Lapas attēli
PDF
ePub

etching in which etchant and UV light irradiation are supplied simultaneously.

and Cl, gas pressure are investigated. GaAs(111)A occurs. Surface morpholEtching profiles and surface morphology is better than that of conventional ogy are also observed. Xe/Hg lamp power, etchant supply time, and substrate temperature are fixed through all experiments at 0.19 W/cm2, 1 second, and 10 °C, respectively.

(1) UV irradiation time dependence: The Cl, gas pressure was 1 x 104 Torr and evacuation time was 12 seconds. Etching rate is saturated for an irradiation time of more than 20 seconds. This means that 20 seconds of irradiation is enough to promote surface reaction of adsorbed etchant and desorption of etching products.

Although no self-limiting process was obtained in the current DPE system, the etched depth can be controlled by sequence time alone if the etchant pressure is controlled precisely. Crystallographic atomic-layer-controlled etching like DPE is expected to play an important role in the fabrication of ISIT or quantum effect devices.

MASUHARA MICROPHOTOCONVERSION PROJECT: MICROCHEMISTRY BY

PHOTON TECHNIQUES

Microtechnology is now recognized

(2) Cl gas evacuation time dependence: The Cl gas pressure was 1 x 104 Torr and UV irradiation time Project Director: Hiroshi Masuhara was 20 seconds. The etching rate has a plateau region with the etchant evacuation time from 3 to 12 seconds. This indicates that the amount of adsorbed etchant is constant during this time. In the region less than 3 seconds, the residual etchant probably contributes to the etching. In the region more than 12 seconds, the etchant doesn't seem to adsorb in the same amount any more and probably desorbs from the substrate gradually.

(3) Cl, pressure dependence: The UV irradiation time was 6 seconds and the etchant evacuation time was 6 seconds. For these conditions, no saturated region is obtained. This means that there is no self-limiting of adsorption. Therefore, the etchant gas pressure must be controlled precisely in order to control the etching rate. The gas injection time and substrate temperature, however, should be considered for the probability of the selflimiting process.

(4) Etching profile and surface morphology: DPE exhibits crystallographic etching because no etching of

as a general trend and affords various possibilities in science, as microelectronics, microoptics, microsurgery, micromachine, and so on. When a reaction vessel is reduced to a micrometerorder dimension, the contribution of surface and interface to the chemical and physical properties of solution increases. As an example, the viscosity of a liquid increases and intermolecular interactions in solution could be influenced to a greater extent by reducing the size of a reaction vessel. Clearly, chemistry in micrometer dimensions is extremely important and worthy to be studied. Nevertheless, microchemistry and chemical microengineering have never been discussed as one of the microtechnologies. We expect exploratory research on chemical and materials conversion in micrometer size dimensions to be promising as a new science and technology.

To realize the idea, a variety of methods to prepare minute reaction sites as well as to measure and control reactions should be developed. Recent progress in laser and microfabrication

techniques contribute to the problem. Laser light is monochromatic and intense, interferes with each other, and can be pulsed and focused to a wavelength order spot. Furthermore, it is possible to follow molecular energyrelaxation processes and chemical reactions in small dimensions with picosecond time resolution. This means we

have an "eye" for observing chemistry micrometer dimensions. By utilizing the optical pressure of a laser beam, we can choose a single particle in a dispersed solution and manipulate and fix the particle at a certain spacial position. The surface of an individual particle is photochemically modified, and a small area of the surface is fabricated. We can say we have a potential "hand” for microchemistry.

In general, a reaction field is intrinsically important to control chemical reactions; therefore, it is strongly suggested to prepare a micrometer size small reaction field. This is now possible by introducing various microfabrication techniques: laser ablation, microlithography, scanning electrochemical microscope, chemical vapor deposition, and microelectrochemistry. The surface of semiconductors, metals, polymeric materials, etc. is physically and chemically modified. Spatial micropatterns can be arbitrarily introduced onto a small area of the material's surface. This means we have a “field" for microchemistry.

Thus, chemical reactions and materials conversion in micrometer dimensions are made possible by photon techniques and very wide research fields have been opened. Scientific and technological products are classified into the following three subjects. The first concerns the development of spaceand time-resolved spectroscopy and elucidation of micrometer size effects upon physical and chemical dynamics, which can be revealed by microspectroscopy. Although molecular relaxation phenomena and chemical reactions in micrometer small volumes have

never been explored, such studies are an extremely interesting subject.

