Evaluation of hafnium nitride thin films sputtered from a hafnium nitride target

Hafnium nitride (HfN) thin films were prepared on Si (100) substrates by radio frequency magnetron sputtering with a compound target. Nitrogen composition, work function and electrical resistivity were investigated to evaluate thin film properties. Nitrogen composition and work function had little dependence on argon gas pressure and radio frequency power. Electrical resistivity showed strong correlation with the substrate temperature. When thin films were fabricated at room temperature, the electrical resistivity was 100 μΩ cm, and it became lower with an increase in the substrate temperature. When the films were fabricated at 600 °C, the resistivity became less than 50 μΩ cm.     

Mass analysis of biological macromolecules at atmospheric pressure using nonresonant femtosecond laser vaporization and electrospray ionization

A nonresonant femtosecond laser pulse, with an intensity of 10(13) Wcm(-2), vaporizes proteins and biomolecules intact, regardless of molecular structure, size or electronic structure for subsequent electrospray ionization and transfer into a mass spectrometer. Rapid, direct analysis from dried sample, aqueous solution and cellular material is demonstrated at atmospheric pressure using laser electrospray mass spectrometry (LEMS). Measurements are presented for lysozyme (14.3 kDa), hemoglobin from human blood, ovalbumin (45 kDa) from hen egg white and phospholipids from hen egg yolk. Mass analysis of biological material is performed without dilution, extraction or sample preparation, other than placing the biological material onto the sample plate.     

Growth of Ti:sapphire single crystal thin films by pulsed laser deposition

This paper documents the growth of single crystal Ti:sapphire thin films, typically 10 μm thick, on undoped sapphire substrates using pulsed laser deposition from a Ti:sapphire single crystal target with a doping level of 0.1 wt.% Ti₂O₃. These thin films are shown to have very high crystal quality using ion beam channelling and X-ray diffraction techniques. The degree of titanium incorporation into the films is investigated using inductively coupled plasma mass spectrometry and particle induced X-ray emission. These techniques show that levels of up to 0.08 wt.% Ti₂O₃ are present in the deposited layers.     

Cu(In,Ga)Se2 thin films and devices sputtered from a single target without additional selenization

Typically, Cu(In,Ga)Se₂ (CIGS) thin films for photovoltaic devices are deposited by co-evaporation or, alternately, by deposition of the metals with or followed by treatment in a selenium environment. In this article, we describe CIGS films that are instead deposited by RF magnetron sputtering from a single quaternary target without any additional selenization. Devices built with these films exhibit efficiencies as high as 8.9%. We demonstrate that deposition power can be varied in order to change the film morphology and improve device performance.     

Texture, residual stress and structural analysis of thin films using a combined X-ray analysis

Advanced thin films for today's industrial and research needs require highly specialized methodologies for a successful quantitative characterization. In particular, in the case of multilayer and/or unknown phases a global approach is necessary to obtain some or all the required information. A full approach has been developed integrating novel texture and residual stress methodologies with the Rietveld method (Acta Cryst. 22 (1967) 151) (for crystal structure analysis) and it has been coupled with the reflectivity analysis. The complete analysis can be done at once and offers several benefits: the thicknesses obtained from reflectivity can be used to correct the diffraction spectra, the phase analysis help to identify the layers and to determine the electron density profile for reflectivity; quantitative texture is needed for quantitative phase and residual stress analyses; crystal structure determination benefits of the previous. To achieve this result, it was necessary to develop some new methods, especially for texture and residual stresses. So it was possible to integrate them in the Rietveld, full profile fitting of the patterns. The measurement of these spectra required a special reflectometer/diffractometer that combines a thin parallel beam (for reflectivity) and a texture/stress goniometer with a curved large position sensitive detector. This new diffraction/reflectivity X-ray machine has been used to test the combined approach. Several spectra and the reflectivity patterns have been collected at different tilting angles and processed at once by the special software incorporating the aforementioned methodologies. Some analysis examples will be given to show the possibilities offered by the method.     

