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We report a novel, ambient pressure, continuous gas-phase, synthesis of Si-QDs by direct pyrolysis of cyclohexasilane (CHS, Si6H12), a liquid hydrosilane. We also report that using a low activation energy precursor such as Si6H12 enabled effective gas-phase reduction of the hydrosilane leading to better nucleation of Si nanoparticles than other hydrosilanes. By suitably designing the reactor length and its temperature profile, the structure of the Si-QDs are rendered amorphous or crystalline. The as-synthesized Si-QDs were thermally hydrosilylated with 1-dodecene and their properties examined. High resolution transmission electron microscopic (HRTEM) analysis revealed that the nano-crystalline Si-QDs (Si-NCs) have an average size of 2.0 nm. The amorphous Si-QDs (a-Si-QDs) and the Si-NCs samples exhibited UV-Vis absorptions below 300 and 375 nm, respectively. The a-Si-QDs and Si-NCs excited at 300 nm showed PL emissions at ∼370 nm and 374 nm, respectively, while the latter showed additional characteristic emissions at 403, 425 and 457 nm. The quantum yields were determined to be 9 and 13%, respectively, with PL relaxation life times of 6.5 and 13 ns, respectively.

Silicon (Si) thin films were produced using an aerosol assisted atmospheric pressure chemical vapor deposition technique with liquid hydrosilane precursors cyclopentasilane (CPS, Si5H10) and cyclohexasilane (CHS, Si6H12). Thin films were deposited at temperatures between 300 and 500 °C, with maximum observed deposition rates of 55 and 47 nm/s for CPS and CHS, respectively, at 500 °C. Atomic force microscopic analyses of the films depict smooth surfaces with roughness of 4–8 nm. Raman spectroscopic analysis indicates that the Si films deposited at 300 °C and 350 °C consist of a hydrogenated amorphous Si (a-Si:H) phase while the films deposited at 400, 450, and 500 °C are comprised predominantly of a hydrogenated nanocrystalline Si (nc-Si:H) phase. The wide optical bandgaps of 2–2.28 eV for films deposited at 350–400 °C and 1.7–1.8 eV for those deposited at 450–500 °C support the Raman data and depict a transition from a-Si:H to nc-Si:H. Films deposited at 450 oC possess the highest photosensitivity of 102–103 under AM 1.5G illumination. Based on the growth model developed for other silanes, we suggest a mechanism that governs the film growth using CPS and CHS.

We present a combined theoretical and experimental study of the morphology and conductivity of thin silicon films crystallized with a 355-nm-pulsed laser from amorphous silicon on a variety of substrates. Amorphous silicon (a-Si) films were grown through plasma-enhanced chemical vapor deposition and crystallized using a frequency-tripled Nd:YVO4 laser. The films were characterized using optical, scanning electron, and atomic force microscopy, Raman spectroscopy and X-ray diffraction. To interpret the measurements, the influence of the thermal properties of the substrate material on the crystallization process was simulated by numerically solving the heat diffusion equation in response to individual laser pulses. In contrast to the simulations, our measurements show a much stronger dependence of the electronic and morphological characteristics of the films on the nature of the underlying material, which we interpret through variations in the wettability of liquid silicon (L-Si) on the substrate.

Graphene-based plasmonic devices have recently drawn great attention. However, practical limitations in fabrication and device architectures prevent studies from being carried out on the intrinsic properties of graphene and their change by plasmonic structures. The influence of a quasi-infinite object (i.e., the substrate) on graphene, being a single sheet of carbon atoms, and the plasmonic device is overwhelming. To address this and put the intrinsic properties of the graphene-plasmonic nanostructures in focus, we fabricate large-area, freestanding, single-layer graphene-gold (LFG-Au) sandwich structures and Au nanoparticle decorated graphene (formed via thermal treatment) hybrid plasmonic nanostructures. We observed two distinct plasmonic enhancement routes of graphene unique to each structure via surface-enhanced Raman spectroscopy. The localized electronic structure variation in the LFG due to graphene-Au interaction at the nanoscale is mapped using scanning transmission X-ray microscopy. The measurements show an optical density of ∼0.007, which is the smallest experimentally determined for single-layer graphene thus far. Our results on freestanding graphene-Au plasmonic structures provide great insight for the rational design and future fabrication of graphene plasmonic hybrid nanostructures.

Zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) thin films were deposited via atmospheric pressure plasma enhanced chemical vapor deposition. A second-generation precursor, bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)( N , N ′-diethylethylenediamine) zinc, exhibited significant vapor pressure and good stability at one atmosphere where a vaporization temperature of 110 °C gave flux ~ 7 μmol/min. Auger electron spectroscopy confirmed that addition of H 2 O to the carrier gas stream mitigated F contamination giving nearly 1:1 metal:oxide stoichiometries for both ZnO and AZO with little precursor-derived C contamination. ZnO and AZO thin film resistivities ranged from 14 to 28 Ω·cm for the former and 1.1 to 2.7 Ω·cm for the latter.

Amorphous hydrogenated silicon-based multilayer coatings were deposited on 301 stainless steel (SS301) and Ti–6Al–4V alloy substrates using plasma enhanced chemical vapor deposition (PECVD), in order to integrate the advantages of the respective layers. Corrosion and tribo-corrosion behaviors of the complete coating/substrate system on different substrates were investigated. The SiN/SiC double-layer coating substantially improved the corrosion resistance of the metals: For SS301, the corrosion current, i corr , was reduced by more than three orders of magnitude, and the breakdown voltage was increased from 0.34 to 1.37 V. For Ti–6Al–4V, the i corr was decreased by a factor of ~ 50. Particularly, the Ti–6Al–4V/SiN/SiC multilayer system exhibited excellent anti-corrosion properties according to potentiodynamic polarization measurements, due to the superior corrosion resistance of both the Ti–6Al–4V substrate and the silicon-based coatings. Further enhancement of the tribo-corrosion resistance has been achieved by applying an amorphous hydrogenated carbon (a-C) coating as a top layer in the three-layer system. In the tribo-corrosion test in 1 wt.% NaCl solution, the SiN/SiC/a-C coating reduced the wear rate and the friction coefficient by a factor of ~ 175 and ~ 4, respectively, compared with the bare Ti–6Al–4V. The Ti–6Al–4V/SiN/SiC/a-C multilayer system integrates in synergy the advantages of the respective layers, and its versatility makes it a particularly attractive candidate for applications in different harsh working environments.

Amorphous hydrogenated silicon carbonitride (a-SiCN:H) thin films are synthesized by atmospheric pressure plasma enhanced chemical vapor (AP-PECVD) deposition using the Surfx Atomflow{trademark} 250D APPJ source with triethylsilane (HSiEt{sub 3}, TES) and nitrogen as the precursor and the reactive gases, respectively. The effect of the substrate temperature (T{sub s}) on the growth characteristics and the properties of a-SiCN:H films was evaluated. The properties of the films were investigated via scanning electron microscopy (SEM), atomic force microscopy (AFM) for surface morphological analyses, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) for chemical and compositional analyses; spectroscopic ellipsometry for optical properties and thickness determination and nanoindentation to determine the mechanical properties of the a-SiCN:H films. Films deposited at low T{sub s} depict organic like features, while the films deposited at high T{sub s} depict ceramic like features. FTIR and XPS studies reveal that an increases in T{sub s} helps in the elimination of organic moieties and incorporation of nitrogen in the film. Films deposited at T{sub s} of 425 C have an index of refraction (n) of 1.84 and hardness (H) of 14.8 GPa. A decrease in the deposition rate between T{sub s} of 25 and 250 C and increase inmore » deposition rate between T{sub s} of 250 and 425 C indicate that the growth of a-SiCN:H films at lower T{sub s} are surface reaction controlled, while at high temperatures film growth is mass-transport controlled. Based on the experimental results, a potential route for film growth is proposed.« less

Applications of hard protective nanocomposite coatings are frequently limited by insufficient adhesion related to high stress. In the present work, we study the effect of an intermediate Cr layer on top of the stainless steel 410 (SS410) substrate on the performance of the nanocomposite (nc) TiN-based coatings prepared by plasma enhanced chemical vapor deposition. The Cr layer was found to enhance the corrosion resistance of the SS410 substrate by a factor of 280 in terms of corrosion current, and to increase adhesion of the TiN coating by a factor of 4. We show that for the nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings, the substantial improvement of the corrosion resistance can be attributed to the combination of the inertness of the Cr layer, and of the densely packed homogeneous nc structure of the nc coatings containing Si and/or C in comparison to columnar crystalline TiN coatings.