Secondly, we will study the physical and chemical properties of a single individual particle that is trapped by optical pressure, elucidate mechanics of particle motions and intraparticle interactions, and construct micrometer structures by photochemical adhesion of particles. This is a novel subject and is called the chemistry of a single microparticle.

The third is microfabrication and microfunctionalization of polymeric materials by laser and microfabrication techniques. Preparation of a series of micrometer reaction sites with different chemical and physical functions and their spatial arrangement will afford a new dynamic function. Toward our final goal, we are exploring a prototype of integrated microchemical systems, utilizing our original techniques of microchemistry: "eye," "hand," and "field."

The project consists of three groups dealing with laser spectroscopy, microfabrication techniques, and reaction control. During these 3 years we have presented 57 and 30 papers to domestic and international symposia, respectively, and presented a lot of reviews and invited lectures. Now 14 researchers including 3 foreign scientists are working.

1. Dynamic Microspectroscopy Group (Kyoto Research Park Co. Ltd., Kyoto). A new class of spectroscopy for elucidating picosecond chemical processes in micrometer small dimensions is being developed. A laser trapping technique of microparticles is combined with time-resolved spectroscopy, photochemical reaction, and laser fabrication, which is now constructed as a laser manipulation-spectroscopy-reaction system. The results will open a new way to control chemical reactions arbitrarily in three-dimensional space.

We previously reported a variable angle, time-resolved, total-internalreflection fluorescence spectroscopy for

elucidating structure and dynamics in the surface/interface layers of solids and liquids (Ref 10). It has been clarified that the properties in the surface/ interface layers with thickness of 0.1 micron were different from those in the bulk (Ref 11). Analogous results were obtained for photophysical properties of molecules in alcohols and water.

To measure transient absorption spectra and their rise/decay dynamics, we have developed two types of new spectroscopic techniques where a subpicosecond (ps) white continuum was used as the monitoring light (Ref 12). One is to introduce sub-ps excitation and monitoring pulses into microscope optics, which enables us to obtain absorption spectra of a single microcrystal, a liquid droplet, and molecules in porous glasses. The other is a new technique called sub-ps transient grating spectroscopy. The excitation pulse forms a transient grating that diffracts the probing continuum. The diffraction efficiency as a function of wavelength of the probing continuum is related to transient absorption spectra in the excited states of chemical intermediates. The high sensitivity of the novel spectroscopic technique promises future applications to study chemical reactions in micrometer small dimensions.

In addition to these methods, a laser manipulation-spectroscopy-reaction system has been developed.

2. Microchemical Function Group (Central Research Laboratories, Research Laboratories, Idemitsu Co. Ltd., Sodegaura). Using various fabrication techniques, micrometer sites with chemical functions are created on the surface of polymers, metals, and semiconductors. Furthermore, arrays of reaction sites with different functions are fabricated as a prototype of an integrated chemical system.

With a scanning electrochemical microscope (SECM), we have achieved in situ observation and fabrication of a

material's surface in solution. A fluorescence micropattern is produced on an ionic conducting polymer film. The film contains a fluorescent dye and a quencher, and the latter was decomposed electrochemically along a locus of an SECM tip. Therefore, the scanned area emits the letter "M." This indicates that the SECM can act as a new method for electrochemical modification of a small area on a material's surface.

Microelectrodes were fabricated by microlithographic techniques and used for pH sensing and photoelectrochemical reactions (Ref 13). Photodecomposition of water was performed on microarray electrodes of Pt and TiO, under a microscope. Spectral measurements also have been performed to elucidate the photoelectrochemical mechanism.

Micrometer patterns of polymerized phthalocyanine derivatives were prepared by developing a new technique called area-selective chemical vapor deposition.

3. Microconversion System Group (Research Institute for Production Development, Kyoto). Characteristic micrometer size effects upon chemical reactions are studied, and new methods for controlling chemical reactions in small dimensions are developed. Furthermore, the laser manipulationspectroscopy-reaction system is applied to reveal and control chemical reactions and to construct microstructures for creating a prototype of a microchemical factory.

