- Email: [email protected]
Nanoscale materials and processing — The Multidisciplinary University Research Initiative Center for Nanoscale Materials and Processing at the Loker Hydrocarbon Research Institute (LHRI), University of Southern California
Supramolecular Science 2 (1995) 233-236 C‘ 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 0968-5677/95/$10.00
Supramolecular
Science Laboratory profile
Nanoscale Materials and Processing The Multidisciplinary University Research Initiative Center for Nanoscale Materials and Processing at the Loker Hydrocarbon Research Institute (LHRI), University of Southern California Charles Y.-C. Lee Air Force Office of Scientific DC 20332-000 1, USA
Research/NL,
110 Duncan Ave., Suite 6115, Boiling
AFB,
and Larry R. Dalton and George A. Olah Loker Hydrocarbon Research CA 90089- 166 1, USA
Institute,
University
Nanostructure and supramolecular science are concerned with comparable material dimensions, that features of is, materials with critical structural nanometer dimensions (1 nm-1 pm). However, research in these disciplines is approached from different science frequently perspectives. Supramolecular involves chemists and molecular biologists focusing on ever larger molecules or ensembles of molecules. Nanostructure science, on the other hand, typically involves solid state materials scientists attempting to produce materials characterized by nanometer rather than micron dimensions. and utilize The drive to create, characterize nanometer structures is motivated by two factors: (1) The possibility of realizing materials exhibiting new properties and (2) the miniaturization of advanced devices. In regard to the former, it is well known that the macroscopic properties can be controlled by morphological features at the nanometer scale. For example, it is known that miscible blends exhibiting single glass transition temperatures have domain sizes scale. More recent examples include in that enhancement of nonlinear optical properties by nanocomposites, lowering of densification temperature of ceramic nanoparticles and quantum confinement effects. Downsizing of advanced devices include the development of high density data storage, ultramicroelectromechanical systems electronics, and (MEMS). Three tools are needed to exploit technologies at the nanometer scale: (1) The ability to ‘see’ nanometer
of Southern
California,
Los Angeles,
structures is critical and has recently become possible with techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). (2) The ability to test or perform diagnostic measurements of properties of nanoscale structures is less advanced and the ability to test mechanical, electrical, optical and magnetic properties over relevant dimensions needs development. (3) The ability to control size, shape, distribution and placement of nanoscale structures is critical. The means to carry out this last item for organic and polymeric materials may be different from that required for inorganic materials such as semiconductors. The Polymeric and Organic Materials Program of Air Force Office of Scientific Research is interested in developing fundamental tools to manipulate organic and polymeric materials for advanced applications that utilize nanotechnology. A center, funded by the Air Force Office of Scientific Research, is established to address this objective. The center focuses on organic and polymeric materials to complement other efforts in inorganic and semiconductor materials. The basic knowledge acquisition of this program is tailored so that knowledge acquired can be potentially useful for the applications mentioned above. The Multidisciplinary University Research Initiative Center for Nanoscale Materials and Processing is located at the Loker Hydrocarbon Research Institute (LHRI) of the University of Southern California with satellite research programs at Cornell (headed by J. Frechet), California Institute of Technology (headed by
SUPRAMOLECULAR
SCIENCE Volume 2 Numbers 3-4 1995
233
Supramolecular
Science
Laboratory
profile
R. Grubbs), North Carolina State University (headed by C. Gorman) and the State University of New York at Buffalo (headed by P. Prasad). The Department of Defense funding of approximately $6.7 million dollars is matched by a $2.0 million dollar contribution from USC to equipment and research staff salaries and the center benefits from location in the newly constructed Catherine B. Loker Research Wing of the LHRI. Projects have been defined in the following areas: (1) STM/AFM nanolithography and dendrimeric materials; (2) polymer microspheres and morphological resonances; (3) molecular self-assembly and ordered phases; (4) sequential synthesis; (5) external field induced ordering; and (6) sol-gels, micelles, and LB methods. The project on STM nanolithography focuses on developing a systematic approach for achieving two dimensional organization controlled to nanoscale dimensions and on characterizing and addressing individual nanoscale units within an ordered twodimensional matrix. Issues to be addressed include control of nanoscale molecule-substrate interaction, movement and positioning of nanoscale moieties exploiting STM probe-molecule interactions, control of chemical and physical communication between nanoscale moieties, the ability to define the electronic properties of individual units, and the ability to systematically modify the properties of individual moieties. An example of the application of the above principles of STM nanolithography is the development of the next