Diamond-like carbon films prepared by pulsed-laser evaporation

Diamond-like carbon thin films were prepared by pulsed-laser evaporation. In this method a carbon target was irradiated by a XeCl laser with a power density of 3×10⁸ W/cm² and carbon atoms, together with a small number of ions, were produced. Deposition rates and film properties changed sensitively with substrate temperature. The films deposited at 50°C were diamond-like, having reasonable hardness, high refractive index (2.1–2.2 at 633 nm), optical transparency in the infrared, electrical resistivity of 10⁸ cm and chemical inertness (no dissolution in a HFHNO₃ solution). The band gap measured from optical absorption was 1.4 eV. Raman spectrum and infrared absorption, whose features varied with the substrate temperature, were also measured. The films were amorphous and no crystallinity was observed, as confirmed by x-ray diffraction, transmission electron diffraction and Raman spectroscopy. Hydrogen atoms were incorporated in the films with a typical H/C ratio of 0.3. The application of a negative bias to the substrate modified the deposition due to the presence of ions.     

An experimental investigation of inhomogeneities in resonant infrared matrix-assisted pulsed-laser deposited thin polymer films

Thin polymer films are deposited using matrix-assisted pulsed-laser evaporation and subsequently are characterized by scanning electron and atomic force microscopies. An Er : YAG laser (2937 nm, 350 μs) is used as a light source and the effect of the energy density supplied by the laser on the morphology of the deposited films is investigated. It is found that the appearance of undesirable non-uniform morphological features arises from either poor solubility of the guest molecules or insufficient energy density provided by the laser to vaporize the entire ejected volume. In addition, the surface roughness of two guest–host systems is found to depend linearly on the polymer concentration. These results allow us to better understand earlier work in the field and to establish a framework by which MAPLE films may be improved.     

Absorption bistability in evaporated ZnSex thin films

Intrinsic absorption bistability in ZnSe_1.36 thin films, produced by thermal evaporation is observed. The influence of laser pulse duration and resonator mirror reflectivity is studied experimentally and theoretically. Compared to ZnSe elements prepared by other methods, the evaporated films allow a longer operation wavelength of 514 nm, a low threshold power of 10 mW and a smaller element size below 10 m³.     

Tunable UV laser photolysis of organometallics with product detection by laser mass spectroscopy: Trimethylaluminum

We use tunable UV laser light in the region 200–320 nm, produced by frequency doubling the output of a dye laser, for the decomposition of organometallic compounds. This method has been applied to TMA, trimethylaluminum Al(CH₃)₃. Only the TMA monomer absorbs UV light for >220 nm. TMA decomposes by one-photon absorption mainly into two channels: aluminum atoms Al plus organic fragments, and aluminummonomethyl AlCH₃ molecules plus organic fragments. The ratio [Al]/[AlCH₃] is wavelength dependent. We present a mechanism to explain the photolysis of trimethyl compounds of group III elements (Al, Ga, In).     

The effect of argon gas pressure on structural,morphological and photoluminescence properties of pulsed laser deposited KY<Subscript>3</Subscript>F<Subscript>10</Subscript>:Ho<Superscript>3+</Superscript> thin films

KY₃F₁₀:Ho³⁺ thin films were deposited by a pulsed laser deposition technique with Nd–YAG laser radiation (λ = 266 nm) on (100) silicon substrate. The XRD and FE-SEM results show improved crystalline structure for the film deposited at a pressure of 1 Torr. The AFM results show that the RMS roughness of the films increases with rise in argon gas pressure. The EDS elemental mapping shows Y-excess for all the films deposited under all pressures, and this is attributed to its higher mass and low volatility as compared to K and F. XPS analysis further confirmed Y-excess in the deposited films. Green PL emission at 540 nm was investigated at three main excitation wavelengths, namely 362, 416 and 454 nm. The PL emission peaks increase with rise in background argon gas pressure for all excitation wavelengths. The highest PL intensity occurred at excitation of 454 nm for all the thin films. In addition, faint red (near infrared) emission was observed at 750 nm for all the excitations. The green emission at 540 nm is ascribed to the ⁵F₄–⁵I₈ and ⁵S₂–⁵I₈ transitions, and the faint red emission at 750 nm is due to the ⁵F₄–⁵I₇ and ⁵S₂–⁵I₇ transitions of Ho³⁺.     

