The role of nitrogen in the deposition of polycrystalline diamond films

The role of nitrogen in the formation of polycrystalline diamond films prepared using a microwave plasma CVD system has been studied using micro-Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Although the nitrogen concentration in the films was too low to be detected by XPS, the Raman spectrum was found to be significantly affected by the nitrogen flow ratio. The intensity of the Raman peak at 1480 cm⁻¹ significantly decreases, whereas that of 1190 cm⁻¹ peak remains almost unchanged in comparison with the 1350 and 1550 cm⁻¹ peaks with increasing nitrogen flow ratio. In contrast, the preferentially (111)-orientated growth and the growth rate were little influenced by the nitrogen flow ratio. These results indicate that nitrogen plays a special role in the formation and structure of the polycrystalline diamond films studied in this report.     

Characterization of B-doped polycrystalline diamond films using thermally stimulated luminescence

The effect of different rates of boron incorporation during the growth in diamond on the thermoluminescence (TL) features of this material is investigated. TL studies performed between liquid nitrogen temperature (LNT) and 320 K show some phosphorescence and two other peaks at 226 and 266 K. For the first time, boron level in polycrystalline diamond films was identified by TL by an intense glow peak at 226 K and activation energy of about 0.35 eV. For this main peak, spectral analysis shows a prominent broad band luminescence peaking at 2.56 eV. At 77 K, another emission band was observed at 2.22 eV. This is in agreement with the fact that the recombination mechanisms involve two different recombination centers and, therefore, phosphorescence at 77 K and the main peak at 226 K are of different nature, i.e. the TL peak at 226 K is due to boron while phosphorescence is hence, probably due to a shallow donor level. The behavior of TL intensity relative to the main component at 226 K observed on all the films and linked to boron level decreases with increasing boron concentration.     

Influence of sulfur on the structural, surface properties and photocatalytic activity of sulfated TiO2

TiO₂ materials were prepared by sol–gel method and then impregnated with sulfuric acid and calcined using different temperatures and atmosphere (air and nitrogen). Systematic variation of these two experimental parameters makes possible to modulate the amount of surface sulfur from the impregnation procedure. The best photocatalyst for liquid phenol degradation was obtained after calcination at 700 °C in air, while gas toluene degradation optimum performance is obtained by calcination at 700 °C in nitrogen from 500 °C. Structural analysis of these materials by XRD, micro-Raman spectroscopy and FE-SEM shows that once calcined at 700 °C the material was a well-crystallized, high surface area anatase structure in all cases. The surface characterization by FTIR and XPS confirms the presence of a higher amount of sulfur species and acidic OH groups in samples partially calcined in nitrogen, and a low XPS O/Ti-atomic ratio with the O 1s peak shifted to higher binding energies (1.8 vs. 2 ± 0.1 and 530.4 eV vs. 529.8 eV, respectively, against the reference materials) for samples calcined at 700 °C, temperature at which most of sulfate species have been evolved. The paper presents an attempt to correlate the contribution of the observed structural defects within the anatase sub-surface layers and surface acidity to the different photoactivity behaviour exhibited for phenol liquid phase and toluene gas phase photodegradation.     

Tuning PL emission energy and bandgap with Ni dopant of MgO thin films

In this study, for the first time, the effect of Nickel (Ni) additive on Magnesium oxide (MgO) thin films produced by using successive ionic layer adsorption and reaction technique (SILAR) was investigated. Absorption, photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) measurements were executed to examine how the optical, structural and morphological properties of the samples were affected by the addition of Ni. In the absorption analysis, it was noted that the band gaps of the MgO samples decreased from 4 eV to 3.5 eV with the increase of Ni dopant concentrations. Also, the transmittance values of MgO nanostructures decreases with the increase of Ni contribution, and in the same way, the reflection measurements show that the reflection of MgO decreases with the increase of Ni doping. PL measurements revealed that the fabricated structures radiate around 410 nm and 730 nm. According to XRD measurements, besides the cubic structure of the samples, NiO formations were detected inside the MgO thin film samples due to the increase in Ni dopant. XPS measurements have proven the presence of Ni doping in MgO. SEM measurements showed that all samples exhibited nanowall structure. All these results demonstrate that Ni doping on MgO thin films can be achieved by using SILAR deposition technique.     

