA base‐pairing allows for complex yet easily controlled assembly. This Review highlights the characteristics of these PAEs that enable controlled assembly behaviors analogous to atomic phenomena, which allows for rational material design well beyond what can be achieved with other crystallization techniques.     

Chemical bond manipulation for nanostructure integration on wafer scale

In this paper, we have briefly summarized our activity in the area of chemical bond manipulation for the integration of nanostructures on a full wafer scale. Chemical bond manipulation involves a judicious combination of surface phenomena: reactions or diffusion, and growth process such as molecular beam epitaxy (MBE). Here, we present our results on oxidation, metallization and nitridation and their role in the formation of nanostructures. We find that oxygen changes the bonding partner from Ge to Si and this phenomenon can be controlled by controlling the annealing temperature. We have employed this phenomenon for the fabrication of novel, multiperiod Si/SiO₂/Ge layered structure which exhibits interesting light emitting properties. Further, by making use of selective diffusion of cobalt atoms through Ge layers it is possible to incorporate metallic features into Ge quantum dots. Moreover, it is possible to fabricate Si nanopillars through high temperature reaction of nitric oxide. NO molecules dissociate on the surface and nitrogen atoms thus produced form nitride islands. These islands act as protective masks for the etching of Si by the oxygen atoms, through the desorption of SiO species. Occurrence of these two simultaneous processes result in the formation of nanometre-sized Si pillars capped by silicon nitride. All these results emphasize the fact that we can extend information obtained through traditional surface science experiments for the fabrication of novel structures on a full wafer scale.     

Point defect configurations of supersaturated Au atoms inside Si nanowires

Aberration-corrected scanning transmission electron microscopy (STEM) is used to reveal individual Au atom configurations inside Si nanowires grown by Au-catalyzed vapor-liquid-solid (VLS) molecular beam epitaxy (MBE). We identify a substitutional and three distinct interstitial configurations, one of which has not been previously identified. We confirm the stability of the observed point defect configurations by density functional theory (DFT) calculations. The observed number densities of the various configurations are in accord with their calculated formation energies. The concentration of Au atoms is larger than the solubility limit, but the effect may be caused by the STEM beam.     

Atom Rearrangement by Cyclic Electron “Shaking”

The arrangement of atoms comprising a material determines its properties. Thus, atom arrangement controllability can substantially facilitate the creation of new materials such as functional materials. Relevant materials science research has relied heavily on heat treatments. This study investigates the phenomenon of atom rearrangement by applying a high-frequency alternating current without heating. The proposed method spontaneously rearranges atoms to produce a dense crystal plane oriented parallel to the electron flow. The atoms are “shaken” by generating mechanical interaction between electrons and atoms. Transmission electron microscopy reveals the enlarged crystal grains and an increase in close-packed planes resulting from the self-alignment of the atoms along the direction of electron flow. Conventional heat treatments cannot result in such phenomena because heat treatments induce random vibration of the atoms. In contrast, the current flow in the high-frequency alternating current enables direction-specific vibration of the atoms. This novel technique could be applied to develop new functional materials that are difficult to obtain via conventional heat treatment methods. Furthermore, this atom rearrangement technology can be applied to expand the field of materials science research.     

Quasi‐Solid‐State Single‐Atom Transistors

The single‐atom transistor represents a quantum electronic device at room temperature, allowing the switching of an electric current by the controlled and reversible relocation of one single atom within a metallic quantum point contact. So far, the device operates by applying a small voltage to a control electrode or “gate” within the aqueous electrolyte. Here, the operation of the atomic device in the quasi‐solid state is demonstrated. Gelation of pyrogenic silica transforms the electrolyte into the quasi‐solid state, exhibiting the cohesive properties of a solid and the diffusive properties of a liquid, preventing the leakage problem and avoiding the handling of a liquid system. The electrolyte is characterized by cyclic voltammetry, conductivity measurements, and rotation viscometry. Thus, a first demonstration of the single‐atom transistor operating in the quasi‐solid‐state is given. The silver single‐atom and atomic‐scale transistors in the quasi‐solid‐state allow bistable switching between zero and quantized conductance levels, which are integer multiples of the conductance quantum G₀ = 2e²/h. Source–drain currents ranging from 1 to 8 µA are applied in these experiments. Any obvious influence of the gelation of the aqueous electrolyte on the electron transport within the quantum point contact is not observed.     

