Meetings & Events

fall 1997 logo1997 MRS Fall Meeting & Exhibit

December 1 - 5, 1997 | Boston
Meeting Chairs:
 Harry A. Atwater, Peter F. Green, Dean W. Face, A. Lindsay Greer 

Symposium AA—Covalently Bonded Disordered Thin-Film Materials



James Jaskie, Motorola Inc
David McKenzie, Univ of Sydney
William Milne, Cambridge Univ
Michael Siegal, Sandia National Laboratories

Symposium Support

  • Blazers Process Systems
  • Motorola, Inc.
  • Sandia National Laboratories

Proceedings published as Volume 498
of the Materials Research Society
Symposium Proceedings Series.

* Invited paper

Chair: Ellen B. Stechel 
Tuesday Morning, December 2, 1997 
St. George B/C/D (W)

9:00 AM *AA1.1 
STRUCTURAL TRENDS IN AMORPHOUS CARBON. K.M. Ho, Dept of Physics and Ames Laboratory, Iowa State University, Ames, IA.

Amorphous carbon (a-C) films over a wide range of densities can be obtained experimentally by using a variety of deposition techniques. To investigate the change in properties of such films as a function of density, we have generated a-C structures with densities from 1.0g/cm3 to 3.4g/cm3 using tight-binding molecular dynamics simulations. The structural, vibrational and electronic properties of these structures are compared with those of amorphous carbon films obtained experimentally.

9:30 AM *AA1.2 

We report on quantum molecular dynamics simulations of C deposition on a semiconducting surface [1]. Our results show that under certain deposition conditions, C's act as building blocks on a nanometer scale to form a thin film of nearly defect-free molecules. The C's behave as carbon superatoms, with the majority of them being three- or four-fold coordinated, similar to carbon atoms in amorphous systems. The microscopic structure of the deposited film supports recent suggestions about the stability of a new form of carbon, the hyperdiamond solid. Furthermore we present the results of a compartive study of ordered and disordered C solids, which have been studied mimicking gas phase deposition conditions [2].

10:30 AM *AA1.3 
GENERATING STRUCTURAL MODELS OF AMORPHOUS TETRAHEDRAL CARBON. Peter A. Schultz, E. B. Stechel, Sandia National Laboratories, Albuquerque, NM.

We present the results of a systematic first-principles investigation of the requirements for developing reliable structural models for amorphous tetrahedral carbon (atC), and relate those structural models to physical properties of this material. Within a linear combination of atomic orbitals formulation of density functional theory, we show that to treat accurately the highly defected local structures found in atC requires large variational flexibility within the basis used to represent the carbon atoms. A key figure of merit, the proportion of three-fold atoms, can triple in going from a minimal basis to a high quality basis. The challenge stems from two principal sources. First, it is necessary to accurately describe the relative energetics of a wide variety of highly defected local structures. Second, it is necessary to have sufficient variational flexibility to negotiate transition regions between different bonding topologies, and relax to lower energy structures. The basis-converged calculations agree well with experimental observables, such as the presence of four-member rings, the lack of dangling bonds, and a gap. However, they predict a much larger proportion of three-fold atoms than estimated from simple analyses of EELS and neutron scattering experiments. We show that the larger proportion of three-fold atoms is indeed consistent with the properties of atC, and imply that there are flaws in the simplifying assumptions that go into constructing experimental estimates of coordination numbers. These results highlight the perils of assuming highly simplified models for atC before the correct physics has been identified and built into the models. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DEAC0494AL85000.

11:00 AM AA1.4 
AN AB-INITIO STUDY OF NITROGEN INCORPORATION INTO CARBON SYSTEMS: DOPING & NITRIDE FORMATION. G. Jungnickel, J. Widany, F. Weich, P. Sitch, Th. Frauenheim Technische Universität, Institut für Physik, Chemnitz, GERMANY.

The study of the behavior of nitrogen in carbon systems is an arc of intense material research. These are two main goals to be addressed: the shallow n-type doping of diamond or any other hard carbon modification and the formation of theoretically predicted low-compressibility C3N4 crystalline forms. Since despite considerable efforts both problems remain still unsolved, we are going to study the chemistry of nitrogen incorporation into crystalline as well as amorphous modifications on an atomistic level by using the density-functional molecular-dynamics method. At low N-concentrations, 15% and high mass densities of 3.0 to 3.5 g/cm3, the highly tetrahedral amorphous carbon can be regarded as heavily N-doped ta-C material. The N's are merely substituted into the network, binding to both sp2 and sp3 carbon. However, shallow doping quality is never achieved, since donated electrons are lost into deep C-defects and/or *-states. As the result the Fermi-energy shifts towards midgap. A very similar situation can be shown to prevent any N n-type doping of CVD diamond as well, strongly violating the electronic device quality of the diamond films. Since other atom types due to their low solubilities provide no alternative, we are going to predict novel sp2-bonded, wide band gap, hard forms of carbon. By the occurance of isolated strong double bonds alternating with single bonds they provide favorable bonding constraints to accommodate both N & B as shallow substitutional dopants. Focusing further on high-density amorphous materials at 3:4 CN-composition, we observe clear trends counteracting the formation of low-compressibility crystalline phases; (i) N-incorporation strongly catalyzes C-undercoordination; (ii) the maximum achieved averaged C- & N-coordinations are 3 & 2 rather than 4 & 3; (iii) there are strong tendencies towards paracyanogen-like bonding which isoenergetically compete with the desires /-C3N4 formation.

11:15 AM AA1.5 
DOPING MECHANISM IN TETRAHEDRAL AMORPHOUS CARBON. Chun-Wei Chen, J Robertson, Cambridge University, Engineering Department, Cambridge, UK.

It is known that tetrahedral amorphous carbon (ta-C) can be doped n-type by nitrogen and now p-type by boron [1,2]. However, the doping efficiency is low as is common in amorphous system. There are various possible reasons for this; for example, N could form the compensated-charged dangling bond complexes, similar to the Street mechanism in a-Si:H[3].We have carried out total energy calculations for various configurations of N in carbon networks and find that unlike in a-Si:H, N prefers to form neutral compensating complexes, such as the pyrrole structure or the =C=N- structure. On the other hand, charged midgap defects are not favored in ta-C because of the high correlation energy [4]. This means that luminescence will not be degraded by doping in ta-C.

11:30 AM AA1.6 
NATURE OF GRAIN BOUNDARIES IN NANOCRYSTALLINE DIAMOND BY ATOMISTIC SIMULATIONS. P. Keblinskia,b, D. Wolfa, S.R. Phillpota, and H. Gleiterb, aMaterials Science Division, Argonne National Laboratory, Argonne, IL; bForschungszentrum Karlsruhe, Karlsruhe, GERMANY.

Using atomistic simulation, we found that most grain boundaries in nanocrystalline diamond, are highly disordered and contain up to 80% of the atoms exhibiting local sp2 bonding. This is consistent with the results of Raman spectra of nanocrystalline diamond films showing the presence of 1-2% of sp2-bonded carbon that can be assigned to the atoms residing at the grain boundaries. We find that despite the large fraction of carbon atoms in the grain boundaries being three coordinated they are poorly connected to each-other, therefore, graphite-like electrical conduction through the grain boundaries is unlikely without `'bridging'' impurities. Surprisingly, based on their fracture energies, the high-energy, large unit-cell boundaries are more stable against brittle decohesion into free surfaces than low-energy ones and perhaps even the perfect crystal.

Chairs: William I. Milne and Michael P. Siegal 
Tuesday Afternoon, December 2, 1997 
St. George B/C/D (W)

1:30 PM *AA2.1 
RAMAN SPECTROSCOPY OF AMORPHOUS CARBON. D.R. Tallant, T.A. Friedmann, N. Missert, M. Siegal and J. Sullivan, Sandia National Laboratories, Albuquerque, NM.

Traditional forms of inorganic carbon include diamond and graphite. Modem preparation techniques. including chemical vapor deposition (CVD), pulsed laser deposition (PLD) and filtered arc processes have produced new forms of inorganic carbon related to, but distinct from, diamond and graphite. These new forms include CVD diamond, diamond-like-carbon (DLC), fullerenes and nanotubes, and amorphous carbon. Raman spectroscopy has a powerful capability to discriminate between these materials and yield insight into their structure. As an introduction to the Raman spectroscopy of amorphous carbon, I will review the distinguishing structural and compositional aspects of the various forms of inorganic carbon and show how their structures are expressed in Raman active vibrational modes. Raman spectroscopy can not only distinguish amorphous carbon from other inorganic species but has helped to confirm that amorphous carbon includes a range of structural species. These structural species are characterized by differences in their ratios of sp3 to sp2 bonding, among other factors. I will show how the structural variations of amorphous carbon are expressed in their Raman spectra and how they correlate to preparation conditions and important physical properties, such as hardness, transparency, resistivity and field emission. I will describe how resonance enhancement affects the Raman signature and that its involvement in the Raman scattering process makes it important how the Raman experiment is carried out. Finally I will describe a simple model involving sp2-bonded ring structures, which appears to be consistent with at least some aspects of amorphous carbon structure. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-ACO4-94AL85000.

2:00 PM AA2.2 
QUANTITATIVE STUDIES OF TETRAHEDRAL BONDING IN AMORPHOUS CARBON FILMS USING ULTRAVIOLET RAMAN SPECTROSCOPY. Kai Gilkes, East Anglia Univ, School of Physics, Norwich, UNITED KINGDOM; Howard Sands and David Batchelder, Leeds Univ, Dept of Physics, Leeds, UNITED KINGDOM; John Robertson and Bill Milne, Cambridge Univ, Dept of Engineering, Cambridge, UNITED KINGDOM.

Amorphous carbon films deposited using medium energy ion beams can contain up to 85% sp3 sites, and have found applications as protective coatings and electron emitters. Recently, the presence of sp3 sites in films deposited from a filtered cathodic vacuum arc was observed directly for the first time using ultraviolet Raman spectroscopy with 244 nm excitation (K.W.R. Gilkes et al, Appl. Phys. Lett. 70 (1997), 1980). In this paper we present a quantitative analysis of the ultraviolet Raman spectra in terms of the relative contribution from and bonds in the material, and use this to discuss the changes observed in the spectra when the ion energy - and hence sp3:sp2 ratio - is varied.

2:15 PM *AA2.3 
ANALYSIS AND MODIFICATION OF AMORPHOUS AND PARTIALLY-CRYSTALLINE THIN FILMS. N. J. DiNardo, T. W. Mercer, Drexel Univ, Dept of Physics, Philadelphia, PA; L. J. Martinez-Miranda, Univ. of Maryland, Dept of Nuclear and Materials Engineering, College Park, MD; M. P. Siegal, T. A. Friedmann, J. R. Sullivan, Sandia National Laboratory, Albuquerque, NM; R. V. Plank, J. M. Vohs, Univ of Pennsylvania, Dept of Chemical Engineering, Philadelphia, PA.