generation of electronic computing elements by synthesis and spatial organization of nanoscale information bearing units (IBUs). One approach to synthesizing nanoscale IBUs involves a dendritic synthesis approach proceeding from a core capable of bistable properties to a periphery which effects isolation of IBUs and defines intermolecular interactions relevant to positioning of IBUs, (Figures l-3). Polymer microspheres of nanoscale dimensions can be prepared by a variety of novel self-assembly procedures. Indeed, compositionally complex materials can be prepared so that a systematic variation in index of refraction, dielectric properties, chemical reactivity, etc. can be achieved from the core to the periphery of the microspheres. In like manner, the chemistry exists for effecting precise control of interactions between microspheres. Among the many properties that depend upon the size and shape of nanoscale structures, the propagation of nanometer wavelength light will be dramatically influenced by interaction with such particles. For example, when circumference of a chromophore-coated microsphere is a multiple of the wavelength of incident light, the light can become trapped in the chromophore layer and build up (i.e. undergo morphological resonance) analogous to the confinement of radiofrequency and microwave electromagnetic radiation in metal cavities of centimeter and millimeter dimensions. Such phenomena can be exploited for the development of high density
optical memories exploiting the spectral dimension, i.e. the memory density is increased over a normal spatially-defined density limitation by the number of spectral holes that can be burned by morphological resonances. In preliminary studies, the burning of nine holes in a 20 nanometer spectral window was demonstrated. This result suggests that, for normal chromophores such as azobenzenes, memory density can be improved by two orders of magnitude above that defined by spatial limitations. Memory density can be further improved by more precise control of structural variations at nanoscale dimensions which leads to narrower morphological resonances (that is, higher quality or Q factors). Professors Jean Frechet (Cornell) and Robert Grubbs (Cal Tech) head a project aimed at advancing the preparation of nanoscale structures by developing synthetic methods exploiting molecular self-assembly. Frechet will lead an effort focused upon preparation of functionalized and self-assembled dendrimers including unsymmetrically functionalized dendrimers, monodisperse surface-reactive nanoclusters, and molecularly insulated inorganic-organic composite nanoscopic wires. The research project headed by Frechet also contributes materials to the STM nanolithography project described above. Grubbs will lead an effort focused upon the preparation of block copolymers capable of exhibiting nanoscale phases including ordered phases. Mark Thompson of USC heads a program to use sequential synthesis methods to prepare new electronic components such as light emitting diodes. Thompson will focus on the use of metal phosphonate compounds; these materials are very stable and insoluble and can be
234
3-4 1995
SUPRAMOLECULAR
SCIENCE Volume
2 Numbers
Figure 1 Proposed dendrimeric capping of discrete semiconductor clusters. The tetrahedral core consists of S (A), SPh (a), and M (*) units. The four dendrimeric ligands and the crosslinks between them form the periphery of the information bearing unit
Supramolecular
1
Science Laboratory profile
6-j
“i” Y? 4 1.o 4 CO 0
7
\
co
0
(-0 0
I)
0
0
.
‘/
0
0PO
\
P
0
0
1’
HO
\/
CP
Figure 2
I’
11
0
The structure
.’
I
0
2
0
of a dendrimeric
ligand is shown
easily used to organize organic groups in the solid state. Paras Prasad at SUNY-Buffalo (working with David Williams at Eastman Kodak) will also utilize sequential synthesis methods, Langmuir-Blodgett lilm fabrication, to prepare thin films of precisely controlled thickness. Such thickness control can be used to achieve phase matched frequency doubling of infrared lasers. External forces will be used to achieve nanoscale ordering. Such a project is viewed as a complement to those exploiting molecular self-assembly and sequential
Figure 3
Representative
chemical
modification
of the periphery
synthesis methods to achieve ordered structures. External forces to be most actively investigated include electrical and electromagnetic fields. In particular, electric field poling and laser poling will be used to achieve noncentrosymmetric molecules organization necessary in the fabrication of nanophotonic and nanoelectronic devices. Prototype devices will be utilized not only in communication applications but also in sensor applications including biomedical sensing and radar applications. Finally, Paras Prasad of SUNY-Buffalo directs a
of IBUs to control
SUPRAMOLECULAR
surface interactions
SCIENCE Volume 2 Numbers 3-4 1995
235
Supramolecular
Science Laboratory profile
project on multiphasic nanostructured composites exploiting sol-gel, micellar, and colloidal particle processing methods. For example, sol-gel methods will be used to prepare nanoscale metal organic cores coated with metal oxide materials. Such active organicdoped nanoparticles have uses in the fields of nonlinear
236
SUPRAMOLECULAR
optics, lasers, liquid chromatography, and nanosensors. Such structures may also exhibit morphological resonances as described above for chromophore-coated polymer microspheres. Sol-gel processing can also be used to develop nanostructures for optical limiting applications.