Growth and characterizations of dual ion beam sputtered CIGS thin films for photovoltaic applications

The growth of CIGS thin films on soda-lime glass substrates at different substrate temperatures by dual ion beam sputtering system in a single-step route from a single quaternary sputtering target with the composition of Cu (In_0.70 Ga_0.30) Se₂ was reported. The effects of the substrate temperature on structural, optical, morphological and electrical properties of CIGS films were investigated. Stoichiometry of one such film was investigated by X-ray photoelectron spectroscopy. All CIGS films had demonstrated a strong (112) orientation located at 2θ ~26.70^o, which indicated the chalcopyrite structure of films. The value of full-width at half-maximum of (112) peak was reduced from 0.58° to 0.19° and crystallite size was enlarged from 14.98 to 43.05 nm as growth temperature was increased from 100 to 400 °C. However, atomic force microscope results showed a smooth and uniform surface at lower growth temperature and the surface roughness was observed to increase with increasing growth temperature. Hall measurements exhibited the minimum film resistivity of 0.09 Ω cm with a hole concentration of 2.42 × 10¹⁸ cm^?3 and mobility of 28.60 cm² V^?1 s^?1 for CIGS film grown at 100 °C. Film absorption coefficient was found to enhance nominally from 1 × 10⁵ to 2.3 × 10⁵ cm^?1 with increasing growth temperature from 100 to 400 °C.     

Development of a fatigue testing system for thin films

Only a few works on fatigue behavior of thin films under tension–tension loading can be found because of some limitations of a testing system. In this study, a fatigue testing system capable of performing load controlled tension–tension fatigue tests even for ductile thin films was developed by using an electrodynamic actuator. With the system, fatigue testing can be performed over a wide range of loading frequency. Besides, a capacitive displacement gauge was developed to measure the monotonic and cyclic deformation of thin films with high resolution during fatigue testing. As the displacement gauge is stable and its response is so fast, the displacement can be measured instantaneously and continuously during fatigue testing of high frequency.     

Use of sol-gels as solid matrixes for trace analysis by UV laser ablation and laser-enhanced ionization detection

Zirconium and silicon sol-gels were investigated as solid materials for trace elemental analysis of pelletized solid samples by laser ablation and laser-enhanced ionization. The highly homogeneous dispersion of an internal standard spiked in the solid material obtained with the sol-gel formation process leads to a significant improvement in signal repeatability and to an increase in the precision of measurements through better correction of variations in the laser ablation rate. Signal repeatability values of 5-8% RSD were obtained for Pb in NIST 1632c Bituminous Coal sample pellets prepared using both sol-gels, as compared to 9-21% for graphite-based sample pellets. Furthermore, the zirconium sol-gel was shown to offer better resilience to signal bias due to preferential ablation and a more accurate correction of ablation rate using the internal standardization method.     

Preparation of Al-Cu-Fe thin films by vapor deposition technique from a single source

In this paper, we report the formation of stable icosahedral Al-Cu-Fe quasicrystalline thin films by thermal vapor deposition techniques (indirect heating and e-beam heating) from a single source. Deposition of these films by a single-source indirect heating method, in the stable icosahedral phase, is reported for the first time. A direct comparison between the two different heating methods has been made. The final compositions of the prepared films with desired properties were found to be Al_62.9Cu_24.6Fe_12.5 (indirect heating method) and Al_63.1Cu_24.5Fe_12.4 (e-beam method), respectively. The resistivities of the films prepared by both methods were ∼2000 μΩ cm at room temperature and ∼4000 μΩ cm at 10 K.     

Characterization of sputtered SmCo thin films for light element contamination using RBS and HIERDA techniques

Samarium cobalt films were prepared on silicon substrates with and without a chromium buffer layer at room temperature and 600°C using direct current unbalanced magnetron sputtering. For obtaining ideal magnetic properties, the films should be free from impurities, such as O, Al and others. Rutherford backscattering spectrometry and heavy ion elastic recoil detection analysis were used to determine the composition and film thickness and to monitor the light element contamination across film thickness. X-ray diffractometer and superconducting quantum interference device were employed to characterize the structure and magnetic properties of the films, respectively. The results obtained led to an improved design of the ground shield and the use of a sorption pump to effectively minimize aluminium and oxygen concentration in the films, respectively.     

Hydrothermal synthesis of single crystal thin films of magnetic garnets and their analysis

A method of growing epitaxial films of yttrium-gadolinium iron garnets, containing approximately 1 atom per formula unit of gallium which are suitable for supporting 5 μm diameter magnetic bubbles, is described. A technique of reducing the substrate etching prior to film growth is given. In order to establish that the high gallium concentrations in the films were in fact obtained we used the technique of chemical analysis of radioactive isotope tracers.     