Pulsed laser deposition of Eu:Y2O3 thin films on (0001) α-Al2O3

This paper focuses on the preparation and characterization of crystalline thin films of rare-earth-doped sesquioxides (Y₂O₃, Lu₂O₃) grown by pulsed laser deposition on single-crystal (0001) sapphire substrates. X-ray diffraction measurements show that the films with thicknesses between 1 nm and 500 nm were highly textured along the 111 direction. Using Rutherford backscattering analysis, the correct stoichiometric composition of the films was established. The emission and excitation spectra of europium-doped films with a thickness 100 nm look similar to those of the corresponding crystalline bulk material, whereas films with a thickness 20 nm show a completely different emission behavior. PACS 68.55.Jk; 78.66.Nk; 81.15.F     

Optical CO gas sensing using nanostructured NiO and NiO/SiO2 nanocomposites fabricated by PLD and sol–gel methods

Several kinds of NiO-based nanostructured films were prepared by pulsed-laser deposition (PLD) and sol–gel method, and CO sensing properties (1%, balanced by N₂) of these films were studied. The sensitivity, defined as a difference of optical transmittance by gas atmospheric change (T=T(CO)-T(air)), increased with increasing NiO content for the sol–gel prepared films, and increased with the film thickness for the laser deposited NiO films. Sol–gel films exhibited shorter response time than NiO films prepared by PLD under low Ar pressure of 6.7×10^-2 Pa indicating a better gas permeability. A shorter response time was also obtained upon raising argon pressure from 6.7×10^-2 Pa to 8.0 Pa during laser ablation due to the morphological change. Covering a NiO film even with a very thin (0.8 nm) layer of SiO₂ by sputtering drastically reduced the CO sensitivity. The multilayered NiO/SiO₂ films were substantially less sensitive to the CO gas than NiO films due to the same reason. Sensing mechanism of the NiO films is due to catalytic CO oxidation that reduces the concentration of adsorbed O₂ species and results in optical transmittance increase upon change in the environment from air to CO. PACS 81.15.Fg; 81.20.Fw; 83.85.Gk     

Polymer films filled with organic molecules by CO2 laser evaporation in vacuum

A new p-type of material for organic field-effect transistors (OFETs) is 5,5′-di(9,9′-di-(butyl)-fluorene′)-2,2′-bithiophene (DBFBT). DBFBT films have been prepared by casting, by thermal evaporation in vacuum, and by means of CO₂ laser evaporation. The photon energy from a CO₂ laser is too small to break chemical bonds of the DBFBT molecule, but the heating rate is extremely high. Pressed pellets of powders composed of DBFBT and polychlorotrifluoroethylene (PCTFE) were used as targets for the fabrication of films. These targets were irradiated by a laser beam of 40 W cw-power and 0.5 cm diameter. The deposition rate was 30-50 nm/s. The films have been characterised by optical spectroscopy and by AFM. The structure of DBFBT films produced by casting from solution and thermal deposition is composed of elongated crystals, while the laser deposited layers show cluster structure. By FTIR the films show the absorption band of pure DBFBT, with intensity proportional to the DBFBT concentration in the PCTFE matrix. The absorption bands for a pure DBFBT film, for a film with 22 vol.% and with 34 vol.% of DBFBT in the PCTFE matrix are situated at 274, 298 and 402 nm, where the latter is the most intense one. No significant difference in the band positions of all samples has been found. We concluded that no interaction between chromophore and matrix occurs. The DBFBT molecules in the PCTFE matrix did not oxidize during storage under ambient condition over a period of a year.     

Processing of C<Subscript>60</Subscript> thin films by Matrix-Assisted Pulsed Laser Evaporation (MAPLE)

Thin films of fullerenes (C₆₀) were deposited onto silicon using matrix-assisted pulsed laser evaporation (MAPLE). The deposition was carried out from a frozen homogeneous dilute solution of C₆₀ in anisole (0.67 wt%), and over a broad range of laser fluences, from 0.15 J/cm² up to 3.9 J/cm². MAPLE has been applied for deposition of fullerenes for the first time and we have studied the growth of thin films of solid C₆₀. The fragmentation of C₆₀ fullerene molecules induced by ns ablation in vacuum of a frozen anisole target with C₆₀ was investigated by matrix-assisted laser desorption/ionization (MALDI). Our findings show that intact fullerene films can be produced with laser fluences ranging from 0.15 J/cm² up to 1.5 J/cm².     

Efficient Continuous Wave-laser emission of Pr3+-doped fluorides at room temperature

We report, to our knowledge for the first time, Continuous Wave (CW) laser emission at room temperature of Pr:LiYF₄ (Pr.YLF) at six wavelengths: 522, 545, 607, 639.5, 720 and 907.4 nm. The pump source was an argon-ion laser tuned to a wavelength of = 457.9 nm. The maximum output powers at 522 nm (³P_i ³H₅) and 639.5 nm (³P₀ ³F₂) were 144 and 266 mW, respectively. We also observed CW laser action of Pr:GdLiF₄ (Pr: GLF) at = 639 nm and of Pr:KYF₄ (Pr: KYF) at = 642.5 nm.     

