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Key factors in C 1s photoelectron spectroscopy for realistic samples of single crystal diamonds are remarked. Basic equations for angle-dependent photoelectron spectroscopy applied to single crystal diamond samples are described in Appendix A. Carbon 1s photoelectron spectroscopic works so far reported for hydrogen-terminated and oxygen-terminated diamond (001) and (111) samples were reviewed placing special attention on surface C 1s components with reference to the key factors. The results showed diversity in C 1s photoelectron spectra so far reported. We had three specific subjects of the study in C 1s XPS; the first is that we have reconfirmed the phenomenon that surface conductive layers resumed when smooth non-doped CVD C(111)-O samples were annealed in vacuum [Diam.Rela.Mate.18(2009)206]. A single C 1s XPS surface component was found for a smooth C(111)-O sample before the vacuum-anneal, which was attributed to surface carbon atoms in C O H bonding. The second subject is that dependence of C 1s XPS spectra on surface sensitivity has been measured for all the samples with different surface roughness of C(001)-O, C(111)-O, C(001)-H, and C(111)-H. The results were converted to the energy difference between the Fermi-level (Ef) and valence band maximum (Ev) on the probing depth from the surface. All the samples showed downward bending of Ev toward the surface. For the C(001)-H samples, this was a reconfirmation of previous work [Surf.Sci.604(2010)1148]. For the C(001)-H and C(111)-H samples, various degrees of downward band bending toward surface were observed and analyzed with two-dimensional band simulation. It was concluded that another source of holes such as shallow acceptors is present in a deeper region of the surface in addition to holes very close to surface caused by the charge-transfer-doping. The third subject is that C 1s XPS spectra for superconducting C(111)-O samples showed a lattice distortion of ~9 monolayers near the surface.

Although Ti-based ohmic contacts are often used in the fabrication of diamond electronic devices, researches on the barrier height (ϕB) of this contact are very limited and no consistent values have been reached. In this study, a direct determination of ϕB was performed using X-ray photoelectron spectroscopy. An array of μm-size Ti/Au ohmic electrodes was made on a lightly boron-doped p-type diamond (001) surface, and C 1 s and Au 4f7/2 XPS spectra were measured. The peak binding energies of the spectra from the sample and from reference samples were compared, and ϕB was determined to be ~ 0.63 ± 0.13 eV for the p-type diamond (001). The result is compared with those of previous works and discussed. Prime novelty statement The Ti-based ohmic contacts are often used in the fabrication of diamond electronic devices. Although reasonably low specific contact resistances between 10− 5 and 10− 7 Ωcm2 at room temperature have been obtained for the Ti-based ohmic contacts, the barrier height of the contact has not been determined consistently. In this study, the barrier height of the Ti-based ohmic contact on a p-type diamond (001) is directly determined by X-ray photoelectron spectroscopy to be 0.63 ± 0.13 eV.

The structural properties of optically thin (15 nm) silver (Ag) films deposited on SiO2/Si(100) substrates with a germanium (Ge) nucleation layer were studied. The morphological and crystallographical characteristics of Ag thin films with different Ge nucleation layer thicknesses were assessed by cross-sectional transmission electron microscopy (XTEM), reflection high-energy electron diffraction (RHEED), X-ray diffractometry (XRD), grazing incidence X-ray diffractometry (GIXRD), X-ray reflection (XRR), and Fourier transform infrared spectroscopy (FTIR). The surface roughness of Ag thin films was found to decrease significantly by inserting a Ge nucleation layer with a thickness in the range of 1 to 2 nm (i.e., smoothing mode). However, as the Ge nucleation layer thickness increased beyond 2 nm, the surface roughness increased concomitantly (i.e., roughing mode). For the smoothing mode, the role of the Ge nucleation layer in the Ag film deposition is discussed by invoking the surface energy of Ge, the bond dissociation energy of Ag-Ge, and the deposition mechanisms of Ag thin films on a given characteristic Ge nucleation layer. Additionally, Ge island formation, the precipitation of Ge from Ag-Ge alloys, and the penetration of Ge into SiO2 are suggested for the roughing mode. This demonstration of ultrasmooth Ag thin films would offer an advantageous material platform with scalability for applications such as optics, plasmonics, and photonics.