Isotope Substitution Extends the Lifetime of Organic Molecules in Transmission Electron Microscopy

Structural characterisation of individual molecules by high‐resolution transmission electron microscopy (HRTEM) is fundamentally limited by the element and electron energy‐specific interactions of the material with the high energy electron beam. Here, the key mechanisms controlling the interactions between the e‐beam and C–H bonds, present in all organic molecules, are examined, and the low atomic weight of hydrogen—resulting in its facile atomic displacement by the e‐beam—is identified as the principal cause of the instability of individual organic molecules. It is demonstrated theoretically and proven experimentally that exchanging all hydrogen atoms within molecules with the deuterium isotope, and therefore doubling the atomic weight of the lightest atoms in the structure, leads to a more than two‐fold increase in the stability of organic molecules in the e‐beam. Substitution of H for D significantly reduces the amount of kinetic energy transferred from the e‐beam to the atom (main factor contributing to stability) and also increases the barrier for bond dissociation, primarily due to the changes in the zero‐point energy of the C–D vibration (minor factor). The extended lifetime of coronene‐d₁₂, used as a model molecule, enables more precise analysis of the inter‐molecular spacing and more accurate measurement of the molecular orientations.     

Controlled manipulation of carbon nanopillars and cantilevers by focused ion beam

We explore a novel phenomenon of focused ion beam (FIB) induced bending of carbon nanopillars or cantilever structures. The bending occurs towards the ion beam during scanning. The explanation of this bending has been sought on the basis of a model which considers temperature rise and gradients caused by the impinging ion beam. The process is controllable and reversible, which makes it highly suitable for in?situ manipulation to make desired 3D shapes by the piecewise bending of the nanopillars and cantilever structures during their fabrication using electron beam or FIB chemical vapor deposition (EB-CVD or FIB-CVD). Its usefulness in the fabrication of nanosize mechanical components has been demonstrated by making a branch structure from a single cantilever.     

New Developments in Transmission Electron Microscopy for Nanotechnology

High‐resolution transmission electron microscopy (HRTEM) is one of the most powerful tools used for characterizing nanomaterials, and it is indispensable for nanotechnology. This paper reviews some of the most recent developments in electron microscopy techniques for characterizing nanomaterials. The review covers the following areas: in‐situ microscopy for studying dynamic shape transformation of nanocrystals; in‐situ nanoscale property measurements on the mechanical, electrical and field emission properties of nanotubes/nanowires; environmental microscopy for direct observation of surface reactions; aberration‐free angstrom‐resolution imaging of light elements (such as oxygen and lithium); high‐angle annular‐dark‐field scanning transmission electron microscopy (STEM); imaging of atom clusters with atomic resolution chemical information; electron holography of magnetic materials; and high‐spatial resolution electron energy‐loss spectroscopy (EELS) for nanoscale electronic and chemical analysis. It is demonstrated that the picometer‐scale science provided by HRTEM is the foundation of nanometer‐scale technology.     

电子束钎焊温度场PID控制系统

为了将电子束应用于精密构件及热敏感性材料钎焊,以适应复杂形状曲线钎焊缝的要求,采用电子束扫描轨迹编辑及在线调节、钎焊温度实时采集及PID控制器构建真空电子束钎焊温度闭环控制系统.研究表明:本控制方法可实现在焊接过程中电子束按设定轨迹对工件进行扫描加热的同时,对被加热工件温度进行在线检测及实时调节.采用电子束扫描轨迹编辑及在线调节可以适应各种形状曲线钎焊缝、特殊材料及热敏感性材料的钎焊要求;只要适当选取PID参数,采用PID控制器可以对钎焊温度进行有效控制.该方法提高了电子束钎焊温度控制的精确性和适应性,有利于钎焊质量的提高.     

