Hiroyuki Kageshima

Shimane University · Department of Applied Physics

The nitrogen-doping effect on vacancy aggregation in Si is studied by comparing total energies of various complexes of nitrogen atoms and Si vacancies in terms of first-principles calculations. Two nitrogen atoms are found to form a stable complex with two Si vacancies, strongly suggesting that a supersaturation of “isolated” Si vacancies in growth...

The epitaxial graphene growth mechanism on SiC(0001) surfaces is studied based on the energetics via the first-principles calculation. It is found that a Si terminated surface is important for the epitaxial growth of thin flat graphene sheets. This surface encourages the growth of graphene sheets because the surface Si atoms act as catalyst. Si des...

A method of calculating momentum matrix elements using pseudopotentials is proposed. A core-repair term is introduced in the method to eliminate errors created by the poor representation of the atomic core region by the pseudopotentials. Calculating the core-repair term requires fewer computational resources especially for separable form pseudopote...

The stability and reactivity of steps in the initial stage of the graphene growth by sublimating the SiC(0001) surface is theoretically studied by the first-principles calculation. The steps are not necessarily unstable and reactive during the formation of the zeroth graphene layer. Temperature, Si pressure, and C coverage affect the stability and...

Employing the first-principles calculation, the detailed energy landscape of the path for the Si emission from the interface into the oxide is studied. It is found that the barrier height almost reproduces the experimental values, which indicates that the Si emission surely corresponds to the diffusion of SiO interstitial. It is also found that the...

The reactions of NO molecule at 4H-SiC/SiO2 interface on various plane orientations are theoretically investigated using density functional calculations to clarify microscopic mechanisms of NO post oxidation annealing (POA) process. We find that the energy barriers for nitrogen incorporation reaction are smaller than those for nitrogen desorption i...

Recent observations of macroscopic quantum condensation using electron-hole (e-h) bilayers have activated the research of its application to electronics. However, to the best of our knowledge, no attempts have been made to observe the condensation in silicon, the major material in electronics, due to the lack of technology to form closely-packed an...

An array of embedded graphene ribbons, whose edges connect to a buffer layer, can be grown on 4HSiC(0001). The Raman D peak intensity of the armchair edge of the ribbon shows the same polarization dependence as that of the non-connected armchair edge of graphene. Considering the Raman scattering process of the D peak, this polarization dependence i...

We investigate structural changes in Si islands deposited at room temperature on epitaxial few-layer graphene on SiC(0001) during subsequent annealing. Annealing causes the Si islands move on epitaxial graphene thicker than monolayer with monolayer-deep trenches left behind. In contrast, Si islands do not form trenches on monolayer graphene, but th...

Using the first-principles calculation, the diffusion path is explored in the Si emission from the interface into the Si oxide surface during the Si oxidation process, by assuming that the Si emission dominantly consists of a SiO interstitial diffusion. Searching for the diffusion path was succeeded and the energy profile of diffusion path can be e...

The origin of chemical vapor deposition (CVD) growth direction difference in graphene/hexagonal boron nitride (hBN) heterostructures is theoretically studied. The study is focused on the advance in energy gain by H termination of the bare hBN N edge on the Cu(111) surface comparing with that of the bare graphene edge. It is found that the differenc...

In this study, stacked graphene diodes were fabricated via direct bonding using single-crystal graphene on a SiC substrate. Switching and S-shaped negative resistance were observed in the junction electrical properties measured via the 4-terminal configuration. The high-resistance state switched to the low-resistance state after applying a maximum...

The reactions of N2O and NH3 molecules at the interface between 4H-SiC and SiO2 during post oxidation annealing (POA) are theoretically investigated using ab initio calculations. We find that the reactions of N2O molecule at (0001) and (0001) interfaces result in the desorption of carbon oxide molecules in addition to Si - N bond formation. For the...

