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The temporal current stability and the current fluctuations of the field emission current obtained from ultrananocrystalline diamond (UNCD) films were investigated. The films were synthesized by Ar-rich dc plasma assisted hot filament chemical vapor deposition. The field emission properties were correlated to the films’ composition (sp2 and sp3 bonded carbon volume fractions) and nanostructure. The compositional analysis was done by modeling the films’ spectroscopic ellipsometry [Ψ (E), Δ (E)] data by using a two layer structure and the Bruggeman effective medium approximation. The results indicate that the local field enhancement in UNCD films is related to their intrinsic morphology at the diamond-grain boundary-vacuum interface, and the sp3/sp2 carbon volume fraction plays a significant function on the short- and long-term current stabilities of field emitted electrons. [ABSTRACT FROM AUTHOR]

Nascent SH(X 2Πi, v‘=0,1) and SD(X 2Πi, v‘=0,1) rotational state population distributions, spin–orbit state population ratios, and Λ-doublet state population ratios have been measured following the UV excimer laser photodissociation of H2S (λ=193, 222, and 248 nm) and D2S (λ=193 and 222 nm), respectively. Nascent SH(X 2Πi, v‘=0) rotational state distributions following 193 nm photodissociation of cold H2S in a free jet expansion vs 300 K H2S in a flowing gas cell were essentially the same, indicating that photofragment angular momentum must be originating predominantly in the dissociation event, and not from rotational energy contained in the parent triatom. Laser excitation spectra of SH(X 2Πi, v‘=1) and SD(X 2Πi, v‘=1) have been recorded for the first time. Rotational state distributions for SH(X 2Πi, v‘) and SD(X 2Πi, v‘) are independent of v‘. Λ-doublet population ratios of the nascent photofragments are essentially unity for all the cases measured. The nascent rotational state distributions are consistent with an impact parameter model for the dissociating triatomic molecule. [ABSTRACT FROM AUTHOR]

This article reports the superparamagnetic behavior of metal-free nitrogen-doped graphene quantum dots (N-GQDs). The pulsed laser ablation (PLA) method was utilized to synthesize N-GQDs with an average diameter of 3.45 nm and a high doping level (N/C) of 1.4. Magnetic properties of as-synthesized N-GQDs were explored by performing magnetization vs magnetic field (M–H) and magnetization vs temperature (M–T) measurements. M–H plots measured in a temperature range of 2–300 K revealed the superparamagnetic behavior of N-GQDs. The value of saturation magnetization was found to be directly correlated to nitrogen concentration and a saturation magnetization up to 28.7 emu/g was obtained at room temperature (300 K). M–T measurements with zero-field-cooled (ZFC) and field-cooled (FC) conditions were employed to study anisotropy energy barriers and blocking temperature. A variation in the blocking temperature (TB) from 288 to 61 K was observed when the external magnetic field (H) was changed from 0.1 to 0.6 T. The origin of superparamagnetism was attributed to the presence of graphitic nitrogen bonding configuration and defect states. The observed superparamagnetic properties along with the optical properties of N-GQDs create an opportunity for developing materials for biomedical applications and data recording devices. [ABSTRACT FROM AUTHOR]

Filtration has emerged as a critical technology to reduce waterborne diseases caused by poor water quality. Filtration technology presents key challenges, such as membrane selectivity, permeability and biofouling. Nanomaterials can offer solutions to these challenges by varying the membranes’ mechanical and bactericidal properties. This research uses nanodiamond particles with facile surface functionality and biocompatibility properties that are added to membranes used for filtration treatments. Scanning and transmission electron microscopy (SEM and TEM) and Fourier transform infrared spectroscopy (FTIR) were performed to study the membrane surface. FTIR spectra confirms an increase in oxygen functional groups onto the ultradispersed diamond’s (UDD) surface following acid treatment. SEM images show particle deagglomeration of functionalized UDD at the membrane surface. Tensile strength tests were done to measure the UDD mechanical properties and Coliscan membrane filtration characterization was performed to determine the filter effectiveness. Polyether sulfone (PES) and polyvinylidene (PVDF) membranes expressed a change in their yield point when UDD was incorporated into the porous matrix. A significant microorganism reduction was obtained and confirmed using t-test analysis at a 95% level of confidence. UDD-embedded membranes exhibit a significant bactericidal reduction compared to commercial membranes suggesting these membranes have the potential to enhance current membrane filtration systems. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotube (CNT)/diamond composite has been fabricated by hot filament chemical vapor deposition on a silicon substrate using iron as catalyst. The material characteristics of this monolithic structure were examined by electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and electron energy loss spectroscopy. The composite material shows the presence of carbon nanotubes of several microns in length together with conspicuous diamond microcrystals of sizes ranging from 0.5 to 2.0μm. The CNTs protrude from the diamond microcrystals and become entangled around them as they grow. This monolithic CNT/diamond composite provides an intrinsic heat dissipation mechanism for CNTs during field emission and exhibits low turn on field, large field enhancement factor, and an excellent current stability over a period of 44h. [Copyright &y& Elsevier]

