Mediatorless N2 incorporated diamond nanowire electrode for selective detection of NADH at stable low oxidation potential

[[abstract]]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.[[booktype]]紙本[[booktype]]電子

Enhancement in electron field emission in ultrananocrystalline and microcrystalline diamond films upon 100 MeV silver ion irradiation

[[abstract]]Enhanced electron field emission (EFE) behavior was observed in ultrananocrystalline diamond (UNCD) and microcrystalline diamond (MCD) films upon irradiation with 100 MeV Ag9+-ions in a fluence of 5×1011 ions/cm2. Transmission electron microscopy indicated that while the overall crystallinity of these films remained essentially unaffected, the local microstructure of the materials was tremendously altered due to heavy ion irradiation, which implied that the melting and recrystallization process have occurred along the trajectory of the heavy ions. Such a process induced the formation of interconnected nanocluster networks, facilitating the electron conduction and enhancing the EFE properties for the materials. The enhancement in the EFE is more prominent for MCD films than that for UNCD films, reaching a low turn-on field of E0 = 3.2 V/μm and large EFE current density of Je = 3.04 mA/cm2 for 5×1011 ions/cm2 heavy ion irradiated samples.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子

Enhanced electron field emission properties by tuning the microstructure of ultrananocrystalline diamond film

[[abstract]]Synthesis of microcrystalline-ultrananocrystalline compositediamond (MCD-UNCD) films, which exhibit marvelous electron field emission (EFE) properties, was reported. The EFE of MCD-UNCD compositediamondfilm can be turned on at a low field as 6.5 V/μm and attain large EFE current density about 1.0 mA/cm2 at 30 V/μm applied field, which is better than the EFE behavior of the nondoped planar diamondfilms ever reported. The MCD-UNCD films were grown by a two-step microwave plasma enhanced chemical vapor deposition (MPECVD) process, including forming an UNCD layer in CH4/Ar plasma that contains no extra H2, followed by growingMCD layer using CH4/H2/Ar plasma that contains large proportion of H2. Microstructure examinations using high resolution transmission electron microscopy shows that the secondary MPECVD process modifies the granular structure of the UNCD layer, instead of forming a large grain diamond layer on top of UNCDfilms. The MCD-UNCD compositediamondfilms consist of numerous ultrasmall grains (∼5 nm in size), surrounding large grains about hundreds of nanometer in size. Moreover, there exist abundant nanographites in the interfacial region between the grains that were presumed to form interconnected channels for electron transport, resulting in superior EFE properties for MCD-UNCD compositefilms.[[incitationindex]]SCI[[booktype]]電子版[[booktype]]紙

Modification of ultrananocrystalline diamond film microstructure via Fe-coating and annealing for enhancement of electron field emission properties

[[abstract]]The interaction between Fe-coatings and ultrananocrystalline diamond (UNCD) films during annealing was investigated in detail using transmission electron microscopy. The thin Fe-coating first formed nanosized Fe-clusters and then catalytically dissociated the diamond, re-precipitating carbon to form nanosized graphite clusters. These clusters formed conducting networks that facilitated electron transport and greatly improved the electron field emission (EFE) properties of the UNCD films. The extent of enhancement varied markedly with annealing temperature and atmosphere. For H2-annealed films, EFE behavior was optimized by annealing at 900 °C. EFE was turned on at (E0)H2 = 1.2 V/μm, attaining EFE current density of (Je)H2 = 772.0 μA/cm2 at an applied field of 8.8 V/mm. These characteristics were superior to those of UNCD films NH3-annealed at 850 °C. The inferior EFE properties for the NH3-annealed samples were attributed to reaction of NH3 with the hydrocarbon phase that encapsulated the nanosized diamond grains, hindering Fe–diamond interaction.[[booktype]]紙

Effect of gigaelectron volt Au-ion irradiation on the characteristics of ultrananocrystalline diamond films

[[abstract]]The effect of 2.245 GeV Au-ion irradiation/postannealing processes on the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films was investigated. Au-ion irradiation with a fluence of around 8.4×1013 ions/cm2 is required to induce a large improvement in the EFE properties of the UNCD films. Postannealing the Au-ion irradiated films at 1000 °C for 1 h slightly degraded the EFE properties of the films but the resulting EFE behavior was still markedly superior to that of pristine UNCD films. Transmission electron microscopy examinations revealed that the EFE properties of the UNCD films are primarily improved by Au-ion irradiation/postannealing processes because of the formation of nanographites along the trajectory of the irradiating ions, which results in an interconnected path for electron transport. In contrast, the induction of grain growth process due to Au-ion irradiation in UNCD films is presumed to insignificantly degrade the EFE properties for the films as the aggregates are scarcely distributed and do not block the electron conducting path.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

Bias-enhanced nucleation and growth processes for improving the electron field emission properties of diamond films