SCIENCE Volume 2 Numbers 3-4 1995
Supramolecular
Science Laboratory profile
Nanoscale Materials and Processing The Multidisciplinary University Research Initiative Center for Nanoscale Materials and Processing at the Loker Hydrocarbon Research Institute (LHRI), University of Southern California Charles Y.-C. Lee Air Force Office of Scientific DC 20332-000 1, USA
Research/NL,
110 Duncan Ave., Suite 6115, Boiling
AFB,
and Larry R. Dalton and George A. Olah Loker Hydrocarbon Research CA 90089- 166 1, USA
Institute,
University
Nanostructure and supramolecular science are concerned with comparable material dimensions, that features of is, materials with critical structural nanometer dimensions (1 nm-1 pm). However, research in these disciplines is approached from different science frequently perspectives. Supramolecular involves chemists and molecular biologists focusing on ever larger molecules or ensembles of molecules. Nanostructure science, on the other hand, typically involves solid state materials scientists attempting to produce materials characterized by nanometer rather than micron dimensions. and utilize The drive to create, characterize nanometer structures is motivated by two factors: (1) The possibility of realizing materials exhibiting new properties and (2) the miniaturization of advanced devices. In regard to the former, it is well known that the macroscopic properties can be controlled by morphological features at the nanometer scale. For example, it is known that miscible blends exhibiting single glass transition temperatures have domain sizes scale. More recent examples include in that enhancement of nonlinear optical properties by nanocomposites, lowering of densification temperature of ceramic nanoparticles and quantum confinement effects. Downsizing of advanced devices include the development of high density data storage, ultramicroelectromechanical systems electronics, and (MEMS). Three tools are needed to exploit technologies at the nanometer scale: (1) The ability to ‘see’ nanometer
of Southern
California,
Los Angeles,
structures is critical and has recently become possible with techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). (2) The ability to test or perform diagnostic measurements of properties of nanoscale structures is less advanced and the ability to test mechanical, electrical, optical and magnetic properties over relevant dimensions needs development. (3) The ability to control size, shape, distribution and placement of nanoscale structures is critical. The means to carry out this last item for organic and polymeric materials may be different from that required for inorganic materials such as semiconductors. The Polymeric and Organic Materials Program of Air Force Office of Scientific Research is interested in developing fundamental tools to manipulate organic and polymeric materials for advanced applications that utilize nanotechnology. A center, funded by the Air Force Office of Scientific Research, is established to address this objective. The center focuses on organic and polymeric materials to complement other efforts in inorganic and semiconductor materials. The basic knowledge acquisition of this program is tailored so that knowledge acquired can be potentially useful for the applications mentioned above. The Multidisciplinary University Research Initiative Center for Nanoscale Materials and Processing is located at the Loker Hydrocarbon Research Institute (LHRI) of the University of Southern California with satellite research programs at Cornell (headed by J. Frechet), California Institute of Technology (headed by
SUPRAMOLECULAR
SCIENCE Volume 2 Numbers 3-4 1995
233
Supramolecular
Science
Laboratory
profile
R. Grubbs), North Carolina State University (headed by C. Gorman) and the State University of New York at Buffalo (headed by P. Prasad). The Department of Defense funding of approximately $6.7 million dollars is matched by a $2.0 million dollar contribution from USC to equipment and research staff salaries and the center benefits from location in the newly constructed Catherine B. Loker Research Wing of the LHRI. Projects have been defined in the following areas: (1) STM/AFM nanolithography and dendrimeric materials; (2) polymer microspheres and morphological resonances; (3) molecular self-assembly and ordered phases; (4) sequential synthesis; (5) external field induced ordering; and (6) sol-gels, micelles, and LB methods. The project on STM nanolithography focuses on developing a systematic approach for achieving two dimensional organization controlled to nanoscale dimensions and on characterizing and addressing individual nanoscale units within an ordered twodimensional matrix. Issues to be addressed include control of nanoscale molecule-substrate interaction, movement and positioning of nanoscale moieties exploiting STM probe-molecule interactions, control of chemical and physical communication between nanoscale moieties, the ability to define the electronic properties of individual units, and the ability to systematically modify the properties of individual moieties. An example of the application of the above principles of STM nanolithography is the development of the next generation of electronic computing elements by synthesis and spatial organization of nanoscale information bearing units (IBUs). One approach to synthesizing nanoscale IBUs involves a