Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/26—Deposition of carbon only
  • C23C16/27—Diamond only
  • C23C16/274—Diamond only using microwave discharges
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
  • B01J3/06—Processes using ultra-high pressure, e.g. for the formation of diamonds; Apparatus therefor, e.g. moulds or dies
  • B01J3/065—Presses for the formation of diamonds or boronitrides
  • B01J3/067—Presses using a plurality of pressing members working in different directions
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/25—Diamond
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/25—Diamond
  • C01B32/26—Preparation
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/26—Deposition of carbon only
  • C23C16/27—Diamond only
  • C23C16/277—Diamond only using other elements in the gas phase besides carbon and hydrogen; using other elements besides carbon, hydrogen and oxygen in case of use of combustion torches; using other elements besides carbon, hydrogen and inert gas in case of use of plasma jets
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/26—Deposition of carbon only
  • C23C16/27—Diamond only
  • C23C16/278—Diamond only doping or introduction of a secondary phase in the diamond
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/26—Deposition of carbon only
  • C23C16/27—Diamond only
  • C23C16/279—Diamond only control of diamond crystallography
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
  • C30B25/10—Heating of the reaction chamber or the substrate
  • C30B25/105—Heating of the reaction chamber or the substrate by irradiation or electric discharge
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/04—Diamond
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
  • C30B29/605—Products containing multiple oriented crystallites, e.g. columnar crystallites
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/04—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of carbon-silicon compounds, carbon or silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
  • H01J1/02—Main electrodes
  • H01J1/30—Cold cathodes, e.g. field-emissive cathode
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2203/00—Processes utilising sub- or super atmospheric pressure
  • B01J2203/06—High pressure synthesis
  • B01J2203/065—Composition of the material produced
  • B01J2203/0655—Diamond
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2201/00—Electrodes common to discharge tubes
  • H01J2201/30—Cold cathodes
  • H01J2201/304—Field emission cathodes
  • H01J2201/30446—Field emission cathodes characterised by the emitter material
  • H01J2201/30453—Carbon types
  • H01J2201/30457—Diamond

Definitions

• the UNCD films have grain boundaries are almost atomically abrupt (-0.5 nm). and have been measured on the average of 0.3 to 0.4 nm. These UNCD films exhibit exceptional mechanical, and tribological properties, the latter particularly applicable to the development of a new microelectromechanical system (MEMS) technology based on UNCD.
• MEMS microelectromechanical system
• UNCD shall be defined as films grown from C 2 dimers, as set forth in the '776 patent.
• This invention relates to n-type doping of UNCD films, that is films with average grain size of less than about 15 nm, as opposed to films with larger grain sizes, such as microcrystalline or nanocrystalline diamond.
• UNCD films that is films with average grain size of less than about 15 nm, as opposed to films with larger grain sizes, such as microcrystalline or nanocrystalline diamond.
• an object of the present invention to provide an electrically conducting ultrananocrystalline diamond film having about 10 19 atoms/cm 3 nitrogen with an electrical conductivity of not less than about 0.1 ⁇ "1 cm “1 having a voltammetric response in the presence of Fe(CN) 6 "3M , Ru(NH 3 ) 6 + +3 , methyl viologen and 4-te/t-butylcatechol similar to high quality microcrystalline diamond, indicating that the nanocrystalline films are active without any conventional pretreatment, and posses semimetallic electronic properties over a potential range from 0.5 to - 1.5 V (vs. SCE).
• Another object of the present invention is to provide an electrically conducting ultrananocrystalline diamond film of the type set forth useful as diamond film electrodes with continuous pin-hole free surface at thickness in the order of about 750 A to about 2000 ⁇ in electrochemical cells operating at over voltages of about 2.5 volts to degrade or destroy organic contaminants.
• Another object of the invention is to provide field emission devices using the nitrogen doped UNCD films disclosed herein as flat panel displays, cold cathode devices in traveling wave tubes, satellite thrusters, x-ray machines and devices.
