Gold nanoparticle-ultrananocrystalline diamond hybrid structured materials for high-performance optoelectronic device applications.

Hybridization of gold nanoparticles in the ultrananocrystalline diamond materials improves the electrical conductivity of the materials to a high level of 230 (Ω cm)(-1) with a sheet carrier concentration of 8.9 × 10(20) cm(-2). These hybrid materials show enhanced electron field emission (EFE) properties, viz. a low turn-on field of 2.1 V µm(-1) with a high EFE current density of 5.3 mA cm(-2) (at an applied field of 4.9 V µm(-1)) and the life-time stability up to a period of 372 min. The fabrication of these hybrid materials with high conductivity and superior EFE behaviors is a direct and simple process which opens new prospects in flat panel displays and high brightness electron sources.

Enhanced electron field emission properties of conducting ultrananocrystalline diamond films after Cu and Au ion implantation.

The effects of Cu and Au ion implantation on the structural and electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were investigated. High electrical conductivity of 186 (Ω•cm)(-1) and enhanced EFE properties with low turn-on field of 4.5 V/µm and high EFE current density of 6.70 mA/cm(2) have been detected for Au-ion implanted UNCD (Au-UNCD) films that are superior to those of Cu-ion implanted UNCD (Cu-UNCD) ones. Transmission electron microscopic investigations revealed that Au-ion implantation induced a larger proportion of nanographitic phases at the grain boundaries for the Au-UNCD films in addition to the formation of uniformly distributed spherically shaped Au nanoparticles. In contrast, for Cu-UNCD films, plate-like Cu nanoparticles arranged in the row-like pattern were formed, and only a smaller proportion of nanographite phases along the grain boundaries was induced. From current imaging tunneling spectroscopy and local current-voltage curves of scanning tunneling spectroscopic measurements, it is observed that the electrons are dominantly emitted from the grain boundaries. Consequently, the presence of nanosized Au particles and the induction of abundant nanographitic phases in the grain boundaries of Au-UNCD films are believed to be the authentic factors, ensuing in high electrical conductivity and outstanding EFE properties of the films.

Electron field emission enhancement of vertically aligned ultrananocrystalline diamond-coated ZnO core-shell heterostructured nanorods.

Enhanced electron field emission (EFE) behavior of a core-shell heterostructure, where ZnO nanorods (ZNRs) form the core and ultrananocrystalline diamond needles (UNCDNs) form the shell, is reported. EFE properties of ZNR-UNCDN core-shell heterostructures show a high emission current density of 5.5 mA cm(-2) at an applied field of 4.25 V µm(-1) , and a low turn-on field of 2.08 V µm(-1) compared to the 1.67 mA cm(-2) emission current density (at an applied field of 28.7 V µm(-1) ) and 16.6 V µm(-1) turn-on field for bare ZNRs. Such an enhancement in the field emission originates from the unique materials combination, resulting in good electron transport from ZNRs to UNCDNs and efficient field emission of electrons from the UNCDNs. The potential application of these materials is demonstrated by the plasma illumination measurements that lowering the threshold voltage by 160 V confirms the role of ZNR-UNCDN core-shell heterostructures in the enhancement of electron emission.

Mediatorless N(2) incorporated diamond nanowire electrode for selective detection of NADH at stable low oxidation potential.

The electrocatalytic properties of a N2 incorporated diamond nanowire (N-DNW) unmodified electrode towards the oxidation of nicotinamide adenine dinucleotide (NADH) was critically evaluated. The electrochemical behavior of the N-DNW unmodified electrode was examined and compared with that of boron-doped diamond, glassy carbon electrode, and graphite electrodes. The N-DNW electrode had high selectivity and high sensitivity for the differential pulse voltammetric detection of NADH in the presence of ascorbic acid at the lower and stable oxidation potential. Moreover, it exhibited strong stability after prolonged usage. The oxidation peak potential at the N-DNW electrode remained unchanged even after exposure to the solution, followed by washing, drying, and storage in laboratory air for 20 days, with minimization of surface contamination. Therefore, the N-DNW unmodified electrode shows promise for the detection of NADH and is attractive for use in a dehydrogenase based biosensor and other analytical applications.

Improvement in tribological properties by modification of grain boundary and microstructure of ultrananocrystalline diamond films.