Dual excimer and CO2 laser etching studies of polyethylene terephthalate

Polyethylene terephthalate (PET) films preheated with a pulsed CO₂ laser have been ablatively etched with an XeCl laser. The observed reduction in ablation threshold, from 170 to 140 mJ cm^–2, is consistent with a thermal mechanism for XeCl laser ablation of PET. Transient changes in the UV absorption coefficient of PET caused by heating with pulsed CO₂ laser radiation have also been studied and a significant increase in absorption observed at 308 nm. Permanent changes in the ultraviolet absorption of PET following exposure to low fluence XeCl laser radiation are also reported.     

First diode-pumped Yb-doped solid-state laser continuously tunable between 1000 and 1010 nm

We demonstrate that the ytterbium-doped medium Yb:YSO can provide laser oscillation in the 1000–1010 nm wavelength range under diode pumping around 980 nm. Ytterbium-doped Y₂SiO₅ crystal has been chosen for its high emission cross section around 1 m combined with a strong absorption line at 978 nm. We have developed an original pumping architecture that permits us to overcome problems due to the small difference between pump and laser wavelengths. In this way, laser emission continuously tunable in the 1000–1010 nm wavelength range has been obtained with more than 100 mW of output power. This kind of laser is the first step toward a metrological source around 500 nm stabilized on an I₂ absorption line. Furthermore, 100 mW of laser light has been obtained at 998.5 nm, leading to a remarkably low quantum defect of 2.1%. PACS 42.55.Xi; 42.60.Pk; 42.72.Ai     

Synthesis and optical properties of basic fuchsin dye-doped PMMA polymeric films for laser applications: wide scale absorption band

Basic fuchsin dye-doped poly(methyl methacrylate) polymeric films were sensitized with various dye concentrations ranging from 0.0833 to 1.667 wt% of basic fuchsin. Their structure, linear absorption, and optical limiting properties were examined. The films were prepared using a simple and fast casting technique dissolved in chloroform for both the dye and the polymer. Structural characterizations were achieved by XRD, and the films showed an amorphous hump supporting the noncrystalline structure of studied polymeric composites. Spectrophotometer measurements were used to estimate the spectral absorption measurements of the films such as transmittance, absorbance with the calculations of absorption index (k), and optical energy band gap (E _g ) in the wavelength region from 190 to 2500 nm. Results show that the optical constants change with increasing the dye doping concentrations. It has been found that optical energy gap (E _g ) appearing that, both direct and indirect optical transitions are conceivable for these films. Optical limiting properties of the films with various dye concentrations were studied using a continuous wave He–Ne laser operating at 632.8 nm. The results appeared that the sample has an obvious optical limiting effect. The designed BF/PMMA composites can be applicable in wide-scale applications.     

Structural and optical properties of ZnO thin films on (111) CaF2 substrates grown by magnetron sputtering

ZnO thin films were grown on (111) CaF₂ substrates by magnetron sputtering at room temperature. Structural and optical properties of the ZnO thin films were studied. XRD analysis showed that the ZnO thin films had the (002) preferential orientation. The transmittance of ZnO thin films was over 80% in the visible range. The optical band gap of the ZnO thin films was 3.26 eV. The optical constants (n,k)$(n,k)$ of the ZnO thin films in the wavelength range 300–1000 nm were obtained by infrared spectroscopic ellipsometry measurement. PL spectra of ZnO thin films showed strong UV near-band-edge emission peak at 376.5 nm and weak visible red emission at 643.49 nm using He–Cd laser as the light source, using a synchrotron radiation light source PL spectra showed three emission peak at 320 nm, 410 nm and 542 nm respectively.     

Stimulated emission and laser action of Pr3+-doped YA1O3

Groundstate absorption, fluorescence, excited-state absorption, and stimulated emission of Pr:YA1O₃ were measured in dependence on the polarization. The results reflect the anisotropy of the host lattice. Especially the polarized spectra of the stimulated emission fit very well with the laser data of this material. Seven cw laser transitions in the visible spectral range obtained so far in Pr:YA1O₃ with argon-ion laser pumping were identified in the spectra of the stimulated emission. In addition, two infrared cw laser transitions were realized. The best results were achieved for the³ P ₀³ F ₄ laser transition at 746.9 nm with a maximum slope efficiency of 24.6%, a maximum output power of 49.6 mW, and a laser threshold of 25 mW.     