Thin films of light atomic weight elements in amorphous, partially-crystalline, or crystalline forms have applications in a broad range of technologies. For example, amorphous tetrahedral carbon (a-tC) and polymeric thin films impact electronic materials technology as electron- and light-emitting device elements, respectively. A lack of crystallinity introduces complexity in the experimental and theoretical characterization of these materials but is not necessarily a limiting factor in their performance. While the growth process is clearly a major factor governing the physical properties of a film, interactions with the substrate are also important, so surface and interface analysis provides an important complement to bulk measurements. Currently, the fundamental and applied aspects of the atomic, electronic, and vibrational structure of these complex materials are being elucidated by novel approaches combining a variety of experimental techniques with theoretical calculations. This paper focuses on several approaches in the characterization and modification of thin films made possible by recent experimental advances. The structural and electronic properties of two model systems are considered as examples: a-tC thin films grown by pulsed laser deposition (PLD) and polyaniline thin films grown by vapor deposition. First, scanning probe microscopies and x-ray scattering are used to investigate the structural aspects of a-tC films as a function of PLD growth conditions. The possible connection of nanoscale surface modification and characterization with electron emission properties will be discussed. Second, high resolution inelastic electron scattering spectroscopy and other surface techniques are used to obtain information on both interfacial aspects of the growth of polyaniline thin films and the microscopic and macroscopic aspects of electrical conductivity upon doping. Comparisons will be made with other studies that address properties of analogous crystalline systems as appropriate. A brief assessment of the broader problem of analyzing these systems will be given. We acknowledge funding from the Department of Energy and the National Science Foundation.

3:15 PM AA2.4 
CHARACTERIZATION OF COVALENTLY BONDED NANOSTRUCTURED MATERIALS USING SYNCHROTRON-BASED CORE-LEVEL PHOTOABSORPTION AND FLUORESCENCE. J.A. Carlisle, Virginia Commonwealth University, I. Jimenez, D.G.J. Sutherland, and L.J. Terminello, Lawrence Livermore National Laboratory, T.A. Callcott, University of Tennessee, D.L. Ederer, Tulane University.

Over the past several years, we have devoted much effort toward developing synchrotron-based techniques for the characterization of robust material systems, in particular nanostructured materials. These materials are difficult to characterize due to their inherent lack of long-range order, which renders commonly used techniques such as x-ray diffraction and Raman spectroscopy ineffective. Synchrotron-based techniques, such as core-level photoabsorption (also know as NEXAFS or XANES) and soft-x-ray fluorescence (SXF), overcome these difficulties since they are direct probes of the local bonding structure. These techniques also permit element-specific bonding information to be obtained, making them capable of probing the bonding structure of multi-elemental systems (such as boron nitride and gallium nitride) in an element-selective way. In this presentation, we demonstrate the use of these techniques to characterize various nanostructured thin film systems, concentrating on CVD diamond, diamond-like, and boron nitride thin flims. Each of these systems present difficulties, owing to their disordered nature, in correlating growth conditions to desired material properties.

3:30 PM AA2.5 
TEM AND EELS INVESTIGATION OF AMORPHOUS DIAMOND COATED FIELD EMITTERS. A.F. Myers, M.Q. Ding, S. M. Camphausen, W.B. Choi, J.J. Cuomo and J.J. Hren, Materials Science and Engineering Dept, North Carolina State University, Raleigh, NC; E.B. Steel, Surface and Microanalysis Science Div, Chemical Science and Technology Laboratory, NIST, Gaithersburg, MD.

The microstructure of amorphous diamond films deposited on Mo field emitters by pulsed laser ablation and by cathodic arc deposition techniques was studied using transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Undoped films and films doped with nitrogen and with phosphorous were included in this study. Both the undoped and N-doped carbon films deposited by laser ablation showed improved electron emission characteristics as compared to the same uncoated Mo needles. The cathodic arc deposited films showed similar improvements in the emission properties. The EELS spectra and TEM images were recorded with a Philips CM300 FEG TEM, equipped with a Gatan parallel acquisition EELS spectrometer. The operating voltage was 300 keV. TEM showed that the emitters were uniformly coated and that a columnar microstructure usually existed in the films. The sp2/sp3 content of the coatings was determined from EELS spectra using Bruley's two-window technique; graphitized carbon was used as the calibration standard. The coating microstructure and the concentration of sp2 to sp3 carbon bonds in the films will be presented and discussed in relation to the observed electron emission improvements.

3:45 PM AA2.6 

Amorphous tetrahedrally-coordinated carbon films contain both 4-fold and 3-fold coordinated carbon atoms. First principles calculations reveal that the 3-fold coordinated atoms link up to form chain-like structures in a matrix of predominantly 4-fold coordinated carbon. When the films are annealed at temperatures above 100 degrees Celsius, the concentration and/or distribution of 4-fold and 3-fold atoms are altered, leading to large changes in electrical conductivity. We have combined measurements of the thermal evolution of electrical conductivity with stress relaxation measurements to deduce the electronic transport mechanism in these materials. The change in electrical conductivity following annealing is found to be exponentially proportional to the deduced change in 3-fold atom concentration. This indicates that the electrical conductivity in these films is determined by carrier tunneling (i.e. hopping transport), which leads to an intrinsic heterogeneity in current conduction through the film. Regions of enhanced current conduction are expected along preferred hopping pathways, with reduced current elsewhere. This heterogeneity in electronic transport within the film can also be significant for surface and interface electronic transport processes. Sandia is a multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Co., for the U.S. Dept. of Energy under Contract DE-AC04-94AL85000.

4:00 PM AA2.7 
PHOTOCONDUCTIVITY OF DIAMOND-LIKE CARBON. A. Ilie, M. Rattier, N. Conway, B. Kleinsorge, J. Robertson, W.I. Milne, Engineering Dept, Cambridge University, Cambridge, UNITED KINGDOM.

We have investigated the photoconductivity in tetrahedrally bonded amorphous carbon (ta-C) and hydrogenated ta-C (ta-C:H) in the undoped films and as a function of nitrogen and boron doping. Transport and recombination parameters were derived from the data. Ta-C(:H) are found to be low mobility solids with a #215#u product of order 10-12 cm2/V. The photoconducitvity shows a sublinear dependence on light intensity over awide temperature range. The photon energy was varied, to study the effect of exciting into the extended states at higher energy. This is the first thorough study of photoconductivity in diamond-like carbon.

4:15 PM AA2.8 
OPTICAL PROPERTIES OF CARBON THIN FILMS CONTAINING NANOPARTICLES. M Chhowalla, K G Lim, A I Munindradasa, I Alexandrou and G A J Amaratunga , University of Liverpool, Dept of Elec Eng and Electronics, Liverpool, UNITED KINGDOM.

The incoporation of carbon nanoparticles in the forms of nanotubes and bucky onions have shown to improve the mechanical properties of amorphous carbon (a-C) thin films. In this paper we report on the change in the optical properties of a-C films containing nanoparticles. Here we study the optical band gap, index of refraction and extinction coefficient of these films. The optical band gap in highly tetrahedral amorphous carbon (ta-C) is found to be around 2 eV. The gap decreases almost linearly with the sp fraction. It is theorized that the clustering of the sp sites leads to a reduction in the band gap. In this paper, we study the influence of large sp clusters in forms of graphitic nanoparticles on the optical of ta-C. We find that the optical gap remains around 1.8 eV even with the large inclusions of clustered nanoparticles. Furthermore, the gap remains close to 1.8 eV even when the sp fraction in the amorphous carbon is increased. The index of refraction however is found to decrease with the sp fraction indicating a reduction in density.

4:30 PM AA2.9
INVESTIGATION OF THE OPTICAL AND ELECTRICAL PROPERTIES OF DOPED AND UNDOPED DIAMOND-LIKE CARBON FILMS. Bo K. Kim and Timothy A. Grotjohn, Michigan State University, Dept. of Electrical Engineering, East Lansing, MI.

The deposition conditions used to produce diamond-Iike carbon films permit the deposition of films with a wide variation in properties including optical adsorption, refractive index, and electrical conductivity. This paper reports on the optical and electrical properties of diamond-like carbon films as a function of the deposition conditions. The films studied were deposited using an ECR plasma source with an rf biased substrate holder. Deposition conditions varied included rf bias power, source gas mixture and flow rate, and substrate temperature. The nominal deposition conditions utilized include an input gas mixture of methane and argon, pressure of 2-10 mTorr, and rf induced bias of 50-200 volts. Additionally, various dopants/impurities were introduced including nitrogen and boron. The deposition plasma conditions were characterized via several diagnostics including induced bias on the substrate and ion flux to the substrate. The films deposited were characterized a variety of ways including mass density, infrared absorption, Raman spectrum, visible absorption, refractive index, electrical conductivity, and photoconductivity measurements. This paper will report on the correlations between the deposition reactor input conditions, film composition, optical properties, and electrical properties for diamond-like carbon films.

Chairs: David McKenzie and John Robertson 
Wednesday Morning, December 3, 1997

8:30 AM *AA3.1 
CARBON FILMS FOR FIELD EMISSION DISPLAY APPLICATIONS. B.F. Coll, J.E. Jaskie, and A.A. Talin, Motorola Phoenix Corporate Research Laboratories, Tempe, AZ.

Filtered cathodic vacuum arc (FCVA) is a unique PVD tool capable of depositing carbon films with a wide range of properties and compositions. Depending on the growth conditions, films consisting of tetrahedral, amorphous carbon (t-aC), nanotubes in an amorphous matrix, and carbon nitride (C:N) can be synthesized. In this paper we report on several types of carbon films deposited at Motorola by FCVA for application in `next-generation', low-voltage field emission displays (FEDs). We describe the microstructure, surface morphology, chemical bonding, and the electron emission characteristics of these films as studied by a variety of techniques, including HRTEM, EELS and Raman spectroscopy. We present the emission results in the context of FED requirements.

9:00 AM *AA3.2 
FORMATION OF AMORPHOUS DIAMOND FILMS BY ENERGETIC CONDENSATION. J.J. Cuomo, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC.

Trends in recently reported data on high sp3 fraction (up to 95%), non-hydrogenated amorphous carbon films deposited by ion beam sputtering and laser vaporization are examined. The degree of sp3 film character is found to depend upon the deposition technique as well as the substrate temperature and thermal diffusivity. The data suggest that the combination of incident particle kinetic energy, surface accommodation, and angle of incidence determine the physical properties of the resultant film. A model is proposed for the condensation of energetic carbon atoms into the amorphous diamond (t-aC) in which a quench-type surface accommodation mechanism is operative. Hard carbon films can be prepared by the condensation of energetic carbon species at and below room temperature. These amorphous films are primarily tetrahedrally coordinated and contain high fractions of sp3 bonding leading to the terminology amorphous diamond (t-aC). Field emission from these and other forms of carbon has been considered previously, but is generally unstable or based on surface treatments which limit their operating conditions. We report electron emission from nitrogen doped amorphous diamond and Cs containing amorphous diamond films. The amorphous Cs carbon composite films showed electron emission at applied fields as low as 7 Volts per micron. This emission characteristic is relatively insensitive to surface treatment; films left under ambient laboratory environment for more that six months show these favorable characteristics with no pretreatment. The fabrication process and emission properties of these films are described.

9:30 AM AA3.3 
MODELLING OF THE ION BEAM DEPOSITION PROCESS OF COVALENTLY BONDED DIAMONDLIKE MATERIALS. H.C. Hofsäss, M. Sebastian, H. Feldermann, R. Merk and C. Ronning, Fakultät für Physik, Universität Konstanz, Konstanz, GERMANY.