Diamond thin film has outstanding physical and chemical properties. Diamond-on-iridium configurations have been prepared by several methods, such as microwave enhanced plasma CVD, direct currency plasma CVD, and hot filament CVD. In this study, an Ir interlayer was deposited on single crystal sapphires (Al 2 O 3 ) with A-planes {1120} by an RF magnetron sputtering method after annealing samples. In addition, a diamond thin film was deposited by a microwave enhanced plasma chemical vapor deposition (MPCVD) method using a mixture of hydrogen and methane gases after a bias enhanced nucleation (BEN) procedure. Ir (001) was grown on the A-plane of sapphire by X-ray pole figure measurement. Diamond thin films were synthesized on each Ir/sapphire substrate and characterized by SEM, Raman spectroscopy. D {100} faces were exhibited in substantial areas of diamond films, and a flat D {100} plane was partially obtained. It is considered that diamond thin films on Ir {100} were mainly grown towards the direction and were epitaxially grown in part.

A simple method of sample treatment for angle-scan X-ray photoelectron diffraction (XPD) for insulating diamond is demonstrated. The resulting XPD patterns have shown that a quantitative measure of near-surface atomic order is obtained for the insulating diamond. This simple method may be applied in principle to any insulating material, which enables non-destructive characterization of near-surface order of insulating materials by XPD.

Heavily nitrogen (N)-doped polycrystalline diamond is reported to have excellent electron emission properties although its emission sites are limited. This report describes the fabrication processes, characterisation and electron emission properties of N-doped heteroepitaxial diamond which posses high potential as broad area emitter devices. We have obtained epitaxial diamond films on iridium (Ir) substrates by hot filament CVD using urea [(NH 2 ) 2 CO] as a dopant for N. The Ir substrates are bias treated via direct current plasma CVD (d.c. plasma CVD) method prior to the growth. Surface of the deposited films is smooth and continuous in scanning electron microscopy (SEM) observation. The epitaxial diamond growth is confirmed from reflective high energy electron diffraction (RHEED) pattern. It is found that the electron emission from heteroepitaxial diamond film is dominated by standard Fowler-Nordheim type emission due to the existence of strong electric field in the vacuum with the value of 26 V/μm.

Electron emission from both the hydrogenated and the oxidized boron-doped heteroepitaxial diamond with smooth surface is studied in order to understand the effect of adsorption on electron emission. B-doped heteroepitaxial diamond is grown on iridium (Ir) by direct current plasma chemical vapor deposition (CVD). A relatively smooth surface is obtained. The Cls peaks in X-ray photoelectron spectroscopy (XPS) for the hydrogenated and oxidized diamond surfaces are 284.1 and 285.6 eV, respectively. The threshold voltage of the hydrogenated diamond surface in the electron emission is lower than that of the oxidized diamond surface. The emission barrier height ratio of the hydrogenated diamond surface to the oxidized diamond surface is estimated to be 2.6 from the slopes of Fowler–Nordheim (F–N) plots. The change in the emission properties might be examined by the surface dipole formed on diamond surface from the XPS results and the F–N plots.

sp 3 and sp 2 -rich nitrogen (N)-doped diamond electron emitters are prepared by modifying the substrate temperature. Their electron emission properties have been measured in order to examine the effect of the sp 2 /sp 3 ratio on the electron emission from N-doped diamond. The obtained electron emitters have been characterized by reflective high energy electron diffraction, X-ray diffraction and Raman spectroscopy. The electrical resistivities of the sp 3 -rich diamond is 100 G Ω cm or higher while that of the sp 2 -rich diamond is 100 Ω cm. In electron emission characteristics, the threshold voltage of the sp 3 -rich emitter is found to be lower than that of the sp 2 -rich emitter. From the threshold voltage versus the anode-diamond spacing characteristics, it has been found that most of the anode voltage drops in the bulk of the sp 3 -rich emitter and almost no voltage drop takes place in the sp 2 -rich emitter. The difference in electron emission properties should be explained by the resistivity of the N-doped diamond bulk.