• FIG. 1 (a) is a graphical representation of the relationship of the concentration of CN radicals as a function of nitrogen in the plasma;
• FIG. 1(b) is a graphical representation of the relationship of the concentration of C 2 radicals as a function of nitrogen in the plasma;
• FIG. 2 (a) is a graphical representation of the relationships of total nitrogen content (left axis) and room-temperature conductivity (right axis) in a UNCD film as a function of nitrogen in the plasma;
• FIG. 2(b) is an Arrhenius plot of conductivity data obtained in the temperature range 300-4.2 K for a series of UNCD films synthesized using different nitrogen concentrations in the plasma as shown;
• FIG. 3 is a graphical representation of relationship of the concentration of nitrogen incorporated in the UNCD films versus the percent nitrogen in the feed gas of the plasma;
• FIGS. 4(a)-(d) are UV Raman spectra of UNCD films: a) without nitrogen in the gas chemistry, and with b) 2%, c) 10% and d)20% nitrogen, showing that all the nitrogen-added films have approximately the same sp 2 ;sp 3 ratio, which is increased 25-30% over the non-nitrogen film;
• FIG. 5 is EELS spectra of a UNCD film with 2% nitrogen and without nitrogen in the plasma, showing a distinct shoulder in the nitrogen film indicating sp 2 bonded carbon;
• FIGS. 6(a)-6(d) Low and high resolution TEM micrographs of a.) 0% N2 b.) 5% N2 UNCD, c.) 10% N2 UNCD, and d.) 20% N2 UNCD films.
• Low resolution micrographs are on the left, high resolution on the right. The figures are scaled so that the low resolution micrographs are 350 nm by 350 nm and the high resolution ones are 35 nm by 35 nm;
• FIG. 7 is a graphical representation of the relationship of the onset field emission as a function of the percent nitrogen in the plasma;
• FIGS. 8(A)-(B) are graphical representations of the Visible Raman spectra of (A) nanocrystalline diamond films deposited from 0, 2, 4 and 10% N 2 in the source gas mixture and (B) is a microcrystalline, boron-doped diamond film;
• FIG. 9 is a graphical representation of a UV Raman spectra of nanocrystalline diamond films deposited from 1 , 5 and 10% N 2 in the source gas mixture;
• FIGS. 10(A)-(B) are graphical representations of SIMS data for nanocrystalline diamond films.
• FIG. 11 are cyclic voltammetric i-E curves for nanocrystalline diamond thin films deposited from 1% CH 4 /1% N 2 /98% Ar, 1% CH 4 /2% N 2 /97% AR, 1 % CH 4 /4% N 2 /95% Ar and 1 % CH 4 /5% N 2 /94% Ar. Electrolyte: 1 M KCI. Scan rate: 0.1 V/s.
• FIGS. 12(A)-(B) are cyclic voltammetric i-E curves for nanocrystalline diamond thin films deposited from (A) 1% CH 4 /99% Ar, (B) 1% CH 4 /2% N 2 /97% Ar, (c) 1 % CH 4 /4% N 2 /95% Ar and (D) 1% CH 4 /5% N 2 /94% Ar.
• Electrolyte 0.1 M HCIO 4 .
• Scan rate 0.1 V/s;
• FIGS. 13(A)-(B) are graphical representation of cyclic voltammetric data for nanocrystalline diamond thin films.
• A Plots of the oxidation peak current versus the scan rate 1/ ⁇
• Analyte concentration 1 mM.
• Electrolyte 1 M KCI.
• B Plots of the oxidation peak current versus the analyte concentration. Electrolyte: 1M KCI. Scan rate: 0.1 V/s;
• FIG. 14 show oxidation-reduction reactions for a variety of compounds.
• FIG. 15 is a schematic diagram of a field-emission cold cathode using the n-doped UNCD.
• This invention relates to the incorporation of dopants into UNCD thin films, in particular, the incorporation of nitrogen via the addition of N 2 gas to the carbon containing noble gas plasma.
• N 2 gas nitrogen-containing UNCD thin films
• nitrogen-containing UNCD thin films can be used as electrochemical electrodes over a 4 eV potential range and exhibit semimetal-like electronic properties.
• nitrogen may introduce changes in morphology and electronic structure within the GBs that may lead to enhanced electronic transport, since simulation indicate that introduction of nitrogen into high-angle twist diamond GBs is energetically favored by 3-5 eV compared to substation into the grains.
• inventive films were grown on a variety of metals and non-metals using microwave plasma chemical vapor deposition with gas mixtures of Ar/CH 4 (1%-2%)/N 2 (1-20%) at total pressures of 100 Torr and 800 W of microwave power, while the substrates were maintained at temperatures from about 350 to 800°C.
• UNCD films Essentially all the grains of UNCD films have the stated grain sizes, and by essentially all we mean greater than about 90% and preferably greater than about 95%. Moreover, UNCD films may be produced using up to about 2% by volume of C.H 4 or a precursor thereof or C 2 H 2 or a precursor thereof or a C 60 compound. UNCD films exhibit a number of interesting materials properties, including enhanced field emission, and electrochemical, as well as mechanical, tribological, and conformal coating properties suitable for microelectromechanical system devices.
