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come truer to some extent by the inven- In the Structure Control Group, Atomic-Scale Observation of tion of the scanning tunneling micro- they are studying various techniques to Material Structures: An scope (STM). The STM was invented manipulate an atom or a group of atoms Important Role of Theory as a tool to observe atoms, but it is also by using the STM. For this purpose, useful to manipulate atoms. In fact, they have developed hardware and Satoshi Watanabe, Basic Analysis Group several amazing demonstrations have software that can control the motion of been made of the manipulation of an an STM tip, the mode of application of Rapid development of experimenatom or several atoms by using the the voltage to the tip, etc. in a sophisti- tal techniques in these days such as the STM. However, in most cases, the cated manner. In order to directly invention of scanning tunneling microsmechanisms of the manipulation have measure the electric properties of copy (STM) has made it possible to not been clarified and the reproduci- micromaterials and micropatterns
and micropatterns observe material structures on the bility of it is insufficient. Namely, many created by the technique, a novel appa- atomic scale. However, the interpretascientific and technical hurdles remain ratus, which consists of an STM and a tion of obtained experimental results, in order to master this new technology. low-temperature measurement cham- such as STM images, is not necessarily
Our Atomcraft project has been ber connected with a sample transfer straightforward. First-principle theoorganized to make systematic studies rod, is now under construction. Such a retical calculations are often very helpto overcome such scientificand techni
measurement has already been done ful to derive a reliable conclusion from cal hurdles and apply the results to the with another STM for a double tunnel- such experimental results. In this paper, various fields mentioned above. For ing junction with a liquid crystal mole- we would like to demonstrate it by these purposes, our project has three cule as the intermediate electrode, the taking the structure analysis of the research groups, i.e., the Basic Analy- two outer electrodes being an STM tip
two outer electrodes being an STM tip Si(111)rt3xrt3-Ag surface, which has sis, Structure Control, and Surface and a Pt substrate, and a series of single- been a pending problem in surface sciMeasurement Groups.
electron tunneling events have been ence for more than 20 years, as an We attach importance to the close observed at room temperature. In example. cooperation between experimentalists addition to these, a molecular beam Aono, the director of this project, and theorists, so that we have three epitaxy apparatus equipped with a novel and coworkers (Ref 39) have recently theorists in the Basic Analysis Group. ion scattering spectrometer has been proposed a new structural model, or The theorists are making calculations constructed to control the composi- the modified honeycomb-chainedof electronic structure, atomic struc- tion of the growing outermostatomic trimer model, for this surface. This model ture, atomic motion, atom transfer by a layer at will.
is consistent with most of the reported field, etc. by using a supercomputer. As already mentioned, the key to experimental results regarding atomic An interesting fact has been found manipulate an atom or a group of atoms geometry, but it has not been deterrecently. It is usually believed that by using the STM is to clarify the mech
by using the STM is to clarify the mech- mined if this model is consistent with protrusions in an observed STMimage anisms of the manipulation. The Sur- those experimental results that are correspond to individual atoms, but face Measurement Group has been related to electronic properties. In this is actually wrong. According to the studying the mechanisms in coopera- particular, this model appears to be theoretical calculations of the STM tion with the Structure Control Group. inconsistent with reported STM images image of the Si(111)rt3xrt3-Ag surface, For example, if we apply an appropri- (Ref 40) at first sight; bright spots in which agree well with a corresponding ate positive or negative voltage to an the STM images, which correspond to observed STM image, each protrusion STM tip (Ag, W, Au, or Pt) and scan protrusions, are arranged in a honeyin the STM image does not correspond the tip parallel to a Si(111) surface, we comb structure, while the Ag atoms to any atom but corresponds to the can create a desired nanometer etching forming the top layer of the model have center of three Ag atoms. That is, pattern on the Si(111) surface. On the no honeycomb arrangement at all. We observed STM images do not always basis of detailed experiments done by have theoretically calculated (Ref 40 represent the arrangement of atoms. changing various parameters widely, it and 41) the electronic structure and The experimentalists in this group are has been found that the nanometer the STM image of this model from first constructing a novel apparatus to obtain etching is caused by the field evapora- principles using the local density funcinformation on the species and num- tion of surface Si atoms as positive or tional method. The calculated electronic ber of atoms transferred by a field. negative ions depending on the polar- structure agrees very well with reported
ity of the voltage applied to the tip. experimental results on electronic properties such as photoemission As one of the applications of the a cluster of atoms on a sample surface (Ref 42) and inverse photoemission incremental charging of a fine metal using an STM tip. The most recent (Ref 43,44) spectra. The calculated STM particle, a single electron transistor was striking report was done by Eigler et al. images also agree very well with the proposed by Likharev (Ref 47) in 1987. (Ref 53); they demonstrated that it was reported STM images (Ref 40); it has After that, many people have tried to possible to exchange a single Xe atom been found that each bright spot in the realize such a transistor by using micro- between an STM tip and a Ni surface at observed STM images represents neither lithography techniques; the key to real- will, if the tip and the surface were Ag nor Si atom but corresponds to the ize such a transistor is to make very cooled to 4 K. However, in almost all center of three Ag atoms.
