Ph.D. Thesis Introduction

This is a HTML version of the introduction to my thesis "Tools for In-situ Manipulation and Characterisation
of Nanostructures
":

1.1 A Perspective on Nanomanipulation

In his famous speech "There is plenty of room at the bottom" in 1959, Richard Feynman discussed how to manipulate and control things on a small scale in order to achieve electronic and mechanical systems with atomic sized components. He concluded that the development of technologies to construct such small systems would be interdisciplinary, combining fields such as physics, chemistry and biology, and would offer a new world of possibilities that could radically change the technology around us. A few years later, in 1965, Gordon Moore [9] noted that the number of transistors on a chip had roughly doubled every other year since 1959, and predicted that the trend was likely to hold as each new generation of microsystems would help to develop the next generation at lower prices and with smaller components. Together with Robert Noyce, Moore founded the company Intel in 1969 which has since been dedicated to fulfill Moore’s law. The impact on society and our lives of the continuous downscaling of systems is profound, and continues to open up new frontiers and possibilities. However, no exponential growth can continue forever, and the semiconductor industry will eventually reach the atomic limit for downsizing the transistor.

Today, as that limit still seems to be some 20 years in the future, the growth is beginning to take new directions, indicating that the atomic limit might not be relevant in the future. The semiconductor devices show an increased diversification, dividing for instance processors into very different systems such as processors for cheap disposable chips, low power portable devices or high processing power devices. This diversity seems to increase on all levels in technology. As the components become so small that quantum effects become important on the nanoscale, completely new devices and possibilities begin to open up that were not possible with the bulk materials of the today’s technology. The visions of Feynman is shared by many others: Nanotechnology is seen as a generally useful cross disciplinary technology, which has the potential to create a coming "industrial" revolution that will have profound impact on society and everyday life, comparable to electricity or information technology.

1.1.1 Nanocomponents and methods

As an emerging technology, the methods and components of nanotechnology as a whole are under continuous development and each generation is providing a better foundation for the following. With regards to the methods, the scanning tunneling microspore (STM) and atomic force microscope (AFM) were developed in the 1980’s and opened up completely new ways to investigate nanoscale materials. An important aspect was the new possibility to manipulate nanoscale objects. Transmission and scanning electron microscopes (TEM and SEM) had been available since the 50’s, but mainly offered the possibility to passively image rather than actually measure and interact with the sample.

Several new nanoscale components were also discovered: the C60 buckyball molecule [10] and later the carbon nanotube [11]. In the last years, nanowires such as silicon nanowires have also proven to be essential building blocks in nanodevices [12][13]. The applications of such nanocomponents span all aspects of technology: Electronics [14], optics/photonics [15], medical, biochemical [16]. But to date few - if any - real products are available with nanoscale components (apart from traditional nanoscale products that can be sold in buckets, such as paint with nanoparticles or catalytic particles for chemical reactors). Prototype device have been demonstrated and individual components created, but actual production is still to come. As when integrated electronics were developed, nanotechnology is currently in the phase where component production methods, characterization methods, and tools for manipulation and integration are evolving by mutual support and convergence.

A main problem is reliable integration of the nanoscale components into existing systems or microchips since the production methods are often not compatible. For fabrication of devices with integrated nanocomponents, the optimal manipulation technique would of course be to have the individual components self-assembling or grow into the required complex system[17][18]. Self assembly of devices in liquids is a large and expanding field within nanotechnology but usually requires the components to be covered in various surfactants, which usually also influence the component properties. The prevailing integration technique for nanowire systems seems to be electron beam lithography (EBL) of metal structures onto substrates with randomly positioned nanowires deposited from liquid dispersions[19]. By using flow alignment or electrical fields, the wire deposition from liquids can be controlled to some extent [20]. The EBL method has allowed for systematic investigations of nanowires and tubes electrical properties and creation of high performance electronic components such as field-effect transistors and chemical sensors. These proof of principle devices are some of the few but important demonstrations of what nanotechnology might offer. In addition nanomechanical structures have also recently been demonstrated, such as rotational actuator with a carbon nanotube axis built by Han et al. [21].

