Electronic Conduction through Monolayer Amorphous Carbon Nanojunctions

The electronic conduction mechanism occuring in amorphous thin films is quite complicated. In amorphous carbon films it is further exacerbated by the rich diversity of its microstructure as well as the large number of gap states present in the films. One of the main reasons for the tunability of the optical band gaps of these films not being exploited in active devices, has been the inability firstly to reduce the gap states to an acceptable level, and secondly finding suitable dopants that are electrically active at room temperature. The large number of gap states in the films further exacerbates its problems by not allowing suitable barriers (eg. Schottky) to be formed on to the amorphous carbon films. In this paper we hope to first divide the amorphous carbon thin films into two main categories. Namely, diamond-like carbon films which have a high precentage of C-C sp 3 bonding, and polymer-like carbon films that also have a high percentage of sp 3 bonding which is a mixture of C-C and C-H bonds, and have a high percentage of hydrogen as well as large optical band gaps. Recent results based on ion implantation using ions such as N, B, C will be contrasted to in-situ dopant incorporation via a gaseous source., and is shown to be a very powerful technique of modifying the conduction properties. It will be shown that in the diamond-like films the conduction properties are usually controlled via Poole-Frenkel type defect conduction, while for the polymer-like films it is more a space charge based bulk and possibly, barrier controlled process. But, due to the large band gaps of these films it is difficult to distinguish between the bulk effects and the barrier effects.

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The Resolution and Contrast in Biological Sections Determined by Inelastic and Elastic Scattering

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100071569 ◽

1973 ◽

Vol 31 ◽

pp. 224-225

Author(s):

D. L. Misell

Keyword(s):

Electron Microscopy ◽

Adverse Effect ◽

Elastic Scattering ◽

Inelastic Scattering ◽

Amorphous Carbon ◽

Polymeric Materials ◽

Chromatic Aberration ◽

Image Resolution ◽

Quantitative Estimates ◽

Elastic Ratio

In the electron microscopy of biological sections the adverse effect of chromatic aberration on image resolution is well known. In this paper calculations are presented for the inelastic and elastic image intensities using a wave-optical formulation. Quantitative estimates of the deterioration in image resolution as a result of chromatic aberration are presented as an alternative to geometric calculations. The predominance of inelastic scattering in the unstained biological and polymeric materials is shown by the inelastic to elastic ratio, I/E, within an objective aperture of 0.005 rad for amorphous carbon of a thickness, t=50nm, typical of biological sections; E=200keV, I/E=16.

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Observation of Atom Rows in Thorium Pyromellitate Using a Field Emission STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010007802x ◽

1977 ◽

Vol 35 ◽

pp. 80-81

Author(s):

H. Todokoro ◽

S. Nomura ◽

T. Komoda

Keyword(s):

Field Emission ◽

Amorphous Carbon ◽

Carbon Film ◽

Dark Field Image ◽

Dark Field ◽

Amorphous Carbon Film ◽

Atomic Size ◽

Wide Range ◽

A Chain

It is interesting to observe polymers at atomic size resolution. Some works have been reported for thorium pyromellitate by using a STEM (1), or a CTEM (2,3). The results showed that this polymer forms a chain in which thorium atoms are arranged. However, the distance between adjacent thorium atoms varies over a wide range (0.4-1.3nm) according to the different authors.The present authors have also observed thorium pyromellitate specimens by means of a field emission STEM, described in reference 4. The specimen was prepared by placing a drop of thorium pyromellitate in 10-3 CH3OH solution onto an amorphous carbon film about 2nm thick. The dark field image is shown in Fig. 1A. Thorium atoms are clearly observed as regular atom rows having a spacing of 0.85nm. This lattice gradually deteriorated by successive observations. The image changed to granular structures, as shown in Fig. 1B, which was taken after four scanning frames.

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Electron-diffraction studies of amorphous carbon thin films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100151337 ◽

1993 ◽

Vol 51 ◽

pp. 1100-1101

Author(s):

David A. Muller

Keyword(s):

Thin Films ◽

Electron Diffraction ◽

Amorphous Carbon ◽

Glassy Carbon ◽

Spherical Structure ◽

Local Ordering ◽

Carbon Arc ◽

Similar Appearance ◽

Carbon Thin Films ◽

Large Spherical

The sp2 rich amorphous carbons have a wide variety of microstructures ranging from flat sheetlike structures such as glassy carbon to highly curved materials having similar local ordering to the fullerenes. These differences are most apparent in the region of the graphite (0002) reflection of the energy filtered diffracted intensity obtained from these materials (Fig. 1). All these materials consist mainly of threefold coordinated atoms. This accounts for their similar appearance above 0.8 Å-1. The fullerene curves (b,c) show a string of peaks at distance scales corresponding to the packing of the large spherical and oblate molecules. The beam damaged C60 (c) shows an evolution to the sp2 amorphous carbons as the spherical structure is destroyed although the (220) reflection in fee fcc at 0.2 Å-1 does not disappear completely. This 0.2 Å-1 peak is present in the 1960 data of Kakinoki et. al. who grew films in a carbon arc under conditions similar to those needed to form fullerene rich soots.

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Scanning Tunneling Microscopy of Amorphous Carbon Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180343 ◽

1990 ◽

Vol 48 (1) ◽

pp. 318-319

Author(s):

Mircea Fotino ◽

D.C. Parks

Keyword(s):

Scanning Tunneling Microscopy ◽

Amorphous Carbon ◽

Carbon Films ◽

Atomic Scale ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Amorphous Carbon Films ◽

Image Optimization ◽

Step Procedure ◽

Stm Images

In the last few years scanning tunneling microscopy (STM) has made it possible and easily accessible to visualize surfaces of conducting specimens at the atomic scale. Such performance allows the detailed characterization of surface morphology in an increasing spectrum of applications in a wide variety of fields. Because the basic imaging process in STM differs fundamentally from its equivalent in other well-established microscopies, good understanding of the imaging mechanism in STM enables one to grasp the correct information content in STM images. It thus appears appropriate to explore by STM the structure of amorphous carbon films because they are used in many applications, in particular in the investigation of delicate biological specimens that may be altered through the preparation procedures.All STM images in the present study were obtained with the commercial instrument Nanoscope II (Digital Instruments, Inc., Santa Barbara, California). Since the importance of the scanning tip for image optimization and artifact reduction cannot be sufficiently emphasized, as stressed by early analyses of STM image formation, great attention has been directed toward adopting the most satisfactory tip geometry. The tips used here consisted either of mechanically sheared Pt/Ir wire (90:10, 0.010" diameter) or of etched W wire (0.030" diameter). The latter were eventually preferred after a two-step procedure for etching in NaOH was found to produce routinely tips with one or more short whiskers that are essentially rigid, uniform and sharp (Fig. 1) . Under these circumstances, atomic-resolution images of cleaved highly-ordered pyro-lytic graphite (HOPG) were reproducibly and readily attained as a standard criterion for easily recognizable and satisfactory performance (Fig. 2).

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