Amorphous hydrogenated silicon-carbide (a-SiC:H) coatings appear very attractive due to their superior optical and mechanical properties and chemical inertness. In the present work a-SiC:H coatings were prepared by PECVD on stainless steel 301 (SS301) and Ti–6Al–4V (TiAlV) substrates at a temperature of 300 °C, using different SiH4/CH4 precursor ratios. We systematically studied such mechanical properties as hardness, reduced Young's modulus and elastic recovery using depth-sensing indentation, their tribological characteristics such as coefficient of friction and wear coefficient using the pin-on-disc method, as well as their corrosion and tribo-corrosion behaviors. a-SiC:H films (∼ 3 μm thick) prepared on SS301 and TiAlV at optimal deposition conditions exhibited a hardness of 23.5 GPa, reduced Young's modulus of 160 GPa, and elastic rebound of 73%. They showed a friction coefficient of ∼ 0.35, and a wear rate of 10 × 10−6 mm3/Nm. These values are low compared to ∼ 0.85 and ∼ 0.5, 240 × 10−6 mm3/Nm and 700 × 10−6 mm3/Nm for SS301 and TiAlV, respectively. The films exhibited a very high corrosion and tribo-corrosion resistance on both metallic substrates. The coating behavior is correlated with the microstructure and composition, determined by complementary characterization techniques including ERD, FTIR and Raman analyses.

The use of hard and superhard nanocomposite (nc) coatings with tailored functional properties is limited when applied to low alloy steel substrates due to their low load carrying capacity. Specifically in this work, in order to enhance the performance of martensitic SS410 substrates, we applied a duplex process which consisted of surface nitriding by radio-frequency plasma followed by the deposition of single layer (TiN, nc-TiN/a-SiNx or nc-TiCN/a-SiCN) or multilayer (TiN/nc-TiN/a-SiNx, TiN/nc-TiCN/a-SiCN) coating systems prepared by plasma enhanced chemical vapor deposition (PECVD). We show that plasma nitriding gives rise to a diffusion layer at the surface due to diffusion of nitrogen and formation of the α-Fe and e-Fe2N phases, respectively, leading to a surface hardness, H, of 11.7 GPa, compared to H = 5 GPa for the untreated steel. Among the TiN, nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings, the latter one possesses the highest H value of 42 GPa and the highest H3/Er2 ratio of 0.83 GPa. Particularly, the TiN/nc-TiCN/a-SiCN multilayer coating system exhibits superior tribological properties compared to single layer TiN and multilayer TiN/nc-TiN/a-SiNx coatings: this includes excellent adhesion, low friction (Cf = 0.17) and low wear rate (K = 1.6 × 10− 7 mm3/N m). The latter one represents an improvement by a factor of 600 compared to the bare SS410 substrate. The significance of the relationship between the H/E and H3/Er2 ratios and the tribological performance of the nano-composite coatings is discussed.

Influence of the deposition parameters and the substrate bias voltage on the optical, compositional and the surface properties of DC magnetron-sputtered silicon nitride thin films are studied. Silicon nitride thin films are deposited on silicon (100) and quartz substrates at different partial pressures of nitrogen and discharge currents. The variation in the refractive index and the optical band gap of these films is studied. Compositional variation has been studied using Rutherford backscattering spectroscopy (RBS). Silicon nitride thin films deposited at $3 \times 10^-^2$ Pa partial pressure of nitrogen with $2.5 mA/cm^2$ cathode current density showed an optical band gap of 4.3 eV and refractive index of 2.04 (at 650 nm). Nitrogen to silicon ratio in the film is 1.31, and the roughness of the films is 2.3 nm. Substrate bias during deposition helped in changing the optical properties of the films. Substrate bias of -60V resulted in films having near stoichiometry with N/Si ratio 1.32, and the optical band gap, refractive index, and the roughness are 4.8 eV, 1.92 and 0.78 nm, respectively.