Thin films of tetrahedrally bonded amorphous carbon (ta-C), cubic boron nitride (c-BN) and related compounds are commonly grown by deposition of energetic ions For the case of ta-C deposited by mass selected ion beam deposition (MSIBD) a characteristic energy and temperature dependence of the fraction of sp3-bonded atoms was experimentally observed. The sp3-fraction reaches a maximum above 80% for ion energies between 100 and 200 eV and decreases slowly to about 40-50% at an ion energy of 2 keV. Qualitatively, the phase formation can be described by the subplantation model as a volume process far from equilibrium. Simple quantitative models assuming point-like energy deposition, however, do not explain the observed energy dependence. In this contribution, we present a quantitative interpretation of the subplantation model, which takes into account the processes of energy deposition and energy dissipation in more detail. In our model, rearrangement of atoms during a thermal-spike is the dominant mechanism for the formation of the diamond-like phase We apply this model to the ion beam deposition of ta-C and show that the formation of a dense sp3-bonded ta-C phase requires a large number of reordering processes to achieve complete rearrangement of atoms within the ion impact volume. This is opposite to previous interpretations of the subplantation model.

10:15 AM *AA3.4 
RESIDUAL STRESS IN AMORPHOUS- TETRAHEDRAL CARBON FILMS#253#. T. A. Friedmann, Sandia National Laboratories, Albuquerque, NM.

Amorphous tetrahedral carbon (a-tC) films grown at room temperature typically have residual compressive stresses of 6 - 10 GPa. Stress induced spallation limits the ultimate film thickness to < 200 nm, severely limiting the utility of a-tC films. We have found a way around this problem. Namely, a-tC films annealed for short times at 600 #176#C relax to near zero residual stress. Surprisingly, Raman and EELS spectra of the films before and after annealing are nearly identical indicating the a-tC retains its idiamond-likei character. This information has been used to grow micron thick, stress free a-tC films by repeated room temperature deposition and annealing. These films show hardness and stiffness approaching that of crystalline diamond with excellent wear properties. In addition, an in situ technique for measuring changes in wafer curvature with time has been used to measure the stress build up during growth, and subsequent relaxation during annealing of a-tC films grown by pulsed laser deposition. The stress buildup is directly correlated with the laser fluence, indirectly supporting the isubplantationi growth model. The relaxation data show evidence of multiple energy-barrier heights that are activated with increasing temperature. A simple model of the stress relaxation will be presented that is consistent with the data, and that has been used to fit transport data measured on annealed a-tC films.

10:45 AM AA3.5 
STRUCTURAL CHARACTERIZATION OF THE THERMAL EVOLUTION OF TETRAHEDRALLY COORDINATED AMORPHOUS CARBON FILMS. L.J. Martinez-Miranda, University of Maryland, College Park, MD; J.P. Sullivan, T.A. Friedmann and M.P. Siegel, Sandia National Laboratories, Albuquerque, NM; N.J. DiNardo, Drexel University, Philadelphia, PA.

We present the results of a structural analysis of tetrahedrally coordinated amorphous carbon films (a-tC) prepared by pulsed laser deposition (PLD), using different post-deposition annealing temperatures. Five a-tC samples, as deposited, and annealed at 200C, 300C, 4000C, 500C and 600C respectively, were studied using combined xray reflectivity and low angle scattering measurements. The critical angle was used to extract an average film density for the films. The resulting scans were fit to obtain a better value of the density of the films, as well as the thickness and roughness of both film and interface. The fitted densities were slightly larger than those obtained directly from the critical angle, they decrease as a function of increasing annealing temperature, following the same trend observed directly from the scans The roughness of both the film surface and the interface increases at 200C and 300C. This is followed by further interface and film evolution a annealing temperatures greater than 400C. The density of the interface decreases at higher annealing temperature, suggesting the evolution of a ``reaction'' layer. Analysis of the reflectivity signals is consistent with both the evolution of a multilayer structure or a striped domain structure.

11:00 AM AA3.6 
CATHODIC ARC DEPOSITION OF TETRAHEDRAL AMORPHOUS CARBON: INFLUENCE OF PROCESS PARAMETERS ON MICROSTRUCTURE AND HARDNESS. S.P. Bozeman, D.A. Baldwin, D. Chacko-Davis, Commonwealth Scientific Corporation, Alexandria, VA; S.M. Camphausen, J.J. Cuomo, North Carolina State University, Raleigh, NC.

The cathodic arc provides a method for depositing extremely hard thin carbon films. These films are potentially useful in a variety of tribological applications including protection of magnetic media and recording heads. Effective application of this technology requires an improved understanding of the influence of process parameters on the microstructure and hardness of the deposited films. Previous deposition on nanoscale needles [1] indicated that deposition at oblique angles results in a more graphitic film with a columnar microstructure. In this work, we use a commercially available filtered cathodic arc to deposit tetrahedral amorphous carbon at several deposition angles, bias voltages, and arc currents. We will present information on the microstructure obtained via TEM, the hardness using nanoindentation and deposition rate via film thickness measurements.

11:15 AM AA3.7 
INFLUENCE OF ANNEALING ON THE MICROSTRUCTURE OF AMORPHOUS CARBON THIN FILMS FOR MAGNETIC HARD DISKS. Ainissa G. Ramirez, Robert Sinclair, Stanford University, Dept. of Materials Science and Engineering, Stanford, CA.

Amorphous carbon thin films used as protective coatings for magnetic hard disks were annealed at temperatures up to 500C. The associated microstructural changes were analyzed by in situ transmission electron microscopy (TEM), Raman Spectroscopy, and near-edge x-ray-absorption fine structure (NEXAFS) techniques. TEM micrographs show that the amorphous carbon films in contact with the magnetic media increases in graphitic content with annealing. Raman spectra of these films confirm these observations with corresponding changes of Stokes scattering peaks for amorphous carbon. These changes include: an increase in the intensity ratio, ID/IG, which is associated with crystal size/number, and an upward shift of the G-peak, which is associated with the graphite content. NEXAFS measurements indicate the bond-lengths of the films approach graphite at temperatures near 500C. The microstructural changes observed at these temperatures suggest that the metals of the magnetic layers mediate a graphitic transformation, which is similar to the behavior of other eutectic metal-metalliod systems (e.g. Al-Si, Ag-Ge).

11:30 AM AA3.8 
TRIBOCHEMICAL REACTIONS OF Si INCORPORATED DIAMOND-LIKE CARBON FILMS DURING THE INITIAL TRANSIENT PERIOD. Myeong-Geun Kim, Kwang-Ryeol Lee and Kwang Yong Eun, Thin Film Research Center, Korea Institute of Science and Technology, Seoul, KOREA.

Recently, it was reported that Si incoporation to diamond-like carbon (DLC) films reduces the environmental dependence of the tribological behaviors and results in extremely low friction coefficient of less than 0.05 against steel ball. Combined with better adhesion to steel substrates, the Si incorporated DLC (Si-DLC) films have been considered as a strong candidate for low friction wear resistant layers. Previous investigations on the tribochemical reaction suggested that hydrogenated silica debris or hydrophobic surface of Si-DLC is the main reason for the better tribological properties. However, any suggestion is yet to be generally accepted. In the present paper, we report the tribochemical reactions between Si-DLC and steel ball during the initial stage of the tribotest. The films were deposited by RF PACVD using mixtures of silane and benzene gases. Si concentration in the film was varied from 0 to 10 at.% by adjusting the silane fraction in the reaction gases. Ball-on-disk type wear rig was employed for the tribo-test in ambient atmosphere. When Si concentration was less than 5 at.%, initial transient period of high friction coefficient of about 0.2 was commonly observed. However, the initial transient period becomes shorter as the Si concentration increased. With increasing the contact cycles, the friction coefficient decreased to less than 0.1. Auger spectra analysis of the debris showed that only iron oxide debris formed when the friction coefficient was high. However, the decrease in the friction coefficient after the transient period is associated with the formation of silicon oxide debris. It was also observed that surface roughness of the film affects the debris formation behavior and thus the initial transient behavior of the friction coefficients. The mechanism of the tribological behaviors of Si-DLC films will be discussed in terms of the present observations.

Chair: Thomas A. Friedmann 
Wednesday Afternoon, December 3, 1997 
St. George B/C/D (W)

1:30 PM AA4.1 
RELATIONSHIP BETWEEN NUCLEATION AND GROWTH AND MICROSTRUCTURE OF CUBIC BORON NITRIDE FILMS. Kevin F. McCarty, Douglas L. Medlin, and Paul B. Mirkarimi*, Sandia National Laboratories, Livermore, CA.

Boron nitride films are commonly grown using energetic deposition conditions generated by ion- or plasma-assisted processes. For low-energy conditions, graphite-like turbostratic BN (tBN) is produced, and grows with either random orientation or with its basal planes parallel to the substrate. For more energetic conditions, the tBN basal planes are perpendicular to the substrate, as first observed by McKenzie and coworkers. For even more energetic conditions, cubic BN (cBN) is nucleated, but only after a layer of oriented tBN is formed. The degree of crystallographic order in both tBN and cBN is also affected by growth temperature. For sufficiently low temperature, only tBN is formed. With increasing temperature, the order within the graphitic planes of tBN increases. Above some threshold temperature, cBN can grow but not nucleate. At yet higher temperatures (about 150C), cBN can be nucleated as well as grown. High-temperature growth (i.e., 1000C) gives columnar cBN grains, showing that grain growth occurs. We will discuss how energetic deposition causes the tBN basal planes to be normal to the substrate. We will also discuss possible mechanisms of cBN growth and nucleation, showing that the texture and microstructure of both the tBN and the cBN can be explained through reasonable models.

1:45 PM AA4.2 
BORON NITRIDE COATINGS AND MATERIALS FOR USE IN AGGRESSIVE ENVIRONMENTS. Theodore M. Besmann, Woo Y. Lee, Jack P. Young, and Haiming Xiao, Oak Ridge National Laboratory, Oak Ridge, TN.

Boron nitride coatings and structures have demonstrated significant resistance to many corrosive environments. These coatings may have application in the protection of sensors needed for measuring a variety of properties such as temperature and chemistry. In addition, boron nitride materials may offer advantages as structural materials in high temperature materials processing.

2:00 PM AA4.3 
EFFECTS OF ALN ADDITIONS ON THE STABILIZATION OF CUBIC BORON NITRIDE THIN FILMS. Wilfredo Otaño, Russell F. Messier, Lawrence J. Pilione, Materials Research Laboratory, Pennsylvania State University, University Park, PA; Peter F. Carcia, Dupont Central Research and Development, Experimental Station, Wilmington, DE.

The addition of AlN during the deposition of boron nitride thin films is of interest both technologically and scientifically. Aluminum nitride acts as a catalyst in the high pressure/high temperature synthesis of cubic boron nitride where it has been suggested that the packing arrangement of the terminating nitrogen atoms is an epitaxial layer for BN growth. Since the nitrogen sublattice of the cubic phase of BN is fcc, the epitaxial relationship to AlN wurtzite-type seed layers is 5.1 of in-plane misfit for cBN(111)//AlN(0001). Boron nitride thin films were sputtered and AlN added to investigate its effect on the stabilization of the cubic phase. The BN films were deposited on Si (100) substrates by rf unbalanced magnetron sputtering. The deposition pressure was fixed at 2 mTorr and a composition of 10 nitrogen in argon gas was used. In a typical deposition process a hexagonal BN target is rf sputtered while the substrate is biased using a low frequency (218 kHz) dc pulsed excitation signal. A threshold of negative bias voltage at the growing film is defined below which the cubic phase of boron nitride is not stabilized. Films with over 80 of the cubic phase, as measured by FTIR, are deposited for negative bias voltages over that threshold value. A second low frequency dc pulsed power supply was used to reactively sputter the aluminum. AlN was added as an interlayer between the Si substrate and the BN film as well as co-deposited at different sputtering powers. The films were prepared with negative bias voltages close to the threshold value for the cubic phase stabilization. The results of this study and the implications for the stabilization of cubic boron nitride films will be presented.