Grain boundaries and microstructures of ultrananocrystalline diamond (UNCD) films are engineered at nanoscale by controlling the substrate temperature (TS) and/or by introducing H2 in the commonly used Ar/CH4 deposition plasma in a microwave plasma enhanced chemical vapor deposition system. A model for the grain growth is proposed. The films deposited at low TS consist of random/spherical shaped UNCD grains with well-defined grain boundaries. On increasing TS, the adhering efficiency of CH radical onto diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nanosize diamond clusters break due to hydrogen abstraction activated, rendering the diamond phase less passivated. This leads to the C2 radical further attaching to the diamond lattice, resulting in the modification of grain boundaries and promoting larger sized clustered grains with a complicated defect structure. Introduction of H2 in the plasma at low TS gives rise to elongated clustered grains that is attributed to the presence of atomic hydrogen in the plasma, preferentially etching out the t-PA attached to nanosized diamond clusters. On the basis of this model a technologically important functional property, namely tribology of UNCD films, is studied. A low friction of 0.015 is measured for the film when ultranano grains are formed, which consist of large fractions of grain boundary components of sp(2)/a-C and t-PA phases. The grain boundary component consists of large amounts of hydroxylic and carboxylic functional groups which passivates the covalent carbon dangling bonds, hence low friction coefficient. The improved tribological properties of films can make it a promising candidate for various applications, mainly in micro/nanoelectro mechanical system (M/NEMS), where low friction is required for high efficiency operation of devices.

Structural and electrical properties of conducting diamond nanowires.

Conducting diamond nanowires (DNWs) films have been synthesized by N2-based microwave plasma enhanced chemical vapor deposition. The incorporation of nitrogen into DNWs films is examined by C 1s X-ray photoemission spectroscopy and morphology of DNWs is discerned using field-emission scanning electron microscopy and transmission electron microscopy (TEM). The electron diffraction pattern, the visible-Raman spectroscopy, and the near-edge X-ray absorption fine structure spectroscopy display the coexistence of sp³ diamond and sp² graphitic phases in DNWs films. In addition, the microstructure investigation, carried out by high-resolution TEM with Fourier transformed pattern, indicates diamond grains and graphitic grain boundaries on surface of DNWs. The same result is confirmed by scanning tunneling microscopy and scanning tunneling spectroscopy (STS). Furthermore, the STS spectra of current-voltage curves discover a high tunneling current at the position near the graphitic grain boundaries. These highly conducting regimes of grain boundaries form effective electron paths and its transport mechanism is explained by the three-dimensional (3D) Mott's variable range hopping in a wide temperature from 300 to 20 K. Interestingly, this specific feature of high conducting grain boundaries of DNWs demonstrates a high efficiency in field emission and pave a way to the next generation of high-definition flat panel displays or plasma devices.

Preferentially grown ultranano c-diamond and n-diamond grains on silicon nanoneedles from energetic species with enhanced field-emission properties.

The design and fabrication of well-defined nanostructures have great importance in nanoelectronics. Here we report the precise growth of sub-2 nm (c-diamond) and above 5 nm (n-diamond) size diamond grains from energetic species (chemical vapor deposition process) at low growth temperature of about 460 °C. We demonstrate that a pre-nucleation induced interface can be accounted for the growth of c-diamond or n-diamond grains on Si-nanoneedles (Si-NN). These preferentially grown allotropic forms of diamond on Si-NN have shown high electron field-emission properties and signify their high potential towards diamond-based electronic applications.

Microplasma illumination enhancement of vertically aligned conducting ultrananocrystalline diamond nanorods.

Vertically aligned conducting ultrananocrystalline diamond (UNCD) nanorods are fabricated using the reactive ion etching method incorporated with nanodiamond particles as mask. High electrical conductivity of 275 Ω·cm-1 is obtained for UNCD nanorods. The microplasma cavities using UNCD nanorods as cathode show enhanced plasma illumination characteristics of low threshold field of 0.21 V/µm with plasma current density of 7.06 mA/cm2 at an applied field of 0.35 V/µm. Such superior electrical properties of UNCD nanorods with high aspect ratio potentially make a significant impact on the diamond-based microplasma display technology.

Engineering the interface characteristics of ultrananocrystalline diamond films grown on Au-coated Si substrates.