Surface,interface and electronic properties of F8:F8BT polymeric thin films used for organic light‐emitting diode applications

Ultrathin polymeric films consisting of poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (F8) blended with poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) grown onto PEDOT:PSS/ITO/PET were investigated by X‐ray photoelectron spectroscopy (XPS), depth‐profiling XPS, reflection electron energy loss spectroscopy (REELS) and angle‐dependent X‐ray absorption spectroscopy (XAS) to gain information on the films' electronic, order and interface properties. AFM studies provide valuable information on the films' nanotopographical properties and homogeneity. Spectroscopic ellipsometry and photoluminescence spectroscopy were used also to obtain information on the optoelectronic properties. Well‐ordered films were observed from the XAS analysis, measured at the sulfur K absorption edge. XPS measurements demonstrated that the surface composition of the polymer thin films prepared by a spin‐coating wet‐chemical deposition method matches the expected F8:F8BT blend stoichiometry. The interfacial properties were studied through an argon ion sputtering process coupled to the XPS acquisition, showing an enhancement of oxygen components at the interface. The films' inhomogeneity was verified by AFM images and analysis. We obtained a value of 3.1 eV as the electronic bandgap of the F8:F8BT film from REELS data, whereas analysis of the spectroscopic ellipsometry spectra revealed that the optical bandgap of F8:F8BT has a value of 2.4 eV. A strong green emission was obtained for the produced films, which is in agreement with the expected emission due to the 1:19 ratio of the F8 and F8BT blended polymers. © 2018 Society of Chemical Industry     

Spray pressure variation effect on the properties of CdS thin films for photodetector applications

Herein, we report the photosensing property of CdS thin films. CdS thin films were coated onto glass substrates via a spray pyrolysis method using different spray pressures. Prepared films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical and photoluminescence spectroscopy. XRD analysis demonstrated the growth of crystalline CdS films with crystallite sizes varying from 26 to 29 nm depending on the pressure. The SEM and EDAX analyses revealed nearly-stoichiometric CdS films with smooth surfaces and slight variation in grain morphology due to pressure changes. Optical measurements showed a direct bandgap varying from 2.37 eV to 2.42 eV due to pressure changes. A photodetector was also fabricated using the grown CdS films; the fabricated photodetector exhibited good performance depending on the spray pressure. A spray pressure of 1.5 GPa resulted in high photoresponsivity and external quantum efficiency.     

High dose N ion implantation effects on surface treated UNCD films

Ion implantation is commonly used to modify the surface or near-surface properties of materials. In this work, plasma treated ultrananocrystalline diamond (UNCD) films were implanted using 100 and 200 keV high dose (10¹⁶ ions/cm²) nitrogen ions and annealed. Detailed studies have been carried out to reveal the structural and chemical states of the surface treated UNCD films before implantation, as-implanted, and after annealing by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron field emission (EFE) measurements. The high dose N ion implantation induced the formation of amorphous phase, which are converted into graphitic phase after annealing, and improved the field emission properties of UNCD films. The improved field emission is attributed to the surface charge transfer doping mechanism.     

Nanostructured CNx (0 < x < 0.2) films grown by supersonic cluster beam deposition

Nanostructured CN_x thin films were prepared by supersonic cluster beam deposition (SCBD) and systematically characterized by transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The incorporation of nitrogen in the films (0 < x < 0.2) and the nanostructure were controlled by using different synthesis routes. Films containing bundles of well-ordered graphene multilayers, onions and nanotubes embedded in an amorphous matrix were grown alongside purely amorphous films by changing the deposition parameters. Graphitic nanostructures were synthesized without using metallic catalysts. The structural and electronic properties of the films have been studied by EELS. The role played by N in the carbon nanostructures has been deduced from XPS line-shape analysis.     