Abstract: Continuous nanocrystalline diamond (NCD) films were grown in an argon-rich gas atmosphere with relatively high growth rates by sustaining a low power (5 W) DC plasma in a hot filament chemical vapor deposition system (HFCVD). The parameter window for the synthesis of NCD films was studied as a function of argon, methane and hydrogen concentrations, as well as substrate temperature and DC bias. The results are consistent with reports indicating that the DC plasma induces re-nucleation by ion bombardment during the initial growth step and helps to maintain the atomic H and hydrocarbon species near the growing surface. It was found that DC plasma-assisted HFCVD enables high NCD growth rates and expands the parameter window, rendering it unnecessary to heat the filament above 2800 K. [Copyright &y& Elsevier]

Abstract: We have applied Density Functional Theory (DFT) within the Generalized Gradient Approximation to study the behavior of lithium impurities in the diamond lattice. It was found that, although isolated interstitial lithium atoms in tetrahedral sites have a donor state relatively close to the conduction band at 0.35 eV, their behavior is critically affected by adjacent interstitials. Lithium atoms that occupy adjacent interstitial tetrahedral sites cluster spontaneously and induce carbon–carbon bond breaking in their neighborhood. The corresponding charge distribution and electronic density of states analyses show that charge localization takes place at the carbon atoms around the lithium clusters and deeper mid-gap states are introduced in the diamond band gap. The formation energy was found to be 1.88 eV and 3.09 eV, for clusters of two and three lithium atoms, respectively, considered in this study. The calculations also indicate that Li clustering would not take place if Li ions instead of atoms were incorporated interstitially. [Copyright &y& Elsevier]

The electrical properties of graphene on dielectric substrates, such as silicon carbide (SiC), have received much attention due to their interesting applications. This work presents a method to grow graphene on a 6H-SiC substrate at a pressure of 35 Torr by using the hot filament chemical vapor deposition (HFCVD) technique. The graphene deposition was conducted in an atmosphere of methane and hydrogen at a temperature of 950 °C. The graphene films were analyzed using Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray, and X-ray photoelectron spectroscopy. Raman mapping and AFM measurements indicated that few-layer and multilayer graphene were deposited from the external carbon source depending on the growth parameter conditions. The compositional analysis confirmed the presence of graphene deposition on SiC substrates and the absence of any metal involved in the growth process. [ABSTRACT FROM AUTHOR]

Large area single and bilayer graphene are grown on Pt/Ti/SiO2 substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO2 substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO2 substrate at a low filament temperature. The approach paves a novel pathway towards the layer‐controlled growth of graphene on Pt/Ti/SiO2 substrates by HFCVD for frontier applications. [ABSTRACT FROM AUTHOR]

Gadolinium (Gd) and Nickel (Ni) doped bismuth ferrite (BiFeO3) nanoparticles Bi0.925Gd.075Fe0.95Ni0.05O3 (BGFNO) with spontaneous polarization (2.5 μC/cm2) were mechano‐chemically synthesized and used to achieve high capacity retention in lithium sulfur (Li−S) batteries. The BGFNO particles were coupled with single walled carbon nanotubes (SWCNT)/sulfur (S) composite cathodes as well as coated on separator. The X‐ray diffraction of BGFNO@S/SWCNT cathodes show an orthorhombic structure with particle size distribution of 20–26 nm, while Raman spectra substantiate efficient coupling of BGFNO with S/SWCNT cathodes, in agreement with SEM images, showing the interconnected network of composites. The specific discharge capacity of S60BGFNO30SWCNT10 composite cathode @ 200 mA/g together with BGFNO coated separator gains maximum capacity up to 1611 mAh/g and retains up to 1294 mAh/g after 50th cycle with improved capacity retention of 80 % showing suppression of polysulfides formation. The coated separator controls transport of carrier ions and side reactions, however modified cathodes with BGFNO particles acts as trapping center for polysulfides to enhance the electrochemical performance of the cells. The Coulombic efficiency(CE) for BGFNO/S/SWCNT composites @ 100 mA/g attained >98 % and CE @ 200 mA/g it is attained > 80 to 90 % compared to S/SWCNT composites in terms of improved cycle stability and reaction kinetics. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene quantum dots (NGQDs) have gained significant attention due to their various physical and chemical properties; however, there is a gap in the study of NGQDs' magnetic properties. This work adds to the efforts of bridging the gap by demonstrating the room temperature paramagnetism in GQDs doped with Nitrogen up to 3.26 at.%. The focus of this experimental work was to confirm the paramagnetic behavior of metal free NGQDs resulting from the pyridinic N configuration in the GQDs host. Metal-free nitrogen-doped NGQDs were synthesized using glucose and liquid ammonia as precursors by microwave-assisted synthesis. This was followed by dialysis filtration. The morphology, optical, and magnetic properties of the synthesized NGQDs were characterized carefully through atomic force microscopy (AFM), transmission electron microscopy (TEM)), UV-VIS spectroscopy, fluorescence, X-ray photon spectroscopy (XPS), and vibrating sample magnetometer (VSM). The high-resolution TEM analysis of NGQDs showed that the NGQDs have a hexagonal crystalline structure with a lattice fringe of ~0.24 nm of (1120) graphene plane. The N1s peak using XPS was assigned to pyridinic, pyrrolic, graphitic, and oxygenated NGQDs. The magnetic study showed the room-temperature paramagnetic behavior of NGQDs with pyridinic N configuration, which was found to have a magnetization of 20.8 emu/g. [ABSTRACT FROM AUTHOR]