Enhanced electron field emission (EFE) properties have been observed for ultrananocrystalline diamond (UNCD) films grown on Au-coated Si (UNCD/Au-Si) substrates. The EFE properties of UNCD/Au-Si could be turned on at a low field of 8.9 V/µm, attaining EFE current density of 4.5 mA/cm(2) at an applied field of 10.5 V/µm, which is superior to that of UNCD films grown on Si (UNCD/Si) substrates with the same chemical vapor deposition process. Moreover, a significant difference in current-voltage curves from scanning tunneling spectroscopic measurements at the grain and the grain boundary has been observed. From the variation of normalized conductance (dI/dV)/(I/V) versus V, bandgap of UNCD/Au-Si is measured to be 2.8 eV at the grain and nearly metallic at the grain boundary. Current imaging tunneling spectroscopy measurements show that the grain boundaries have higher electron field emission capacity than the grains. The diffusion of Au into the interface layer that results in the induction of graphite and converts the metal-to-Si interface from Schottky to Ohmic contact is believed to be the authentic factors, resulting in marvelous EFE properties of UNCD/Au-Si.

Freestanding ultrananocrystalline diamond films with homojunction insulating layer on conducting layer and their high electron field emission properties.

Freestanding ultrananocrystalline diamond (UNCD) films with homojunction insulating layer in situ grown on a conducting layer showed superior electron field emission (EFE) properties. The insulating layer of the films contains large dendrite type grains (400-600 nm in size), whereas the conducting layer contains nanosize equi-axed grains (5-20 nm in size) separated by grain boundaries of about 0.5-1 nm in width. The conducting layer possesses n-type (or semimetallic) conductivity of about 5.6 × 10(-3) (Ω cm)(-1), with sheet carrier concentration of about 1.4 × 10(12) cm(-2), which is ascribed to in situ doping of Li-species from LiNbO(3) substrates during growth of the films. The conducting layer intimately contacts the bottom electrodes (Cu-foil) by without forming the Schottky barrier, form homojunction with the insulating layer that facilitates injection of electrons into conduction band of diamond, and readily field emitted at low applied field. The EFE of freestanding UNCD films could be turned on at a low field of E(0) = 10.0 V/µm, attaining EFE current density of 0.2 mA/cm(2) at an applied field of 18.0 V/µm, which is superior to the EFE properties of UNCD films grown on Si substrates with the same chemical vapor deposition (CVD) process. Such an observation reveals the importance in the formation of homojunction on enhancing the EFE properties of materials. The large grain granular structure of the freestanding UNCD films is more robust against harsh environment and shows high potential toward diamond based electronic applications.

One-step Ge/Si epitaxial growth.

Fabricating a low-cost virtual germanium (Ge) template by epitaxial growth of Ge films on silicon wafer with a Ge(x)Si(1-x) (0 < x < 1) graded buffer layer was demonstrated through a facile chemical vapor deposition method in one step by decomposing a hazardousless GeO(2) powder under hydrogen atmosphere without ultra-high vacuum condition and then depositing in a low-temperature region. X-ray diffraction analysis shows that the Ge film with an epitaxial relationship is along the in-plane direction of Si. The successful growth of epitaxial Ge films on Si substrate demonstrates the feasibility of integrating various functional devices on the Ge/Si substrates.

Electronic structure, electron field emission and magnetic behaviors of carbon nanotubes fabricated on La0.66Sr0.33MnO3 (LSMO) for spintronics application.

This work elucidates the electronic structure, electron field emission and magnetic anisotropic behaviors of single wall carbon nanotubes (SWCNTs) for the spin-electronics device application grown on the La0.66Sr0.33MnO3 (LSMO)/SrTiO3 (STO) substrate. Micro-Raman spectroscopy, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES) were used for the study of electronics structure. The field emission characteristics were studied from the electron field emission current density (J) versus applied electric field (E(A)) from which the turn-on electric field (E(TOE)) was evaluated. The magnetization behaviors are also presented by the M-H hysteresis loop and were obtained by applying the magnetic field in the parallel and perpendicular direction of the CNTs at 305 K and 5 K temperatures. A magnetic measurement shows that the coercivity of the CNTs/LSMO/STO is higher and has hig anisotropic-nature than the composite LSMO/STO that could be the good material for the future possible spin-electronics device applications.

