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Final Technical Report, 7/-1/92-6/30 ^95 


Tunneling Spectroscopy of Ultrasmail Clusters and Grain: 


K. Likharev 

7 performing organization NAME(S) and ADDR£SS(ES) 

state University of New York at Stony Brook 
Stony Brook, NY 11794-3800 


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AFOSR'A’^ jj- ”7VT 

Dr. Harold Weinstock I • 8 

110 Duncan Ave. 

Bolling AFB, DC 20332-0001 



Approved for public release ; 

dletributiou laoliaited* 

13. ABSTRACT {M^ximum 200 wonis) 

The Final Technical Report describes 
project supported by an AFOSR AASERT 
#AFOSR-91-0445). The report consists 

1. Summary 

2. Main Results 

3. Conclusion and Prospects. 
The main research achievement during 
original instrument for scanning tun 
electronic remote control of a I I its 
of the scanning tip), for a broad ra 



19951002 018 _ 

resuiTs obtained during the research 
Grant #F49620-92-J-0358 (parent grant 
of 3 sections: 

this work has been the development of an 
neling microscopy and spectroscopy, with 
functions (including the coarse approach 
nge of research applications. 


-----hS. NUMBER OF PAGE! 1 


Scanning tunneling microscopy, tunneling spectroscopy, 16 .PRICECODE 

s i ng I e-e 1 ectr onics, nano-obJects, cluster s, thin films mntAtifiM JS* 7ra2 

NSN 7540-01-280-5500 

Standard Form 296 (Rav. 2-89 

I sUI 


AFOSR Grant # F49620-92-J-0358 


Parent Grant # AFOSR-91-0445 

Final Technical Report 

Principal Investigator: Prof. Konstantin K. Likharev 

Address: Department of Physics 

State University of New York 
Stony Brook, NY 11794-3800 

Phone: 516-632-8159 
Fax: 516-632-8774 


Project Period: July 1, 1992 - June 30, 1995 

August 1995 

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1. Summary 

Single-electronics is a new and exciting field of physical and applied 
electronics, which has emerged during the last decade. The physics of this field is based 
on the effects of correlated single-electron tunneling. Their essence is that the transfer of 
single electrons in systems of conducting (metallic, semiconductor, or molecular) 
"electrodes", connected by tunnel barriers of very small area, may be strongly correlated 
either in time, or in space, or both. 

Since 1987, reliable evidence of correlated tunneling has been obtained in 
numerous experiments with normal-metal, superconductor, and semiconductor junctions 
and systems. Preliminary studies of possible applications have shown that single¬ 
electronics may yield a completely new generation of both digital and analog devices 
with unparalleled performance, most notably extremely dense digital circuits with up 
to loll active devices (logic gates and/or memory cells) per square centimeter. 
However, in order to bring single-electronics to practice, numerous problems must be 
solved. In 1991, three research groups at SUNY - Stony Brook, headed by Professors 
Dmitri Averin, Konstantin Likharev and James Lukens, working in collaboration, began 
an AFOSR-supported project in the field of single-electronics. As a result of this effort, a 
solid technological, experimental and theoretical base for single-electronics was 
established at Stony Brook, and several important results have been obtained. 

The main objectives of the present supplementary project have been: 

- to extend the work to scanning tunneling microscopy/spectroscopy (STM/S) of 
various nanostructures (ultimately at low temperatures), and 

- to increase the number of graduate students involved in research in the field of 

During the first two years of the project, the research was carried out in 
collaboration with the group of Dr. Myron Strongin at the Brookhaven National 
Laboratory. The collaboration was very pleasant and fruitful, and provided a substantial 
leverage for our AASERT award. 

Our main research achievement has been the development of an original STM/S 
instrument with electronic remote control of all its functions (including the coarse 
approach), with a broad range of possible applications. This instrument has been used to 
carry out STM studies of a broad variety of nanostructures, including Moire patterns on 
graphite surfaces, monolayers of stearic acid on graphite, atomically-smooth gold thin 
films on mica, monolayers of C 50 buckybaUs on atomically-smooth gold surfaces (in 
particular, modified by extremely thin gold overlayers), and metal-doped diamond-like 

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A more detailed description of the main results of this work is given below. ■ 

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2. Main Results 

A. Simulation of Interaction of Single-Electron Solitons 

For adequate interpretation of anticipated experimental results on single-electron 
charging of ID arrays of nano-objects, we have carried out analytical and numerical 
calculations of interaction of single-electron solitons in such arrays, using simple 
geometrical models. In contrast to previous calculations which had used oversimplified 
assumptions, we have found a natural crossover between the exponential decrease of the 
electrostatic field near the center of the soliton and the virtually unshielded (1/r) decrease 
of the scalar potential at large distances. A simple expression for the stray capacitance 
per period has been derived from these numerical results [1]. 

B. STM/S Instrument with New Piezoelectric Engine 

For our single-electron nanospectroscopy work we would like to have an STM/S 
instrument which could operate at helium and millikelvin temperatures and high vacuum 
without any mechanical links to the ambient environment. (Commercially available low- 
temperature STMs are not applicable in our experimental conditions). This is why we 
have designed and implemented a preliminary version of such an STM/S using a new 
type of piezoelectric engine for the tip position adjustment [2]. 

