Fabrication of polycrystalline silicon thin films on glass substrates using fiber laser crystallization

Laser crystallization of amorphous silicon (a-Si), using a fiber laser of λ = 1064 nm wavelength, was investigated. a-Si films with 50 nm thickness deposited on glass were prepared by a plasma enhanced chemical vapor deposition. The infrared fundamental wave (λ = 1064 nm) is not absorbed by amorphous silicon (a-Si) films. Thus, different types of capping layers (a-CeO_x, a-SiN_x, and a-SiO_x) with a desired refractive index, n and thickness, d were deposited on the a-Si surface. Crystallization was a function of laser energy density, and was performed using a fiber laser. The structural properties of the crystallized films were measured via Raman spectra, a scanning electron microscope (SEM), and an atomic force microscope (AFM). The relationship between film transmittance and crystallinity was discussed. As the laser energy density increased from 10-40 W, crystallinity increased from 0-90%. However, the higher laser density adversely affected surface roughness and uniformity of the grain size. We found that favorable crystallization and uniformity could be accomplished at the lower energy density of 30 W with a-SiO_x as the capping layer.     

Synthesis of carbon coatings employing a plasma torch from an argon-acetylene gas mixture at reduced pressure

Amorphous hydrogenated carbon films (a-C:H) were formed on Si (1 1 1) wafers from an argon-acetylene gas mixture at a reduced pressure of 1000 Pa using a direct current (DC) plasma torch discharge. The Ar/C₂H₂ gas volume ratio varied from 1:1 to 8:1, the distance between plasma torch exit and the samples 0.04-0.095 m. The DC plasma torch technique allows the production of thick (∼90 μm) coatings at 0.3 μm/s growth rates. Raman spectra shape, D and G peak positions and the intensity ratio (I_D/I_G) show an increase of sp³ bond fraction with decreasing acetylene flow in argon plasma. Reflectance of the coatings deposited at Ar/C₂H₂=8:1 is high (∼97%) and slightly increases with increasing distance between samples and plasma torch exit.     

Effects of plasma treatments on structural and electrical properties of methyl-doped silicon oxide low dielectric constant film

In this article, a methyl-doped silicon oxide low k film for use in inter-level dielectric application has been characterized. The structural and electrical properties of films prepared by chemical vapor deposition before and after different etching and photo-resist stripping (PRS) plasma treatments were studied. Structural properties of the low k film with various extents of forming gas and O₂ plasma treatments were reflected by the contents of Si-CH₃ and Si-H bonds. Surface roughness of films with plasma treatments was closely linked to the ratios of the cage- and network-structures of Si-O. Electrical properties of plasma-treated films were dependent on the applications of both etching and PRS plasma chemistries. Forming gas PRS caused the least low k film structural change and electrical deterioration compared with O₂ treatment. Moreover, E_bd of films decreased significantly by CH₂F₂ versus C₄F₈ etch. The best electrical properties of the film was obtained with a leakage current density of < 1 × 10^− 8 A/cm² and a dielectric breakdown strength of ∼3.2 MV/cm after being subjected with C₄F₈ / N₂ / Ar trench etch and forming gas PRS treatment.     

Effects of oxygen addition on electrochromic properties in low temperature plasma-enhanced chemical vapor deposition-synthesized MoOxCy thin films for flexible electrochromic devices

Electrochromic organomolybdenum oxide (MoO_xC_y) films are deposited onto 60 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates by low temperature plasma-enhanced chemical vapor deposition (PECVD) using a precursor of molybdenum carbonyl vapor, which is carried by argon gas, mixed with oxygen gas and synthesized by radio frequency power at room temperature (23 °C). The MoO_xC_y films with modified surface morphology and compositions of varying oxygen contents are proven to offer noteworthy electrochromic performance. Porous surface of the MoO_xC_y film (398 nm thick) provides Li⁺ ion diffusion coefficient value of 1.7 × 10^− 10 cm²/s for Li⁺ de-intercalation at a potential scan rate of 2 mV/s. High x/y value at high surface composition of oxygen to carbon in the MoO_xC_y film offers light modulation with transmittance variation of up to 63% and coloration efficiency of 36 cm²/C at a wavelength of 800 nm for 200 cycles of Li⁺ intercalation and de-intercalation. PECVD-synthesized MoO_xC_y thin films show promising electrochromic properties for applications in flexible electrochromic devices.     