• the number densities of the C 2 and CN radicals formed in the plasma increase proportionally with nitrogen content in the plasma up to 5%, as measured by absorption spectroscopy.
• Secondary ion mass spectroscopy (SIMS) data show that the content of nitrogen in the film saturates at about 1x10 19 atoms/cm 3 (-0.2% total nitrogen content in the film) when the nitrogen concentration in the plasma is 5%.
• the conductivity at room temperature increases dramatically with nitrogen concentration, from 0.016 (1 % N 2 ) to 143 ⁇ " 1 cm “1 (20% N 2 ).
• Temperature dependent conductivity and Hall measurements are both indicative of multiple, thermally activated conduction mechanisms with effective activation energies of ⁇ 0.1 eV. This behavior is very similar to highly-boron- doped microcrystalline diamond. However, the inventors do not believe that nitrogen is acting in the manner boron does. It is believed that conduction occurs via the grain boundaries and not the grains. Tight-binding molecular dynamic simulations have shown that nitrogen incorporation into the high-angle grain boundaries is favored by 3-5 eV over substitution into the bulk. Nitrogen increases the amount of three-fold coordinated carbon atoms in the grain boundaries (GB) and leads to additional electronic states near the Fermi level. The inventors believe that GB conduction involving carbon ⁇ -states in the GB is responsible for the high conductivities. It has been shown that many of these states near the Fermi-level are delocalized over several carbon nearest neighbors.
• inventive films were grown either on Si(100) or insulating silica (SiO 2 ) substrates (for transport measurements) at 800°C, using a CH 4 (1%)/Ar/N 2 gas mixture at a total gas pressure of 100 Torr and 800 W microwave power.
• substrates such as various metals and non-metals may also be used.
• the average C 2 and CN radical densities in the plasma were determined in situ using absorption spectroscopy. These results are shown in FIGS. 1(a) and (b).
• the densities of both the C 2 and CN radicals increase substantially as N 2 gas is added to the plasma, while their ratio changes as well.
• the effect is to increase the density of C 2 dimers by one order of magnitude.
• the relative density of C 2 to CN decreases by a factor of 5. This trend in the data is also reflected by accompanying changes in film morphology, total nitrogen content, and conductivity, as discussed below.
• High-resolution transmission electron micrographs (HRTEM) from UNCD films synthesized using either 1% or 20% N 2 in the plasma show substantial microstructural changes, as shown in Fig. 6(a)-6(d).
• HRTEM transmission electron micrographs
• the morphology of the films remains largely unchanged, with the average grain size and average GB widths increasing only slightly.
• both the average grain size and average GB widths increase significantly, to 12 and 1.5 nm, respectively.
• Films made using 20% N 2 have average grain sizes about 15 nm and average GB width of 2 nm.
• the contrast in the HRTEM images between the GBs and the diamond grains suggests that the GBs are less dense than the grains. We believe this is evidence of an increase in sp 2 bonding in these regions of the films.
• the inventive films have a substantially different microstructure than prior art films.
• Zhou et al. in J. Appl. Phys. 82(9), 1 November 1997 report a nanocrystalline thin film grown from N 2 /CH 4 microwave plasma.
• the Zhou et al. films were grown in an entirely different plasma than the inventive materials described herein.
• the Zhou et al. plasma contained no nobel gas, whereas the predominant portion of the plasma used to grow the inventive material is a nobel gas. With N 2 present in the 20-25 volume percent range and carbon present in the 2 atom percent range, the nobel gas would be present in an amount of at least 73 volume percent for the inventive process and materials produced thereby.
• the Zhou et al. material does not have the same microstructure as the inventive films.
• the inventive materials have a clear grain + GB morphology, whereas the films studies by Zhou et al. do not, as shown in Fig. 3 of that paper.
• the average grain size of the Zhou et al. material is believed to be substantially larger (about 30-50 nm, based again on Fig. 3 of their paper) than the average grain size of the inventive material, which is between about 2 nm or less to about 15 nm.
• FIG. 2(a) shows secondary ion mass spectroscopy (SIMS) data for the total nitrogen content in the films as a function of the percentage of N 2 gas added to the plasma.
• SIMS secondary ion mass spectroscopy
• Hall measurements have been made on two of the UNCD films grown with 10% and 20% nitrogen in the plasma.
• the carrier concentrations for the 10% and 20% N 2 samples were found to be 2.0x10 19 and 1.5x10 20 cm “3 , respectively.