Micrometer size effects have been studied for oil droplets fixed in gelatin films as well as for photoresponsiveness of microgels. A change in the excited-state dimer formation efficiency of a dye suggests that the droplet becomes viscous and/or the effective concentration of the solute becomes lower as the diameter of the droplet is reduced. The rate of photoinduced volume expansion of the microgels is now examined

in detail by simultaneous measurements of volume and absorption spectral changes (Ref 14). This makes it possible to interpret the unique behavior of the photoinduced volume expansion reaction of the gels in terms of the diffusion theory of gels.

We have succeeded in controlling a photochromic reaction by albumins. The thermal back reaction of merocyanine to spiropyran was analyzed by assuming an enzymatic-like reaction between the molecule and albumins, and the reaction rate was confirmed to be accelerated by two orders of magnitude in the presence of albumins. This suggests a new way of photochemical control of reactions in a micrometer field.

index droplet in solution, which cannot

be achieved by the conventional manipbe achieved by the conventional manipulation technique, were successfully accomplished using an "optical caging" method with our laser system. Furthermore, simultaneous trapping of multiple particles was made possible by scanning laser beams, producing micrometer-size spatial patterns as well as driving particles along the locus of the laser beams (Ref 20,21). This system was extended and combined with a

pulsed Nd3+:YAG laser that induces photochemical reactions. The system is called a laser manipulationlaser manipulationspectroscopy-reaction system (Ref 22). As an example, photopolymerization was employed for adhesion of polymer particles, by which integrated strucChemical applications of the laser tures of polymer particles were assemmanipulation-spectroscopy-reaction bled with two trapping laser beams. system are very fruitful.

Dynamic Functions of a Lasing Microsphere

Keiji Sasaki, Dynamic Spectroscopy Group

The interaction between laser light and a microsphere such as a liquid droplet, a polymer latex particle, or a microcapsule leads to two interesting phenomena. One concerns optical trapping of a microsphere induced by optical momentum changes. The other is optical resonance within a microsphere, in which light propagates in a circumferential manner to create a standing wave field similar to that in a laser cavity. We have applied these phenomena to realize spatial, dynamical, and chemical manipulation of individual microspheres and for fabricating minute reaction fields (Ref 15,16).

We developed a laser scanning laser scanning micromanipulation system, in which two trapping laser beams were independently scanned by computercontrolled galvano mirrors (Ref 1719). Laser trapping and manipulation of a metal particle or a low refractive

We have succeeded, for the first time, in simultaneous optical trapping and losing of a dye-doped polymer particle suspended in water. Laser oscillation was confirmed by the appearance of sharp resonance peaks in the emission spectrum. Photon tunneling from a lasing microspherical cavity to the other particle was also demonstrated by using the two-beam trapping technique. Optically manipulated lasing microspheres are promising in surface profiling, and microspectroscopic measurements, and act as a novel light source for photochemical reactions in small geometries.

Micrometer Selective Deposition of Polymers

Atsushi Sekiguchi, Microchemical Function Group

is required. In this work, we first developed an area-selective chemical vapor deposition (CVD) method and then demonstrated that it could produce micrometer size patterns of copper phthalocyanine derivatives from 1,2,4,5-tetracyanobenzene (TCNB) (Ref 23,24).

Copper films were patterned on silicon wafers by photolithography and wet etching techniques. The siliconcopper substrate was sealed in a glass tube with TCNB and heated at different temperatures. Over a narrow temperature range, selective CVD was achieved to produce copper phthalocyanine thin films on the copper patterns. By thermal annealing the films were converted to a polymer of the copper phthalocyanines, and their chemical/physical properties were greatly improved. Indeed, the conductivity of the copper phthalocyanine films proved to be higher than that prior to thermal annealing (Ref 25).

In order to apply the technique to fabricate microchemical functional sites, an area-selective CVD of copper phthalocyanines was also performed on insulating and optically transparent materials (Ref 26).

Since copper phthalocyanine and its polymers are expected to be photoactive materials, sensing materials, and catalysts, the present technique has enormous promise. Further applications of the selective CVD method to other organic compounds and fabrication of materials surfaces should eventually allow one to prepare microphotoconversion systems.