Si)の熱酸化過程は，①酸化性分子の酸化膜中拡散， ②界面での酸化性分子と Si の反応，③反応に伴う界面での格子 間 Si 原子の発生と輸送と酸化吸収，④酸化された部分の体積膨 張と粘性流動と変形，の 4 つの過程から成っており，これらの過 程全てが④によって発生する応力分布の影響を受けて抑制された り促進されたりし，それがまた応力分布自体に影響を与え，酸化 過程全体の進 しん 捗 ちよく も左右する．平坦な Si の熱酸化ではこのような 複雑さは目立たず一見①と②だけで簡便に理解できるように見え るが，Si 立体ナノ構造の熱酸化になるとその複雑さがたちまち露 見する．本稿では，Si 熱酸化過程のこのような微視的な観点か らの全体像に関して我々の研究を中心に紹介する． 1. まえがき シリ...

The incorporation behavior of N atoms at 4H-SiC/SiO 2 interface is theoretically investigated on the basis of ab initio calculations. We find that the incorporation energy of N atoms at the Si-face interface is ranging from –1.87 to –1.12 eV, which is much higher than those at the C-face and m-face interfaces. Furthermore, the incorporation of O at...

The vibrational properties of different Ge phases formed on Ag(111) thin films by the Ge segregation method were investigated using in situ Raman spectroscopy. As the segregation temperature is increased, the striped phase, the less-ordered phase and the long-range ordered phase appear in that order. While the less-ordered and long-range ordered ph...

Effects of the coexistence of dry and wet oxidants on the reaction process at SiO 2 /4H-SiC(0001) and (0001) interfaces during SiC oxidation are systematically investigated by performing ab initio calculations. We find characteristic features of the interfacial reaction mechanisms, which are dependent on the plane orientation and wet oxidation cond...

The role of edge termination is theoretically studied for the growth direction selectivity in chemical vapor deposition of graphene heterostructures with hexagonal boron nitride. It is found that the graphene island with hydrogen-free edge and the hexagonal boron nitride island with hydrogen-terminated edge induces the lateral and the vertical grow...

The strain dependence of stability and diffusion barrier height of the O vacancy in Si oxide is examined using the first-principles calculation. It is found that the stability and the diffusion barrier height increase as the oxide is compressed. The analysis shows that the diffusion barrier height is determined by the Si–Si distance of the O vacanc...

The reaction of the NO molecule at the 4H-SiC/SiO 2 interface after dry oxidation is theoretically investigated on the basis of ab initio calculations. On the Si-face, the reaction of the NO molecule results in the dissociation of the C–C single bond and the formation of Si 4 –N bonds with the CO 2 molecule. In contrast, the C=C double bond changes...

Ferromagnetism was observed in a Pt(100) ultrathin film deposited on a SrTiO3(100) substrate. The ferromagnetism, which appears in films with thicknesses of 2.2-4.4 nm, periodically changes with a period of approximately 1 nm (5-6 ML) depending on the film thickness. This is consistent with the period derived from the quantum-well states formed in...

4H-SiC is a key material for applying in power electronics devices because of its superior physical properties. Furthermore, SiO 2 oxide films which are crucial for manufacturing electronic devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) are easily obtained in 4H-SiC. However, a large number of defects are generated at...

The reaction processes of O 2 molecule with wet oxidant such as H 2 O molecule at the interface between 4H-SiC and SiO2 are investigated by performing ab initio calculations. On the Si-face, the formation of CO molecule from O2 molecule occurs without the reaction of H2O molecules. The calculated energy barrier for the CO formation from O2 molecule...

We demonstrate controlled chemical vapor deposition growth of lateral and vertical heterostructures of graphene and hexagonal boron nitride (h-BN) on Cu substrates by changing supply sequence of their precursors. When the graphene precursors are switched by the h-BN precursors, h-BN grows from the edges of the existing graphene islands, resulting i...