To avoid surface treatments, nanotubes and whiskers/wires can be grown on chips and microsystems directly from prepatterned catalytic particles, though promising for future large scale production of devices, few working devices have been made by the method to date [22][23][24]. The self-assembly method is likely to be important for future large scale production, but nanomanipulation will probably be a key technique to use to test prototypes and individual structures before developing self-assembly processes to mass-produce these devices.

A more active approach to creating nanowire structures is to use scanning probe microscopy (SPM) to push, slide and roll the nanostructures over surfaces[25][26]. The SPM manipulation has been used to create and study nanotube junctions [26] and field effect transistors[27]. The ability to manipulate individual nanoscale objects would be very useful for building proof-of-principle devices and prototypes, characterizing and testing components and could hence become an important factor in the self-sustaining development of nanotechnology.

1.1.2 Nanomanipulation Systems

To observe the manipulation process, in-situ SEMor TEMmanipulation seems preferable. AFM (or STM) does have the resolution to image nanoscale objects, even at atomic resolution, but the imaging frame rate is usually rather slow compared to SEM orTEMand the structures will normally have to be planar. SEMoffers the possibility of high frame rates; almost nanometer resolution imaging of three-dimensional objects; imaging over a large range of working distances; and ample surrounding volume in the sample chamber for the manipulation setup. TEM has a much more limited space available for the sample and manipulation systems but can on the other hand
provide atomic resolution. For detailed studies of the nanowires’ structure, TEM is a useful tool, but for the assembly of nanoscale components of a well defined structure, such as batch fabricated nanowires and nanotubes, the SEM resolution should be sufficient to complete the assembly task.

As the STM and AFM techniques opened up completely new fields of science by allowing the investigator to interact with the sample rather than just observe, development of nanomanipulation tools for SEM and TEM would probably open up for new possibilities as well. The three-dimensional manipulation offers new ways to create three-dimensional nanowire devices, where the EBL and SPM methods are
mainly limited to planar geometries. Recently, commercial systems for such tasks have become available such as the F100 Nanomanipulator System from Zyvex in October 2003. Several research groups have also pursued developing such systems, such as [28][29][25].

To date the tools used for in-situ SEM nanomanipulation have almost exclusively been individual tips (AFM cantilever tips or etched tungsten tips), sometimes tips used together with electron beam deposition have been used to create nanowire devices [30]. Despite the availability of commercial microfabricated grippers in the last couple of years, little has been reported on the use of such devices for handling nanostructures. Some electrical measurements and manipulation tasks have been performed in ambient conditions with carbon nanotube nanotweezers [31][32].


1.2 The present work

For prototyping and research applications an in-situ SEM nanomanipulation setup would open up new possibilities. The actuation units to move tools with nanometer precision are available commercially. At MIC the microfabrication facility also meant that we would be able to design and fabricate unique tools to use in such a setup. The group had in other projects gained experience in the use of microcantilever
chips for measuring the conductivity of surfaces. By changing the design of the chips, microfabricated grippers could be made that might be able to manipulate objects in the in-situ setup. The existing microcantilever systems, both the four point probes but also piezoresistive AFM cantilevers, could also become useful tools within the setup for characterization of nanostructures. Chapter 2 introduces the SEM and TEM instruments and the standard chips available at MIC by the beginning of this project. Then it describes the developed SEM manipulation systems and the TEM-chip characterization method. In this thesis focus will be on investigating and characterizing nanowires and nanotubes, since these rod-shaped components can be complex individual nanosystems such as the hetero nanowire structures developed by the groups of Lieber and Samuelson[17][12]. In Chapter 3 the development of microfabricated grippers for nanomanipulation and how the devices were used for successful manipulation of nanowires is described. Chapter 4 describes how electron beam deposition can be used to directly solder and construct nanostructures. The study was done in an environmental electron microscope and the environmental EBD was discovered to have unique features, such as the possibility to create structures with a solid polycrystalline gold core under suitable conditions. After integrating the nanowires/tubes it would be preferable to be able to verify the successful assembly process and to what extent it had influenced the nanostructure. A special method was developed using microcantilever chips for TEM studies. These "TEM-Chips" were used to investigate carbon nanotubes. These experiments are described in Chapter 5.