• the latter concentration is two orders of magnitude larger than any previous result for n-type diamond, and comparable to the carrier density in heavily boron-doped diamond.
• the negative value of the Hall coefficients indicates that electrons are the majority carriers in each of these films.
• the electrical conductivity of a nitrogen doped UNCD material can be systematically and reproducibly adjusted, permitting a material or film to be made with a predetermined electrical conductivity. For instance, adding 5% nitrogen results in a material having a conductivity of about 0J ( ⁇ cm) "1 while adding 10% nitrogen results in a material having a conductivity of about 30 ( ⁇ cm) "1 , see Figs. 2 (a)(b).
• the ability to predetermine and vary the conductivity of UNCD materials is entirely new and unexpected. Previously materials were made and then their conductivities were measured, but there was no method of making materials having a specifically desired conductivity, until this invention.
• n-type silicon wafers resistivity 0.001 - 1.0 ⁇ -cm
• 0.1 micron diamond powder for approximately 10 minutes.
• the Si substrates were then placed in the PECVD chamber.
• the films were grown at 800°C, 100 Torr total pressure, 100 seem total gas flow rate, and 800 W microwave power. These conditions are by way of example only and are not meant to limit the invention. It is now within the skill of the art to produce ultrananocrystalline diamond using a variety of conditions and techniques.
• the content of the source gas mixture was changed by successively adding N 2 to replace argon in 1% CH 4 / 99% Ar plasmas.
• FIG. 3 displays the secondary ion mass spectroscopy results as nitrogen concentration in the film versus the percent nitrogen in the plasma during film growth. Since the base pressure of the PECVD system is approximately 1 mTorr, about 8 x 10 18 atoms/cm 3 of nitrogen, slightly less than 0.01 atomic percent, is present in the UNCD film due to atmospheric nitrogen contamination.
• the concentration of nitrogen in the film increases an order of magnitude to 2.5 x 10 20 atoms/cm 3 , and continues to rise until about 5% nitrogen is added to the plasma. No further increase in nitrogen in the film is observed even when 20% N 2 is added to the plasma.
• the concentration of nitrogen incorporated in the film therefore saturates at about 8 x 10 20 atoms/cm 3 -
• TEM electron diffraction patterns for a film without added nitrogen and one with 2% nitrogen can be completely indexed on the diamond lattice, no other crystalline phase was found.
• the grain size distribution of such films is on the order of 3-15 nm.
• FIGS. 4(a)-(d) show the UV Raman spectra of UNCD films with varying degrees of nitrogen content.
• the introduction of nitrogen results in an increase in the peak at 1580 cm “1 relative to the peak at 1332 cm “1 , which is the phonon peak for diamond.
• the relative ratio of sp 2 to sp 3 remains roughly independent of the nitrogen concentration.
• the present increase in the sp 2 :sp 3 ratio for the nitrogen films is calculated as 25-30%.
• FIG. 5 shows the electron energy loss spectra (EELS) for UNCD films without nitrogen and with 2% nitrogen to the plasma, respectively.
• the EELS of the nitrogen-grown diamond film reveals the K-edge ⁇ * peak at 291 and a distinct ⁇ * peak originating form the sp 2 carbon K edge at 286 eV.
• the film grown without nitrogen shows only the ⁇ * peak by EELS measurements.
• the field emission measurements were carried out on an apparatus previously described in an article published by D. Zhou et al. in J. Electrochem soc. The field emission measurements were carried out on an apparatus previously described in an article published by D. Zhou et al. in J. Electrochem Sod 44(1997) L224, the disclosure of which is hereby incorporated by references. Briefly, a negative potential is applied to the sample, and the emission current is measured using a Keithley electrometer. A CCD camera is used to estimate the initial starting gap, typically 50 to 100 microns. The distance has been calibrated with a foil with a thickness of 500 microns. The anode is a 2.0 mm diameter tungsten probe with the edges slightly rounded to avoid edge effects.
• An ambient pressure of 10 "8 Torr is maintained in the test chamber by a turbo molecular pump and an ion pump.
• the applied voltage is varied, and the collected current as a function of applied voltage is recorded on a computer system.
• the applied voltage divided by the gap distance yields the applied field.
• the results of the field emission measurements are shown in FIG. 7.
• the film without added nitrogen had an average onset field of 23 V/ ⁇ m, with a best onset value of 10 V/ ⁇ m.
