Jonghan Won

Effect of nitrogen incorporation on electrical properties of boron-doped diamond films

The effect of a small amount of nitrogen incorporated in chemical vapor deposited diamond films on their electrical properties was studied. Upgrading the purity of CH4 gas from the conventional ultra-high purity to the grade with no detection of nitrogen resulted in improvement of electrical properties of the boron-doped homoepitaxial diamond films; the Hall mobility was increased by 4.3 times at the room temperature. Decrease in nitrogen concentration in the diamond films was confirmed by investigating the 2.16 eV center of cathodoluminescence induced by ion beam irradiation and subsequent annealing.

Interfacial analysis of CVD diamond on copper substrates

Abstract Diamond growth on Cu substrate by means of a microwave plasma-assisted chemical vapor deposition (CVD) method has been studied. Scanning electron microscopy (SEM) photographs show that the diamond grains deposited on Cu substrate mainly appear to have triangular (111) faces in comparison with those deposited on Si substrate under the same conditions. High resolution electron microscopy (HREM) research indicates that there exists a graphite intermediate layer between CVD diamond and its Cu substrate in which a small amount of amorphous carbon is embedded. The thickness of the intermediate layer varies from a few up to several tens of nanometers, depending on the local conditions. The cracks are found in some thicker intermediate layer regions, which is considered to be one of the main factors accounting for the adhesion problem. The registry between {111} planes of some diamond particles and the beneath-graphite (0002) planes has also been evidenced by HREM. The appearance of the (111) texturing diamond film is supposed to be closely related to the graphite intermediate layer.

Interface characterization of chemical-vapour-deposited diamond on Cu and Pt substrates studied by transmission electron microscopy

A novel method has been employed to study the interfacial structures of the chemical-vapour-deposited (CVD) diamond on Cu and Pt substrates using high resolution electron microscopy (HREM) without thinning the specimens. The CVD diamond used for the HREM study was directly deposited on the Cu and Pt transmission electron microscopy (TEM) grids by means of microwave plasma-assisted chemical vapour deposition. The HREM images clearly reveal that there exists a graphite intermediate layer between diamond and copper, in which a small amount of amorphous carbon is embedded. A 4 nm graphite transitional layer has also been observed on the platinum substrate. The (0002) planes of the intermediate graphite phase closely parallel the Cu and Pt surfaces. The registry between {111} planes of some diamond particles and the beneath graphites (0002) planes is evidenced by HREM, and the appearance of the (111) texturing diamond grains on Cu and Pt is supposed to be closely related to the graphite intermediate layers.

Order-to-disorder transformation in δ-phase Sc4Zr3O12 induced by light ion irradiation

Polycrystalline δ-phase Sc 4 Zr 3 O 12 was irradiated with 200 keV Ne + ions at cryogenic temperature to fluences ranging from 2 × 10 18 to 1 × 10 21 Ne/m 2 . Irradiation-induced structural evolution was examined by using grazing incidence x-ray diffraction and cross-sectional transmission electron microscopy. An order-to-disorder (O-D) crystal structure transformation (from an ordered δ-phase to a disordered, fluorite phase) was observed to initiate by a fluence of 2 × 10 18 Ne/m 2 , corresponding to a peak ballistic damage dose of ∼0.075 displacements per atom. This displacement damage dose is much lower than the O-D transformation dose threshold found in previous heavy ion irradiation experiments on δ-Sc 4 Zr 3 O 12 [J.A. Valdez et al., Nucl. Instrum. Methods B 250, 148 (2006); K.E. Sickafus et al., Nat. Mater. 6, 217 (2007)]. In this study, we contrast the O-D transformation efficiency of the light Ne ions used in these experiments, to the heavy (Kr) ions used previously, and interpret the differences in terms of enhanced damage efficiency for light ions (greater fraction of surviving defects per defect produced). To better quantify this surviving defect phenomenon, we also present new, additional ion irradiation results on δ-Sc 4 Zr 3 O 12 , obtained from 300 keV Kr 2+ and 100 keV He + ion irradiation experiments.