We report our studies on the responsivity of sulfur-doped diamond films to ultraviolet radiation using two types of device configurations: the planar configuration with electrodes directly on the diamond surface, and the electron field emission configuration with a bias electrode suspended above the diamond surface. Diamond films of different grain sizes were employed: microcrystalline diamond, sub-microcrystalline diamond, and nanocrystalline diamond. The responsivity values of diamond films in the field emission configuration reached ~10mA/W at around 220 nm, which is ~40% higher than that of the planar configuration. These responsivity values of diamond films are comparable to those of commercially available photodiodes in the wavelength range of 210-300 nm, but with the advantage of being solar blind. The responsivity data were correlated with the bandgap structure of sulfur-doped diamond. [ABSTRACT FROM AUTHOR]

We fabricated large area bilayer graphene by hot filament chemical vapor deposition (HFCVD) on Cu foil. The HFCVD technique can represent a significant advantage over other techniques for industrial scaling at low cost. We performed systematic experiments to determine the best parameters to obtain uniform graphene coverage over an area of ~ 16 cm 2 . The experimental growth parameters are grouped into two distinct regions according to the products obtained: (A) continuous bilayer graphene with low defect density and (B) continuous bilayer graphene with high defect density. The optimum graphene films obtained are uniform bilayer with low defect density, greater than 90% transmittance in the visible region, and no gaps. The high quality of the bilayer graphene was confirmed by Raman spectroscopy mapping. The results show that the ratio of 2D to G peak intensities ( I 2D / I G ) is in the 0.9–1.6 range over 90% of the area. Moreover, we employed the static cling property of polyethylene terephthalate (PET) to preserve the integrity of the as-grown graphene films in the transfer process, showing that the graphene films become well attached to the SiO 2 /Si substrates while the PET films were completely peeled off. [ABSTRACT FROM AUTHOR]

The urgent demand for stable electrode materials, especially for the anode, arises in the pursuit of high-energy Li-ion batteries. This research focuses on bismuth oxide (Bi 2 O 3) and uncovers its performance through a straightforward, commercially viable synthesis route, along with the optimization of binders and electrolytes. By employing a sodium carboxymethyl cellulose binder and fluoroethylene carbonate additives, the Bi 2 O 3 anode demonstrates significantly enhanced performance compared to prior studies. It attains an impressive initial capacity of approximately 750 mA h g−1, exhibits excellent rate capability at 1000 mA g−1 and maintains stable cycling performance over 6000 cycles. [ABSTRACT FROM AUTHOR]

Abstract: Non-toxic magnetic-luminescent iron oxide Mn2+-doped zinc sulfide (Fe3O4/ZnS:Mn) composite nanoparticles were synthesized through a one-step chemical deposition route using surface-treated Fe3O4 nanoparticles. High resolution electron microscopy and X-ray diffraction analyses showed that the two individual phases co-exist with a high degree of crystalline quality, no parasitic phases were found. The average crystallite size was around 9nm. At the doping level of 20–25wt% Mn2+, the luminescence signal of the composite at 598nm is very intense, comparable to that of ZnS:Mn. This remarkable effect has been evidenced solely for Fe3O4 Cd2+-based composites, which are toxic. Moreover, the superparamagnetic response of Fe3O4 with near-zero coercivity is successfully retained in the composite. This notable bifunctionality of Fe3O4/ZnS:Mn can enable both in vivo and in vitro biomedical applications. [Copyright &y& Elsevier]

Abstract: Carbon nanotubes (CNTs) have been fabricated on free-standing microcrystalline diamond (FSD) films by hot filament chemical vapor deposition using Ni as catalyst. Micro Raman spectroscopy has been used as a primary technique to characterize the hybrid material, while electron microscopy and electron energy loss spectroscopy served as complementary characterization techniques. The fabricated material shows the presence of multiwall carbon nanotubes of diameters in the range of 10–15nm with a wall thickness of 5–6nm protruding from the free-standing microcrystalline diamond films of crystallite sizes ranging from 0.5 to 2.0μm. The CNT-FSD films show good field emission properties with low turn-on field, large field enhancement factor, and an excellent current stability over a period of 10days. [Copyright &y& Elsevier]