• the figure shows that for nitrogen containing films the average onset field required for emission immediately drops to below 5 V/ ⁇ m for 1% nitrogen added to the plasma, and remains relatively constant for up to 20% N 2 in the plasma. Some film areas had onset fields as low as 2 V/ ⁇ m .
• the measurements represent the average values of at least 12 different areas on one or two samples with the given percent nitrogen. Some of the films had a few areas that did not emit below fields of 40 V/ ⁇ m. These spots were not included in the averages. In general, it was observed that several films without added nitrogen showed distinctly higher onset fields for all examined areas than the nitrogen-added films. Table 1 shows a summary of the data for all the films.
• Field emitters have a wide variety of applications to multiple devices involving electron emission from fabricated field emitter sharp tips or edge structures that are localized at the center of a hole (see Fig. 15).
• the application of a potential between the gate electrode and the field emitter tip produces a very high field on the tip, which results in field-induced emission of electrons.
• Current materials used for producing the field emitter have relatively high threshold fields for emission (about 10 V/ ⁇ ) and/or they exhibit unstable emission current.
• Undoped or n-type or p-type doped UNCD exhibit both very low threshold field (4 V/ ⁇ m) and stable emission current, the two main requirements for operation of cold cathodes based on field emission.
• UNCD based cold cathodes can be used in multiple applications, some of which are:
• Cold cathodes for large systems such as ion beam accelerators, where the electrons are used to generate plasmas needed to produce the ion beams; X-ray sources, where the electrons are used to generate X-rays via electron impact on solid anodes.
• Field emission sources to provide electrons for creating a plasma in a confined chamber for use as a spacecraft thruster.
• the impulse is provided by momentum transfer to the thruster chamber by ion expelled from the plasma.
• N-type doped UNCD materials as disclosed herein have applications to all the devices described above.
• Fig. 15 shows one emitter, in use as is well known in the art, an array of high density emitters may be employed, as for instance in flat panel displays.
• the volume fraction of grain boundaries can be determined using the following equation given by Palumbo et al., Aust, Scripta Metall-Matev. 24(1990), 1347, 2347
• V gb [3 ⁇ (d - ⁇ ) 2 ]/d 3 (Eq. 1)
• ⁇ is the grain boundary thickness and d is the average diameter of the grains. If one chooses 10 nm for the average grain size and a grain boundary width of 0.32 nm, as known, the volume fraction of grain boundaries in 0.09, or 9%, of the film. If 40% of the grain boundaries are sp 2 bonded, then 3.6% of the film is sp 2 , assuming all sp 2 bonded carbon atoms are in the grain boundaries. A 30% increase in sp 2 character as given by the UV Raman equates to 4.7% of the film being sp 2 (0.036 x 1.3).
• Recent density-functional based tight-binding (DFTB) calculations have been performed, which may explain the increase in the sp 2 :sp 3 in the films with nitrogen and show that nitrogen substitution into the grain boundaries rather than into the diamond lattice, is energetically favorable by 2.6 to 5.6 eV, depending on the specific grain boundary site.
• the calculations suggest that three-fold coordinated sites are the lowest energy sites for nitrogen and that these promote sp 2 bonding in the neighboring carbon. The theoretical calculations are thus in agreement with the experimental results, which show a 25-30 % relative increase in sp 2 bonding.
• nitrogen-doped UNCD thin films have been synthesized using a microwave plasma CVD technique with a CH 4 /Ar/N 2 gas mixture.
• Other carbon containing gases also are applicable, as well as other deposition methods and other noble gases, as previously stated.
• the morphology and transport properties of the films are both greatly affected by the presence and amount of CN in the plasma, which varies as N 2 gas is added.
• the HRTEM data indicated that the grain size and GB width of the UNCD films increase with the addition of N 2 in the plasma.
• Our transport measurements indicate that these films have the highest n- type electrical conductivity reported thus far in phase-pure diamond thin films.
• the electrochemical characterization reveals that these films have a wide working potential window in aqueous media ( ⁇ 4V), a very low background voltammetric signal, and excellent activity for several aqueous-based redox analytes without any pretreatment.
• Cyclic voltammetric ⁇ E P values of 60 to 90 mV (0J V/s) for Fe(CN) 6 "3M , Ru(NH 3 ) 6 +3/+2 and methyl viologen are observed.
• the electrochemical response for the redox analytes is almost totally inhibited after 60 minutes of treatment due to excessive film resistance caused by the loss of the ⁇ bonding.
• Figure 8A shows a series of visible Raman spectra for films deposited with and without N 2 in the source gas mixture.