Nucleation study of hydrogenated microcrystalline silicon (μc-Si:H) films deposited by VHF-ICP

Nucleation in the initial stage of hydrogenated microcrystalline silicon (μc-Si:H) film deposition by VHF inductivity-coupled plasma (ICP) has been investigated. When the SiH₄ concentration (R_SiH4 = [SiH₄] / ([SiH₄] + [H₂])) is 6%, the crystallization in the initial 1.1-2.4 nm film deposition is observed at the substrate temperature of 320 °C, while it is decreased to 150 °C by reducing the R_SiH4 to 3%. Furthermore, the nucleation is significantly promoted by H₂ plasma pretreatment as long as 90 s prior to μc-Si:H film deposition. The crystallinity was improved from 33 to 54% and the grain density was increased from 8.0 × 10¹⁰ to 1.7 × 10¹¹ cm^− 2 by the pretreatment. We confirmed no significant change in SiO₂ surface micro roughness after the H₂ plasma pretreatment. The chemical bond states at the SiO₂ surface before film deposition play an important role in nucleation.     

The phase transformation and crystallization kinetics of (1 − x)Li2O–xNa2O–Al2O3–4SiO2 glasses

The phase transformation and crystallization kinetics of (1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses have been studied by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) analysis. The crystallization temperature at the exothermic peak increases from 1171 to 1212 K when the Na₂O content increases from 0 to 0.6 mol. The crystalline phase is composed of spodumene crystallization when the Na₂O content increases from 0 to 0.6 mol. The activation energy of spodumene crystallization decreases from 444.0 ± 22.2 to 284.0 ± 10.8 kJ mol⁻¹ when the Na₂O content increases from 0 to 0.4 mol. Moreover, the activation energy increases from 284.0 ± 10.8 to 446.0 ± 23.2 kJ mol⁻¹ when the Na₂O content increases from 0.4 to 0.6 mol. The crystallization parameters m and n approach 2, indicating that the surface nucleation and two-dimensional growth are dominant in (1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses.     

Rapid thermal-plasma annealing of ZnO:Al films for silicon thin-film solar cells

Rapid thermal annealing of sputter-deposited ZnO and Al-doped ZnO (AZO) films with and without an amorphous silicon (a-Si) capping layer was investigated using a radio-frequency (rf) argon thermal plasma jet at atmospheric pressure. The resistivity of bare ZnO films on glass decreased drastically from 10⁶ to 10³ Ω·cm at maximum surface temperatures T_max above 650 °C, whereas the resistivity increased from 10^− 4 to 10^− 3-10^− 2 Ω·cm for bare AZO films. On the other hand, the resistivity of AZO films with a 30-nm-thick a-Si capping layer remained below 10^− 4 Ω·cm, even after TPJ annealing at a T_max of 825 °C. X-ray diffraction and X-ray photoemission electron studies revealed that the film crystallization of both AZO and a-Si layers was promoted without the formation of an intermixing layer. Additionally, the crystallization of phosphorous- and boron-doped a-Si layers at the sample surface was promoted, compared to that of intrinsic a-Si under identical plasma annealing conditions. The role of the a-Si capping layer on sputter-deposited AZO and ZnO films during TPJ annealing is demonstrated. The effects of the mixing of phosphorous and boron impurities in a-Si:H during TPJ annealing of flat and textured AZOs are also discussed.     

Mechanism of enhanced wettability of nanocrystalline diamond films by plasma treatment

The mechanism of wetting behavior of nanocrystalline diamond films is examined in terms of surface free energy, morphology, and bonding characteristics. The films are prepared by microwave plasma-enhanced chemical vapor deposition using Ar-rich/N₂/CH₄ and Ar-rich/H₂/CH₄ mixtures, followed by microwave hydrogen and oxygen plasma exposures separately. Contact angle measurement with water, ethylene glycol, and formamide reveals that both the as-deposited and hydrogen plasma treated films are hydrophobic, while the oxygen plasma treated film is extremely hydrophilic such that the contact angle is reduced down to almost zero degree. Fourier transform infrared spectroscopy reveals that the hydrogen atoms are dominantly bonded to diamond and amorphous sp³-bonded carbon, and they are removed by the oxygen plasma treatment. For the oxygen plasma treated film, the mean value of oxygen concentration for the top surface to bulk (~ 1 μm) measured by energy-dispersive X-ray spectroscopy is ~ 10 at.%, while that for the top several monolayers surface measured by X-ray photoelectron spectroscopy is much higher at ~ 37 at.%, indicating a higher degree of oxidation toward the surface. The carbon bonding state in the oxidized layer is disordered by incorporation of a large amount of oxygen in form of polar CO bonds, which is accountable for a greater polar component of the apparent surface free energy and stronger dipole-dipole interactions.     