The developed concept for an in-situ nanolaboratory is a versatile system where each part can have several different applications:

With sufficiently small gripper tools for the in-situ nanomanipulation system, pick-and-place assembly of nanodevices might be feasible - possibly with electron beam deposition as a soldering tool for fixing the components and ensuring electrical contact. Such a scheme is resembling the automated pick-and-place of macroscopic electronic components onto printed circuit boards, but applied to objects that are 10000 times smaller. Microgrippers could also find applications such as manipulation of micrometer sized samples for microscopy.

References:

[1] Kristian Mølhave and Ole Hansen. Design of thermal tweezers with piezoresisitive readout. Submitted to Microelec. Eng., 2004.
[2] Kristian Mølhave, Dorte Nørgaard Madsen, , and Peter Bøggild. A simple electron beam lithography system. Accepted by Ultramicroscopy, 2004.
[3] Kristian Mølhave, Dorte Nørgaard Madsen, Søren Dohn, and Peter Bøggild. Constructing, connecting and soldering nanostructures by environmental electron beam deposition. Nanotechnology, 15:1047—1053, 2004.
[4] K. Mølhave, D.N. Madsen, A.M. Rasmussen, A. Carlsson, C.C. Appel, M. Brorson, C.J.H. Jacobsen, and P. Bøggild. Solid gold nanostructures fabricated by electron beam deposition. Nano Letters, 3:1499—1503, 2003.
[5] D.N. Madsen, K. Mølhave, R. Mateiu, A.M. Rasmussen, M. Brorson, C.J.H. Jacobsen, and P. Bøggild. Soldering of nanotubes onto microelectrodes. Nano Letters, 3:47—49, 2003.
[6] K. Mølhave, T.M. Hansen, D.N. Madsen, and P. Bøggild. Towards pick-and-place assembly of nanostructures. Journal of Nanoscience and Nanotechnology, 4:279—282, 2004.
[7] Søren Dohn, Peter Bøggild, and Kristian Mølhave. Direct measurement of resistance of multiwalled carbon nanotubes using micro four-point probes. to be submitted, pages —, 2004.
[8] R. Mateiu, Z.J. Davis, D.N. Madsen, K. Molhave, P. Boggild, A.-M. Rassmusen, M. Brorson, C.J.H. Jacobsen, and A. Boisen. An approach to a multi-walled carbon nanotube based mass sensor. Microelectronic Engineering, 73-74:670—674, 2004.
[9] G. E. Moore. Cramming more components onto integrated circuits. Electronics, 38:—, 1965.
[10] Robert F. Curl and Richard E. Smalley. Probing c60. Science, 3.242(4881):1017—1022, 1988.
[11] S. Iijima. Helical microtubules of graphitic carbon. Nature, 354(6348):56—8, 1991.
[12] C.M. Lieber. Nanowires as building blocks for nanoelectronics and nanophotonics. Electron Devices Meeting, 2003. IEDM ’03 Technical Digest. IEEE International, page 12.3.1, 2003.
[13] L. Samuelson. Self-forming nanoscale devices. Materials Today, 6(10):22—31, 2003.
[14] Y. Cui and C.M. Lieber. Functional nanoscale electronic devices assembled using silicon nanowire building blocks. Science, 291(5505):851—853*, 2001.
[15] Mark S. Gudiksen, Lincoln J. Lauhon, JianfangWang, David C. Smith, and Charles M. Lieber. Growth of nanowire superlattice structures for nanoscale photonics and electronics. Nature, 415(6872):617—620, 2002.
[16] Yi Cui, Qingqiao Wei, Hongkun Park, and C.M. Lieber. Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species. Science, 293(5533):1289—92, 2001.