• Figure 8B shows the spectrum for a microcrystalline diamond film, for comparison. Three bands are observed for all four nanocrystalline films (Fig. 8A): 1125, 1339 and 1560 cm “1 .
• the broad band at 1339 cm “1 is assigned to the first-order phonon mode for diamond, reflective of the sp 3 - bonded microstructure.
• the peak is shifted to higher wavenumbers from the expected 1332 cm "1 position.
• microcrystalline diamond films have a sharp peak at 1332 + 2 cm "1 with a linewidth of 5 to 8 cm '1 (Fig. 8B).
• the significantly broadened and shifted diamond line for the nanocrystalline films results from the decreasing grain size to the nanometer scale.
• the linewidth is a measure of the phonon lifetime. The more defects there are (i.e., grain boundaries), the shorter the phonon lifetime and the broader the linewidth.
• the amorphous sp 2 -bonded carbon peak at 1560 cm "1 results from the ⁇ -bonded carbon atoms in the grain boundaries. The position and intensity of this broad peak depends on the deposition conditions used, the wavelength of the excitation photon and how microstructurally ordered the nondiamond carbon phase is.
• the spectra also contain a feature centered at 1125 cm 1 .
• the relative intensity ratios of the three peaks in the nanocrystalline diamond spectra are shown as a function of the N 2 percentage in the source gas mixture. It can be seen that the ratio of the diamond to the nondiamond band intensities, l 1339 /l 156 o, is largest for the film deposited without N 2 and decreases for the films deposited with the gas. Interestingly, the ratio is independent of the N 2 level.
• An assumption is often made that the relative band intensities reflect the volume fractions of diamond and nondiamond carbon present. In making this assumption, one must consider that the optical probing depth (i.e., sampled volume) can vary with the microstructure of the nondiamond phase. Also, the scattering cross sections for the different types of nondiamond carbon phases possible (mixtures of sp 2 - and sp 3 -bonded carbon) are unknown. Therefore, these data should be used in a relative not an obsolute sense.
• Figure 9 shows the UV Raman spectra for films deposited from CH 4 /Ar with N 2 added.
• the use of visible excitation often gives rise to an intense background luminescence that can mask the Raman line in nanocrystalline diamond, even in films with low sp 2 carbon content.
• the Raman signal for sp 2 -bonded carbon is approximately 50 times more sensitive than diamond using visible excitation (514.5 nm). The signal for diamond is expected to increase relative to that for amorphous or graphitic carbon as the excitation wavelength is shifted toward the UV.
• the spectrum for a 1 % CH 4 /1 % N 2 /98% Ar film shows a moderately intense diamond line at 1332 cm “1 with a linewidth of 25 cm “1 .
• the band intensities for the diamond and nondiamond carbon are roughly the same, but the peak area for the latter is significantly larger.
• the sp 3 /sp 2 band intensity ratios are 1.0, 0.56, and 0.25 for the 1%, 5%, and 10% N 2 levels, respectively, indicating that the fraction of ⁇ -bonded grain boundaries increase with N 2 added.
• Figure 10A and B show dynamic SIMS data for the nitrogen and carbon atomic concentrations in the nanocrystalline films.
• the actual nitrogen and carbon atomic concentrations, as well as the N/C atomic ratios, are listed in Table 3. TABLE 3. Secondary ion mass spectrometry data for nanocrystalline diamond films.
• Figure 10A shows a plot of the N/C atomic ratio versus the percentage of N 2 in the source gas mixture. There is a near linear increase in the ratio with N 2 added up to the 5% level. Above 5%, the amount incorporated levels off.
• the N/C for 0% N 2 in the source gas mixture is not zero but rather 5.97 x 10-4; about two orders of magnitude lower than the ratio in the films deposited from gas mixtures containing N 2 .
• Figure 10B shows profiles of the carbon and nitrogen concentrations as a function of depth for a film approximately 1 ⁇ m thick. The concentration of nitrogen is as high as approximately 5 x 10 20 atoms/cm 3 with uniform distribution through the film.
• Figure 11 shows a series of cyclic voltammetric i-E curves in 1 M KCI for nanocrystalline diamond films containing different levels of incorporated nitrogen. It is clear that the responses between -500 and 1000 mV are very similar irrespective of the level of nitrogen incorporated. The background currents are low and featureless within this potential range. Each is also unchanging with cycle number indicating that the surface structure is stable. The magnitude of the anodic current at 250 mV is approximately 0.4 ⁇ A or 2.0 ⁇ A/cm 2 (geom.) for all of the nanocrystalline films. This is slightly lower than the 2.7 ⁇ A/cm 2 reported previously for nanocrystalline diamond films deposited from C 60 /A 6 .