small capacitors. Recently, a few groups the cases mentioned above, the mechIn this way, we have been able to (Ref 48-50) have succeeded in realiz- anism of the manipulation has not been understand the atomic and electronic ing such a transistor, but it works only clarified. structures of the Si(111)rt3xrt3-Ag at temperatures as low as 4 K. As We have found that if we place an surface very well by combining the mentioned above, the STS tip-molecule- STM tip close to a Si(111) surface and experimental results with the theoret. substrate double tunnel junction causes apply an appropriate positive or negaical calculations.
the incremental charging of the mole- tive voltage to the tip, Si atoms are
cule. We added the third electrode to removed from the surface (Ref 54). Atomic-Scale Control of
this double tunneling junction to real- That is, a hole is created on the surface. Electron Movement
ize a single electron transistor of a Ifwescan the tip parallel to the surface,
capacitive type that works even at room a ditch is created on the surface. The Hitoshi Nejoh, Group Leader, Structure temperature. In this transistor, islands diameter of the hole and the width of Control Group
of Pt-Pd deposited on a Sio, substrate the ditch can be controlled by changing
act as the source and the drain and the the magnitude and duration of the Although many liquid crystal (LC) STS tip acts as the gate in the usual voltage (Ref 54). In this way, we can molecules have been imaged using FET. This single electron transistor create a desired nanometer-scale etchscanning tunneling microscopy (STM), was currently biased and the output ing pattern on the Si surface (Ref 54). little has been done on their scanning voltage was measured. The output As we can suppose easily, this techtunneling spectroscopy (STS). On the voltage versus input voltage charac- nique will be of great importance in the other hand, many people have observed teristic agrees with theoretical simula- near future in relation to the realizathe incremental charging of a fine metal tions by Likharev (Ref 47), although tion of novel nanometer-scale devices, particle on a thin insulated layer formed the output voltage has an offset. We huge memories, etc. on a metal substrate by using STS. attribute this offset to a current through In order to clarify the mechanism of However, the incremental charging, the surrounding media of the single the removal of Si atoms from the Si which is due to Coulomb blockade electron transistor.
surface, we have observed how the (Ref 45), has been observed only at
amount of removed Si atoms depends temperatures as low as 4 K, since the Atomic-Scale Control of
on various experimental parameters (the charging energy associated with the Material Structures
polarity, magnitude, duration of the incremental charging is smaller than
voltage applied to the tip, the electron the thermal fluctuation at room Ataru Kobayashi, Surface Measurement tunneling current between the tip and temperature. In the present study, we Group
the surface, and the material of the tip) have measured the tunneling current
(Ref 54 and 55). From detailed expervia one of the LC molecules on a Pt(111) The scanning tunneling microscope iments we have found the following substrate by using STS and have (STM), which was invented by Binnig mechanism. If we apply an appropriate succeeded in observing the incremental and Rohrer (Ref 51), is useful not only positive (negative) voltage to the STM charging at room temperature (Ref 46). to “observe” atoms but to “manipu- tip, a strong positive (negative) field is This is interpreted as follows. Since the late"atoms. The first demonstration of created at the Sisurface, and the strong size of the molecule is very small, the the latter was done by Becker et al. field ionizes Si atoms at the surface capacitance values between the STS (Ref 52); they manipulated a single atom into a negative (positive) ion and pulls tip and the molecule and that between on a Ge surface by using an STM tip, them apart from the surface. That is, Si the molecule and the substrate are so although the reproducibility of the atoms at the surface evaporate as a small that the charging energy is larger manipulation was not necessarily good. negative or positive ion, depending on than the thermal fluctuation at room After that, many reports have appeared the polarity of the tip voltage. The field temperature.