SAKAKI QUANTUM WAVE
PROJECT: MANIPULATION
OF ELECTRON WAVES
IN A QUANTUM
MICROSTRUCTURE

Organic thin films have received much attention because of their new chemical/physical properties and functions that are not expected for inorganic materials. In order to prepare Project Director: Hiroyuki Sakaki functional chemical reaction sites based on organic compounds, fabrication of films with micrometer spatial resolution

The aims of this project are threefold: (1) exploration of the design

methodology and the fabrication technology of materials at an atomic scale to control electron waves within a solid, (2) analyses and predictive syntheses of new quantum phenomena in semiconductor microstructures having future sizes comparable with electron wavelength (100 Å), and (3) clarification of the advantages and limits of electronic and optical devices using such new phenomena and/or new materials.

For these purposes, we are studying (1) material and process technologies at an atomic scale to fabricate quantum microstructures, (2) the physics of electron wave phenomena in quantum microstructures and their application to devices, and (3) the formation of quantum hybrid materials using novel components such as organic materials to expand the controllability of quantum waves.

We have successfully set up and now fully exploit the fabrication and characterization facilities for quantum microstructures. Though most of the fabrication efforts are devoted to clarifying various elementary processes such as microscopic processes of growth, deposition, and etching at present, we will combine them in order to build quantum microstructures in the near future and will make an effort to investigate their properties. In the field of theoretical studies, we have been and will be continually pursuing to propose novel ideas based on quantum waves and to deepen these understandings.

Fabrication of Microstructures by Atomic-Layer-Controlled Growth System

Akira Usui, Quantum Hyperstructure Group (Electrotechnical Laboratory, Tsukuba)

It is desired to develop growth technologies with a self-limiting growth mechanism for the fabrication of microstructures such as quantum wires

(QW) and quantum boxes (QB). Atomic layer epitaxy (ALE) is one of the promising technologies to realize these structures because of the digital nature of monolayer/cycle growth. This characteristic is due to the chemical interaction saturation between a substrate surface and a reactant source gas. In this report, the growth study of microstructures by chloride ALE is presented (Ref 27). First, the growth kinetics study of chloride ALE using in situ optical reflection measurements during ALE growth is described. Clear reflection intensity saturation was observed, corresponding to self-limiting growth. The nature of the surface that causes the self-limiting growth was also discussed. Second, T-shaped QW structures were grown by sidewall epitaxy of ALE. Two kinds of structures were tried. One was fabricated by the overgrowth of GaAs/ InGaP by ALE on the cleaved edge of quantum wells. The other was formed by sidewall epitaxy on the (111)B planes, which appeared by in situ selective gas arching of quantum wells. Conditions for obtaining mirror-like and smooth surfaces by gas etching for InGaP/GaAs heterostructures are also presented. Finally, band discontinuity between InGaP and GaAs was evaluated by photoluminescence (PL) and PL excitation spectroscopy of InGaP/GaAs quantum wells grown by ALE (Ref 28,29). The discontinuity of conduction bands was found to be approximately 0.06 eV. This result will be used to design the T-shaped quantum wire structures.

Making Quantum Wire Structures by Molecular Beam Epitaxy

A. Shimizu, Exploratory Device and Physics Group

Molecular beam epitaxy (MBE), in which crystal growth occurs in ultrahigh vacuum conditions, is one of the most promising techniques for

fabrication of quantum microstructures. A newly designed ultra-high vacuum system has been established in order to fabricate inversion-type quantum wires (QWIs) by etching the sample of quantum wells into V-shaped grooves and by subsequent regrowth on the etched sidewalls (Ref 30). The formation of the V-grooves has been achieved by in situ microlithography of GaAs using electron beam assisted gas etching. A second method to make QWIs by MBE, growth on a reverse-mesa shaped GaAs substrate, is now in progress (Ref 31). This method takes advantage of the appearance of (111)B facets on the grown layer, which is due to the fact that the mobility of Ga atoms on the surface greatly depends on the crystallographic orientations. A 1-micron-wide modulation-doped structure formed on the (111)B facet has proven to be good enough to have a twodimensional electron gas by observing the Shubnikov-de Haas oscillation in magnetoresistance.

In order to characterize quantum microstructures, a measurement system using ultra-short-pulse lasers, a superconducting magnet, and an FTIR spectrometer has been installed.

In the field of theoretical analysis, we estimated some properties of QWIS and designed several novel quantum devices (Ref 32-35).

