The potential of diamond films for future semiconductor applications is partly limited by current growth techniques. This limitation can be addressed by achieving an atomic-level understanding of the growth processes. Using atomic force microscopy with atomic resolution, we examined diamond surfaces and observed specific structures, where odd numbers of dimers form ribbonlike configurations. Formed in the nonequilibrium environment of plasma, these structures were evaluated as the most stable configurations through density-functional-theory calculations. Our findings provide a crucial foundation for optimizing the film growth process.

To achieve atomic-level characterization of the diamond (001) surface, persistent efforts have been made over the past few decades. The motivation behind the pursuit extends beyond investigating surface defects and adsorbates; it also involves unraveling the mystery of the smooth growth of diamond. However, the inherently low conductivity and the short C-C bonds render atomic resolution imaging exceptionally challenging. Here, we successfully overcame these challenges by employing non-contact atomic force microscopy with reactive Si tips. Atomic resolution imaging was achieved even at room temperature. With density-functional-theory calculations, we clarified that the critical factors for atomic resolution are in the formation of tilted C-Si bonds between scanning probes and surfaces, along with reordering of the surface C-C dimers. Implications of the findings extend beyond the realm of surface characterization. The present atomic-resolution microscopies drive future advancements in diamond technologies by providing avenues for identifying dopants and constructing artificial nanostructures.

Trench-type inversion-channel diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) are considered the ultimate low-loss power devices due to their superior material properties and structural advantages. The formation of diamond trenches with {111} sidewalls is essential for realizing these devices. Our recently developed thermochemical etching technique using Ni films in water vapor enables the formation of such trenches, which is challenging when conventional methods are used. However, under the standard etching temperature conditions, macrosteps of submicron scale or larger form on the sidewalls, hindering the formation of high-quality MOS interfaces and inversion channels. In this study, we systematically investigated the relationship between the etching temperature and the sidewall flatness to identify the optimal conditions for suppressing macrostep formation. Our findings indicate that macrosteps form on the sidewalls at temperatures of 940 °C or higher. In contrast, nanoscale-flat {111} sidewalls without macrosteps detectable by SEM were successfully fabricated at lower temperatures. This improvement in sidewall flatness was primarily attributed to the extended etching time for the sidewalls. These findings provide critical insights and a fundamental technique for fabricating trench-type inversion-channel diamond MOSFETs, thereby contributing to the advancement of next-generation low-loss power devices.

Our group developed the first inversion-type p-channel diamond metal-oxide-semiconductor field-effect transistor, which featured normally off properties by employing water vapor annealing treatments for the oxygen-terminated diamond surface. Despite the comprehensive device-grade characterization, the impact of water vapor annealing treatments on the Al2O3/diamond interface has not been investigated in detail. In this work, we fabricated four diamond metal-oxide-semiconductor (MOS) capacitors without and with water vapor annealing treatments for various times of 30 min, 1 h, and 2 h and conducted the cycle capacitance-voltage (C-V) and simultaneous C-V measurements. The large cycle C-V shift existed in the sample without water vapor annealing treatment, whereas it was significantly suppressed by water vapor annealing treatments, indicating the effective passivation of the traps with long time constants. The simultaneous C-V results showed a similar trend that the frequency dispersion of the simultaneous C-V was dramatically reduced with water vapor annealing treatments, and the interface quality of Al2O3/diamond had a slight dependence on the water vapor annealing times. Based on simultaneous C-V measurements, the interface state density (D-it) at an energy level of 0.2-0.6 eV from the valence band edge of diamond was extracted for the different MOS capacitors. The D-it was reduced by one order of magnitude with water vapor annealing treatments, and it almost did not change with the water vapor annealing times. Besides, the flat band voltage shift and effective fixed charge were also dramatically reduced by water vapor annealing. The possible physical reason for the interface improvement by water vapor annealing treatments was discussed.

We elucidate the carrier transport mechanism from the p+-layer (metallic-conduction) to the n-layer (band-conduction) in a diamond p+–n junction, which is the basic structure of diamond devices. We fabricate Schottky–pn diodes containing p+–n junctions and analyze the temperature dependence of electrical properties in the forward bias region. At temperatures higher than the cryogenic region, free holes transport from the p+-layer to the n-layer. In the cryogenic region, which is insufficient to excite holes to the valence band, the direct transport of holes from the effective carrier conduction level in the p+-layer to the n-layer by tunneling becomes dominant.