dendritic synthesis approach proceeding from a core capable of bistable properties to a periphery which effects isolation of IBUs and defines intermolecular interactions relevant to positioning of IBUs, (Figures l-3). Polymer microspheres of nanoscale dimensions can be prepared by a variety of novel self-assembly procedures. Indeed, compositionally complex materials can be prepared so that a systematic variation in index of refraction, dielectric properties, chemical reactivity, etc. can be achieved from the core to the periphery of the microspheres. In like manner, the chemistry exists for effecting precise control of interactions between microspheres. Among the many properties that depend upon the size and shape of nanoscale structures, the propagation of nanometer wavelength light will be dramatically influenced by interaction with such particles. For example, when circumference of a chromophore-coated microsphere is a multiple of the wavelength of incident light, the light can become trapped in the chromophore layer and build up (i.e. undergo morphological resonance) analogous to the confinement of radiofrequency and microwave electromagnetic radiation in metal cavities of centimeter and millimeter dimensions. Such phenomena can be exploited for the development of high density
optical memories exploiting the spectral dimension, i.e. the memory density is increased over a normal spatially-defined density limitation by the number of spectral holes that can be burned by morphological resonances. In preliminary studies, the burning of nine holes in a 20 nanometer spectral window was demonstrated. This result suggests that, for normal chromophores such as azobenzenes, memory density can be improved by two orders of magnitude above that defined by spatial limitations. Memory density can be further improved by more precise control of structural variations at nanoscale dimensions which leads to narrower morphological resonances (that is, higher quality or Q factors). Professors Jean Frechet (Cornell) and Robert Grubbs (Cal Tech) head a project aimed at advancing the preparation of nanoscale structures by developing synthetic methods exploiting molecular self-assembly. Frechet will lead an effort focused upon preparation of functionalized and self-assembled dendrimers including unsymmetrically functionalized dendrimers, monodisperse surface-reactive nanoclusters, and molecularly insulated inorganic-organic composite nanoscopic wires. The research project headed by Frechet also contributes materials to the STM nanolithography project described above. Grubbs will lead an effort focused upon the preparation of block copolymers capable of exhibiting nanoscale phases including ordered phases. Mark Thompson of USC heads a program to use sequential synthesis methods to prepare new electronic components such as light emitting diodes. Thompson will focus on the use of metal phosphonate compounds; these materials are very stable and insoluble and can be
234
3-4 1995
SUPRAMOLECULAR
SCIENCE Volume
2 Numbers
Figure 1 Proposed dendrimeric capping of discrete semiconductor clusters. The tetrahedral core consists of S (A), SPh (a), and M (*) units. The four dendrimeric ligands and the crosslinks between them form the periphery of the information bearing unit
Supramolecular
1
Science Laboratory profile
6-j
“i” Y? 4 1.o 4 CO 0
7
\
co
0
(-0 0
I)
0
0
.
‘/
0
0PO
\
P
0
0
1’
HO
\/
CP
Figure 2
I’
11
0
The structure
.’
I
0
2
0
of a dendrimeric
ligand is shown
easily used to organize organic groups in the solid state. Paras Prasad at SUNY-Buffalo (working with David Williams at Eastman Kodak) will also utilize sequential synthesis methods, Langmuir-Blodgett lilm fabrication, to prepare thin films of precisely controlled thickness. Such thickness control can be used to achieve phase matched frequency doubling of infrared lasers. External forces will be used to achieve nanoscale ordering. Such a project is viewed as a complement to those exploiting molecular self-assembly and sequential
Figure 3
Representative
chemical
modification
of the periphery
synthesis methods to achieve ordered structures. External forces to be most actively investigated include electrical and electromagnetic fields. In particular, electric field poling and laser poling will be used to achieve noncentrosymmetric molecules organization necessary in the fabrication of nanophotonic and nanoelectronic devices. Prototype devices will be utilized not only in communication applications but also in sensor applications including biomedical sensing and radar applications. Finally, Paras Prasad of SUNY-Buffalo directs a
of IBUs to control
SUPRAMOLECULAR
surface interactions
SCIENCE Volume 2 Numbers 3-4 1995
235
Supramolecular
Science Laboratory profile
project on multiphasic nanostructured composites exploiting sol-gel, micellar, and colloidal particle processing methods. For example, sol-gel methods will be used to prepare nanoscale metal organic cores coated with metal oxide materials. Such active organicdoped nanoparticles have uses in the fields of nonlinear
236
SUPRAMOLECULAR
optics, lasers, liquid chromatography, and nanosensors. Such structures may also exhibit morphological resonances as described above for chromophore-coated polymer microspheres. Sol-gel processing can also be used to develop nanostructures for optical limiting applications.
SCIENCE Volume 2 Numbers 3-4 1995