Tungsten nitride thin films were deposited using unbalanced magnetron sputtering system. The effect of the ratio of nitrogen partial pressure to the total pressure during deposition and the substrate bias on the tungsten nitride formation has been studied. The glow discharge characteristics of the process have been studied in order to determine the deposition parameters. It is observed that nitrogen partial pressure ratio 0.4 and cathode current of 200mA favors the formation of the $W_2N$ films. The variation in the electrical resistivity of the films has been studied as a function of nitrogen partial pressure and substrates bias. A minimum resistivity of $406\mu\Omega$cm is observed for tungsten nitride films prepared at 70V bias. X-ray diffraction analysis of the films indicate the formation of $\beta-W_2N$ (1 0 0) phase at the partial pressure ratio of 0.4. The effects of the bias on the structural properties were also studied at this condition. The internal stress and the particle size of the deposited films were calculated and it was found that there is no appreciable change with the applied bias voltage.

The effect of substrate orientation and ion bombardment during the growth on the structure and properties of TiN films deposited by reactive unbalanced magnetron sputtering has been reported. Films deposited at a nitrogen partial pressure of 5×10–5 mbar and a current density of 2.50 mA cm–2 were golden yellow in color, characteristic of stoichiometric TiN. The effect of Si(100) and Si(111) substrates on the TiN film along with the substrate bias has been investigated. With an increase in the substrate bias on Si(111) substrate, TiN(111) is the most preferred orientation. On a Si(100) substrate with an increase in the substrate bias, TiN(220) orientation has been observed. The influence of the substrate on the growth of TiN films has been explained in terms of surface energy. The variation of grain size, resistivity, and the internal stress of TiN films as the function of substrate bias have also been investigated.

We report the deposition of silicon thin films at high rates using atmospheric pressure chemical vapor deposition (AP-CVD) with cyclohexasilane (CHS), a liquid-hydrosilane. A precursor solution of CHS in cyclooctane was aerosolized and subsequently vaporized prior to contacting with the substrate. Using CHS, Si thin films were obtained at temperatures as low as 300 °C. A deposition rate of ∼50 nm/s was observed at 500 °C; while good-quality Si films were realized at 400 °C. Structural analysis of the films indicates a combination of amorphous and nano-crystalline Si phases, withe 2–3 orders of photoconductivity.

Amorphous hydrogenated silicon carbide (a-SiCx:H) coatings were deposited on stainless steel 301 (SS301) using plasma enhanced chemical vapor deposition with the methane gas flow ranging from 30 to 90 sccm. XRD spectra confirmed the amorphous structure of these coatings. The as-deposited coatings all exhibited homogenous dense feature, and no porosities were observed in SEM and AFM analysis. The a-SiCx:H coatings remarkably increased the corrosion resistance of the SS301 substrate. With the increase of the C concentration, the a-SiCx:H coatings exhibited significantly enhanced electrochemical behavior. The a-SiCx:H coating with the highest carbon concentration acted as an excellent barrier to charge transfer, with a corrosion current of3.5×10-12 A/cm2and a breakdown voltage of 1.36 V, compared to2.5×10-8 A/cm2and 0.34 V for the SS301 substrate.

Atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) using Surfx Atomflow(TM) 250D APPJ was utilized to synthesize amorphous silicon carbonitride coatings using tetramethyldisilizane (TMDZ) and hexamethyldisilizane (HMDZ) as the single source precursors. The effect of precursor chemistry and substrate temperature (T(s)) on the properties of a-SiCN:H films were evaluated, while nitrogen was used as the reactive gas. Surface morphology of the films was evaluated using atomic force microscopy (AFM); chemical properties were determined using Fourier transform infrared spectroscopy (FTIR); thickness and optical properties were determined using spectroscopic ellipsometry and mechanical properties were determined using nanoindentation. In general, films deposited at substrate temperature (T(s))200 °C contained organic moieties, while the films deposited at T(s)200 °C depicted strong Si-N and Si-CN absorption. Refractive indices (n) of the thin films showed values between 1.5 and 2.0, depending on the deposition parameters. Mechanical properties of the films determined using nanoindentation revealed that these films have hardness between 0.5 GPa and 15 GPa, depending on the T(s) value. AFM evaluation of the films showed high roughness (R(a)) values of 2-3 nm for the films grown at low T(s) (250 °C) while the films grown at T(s) ≥ 300 °C exhibited atomically smooth surface with R(a) of ~0.5 nm. Based on the gas-phase (plasma) chemistry, precursor chemistry and the other experimental observations, a possible growth model that prevails in the AP-PECVD of a-SiCN:H thin films is proposed.