Boron nitride (BN) nanostructures are structural analogues of carbon nanostructures but have completely different bonding character and structural defects. They are chemically inert, electrically insulating, and potentially important in mechanical applications that include the strengthening of light structural materials. These applications require the reliable production of bulk amounts of pure BN nanostructures in order to be able to reinforce large quantities of structural materials, hence the need for the development of high-yield synthesis methods of pure BN nanostructures. Using borazine (B3N3H6) as chemical precursor and the hot-filament chemical vapor deposition (HFCVD) technique, pure BN nanostructures with cross-sectional sizes ranging between 20 and 50 nmwere obtained, including nanoparticles and nanofibers. Their crystalline structure was characterized by (XRD), their morphology and nanostructure was examined by (SEM) and (TEM), while their chemical composition was studied by (EDS), (FTIR), (EELS), and (XPS). Taken altogether, the results indicate that all the material obtained is stoichiometric nanostructured BN with hexagonal and rhombohedral crystalline structure. [ABSTRACT FROM AUTHOR]

The 193 nm photolysis of SO2 has been studied by monitoring the infrared emission of the vibrationally excited species using time-resolved FTIR emission spectroscopy. Evidence for a direct electronic transition from the C state to the ground state of SO2 was found in addition to photodissociation following the 193 nm excitation. Relaxation rate constants for the observed vibrationally excited species, SO, SO2(ν1), and SO2(ν3), were calculated from the experimental decays. [Copyright &y& Elsevier]

Nanocrystalline diamond (NCD) thin films offer applications in various fields, but the existing synthetic approaches are cumbersome and destructive. A major breakthrough has been achieved by our group in the direction of a non-destructive, scalable, and economic process of NCD thin-film fabrication. Here, we report a cheap precursor for the growth of nanocrystalline diamond in the form of paraffin wax. We show that NCD thin films can be fabricated on a copper support by using simple, commonplace paraffin wax under reaction conditions of Hot Filament Chemical Vapor Deposition (HFCVD). Surprisingly, even the presence of any catalyst or seeding that has been conventionally used in the state-of-the-art is not required. The structure of the obtained films was analyzed by scanning electron microscopy and transmission electron microscopy. Raman spectroscopy and electron energy-loss spectroscopy recorded at the carbon K-edge region confirm the presence of nanocrystalline diamond. The process is a significant step towards cost-effective and non-cumbersome fabrication of nanocrystalline diamond thin films for commercial production. [ABSTRACT FROM AUTHOR]

We investigate the stability of the orange band photoluminescence (PL) of bifunctional nanoparticles of Mn2+-doped ZnS at 5% (ZnS:0.05Mn). These 4-nm nanoparticles are synthesized via a one-step inorganic chemical route under ambient conditions. The phase, crystallinity, and morphology are analyzed via X-ray and electron diffractions and high-resolution electron microscopy. Based on the thermally activated carrier-transfer model, it is found that orange emission is rather stable at low temperatures and possesses thermal activation energy of ∼18 meV. The analysis of the PL decay curves suggests the coexistence of multiple lifetimes, that the shortening observed in PL lifetime is not due to the Mn2+ ions, and that the orange band decay is stable in temperature range from 10 K to 300 K. The measured M-H hysteresis loops demonstrate that ZnS:0.05Mn nanoparticles exhibit ferromagnetic ordering below 30 K, unlike its bulk counterpart. No magnetic field dependence of the Mn2+ PL intensity is observed up to 1 T. The stability of the PL signal when subject to an applied magnetic field is discussed. This study offers experimental evidence to test low-dimensional dilute magnetic semiconductor models and widens the range of applications of ZnS:Mn nanostructures beyond optoelectronics. [ABSTRACT FROM AUTHOR]

Free standing graphene-diamond hybrid films have been fabricated using saturated hydrocarbon polymers as seeding material by hot filament chemical vapor deposition technique. The films are characterized with x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). The XRD shows the characteristic diffraction peaks of both diamond and graphene. The Raman spectrum shows the characteristic band of diamond at 1332 cm-1 and D, G, and 2D bands of graphene at 1349, 1592, and 2687 cm-1, respectively. Both SEM and TEM depict the presence of diamond and graphene in the films. The EELS recorded in the carbon K-edge region also shows the signature peaks of diamond and graphene. The free standing hybrid films exhibit a remarkably low turn-on field of about 2.4 V/μm and a high emission current density of 0.1 mA/cm2. Furthermore, emission currents are stable over the period of 7 days. The superior field emission characteristics of the free standing graphene-diamond hybrid films are attributed to the heat sink capability of diamond and high electrical conductivity of graphene. [ABSTRACT FROM AUTHOR]

In the ongoing quest for energy production by nonconventional methods, energy conversion by vacuum and solid-state thermionic emission devices is one of the potentially efficient pathways for converting thermal energy directly into electrical power. The realization of practical of thermionic energy conversion devices strongly depends on achieving low work function materials, which is thus far a limiting factor. In an attempt to develop a new low work function thermionic material, this work reports thermionic emission energy distributions (TEEDs) from nanocrystalline diamond (NCD) films in the temperature range from 700 to 900 °C that reveal a consistent effective work function of 3.3 eV. The NCD films also exhibit emission peaks corresponding to higher work functions as indicated by shifts in their energy position and relative intensity as a function of temperature. These shifts thus appear to be related to instabilities in the NCD’s surface chemistry. The analysis of these data yields information on the origin of the low effective work function of NCD. [ABSTRACT FROM AUTHOR]

Investigates the pulsed laser ablation of an aluminum target at 193, 248 and 351 nanometer by fluorescence spectroscopy. Measurement of the ablated atom velocity distributions; Dependence of the velocity distributions on the vaporization laser fluence; Mechanism behind the production of hyperthermal distributions.