Fabrication of hydrophobic/super-hydrophobic nanofilms on magnesium alloys by polymer plating

Hydrophobic/super-hydrophobic nanofilms with improved corrosion resistance were fabricated on the surfaces of Mg-Mn-Ce magnesium alloy by a surface modification technique, named as polymer plating, which has been developed to modify superficial characteristics of magnesium alloys with polymeric nanofilms through synthesized organic compounds of triazine dithiol containing functional groups. The nanofilms were prepared by the electrochemical and polymerization reactions during polymer plating analyzed from characteristics of Fourier transform infrared spectrophotometer, X-ray photoelectron spectroscopy and scanning electron microscopy. The fabricated nanofilms changed the surface wettability of blank magnesium alloy from hydrophilic to hydrophobic with contact angle 119.0° of distilled water with lower surface free energy of 20.59 mJ/m² and even super-hydrophobic with contact angle 158.3° with lowest surface free energy of 4.68 mJ/m² by different functional nanofilms on their surfaces. Alteration of wettability from hydrophilic to hydrophobic and super-hydrophobic resulted from their low surface free energy and surface morphology with micro- and nano-rough structures. The corrosion behaviors from potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) show that the super-hydrophobic nanofilm has higher corrosion resistance and stability in 0.1 mol/L NaCl solution and lower corrosion current density (I_corr) with R_ct increasing two orders of magnitude of 16,500 Ω·cm² compared to that obtained for blank of 485 Ω·cm².     

In-situ energy-dispersive X-ray diffraction of metal sulfide assisted crystallization of strongly (001) textured photoactive tungsten disulfide thin films

Highly (001) textured tungsten disulphide (WS₂) thin films were grown by rapid metal (Ni, Pd) sulfide assisted crystallization of amorphous reactively sputtered sulfur-rich tungsten sulfide (WS_3 + x) and by metal sulfide assisted sulfurization of tungsten metal films. The rapid crystallization was monitored by real-time in-situ energy dispersive X-ray diffraction (EDXRD). Provided that a thin nickel or palladium film was deposited prior to the deposition of WS_3 + x or W, the films crystallized very fast (about 20 nm/s) at temperatures above the metal sulfide eutectic temperature. After crystallization, isolated MeS_x crystallites are located on the surface of the WS₂ layer, which was proved by scanning electron microscopy. The metal sulfide assisted crystallized WS₂ layers exhibit a pronounced (001) orientation with large crystallites up to 2 µm. The in-situ EDXRD analysis revealed distinct differences of the two crystallization routes from tungsten and from amorphous, sulfur-rich WS_3 + x precursors, respectively. The crystallized WS₂ films showed photoactivity. Combined with the high absorption coefficient of 10⁵ cm^− 1 and a indirect band gap of 1.8 eV these properties make such films suitable for absorber layers in thin film solar cells.     

Magnetic flux pinning and flux jumps in polycrystalline MgB2

MgB₂ polycrystalline samples were fabricated under varying conditions of isostatic pressing in argon gas. The critical current densities (J_C) were determined through measurements of hysteresis loops, and the highest value of J_C at 10 K was 1.9 × 10⁴ A/cm² at 4.8 T. The depinning temperatures were measured at various magnetic fields using the vibrating reed technique. Flux jumps appeared below 7.4 K. The hysteresis loops were carefully examined to determine the temperature and magnetic field range where flux jumps appeared.     

Effect of processing on the properties of Bi3.15Nd0.85Ti3O12 thin films

Various crystallization parameters were studied during the fabrication of Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) thin films on Pt/Ti/SiO₂/Si (100) by metal organic solution decomposition method. The effect of crystallization processes, crystallization ambients on the properties of BNdT thin films such as orientation, ferroelectric properties were examined. By adopting different fabrication processes, it is possible to get both highly c-axis oriented as well as randomly oriented thin films. Highly c-axis oriented BNdT thin film showed a large remnant polarization (2P_r) of 70 μC/cm² at an applied voltage of 10 V and exhibited a fatigue free behavior unto 2 × 10⁹ switching cycles. The improved ferroelectric properties of BNdT thin films suggest their suitability for high density ferroelectric random access memory applications.     