Anisotropic Shape Changes of Silica Nanoparticles Induced in Liquid with Scanning Transmission Electron Microscopy

Liquid‐phase transmission electron microscopy (TEM) is used for in‐situ imaging of nanoscale processes taking place in liquid, such as the evolution of nanoparticles during synthesis or structural changes of nanomaterials in liquid environment. Here, it is shown that the focused electron beam of scanning TEM (STEM) brings about the dissolution of silica nanoparticles in water by a gradual reduction of their sizes, and that silica redeposites at the sides of the nanoparticles in the scanning direction of the electron beam, such that elongated nanoparticles are formed. Nanoparticles with an elongation in a different direction are obtained simply by changing the scan direction. Material is expelled from the center of the nanoparticles at higher electron dose, leading to the formation of doughnut‐shaped objects. Nanoparticles assembled in an aggregate gradually fuse, and the electron beam exposed section of the aggregate reduces in size and is elongated. Under TEM conditions with a stationary electron beam, the nanoparticles dissolve but do not elongate. The observed phenomena are important to consider when conducting liquid‐phase STEM experiments on silica‐based materials and may find future application for controlled anisotropic manipulation of the size and the shape of nanoparticles in liquid.     

Mesoporous Nitrogen‐Doped Carbon‐Nanosphere‐Supported Isolated Single‐Atom Pd Catalyst for Highly Efficient Semihydrogenation of Acetylene

Semihydrogenation of acetylene in the ethylene feed is a vital step for the industrial production of polyethylene. Despite their favorable reaction activity and ethylene selectivity, the Pd‐based intermetallic compound and single‐atom alloy catalysts still suffer from the limitation of atomic utilization derived from the partial exposure of active Pd atoms. Herein, a hard‐template Lewis acid doping strategy is reported that can overcome the inefficient utilization of Pd atoms. In this strategy, N‐coordinated isolated single‐atomic Pd sites are fully embedded on the inner walls of mesoporous nitrogen‐doped carbon foam nanospheres (ISA‐Pd/MPNC). This synthetic strategy has been proved to be applicable to prepare other ISA‐M/MPNC (M = Pt and Cu) materials. This ISA‐Pd/MPNC catalyst with both high specific surface area (633.8 m² g^?1) and remarkably thin pore wall (1–2 nm) exhibits higher activity than that of its nonmesoporous counterpart (ISA‐Pd/non‐MPNC) catalyst by a factor of 4. This work presents an efficient way to tailor and optimize the catalytic activity and selectivity by atomic‐scale design and structural control.     

Nanoarchitectonics for Controlling the Number of Dopant Atoms in Solid Electrolyte Nanodots

Controlling movements of electrons and holes is the key task in developing today's highly sophisticated information society. As transistors reach their physical limits, the semiconductor industry is seeking the next alternative to sustain its economy and to unfold a new era of human civilization. In this context, a completely new information token, i.e., ions instead of electrons, is promising. The current trend in solid‐state nanoionics for applications in energy storage, sensing, and brain‐type information processing, requires the ability to control the properties of matter at the ultimate atomic scale. Here, a conceptually novel nanoarchitectonic strategy is proposed for controlling the number of dopant atoms in a solid electrolyte to obtain discrete electrical properties. Using α‐Ag_2+δS nanodots with a finite number of nonstoichiometry excess dopants as a model system, a theory matched with experiments is presented that reveals the role of physical parameters, namely, the separation between electrochemical energy levels and the cohesive energy, underlying atomic‐scale manipulation of dopants in nanodots. This strategy can be applied to different nanoscale materials as their properties strongly depend on the number of doping atoms/ions, and has the potential to create a new paradigm based on controlled single atom/ion transfer.     

控制O2流量生长结状 ZnO微纳米棒及其特性研究

采用热蒸发法以锌粉和二水醋酸锌作为源材料在Si（111）衬底上制备了高密度的ZnO微纳米棒，制得的每根ZnO棒明显分为直径不同的四段．利用X射线衍射、扫描电镜、透射电镜、拉曼光谱和光致发光谱等测试手段对制备的样品进行了形貌、结构和光学性能的分析，结果表明制备的ZnO棒晶体质量良好，仅存在很少量的缺陷.通过讨论该结构的生长机理，发现O2分压对制备的ZnO微纳米棒的形貌有显著的影响，调节O2流量可控制ZnO纳米结构的形貌．