Electron emission from boron (B)- and nitrogen (N)-doped diamond electron emitter with silver (Ag)-loaded conductive epoxy, titanium (Ti)/gold (Au), aluminum (Al) and amorphous carbon contacts are studied. Both Ti/Au and amorphous carbon contacts on B-doped diamond electron emitters lead to lower turn-on voltage compared to other contacts, while the turn-on voltage of N-doped diamond electron emitter is independent on the backcontacts.

An Ir layer was epitaxially grown on a MgO(100) substrate by radio frequency magnetron sputtering, and was used as the substrate for the epitaxial growth of diamond by microwave plasma-assisted chemical vapor deposition (MPCVD) using CH4–H2 systems. The Ir(100) layer was then bias-treated under a wide variety of conditions. Thus, a bias voltage of −150 V, a methane concentration of 3%, and a continuation of 15 min, were determined to be the optimum conditions. In the subsequent diamond growth step, oriented diamond particles, 100–250 nm in size with pyramidal structures, were formed at a population density of (0.15–1.5)×108 cm−2. It is noteworthy that the fraction of oriented particles was nearly unity. Tilted or rotated diamond particles were seldom observed. Substrate erosion and graphitic carbon formation, also often observed in the case of Ni and Pt substrates, were not found during the diamond deposition on the Ir(100) substrate.

n -Type semiconducting diamond thin films were successfully grown by microwave plasma CVD using phosphine (PH 3 ) as a dopant source. The addition of PH 3 in the gas ambient strongly influences the optimal growth condition for diamond. The {111} surface of diamond was found to be the best surface as a substrate for the growth of phosphorous (P) doped diamond. At a methane to hydrogen ratio of 0.15% and a substrate temperature of 950 °C, smooth {111} oriented homoepitaxial diamond thin films are obtained even with the addition of PH 3 up to 1000 ppm to CH 4 . The epitaxial films grown with PH 3 /CH 4 : 600–20 000 ppm have shown clear n -type conduction by Hall effect measurements over a wide temperature range. An activation energy of electron of 0.46 eV was deduced from the temperature dependence of the carrier concentration. For the best (600 ppm) sample, the Hall mobility of 28 cm 2 /V-s has been obtained at a temperature range around 400–600 K.

Low-pressure chemical vapor deposition growth of graphene on Iridium (Ir) layers epitaxially deposited on α-Al2O3 (0001) substrates was investigated. The X-ray diffraction, Raman and reflection high energy electron diffraction characterizations revealed that graphene films were epitaxially grown on Ir(111) layers, and the in-plane epitaxial relationship between graphene, Ir(111), and α-Al2O3(0001) was graphene ⟨ 11¯00⟩//Ir⟨ 112¯⟩//α-Al2O3⟨ 112¯0⟩. The graphene on Ir(111) was electrochemically transferred onto SiO2/Si substrates. We also demonstrated the reuse of the Ir(111)/α-Al2O3(0001) substrates in multiple growth and transfer cycles.

Pb(Zr0.5Ti0.5)O3 (PZT) thin film was heteroepitaxially grown on an iridium/magnesium oxide (Ir/MgO) (001) substrate using the metalo-organic decomposition method, and its crystal orientation and ferroelectric properties were investigated. The Ir film by rf-magnetron sputtering on a MgO single crystal showed high crystallinity with the full width at half maximum of 0.2°. The obtained PZT film has a tetragonal structure. Reciprocal space mapping revealed that it consisted of only c-axis orientation. The Ir/PZT/Ir capacitor showed the remanent polarization of 45 μ C/cm2 and a coercive force of 100 kV/cm. These large values were derived from 100% 180° domain switching, which state is difficult to realize in bulky single crystal and ceramics because of piezostress relaxation.