Transverse crack growth behavior considering free-edge effect in quasi-isotropic CFRP laminates under high-cycle fatigue loading

The high-cycle fatigue characteristics focused on the behavior of the transverse crack growth up to 10⁸ cycles were investigated using quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates whose stacking sequence was [−45/0/45/90]_s. To assess the fatigue behavior in the high-cycle region, fatigue tests were conducted at a frequency of 100 Hz in addition to 5 Hz. In this study, to evaluate quantitative characteristics of the transverse crack growth in the high-cycle region, the energy release rate considering the free-edge effect was calculated. Transverse crack growth behavior was evaluated based on a modified Paris law approach. The results revealed that transverse crack growth was delayed under the test conditions of the applied stress level of σ_max/σ_b = 0.2.     

Plasma surface interaction in PACVD and PVD systems during TiAlBN nanocomposite hard thin films deposition

In a PACVD system, titanium alloys were exposed to inductive radio-frequency (RF) plasmas of H₂ + N₂ and Ar + BCl₃+H₂ + N₂ gas mixtures for their nitriding and boron nitride respectively. Hard nanocomposite thin films of TiAlN and TiAlBN were formed on Ti-6Al-4V alloys in an inductive RF plasma of Ar + H₂ + N₂ and Ar + 3.5 vol.% of BCl₃ + H₂ + N₂, respectively. The substrates were grounded, i.e., self-biased, during plasma thin film formation for 30 min each. TiAlBN was deposited by sputtering in a reactive PVD system. A quadrupole mass spectrometer (QMS) sampled the plasma at a constant distance of 0.5 cm from the sample surface in real time. The mass species (m/e) at 0.5 cm were recorded during the deposition process. To separate the particles reaching the substrate surface from those leaving it, the nanocomposite thin films coated samples of Ti alloys were introduced in an RF plasma of Ar + H₂ mixture without the presence of N₂ and BCl₃ and negatively biased up to V_b = − 350 V. The QMS at 0.5 cm measures the etched and sputtered species from the surface of the coated samples. Comparing the QMS results between the grounded samples with the monomers in the RF plasma and the negatively biased voltage samples without monomers in the Ar + H₂ plasma the net plasma surface interactions (PSI) were evaluated. The behavior of the coating process of nanocomposite thin films of TiAlN and TiAlBN on the Ti alloy samples is strongly dependent on the plasma surface phenomena.     

Comparison of ferritic and austenitic plasma nitriding and nitrocarburizing behavior of AISI 4140 low alloy steel

This paper compares the ferritic and austenitic plasma nitriding and nitrocarburizing behavior of AISI 4140 low alloy steel carried out to improve the surface corrosion resistance. The gas composition for plasma nitriding was 85% N₂–15% H₂ and that for plasma nitrocarburizing was 85% N₂–12% H₂–3% CO₂. Both treatments were performed for 5 h, for different process temperatures of 570 and 620 °C for ferritic and austenitic plasma treatment, respectively. Optical microscopy, X-ray diffraction and potentiodynamic polarization technique in 3.5% NaCl solution, were used to study the treated surfaces. The results of X-ray analysis revealed that with increasing the treatment temperature from 570 to 620 °C for both treatments, the amount of ε phase decreased and γ′ phase increased. Nitrocarburizing treatment resulted in formation of a more amount of ε phase with respect to nitriding treatment. However, the highest amount of ε phase was observed in the ferritic nitrocarburized sample at 570 °C. The sample nitrided at 620 °C exhibited the thickest layer. The potentiodynamic polarization results revealed that after plasma nitriding and nitrocarburizing at 570 °C, corrosion potential increased with respect to the untreated sample due to the noble nitride and carbonitride phases formed on the surface. After increasing the treatment temperature from 570 to 620 °C, corrosion potential decreased due to the less ε phase development in the compound layer and more porous compound layer formed at 620 °C with respect to the treated samples at 570 °C.     

On the synthesis of ultra smooth ITO thin films by conventional direct current magnetron sputtering

Highly transparent, conductive Sn-doped In₂O₃ (ITO) thin films with a characteristic root mean square surface roughness RMS below 1 nm were obtained from deposition of amorphous ITO and subsequent annealing treatment. ITO thin films with ultra flat surface were produced by (i) controlling crystallization mechanisms (nucleation and growth) of amorphous ITO through optimization of hydrogen content and temperature profile during sputtering and annealing process and (ii) preventing formation of agglomerated atoms/clusters in the gas phase and hence reducing large surface particles through fine tuning the sputtering rate and process pressure. Characterization of the coatings revealed specific resistivities below 2.5 × 10^− 4 Ω cm and transparencies above 90% in the visible range of light.     