To elucidate bottom-up fabrication of heterostructures of two-dimensional materials such as graphene and h-BN, C atom adsorption on Cu(111) surface partially covered with h-BN or graphene is studied by using the first-principles method with van der Waals correction. It is found that the C monomer more difficultly locates under h-BN than under graph...

We demonstrate control of the magnetism of Pd(100) ultrathin films, which show d-electron quantum-well-induced ferromagnetism, via modulation of the interface electronic state using density functional calculation. From an analysis based on the phase model, forming the Au/Pd(100) interface induces hybridization of the wave function of d-electron qua...

We demonstrate control of the magnetism of Pd(100) ultrathin films, which show d-electron quantum-well induced ferromagnetism, via modulation of the interface electronic state using density functional calculation. From an analysis based on the phase model, forming the Au/Pd(100) interface induces hybridization of the wave function of d-electron qua...

Charged vacancies of MoS2 are theoretically studied based on the first-principles calculation. The results for the freestanding single-layer MoS2 show that almost all of vacancies are more stable when they are more negatively charged. Lager vacancies can become high negative charge states. Formation energies of larger vacancies also more drasticall...

The publisher would like to apologize for errors that occurred in the article [E. Fukuda et al., e-J. Surf. Sci. Nanotech. 15, 127 (2017)] published on 14 December, 2017. [DOI: 10.1380/ejssnt.2018.375]

We study the crystal structure of Pd(100) ultrathin films, which show ferromagnetism induced by the quantum confinement effect, using in situ x-ray crystal truncation rod measurement and density functional calculation. The energy gain from the appearance of ferromagnetism in Pd results in flatter and uniform film growth of ferromagnetic Pd films co...

To understand oxidation in three-dimensional silicon, dynamic characteristics of a SiO x system with various stoichiometries were investigated. The calculated results show that the self-diffusion coefficient increases as oxygen density decreases, and the increase is large when the temperature is low. It also shows that the self-diffusion coefficien...

The mechanism of Si pillar thermal oxidation is considered. The Si emission is discussed in the oxidation of three-dimensional structures, which must be fundamentally important to understand the oxidation mechanism. It is confirmed that the Si emission is enhanced in the three-dimensional structures by the geometrical and stress effects. The larger...

We demonstrate changes in the saturation magnetization of Pd(001) ultrathin films exhibiting ferromagnetism in Pd/SrTiO3/BaTiO3 heterostructures due to the strain effect caused by the structural phase transition of BaTiO3 substrates. When a BaTiO3 substrate with a single domain formed by voltage application transitioned from the orthorhombic phase...

The reaction processes at the interface between SiC with 4H structure (4H-SiC) and SiO2 during wet oxidation are investigated by electronic structure calculations within the density functional theory. Our calculations for 4H-SiC/SiO2 interfaces with various orientations demonstrate characteristic features of the reaction depending on the crystal or...

It is expected that the off-state leakage current of MOSFETs can be reduced by employing vertical body channel MOSFETs (V-MOSFETs). However, in fabricating these devices, the structure of the Si pillars sometimes cannot be maintained during oxidation, since Si atoms sometimes disappear from the Si/oxide interface (Si missing). Thus, in this study,...

In past studies, the Si emission phenomenon is one of the issues for fabrication of 3D structure devices such as FinFETs and Vertical MOSFETs. In this paper, it is found that novel Si emission phenomena depending on the surface oxygen concentration of Si wafer occur, when Si pillars patterned less than 100 nm are oxidized. A wafer with high oxygen...

The physical properties of multiatomic vacancies are investigated by first-principles total-energy calculations. The formation energies of various vacancies as functions of chemical potential and charge states are calculated. The relationship between optimized atomic structures and charge states is analyzed. On the basis of the results, it is confi...

We study the crystal structure of Pd(100) ultrathin films, which show ferromagnetism induced by the quantum confinement effect, using in-situ X-ray crystal truncation rod measurement and density functional calculation. The energy gain due to the appearance of ferromagnetism in Pd results in flatter and uniform film growth of ferromagnetic Pd films...