Role of defects in tailoring optical,electronic, and luminescent properties of Cu-doped ZnO films

We present a detailed characterization study on copper-doped ZnO films to correlate the films' electronic and optical properties with the existing native defects in the lattice. In addition, we describe the variation in the concentration of these defects with Cu dopant and temperature. The results of XRD confirmed the single-phase würtzite-structure of the synthesized films. The SEM images showed a homogeneous and dense grain morphology with a granular form and a signature for a hexagonal-like shape. The EDX, XPS, and UV–Vis spectra showed the proper doping of Cu ions into the lattice. The XPS analysis indicated mixed electronic states of both Cu²⁺ and Cu¹⁺ and showed a clear increase in the Cu²⁺ intensity relative to Cu¹⁺, with Cu dopant. The transmittance spectra exhibited an average value above 80% in all doped films in the visible and infrared regions. The overall results indicated a clear link between the films’ optical and electronic responses and the level of the intrinsic defects in the lattice. By increasing the Cu dopant, we find a slight reduction in the energy bandgap (E_g). This is correlated with a clear reduction in the blue emission luminescence band associated with the V_Zn and in the yellow emission band associated with the O_i. On the other hand, we observed a clear enhancement in the green emission band originating from the V_O, and in the emission band related to possible transitions from Zn_i levels to O_i levels. The slight reduction in the E_g signals a weak sp-d hybridization between the ZnO conduction band electrons and the Cu²⁺ ions, which is mediated by the intrinsic defects. With reducing the temperature, the photoluminescence temperature profiles indicated a slight increase in the E_g values and a negligible effect on the distribution of the native defects.     

Fabrication and microstructural characterization of the diamond@amorphous carbon nanocomposite core/shell structure via in-situ polymerization

A novel diamond@carbon core/shell structure, constituting diamond as a hard core and carbon as a soft shell, was synthesized from resole resin and nanodiamond as the starting materials via in-situ polymerization and subsequently high-temperature carbonization. The diamond@carbon nanocomposite was characterized using field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and Fourier transform infrared spectroscopy (FT-IR). The results indicated that the shell material are comprised of amorphous carbon. The thickness of carbon shell was controlled from 502.5 nm to 27 nm by adjusting the concentration of the nanodiamond. As confirmed by TEM, FT-IR and XPS, the diamond@carbon nanocomposite revealed a stable structure, due to the formation of the chemical bonding between diamond and carbon shell after calcination process. Overall, the diamond@carbon nanocomposite abrasives could lead to a reducted surface roughness and damage of SiC wafer comparing with the nanodiamond abrasives, due to the spring-like effect coming from the elastic component of the amorphous carbon shell. Moreover, the as-prepared nanoparticles exhibited better dispersion stability than the pure diamond in the pH range from 8 to 11.     

Cathodoluminescence of fluorine doped amorphous carbon nanoparticles deposited by a filtered cathodic arc plasma system

The fluorine doped amorphous carbon nanoparticles (a-C:F NPs) films with sizes 50-100 nm were deposited on polyethylene terephthalate in an atmosphere of CF₄ by a 90°-bend magnetic filtered cathodic arc plasma system. The surface morphology of a-C:F NPs films was observed by field emission scanning electron microscope and atomic force microscope. The microstructure and chemical bonding nature of the a-C:F NPs films were investigated by Raman, X-ray diffraction and X-ray photoelectron spectroscopy. This work presents cathodoluminescence (CL) spectra of a-C:F NPs films obtained at 1.9-2.4 eV and verifies luminescence from a-C:F NPs films in the visible region. The incorporation of fluorine into the carbon network results in orange emission (∼2.03 eV) due to the transitions between fluorine-related electron levels and σ* states, and the red emission (∼1.97 eV) results from the recombination of carriers in the valence π and conduction π* states. The peak at ∼2.10 eV may result from the defects of the structures in a-C:F NPs films.     

Nanodiamond planar lateral field emission diode

We report the fabrication and field emission characteristics of the nanodiamond planar lateral field emission diode. Nanodiamond films with grain size as small as 5–10 nm have been realized through the process of CH₄/H₂/N₂ microwave plasma enhanced chemical vapor deposition (MPECVD) by employing an effective growth rate reduction technique. Well-controlled processes have been developed; including reactive ion etch (RIE) to pattern the nanodiamond films to fabricate lateral field emission devices with planar lateral fingers. An anode–cathode spacing of 2 μm between the nanodiamond anode and cathode has been achieved. A nanodiamond lateral diode equipped with 6 fingers and an inter-electrode separation of 3 μm exhibits a turn-on voltage of 5.9 V (threshold electric field of 1.9 V/μm), one of the lowest reported for lateral field emission devices, and a high emission current of 1.1 mA ( 183 μA current per finger) at an anode voltage of 100 V ( 30 V/μm). The emission current is found to be stable with 4% fluctuation at 1 mA over 10 h. The nanodiamond lateral device is very promising for applications in vacuum nanoelectronics, sensors, and nanoelectromechanical systems.     