• the background current for polished glassy carbon at this potential and scan rate is near 20 ⁇ A/cm 2 .
• very minor differences are seen in the background voltammograms between -500 and 1000 mV with varying levels of incorporated nitrogen. This indicates that the excess surface charge density int his potential region is not affected significantly by the nitrogen concentration, and the introduction of nitrogen in the grain boundaries does not introduce detectable levels of electroactive carbon sites.
• Figures 12(A)-(D) show cyclic voltammetric i-E curves in 0.1 M HCIO 4 for nanocrystalline diamond films containing different levels of incorporated nitrogen.
• the voltammograms cover a wider potential range than those in Figure 11 , allowing determination of the full working potential window.
• All the films have an anodic limit of approximately 2400 mV (100 ⁇ A or 500 ⁇ A/cm 2 ).
• the current at this potential is mainly due to oxygen evolution and, to a much lesser extent, the oxidation of carbon atoms on the surface.
• the surface oxidation processes may involve both the diamond and grain boundary carbon, and are evidenced indirectly by the anodic charge passed between 1400 and 2200 mV just prior to the exponentially increasing current for oxygen evolution.
• Table 4 shows the cyclic voltammetric ⁇ E P values at 0.1 V/s with iR correction. It can be seen that the largest uncompensated resistance, most of which is the bulk resistance of the electrode, is observed for the 1% CH 4 /99% Ar film. The uncompensated resistance is significantly lower for the films containing nitrogen with a trend of decreasing resistance with increasing nitrogen incorporation.
• the iR corrected data reveal that the ⁇ E p values for methyl viologen, Ru(NH 3 ) 6 +3/+2 and Fe(CN) 6 "2/'3 all decrease with increasing nitrogen incorporation. These relatively low ⁇ E p 's were obtained even though the films received no pretreatment prior to use. This reflects the material's chemical inertness and resistance to fouling by adsorbed impurities.
• the rate of electron transfer for Fe(CN) 6 "3M at metal and sp 2 carbon electrodes is strongly affected several factors.
• the rate of electron transfer increases proportionally with the fraction of exposed edge plane, as detected by Raman spectroscopy.
• surface cleanliness is important as is the electrolyte type and concentration. For example, the involvement of specifically adsorbed cations (e.g., K + ) through a possible surface-bridging interaction has been proposed.
• the rate of electron transfer increases with electrolyte composition in the order of LiCI ⁇ NaCI ⁇ KCI. At the 1 m electrolyte concentration, the rate is about a factor of 10 higher in KCI than in LiCI at both gold and glassy carbon electrodes.
• adsorbed monolayers on sp 2 carbon electrodes can decrease the rate of electron transfer. It has been observed the ⁇ ( ⁇ E P ) increase from 5 to 140 mV after modification of the polished grassy carbon surface with adsorbed monolayers. The level of increase depends on the type and coverage of the adsorbate.
• the rate of electron transfer is also influenced by the physiochemical properties of boron-doped diamond.
• ⁇ E P is very sensitive to the surface termination with the smallest ⁇ E P observed at the clean, hydrogen-terminated surface. After oxygen termination, ⁇ ( ⁇ E p ) increases by over 125 mV but it is reversibly reduced to the original value after removal of the oxygen functionalities by hydrogen plasma treatment (42).
• the sensitivity of the kinetics to surface oxygen is in sharp contrast to the minor effects these functionalities have on the response at sp 2 carbon electrodes.
• the rate of electron transfer is also sensitive to the electrolyte composition and ionic strength with the largest rates observed in Kcl and the smallest in LiCI.
• the rate of electron transfer for Ru(NH 3 ) 6 +3 +2 is relatively insensitive to the surface microstructure, surface oxides and adsorbed monolayers on sp 2 carbon electrodes.
• the rate of electron transfer is insensitive to surface modification with the strong implication that electron transfer does not depend on an interaction with a surface site or functional group.
• the most important factor affecting the rate of electron transfer is the electronic properties of the electrode, specifically the density of electronic states near the formal potential of the redox system. Of course with metal and glassy carbon electrodes, a low density of electronic states is never an issue. However, with the semiconducting/semimetallic properties of diamond, the potential-dependent electronic density of states is an influential factor. This is why ⁇ E P values of 60 to 75 mV are good in agreement with the 70 to 80 V values often observed for boron-doped microcrystalline diamond films at 0.1 V/s.