We report a solution process for the synthesis of crystalline silicon from the liquid silane precursor cyclohexasilane (Si(6)H(12)). Polysilane films were crystallized through thermal and laser annealing, with plasma hydrogenation at atmospheric pressure generating further structural changes in the films. The evolution from amorphous to microcrystalline is characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and impedance spectroscopy. A four-decade enhancement in the electrical conductivity is attributed to a disorder-order transition in a bonded Si network. Our results demonstrate a potentially attractive approach that employs a solution process coupled with ambient postprocessing to produce crystalline silicon thin films.

Indium tin oxide (ITO) films were deposited via atmospheric-pressure plasma-enhanced chemical vapor deposition (APPD) using indium acetylacetonate, indium trifluoroacetylacetonate and tin trifluoroacetylacetonate as metal-organic precursors. A film growth temperature of 300 °C gave highly-transparent films with modest conductivity. Post-deposition thermal treatments gave ITO films with resistivities one to two orders of magnitude higher than those available commercially. Compositional analysis revealed a high carbon content and annealing the films in oxygen at 400 C did not affect the C concentration. A decrease in the fluorine content in the films was observed after annealing with and the onset of crystallization was noted via XRD.

Fluorination of polymer surfaces has technological applications in various fields such as microelectronics, biomaterials, textile, packing, etc. In this study PMMA surfaces were fluorinated using DC glow discharge plasma. Tetrafluoroethane was used as the fluorinating agent. On the fluorinated PMMA surface, static water contact angle,surface energy, optical transmittance (UV–vis), XPS and AFM analyses were carried out. After the fluorination PMMA surface becomes hydrophobic with water contact angle of $107^o$ without losing optical transparency. Surface energy of fluorine plasma-treated PMMA decreased from 35 $mJ/cm^2$ to 21.2 $mJ/cm^2$. RMS roughness of the fluorinated surface was 4.01 nm and XPS studies revealed the formation of C–$CF_x$ and $CF_3$ groups on the PMMA surface.

Polystyrene (PS) and polyethylene (PE) samples were treated with argon and oxygen plasmas. Microwave electron cyclotron resonance (ECR) was used to generate the argon and oxygen plasmas and these plasmas were used to modify the surface of the polymers. The samples were processed at different microwave powers and treatment time and the surface modification of the polymer was evaluated by measuring the water contact angle of the samples before and after the modification.Decrease in the contact angle was observed with the increase in the microwave power for both polystyrene and polyethylene. Plasma parameters were assessed using Langmuir probe measurements. Fourier transform infrared spectroscopy showed the evidence for the induction of oxygen-based functional groups in both polyethylene and polystyrenewhen treated with the oxygen plasma. Argon treatment of the polymers showed improvement in the wettability which is attributed to the process called as CASING, on the other hand the oxygen plasma treatment of the polymers showed surface functionalization. Correlation between the plasma parameters and the surface modification of the polymer is also discussed.

Polystyrene cell-culture substrates were treated with argon glow discharge to make their surfaces hydrophilic. The process was novel in that it used a microwave electron cyclotron resonance (ECR) source for polymer surface modification. The substrates were processed at different microwave powers and time periods, and the surface modification was assessed with by measurement of the water contact angle. A decrease in contact angle was observed with increasing microwave power and processing time. Beyond a certain limit of power and duration of exposure, however, surface deterioration occurred. The optimum conditions for making the surfaces hydrophilic without deterioration of the samples were identified. The plasma parameters were assessed by Langmuir probe measurement. Fourier transform infrared spectroscopy with attenuated total reflectance showed evidence for the induction of hydrophilicity on the surface. The surface micromorphology was examined with scanning electron microscopy. The results prove that the ECR glow discharge was an efficient method for enhancing the wettability of the polymer surfaces.

We present a detailed study of the laser crystallization of amorphous silicon thin films as a function of laser fluence and film thickness. Silicon films grown through plasma-enhanced chemical vapor deposition were subjected to a Q-switched, diode-pumped solid-state laser operating at 355 nm. The crystallinity, morphology, and optical and electronic properties of the films are characterized through transmission and reflectance spectroscopy, resistivity measurements, Raman spectroscopy, X-ray diffraction, atomic force microscopy, and optical and scanning-electron microscopy. Our results reveal a unique surface morphology that strongly couples to the electronic characteristics of the films, with a minimum laser fluence at which the film properties are optimized. A simple scaling model is used to relate film morphology to conductivity in the laser-processed films.