We report the room temperature thermal conductivity of polycrystalline twisted bilayer graphene (tBLG) as a function of grain size measured by employing a noncontact optical technique based on micro-Raman spectroscopy. Polycrystalline tBLG sheets of different grain sizes were synthesized on copper by hot filament chemical vapor deposition. The thermal conductivity values are 1305±122, 971±73, and 657±42 Wm-1K-1 for polycrystalline tBLG with average grain sizes of 54, 21, and 8 nm, respectively. Based on these thermal conductivity values, we also estimated the grain boundary conductance, 14.43±1.21 x 1010Wm-2K-1, and the thermal conductivity for single crystal tBLG, 1510±103Wm-1K-1 . Our results show that the relative degradation of thermal conductivity due to grain boundaries is smaller in bilayer than in monolayer graphene. Molecular dynamics simulations indicate that interlayer interactions play an important role in the heat conductivity of polycrystalline bilayer graphene. The quantitative study of the grain size dependent thermal conductivity of polycrystalline bilayer graphene is valuable in technological applications as well as for fundamental scientific understanding. [ABSTRACT FROM AUTHOR]

Dopamine (DA) is one of the most important catecholamine neurotransmitters of the human central nervous system, and is involved in many behavioral responses and brain functions. Below normal DA levels in biological fluids can lead to different neurodegenerative conditions. For excess DA levels, a failure in energy metabolism is indicated. In this study, a facile room-temperature phosphorescence sensor is developed to detect DA based on l -cysteine capped Mn doped ZnS quantum dots ( l -cys ZnS:Mn QDs). The QDs display a prominent orange emission band peaking at ~598 nm, which is strongly quenched upon addition of DA in alkaline medium. The sensor exhibits a linear working range of ~0.15–3.00 μM, and a limit of detection of ~7.80 nM. These results are explained in terms of a pH-dependent electron transfer process, in which the oxidized dopamine quinone functions as an efficient electron acceptor. The QDs-based sensor shows a high selectivity to DA over common interfering biomolecules (including some amino acids, ascorbic acid, chloride and glucose). The sensor has been successfully applied for the detection of DA in urine samples, yielding recoveries as high as 93%. Our findings indicate that our developed sensor exhibits high sensitivity and reproducibility to determine DA even in biological fluids where DA is at low levels, e.g., in the central nervous system, which is the usual clinical profile of a neurodegenerative disorder associated to the Parkinson's disease. [ABSTRACT FROM AUTHOR]

We report the detection of the ethynyl (C 2 H) radical by (1 + 2) REMPI on the B ̃ 2 A ′ ( T , K a = 0 , 1 , 2 ) ← X ̃ 2 Σ + ( 0 , 3 1 , 0 ) transition. One parallel, B ̃ 2 A ′ ( T , K a = 1 ) ← X ̃ 2 Σ + ( 0 , 3 1 , 0 ) with E eV = 37 , 946 cm - 1 , and two perpendicular transitions, B ̃ 2 A ′ ( T , K a = 0 ) ← X ̃ 2 Σ + ( 0 , 3 1 , 0 ) with E eV = 37 , 927 cm - 1 and B ̃ 2 A ′ ( T , K a = 2 ) ← X ̃ 2 Σ + ( 0 , 3 1 , 0 ) with E eV = 38 , 002 cm - 1 , are observed. The C 2 H radical was generated by the photodissociation of C 2 H 2 at 193 nm. By employing REMPI spectroscopy, we also studied the collisional induced rotational relaxation of C 2 H and measured rotational relaxation rate constants for this radical. The measured rotational relaxation rate constants for several values of J ″ are ( 0.08 – 0.26 ) × 10 - 9 cm 3 molec - 1 s - 1 and ( 0.75 – 1.92 ) × 10 - 9 cm 3 molec - 1 s - 1 for nitrogen buffer gas and acetylene, respectively. [ABSTRACT FROM AUTHOR]

High temperature synthesis methods produce defects in 1D nanomaterials, which ultimately limit their applications. We report here the synthesis of micro-scale boron nitride nanotubes (BNNT) at low substrate temperature (300 °C) using a pulsed CO2 laser deposition technique in the presence of catalyst. The electron microscopic analyses have shown the nanotubes distributed randomly on the surface of the substrate. The average diameter (∼0.25 μm) of a nanotube, which is the highest reported value to date, is estimated by SEM data and confirmed by TEM measurements. These nanotubes are promising for high response deep-UV photoluminescent devices. A detailed synthesis mechanism is presented and correlated with the experimental results. [ABSTRACT FROM AUTHOR]