on the manipulation of a singleatomor evaporation of negative ions observed in the experiments is a new phenome- developments in high-precision real- controlling the phase difference and by non in that there has been little study time computer image analysis, and appli- the definition of the image processed. about it, although recent theoretical cations of electron holography to various studies (Ref 56-58) indicate the possi- fields ranging from physics to biology. Phase Measurements at bility of the phenomenon.
Atomic Dimensions In the course of the present study, A New Method for Real-Time we have clearly observed that even if Electron Holography
Kazoo Ishizuka, Image Analysis Group the tip voltage is zero, a strong field is created at the sample surface because Junji Endo, Fundamental Property Group Electron holograms have been of the contact potential (the difference
mainly processed optically. In this case, in work function) between the tip and A new method for real-time elec- the process is troublesome and requires the surface (Ref 55). This is of general tron holography is proposed and exper
tron holography is proposed and exper- a long processing time. Moreover, it is importance because it is indicated that imentally confirmed to be effective difficult to obtain quantitative results. a strong field is automatically applied (Ref 59). This method is based on fringe To overcome these constraints, we to the sample surface during STM scanning interferometry developed in developed a digital system to process imaging of the surface even if the tip laser optics.
electron holograms based on a pervoltage is small. The strong field possi- As the phase difference between an sonal computer. To increase processbly affects the electronic structure of object wave and a reference wave is ing power, we installed an array prothe surface.
changed from 0 to 2 pi, a brightness at cessor on our system. By using this
each pixel varies in a sinusoidal man- system, we can measure a phase distriTONOMURA ELECTRON- ner. When more than three brightness bution at atomic dimension. We also WAVEFRONT PROJECT: values between 0 to 2 pi are measured proposed a new technique to process EXPLORATION OF
for each pixel, we can calculate a phase an electron hologram from a crystal MICROSCOPIC WORLD value of the sine curve, i.e., a phase specimen. With this technique, we can WITH ELECTRON WAVE value of the object wave passed through obtain phase information from the
the pixel (Ref 60). To realize this method, reconstructed wave, even when the Project Director: Akira Tonomura we controlled an incident angle of the interference fringe spacing is one-third
electron beam step by step by changing of the usual requirement. Although the wave nature of elec- the excitation current of a beam-tilt trons once was evident only in the coil. The increment of the current was Direct Observation of Atomic microscopic region, such as in atoms selected so that a movement of biprism Surface Potentials by and molecules, interference phenom- fringes was equal to 1 Nth (N = integer Electron Holography ena have been observable on the macro- greater than 3) of the fringe spacing. In scopic scale since the advent of a each step, an interference pattern viewed Takayoshi Tanji, Measurement and "coherent” field emission electron beam. through a TV camera was digitized. Observation Group Its use in combination with electron From Ninterference patterns, a phase holography has opened up various new value of each pixel was calculated. Electron holography allows the direct possibilities, since versatile optical The time required to obtain phase and clear observation of how each techniques can be employed in the distribution of the object wave is about potential of Mgand O atoms located at optical reconstruction stage of elec- 1 minute. This value is two orders of an MgO crystalsurface extends farinto tron holography. An actual example is magnitude shorter than that of the a vacuum when an electron beam is the optical and numerical compensa- conventional method in which a photo incident parallel to the surface in a tion for the inevitable aberrations ofan graphic process is employed. The time certain direction, i.e., a profile mode electron lens for higher resolution. In will be further shortened by a factor of (Ref 62-65). addition, the phase of an electron wave one order of magnitude by improve- In high resolution electron microscan now be employed to observe and ment of the image processing method copy, images near the crystal edge are measure microscopic fields and matter (Ref61). The accuracy and image qual- affected by strong Fresnel diffraction, that have been inaccessible by conven- ityobtained in this method have notyet especially in this profile mode. Clear tional electron microscopy, in which been superior to those obtained in the surface images are for the first time only the intensity of the wave is observed conventional method. These problems obtained by the electron phase This study investigates the basic may be caused by inaccuracy in distribution, which greatly reduces the nature of a coherent electron beam,
difficulty in this mode (Ref 66).