This letter presents a clear explanation of the electron emission mechanism of the high-resistivity N-doped diamond cathode. Due to the very low barrier to emission of electrons from the N-doped diamond conduction band into vacuum, electrons in the conduction band of diamond can establish an appreciable leakage current at very low anode voltage. When such a current starts to flow, there is a field which is developed across the diamond bulk. This field is observed as an increase in the electric field at the back contact, causing the injected tunneling current increases exponentially. This process leads to the low threshold emission from the high resistivity N-doped diamond cathode.

A nitrogen (N)-doped diamond-based electron emitter has been fabricated by the sintering technique prior to the chemical vapor deposition process in order to improve the uniformity. There are no spatial differences in reflective electron energy loss spectra (REELS) from the diamond-based electron emitter, suggesting that uniform surface conditions are obtained. The uniform electron emission from the obtained electron emitter is confirmed through emission current vs anode voltage characteristics measurements. It seems that the uniformity of the emitter surface results in uniform electron emission from the diamond electron emitter.

The voltage drop of vacuum and boron (B)-doped diamond electron emitter bulk has been discussed in order to understand the electron emission mechanism of B-doped diamond. It is confirmed that the electron emission from B-doped diamond depends on its film thickness and the localized electron pass/channel is formed in the film. From the results of the threshold voltage versus anode-diamond spacing characteristics, it is found that most of the anode voltage is applied in vacuum, and the high electric field near the B-doped diamond surface is required for the electron emission from B-doped diamond regardless of the film thickness.

Electron spectro-microscopic methods were applied as direct methods of determining the Schottky barrier heights (SBHs) and their spatial distribution for Au- and Ag-Schottky junctions fabricated on an acid-treated oxygen-terminated diamond (001) substrate. Metal layers were formed with two ranges of thickness (3–5 nm for thin layers and 13–100 nm for thick layers) for both Au- and Ag-Schottky junctions. Leading X-ray photoelectron spectroscopy (XPS) core-level peaks of either Au 4f7/2 or Ag 3d5/2 for the metal layers and C 1s for diamond were used as measures of the SBH. For the thick-metal samples, spatially resolved XPS measurements were performed over most of the sample surface. It was found that there is a variation in SBH on the order of 0.1 eV for the large ("high barrier") SBH values and that there are several places where the SBHs were rather small ("low barrier" junction). For the thin-metal samples, less variations in SBH were observed. The average SBH of "high barrier" junctions for the thick-metal samples appeared to be slightly (0.1 eV order) larger than that for the thin-metal samples. XPS images of leading metal core levels tuned for the "high barrier" and "low barrier" SBHs were observed. For the thick-Ag Schottky sample, the resulting Ag 3d5/2 XPS images clearly showed the locations of defective Schottly junctions. It is suggested that the SBHs determined for the thin-metal samples are the average SBHs on the measured surface and that the SBHs determined for the thick-metal samples are the highest SBHs within the measured µm-size metal islands. The presently determined SBHs were compared with previously reported SBHs and reasonable agreement was found. Photoemission electron microscopy (PEEM) images were observed for the thick-Ag Schottky sample and the "low barrier" islands were identified. The methodologies of XPS, XPS imaging, and PEEM used for the thick-metal samples can be applied to any Schottky junction on diamond.

Epitaxial lateral overgrowth (ELO) of diamond on Ir(001)/MgO(001) substrates was demonstrated by using a patterned nucleation and growth method. Epitaxial nucleation areas of fine line shape aligned with various crystal orientations were prepared on an Ir(001) surface before diamond growth. The growth rate of the diamonds in the lateral direction markedly changed depending on both the crystal orientation and the growth conditions. A lateral/vertical growth rate ratio of approximately 4.9 was obtained. The full widths at half maximum of the diamond Raman peak observed at the laterally grown areas were approximately threefold better than that of the vertically grown areas on the nucleation sites.