[17] L. Samuelson, M.T. Bjork, K. Deppert, M. Larsson, B.J. Ohlsson, N. Panev, A.I. Persson, N. Skold, C. Thelander, and L.R. Wallenberg. Semiconductor nanowires for novel onedimensional devices. Physica E, 21(2-4):560—567, 2004.
[18] D.H. Gracias, J. Tien, T.L. Breen, C. Hsu, and G.M. Whitesides. Forming electrical networks in three dimensions by self-assembly. Science, 289(5482):1170—2, 2000.
[19] B. Bourlon, D.C. Glattli, B. Placais, J.M. Berroir, C. Miko, L. Forro, and A. Bachtold. Geometrical dependence of high-bias current in multiwalled carbon nanotubes. Physical Review Letters, 92(2):026804/1—4, 2004.
[20] Y. Huang, X. Duan, Q. Wei, and C.M. Lieber. Directed assembly of one-dimensional nanostructures into functional networks. Science, 291(5504):630—633*, 2001.
[21] Wei-Qiang Han, A.M. Fennimore, T.D. Yuzvinsky, M.S. Fuhrer, J. Cumings, and A. Zettl. Rotational actuators based on carbon nanotubes. Nature, 424(6947):408—410, 2003.
[22] Yuegang Zhang, Aileen Chang, Jien Cao, Qian Wang, Woong Kim, Yiming Li, N. Morris, E. Yenilmez, Jing Kong, and Hongjie Dai. Electric-field-directed growth of aligned singlewalled carbon nanotubes. Applied Physics Letters, 79(19):3155—7, 2001.
[23] M. Saif Islam, S. Sharma, T.I. Kamins, and R. Stanley Williams. Ultrahigh-density silicon nanobridges formed between two vertical silicon surfaces. Nanotechnology, 15(5):L5—L8, 2004.
[24] K.B.K. Teo, M. Chhowalla, G.A.J. Amaratunga, W.I. Milne, D.G. Hasko, G. Pirio, P. Legagneux, F. Wyczisk, and D. Pribat. Uniform patterned growth of carbon nanotubes without surface carbon. Applied Physics Letters, 79(10):1534—6, 2001.
[25] M.R. Falvo, G. Clary, A. Helser, S. Paulson, R.M. Taylor II, V. Chi, F.P. Brooks, Jr., S.Washburn, and R. Superfine. Nanomanipulation experiments exploring frictional and mechanical properties of carbon nanotubes. Microscopy and Microanalysis, 4(5):504—512, 1998.
[26] C. Thelander, M.H. Magnusson, K. Deppert, L. Samuelson, P.R. Poulsen, J. Nygard, and J. Borggreen. Gold nanoparticle single-electron transistor with carbon nanotube leads. Applied Physics Letters, 79(13):2106—8, 2001.
[27] Ph. Avouris, R. Martel, and H.R. Shea. Carbon nanotubes: nanomechanics, manipulation, and electronic devices. Applied Surface Science, 141(3-4):201—209, 1999.
[28] Kensuke Tsuchiya, Akihiro Murakami, Gustavo Fortmann, Masayuki Nakao, and Yotaro Hatamura. Micro assembly and micro bonding in nano manufacturing world. Proceedings of SPIE - The International Society for Optical Engineering, 3834:132—140, 1999.
[29] MinFeng Yu, Mark J. Dyer, George D. Skidmore, Henry W. Rohrs, XueKun Lu, Kevin D. Ausman, James R. Von Ehr, and Rodney S. Ruoff. Three-dimensional manipulation of carbon nanotubes under a scanning electron microscope. Nanotechnology, 10(3):244—252, 1999.
[30] T. Fukuda, F. Arai, and L. Dong. Fabrication and property analysis of mwnt junctions through nanorobotic manipulations. International Journal of Nonlinear Sciences and Numerical Simulation, 3(3-4):753—8, 2002.
[31] P. Kim and C.M. Lieber. Nanotube nanotweezers. Science, 286(5447):2148—50, 1999.
[32] H. Watanabe, K. Shimotani, T. Shigematu, and C. Manabe. Electric measurements of nanoscaled
devices. Thin Solid Films, 438-439:462—466, 2003.