melt structure analysis has been manner can be achieved by mutating PROJECT: QUEST FOR developed using a technique called amino acids on the protein surface and SOLUTION OF MELT
Rayleigh scattering. Recent research reshuffling domains as well as introMYSTERIES
has attempted to combine computer ducing a 2D substratum, which is
modeling with radiographic observa- extremely well defined, using “human Project Director: Shigeyuki Kimura tion of melts.
technology." This is a technology
This project will focus on the changes emergent from biosystems, arising Most products around us are solids that occur in melts over time, will analyze
that occur in melts over time, will analyze from a combination between "biological made from melts--glass, steel, alumi- the changes in melt structure and behav
the changes in melt structure and behav- technology” and “human technology." num, copper wire, plastics, semicon- ior, and will explore new ways to grow The project is composed of three ductors. All are made by cooling melts. crystals. We will use the melts of semi- research groups: Array Design Group, Melts and the ways melts are cooled are conductors and oxide materials and
conductors and oxide materials and Array Engineering Group, and Array critically important. Silicon semicon- follow their changes with sophisticated
follow their changes with sophisticated Characterization Group. In addition ductors must be grown from melted methods including x rays. Other quick to these domestic groups, a research silicon, but impurities enter while the and precise methods will be developed
and precise methods will be developed group from the Laboratory of Thermosilicon is molten. Molten glass must be to determine the causes of changes. dynamics and Physico-Chemical Hydrocooled at just the right rate in order These will include measurements of
These will include measurements of dynamics, the University of Sofia in that the resulting glass has good prop- viscosity, surface tension, density, and Bulgaria, participates in the project. erties. Melts, their microstructures, and heat conduction, as well as research on Each group is individually unique in its their internal movements are critically the measurements themselves. Direct academic major. The point of this kind important, yet little is known about observations of flow pattern in melts of organization in terms of promoting them. Everyone knows that molasses is will be combined with simultaneous the new technology is extensive and slow in January, but knowledge about computer modeling.
there is active fusion of a variety of why is superficial. Since the attractions Our increased understanding of the expertise. The Array Design Group aims between molecules in a melt are stronger microstructure and ordering of melts is to design a protein array based on analysis than in air, we know that the melt must expected to lead to new materials and of interprotein interactions. The major have structure. Yet, because the melt is new processing technology.
techniques used are computational fluid, it is hard to study. It does not
physics, computer graphics, and nuclear stand still for pictures. Despite years of NAGAYAMA PROTEIN
magnetic resonance (NMR) spectrosresearch, our knowledge of melts is ARRAY PROJECT: A
copy. The Array Engineering Group, only partial and mainly founded on TECHNOLOGY EMERGENT which is composed of molecular biolomathematical models. FROM BIOSYSTEMS
gists, protein biochemists, and organic Recently, we have learned that melts
chemists, seeks mass production of change with time, even as they are kept Project Director: Kuniaki Nagayama pure protein specimens underlying the at a constant temperature and in a
protein array. The Array Characterizaconstant environment. It is known that The Protein Array Project is attempt- tion Group is required to fabricate an the crystalline state of an aged melting to establish a universal technology excellent protein array and to define its differs from that of a fresh melt. The of fabricating 2D protein crystals with structure using modern and accurate viscosity of a melt depends not only on desired molecular alignment and crys- morphological techniques like transits temperature but also on how that tal form of excellent quality (protein mission electron microscopy (TEM), temperature was reached. The slow- array). The basic strategy is to explore scanning tunneling microscopy, and ness of molasses depends not only on techniques that can implement the scanning atomic force microscopy. It is how cold it is but also on how fast it was biological principle for making the also expected to develop an ideal subcooled and on how long it has been macromolecule and proteins and then stratum not only for array fabrication cold. It is assumed that this is due to assembling them into intercellular but also for transferring the array on it, differing structures, but our knowledge devices, called organelles (“biological which may possess potential as a protodoes not go beyond this assumption. technology”). Component parts should type device utilizing a protein array.