Gate insulator of vertical MOSFET (V-MOSFET) is formed by silicon oxide. However, Si pillar cannot keep the structure during oxidation process because the Si atoms disappear from bulk (missing-Si). Moreover, the effect of hydrogen annealing for V-MOSFET under the typical condition becomes weaker than that for planer MOSFET. In this study, we reveal...

The advance in the understanding of the mechanism of the silicon oxidation process toward the fine control of 3D MOSFETs is explained. The silicon emission mechanism can be applied to the oxidation process of silicon pillars as well as that of planar silicon. Since the geometrical effect is inevitable for the 3D MOSFETs, the silicon emission mechan...

Recent aggressive progress of the device technology demands development of three-dimensional non-planar channel MOSFETs. The oxidation process of non-planar silicon is one of the most important keys. Silicon oxidation is the fundamental but very important process for fabricating the gate dielectrics/silicon interface, which governs the performance...

Si technology such as downscaling of MOS transistors has been proceeded for the past 20-30 years. However, recently, short channel effect such as leakage current has been one of the critical problems on planer-MOSFET. Further, the downscaling technology is approaching the limit. In order to overcome these problem, Vertical MOSFET (V-MOSFET) is one...

Missing Si in the oxidation of Si pillar structures is investigated by extending the Si emission model to the oxidation of planar structures. The original Si emission model [H. Kageshima et al., Jpn. J. Appl. Phys. 38, L971 (1999)] assumes the emission of excess Si from the interface into the oxide during the oxidation process, the diffusion of the...

Graphene and related two-dimensional (2D) materials are attracting huge attention due to their wide-range potential applications. Because large-scale, high-quality 2D crystals are prerequisites for many of the applications, crystal growth of 2D materials has been intensively studied. We have also been conducting research to understand the growth me...

Graphene and related two-dimensional (2D) materials are attracting huge attention due to their wide-range potential applications. Because large-scale, high-quality 2D crystals are prerequisites for many of the applications, crystal growth of 2D materials has been intensively studied. We have also been conducting research to understand the growth me...

Atomic structures and electronic states of epitaxial graphene on the SiC(11-20) a-face are studied based on the first-principles calculation. It is found that the surface can have two types of the surface, the stable quasi-free-standing structure and the quasi-stable buffer layer structure. The neutral nature, the low interface state density, and t...

The initial oxidation processes on both the C-face and Si-face SiC surfaces are investigated by performing electronic-structure calculations within the density functional theory. We find the characteristic features of stable structures and adsorption-desorption behavior depending on the surface orientation of SiC. The desorption of C atoms as CO mo...

The reaction processes of O 2 molecule at 4H-SiC/SiO 2 interface are investigated by performing electronic-structure calculations within density functional theory. Our calculations demonstrate characteristic features of the reaction depending on the crystal orientation of SiC: The energy barriers of CO formation at the interface are much lower than...

We report the appearance of ferromagnetism in thin films of Pd(100), which depends on film thickness in the range of 3-5 nm on SrTiO3(100) substrates. X-ray magnetic circular dichroism measurement shows the intrinsic nature of ferromagnetism in Pd(100) films. The spontaneous magnetization in Pd(100) films, corresponding to is 0.61 mu(B)/atom, is co...

We report that mobility in quasi-free-standing monolayer graphene grown on SiC(0001), when compared at the same carrier density, depends on the annealing temperature used for hydrogen intercalation. This was verified by measuring mobility in top-gated devices using quasi-freestanding monolayer graphene obtained by annealing at different temperature...

The energetics for the Si desorption and the C adsorption at a [11-20] step on SiC(0001) surface are studied using the first-principles calculation. It is found that the [11-20] step is stable and nonreactive. The stability of the step is thought to govern the surface morphology during the graphene formation. It is shown that the Si pressure and th...