Influence of Co concentration on the structural,optical, morphological and photo-diode properties of cerium oxide thin films

Highly uniform and well-dispersed ring shaped particles of CDC (Cobalt doped cerium oxide) films are successfully deposited by Nebulizer Spray Pyrolysis (NSP) technique. The structural, morphological, optical and photo-diode properties of the films are investigated. Cubic fluorite crystallites are detected by X-ray diffraction pattern with preferred orientation along (111) direction. Co concentrations distress the crystallinity and structural parameters. The transmittance decreases with increasing Co concentration due to the presence of covalent bonds between cerium and oxygen. PL spectra revealed that three consistent sharp and broad peaks observed at 369 (3.31 eV), 394 (3.14 eV) and 425 nm (2.91 eV) correspond to near-band-edge emission (NBE) in UV region, deep level emission (DLE) in violet and blue of the visible region respectively. The deep level emissions result from the recombination of electrons with holes trapped in singly ionized oxygen vacancies (Vo+). Large agglomerated ring, button and spherical crystallites are obtained with the typical size in the range 83–207 nm. XPS analysis exhibits the presence of Ce, Co, O, C and Na in the films that indicates the non-stoichiometric behavior. I-V characteristics show the rectifying nature with a typical forward to reverse current ratio of ~7 in the range −4 to +4 V. The turn-on voltage of the hetero-junction is found to be ~1.7 V. The transient photocurrent behavior indicates that the device has a good stability and quick response to suggests that the prepared heterojunction device can be used as a white light photodetector and UV detector applications.     

Synthesis and electron field emission properties of nanodiamond films

Effects of CH₄/H₂ ratio and bias voltage of the microwave plasma-enhanced chemical vapor deposition (MPE-CVD) process on the nucleation behavior and associated characteristics of nanodiamonds were investigated. While the scanning electron microscopy (SEM) microstructure and Raman crystal structure of the films insignificantly vary with CH₄/H₂ ratio and bias voltage, electron field emission properties of the materials markedly change with these deposition parameters. The predominating factor modifying the electron field emission properties of the nanodiamond films is presumed to be the increase in the proportion of sp²-bonded grain boundaries when the grain size of the nanodiamond films decreases. Between these two major factors, the bias voltage shows more prominent effects on modifying the granular structure of the nanodiamonds than the CH₄/H₂ ratio does. The best electron field emission properties attainable are J_e=500 μA/cm² at 20 V/μm and E₀=8.5 V/μm.     

Field emission from nanodiamond grown with ‘ridge’ type geometrically enhanced features

Cold cathodes for vacuum field emission have many interesting applications including display devices. Chemical vapor deposited (CVD) diamond has long been considered such a candidate. A nanodiamond film with ridge features was grown on a highly doped (resistivity = 0.0035 Ω-cm) n-type silicon substrate by plasma enhanced CVD process using a H2/CH4/N2 gas mixture. The overall planar nanodiamond film was characterized for vacuum field emission in diode configuration. A low turn on field of ~ 2.3 V/µm at 1 µA was observed. The cathode was able to produce 150 µA at a field of 6.6 V/µm. This field emission behavior can be attributed to a combination of high sp2 content, higher electrical conductivity by nitrogen incorporation in the nanodiamond film and a high geometrical field enhancement factor because of the sharp ‘ridge’ like features on the surface.     

Improved physical properties of Al-doped ZnO thin films deposited by unbalanced RF magnetron sputtering

Room temperature Al-doped ZnO (AZO) thin films with improved crystalline and optical properties were grown on normal glass substrates using unbalanced RF magnetron sputtering technique. To modify the plasma density towards the substrate and enhance the crystalline nature, an additional magnetic field ranging from 0 to 6.0 mT has been applied to the AZO target by proper tuning of solenoid coil current from 0 to 0.2 A respectively, which plays a significant role for controlling the physical properties of AZO films. The results from XRD studies indicate that all AZO films were composed of hexagonal wurtzite structure with better crystal quality through the applied magnetic field, ZnO (002) plane as a preferred growth. Furthermore, XPS studies suggested that symmetric chemical shifts in the binding energies for the Zn 2p and O1s levels with applied magnetic field. SEM analysis revealed the formation of a smooth, homogeneous and dense morphological surface with applied magnetic field. From AFM analysis, it was observed that the applied magnetic field strongly influenced the grain size and the films showed decreasing tendency in electrical resistivity. Films exhibited superior optical transmittance more than 94% in the visible region essentially due to the formation of better crystalline nature. The results indicate that improved band gap from 3.10 to 3.15 eV with additional magnetic field varied from 0 to 6.0 mT respectively.     