Diamond is a key material for quantum devices and sensors, microelectromechanical systems, and the next-generation electronic devices. Microfabrication technology of single-crystal diamond (SCD) for device fabrication and processing is required but hardly established. For example, photolithographic techniques using plasma induced etching for the microfabrication of the diamond devices induce damage to its diamond and deteriorate the device-performances. To overcome this problem, we proposed a plasma-free imprint lithographic technique of SCD using nickel (Ni) mold at high temperatures. Prior to contacting with SCD, the native surface oxide film of the Ni mold was reduced by a hydrogen annealing treatment. Then, the samples were contacted with Ni mold closely, and annealed at various temperatures from 800 to 1200 degrees C for 30 min, aiming at the formation of the microstructure on the SCD surface by imprinting the structure of Ni mold based on the carbon solid solution reaction into Ni. After removing the Ni and the formed graphite by acid treatment from the SCD surface annealed at 1000 degrees C, imprints with Ni shape structure are revealed on the SCD surface. This microstructure formation processes requires only short periods of time without any specific equipments. Therefore, this diamond imprint lithography is significant and practical for the development of diamond applications.

A diimine ligand having two [2.2]paracyclophanyl substituents at the N atoms (L1) was prepared from the reaction of amino[2.2]paracyclophane with acenaphtenequinone. The ligand reacts with NiBr2(dme) (dme: 1,2-dimethoxyethane) to form the dibromonickel complex with (R,R) and (S,S) configuration, NiBr2(L1). The structure of the complex was confirmed by X-ray crystallography. NiBr2(L1) catalyzes oligomerization of ethylene in the presence of methylaluminoxane (MAO) co-catalyst at 10–50 °C to form a mixture of 1- and 2-butenes after 3 h. The reactions for 6 h and 8 h at 25 °C causes further increase of 2-butene formed via isomerization of 1-butene and formation of hexenes. Reaction of 1-hexene catalyzed by NiBr2(L1)–MAO produces 2-hexene via isomerization and C12 and C18 hydrocarbons via oligomerization. Consumption of 1-hexene of the reaction obeys first-order kinetics. The kinetic parameters were obtained to be ΔG‡ = 93.6 kJ mol−1, ΔH‡ = 63.0 kJ mol−1, and ΔS‡ = −112 J mol−1deg−1. NiBr2(L1) catalyzes co-dimerization of ethylene and 1-hexene to form C8 hydrocarbons with higher rate and selectivity than the tetramerization of ethylene.

Electron emission plays an important role in diverse applications, from cold cathodes to chemical processes (solvated electrons, water purification), energy generation (thermionic or dye-sensitized solar cells), and even cancer treatment. Here we show that by surface treatment using electrochemically grown polypyrrole the secondary-electron emission and photoelectron emission from boron-doped diamond is enhanced even above the intensity of electron emission from the hydrogen-terminated surface with negative electron affinity. This enhancement is stable in air for at least one month and it persists also in vacuum after thermal annealing. Scanning electron microscopy, Kelvin probe force microscopy, total photoelectron yield spectroscopy as well as surface mapping by Auger and secondary ion mass spectroscopies are used to characterize and correlate the surface electronic and chemical properties. A model of the electron emission enhancement is provided.

Palladium-diimine complexes catalyzed copolymerization of 1-decene with methyl methacrylate (MMA) to produce polymer with vinylene groups in the polymer chain, and a methyl methacrylate group, -CH2-CH(Me)COOMe, at the polymer end. Previous findings of copolymerization catalyzed by Ni complexes with chelating P-O ligands gave a polymer with an unsaturated end group, -CH = C(Me)COOMe. Other alkyl methacrylates such as n-butyl, t-butyl, and i-amyl methacrylates also copolymerized with 1-decene to yield the end-functionalized polymers. Copolymerization of 1-decene with 2-acetylethyl methacrylate yielded polymer with a terminal ester group, whereas 2-hydroxyethyl methacrylate did not undergo copolymerization. Allyl methacrylate reacted with 1-decene to produce copolymer via preferential insertion of C = C double bond of the allyl groups into the metalpolymer bond. Copolymer of 1-decene and isoprenyl methacrylate contained comonomer units formed via insertion of C = C double bonds of the methacrylic group and of isoprenyl group in 76 : 24 ratio.