• the formal potential (i.e., cyclic voltammetric E p/2 value) for this couple is - 218 mV vs. SCE.
• the valence band position of boron-doped microcrystalline diamond has been estimated to be approximately 550 mV vs. SCE. Given the 5.5 eV bandgap and the assumption that the interfacial energetics of nanocrystalline diamond are similar, this means that the formal potential falls within the bandgap (i.e., between the valence and conduction band positions). Therefore, this redox system is not expected to exchange charge directly with either the valence or the conduction band.
• the nearly reversible response indicates that there must be a high density of electronic states present within the bandgap at this potential. These electronic states arise from the nitrogen incorporated and or/the nitrogen- related defects introduced. Theoretical work will be discussed below which indicates the bandgap density of electronic states arises from the ⁇ -bonded carbon in the grain boundaries.
• Methyl viologen also involves simple outer sphere electron transfer at diamond and most other electrodes.
• the rate of electron transfer at diamond is relatively insensitive to surface oxides, grain boundaries and defect density, and the presence of nondiamond carbon impurities.
• Ru(NH 3 ) 6 +3/+2 the most important factor influencing the rate of electron transfer is the density of electronic states at the formal potentials for the two redox reactions. Nearly reversible voltammetric behavior ( ⁇ E p 's from 60 to 90 mV at 0.2 V/s) is typically observed for both the MV +2 /MV + and MV7MV 0 redox couples having a formal potentials of -725 and -1050 mV vs. SCE, respectively.
• MV can form surface phases depending on the experimental conditions and these deposits complicate the process of directly relating the ⁇ E P to the rate of electron transfer.
• the formal potentials are well into the bandgap region, even more negative than the formal potential for Ru(NH 3 ) 6 +3/+2 .
• the relatively low ⁇ E P of 50 to 60 mV for nitrogen-incorporated nanocrystalline diamond indicates these electrodes contain a high density of bandgap electronic states, even these negative potentials.
• 4-methylcatechol exhibits more electrochemical irreversibility as evidenced by the ⁇ E P of 200 to 400 mV. Also, there is a trend of increasing ⁇ E P with increasing nitrogen-incorporation. The more irreversible behavior is also characteristic of all the catechols and catecholamines investigated so far at microcrystalline diamond. Typical ⁇ E P values of 450 to 700 mV at 0.1 V/s are observed. For comparison, ⁇ E P at polished glassy carbon under identical conditions is in the range of 125 to 175 mV (36). The formal potential is positive of that for Fe(CN) 6 "3M so a low density of electronic states is not the reason for the large ⁇ E p .
• Figures 13(A)and (B) show plots of the voltammetric oxidation peak current as a function of the square root of the scan rate and the solution concentration for all four redox analytes.
• the peak current varies linearly with the square root of the scan rate (r 2 ) 0.995) and all plots intercept the y-axis near the origin. This indicates the reactions are limited by semi-infinite linear diffusion of the reactant to the electrode.
• the voltammetric peak current also varies linearly with the concentrations (r 2 ) 0.992) for ail analytes from the 0.1 to 1 mM level. All plots intercept the y-axis near the origin, as expected.
• Electrochemically, these films are excellent electrodes. They are characterized by a wide working potential window ( ⁇ 4 V), low background current and a very active response for Fe(CN) 6 "3/"4 , Ru(NH 3 ) 6 +3/+2 and MV +2 + without any conventional pretreatment.
• ⁇ E p 's in the range of 60 to 90 mV (0.1 V/s) are observed for these three redox systems depending on the nitrogen incorporation.
• ⁇ E p for 4-MC was significantly larger at 200 to 400 mV (0.1 V/s) indicative of slower electrode reaction kinetics compared to the other three redox systems.
• Ultrananocrystalline diamond films doped with nitrogen to render them electrically conducting can be used as electrochemical electrodes which span a potential range of over 4 eV in aqueous solutions such as 0.1 M HC1O 4 .
• Figures 12(A)-(D) shows cyclic voltammetric i-E curves for films deposited from source gas mixtures of methane and vapor containing different amount of nitrogen.
• n-UNCD electrodes are useful for a wide range of oxidation reduction reactions as illustrated in Fig. 14 for Fe(CN) 6 "3 “4 , Ru(NH 3 ) 6 +3/+2 , IrCle “27”3 , and methyl violagen with a high degree of electrochemical activity. More sluggish electrode kinetics are observed for 4-methylcatechol. Apparent heterogeneous electron transfer rate constants of 10 "2 to 10 "1 cm/5 are observed for the highly active reactions without any pretreatment.

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