The surface-enhanced Raman scattering (SERS) of graphene on SiC with Au nanoparticles makes it possible to identify the spectrum of a buffer layer, which is a non-conductive carbon layer located between graphene and SiC, as well as that of graphene. In conventional Raman scattering spectroscopy, SiC peaks are superimposed on the peaks of the buffer...

The C clustering process during the 0th graphene growth on SiC(0001) was investigated by a first principles approach. It was found that the structure of C clusters is not purely-hexagonal but penta-heptagonal, including pentagons and heptagons. We also revealed that mono-ring clusters, the lowest-energy clusters in vacuum, are no longer the ground-...

The role of the step in the initial stage of graphene growth is focused on, and recipe how to improve the domain size of the grown graphene is discussed based on the first-principles calculations. It is considered that keeping the surface smoothness and limiting the number of C aggregation sites are the keys to improve the domain size.

Raman scattering spectroscopy is a well-known optical tool for identifying the properties of graphene such as the number of layers, carrier concentration, and strain. Interaction between incident light and a metallic nanoparticle such as gold or silver enhances the intensity of light, which can be used in Raman scattering spectroscopy. This article...

The diffusion mechanisms of CO and CO2 molecules in SiO2 during SiC oxidation are theoretically investigated by means of total-energy calculations within the density-functional theory. We find characteristic features of the stable structures of carbon oxides depending on polymorph of SiO2. The calculated formation energies and diffusion energy barr...

Low-energy electron microscopy (LEEM) has been used to study the structure, initial growth orientation, growth progression, and the number of layers of atomically thin hexagonal boron nitride (h-BN) films. The h-BN films are grown on heteroepitaxial Co using chemical vapor deposition (CVD) at low pressure. Our findings from LEEM studies include the...

Locally defined nanomembrane structures can be produced in graphene films on a SiC substrate with atomic steps. The contact conductance between graphene and a metal-coated nanoprobe in scanning probe microscopy can be drastically reduced by inducing local buckling of the membranes. Repeatable current switching with high reproducibility can be reali...

We investigated the H desorption process and the surface structure after H desorption in quasi-free-standing monolayer graphene (QFMLG) on silicon carbide (SiC). In situ scanning tunneling microscopy observations revealed that H adatoms preferentially desorb at SiC step edges. We found self-organization of a hexagonal network of QFMLG nanoribbons d...

SiC is a wide-band-gap semiconductor and has an advantage to fabricate electronic devices such as MOSFETs due to the ability to thermally oxidize to SiO2. Despite many studies conducted on the oxidation of SiC, the kinetics such as diffusion and interface reaction is not fully understood. Here, we focus on the diffusion process during SiC oxidation...

The quantum Hall effect has been observed in quasi-free-standing monolayer graphene on SiC for the first time. This was achieved by decreasing the carrier density while applying gate voltage in top-gated devices. The charge neutrality point was also clearly observed, which has not been reported in top-gated structures. The mobilities at constant ca...

Electronic state calculations provide us important information about materials and devices. For silicon oxidation, details of atomic transport, such as diffusion/reaction path and barrier height, can be clarified. For diamond/metal interface, details of Schottky barrier height control mechanism, such as potential variation and electron redistributi...

Calculations of electronic structure of free-standing Pd (100) ultrathin films of 2–6 monolayers (MLs), using first-principles calculation with pseudopotential method, show stable ferromagnetism in 4 ML and induced magnetic phase transition in 3 and 4 MLs by charging. The ferromagnetism, appearing due to large density of states attributed to 4dxz,y...

We use a first-principles approach to analyze the clustering of C atoms during the initial stage of 0th-layer graphene-like growth on SiC(0001). We started the layer with the lowest-energy hexagonal C ring and then let it grow. The growth produced pentagonal rings with a heptagonal ring in a graphene-like (penta-heptagonal) structure. We also studi...

Various physical properties of epitaxial graphene grown on SiC(0001) are studied. First, the electronic transport in epitaxial bilayer graphene on SiC(0001) and quasi-free-standing bilayer graphene on SiC(0001) is investigated. The dependences of the resistance and the polarity of the Hall resistance at zero gate voltage on the top-gate voltage sho...