2:15 PM AA4.4 
PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION OF COVALENT BN-C-H ALLOYS. Z.L. Akkerman, F.W. Smith, Physics Department, City College of the City University of New York, New York, NY.

A plasma-enhance chemical vapor deposition (PECVD) process has been developed for deposition of amorphous alloys of general composition (NBN)xCyHz, Borazine B3N3H6 has been used as a possible stoichiometric source of B and N and acetylene C2H2 as a source of carbon. Uniform transpatert films have been deposited on silicon and quartz with growth rates up to 10 /s at deposition temperatures T250C, operating pressures P 0.1 Torr, and RF power densities 1.1 W/cm. A study of the optical properties of the alloys in the IR and UV-VIS regions has been performed. IR spectra of the alloys indicate vibrations of B-N bonds in planar configuration, unsaturated C-C bonds, as well as B-H, C(sp3)-H, and N-H bonds. UV-VIS spectroscopy has shown that the energy gap of the alloys can be varied by changing the flow ratio of borazine/acetylene in a wide range from 2 up to more than 4 eV. The index of refraction is n2. The mechanical and optical properties of the films evidently show that although separation of B-N and C-C bonds seems to take place, in accordance with our previous predictions, the BN network is significantly influenced by carbon and develops a variety of orientations of the BN sheets. As a result the alloys are much harder thant the PECVD hexagonal boron nitride films prepared without carbon and thus can find important applications as dielectric materials and protective transparent coatings.

3:00 PM AA4.5 
ENERGETIC DEPOSITION OF AMORPHOUS TETRAHEDRAL CARBON NITRIDE FILMS. Jiangtao Hu, Peidong Yang, and Charles M. Lieber, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA.

The growth and properties of carbon nitride films prepared by plasma-assisted pulsed laser deposition have been investigated over a range of reactant energetics and growth temperatures. Time-of-flight mass spectroscopy has been used to characterize systematically the reactant species and energy distributions within the carbon ablation plume as a function of laser fluence and the nitrogen plasma. Carbon nitride films have been grown over a similar range of conditions, and the composition and local atomic structure have been characterized using RBS and electron energy loss spectroscopy (EELS). These studies demonstrate for the first time a well-defined correlation between reactant energetics, nitrogen composition and the fraction of tetrahedral (sp3-bonded) carbon, and identify a nitrogen induced relaxation process in the materials. Electronic structure calculations have been carried out to quantify these results.

3:15 PM AA4.6 

3:30 PM AA4.7 

Amorphous carbon-nitrogen (a-CNx) films deposited onto Si substrates by rf-magnetron sputtering were annealed in vacuum at temperatures between 300 and 800 during 30 minutes. No kind of sequential treatment was performed. The modifications on the film microstructure were monitored by infrared spectroscopy (IR), while the composition and the atomic density were determined by Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). The internal stress was determined by measuring the film-induced bending of the substrates, and the hardness was measured by nanoindentation. The tribological investigation was carried out by means of atomic force microscopy techniques, providing the friction coefficient and the surface roughness. IR spectra show a broad absorption band between 1200 and 1800 cm-1 that corresponds to the D and G Raman bands, typical of a-C films, which become IR active due to nitrogen incorporation. The ratio between the D and G bands increases with the annealing temperature, indicating an increase of the number, or size, of the graphitic domains. The intensity of the band at 2200 cm-1, attributed to a C-N terminating bond, also increases with the temperature. ERDA and RBS results show that oxygen and hydrogen losses occur at low-temperature suggesting that this contamination was due to water molecules trapped in the film. IR results support this interpretation. Nitrogen loss occurs only at temperatures higher than 600. At this temperature, a sharp increase of the film density occurs. The as-deposited a-CNx film is a soft material (paracyanogen-like with hardness of 1 GPa). However, its hardness, and also the internal stress, increase by a factor of six in samples annealed at 700. On the other hand, a reduction of a factor of two in the friction coefficient was determined. These data show that the thermal treatment of a-CNx films results in a more dense and harder material.

3:45 PM AA4.8 
DEPOSITION OF CARBON NITRIDE FILMS BY AN INDUCTIVELY-COUPLING-PLASMA SPUTTERING METHOD. Chia-Yun Hsau, Liang-Yih Chen, Yong-Hau Foo, Franklin Chau-Nan Hong, Dept. of Chemical Engineering, National Cheng kung Univ., Tainan, TAIWAN, R.O.C.

Carbon nitride films have been deposited on Si in an inductively-coupling-plasma (ICP) sputtering system by employing N2 gas and a graphite target to avoid the presence of hydrogen. Optical emission spectroscopy (OES) is employed to characterize the gas species excited by ICP during deposition. The effects of RF power, substrate bias, substrate temperature, total pressure and the C/N2 ratio in the gas are being studied. The results show that the ratio of the amounts of CN single bond to CN triple bond, characterized by Fourier transformation infrared (FT-IR) increases with increasing the RF power. OES observes the same trend of increase in the dissociation and ionization of N2 in ICP. The high concentration of N radicals produced by the high plasma density of ICP seems to favor the formation of CN single bond. Nitrogen composition of the film increases with decreasing the substrate temperature or the substrate bias, and various from 12 to 45. However, the ratio of the amounts of CN single bond to CN triple bond increases with increasing the negative substrate-bias from 0 to -150V. The [CN single bond]/[CN triple bond] ratio decreases with increasing the substrate temperature from 200 to 500C. But the ratio increases with increasing the substrate temperature above 550C although CN single bond composition remains constant, indicating that CN triple bond is not as stable as CN single bond at high temperature.

Chair: Thomas A. Friedmann 
Wednesday Afternoon, December 3, 1997 
4:00 P.M. 
St. George B/C/D (W)

OPTICAL AND ELECTRONIC PROPERTIES OF CARBON NITRIDE THIN FILMS. M. Chhowalla, R.A. Aharanov, G.J. Amaratunga and C.J. Kiely, Univ of Liverpool, Dept of Elec Eng & Electronics, Liverpool, UNITED KINGDOM.

We have deposited carbon nitride (CNx) films by magnetron sputtering at varying nitrogen pressures and substrate temperatures. The films were deposited on silicon, quartz and glass substrates simultaneously. The incoming ion energy was controlled by a radio frequency power supply. A magnet in front of the substrate holder was used to enhance the plasma density. The films deposited at room temperature (RT) were found to have nitrogen content of 40%. These films were semiconducting with an optical bandgap of 2 eV and a RT resistivity of 1012 -cm. CN0.35 films deposited at high substrate temperature (400 - 600oC) were found to be extremely hard (60 GPa) and elastic (elastic recovery of 90 %). The most interesting result we found was that the hard and elastic CN0.35 were also semiconducting with an optical band gap of 1.7 eV, RT resistivity of 1010 -cm and an activation energy of 0.8 eV. In this paper we correlate the novel electrical and optical properties of these CNx films with their microstructure using high resolution transmission electron microscopy and electron energy loss spectroscopy.

STUDIES OF THE GROWTH AND LOCAL ATOMIC BONDING OF a-CxNyHz FILMS. H. Efstathiadis, Z. Akkerman, and F.W. Smith, Dept. of Physics, City College of New York, NY.

A systematic study of the growth and local atomic bonding of a series of a-CxNyHz alloy films prepared via PECVD from mixtures of NH3/C2H2 and N2/C2H2 is presented. The effects of the reactants and their ratio on the film composition, the optical constants, and the optical energy gap have been determined. It is found that the presence of nitrogen and hydrogen in the gas phase during deposition decreases the net film deposition rate due to enchanced etching and that incorporation of nitrogen into the film is limited to N/C0.1. For the films deposited from N2/C2H2 as the concentration of N in the film increases, the concentration of C also increases while the concentration of H decreases. No evidence for the theoretically-predicted C3N4 compound was found. The addition of nitrogen into the film causes the index of refraction and the optical gap to decrease and leads to a redistribution of hydrogen between carbon and nitrogen. Hydrogen is preferentially bonded to nitrogen and there is evidence for N-HN hydrogen bonding in the films. The results of the free energy model (FEM) previously developed for predicting the bonding in a-CxNyHz alloys are compared with these experimental results. The importance of entropy in determining the most stable state of these alloys is demonstrated. A bonding network for the a-C0.69N0.068H0.242 alloy at T = 523 K is proposed. The FEM successfully predicts and explains some of the experimentally-observed properties of the alloys.


Hard a-C(N):H films were deposited onto Si substrates by rf-Plasma Enhanced Chemical Vapor Deposition (PECVD) in C2H2/N2 atmosphere with the N2 partial pressure ranging from 0 to 93. The chemical composition of the films was determined by nuclear techniques, while the film structure was monitored by Infrared (IR) absorption spectroscopy. Nitrogen incorporation up to 23 at. resulted in a decrease on the internal compressive stress from 3.0 to 1.5 GPa, being the hardness values less sensitive to the nitrogen incorporation. IR spectra showed the same trend that was observed in CH4/N2 derived films, with an increasing presence of the nitrogen-containing network terminating groups at the expenses of the C-H stretching bands [1]. The dependence of the film deposition rate upon nitrogen incorporation presents a different behavior from what is observed when other precursor gases are used [1-3]. For these gases, the deposition rate shows a strong reduction upon the increase of the nitrogen-containing gas partial pressure, and seems to be strongly correlated with the amount of nitrogen incorporated in the films. In fact, the deposition rate for a-C:H(N) films with 15 at. of nitrogen is a fifth of what is measured for a-C:H films [1-3]. On the other hand, for C2H2/N2 derived films with a nitrogen content of 23 at. , the deposition rate is 50 lower only. In view of these results, the mechanisms of film formation will be discussed.

GAS PHASE AND GAS-SURFACE CHEMISTRY FOR THE CHEMICAL VAPOR DEPOSITION OF BORON CARBIDE. Stephen J. Harris and Qui-Wang Lee, Physics and Physical Chemistry Dept., General Motors R&D Center, Warren, MI; and John Kiefer, University of Illinois, Chicago, IL.

Although BCl3 is a widely used boron source, the decomposition thermodynamics and kinetics of BCl3 arc almost totally unknown. We used ab initio quantum calculations at the G-2 level of theory to provide a self-consistent set of heats of formation and vibrational frequencies for BHmCln (m+n3). We then calculated potential surfaces and transition state properties for a number of reactions of H, H2, and HCl with the BHmCln species, again using ab initio quantum mechanical techniques. Finally, we converted that thermodynamic and structural information into rate constants, thereby providing for the first time a reaction mechanism which can be used to predict the important pathways for the thermal decomposition of BCl3 in the presence of hydrogen. These calculations were applied to growth of boron carbide. Boron carbide films were grown in a CVD reaction chamber, and the gas phase species were predicted using the CHEMKIN and SPIN codes from Sandia. Based on species measurements and predictions of the model, the growth species supplying most of the boron and carbon to the film are most likely BCl and CH3.

CARBON-NITRIDE THIN FILMS SYNTHESIZED BY ION BEAM SPUTTERING. Reza Valizadeh, John Colligon, Chester Faunce, Steve Donnelly, Suli Suder, Science Institute Dept of Physics, University of Salford, Salford, UNITED KINGDOM.