[[abstract]]The evolution of diamond films in bias-enhanced-nucleation (BEN) and bias-enhanced-growth (BEG) processes was systematically investigated. While the BEN process can efficiently form diamond nuclei on the Si substrates, BEG with large enough applied field (> –400 V) and for sufficiently long periods (>60 min) was needed to develop proper granular structure for the diamond films so as to enhance the electron field emission (EFE) properties of the films. For the films BEG under -400 V for 60 min (after BEN for 10 min), the EFE process can be turned on at a field as small as 3.6 V/μm, attaining a EFE current density as large as 325 μA/cm2 at an applied field of 15 V/μm. Such an EFE behavior is even better than that of the ultrananocrystalline diamond films grown in CH4/Ar plasma. Transmission electron microscopic examination reveals that the prime factor enhancing the EFE properties of these films is the induction of the nano-graphite filaments along the thickness of the films that facilitates the transport of electrons through the films.[[journaltype]]國外[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]US

Origin of platelike granular structure for the ultrananocrystalline diamond films synthesized in H2-containing Ar/CH4 plasma

[[abstract]]The modification on microstructure of diamond films due to the incorporation of H2 species into the Ar/CH4 plasma was systematically investigated. While the hydrogen-free plasma produced the ultrananocrystalline diamond films with equiaxed grains (about 5 nm in size), the hydrogen-containing plasma resulted in platelike grains (about 100×300 nm2 in size). The size of the platelike grains increased with the H2 content in the plasma. Transmission electron microscopy and optical emission spectroscopy reveal that only 0.1%H2 incorporated in the Ar/CH4 plasma is sufficient for inducing the formation of platelike grains, suggesting that the platelike grains are formed via the competition between the attachment and the etching of hydrocarbons onto the existing diamond surfaces. In Ar plasma, the diamond grains were always passivated with hydrocarbons and the active carbon species in the plasma can only renucleate to form nanocrystalline diamond grains. Incorporation of H2 species in the plasma leads to partial etching of hydrocarbons adhered onto the diamond grains, such that active carbon species in the plasma can attach to diamond surface anisotropically, resulting in diamond flakes and dendrites geometry.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

Nanocrystalline diamond microstructures from Ar/H2/CH4-plasma chemical vapour deposition

[[abstract]]The incorporation of H2 into Ar plasma was observed to markedly alter the microstructure of diamond films. The addition of a small percentage of H2 (<1.5%) into the Ar plasma leads to the presence of stacking faults in plate-like diamond grains, the incorporation of 75% H2 induces the formation of the diamond polymorph (8H). Optical emission spectroscopy indicated that addition of H2 into the Ar/CH4 plasma decreased the CH/C2 ratio and increased the proportion of atomic hydrogen. The small proportion of atomic hydrogen in 1.5%H2–Ar plasma can only induce the formation of (111) stacking faults, resulting in scarcely distributed plate-like diamond grains. The large proportion of atomic hydrogen in 75%H2–Ar plasma causes the rapid growth of diamond grains, leading to the formation of polymorphs of diamond lattices. The tuning on the microstructure of the UNCD films by incorporating either small or large amounts of H2 in Ar-plasma can be attributed to the interaction of H-species with the grain boundary hydrocarbons. Such a capability opens up the potential for applications of UNCD films. Despite the complication in granular structure resulted from the CH4/(Ar–H2) plasma chemical vapour deposition, the formation of microstructures can be explained by the same pathway, the competition of the processes (i) formation of a hydrocarbon passivation layer and the re-activation of the hydrocarbon layer and (ii) secondary nucleation and the enlargement of diamond grains.[[incitationindex]]SCI[[booktype]]電子

Field emission enhancement in nitrogen-ion-implanted ultrananocrystalline diamond films

[[abstract]]Enhanced electron field emission (EFE) properties for ultrananocrystalline diamond (UNCD) films grown on silicon substrate were achieved, especially due to the high dose N ion implantation. Secondary ion mass spectroscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy measurements indicated that the N ion implantation first expelled H−, induced the formation of disordered carbon (or defect complex), and then induced the amorphous phase, as the ion implantation dose increased. The postimplantation annealing process healed the atomic defects, but converted the disordered carbon to a stable defect complex, and amorphous carbon into a more stable graphitic phase. The EFE characteristics of the high dose (>1015 ions/cm2) ion-implanted UNCD were maintained at an enhanced level, whereas those of the low dose (<1014 ions/cm2) ion-implanted ones were reverted to the original values after the annealing process. Ion implantation over a critical dose (1×1015 ions/cm2) was required to improve the EFE properties of UNCD films.[[notice]]補正完畢[[booktype]]紙本[[booktype]]電子

STM observation of surface transfer doping mechanism in 3 keV nitrogen ion implanted UNCD films

[[abstract]]3 keV nitrogen ions are implanted into UNCD/Si from our 30 kV ion accelerator. Field emission property is enhanced upon nitrogen implantation in comparision to as-prepared UNCD. STM shows that there is agglomeration of diamond grains. CITS measurements show that diamond grains are the prominent electron emitters while grain boundaries were the prominent emitters for 75 keV N+ implantation. When N atoms are at the surface, electron emission by transfer-doping process appears to be the physical mechanism involved. When they are buried deeper as in the case of 75 keV ions, grain boundary conduction-channel process is valid.[[journaltype]]國外[[booktype]]紙本[[booktype]]電子版[[countrycodes]]US