New π-extended dithiarubicene derivatives were synthesized for application in n-type organic semiconductors.

(bpy)NiBr2 catalyzes the copolymerization of butadiene and norbornene (56:44) in the presence of methylaluminoxane at 30 degrees C. H-1 NMR spectrum of the copolymer contains signals of norbornene units and 1,4-butadiene units and shows the molar ratio of the two monomer units to be 56:44. Copolymerization with a higher portion of norbornene monomer catalyzed by (bpy)NiBr2 affords a solid copolymer rich in norbornene unit, whereas the copolymerization with a higher portion of butadiene forms an oily copolymer rich in butadiene unit. Composition of the monomer units of the copolymer in terms of butadiene/norbornene ratio varies from 12:88 to 91:9, depending on the initial ratio of the monomers; this finding is different from the previous results obtained using Ni catalyst.

Vinylcycloalkanes with 12-, 15-, and 21-membered rings were synthesized from commercially available cycloalkanones or cycloalkyl carboxylic acids derived from malonate and ω-bromo-α-alkenes. Pd complexes with diimine ligands promoted the isomerization polymerization of vinylcycloalkanes with 15- and 21-membered rings to afford polymers having cycloalkylene groups in the main chain. Vinylcycloheneicosane with a 21-membered ring afforded polymers with M n up to 9700, whereas vinylcycloalkanes with smaller ring sizes (8- and 12-membered rings) yielded oligomers with M n = 720–1600.

A major obstacle limiting diamond electronics is dislocations, which deteriorate device properties. As threading dislocations (TDs) are normally inherited from the substrate to the epitaxial layer, control and annihilation of their propagation are important. Herein, metal‐assisted termination (MAT), in which the propagation of dislocations is suppressed by in situ metal doping, is proposed. Heavy W doping is realized by a hot‐filament (HF) chemical vapor deposition (CVD) using heated wires at a high temperature of >2400‐K. A large reduction of TD density is confirmed by cathodoluminescence studies and etch‐pit analysis. The impact of dislocation reduction is investigated electrically. After insertion of the MAT buffer layer, Schottky barrier diodes (SBDs) show improved rectifying action and highly uniform characteristics even when substrates with high dislocation densities (mosaic and heteroepitaxial wafers) are used. The 3D structure of dislocation propagation is successfully captured by two‐photon‐excited photoluminescence (2PPL) imaging of Band‐A luminescence. The 2PPL Band‐A luminescence (without band‐edge excitation) shows high spatial resolution in the depth direction. An abrupt decrease in TD density is captured for heteroepitaxial substrates with an inserted MAT buffer layer. The MAT technique provides an effective approach to realize high‐performance diamond electronics.

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 COH 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.

In this study, mechanical properties and molecular motion at low temperature of novel polyolefin materials with cyclohexane moiety in the chemical structure synthesized by Takeuchi et al., Poly-alilcyclohexane (PACH-3), Poly-pentenylcyclohexane (PPCH-5), Poly-heptenylcyclohexane (PHCH-7) and Poly-undecenylcyclohexane (PUCH-11), were investigated1),2). From DSC results, the melting temperature of the samples decreased with an increase of the alkyl-chain length though, the enthalpy of heat of fusion of them increased with the alkyl-chain length. From DMA result, the α relaxation peak can be observed clearly and the temperature decreased with the alkyl-chain length. The β relaxation peak can also be observed at around -50 °C, and the peak intensity decreased with the alkyl-chain length. Moreover, the γ relaxation can be observed clearly around -100 °C, and the strength of the δ relaxation of PPCH-5 was the largest among these samples. From three-point-bending test result from -150 °C to RT, PACH-3 with the shortest alkyl-chain length had the highest modulus at -150 °C, but its modulus decreased most gradually with temperature and its modulus became the highest at room temperature. On the other hand, from Anharmonic estimation result, Grüneisen constant of PACH-5 in -150~-100 °C was the smallest in these samples. This result was consistent with the strength of the γ relaxation, indicating that an association between its anharmonicity and the molecular relaxation exits and PPCH-5 can be expected to have better mechanical properties at low temperatures because it has suitable cooperation size for a molecular motion which consists of cycro-ring and a certain alkyl-chain length.