Carbon-nitride films have been deposited on Si (100) by ion beam sputtering a vitreous graphite target with Nitrogen and Argon ions with and without concurrent N2 ion bombardment. The sputtering beam energy was varied between 500 and 1500 eV and the assisting beam energy from 200 to 900 eV. The substrate temperature was varied from 200K to 973K. The nitrogen concentration in the deposited films was measured by Rutherford Backscattering (RBS) and Electron Energy Loss Spectroscopy (EELS). Carbon K edge structure obtained from the EELS analysis suggested that the amorphous carbon nitride matrix was predominantly sp2 bonded. This was confirmed by Fourier Transform Infra-Red Spectroscopy (FTIR) analysis which showed the nitrogen was mostly bonded with carbon in nitride (CN) and imine (C=N) groups. The nitrogen concentration varied from 10 at% to 44 at% and depended on the sputtering and ion assisted beam energy as well as ion/atom arrival ratio and substrate temperature. Post bombardment of the deposited film with 20 keV N+ caused to a reduction in the total nitrogen concentration. The microstructure of the film was determined with Transmission Electron Microscopy (TEM) which indicated that the films were amorphous.

STRUCTURE OF CNx/BN:C MULTILAYERS DEPOSITED BY UNBALANCED DUAL CATHODE REACTIVE MAGNETRON SPUTTERING. M. P. Johansson, T. Berlind, N. Hellgren, P. Sandström, L. Hultman, J-E. Sundgren, Department of Physics, Linköping University, Linköping, SWEDEN.

CNx/BN:C multilayers were deposited on Si(001), high speed steel, cemented carbide, martensitic steel, and TiN substrates by unbalanced dual cathode reactive magnetron sputtering from C (graphite) and B4C targets in an Ar/N2 discharge. The CNx and BN:C layers were sequentially sputtered in a gas mixture of 60 Ar and 40 N2, substrate temperatures of 200-500 C and substrates held at floating potential (8-12 V and 25-28 V, respectively). As-deposited films were analyzed with respect to their structure, composition, and mechanical properties by TEM, AES, AFM, XRD, and nanoindentation studies. CNx/BN multilayers with a total film thickness of 0.5 mm and compositional modulation periods between 2.5-10 nm have been studied. As-deposited CN layers exhibited a N concentration of 10 at whereas the BN:C layers had a C concentration of 20 at. A compositional modulation was readily observed by bright field TEM analysis as well as by low-angle XRD reflectivity measurements. However, no satellite reflections were observed by XRD for the multilayer grown at 500 C and a periodicity of 50 #197# which was attributed to an increased interfacial roughness and possibly also interdiffusion between the layers. The surface roughness for the film grown at 300 C with a layer period of 50 #197# was 5-10 #197# (RMS) whereas an increased surface roughness was observed for the film grown at 500 C. Similar to previous studies of magnetron sputtered CN (15-30 at N) and BN:C (10 at C) films, the present CNx/BN:C multilayers revealed an highly oriented hexagonal or turbostratic-like structure with curved and intersecting basal planes. This microstructure was also continuous over the CNx/BN:C interfaces. In agreement with previous results on films exhibiting such an underlying structure, the mechanical response of the system was highly elastic with elastic recoveries as high as 80-90 (at 10 mN load).

SYNTHESIS OF C-N FILMS BY BIAS-ASSISTED HOT FILAMENT CVD. Yoshihisa Watanabe, Hiroshi Kasai, Emil Kawasumi, Yoshiki Amamoto, and Yoshikazu Nakamura, Department of Materials Science and Engineering, National Defense Academy, Kanagawa, JAPAN.

Carbon nitride thin films have been tried synthesizing by various techniques, such as reactive sputtering deposition, ion beam assisted deposition, laser ablation deposition and hot-filament chemical vapor deposition (HFCVD) methods. Recently, successful synthesis of crystalline C3N4 on Ni (100) by bias-assisted HFCVD using a gas mixture of nitrogen and methane was reported. (1) We have improved the bias-assisted HFCVD method by replacing the filament material from tungsten to graphite so that two effects are anticipated; (1) prevention of contamination from the filament and (2) feasibility of synthesis of hydrogen free films without using hydrocarbon gas such as methane. Pure nitrogen gas blew the graphite filament heated at approximately 2000C and the substrate of Si (100) was applied by DC bias voltage. Synthesized films are found to be optically transparent. AFM observations reveal that the surface of the films synthesized without DC bias is covered with many protrusions, of typically 100 nm in height, while the films synthesized with approximately -200 V bias show smooth surface and the protrusions, of typically 20 nm in height, are distributed sparsely. Characterization by X ray diffraction and X ray photoelectron spectroscopy is now in progress.


A series of pulsed laser deposited (PLD) carbon nitride CNx films was prepared in nitrogen ambient with partial pressure PN varying from 0 to 300 mTorr and substrate temperature Ts from 25 to 437C, and another series of CNx films was prepared by ion beam deposition (IBD) with simultaneous nitrogen ion assist, and Ts from 28 to 337C. The N content in the films lies in the range of 0 to 32 at., and decreases with increasing Ts. An IR absorption band, denoted as band I, is observed at 1550 cm-1, and is attributed to the chemical bonds associated with N, such as those in the N-containing rings with sp2 structure and C=N bonds. A band II at 1300 cm-1 is recorded and is ascribed mainly to the carbon rings which contribute to the graphitic nature of the films. Band I of the PLD films deposited at higher PN and lower Ts is shaper and has a larger intensity relative to that of band II, accompanied by a larger optical band gap Eg > 1 eV, and an extremely low electrical conductivity room < 10-13 -1 cm-1, and a very low hardness 1.2 GPa, suggesting that they are polymeric in nature. On the other hand, the intensity of band II for PLD films deposited at lower PN and higher Ts, and that of the IBD films is stronger, reflecting that the film structure is graphitized. In particular, for the IBD films, Eg < 0.2 eV and room 0.1 -1 cm-1, indicating that the films are more graphitic in nature. With this structure, the hardness of IBD films is found to lie in the range of 10 - 16 GPa.

CHARACTERIZATION OF CRYSTALLINE C-Si-N FILMS BY BIAS-ASSISTED HOT FILAMENT CHEMICAL VAPOR DEPOSITION. E.G. Wang, Institute of Physics, Chinese Academy of Sciences, Beijing, CHINA; Chengzhang Wang, Dept of Physics, College of William and Mary, Willamsburg, VA; Changfeng Chen, Dept of Physics, Univ of Nevada, Las Vegas, NV; Yan Chen, Dept of Chemistry, State Univ of New York, Buffalo, NY.

High quality crystalline C-Si-N films on silicon substrate have been synthesized via bias-assisted hot filament CVD using a gas mixture of nitrogen and methane. Scanning electron microscopy images show that a high density of crystalline clusters, which are composed of small columnar crystals with hexagonal facets, has been achieved. Energy dispersive X-ray analysis is used to study the elemental composition. Both X-ray diffraction and transmission electron microscopy analyses suggest the C-Si-N structures with alpha or beta phases. Further first-principles calculations are used to present the structural stability and electronc property. We observe that bulk modulus increases but lattice parameters decrease as Si in Si3N4 is progressively substituted by C. The variation of chemical bonds and charge transfer in the substitutional process is also investigated.

CHARACTERISTICS OF CARBON NITRIDE FILMS PREPARED BY MAGNETIC FILTERED PLASMA STREAM. Aixiang Wei, Shaoqi Peng, Dept. of Physics, Zhongshan University, Guangzhou, China; Dihu Chen, Ning Ke, S.P. Wong, Dept. of Electronic Eng., The Chinese Univ. of Hong Kong, Shatin, HONG KONG.

The carbon nitride films have been formed using magnetic field filtered carbon ion deposition system. The electrical, optical and mechanical properties of films deposited in different N2 partial pressure have been studied. Infrared spectra typically exhibit bands at 2200, 1634, l500 cm-1, showing that the C and N atoms are chemically bonded in the films. The x-ray photoelectron spectroscopy has been employed to measure the atomic ratio of N to C in the films. The N/C ratio reaches 0.45. The room temperature conductivity is about 10-15 (cm)-1. The optical band gap obtained from optical absorption spectra has typical value of 4.0 eV. The experimental values of conductivity and band gap are closed to theoretical prediction. The value of Vickers hardness Hv obtained from measurement are between 4000 and 7000 kg/mm2. The effect of N2 partial pressure is also discussed.

LCVD OF CNx LAYERS FROM NH3 /CCl4 MIXTURE USING CuBr VAPOR LASER. B. Ivanov*, C. Popov**, L. Zambov*, M. Georgiev***, P. Babanov* , V. Shanov* and G. Peev* *Department of Semiconductors, University of Chemical Technology and Metallurgy, Sofia, BULGARIA; ** Central Laboratory of Photoprocesses Academician Jordan Malinowski, Bulgarian Academy of Science, Sofia, BULGARIA; ***Department of Inorganic Chemistry, University of Chemical Technology and Metallurgy, Sofia, BULGARIA.

Deposition of CNx layers using a focused CuBr vapor laser was investigated. The height and growth rate were study as function of process parameters - laser power, scanning speed, substrate temperature and composition of gaseous phase. The element analysis of the layers showed presence of C and N, as well as traces of Cl, with different ratio depending on process parameters. The layers were studied by SEM, FTIR, XPS and AES techniques. On the basis of in situ mass spectrometric investigations of gaseous phase a mechanism of laser induced CNx deposition was proposed.

ION BOMBARDMENT EFFECT IN BORON NITRIDE FILMS FORMATION. Dmitri A. Golosov, Igor V. Svadkovski, Sergey M. Zavadski, Anatoli P. Dostanko, Belarussian State University of Informatics and Radioelectronics, Minsk, BELARUS.

Dual ion beam deposition method has been realized to produce boron nitride films by sputtering from a target of boron nitride (h-BN) using two closed-drift ion sources of the anode-layer version. The effect of preparation conditions on the deposited phase was studied. The current density and ion energy of the bombarding beam (Ar+/N2+) were in the range 0.050-0.400 mA/cm2 and 200-1200 eV respectively. The sputtering current was 200 mA at ion energy 1500 eV. BN films have been deposited on heated (50-700C) silicon surfaces. Infrared (IR) absorption spectroscopy and transmission electron microscopy (TEM) have been used to study the properties of the resulting films. We have examined the relationship between the phase and the ion/atom ratio, energy and momentum transferred into the film.

Chair: James E. Jaskie 
Thursday Morning, December 4, 1997 
St. George B/C/D (W)

8:30 AM *AA6.1 
MODEL FOR EMISSION FROM DIAMOND AND DIAMOND-LIKE CARBON. John Robertson, Engineering Dept, Cambridge University, Cambridge, UNITED KINGDOM.

There is great interest in the low electron affinity of diamond-like carbon(DLC) and diamond and their use as thin film cathodes in Field Emission Displays. However, the field emission mechanism is contentious and an overall band model is needed. Diamond has a low or negative electron affinity and its Schottky barriers are pinned close to its valence band edge, so the main barrier for electrons is at the back contact[1]. This barrier is reduced by deep nitrogen donors as thier depletion layer shortens the tunneling distance. Grain boundaries creat a graded back contact, accounting for the improved emission with decreasing crystallinity in CVD diamond. As DLC has a narrower band gap than diamond, its band edges lies within the diamond gap, re-introducing a barrier at the thin film surface but reducing it at the back. This accounts for the greater emission from undoped DLC than undoped diamond. Nitrogen doping also increases emission in DLC[2,3]because N is a shallow but inefficient donor, which raises the Fermi level and lowers the work function. The main question is whether the field enhancement factor which reduces the Fowler-Nordheim slope is a geometric factor[4] or from some other source.