A phosphorus (P)-doped n-type heteroepitaxial diamond (001) sample was grown in a DC-plasma chemical-vapor-deposition chamber. The crystalline properties of incorporated phosphorus were examined by cathode luminescence. Hall-effect measurement of the sample was performed for the temperature range of 293–870 K. The results of these measurements showed that the bulk properties of the n-type sample are comparable to those of previously reported homoepitaxial P-doped n-type diamond (001) samples. The work function of the heteroepitaxial sample was measured by photoemission electron microspectroscopy. The Fermi-level positions at the surface and at a Au Schottky junction of the sample were determined by X-ray photoelectron spectroscopy. Knowing the bulk properties and the critical values of the energy band structure, the whole energy band diagrams at the surface and at the Schottky junction of the sample were evaluated by solving the Poisson equation. The resulting surface electronic structure of the sample was qualitatively different from those of the previously reported H-terminated P-doped n-type diamond (111) surface and heavily P-doped H- and O-terminated diamond (111) surfaces. The presence of ∼0.02 ML of Sn impurity is tentatively ascribed to the peculiarity of the surface electronic structure of the heteroepitaxial sample. The Schottky barrier height of ∼4.2 eV determined for the present sample was consistent with those of previously reported n-type diamond (111) and (001) samples. It is noted that the Schottky barrier height may be determined by the Fermi-level pinning states at the junctions irrespective of the type of dopant to diamond.

Bias-treatment (BT) is widely used as an initial seeding process of chemical vapor deposition (CVD) growth of diamonds. In a BT, substrates are negatively biased by an order of hundred volts so that positive ions in the plasma of CVD gas source bombard the substrate to form 'seeds' of diamond growth. Bias-treated 1-inch-diameter () Ir(001)/MgO(001) substrates were used as the substrates of the CVD growth of 1-inch- diamond (001) thick films. XPS (X-ray Photoelectron Spectroscopy) spectra and C 1s and Ir 4f XPD (X-ray Photoelectron Diffraction) patterns were measured for the BT 1-inch- samples. 5 typical portions on the sample were measured; one at the central portion and the other 4 were peripheral portions, 90° apart from each other and ~4 mm from the edge of the sample. The uniformity of the result over the 5 portions was confirmed. The coverage of carbon layers on the sample after BT was evaluated to be ~ 50 ML in the unit of monolayer of Ir(001)1x1 surface. A quantitative measure of the effect of BT, A45° (the degree of variation of XPD pattern as defined as Imax−Imin/Ia, where Imax, Imin and Ia are the maximum, minimum and average intensities of photoelectrons in an azimuthal diffraction pattern at the polar angle of 45°, respectively), was examined for C 1s and Ir 4f core-levels for the 1-inch- BT samples. The A45° values appeared to be ~3% and ~17% for C 1s and Ir 4f, respectively. The results were compared with those for other bias-treated smaller samples reported so far. The A45° value of ~3% for C 1s is found to be very small compared to the corresponding values for the smaller samples reported so far. Thus, the method of BT for the present 1-inch- sample was found to have a large margin of improvement in terms of A45° for C 1s XPD.

The relationship between the electron emission properties of a boron-doped chemical vapor deposited polycrystalline diamond thin film and the oxygen coverage on the diamond surface is systematically investigated. The threshold voltage of electron emission becomes higher with increasing oxygen coverage on the surface. The change of emission barrier height estimated from the slopes of Fowler-Nordheim plots and from the coverage of adsorbed oxygen atoms is evaluated. From the results, it was speculated that the emission barrier height was changed by the surface dipole layer that was formed by oxygen atoms on the diamond surface and led to the changes in the electron emission properties.

Epitaxial growth of diamond on iridium thin films was performed by direct-current plasma chemical vapor deposition with ion irradiation pretreatment of the substrate. Pyramidal epitaxial diamond particles with a number density of ∼108 cm-2 were grown on the iridium film. The epitaxial relation is written as (100) diamond//(100) iridium and [001] diamond//[001] iridium. Tilting of the epitaxial relation, as occasionally observed for diamond on silicon or beta silicon carbide, is scarcely observed. Erosion,as observed for diamond on nickel substrates, is not observed. The effect of the ion irradiation of the substrate is discussed briefly.