Induction and regulation of differentiation in neural stem cells on ultra-nanocrystalline diamond films.

The interaction of ultra-nanocrystalline diamond (UNCD) with neural stem cells (NSCs) has been studied in order to evaluate its potential as a biomaterial. Hydrogen-terminated UNCD (H-UNCD) films were compared with standard grade polystyrene in terms of their impact on the differentiation of NSCs. When NSCs were cultured on these substrates in medium supplemented with low concentration of serum and without any differentiating factors, H-UNCD films spontaneously induced neuronal differentiation on NSCs. By direct suppression of mitogen-activated protein kinase/extracellular signaling-regulated kinase1/2 (MAPK/Erk1/2) signaling pathway in NSCs using U0126, known to inhibit the activation of Erk1/2, we demonstrated that the enhancement of Erk1/2 pathway is one of the effects of H-UNCD-induced NSCs differentiation. Moreover, functional-blocking antibody directed against integrin beta1 subunit inhibited neuronal differentiation on H-UNCD films. This result demonstrated the involvement of integrin beta1 in H-UNCD-mediated neuronal differentiation. Mechanistic studies revealed the cell adhesion to H-UNCD films associated with focal adhesion kinase (Fak) and initiated MAPK/Erk1/2 signaling. Our study demonstrated that H-UNCD films-mediated NSCs differentiation involves fibronectin-integrin beta1 and Fak-MAPK/Erk signaling pathways in the absence of differentiation factors. These observations raise the potential for the use of UNCD as a biomaterial for central nervous system transplantation and tissue engineering.

High-temperature annealing effects on multiwalled carbon nanotubes: electronic structure, field emission and magnetic behaviors.

This work elucidates the effects of high-temperature annealing on the microscopic and electronic structure of multiwalled carbon nanotubes (MWCNTs) using high-resolution transmission electron microscopy, micro-Raman spectroscopy, X-ray diffraction, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES), respectively. The field emission and magnetization behaviors are also presented. The results of annealing are as follows: (1) MWCNTs tend to align in the form of small fringes along their length, promote graphitization and be stable in air, (2) XANES indicates an enhancement in oxygen content on the sample, implying that it can be adopted for sensing and storing oxygen gas, (3) the electron field emission current density (J) is enhanced and the turn-on electric field (E(TOE)) reduced, suggesting potential use in field emission displays and as electron sources in microwave tube amplifiers and (4) as-grown MWCNTs with embedded iron nanoparticles exhibits significantly higher coercivity approximately 750 Oe than its bulk counterpart (Fe(bulk) approximately 0.9 Oe), suggesting its potential use as low-dimensional high-density magnetic recording media.

The effect of ultra-nanocrystalline diamond films on the proliferation and differentiation of neural stem cells.

The interaction of ultra-nanocrystalline diamond (UNCD) with neural stem cells (NSCs) has been studied along with its surface modification in order to improve its function as a biomaterial. Hydrogen- and oxygen-terminated UNCD films were compared with standard grade polystyrene in terms of their impact on the growth, expansion and differentiation of NSCs. When NSCs were cultured on these substrates in low serum and without any differentiating factors, hydrogen-terminated UNCD films spontaneously induced cell proliferation and neuronal differentiation. Oxygen-terminated UNCD films were also shown to further improve neural differentiation, with a preference to differentiate into oligodendrocytes. Hence, controlling the surface properties of UNCD could manipulate the differentiation of NSCs for different biomedical applications. These observations raise the potential for the use of UNCD as a biomaterial for central nervous system transplantation and tissue engineering.

The effect of ion implantation on field emission property of nanodiamond films.

Nanocrystalline diamond films prepared by microwave plasma enhanced chemical vapor deposition (MPECVD) were implanted using 110 keV nitrogen ions under fluence ranging from 10(13)-10(14) ions/cm2. Scanning Electron Microscopy (SEM) and Raman spectroscopy were used to analyze the changes in the surface of the films before and after ion implantation. Results show that with nitrogen ion implantation in nanocrystalline diamond film cause to decrease in diamond crystallinity. The field emission measurement shows a sharp increase in current density with increase in dose. The ion implantation also alters the turn on field. It is observed that the structural damage caused by ion implantation plays a significant role in emission behaviour of nanocrystalline diamonds.