9:00 AM *AA6.2 
ELECTRON FIELD EMISSION FROM CARBON FILMS. Olivier M. Kuettel, Oliver Groening, Leon Diederich, Lars Ola Nilsson and Louis Schlapbach, Physics Institute, University of Fribourg, Fribourg, SWITZERLAND.

Carbon based materials are well known for electron emitting applications. However, the emission mechanism is not well understood. While electron injection into the conduction band of nanocrystalline diamond particles having a negative electron affinity (NEA) is very often discussed in the literature we will focus on a different model. From I/V as well as from energy resolved field emission measurements we conclude that at the emission sites local fields in the order of 5000-6000 V/micrometer are present. The talk will discuss how such high fields could be produced at the surface of a carbon film. HRSEM and a combination of AFM/STM was used to further characterize the emission sites. We will present evidence for a model which assumes high local fields. We have introduced in the past an activation concept for field emission which will briefly be reviewed. Electron field emission results from CVD plasma deposited amorphous carbon as well as from arc deposited undoped and nitrogen containing films will be discussed. We will address the question how a workfunction reduction in the order of 2-3 eV can be produced on such films.

10:00 AM AA6.3 

Electron emission from pulsed laser deposited amorphous carbon thin films is sensitive to the mixture of 3-fold and 4-fold coordinated bonds as determined by growth conditions. Annealing at temperatures above 100#176#C increases the perpendicular conductivity suggesting a concomitant change in bonding. Emission measurements as a function of annealing temperature indicate that the emission characteristics are also sensitive to the thermal evolution of carbon-carbon coordination. We have observed up to an order of magnitude increase in the emission current at fixed field after annealing to temperatures of 600#176#C. The magnitude of the increase depends upon the initial bonding coordination, where larger changes occur for materials with initially high perpendicular resistivity.

10:15 AM AA6.4 

There have been a number of recent reports on Field Emission from Diamond Like Carbon Films. However, there is still much debate as to the exact emission mechanism. In diamond it has been observed by Geis et al (1) that the main barrier to emission exists at the back contact. For DLC on the other hand it has been previously shown theoretically (2) that the principle barrier to emission is at the front surface. In order to test whether emission in ta-C is affected by the surface condition of the films we have carried out a series of field emission experiments on Filtered Cathodic Vacuum Arc (FCVA) produced ta-C films. ta-C is known to have a 2-3 nm thick sp2 rich layer on its surface. In order to test whether the surface layer has an effect on emission, measurements have been made before and after the surface has been etched in an oxygen plasma. The effect of the back contact was also ascertained by measurements on identical films produced on metal substrates of different work function and n-and p-type c-Si.

10:30 AM AA6.5 
ELECTRON FIELD EMISSION FROM MULTILAYERED TETRAHEDRAL AMORPHOUS CARBON FILMS. X.Shi, S.R.P.Silva*, L.K.Cheah, and B.K.Tay, School of Electrical and Electronic Engineering, Nanyang Technological University, SINGAPORE; * Department of Electronic and Electrical Engineering, University of Surrey, UNITED KINGDOM.

Multilayer structures which constitute of nitrogen doped tetrahedral amorphous carbon (n+-ta-C) film on intrinsic ta-C layer have been fabricated using the filtered cathodic vacuum arc (FCVA) technique and used to obtain the electron field emission. Low voltage dc biases were applied between the layers in conjunction with the conventional electric field applied between the cathode and anode. It has been demonstrated that by varying the low dc bias voltage, the critical electric field for the electron emission can be varied between 15V/um and 30V/um. The emission current density too can be enhanced using such multilayer structures. It has been observed that the switching characteristics of the field emission can be improved considerably by the low voltage switching between the multilayer. A possible mechanism for the switching and the improvement in the emission characteristics is proposed.

10:45 AM AA6.6 
A FIELD EMISSION STUDY OF THE CRITICAL PARAMETERS OF AMORPHOUS CARBON FILMS DEPOSITED ON A VARIETY OF CARBONACEOUS SUBSTRATES. A.P. Burden, R. Forrest and S.R.P. Silva, School of Electronic and Electrical Engineering, Information Technology & Mathematics, University of Surrey, Guildford, UNITED KINGDOM; G.A.J. Amaratunga, Department of Electronic and Electrical Engineering, University of Liverpool, Liverpool, UNITED KINGDOM.

Field emission of electrons from the surface of amorphous diamond-like carbon (DLC) films holds promise for the development of inexpensive bright flat-panel displays. Studies have traditionally focused on depositing DLC films onto silicon and metal substrates. Recent results suggest that the energy barrier between the back-contact and the film is as important in the electron-emission rate-limiting process as the interface between the DLC film and the vacuum. Ultimately, a successful system requires efficient electron injection into the film as well as the ease of electron emission from its surface. Future applications of these systems cite polymeric substrates as inexpensive large area panel supports. DLC films containing different quantities of hydrogen and nitrogen have been deposited on to a variety of carbonaceous substrates, including graphite and conducting polymer composites, using radio-frequency plasma-enhanced chemical vapour deposition. In-situ plasma treatment of the substrate prior to film deposition is used to optimise the electronic and microstructural properties of the substrate-film interface. Scanning Electron Microscopy and Atomic Force Microscopy have been used to characterise the surface morphology of substrates and films deposited with a variety of pre-treatments and film-generating parameters. We have shown that the use of oxygen-containing plasma pre-treatments can be used to micro-texture the conductive polymer composite surface which proves to be beneficial to the field emission properties of the system. The field emission characteristics of the resulting film/substrate combinations are correlated with electron microscopy and other analytical techniques.

Chair: James E. Jaskie 
Thursday Morning, December 4, 1997 
11:00 A.M. 
St. George B/C/D (W)

CESIUM-ENHANCED R.F. MAGNETRON DEPOSITION OF CARBON NITRIDE AND DIAMOND-LIKE CARBON FILMS. Ivan H. Murzin, Gary S. Tompa, Structured Materials Industries, Inc., Piscataway, NJ.

We report the design, manufacturing and testing of a new negative carbon ion source that can be used to produce electron emitting carbon nitride and diamond-like carbon (DLC) films. The source consists of a conventional magnetron sputtering gun modified to include the high voltage electrodes and a cesium oven to provide delivery of vaporized cesium to a carbon target installed in the magnetron gun head. The argon and argon - nitrogen gas mixtures were used to ignite the plasma. The sputtered carbon ions were negatively charged, because cesium layer on top of a carbon target lowered the surface work function of carbon surface. The deposition rate of carbon was recorded for the powers from 0 to 150 W and was found to increase by an order of magnitude in comparison with that recorded using pure Ar plasma. We also measured the current absorbed by the substrate as a function of cesium oven temperature and other ion source characteristics. We compare the electron emitting, mechanical, optical and other properties of the several carbon nitride and DLC films deposited with and without cesium.

FIELD EMISSION FROM NITROGEN-DOPED DIAMOND FILM. Minseo Park, Leah Bergman, Robert J. Nemanich, and Jerome J. Cuomo, Department of Materials Science and Engineering and Department of Physics, North Carolina State University, Raleigh, NC.

Nitrogen-doped diamond using melamine (C3H6N6) as a nitrogen source was synthesized for the first time to our knowledge. Since melamine molecule has existing cyclic C-N bonded ring, it is expected that the incorporation of nitrogen on substitutional diamond lattice should be facilitated. Preliminary result shows that nitrogen was successfully doped to diamond without degrading the quality of the diamond. Nitrogen-doped diamond deposited on planar silicon surfaces and field emitter arrays of silicon are used to study the effect of geometry of the substrate on electron field emission. The possible role of molecular structure of melamine on enhancement in nitrogen incorporation will be analyzed. The effect of nitrogen impurity on field emission will also be discussed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, photoluminescence spectroscopy (PL), and field emission measurement will be shown.

THE INTERACTION OF CARBON WITH THE DIAMOND SURFACE: A PHOTOELECTRON SPECTROSCOPY STUDY. P. Reinke and P. Oelhafen, Universitat Basel, Basel, SWITZERLAND; R. Locher, Fraunhofer Institut fur Angewandte Festkorperphysik, Freiburg, GERMANY.

The investigation of the interaction of the diamond surface with adsorbates is an important step toward the understanding of the diamond growth process, and offers the opportunity to adjust the electronic and electron emission properties of the surface. In the study presented here, we deposited 0.1 to 100 monolayers of carbon from an electron beam evaporation source on polycrystalline diamond films with and without preferential orientation. Photoelectron spectroscopy in the ultraviolet and X-ray regime was employed to characterize the surface. In the absence of hydrogen the growth of an amorphous or graphitic film (at elevated temperatures) is observed. The diamond surface does in contrast to some metals, not decisively influence the nature of the deposited film. The electronic structure of the diamond surface is severely altered by the adsorbing carbon species. The introduction of electronic states in the gap of the diamond band structure through the adsorbent leads to characteristic changes in the electronic structure such as surface reconstruction, band bending, and the position of the valence band maximum. It will be discussed how the well defined introduction of sp2 carbon (p- states) influences the electron emission properties of the surface.


Diamond-like-carbon (DLC) films have received attention because of excellent eloctron emission characteristics for cold cathode source #245# n vacuum microelectronics. In the present work, we have deposited thin films of covalently bonded carbon by rf-plasma assisted chemical vapor deposition, and examined the effects of deposition variables and growth mechanism on the electron emission characteristics. It was clear that the deposited films were predominantly amorphous but the ratio of sp2 and sp3 affected their structural, optical, and electrical characteristics. The bonding spectra and microstructures were controlled by energetic ions depending on deposition conditions. The DLC films containing large portion of sp3-bonds were obtained at substrate temperature less than 300C. Raman and IR spectroscopy analyses identified the deposited materials as DLCs containing a wide range of hydrogen content depending on CH4 content, deposition temperature, and rf power. From the measurement of field emission characteristics, turn-on voltage was lowered and maximum anode current was #245#ncreased for 1000ÅDLC-coated Si emitter tips. In addition, NF3 plasma exposure on the film has been effectively utilized just after deposition to selectively remove graphite phase and retain diamond phase. The resultant surface and the electron emission charactenstics were analyzed and compared to the films without subsequent plasma etching.

THE ELECTRICAL AND ELECTRON EMISSION CHARACTERISTICS OF DIAMOND-LIKE CARBON FILMS PREPARED ONTO Pt-COATED SILICON BY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION. Kwang Bae Lee, Mun Sik Kang, Kyung Woon Park, Tae Woo Kim, Mi Ran Lee, Sangji Univ, Dept of Physics, Kangwondo, KOREA; Chong Tak Kim, Sangji Jr College, Dept of Electronics, Kangwondo, KOREA; Byung Kwon Ju, KIST, Div of Electronics and Information Technology, Seoul, KOREA; Jin Jang, Kyung Hee Univ, Dept of Physics, Seoul, KOREA.