We report the optical and electrical properties of chemically-doped bilayer graphene stack by tetracyanoethylene, a strong electron acceptor. The Tetracyanoethylene doping on the bilayer graphene via charge transfer was confirmed by Raman spectroscopy and Infrared Fourier transform spectroscopy. Doped graphene shows a significant increase in the sheet carrier concentration of up to 1.520×1013 cm-2 with a concomitant reduction of the sheet resistance down to 414.1 Ω/sq. The high optical transmittance (ca. 84%) in the visible region in combination with the low sheet resistance of the Tetracyanoethylene-doped bilayer graphene stack opens up the possibility of making transparent conducting electrodes for practical applications. [ABSTRACT FROM AUTHOR]

Oxidized single-wall carbon nanotubes were chemically attached to a modified copper substrate by means of a 4-aminothiophenol (4-ATP) self-assembly monolayer (SAM). This bottom up approach offers a low cost route to attach carbon nanotubes by using a condensation reaction. Here, the exposed amine from the 4-ATP SAM reacts with the carboxylic group (COOH) on the CNT. The reaction was followed using ATR-FTIR and the surface was characterized using SEM, XPS, and Raman. The analytical techniques used on this study suggest that the condensation reaction employed using a carbodiimide such as 1-Ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) produced SWCNT attached to the copper substrate. [ABSTRACT FROM AUTHOR]

We report unipolar resistive switching suitable for nonvolatile memory applications in polycrystalline BiFeO3 thin films in planar electrode configuration with nonoverlapping Set and Reset voltages, On/Off resistance ratio of ~104 and good data retention (verified for up to 3,000 s). We have also observed photovoltaic response in both high and low resistance states, where the photocurrent density was about three orders of magnitude higher in the low resistance state as compared to the high resistance state at an illumination power density of ~100 mW/cm². Resistive switching mechanisms in both resistance states of the planar device can be explained by using the conduction filament (thermo-chemical) model. [ABSTRACT FROM AUTHOR]

We report the photovoltaic properties of doped ferroelectric [Bi0.9La0.1][Fe0.97Ti0.02Zr0.01]O3 (BLFTZO) thin films. Polycrystalline BLFTZO films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition technique. Al-doped ZnO transparent top electrodes complete the ZnO:Al/BLFTZO/Pt metal-ferroelectric-metal capacitor structures. BLFTZO showed switchable photoresponse in both polarities. The open circuit voltage (VOC) and short circuit current (JSC) were found to be ~0.022 V and ~650 μA/cm², respectively after positive poling, whereas significant difference in VOC ~ 0.018V and JSC ~ 700 μA/cm² was observed after negative poling. The observed switchable photocurrent and photovoltage responses are explained on the basis of polarization flipping in BLFTZO due to the applied poling field. [ABSTRACT FROM AUTHOR]

AlPO4 nanoparticles were synthesized via chemical deposition method and used for the surface modification of MoO2 to improve its structural stability and electrochemical performance. Structure and surface morphology of pristine and AlPO4-coated MoO2 anode material were characterized by electron microscopy imaging (SEM and TEM) and X-ray diffraction (XRD). AlPO4 nanoparticles were observed, covering the surface of MoO2. Surface analyses show that the synthesized AlPO4 is amorphous, and the surface modification with AlPO4 does not result in a distortion of the lattice structure of MoO2.The electrochemical properties of pristine and AlPO4-coated MoO2 were characterized in the voltage range of 0.01-2.5V versus Li/Li+. Cyclic voltammetry studies indicate that the improvement in electrochemical performance of the AlPO4-coated anode material was attributed to the stabilization of the lattice structure during lithiation. Galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) studies reveal that the AlPO4 nanoparticle coating improves the rate capability and cycle stability and contributes toward decreasing surface layer and charge-transfer resistances. These results suggest that surface modification with AlPO4 nanoparticles suppresses the elimination of oxygen vacancies in the lattice structure during cycling, leading to a better rate performance and cycle life. [ABSTRACT FROM AUTHOR]

Abstract: Chemical sensors based on tin dioxide-carbon nanotubes (SnO2-CNT) composite films were fabricated by hot filament chemical vapor deposition (HF-CVD) technique. The composite films consist of SnO2 nanoparticles highly dispersed on the CNTs surface. Their resistivity is highly sensitive to the presence of adsorbates, which become easily attached or detached at room temperature and ambient pressure depending on their gas phase concentration. We systematically studied the sensitivity of the SnO2-CNT composite films for ethanol, methanol and H2S. The results were also compared to those for SnO2 and CNTs separately. It is shown that the SnO2-CNT composite films can detect ethanol, methanol and H2S down to ppm levels below OSHA's permissible exposure limits at room temperature and ambient pressure. Moreover, they self-recover within 1min without requiring any heating or energy source. [Copyright &y& Elsevier]