The engine consists of a 60° quartz prism (carrying the piezo-tube STM scanner) 
which can move along a 60° cut in a Macor body of the sample holder. A spring presses 
the prism against 4 shear-motion piezo plates ("legs") which are glued to the body. 
During the first stage of each crude approach step, the voltage on all the legs is changed 
simultaneously. The upper surfaces of the prisms shift along the cut, and carry the prism 
with them. Then the voltage is removed from the legs one-by-one; during this stage the 
prism stays in place, because at each instant its friction against 3 static legs overweighs 
the friction against 1 moving leg. 

Our engine, and the STM/S as a whole, operates reliably at room temperatures 
(both in air and high vacuum) and has been applied to studies of several nanosystems 
which seemed promising for the observation of correlated single-electron tunneling 

C. STM/S Studies of Nanostructures 

C.l. Moire patterns on HOPG 

Highly oriented pyrolythic graphite (HOPG) is a commonly used substrate for 
STM/S applications. Using our STM/S we could observe atomic patters on the HOPG 
surfaces, including the Moird patterns associated with variations of local stacking [2], 
without any vibration isolation. We have discovered an extended electronic effect from a 
single atomic vacancy, and measured the decay factor along the c-axis and various bias 
voltage dependent topographies for the Moird patterns [3]. These results may be very 
useful for further studies of ultrasmall particles and clusters on HOPG substrates. 

C.2. Macromolecules on HOPG 

To fix ultrasmall conducting particles on a graphite surface, Langmuir-Blodgett 
films of stearic acid mixed with l, 7 -(CH 3 ) 2 -l, 2 -C 2 BioHgTl(C)CC)CF 3)2 molecules 
were prepared using distilled water, and transferred onto freshly cleaved HOPG substrate 
using the Langmuir-SchSfer method. Our STM study has shown that the surfaces of the 
graphite substrates had been modified. We have determined that the modification was 
caused by the solvent intercalation. While being detrimental for our particular attempt to 
fix organic clusters on the surface, this effect may be useful in general to characterize 
surface damage caused by different sample preparation techniques. 

C.3. Au (111) and 

Gold films were deposited at 440°C on pre-baked mica substrates. Using our 
STM we could get atomic resolution on these films in air. The STM studies have shown 
that atomically flat regions on the films were ~0.1 |im wide. By evaporation of 
buckyballs (C 50 ) on the surface we could obtain and image well-ordered single- 
molecular layers with hexagonal structure [4]. To our surprise, the morphology of these 
structures changes dramatically after adding one more Au overlayer. While the first C 50 
monolayer remained flat, the extra buckyballs formed clusters with an average size of 8 

C. 4, Some other applications 

Our STM/S instrument has been used for some purposes beyond the scope of this 
project (the corresponding research costs were covered from funds different from the 
AASERT award). For example, the BNL group have used this instrument to study metal- 
containing diamond-like nanocomposites (a-C:H)/(a-Si:0)/Me films [ 4 ]. The electrical 
and structural properties of these films could be controlled by several means, e.g., metal 
doping, therm^ annealing and probably high field (or heating) in the vicinity of an STM 
tip. Using STM, the annealing- induced sp^-to-sp^ transformation (which may provide 
an interesting way to engineer nanostructured samples) has been observed [ 4 ]. 

3. Conclusion and Prospects 

Unfortunately, we have not been able to find sufficiently stable objects which 
could exhibit correlated single-electron tunneling effects at room temperature. On the 
other hand, low-temperature (~5 K) operation of our instrument was not stable enough 
for its systematic use. Nevertheless, the instrument has turned out to be extremely useful 
for several room-temperature studies of issues closely related to the future development 
of nanoelectronics. Our current plans are to use it mostly for in-situ studies of the 
thermal growth of very thin (~ 2 -nm) aluminum oxide layers used as tunnel barriers in 
niobium-trilayer tunnel junctions for our single-electronics research within our parent 
AFOSR project, as well as for superconductor electronics work funded by DoD's URI 
through another AFOSR grant. 


1. K.K. Likharev K. Matsuoka, "Electron-Electron Interaction in Linear Arrays 
of Small Tunnel Junctions", submitted to Appl. Phys. Lett. (July 1995). 

2. Z.Y. Rong and P. Kuiper, "Electronic Effects in Scanning Tunneling Microscopy: 
Moird Pattern on a Graphite Surface", Phys. Rev. B 48,17427 (1993). 

3. Z.Y. Rong, "Extended Modifications of Electronic Structures Caused by Defects: 
Scanning Tunneling Microscopy of Graphite", Phys. Rev. B 50, 1839 (1994). 

4. Z.Y. Rong and L. Rokhinson, "STM Study of Gold-overlayer Formation on CgQ 
Monolayers", Phys. Rev. B 49,7749 (1994). 

5. Z.Y. Rong, M. Abraizov, B. Dorfman, M. Strongin, X.-Q. Yang, D. Yan, and F. 
H. Poliak, "Scanning Tunneling Microscopy of Diamond-like Nanocomposite 
Films", Appl. Phys. Lett. 65, 1379 (1994).