We have prepared DLC films by means of plasma enhanced chemical vapor deposition (PECVD) from a mixed gas of CH4 and H2. Our capacitive coupled PECVD system has two electrodes which are placed vertically in order to prevent from piling up the long lived and large CHn radicals. For three types of substrates, such as Corning 7059 glass, bare Si wafers and Pt-coated Si wafers as substrates, we found that the optimum deposition conditions to get hard and uniform DLC films were different. One of the important deposition conditions is the distance from the cathode plate to the anode one, which implies that the formations of both the ion sheath and the self-bias field are different for the insulating substrate and the metal substrate. The range of the distance between the electrodes to get hard DLC films onto the metal substrate is shorter than that onto the insulating substrate. The electrical conductivity was measured as a function of the hydrogen contents. The electrical conductivity decreases with the increase of the hydrogen contents in DLC film. The emission current characteristics of DLC films were measured as a function of the electrical conductivity and the hydrogen contents. The turn-on fields are in the range of 10 to 20 V/m which are related to the electrical conductivity and the hydrogen contents. The field emission characteristics of DLC films deposited onto Pt-coated Si wafers show the stable behaviors without the formation of any craters, which are believed to be due to the ohmic contact with Pt-lower electrode.

Chair: Nancy A. Missert 
Thursday Afternoon, December 4, 1997 
St. George B/C/D (W)

1:30 PM *AA8.1 
LOW FIELD ELECTRON EMISSION FROM NANO-STRUCTURED DIAMOND. W. Zhu, G.P. Kochanski and S. Jin, Bell Laboratories, Lucent Technologies, Murray Hill, NJ.

We report on electron emission at extremely low fields from nano structured diamond. The cold cathode emitters consist of a layer of nanometer-size diamond particulates coated on a silicon substrate which is subsequently heat treated at 650C in a hydrogen plasma for activation. Electron emission at applied fields as low as 1 V/m is observed for an average current density of 10 mA/cm2. This is the lowest emission field ever reported for any field emitting materials. We attribute this excellent emission property to the low electron affinity associated with the diamond surface and the high defect density in the small-size particles. Nano-structured diamond emitters are useful for applications such as flat panel displays as, in addition to the very low fields required, they can easily be deposited on large area substrates by low-cost coating techniques and do not require complicated microtip fabrication processes.

2:00 PM AA8.2 
ELECTRON EMISSION PROPERTIES OF SILICON FIELD EMITTER ARRAYS COATED WITH NANOCRYSTALLINE DIAMOND FROM FULLERENE PRECURSORS*. Timothy D. Corrigan1, 3, Thomas G. McCauley1, Dan Zhou1, Alan R. Krauss1, Orlando Auciello1, Dieter M. Gruen1, Dorota Temple2, Gary E. McGuire2, and R.P.H. Chang3; 1 Materials Science and Chemistry Divisions, Argonne National Laboratory, Argonne, IL; 2 Electronics Technology Division, MCNC, Research Triangle Park, NC; 3 Department of Materials Science and Engineering, Northwestern University, Evanston, IL.

In this paper, we report on a substantial lowering of the threshold field for electron field emission from Si field emitter arrays (FEA), which have been coated with a thin layer of nanocrystalline diamond by microwave plasma-assisted chemical vapor deposition (MPCVD) from fullerene (C60) precursors. Various surface pretreatments, including hydrogen plasma etching and bias-enhanced nucleation (BEN), are shown to affect the degree of coverage, conformality, and morphology of the diamond coating. The coated arrays have been characterized by field emission scanning electron microscopy (FESEM), micro-Raman spectroscopy, and x-ray diffraction (XRD). In particular, hydrogen plasma etching prior to BEN and subsequent growth in an Ar/C60/H2 discharge appears to promote continuous, conformal coating of the base plane and emitter tip structures, while BEN and growth without hydrogen plasma etching resulted in preferential growth of needlelike structures on the apical surfaces of the emitter tips. Electron emission was not observed from the uncoated arrays up to fields of 20 V/m. Emitter arrays with smooth, continuous coatings and needlelike structures exhibited electron emission at threshold fields of approximately 6 V/mm and 3.5 V/m, respectively. The lower threshold field for the latter array may be due to secondary field enhancement near the apex of each emitter tip due to the presence of the needlelike structures. The effects of alternative surface pretreatments and carbon precursors, as well as plasma hydrogen content during growth and substrate temperature, are also discussed.

2:15 PM AA8.3 
ELECTRON EMISSION CHARACTERISTICS OF AMORPHOUS DIAMOND COATED FIELD EMITTERS. W.B. Choi, M.Q. Ding, A.F. Myers, J.J. Cuomo, and J.J. Hren, Dept. of Materials Science and Engineering, North Carolina State Univ., Raleigh, NC.

The field emission characteristics of amorphous diamond coatings on needle-shaped molybdenum and silicon emitters were measured and analyzed. Nitrogen doped a-diamond/emitter shows significantly higher emissivity than bare emitter. Current conditioning improves current stability and enhances the current density. Thick coatings lower the emissivity and change the slope of the I-V curve. The slope change of the I-V curves can be attributed to a transition of the emission mechanism from 'contact-limited' to 'bulk-limited' transport, probably related to the high trap density. Annealing improved the emissivity and changed the slope of the I-V curve. The microstructure of the a-diamond/Mo emitter was investigated by transmission electron microscopy and correlated with I-V data. In this presentation, I-V characterization of a-diamond coated field emitters and field emission energy distribution data will be discussed.

2:30 PM AA8.4 
FIELD EMISSION IN THE MULTILAYER CATHODES WITH A QUANTUM WELL. Vladimir G. Litovchenko, Anatoli A. Evtukh, Institute of Semiconductor Physics of the Ukrainian Academy of Sciences, Nina Goncharuk, Vasiliy Chaika, Research Institute ''Orion", Kiev, UKRAINE.

Numerical simulation of resonant and non-resonant field emission in Si-SiO2-Si-SiO2 multilayer cathodes(MLC) with the quantum well(QW) which takes into account the tunnel process of electrons from the three-dimensional electron density states of the emitter conductive band has been carried out. The influence of the external electric field, temperature, MLC parameters and emitter doping on the resonant characteristics of current was analyzed. Investigation has shown that peak current density of MLC with optimal thin barriers and sufficiently wide QW layers can exceed up to some times the current density of conventional cathodes at resonant value of electric field. If a width of QW increases the number of current resonant maxima (CRM) is multiplied. They shift towards the lower electric field values and become more narrow if both QW and potential barriers width increases. Under temperature reduction the CRM is contracted due to electron impulse relaxation time increasing and redistribution of the electron state density in the emitter conduction band. Reduction of the emitter doping from 5x1019sm-3 leads to reduction of the non-resonant and resonant current density at 102 times and shifts of the CRM towards smaller electric field about 5x106 V/cm without current resonant overfall changing. It is stipulated by the less electron state density and by its less energy dependence in a non degenerated semiconductor conduction band, than in the degenerated one.

Chair: William I. Milne 
Thursday Afternoon, December 4, 1997 
3:15 P.M. 
St. George B/C/D (W)

FORMATION AND RELAXATION OF COMPRESSIVE STRESS IN ION BEAM DEPOSITED TETRAHEDRAL AMORPHOUS CARBON. H.C. Hofsäss, M. Sebastian, H. Feldermann, R. Merk and C. Ronning, Fakultät für Physik, Universität Konstanz, Konstanz, GERMANY.

High compressive stress of up to 10 GPa in thin films of tetrahedrally bonded amorphous carbon (ta-C) causes adhesion problems and is the most significant limitation for their application as thin film coating material. In several experimental and theoretical studies the compressive stress was correlated to the sp3- bonding fraction, implying that low stress ta-C films are difficult or impossible to grow. In this contribution, we present a systematic study of the compressive stress in ta-C films grown by mass selected ion beam deposition. We investigate the stress as a function of ion energy and substrate temperature during deposition and as a function of post-deposition annealing conditions. By annealing to 600C, the compressive stress can be reduced by more than an order of magnitude without a decrease in the sp3-content, in agreement with recent results of Friedman et al [1]. We cannot confirm a clear correlation between compressive stress and sp3-content in as deposited ta-C films. With increasing ion energy, the compressive stress decreases more rapidly than the sp3-content leading to low stress diamondlike films whereas 10 GPa is a typical compressive stress for a 100 eV film with 80% sp3-fraction, a film grown at 1 keV has still a 50% sp3-fraction but only about 2 GPa compressive stress.

STRUCTURAL AND ELECTRICAL PROPERTIES OF PHOSPHORUS DOPED AMORPHOUS DIAMOND. S.M. Camphausen, J.J. Cuomo, North Carolina State University, Raleigh, NC; S.P. Bozeman, Commonwealth Scientific Corporation, Alexandria, VA; A.F. Myers, Surface and Microanalysis Science Division, Gaithersburg, MD.

Hard Carbon films can be prepared by the condensation of energetic carbon species at or below room temperature. These amorphous films are primarily tetrahedrally coordinated leading to the terminology amorphous diamond. These films have been successfully doped with phosphorous up to 1 atomic % by other researchers by using a graphite-phosphorous target [1]. We have also investigated evaporated phosphorous in conjunction with a filtered cathodic arc to incorporate it into the films. We have successfully incorporated phosphorus up to 30 atomic % into the films using this technique. SEM and XPS measurements indicated clustering of some of the phosphorus. We will discuss bonding of both the carbon and phosphorus as determined by TEM and PEELS.

THEORETICAL AND EXPERIMENTAL STUDIES OF THE DEFECTIVENESS OF TETRAHEDRAL AMORPHOUS MATERIALS. H.C. Ong1, C.J. Yu2, J.Y. Dai1, and R.P.H. Chang1, 1Department of Materials Science and Engineering, 2Department of Physics Northwestern University, Evanston, IL.

Tetrahedral amorphous thin film materials prepared from various techniques are known to compose of different degree of defectiveness which generally has negative effects on the device performance. Unlike their crystalline counterparts, probing of the defectiveness in amorphous materials is difficult because of the lack of long range order in these materials which makes most of the conventional structural measurements such as TEM and x-ray diffraction unavailable. Hence, the development of new method to identify the imperfection is essential to the improvement of the level of material quality towards the device standard. Here, we have calculated the dielectric functions of a-SiC and a-C with two structural perfection, relaxed and strained or otherwise defective, based on the tetrahedron model and effective medium theory. Experimental dielectric functions of amorphous SiC and C thin films prepared in various conditions have been measured and are compared with the theoretical spectra. It is proposed that the amorphous materials prepared from ion-implantation and pulsed laser deposition share a very similar level of defectiveness but, on the other hand, completely different from those of thermal evaporation and CVD. In addition, understanding the imperfection of the materials allow us to predict the microstructure of a-SiC and a-C such as their chemical ordering and graphitic concentration. Our predictions are found to be consistent with the results obtained from electron energy loss spectroscopy (EELS), Auger electron spectroscopy, and IR spectroscopy.

QUANTIFYING THE VOLUME FRACTION OF AMORPHOUS CARBONS IN NANODIAMOND THIN FILMS*, Lu-Chang Qin and Dieter M. Gruen, Materials Science and Chemistry Division, Argonne National Laboratory, Argonne, IL.

In the microstructure study of nanocrystalline diamond thin films grown from Ar/C60 or Ar/CH4 microwave plasma assisted chemical vapor deposition, an open question is if there is a large fraction of the film that is made of amorphous carbon, either sp2 bonded glassy carbon or sp3-bonded diamondlike amorphous carbon, or both. High-resolution electron microscopy can only provide partial answer to this question, since at best only a selected sets of crystallites, which are oriented in such a way that their {111} lattice planes are aligned parallel to the incident imaging electron beam, give rise to lattice fringes when the 0.20 nm lattice spacing is resolved. A quantitative technique has been developed to obtain the relative volume fraction of amorphous carbon in nanodiamond thin films. This analysis employs quantitative measurement of scattered electron intensities, Ia and Ic from the amorphous portion and a reference crystallite, respectively. They are related to the number of scattering atoms by the following relationship: Ia/Ic1.5Na/Nc2, where Na and Nc are the total number of atoms of the scattering amorphous portion and the reference diamond crystallite, respectively. Detailed analysis procedure will be presented that would allow one to detect the presence of amorphous carbon with accuracy about 1% in nanodiamond thin films that are composed of 10-15 nm diamond crystallites.