Abstract: We report for the first time the fabrication of nanostructured ferromagnetic lanthanum strontium manganite La0.67Sr0.33MnO3 (LSMO) conformally coated onto bamboo-like carbon nanotubes (BCNTs) by pulsed laser deposition. Scanning electron microscopy revealed that one-dimensional LSMO/BCNTs with diameters ranging from 100-160nm and lengths over 10μm were obtained. Line-scanned energy-dispersive X-ray spectroscopy profiles, selected area electron diffraction rings, and energy-filtered transmission electron microscopy maps provided further insight into the hybrid nanostructures. LSMO/BCNT and BCNT were also investigated via in situ electrical probing in a transmission electron microscope using a piezo-driven scanning tunneling microscopy holder. Modeling of the I–V characteristics of individual hybrid nanotubes yielded the resistivity, bandgap, and electron density of LSMO and BCNT. The results show that the transport properties of LSMO/BCNT are superior to those of BCNT. This research advances the integration of oxide materials and carbon nanotubes, bringing forth new avenues for miniaturization and fabrication of one-dimensional core-multishell materials with multifunctional properties that can be used as building blocks in nanodevices. [Copyright &y& Elsevier]

Abstract: Graphene has been the subject of intense research in recent years due to its unique electrical, optical and mechanical properties. Furthermore, it is expected that quantum dots of graphene would make their way into devices due to their structure and composition which unify graphene and quantum dots properties. Graphene quantum dots (GQDs) are planar nano flakes with a few atomic layers thick and with a higher surface-to-volume ratio than spherical carbon dots (CDs) of the same size. We have developed a pulsed laser synthesis (PLS) method for the synthesis of GQDs that are soluble in water, measure 2–6nm across, and are about 1–3 layers thick. They show strong intrinsic fluorescence in the visible region. The source of fluorescence can be attributed to various factors, such as: quantum confinement, zigzag edge structure, and surface defects. Confocal microscopy images of bacteria exposed to GQDs show their suitability as biomarkers and nano-probes in high contrast bioimaging. [Copyright &y& Elsevier]

Abstract: Two distinct forms of carbon, ultra nanocrystalline diamond (UNCD) and carbon nanotubes (CNTs), were synthesized in a single-step process via hot filament chemical vapor deposition for the first time. The synthesized structure displays unique hierarchical flower-like clusters of vertically aligned carbon nanotubes with diameters ranging from 30 to 50nm conformally coated with UNCD having a grain size in the range of 3–5nm. The seeding employed a mixture of diamond and nickel nano powders dispersed in a polymer melt, which promoted the self-assembly of sp2 and sp3 carbon into hierarchical structures. The UNCD decorated tubes show good field emission properties with low turn-on field, large field enhancement factor, and an excellent current stability over a period of over 400h. The ability to synthesize flower like structures of CNTs decorated with UNCD by a single-step process opens up new possibilities for the fabrication of robust nanoelectronic devices. [Copyright &y& Elsevier]

We report the first direct synthesis of graphene on SiO2/Si by hot-filament chemical vapor deposition. Graphene deposition was conducted at low pressures (35 Torr) with a mixture of methane/hydrogen and a substrate temperature of 970 °C followed by spontaneous cooling to room temperature. A thin copper-strip was deposited in the middle of the SiO2/Si substrate as catalytic material. Raman spectroscopy mapping and atomic force microscopy measurements indicate the growth of few-layers of graphene over the entire SiO2/Si substrate, far beyond the thin copper-strip, while X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy showed negligible amounts of copper next to the initially deposited strip. The scale of the graphene nanocrystal was estimated by Raman spectroscopy and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Abstract: Spontaneously detaching self-standing diamond films were successfully fabricated using saturated hydrocarbon polymers as seeding source by hot filament chemical vapor deposition (HFCVD) technique. X-ray diffraction confirmed the crystal structure of diamond. The microcrystalline morphology of the diamond films was analyzed by atomic force microscopy (AFM) and scanning electron microscopy. Raman spectra from the front and back sides of the films show the characteristic diamond band at 1332cm−1 and no carbide layer. EELS spectra also show the signature features of diamond. The use of hydrocarbon polymers as seeding source will improve the cost-effectiveness of the fabrication of diamond wafers by simplifying the fabrication process. [Copyright &y& Elsevier]

Abstract: The photodissociation of borazine, B3N3H6, following 193nm excitation was studied by Time of Flight Mass Spectrometry (TOFMS). For one-laser experiments, the TOF mass spectrum following borazine excitation consists of m/e peaks that can be attributed exclusively to borazine ion species, i.e., no photofragments are observed. In the two-laser experiments, the TOF mass spectrum can be assigned to peaks corresponding to B3N3H6 +, B3N3H5 +, and a small amount of BHNH+ ions. We conclude that a significant channel of borazine photodissociation at 193nm is the production of the B3N3H5 radical and H atom. The photodissociation process related to production of BHNH species is most likely due to a two-photon process. [Copyright &y& Elsevier]