Electronic and Optical Properties of Organic Quantum Structures

Hitoshi Akimichi, Quantum Hybrid Materials Group

Novel quantum structure devices using organic materials are expected to show interesting properties. Conjugated pi-electron materials such as oligothiophenes and oligoacenes can be excellent candidates for these devices. To investigate the structural, electronic, and optical properties of these materials, we fabricated pure and well-ordered

thin films of the materials using an ultra-high vacuum evaporation chamber.

In this report, we show the field effect transistor (FET) characteristics of the alkyloligothiophenes (degree of polymerization: 3-6), oligoacenes, and other pi-electron materials (Ref 36). As a result, we have found that the materials with smaller ionization potential have larger mobility. Structural control of oligoacene (pentacene, tetracene) thin films under various evaporation conditions is currently under investigation by optical absorption spectroscopy and x-ray diffraction (Ref 37,38). The results for layered structure with two different species of oligoacenes are also reported.

IKEDA GENOSPHERE
PROJECT: HOW DO WE
ACCESS HUMAN GENOME
ORGANIZATION?

Project Director: Joh-E Ikeda

All of the characteristics of every organism depend on genetic information. It is the DNA molecule, the genetic instructions inscribed in every cell, that tells a body how to grow, survive, and reproduce. The DNA molecule, a densely packed configuration with nuclear proteins in the cell, is constructed of an unbroken string of billions of nucleotides. These genetic sequences are commands for protein subunits, enzymes, and hormones; commands for turning genes on and off; the recipe for how the configuration of the chromosomes can change during the cell cycle; and the recipe for how the cells can divide and differentiate. All genetic material harbored in a cell's nucleus is called the genome. The genome also governs behavior related to various activities, including neural.

For many years it has been generally considered that the genome is a biolinguistics composed of four nucleotides. We are exploring the idea that

equally important for the expression Three-Dimensional
and regulation of the genomic infor- Reconstruction of
mation are the geometry of the genome Chromosomes in a Cell
and the positional orientation of the
chromosomes within the cell. From this
perspective we prefer not to sequence
all of the human genome. Instead, we
are taking the view that the many DNA
sequences without any known biologi-
cal functions at the moment may have
significance in the geometry of the
genome.

Yoshitaro Nakano and Kouichi Kojima,
Research Group of Chromosome
Dynamics

Our current studies are to identify
the genes, chromosome domains, and
DNA sequences that are responsible
for the mental faculties and genomic
behavior related to chromosome pair-
ing. To this end, specific regions of
human chromosomes are being laser
microdissected and then segmented
according to chromosome maps and
the generated regional chromosome
DNA clones are studied. New instru-
ments are also being developed that
will allow such a real-time monitoring
of human chromosomes within a cell as
to their relative positions and orienta-
tions within a nucleus. These new devices
will result in a real-time, three-
dimensional human genome atlas.

Molecular Studies of the
Functional Domains of the
Human Genome

Little is known about the structure of nuclei, but it is thought that chromosomes occupy a discrete territory in the interphase nucleus and specific chromatin arrangements reflect processes of cellular differentiation and cell specific gene expression. To investigate the three-dimensional organization of chromosomes in nuclei and its possible functional significance, we are constructing equipment with which we can visualize intranuclear threedimensional chromosome topography.

Though any optical microscopic image of the specimen is contaminated with out-of-focus information, the digital image processing method can remove its contribution. At first we obtained characteristic three-dimensional frequency response of the optical system by direct experimental measurement using fluorescent microbeads. Then we used the frequency response to obtain the true image by the Fourier transform of the observed image.

[blocks in formation]

New methodologies need to be Project Director: Masakazu Aono developed to study the genomes of higher organisms such as humans because they have far larger quantities of information and more complex functions than those of bacteria. We have established methods to dissect specific domains of chromosomes and analyze the information or functional units within them. By these means, it will be possible to investigate the higher phenomena of life such as mental activity in humans.

"Atomcraft," which is our newly coined word, expresses a new world of possibilities where we may manipulate an atom or a group of atoms at will to create artificial micromaterials with novel atomic arrangement and electronic properties, nanometer micropatterns exhibiting a novel electronic or optical function and for huge memories, etc. Although this was only a dream a decade ago, the dream has

« iepriekšējāTurpināt »