The scientific tools for studying melt then be automatically assembled to give The Bulgarian team specializes in the structure are just now being established. final forms through mutual recogni- process of lattice formation since the There are new technologies using x rays tion (specific interaction manifested array formation is directed firstly by and neutron beams. For melts that can through structural information). The lattice formation as well as the followbe studied with light, a new method of direction of such structuring into a 2D ing crystallization.
The Array Design Group has been contrast, reactions taking place in liv- (1) Atomic Recognition Group: engaged mostly in analysis of electro- ing organisms can be grasped as “inev- Various systems have been designed as static interactions that likely contrib- itable or necessitated outcome” rather elements for recognizing metal ions, in ute predominantly toward the crystals than “probability.” These two positions which a site for chemically binding a lization process: computational simu- are totally different: the former sees metal ion and a reporter site are introlation of the 2D crystallization process chemical reactions as phenomena duced in a calixarene. The reporter site of the poker chip model and analysis of explainable by molecular dynamics, is for outputting the binding as a physatomic interactions found in the protein- while the latter reactions are charac- ical signal, such as fluorescence or protein interface of real 3D crystals of terized as proceeding by way of“recog- luminescence, or an electrochemical proteins. The simulation experiment nition process.”
signal. Some systems have excellent of the poker chip model, in which edge A primary objective of our research potential as elements capable of recogboth positive and negative charges are in this project is to analyze the “recog- nizing metal ions. hexagonally distributed, succeeds in nition process" from a chemist's viewdesigning a uniformly aligned array, point and to construct this process at (2) Molecular Recognition Group: trimmer-unit array, etc. The analysis of the molecular level. This can be accom- Studies are currently being conducted the 3D crystals illustrates that electro- plished only if we establish a powerful mainly with saccharides as guest molestatic pairing, such as salt-bridge and methodology and the tools to imple- cules. Various phenyl borates are synhydrogen bonding, principally governs ment it. Fortunately, now we have thesized and used as the hosts for studycrystallization of proteins. The Array “calixarenes,” which have increasingly ing selective recognition of the guest Engineering and Characterization been attracting the attention of many saccharides. Groups have shown that the quality of chemists as “the third inclusion com- Methods for the preparation of novel array depends significantly on the purity pound” following cyclodextrin and calixarenes are being established, in of the protein specimen using horse crownethers. Evidence is mounting that which the OH groups are selectively spleen ferritin. They also obtained a as single compounds calixarenes can substituted with amino groups or preliminary clue as to possibly control- be designed as elements capable of deoxylated. The resulting calixarenes ling the crystal form by examining fer- recognizing atoms and molecules and are promising elements for molecular ritin from different species, in which also that as molecular assemblies they recognition. not many numbers of amino acids are are capable of exhibiting very unique different from each other. Using poly- and interesting functions.
(3) Intelligent Assembly Group: styrene lattices the Bulgarian team has Thus, the project consists of three Studies in progress are aimed at condeveloped a basic and very universal groups: (1) the Atomic Recognition Structing higher structures by assemmethod that enables governing the Group, (2) the Molecular Recognition bling the modified calixarenes to develop process of lattice formation of sub- Group, and (3) the Intelligent Assembly new functions that cannot be obtained micron particles by adjusting water level Group. These groups will be working by a single calixarene. The assembly of the particle suspension laid on a 2D in cooperation, by using calixarenes methods being tried include gellation, substratum. These research products and related compounds as the “tools,” polymerization, liquid crystallization, are to be combined and reorganized as to answer the question, “What is and micelle formation. It has been found set advanced research subjects in order recognition?”
that certain calixarenes and crownetherto approach the process toward the
bearing compounds act as gellators of final goal of the project. Research Activities and
organic fluids, and studies are being Results So Far
done to elucidate the gellator mechaSHINKAI CHEMIRECOGNICS
nism in connection with the recogniPROJECT
One year has passed since the Shinkai tion of metal ions.
Project was launched. As of September Project Director: Seiji Shinkai
1991, the project consists of 12
researchers. While the project's research Introduction
activities are still generally at the begin
ning stage, we have obtained some interChemical reactions have conven- esting and novel results, as summarized tionally been explained in terms of the below. "collision probability” among molecules governed by thermodynamics. In