Resonant infrared matrix-assisted pulsed laser evaporation of TiO2 nanoparticle films

The successful development of flexible, high performance thin films that are competitive with silicon-based technology will likely require fabricating films of hybrid materials that incorporate nanomaterials, glasses, ceramics, polymers, and thin films. Resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) is an ideal method for depositing organic materials and nanoparticles with minimal photochemical or photothermal damage to the deposited material. Furthermore, there are many nonhazardous solvents containing chemical functional groups with infrared absorption bands that are accessible using IR lasers. We report here results of recent work in which RIR-MAPLE has been employed successfully to deposit thin films of TiO₂ nanoparticles on Si substrates. Using an Er:YAG laser (λ=2.94 μm), we investigated a variety of MAPLE matrices containing –OH moieties, including water and all four isomers of butyl alcohol. The alcohol isomers are shown to provide effective and relatively nontoxic solvents for use in the RIR-MAPLE process. In addition, we examine the effects of varying concentration and laser fluence on film roughness and surface coverage.     

Spectroscopic and travelling-wave lasing characterisation of tetraphenylbenzidine and di-naphtalenyl-diphenylbenzidine

The organic light emitting diode (OLED) hole transport molecules N,N,N’,N’-tetraphenylbenzidine (TPB, triphenylamine dimer TAD or TPD) and N,N’-bis(2-naphtalenyl)-N,N’-bis(phenylbenzidine) (β-NPB, naphtyl-diphenylamine dimer β-NPD), dissolved in tetrahydrofuran (THF) and as neat film, are characterized by optical absorption and emission spectroscopy. The absorption and stimulated emission cross-section spectra, the fluorescence quantum distributions, fluorescence quantum yields, degrees of fluorescence polarization, and fluorescence lifetimes are determined. The lasing behaviour is studied by picosecond laser pulse excitation (excitation wavelength 347.15 nm, pulse duration 35 ps). The excited-state absorption at the pump laser wavelength is determined by saturable absorption measurement. Low-Q laser oscillation of TPB in THF is achieved by transverse pumping of the dye in a cell. The excited-state absorption of TPB in THF at the laser wavelength is extracted from the laser threshold. In TPB neat films, wave-guided travelling-wave lasing was obtained. No laser action was achieved for β-NPB because of small S₁-S₀ stimulated emission cross-section, and the presence of excited-state absorption in the fluorescence wavelength region. The TPB and β-NPB results are compared with the corresponding spectroscopic and lasing behaviour of the related methyl-substituted triphenylamine dimers, 3-methyl-TPD and 4-methyl-TPD, which are well established OLED hole transport materials.     

Optical Properties of Films of Cu x Ag1−x InSe2 Solid Solutions Obtained by Laser Evaporation

The structure and optical properties of the films of ternary compounds AgInSe₂, CuInSe₂ and Cu _x Ag_1–x InSe₂ solid solutions obtained by pulsed laser evaporation are investigated. It has been established that the films like bulk crystals have the structure of chalcopyrite. By the transmission and reflection spectra near the edge of natural absorption the refractive index and coefficient of optical absorption are calculated and the energies of interband transitions and the crystalline and spinorbit splitting are determined.     

Pulsed laser deposition of Er:BaTiO3 for planar waveguides

Laser radiation is used for the deposition of dielectric erbium doped BaTiO₃ thin films for photonic applications. Pulsed laser deposition with KrF excimer laser radiation (wavelength 248 nm, pulse duration 20 ns) is used to grow dense, transparent, amorphous, poly-crystalline and single crystalline erbium doped BaTiO₃ thin films. Visible emission due to up-conversion luminescence (wavelength 528 nm and 548 nm) under excitation with diode laser radiation at a wavelength of 970–985 nm is investigated as a function of the erbium concentration of 1–20 mol% and structural film properties. PACS 81.15.Fg; 42.55.Wd; 68.55; 78.55.Hx     

Preparation of single-crystal-like MgO films on Si and orientation control of platinum films on MgO/Si

Growth of a Pt/MgO bilayer on Si(100) was investigated by pulsed-laser deposition. The growth modes of both MgO and platinum films are layer-by-layer growth, which were revealed by in situ reflection high energy electron diffraction observations. Two kinds of orientations of platinum films, viz. epitaxially (100) and (111)-oriented platinum films, were obtained on the same MgO(100)/Si(100) substrate only by varying the laser fluence. The effect of laser fluence on the orientation of platinum films is briefly discussed. The platinum films prepared in our experiments are epitaxially grown and exhibit atomic-scale surface flatness. It is believed that the improvement in the quality of platinum films can be attributed to the perfectly single-crystalline quality of the MgO buffer layer, which was further confirmed by the excellent dielectric properties. For a 150 nm thick MgO film, the leakage current density was found to be 10^-7 Acm^-2 with an electric field of 8×10⁵ Vcm^-1 and the relative dielectric constant (_r) was 10.6. PACS 68.55.Jk; 81.15.Fg; 85.50.Gk