Properties of silicon-based nanocapacitor are studied from first principles. The nanocapacitor consists of electrodes of the silicon-based material planar polysilane. Nonclassical effects are analyzed by changing both the electrode spacing and the applied bias simultaneously. Even when the electrode spacing is fixed, the effective electrode spacing...

With the aim of developing a single-crystal graphene substrate indispensable to graphene's practical applications, we are investigating the structural and physical properties of graphene epitaxially grown on SiC by thermal decomposition. We grow monolayer and bilayer graphene uniformly on a micrometre scale on the Si face of SiC in an Ar environmen...

Quasi-free-standing bilayer graphene was grown by hydrogen intercalation of epitaxial monolayer graphene on SiC(0001). A larger size of stacking domains compared to that of epitaxial bilayer graphene grown on SiC(0001) was observed in a low-energy electron microscopy analysis of its morphology. By evaluating its electronic transport characteristics...

Quasi-free-standing bilayer graphene was grown by hydrogen intercalation of epitaxial monolayer graphene on SiC(0001). A larger size of stacking domains compared to that of epitaxial bilayer graphene grown on SiC(0001) was observed in a low-energy electron microscopy analysis of its morphology. By evaluating its electronic transport characteristics...

Atomic structures and electronic properties of graphene islands on SiC(0001) surfaces are theoretically studied. Two kinds of atomic structures embedded in the SiC surface are proposed. It is also revealed that the graphene zigzag ribbons with those embedded structures show the magnetoelectric effect.

Suppressed effective dielectric constants are found by the first-principles study at the center of atomically thin Si-nanofilm channel in the full inversion regime under field effect due to symmetric double gate. This is unique for the inversion regime and should come from the external electric field due to the symmetric double gates.

Magnetic properties of manganese (Mn) nanosilicide embedded in thin silicon-on-insulator (SOI) layers are investigated. Mn nanosilicide formed by Mn+ ion implantation into a thin SOI layer followed by a thermal annealing at 600–900°C shows soft ferromagnetism or superparamagnetism at 5K. A monotonic decrease of the saturation magnetization is obser...

Carrier density and temperature-dependent transport properties of monolayer graphene grown on SiC(0001) were systematically studied. With increasing temperature, resistivity at the charge neutrality point decreases, while resistivity away from the charge neutrality point, where the carrier density is above 1 × 1011 cm−2, increases. From Hall measur...

The growth of epitaxial graphene on the SiC(0001) surface is theoretically studied by assuming silicon (Si) sublimation from the surface. Our results indicate that a new graphene sheet grows from the interface between the old graphene sheets and SiC substrate, as found in our previous study on graphene growth by carbon (C) deposition. Graphene grow...

The growth of epitaxial graphene on the SiC(0001) surface is theoretically studied by assuming silicon (Si) sublimation from the surface. Our results indicate that a new graphene sheet grows from the interface between the old graphene sheets and SiC substrate, as found in our previous study on graphene growth by carbon (C) deposition. Graphene grow...

Two of our recent theoretical efforts on elucidating the functions of graphene are reported. A first-principles calculation of the growth process of graphene islands on SiC(0001) shows that an embedded structure is energetically preferable. Island with this embedded structure do not have any broken dangling bonds at their edges. Their electronic st...

Bilayer graphene was grown on the Si-face of SiC by thermal decomposition. Its electronic properties were investigated in top-gate Hall bar devices. By controlling the carrier density using gate voltage, we were able to access the charge neutrality point. The conductance at the charge neutrality point showed a strong temperature dependence, and its...

Bilayer graphene was grown on the Si-face of SiC by thermal decomposition. Its electronic properties were investigated in top-gate Hall bar devices. By controlling the carrier density using gate voltage, we were able to access the charge neutrality point. The conductance at the charge neutrality point showed a strong temperature dependence, and its...