Abstract: The SH and CS radicals produced during sulfur-assisted hot filament chemical vapor deposition (HFCVD) were studied by cavity ringdown spectroscopy (CRDS) by detecting the A(0)←X(0) transition near 323 and 259nm, for SH and CS, respectively. CRDS is a non-intrusive spectroscopic diagnostic tool suitable for measuring trace amounts of gas species in hostile, reactive environments such as that of chemical vapor deposition (CVD). The SH and CS radicals are thought to play important roles in the gas-phase and heterogeneous chemistry of sulfur-assisted HFCVD synthesis of nano-structured carbon-based materials. A detailed analysis of the rotationally resolved SH and CS spectra led to an estimate of their effective rotational temperature and number density. [Copyright &y& Elsevier]

The effects of heavy-ion radiation over the electron field emission (EFE) properties of sulfur-doped nanocomposite carbon (n-C:S) films were investigated. Two identical sets of n-C:S films were prepared in a hot-filament chemical vapor deposition system using CH4, H2 and H2S. Films with various sp3 C and sp2 C fractions were present within each set. Raman spectroscopy revealed the composite nature of the films. One set of films was submitted to a 20 krad dose of energetic Si and Fe ions (GeV/amu) at Brookhaven National Laboratory''s alternating gradient synchrotron. Films originally having poor EFE properties showed a dramatic emission enhancement as a result of irradiation, while those having good EFE properties before irradiation showed a small emission improvement upon irradiation. This improved EFE behavior is explained as due to the formation of conductive trigonal carbon nano-channels within the tetragonally-bonded carbon matrix. The diameter of these trigonal carbon nano-channels is small enough to produce large local field enhancement, and large enough to withstand the relatively large emitted current densities. A mechanism is proposed for the creation of this graphitic carbon nano-wire network within the tetragonal carbon matrix upon energetic irradiation. The results suggest that radiation-hardened cold cathodes can be fabricated using nanocomposite carbon materials that would remain stable in their EFE properties while exposed to ionizing radiation. [Copyright &y& Elsevier]

Stable field emission currents and low fluctuations are important feasibility requirements for the application of materials in field emission devices and displays. The current stability and current fluctuations of field emitted electrons from graphene films are investigated for the periods of 24 and 100 h. The graphene films showed different percentage of variation from the initial current density for different films ranging from 6% to 46% and the standard deviation in the range of 2–6 μA/cm2. The short- and long-term stability and fluctuations of the graphene films are reported and the causes for degradation of the emission current are discussed. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) were produced on nickel filled carbon nanofiber substrates. The carbon source was provided by irradiation of pyrolytic graphite. The mean outer diameter of the CNTs, which was identified as multiwalled carbon nanotubes, varies in the range of 5–15 nm. The crystallographic structures, chemical compositions, and bond structures of the carbon materials were investigated. The modified crystal structure was attributed to better lattice arrangement resulting from increased lattice vibration at high substrate temperature. The improved electron field emission behavior of the obtained sample at higher temperature could be caused by the increasing effective emission sites. [ABSTRACT FROM AUTHOR]

Metal nanoparticles have significant interaction cross-sections with electromagnetic waves due to their large surface area-to-volume ratio, which can be exploited in cancer radiotherapy to locally enhance the radiation dose deposition in tumors. We developed a new type of silver nanoparticle composite, PEGylated graphene quantum dot (GQD)-decorated Silver Nanoprisms (pGAgNPs), that show excellent in vitro intracellular uptake and radiosensitization in radiation-sensitive HCT116 and relatively radiation-resistant HT29 colorectal cancer cells. Furthermore, following biodistribution analysis of intravenously injected nanoparticles in nude mice bearing HCT116 tumors radiosensitization was evaluated. Treatment with nanoparticles and a single radiation dose of 10 Gy significantly reduces the growth of colorectal tumors and increases the survival time as compared to treatment with radiation only. Our findings suggest that these novel nanoparticles offer a promising paradigm for enhancing colorectal cancer radiation therapy efficacy. [ABSTRACT FROM AUTHOR]

Various types of 2D/2D prototype devices based on graphene (G) and boron nitride nanosheets (BNNS) were fabricated to study the charge tunneling phenomenon pertinent to vertical transistors for digital and high frequency electronics. Specifically, G/BNNS/metal, G/SiO2, and G/BNNS/SiO2 heterostructures were investigated under direct current (DC-bias) conditions at room temperature. Bilayer graphene and BNNS were grown separately and transferred subsequently onto the substrates to fabricate 2D device architectures. High-resolution transmission electron microscopy confirmed the bilayer graphene structure and few layer BNNS sheets having a hexagonal B3-N3 lattice. The current vs voltage I(V) data for the G/BNNS/Metal devices show Schottky barrier characteristics with very low forward voltage drop, Fowler-Nordheim behavior, and 10−4 Ω/sq. sheet resistance. This result is ascribed to the combination of fast electron transport within graphene grains and out-of-plane tunneling in BNNS that circumvents grain boundary resistance. A theoretical model based on electron tunneling is used to qualitatively describe the behavior of the 2D G/BNNS/metal devices. [ABSTRACT FROM AUTHOR]