THE EFFECT OF SHORT AND MEDIUM RANGE BONDING ON THE VIBRATIONAL FEATURES OF AMORPHOUS CARBON BASED BINARY ALLOYS. G. Compagnini, Dipartimento di Scienze Chimiche, Catania, ITALY; and G. Fonti, Istituto Nazionale per la Fisica della Materia Corso, Catania, ITALY.

Amorphous carbon based binary alloys are considered materials of current interest in several fields from microelectronics to optical coatings and one of the widest used characterization tool in the study of this materials is vibrational spectroscopy. In this work we report some results concerning Raman characterization of covalently bonded amorphous silicon carbon thin films (100 nm) alloys obtained by ion implantation of carbon ions into a silicon or germanium matrix. Ion implantation has been performed with multiple energy implants in order to obtain a uniform carbon concentration all over the film thickness. It will be shown that compositional disorder is present in our samples even at the stoichiometric concentrations (50 carbon at.%) as deduced by the presence of three vibrational features in the Raman spectra. These are found at around 540, 780 and 1450 cm-1 in a-SiC films and are due to SiSi, Si-C and C-C vibrations respectively. A quantitative measure of the compositional disorder will be also given by using either Raman and infrared spectroscopies in samples with different carbon content. The position and shape of vibrations belonging to the above mentioned three subsystems is however strongly dependent from the chemical environment in which they are embedded. It will be shown, for instance, that the C-C vibrational feature shifts in position and changes in shape, in going from a-C to a-SiC through a-GeC films giving rise to a second shell effect useful to characterize this kind of samples.

DOPING INDUCED INTERNAL STRESS REDUCTION IN DIAMOND-LIKE CARBON FILMS DEPOSITED BY PULSED LASER DEPOSITION. Q. Wei, A.K. Sharma, S. Oktyabrsky, K. Jagannadham, J. Sankara and J. Narayan, Dept. of Materials Science and Engineering, North Carolina State Univ., Raleigh, NC. aDept. of Mechanical Engineering, North Carolina AT State Univ., Greensboro, NC.

We have investigated the effect of dopants on the reduction of internal compressive stress in diamond-like carbon(DLC) films prepared by pulsed laser deposition on Si(100) substrates. We used a novel target configuration to incorporate dopants into DLC films by sequential pulsed laser ablation of two targets. The dopants studied include copper, titantium and silicon. All the films were deposited at room temperature for 50 minutes at a repetition rate of 10 Hz with KrF excimer laser(=248nm) with an energy density close to 3.0J/cm2. The thickness of the DLC films deposited was measured to be 400-600nm using a profilometer. The composition of the films was determined by X-ray photoelectron spectroscopy (XPS). Raman spectroscopy using a 514nm green light was employed to analyze the chemistry of the films. The shifts of the G-peak position in the Raman spectrum, due to different concentration of doped atoms, were used to fingerprint the internal stress changes. All of the films showed a Raman spectrum typical of DLC films containing high fraction of sp3 bonded carbon species, with G-peak centered at 1511-1560cm-1. The shift of the G-peak due to the presence of dopants was observed for all the DLC films. It was found that Ti has the strongest tendency to reduce the compressive stress of DLC films, followed by copper. This effect increases with increasing concentration of dopants. Silicon was also observed to have this effect, but the G-peak position did not appear to shift with different Si concentrations. Buckling occurred in the as-deposited, undoped DLC film because of the accumulation of a large compressive stress in the film, while all the doped DLC films showed good adhesion to the substrate. These results are discussed taking into account the atomic structure of the amorphous DLC films as well as the structure and properties of the dopants. They suggest an approach for growth and applications of thick DLC films.

HIGH RATE DEPOSITION OF ta-C:H USING AN ELECTRON CYCLOTRON WAVE RESONANCE PLASMA SOURCE. N.A. Morrison, W.I. Milne, J. Robertson, Cambridge University, Engineering Dept, Cambridge, UNITED KINGDOM; M. Weiler, Forschungs zentrum Rossendorf, GERMANY; I. Hutchings, Materials Science Dept, Cambridge University, Cambridge, UNITED KINGDOM; L.M. Brown, Physics Dept, Cambridge University, Cambridge, UNITED KINGDOM.

A compact, RF electron cyclotron wave resonance (ECWR) source has been developed for the high rate plasma deposition of hydrogenated tetrahderal amorphous carbon (ta-C:H). The ECWR provides growth rates up to 2 nm/s and independent control of the deposition rate and ion energy. The ta-C:H is deposited using acetylene as a source gas and is found to have sp3 contents up to 70%. The ta-C:H films have been characterised in terms of their bonding,, stress, hardness, friction coefficient and adhesion. The ECWR also provides a very high dissociation of N2 gas, and a further experiments were carried out towards the deposition of CNx and C3N4 materials.

AMORPHOUS DIAMOND-LIKE CARBON FILMS PREPARED BY SADDLE-FIELD GLOW-DISCHARGED METHOD: DOPING WITH BORON AND PHOSPHORUS. W. Chan, F. Gaspari, E. Moreno, S. Zukotynski, Univ of Toronto, Dept of Electrical and Computer Engineering, Toronto, CANADA; Tatiana Allen, Univ of Tennessee at Chattanooga, Dept of Physics, Geology, and Astronomy, Chattanooga, TN.

We employed the method of saddle-field glow discharge deposition [1], to produce amorphous hydrogenated diamond-like carbon (DLC) films. The technique uses a five parallel electrode plasma apparatus, which allows for independent control of the discharge, and of the substrate bias relative to the plasma [2]. Deposition of undoped films was carried out using ultra-pure methane; the setup also allows to dope the films with boron and phosphorus from the gas phase. Two series of samples were deposited: one at substrate temperature 200oC, and the other at 400oC (200-series and 400-series respectively). The 200-series contains undoped DLC sample, 5 phosphorus-doped samples, and 5 boron-doped samples. The 400-series contains one undoped DLC sample, one phosphorus-doped sample and one boron-doped sample. The amount of the dopant in the film was measured by Secondary Ion Mass Spectroscopy (SIMS) method, and it was found that the impurity concentration in the film corresponds to the dopant concentration in the gas phase. The amount of sp3 (diamond-like) bonds in the film was measured by x-ray stimulated Auger electron spectroscopy (XAES). Our deposition method allows preparation of high quality undoped DLC films (up to 97 of sp3 bonding ) [1]. In order to study the effects of doping on the sp3 content, and to maximize growth rates, we chose a set of deposition parameters which produced films with about 50 of sp3 content both for the 200-series and for the 400-series. The optical energy gap Eg was obtained by the Tauc method from the optical absorption measurements. It was found that Eg depends on the deposition temperature and does not depend on the doping level. In order to study the temperature dependence of conductivity, the samples were heated from room temperature to the deposition temperature of the film, because at higher temperatures the hydrogen will effuse from the film, changing the properties of the film. We found that in the temperature region up to 200oC the resistance of all the samples in 200-series was higher than could be measured. For the 400-series, all samples exhibit a thermally activated conductivity at the temperature region 225 - 380oC. Doping with boron is more efficient than doping with phosphorus. For the boron-doped sample there are two different slopes in the temperature dependence of conductivity. We believe that they correspond to conductivity over localized states at lower temperatures and conductivity over extended states at higher temperature. The activation energy for the latter is very close to the optical energy gap Eg for this sample.

PRESSURE AND BIAS DEPENDENT OF DLC FILM BY DC SADDLE-FIELD CVD. Y.Z. Yoo, Y.G. Jeong*, J.S. Oh*, J.H. Kim*, H.G. Jang*, G.S. Kim*, H.G. Kim, Dept of Material Science Engineering, Kwangju Institute of Science and Technology, Kwangju, KOREA; *Kumho Information and Telecommunications Laboratory, KOREA.

Diamond-like carbon (DLC) thin film were deposited on p-type Si(100) and corning glass 7059 to investigate the effect of substrate conductivity on film properties by DC saddle-field plasma enhanced CVD using pure methane gas or hydrogen mixed methane at a wide range of pressure and substrate bias. The gas pressure from 10 mtorr to 150 mtorr and substrate bias voltage from -100V to 400V were employed to investigate the effect of pressure and bias on the DLC film growth. The hydrogen/methane ratio was also varied from 50 to 80 to study the effect of hydrogen on film properties. Surface morphology changes of film grown at different pressure and bias voltage were measured by atomic force microscopy. Microstructural properties of DLC were analyzed by fourier transform infrared spectroscopy, Raman, ultra violet spectroscopy, X-ray photoelectron spectroscopy, rutherford backscattering spectroscopy and elastic recoil detection techniques. Film thickness was measured to be about 1000 by RBS. Peak intensities of C-H stretching vibration increased with pressure and decreased with increasing substrate bias. This indicates that the concentration of unbound hydrogen in the film decreases with increasing pressure. Different micro structures were observed in the DLC film on glass and Si due to the different electrical conductivities of substrate. We observed the emission of white photoluminescence light from films with naked eyes even at room temperature. We will discuss the film growth rate, photoluminescence, hydrogen content, microstructural and mechanical properties of DLC as a functions of various growth parameters.

AN AB INITIO MOLECULAR ORBITAL STUDY ON PLASMA SURFACE REACTIONS OF GROUP IV COMPOUNDS. Kota Sato, Hitoshi Haruta, Yukinobu Kumashiro, Yokohama National Univ., Faculty of Engineering, Dept of Materials Science, Yokohama, JAPAN.

Plasma surface reactions of silicon and carbon compounds are compared by using an ab initio molecular orbital method. As silicon and carbon compounds are covalently bonded compounds and we treat precise local structures without translational symmetry, molecular orbital methods are considered to be sutable as theoretical procedures. The Hartree-Fock method was used for the geometry optimization. Electron correlations were taken into account by the second order perturbation theory for calculating energies of optimized structures. A 3-21G basis set was mainly used for the calculation. As for silane plasma CVD, a hydrogen elimination mechanism with a low activation energy in some atomic layers below the top surface was discovered by us by the theoretical procedure. (See eq(1) and (2).) 
Si+SiHSiSi+H (1) 
SiH+HSi + H2 (2) 
In this mechanism, dangling bonds play an important role. If the network is formed by this mechanism, hydrogens around dangling bonds are expected to be removed. This expectation was consistent with the Inhomogeneous hydrogen distribution determined by ESR and NMR. In this study, infinitely large surface is modeled by small clusters. Thus, the dependence of the results on the cluster size is examined. In the case of the silicon system, the activation energy of eq. (1) decreases, as the cluster size becomes larger. For the largest cluster, the activation energy is 18.2 koal/mol. On the other hand, the activation energy of eq. (3) of carbon system becomes larger as the cluster size becomes large. 
C+CH CC + H (3) 
For the largest cluster, the activation energy Is 58.4 koal/mol. Thermodynamically, silicon and carbon systems show similar results. Thus, both the systems take a similar hydrogen elimination mechanism at high substrate temperatures, while the different kinetically favorable mechanism is expected for the carbon system at low substrate temperatures. As one of these reactions, we proposed a reaction shown in eq. (4) which creats sp2 carbons. 
CnH2n+1CnH2n + H (4)