Characteristics of nano-crystalline diamond films prepared in Ar/H2/CH4 microwave plasma

Characteristics of nano-crystalline diamond (NCD) thin films prepared with microwave plasma chemical vapor deposition (CVD) were studied in Ar/H₂/CH₄ gas mixture with a CH₄ gas ratio of 1-10% and H₂ gas ratio of 0-15%. From the Raman measurements, a pair of peaks at 1140 cm^− 1 and 1473 cm^− 1 related to the trans-polyacetylene components peculiar to nano-crystalline diamond films was clearly observed when the H₂ gas ratio of 5% was added in Ar/H₂/CH₄ mixture. With an increase of H₂ gas content up to 15%, their peaks decreased, while a G-peak at roughly 1556 cm^− 1 significantly increased. The degradation of NCD film quality strongly correlates with the decrease of C₂ optical emission intensity with the increase of hydrogen gas contents. From the surface analysis with atomic force microscopy (AFM), it was found that grain sizes of NCD films were typically of 10-100 nm in case of 5% H₂ gas addition.     

Optical, electrical and structural properties of Cu2Te thin films deposited by magnetron sputtering

Thin films of Cu₂Te were deposited, at room temperature, on glass substrates by magnetron sputtering from independent Cu and Te sources. This work presents the effect of annealing temperature on the optical, structural, and electrical properties of sputtered Cu₂Te films. Annealing above 300 °C resulted in stoichiometric and near stoichiometric Cu₂Te phases, whereas temperatures above 400 °C yielded films with single Cu₂Te phase. In contrast, annealing at temperatures of 250 °C and below resulted in mixed phases of CuTe, Cu₇Te₅, Cu_1.8Te, and Cu₂Te. Analyses of transmittance and reflectance measurements for Cu₂Te indicate that photon absorption occurs via indirect band transitions for incident photons with energy above the band gap energy and free carrier absorption below the band gap energy. The determined indirect band gap was 0.90 eV and its associated phonon energy was 0.065 eV. Optical phonon scattering was identified as the mechanism through which the momentum is conserved during absorption by free carriers. Electrical measurements show p-type conductivity and highly degenerate semiconducting behavior with a hole carrier concentration p = 5.18 × 10²¹ cm^− 3.     

On the crystallization behavior of amorphous Fe-Cr-Mo-B-P-Si-C powder prepared by mechanical alloying

The crystallization behavior and thermal stability of Fe-Cr-Mo-B-P-Si-C amorphous alloy, prepared by mechanical alloying (MA), were investigated by using differential scanning calorimetry (DSC). One exothermic peak was observed on DSC traces, implying that the crystallization process undergoes only one stage. The crystallization kinetic parameters, including activation energy (E_a), Avrami exponent (n) were determined with non-isothermal analysis method based on the DSC data. The results suggest that the crystallization mechanism is governed dominantly by a three-dimensional diffusion-controlled growth. In addition a relatively high value of activation energy of crystallization (386.04 ± 10 kJ/mol) was found, indicating that this amorphous alloy has high thermal stability.     

Raman spectroscopic study of structure of WO3La2O3B2O3 glasses with no color and crystallization of LaBWO6

Glasses with the nominal compositions of xWO₃25La₂O₃(75 − x)B₂O₃ (mol%) with x = 15, 25, and 50 were prepared using a conventional melt quenching method, and their structure and crystallization behavior were examined from Raman scattering spectra and X-ray diffraction analyses. The glasses are colorless in the visible light region and give the optical band gap energy of 3.49-3.61 eV. The glass transition and crystallization temperatures and the thermal stability against crystallization decrease with increasing WO₃ content. The strong Raman bands at 840 and 940-960 cm⁻¹ suggest that the main coordination state of W⁶⁺ ions in the glasses is isolated (WO₄)²⁻ tetrahedral units. The formation of WO₆ octahedral units is also suggested in the glasses with high WO₃ contents. The main crystallization mechanism in the glasses is the surface crystallization, and the glass of 50WO₃25La₂O₃25B₂O₃ shows the crystallization of LaBWO₆ single phase. The present study proposes that WO₃La₂O₃B₂O₃ glasses and crystallized glasses are very interesting as optical functional materials.