Co90Fe10/Cu spin-valve structures were prepared by RF and DC magnetoron sputtering method. X-ray diffraction data showed that the spin-valves pn sapphire substrate exhibited good fcc (111) preferred orientations. The maximum value of Δρ/ρ0 was 11% which was larger than that obtained for Co/Cu spin-valve structures.

Diamond thin films have been formed by dc plasma chemical vapor deposition from a gaseous mixture of methane and hydrogen (gas ratio (CH4/H2); 2/100, total gas pressure; 2.66×104 Pa) with a growth rate of ∼20 µm/h. During the course of diamond growth, characteristics of the plasma were measured by the Langmuir single probe method and also by emission spectrometry. From the characterization of the plasma, it was found that the degree of ionization was rather low (∼10-7), and the statistical temperature of hydrogen gas was ∼5×103 K. By a thermodynamic investigation at the gas temperature around 5×103 K, it was revealed that the source gases (H2 and CH4) of over 99% are decomposed to neutral atomic hydrogen and atomic carbon.

Diamond thin films have been formed on molybdenum substrates with a mixture of methane and hydrogen gas using the electron-assisted chemical vapor deposition (EACVD) method. The surface morphology, crystal structure and composition of the films obtained were characterized by scanning electron microscopy, reflection high energy electron diffraction and secondary ion mass spectrometry. The experimental results revealed that substrate heating is necessary to eliminate the hydrogen atoms occluded into the film during the course of diamond deposition. The hydrogen is frozen in the film without the substrate heating. This may prohibit the rearrangement of the carbon atoms in the film and will produce an amorphous film.

Diamond thin films are produced by DC plasma chemical vapor deposition on Si(111) with a high growth rate (20 μm/h) at a substrate temperature of 800 ° C. The films obtained are characterized by electron and X-ray diffraction, scanning electron microscopy and Raman spectrometry. The characteristics of the DC discharge plasma in the process of diamond growth are measured by the Langmuir single probe method and emission spectrometry. Diamond thin films formed by DC plasma chemical vapor deposition are shown to have almost the same properties as natural diamond. It is found that, in the plasma where the diamond can be grown, atomic hydrogen and carbon are in stable state from Langmuir single probe and emission spectrometry measurements.

Diamond thin films were produced by electron-assisted chemical vapour deposition which was originally proposed by the present authors. The films were produced mainly on SiC with a high growth rate (3–5 μm h−1) and at a relatively low temperature (823 K). The films obtained are characterized by electron and X-ray diffraction, electron energy loss spectrometry, Raman scattering, laser microprobe mass analysis, secondary ion mass spectrometry and IR absorption spectrometry. Their general properties such as hardness, thermal conductivity, specific gravity and electrical resistivity are also measured. From these results, diamond thin films formed by electron-assisted chemical vapour deposition are shown to have almost the same characteristics as natural diamond. The influence of the electron bombardment on the film growth is discussed in relation to the decomposition of reactant gases (CH4 and H2).

Diamond thin films have been formed by dc plasma chemical vapor deposition with a high growth rate (∼20 μm/h). The diamond has been grown from methane (CH4) and hydrogen (H2) mixed gases on Si and α‐Al2O3 substrates at a pressure of 200 Torr without surface scratching by diamond or c‐BN powder. The obtained films have good crystallinity in the sense of electron and x‐ray diffraction. Vicker’s hardness of the film is the same as that of natural diamond (∼10 000 kg/mm2). The influence of the dc discharge in a low vacuum (∼200 Torr) on diamond synthesis will be discussed briefly.

During the course of diamond growth by dc plasma chemical vapor deposition, characteristics of the plasma have been measured by means of the Langmuir single probe method and emission spectrometry. For the source gas system of hydrogen and methane (gas ratio: CH4/H2=2/100, total gas pressure: 2.66×104 Pa), it is revealed that the statistical temperatures of hydrogen atoms and electrons in the positive column of the plasma are obtained to be 4.8×103–5.3×103 K and 1×105–1.1×105 K, respectively. The amount of ionized species is fairly small. By calculating the equilibrium constant of gas molecules in these gas temperature ranges, it is found that molecules over 99% H2 and CH4 are decomposed to the neutral H and C atoms.