Investigation on surface of boron-doped CVD diamond by cathodoluminescence spectroscopy

Abstract Boron-doped polycrystalline and homoepitaxial CVD diamond films were investigated by cathodoluminescence (CL) spectroscopy. By CL imaging and by variation in the electron penetration depth, segregation of the 535 nm luminescence center at the growth surface and the interface of Si/diamond was confirmed. After etching by hydrogen plasma, or oxidization by annealing or plasma, the segregation of the 535 nm center still remained. Annealing in oxygen or oxidization by plasma induced the broad emission band at 500 nm enhanced in a near surface layer of electron penetration depth for 3–5 kV. The 500 nm band appeared remarkably in thin B-doped films with a large quantity of grain boundaries. The bulging of the 500 nm band was not observed in either homoepitaxial films or undoped films.

Structural analysis of ion-implanted chemical-vapor-deposited diamond by transmission electron microscope

Abstract A transmission electron microscope (TEM) study of ion-implanted chemical-vapor-deposited (CVD) diamond is presented. CVD diamond used for transmission electron microscope observation was directly deposited onto Mo TEM grids. As-deposited specimens were irradiated by C (100 keV) ions at room temperature with a wide range of implantation doses (1012–1017/cm2). Transmission electron diffraction (TED) patterns indicate that there exists a critical dose (Dc) for the onset of amorphization of CVD diamond as a result of ion induced damage and the value of critical dose is confirmed to be about 3 × 1015/cm2. The ion-induced transformation process is clearly revealed by high resolution electron microscope (HREM) images. For a higher dose implantation (7 × 1015/cm2) a large amount of diamond phase is transformed into amorphous carbon and many tiny misoriented diamond blocks are found to be left in the amorphous solid. The average size of these misoriented diamond blocks is only about 1–2 nm. Further bombardment (1017/cm2) almost kills all of the diamond phase within the irradiated volume and moreover leads to local formation of micropolycrystalline graphite.

Formation processes of iron silicide nanoparticles studied by ex situ and in situ transmission electron microscopy

The formation processes of iron silicide nanoparticles dependent on thermal annealing were examined by ex situ and in situ transmission electron microscopy (TEM). An Fe thin film with a thickness of ∼2 nm was deposited on a Si(100) substrate at room temperature using an electron-beam evaporation method, followed by thermal annealing at temperatures ranging from 573 to 1173 K. Ex situ TEM observations showed that pyramidal β-FeSi2 particles (1173 K) were formed via the e-FeSi layer (573 K) and the γ-FeSi2 particle (873 K). Detailed observations by in situ TEM indicated that an amorphous Fe-Si layer was formed on the Si substrate in the as-deposited specimen. This amorphous layer was crystallized into e-FeSi after thermal annealing and then hemispherical e-FeSi particles together with metastable γ-FeSi2 were formed just beneath the surface of the Si substrate. With increasing annealing temperature, the e phase changed to hemispherical γ-FeSi2 nanoparticles and finally the γ-FeSi2 particles transformed into ...

Structural modification of ion‐implanted and postannealed polycrystalline diamond studied by transmission electron microscopy

We have presented a convenient and effective method to ex situ study ion‐implanted and postannealed polycrystalline diamond by transmission electron microscopy (TEM) without thinning the specimens. Chemical‐vapor‐deposited (CVD) diamond used for transmission electron microscopy study was directly deposited onto Mo TEM grids, and then implanted and postannealed. TEM images clearly reveal that there exists an ion‐induced amorphous layer on the as‐implanted CVD diamond surface, in which graphitelike structure is embedded. The amorphization processes depend on the irradiation conditions. Hydrogen plasma treatment was employed to anneal the as‐implanted CVD diamond. High resolution electron microscopy images indicate that hydrogen plasma treatment can effectively remove the ion‐induced surface amorphous layer without graphitizing the diamond. After treatment, high density ball‐like diamond blisters appear on the surface, of which the average diameter is only about 2.5 nm, implying the critical size for the sta...

The fabrication of Ni quantum cross devices with a 17 nm junction and their current-voltage characteristics

Quantum cross (QC) devices which consist of two Ni thin films deposited on polyethylene naphthalate substrates with their edges crossing have been fabricated and their current-voltage characteristics have been investigated. The cross-sectional area between the two Ni electrodes, which was obtained without the use of electron-beam or optical lithography, can be as small as 17 nm x 17 nm. We have successfully obtained ohmic current-voltage characteristics, which show good agreement with calculation results within the framework of the modified Anderson model. The calculated results also predict a high switching ratio in excess of 100,000:1 for QC devices having the molecule sandwiched between the Ni electrodes. This indicates that QC devices having the molecule can be expected to have potential application in novel switching devices.