Early stage of diamond growth at low temperature

We investigate the first stages of nanocrystalline diamond (NCD) thin film growth at low substrate temperature. NCD films were grown on silicon substrates by microwave plasma enhanced chemical vapor deposition (CVD) for 0–300 min at a temperature of 410 °C. Si substrates were ultrasonically seeded in suspension of detonation nanocrystalline diamond powder. The seeding density approached values up to 1 ⁎ 10¹² cm^− 2, which allows growth of ultra-thin fully closed layers. Stagnation of the AFM roughness indicates that the low temperature NCD growth is a) delayed due to the surface contamination of the used nanodiamond powder and b) possibly dominated by the growth in the lateral direction. XPS measurements showed that the measured surface exhibits changes from a multi-phase composite (seeding layer) to single-phase one (NCD layer).     

Strong Near‐Infrared Photoluminescence Emission of (003)‐Oriented MgTiO3 Thin Films

In this study, ilmenite‐MgTiO₃ films were sputtered on p‐type Si(111) substrates and the extrinsic effects, such as grain size, crystallinity, and orientation of photoluminescence (PL) properties of the films are discussed. To reduce the effect of oxygen vacancies (act as shallow defects) on PL emissions in the films, oxygen (O₂) was introduced as the sputtering gas and the excitation light source (λ = 532 nm) which has a corresponding energy (hν = 2.33 eV) below the shallow defect states was used. In this study, intense near‐infrared (NIR) PL emission centered at 810.1 nm at room temperature can be observed when the MgTiO₃ thin films exhibit the preferred (003)‐orientation and accompanied by the presence of hexagon‐shaped grains. In this study, the experiment results reveal that the NIR emission intensity of MgTiO₃ films highly depend on crystal orientation and/or grain morphology.     

Experimental comparison of N(1s) X-ray photoelectron spectroscopy binding energies of hard and elastic amorphous carbon nitride films with reference organic compounds

In this work, hard and elastic amorphous carbon nitride (a-CN_x) films were deposited by DC magnetron sputtering on heated Si(001) substrates at 400 °C. Nanoindentation results confirmed that the films were highly compliant and had high elastic recovery. X-ray photoelectron spectroscopy (XPS) was used to investigate nitrogen bonding by directly comparing the N(1s) spectra of a-CN_x with the N(1s) peak positions of a variety of organic compounds that were characterized in the same XPS system. The N(1s) XPS spectra of hard and elastic a-CN_x is resolved into two dominant intensity contributions at 398.5 and 400.6 eV. We show that the N(1s) spectra of a-CN_x do not conclusively support a film-structure model with nitrogens bonded to sp³ carbons. We offer an alternate interpretation based on the presented data and previous XPS, nuclear magnetic resonance (NMR), and computational work. Together, the data suggest that hard and elastic a-CN_x consists of an sp² carbon network and that single-atom vacancy defects, as found in a graphite layer, may be present in the material. This implies that the low binding energy N(1s) component at 398.5 eV may be due to pyridine-like nitrogen bonded at the perimeter of a vacancy defect.     

Direct Growth and Photoluminescence of SiO<Subscript>x</Subscript> Nanowires and Aligned Nanocakes by Simple Carbothermal Evaporation

The growth of SiO_x nanowires and nanocakes on an Au-coated n-type-Silicon (100) substrate was achieved via carbothermal evaporation. The effects of the Au layer thickness and the rapid heating rate on the morphology of obtained SiO_x nanowires were investigated. A broad emission band from 290 to 600 nm was observed in the photoluminescence (PL) spectrum of these nanowires. There are four PL peaks: one blue emission peak 485 nm (2.56 eV) two green bands centered at 502 nm (2.47 eV) and 524 nm (2.37 eV) for nanocakes and one ultraviolet emission peak at 350 nm (3.54 eV) and a hemisphere curve over the bluish green area taken for SiO_x nanowires. These emissions may be related to the various oxygen defects and twofold coordinated silicon lone pair centers.