Electrical and optical properties of reactive sputtered TiO x thin films for uncooled IR detector applications

Nanostructured titanium oxide (nano-TiO _x ) thin films for uncooled IR detectors were fabricated by dc reactive magnetron sputtering and post-deposition annealed in oxygen atmosphere. The crystalline structure and surface morphology were characterized by glancing incidence X-ray diffraction (GIXRD) and field emission scanning microscopy. The results of GIXRD measurements indicate that TiO _x thin film deposited at room temperature is amorphous. A mixture of anatase and rutile nanocrystalline structure phase were present in oxygen annealed TiO _x thin film. A weak absorption peak around 438 cm^?1 corresponding to Ti–O stretching vibration is observed by Fourier transform infrared spectroscopy with annealed TiO _x thin film. The X-ray photoelectron spectra reveals Ti³⁺ and Ti⁴⁺ ions are coexisting in TiO _x films. The optical spectra of the films indicate that the optical absorption edge of the nano-TiO _x film exhibits a red shift compared to the as-deposited film. Furthermore, compared to bulk TiO _x , a blue shift was observed in both of the deposited and annealed films due to quantum size effect. The dependence of resistivity on temperature reveals both the absolute value of temperature coefficient of resistivity (TCR) and activation energy of TiO _x thin film increase significantly after annealing in oxygen.     

Microstructural characterizations and hardness evaluation of d.c. reactive magnetron sputtered CrN thin films on stainless steel substrate

Chromium nitride (CrN) thin films were deposited on stainless steel (grade: SA304) substrate by using d.c. reactive magnetron sputtering and the influence of process parameters such as substrate temperature, pressure, and power on their microstructural characteristics were investigated in the present work. The CrN films were characterized with X-ray diffraction (XRD) to reveal the formation of different phases and its texture. The films showed the (111) preferred orientation but its intensity decreased, while intensity of peak (200) increased with increase in working pressure. The mixture of CrN and Cr₂N phases were identified at low working pressure and temperature. The preferred orientations of CrN thin films are strongly influenced by sputtering conditions, thickness, and the induced residual stress in the films as observed in the present work. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the morphology and surface topography of thin films, respectively. The study shows that the hardness of films strongly depends on the grain size and the film density, which are influenced by combined effect of the working pressure, temperature, and power of the sputtering process.     

Fabrication of particle free epitaxal AlN thin films by reactive PLD combined with an electron beam and a rotating crucible

An AlN epitaxial film without projections or spiral growth features was successfully fabricated on a (0 0 0 1) sapphire substrate by reactive laser ablation of a liquid Al target in NH₃ using a 248 nm laser. The liquid Al target was prepared with an electron beam in a rotating crucible. The surface of the rotating liquid Al target was always smooth. Spiral growth features were greatly suppressed. AlN films have a surface roughness less than 0.3 nm. The X-ray rocking curve's narrowest FWHM was 180 arcsec, which is nearly identical to that recently reported in films grown by MOCVD or reactive MBE.     

Analysis of polyacrylamide gels for trace metals using diffusive gradients in thin films and laser ablation inductively coupled plasma mass spectrometry

A simple method for the analysis of polyacrylamide diffusive gradients in thin film (DGT) gels by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), employing a novel use of (115)In internal standardization, has been developed. This method allows the determination of Co, Ni, Cu, Zn, Cd, and Pb concentrations (at the DGT filter face) or fluxes in sediments at a spatial resolution of 100 microm. Single-layered gels, using an optimized laser defocus of 4000 microm at 400 mJ power, showed high precision (generally approximately 10%) and a linear response during solution deployment. Of the elements Sc, In, Ba, La, Ce, and Tb, Ba most closely tracked variations in laser energy and showed the highest analytical precision but could not be used as an internal standard due to its elevated presence in natural sediments. Therefore, internal standardization, necessary to normalize data collected on different days, was carried out using (115)In contained within a second layer of backing gel and dried along with the analyte layer as a dual-gel disk. This multilayered gel standard required a laser defocus setting of 1000 microm and a laser power of approximately 800 mJ. Analytical precision for a 64-spot ablation grid at 100-microm spacing was approximately 10%. Verification of this method was carried out on DGT sediment probes deployed in Priest Pot (English Lake District). Results obtained by conventional slicing techniques and aqueous elution agreed with laser ablation results when the different sampling areas were considered. The elution results varied by a factor of <2, whereas the laser ablation technique showed a variability of approximately 4, indicating localized elevated concentrations of Co. This higher resolution LA-ICPMS method could ultimately lead to an improved understanding of the geochemical processes responsible for metal uptake and release in sediments.     

Piezoelectric thin films: evaluation of electrical and electromechanical characteristics for MEMS devices

We present a new measurement method to characterize piezoelectric thin films utilizing a four-point bending setup. In combination with a single- or a double-beam laser interferometer, this setup allows the determination of the effective transverse and longitudinal piezoelectric coefficients e31,f and d33,f, respectively. Additionally, the dielectric coefficient and the large signal electrical polarization are measured to add further important characteristics of the film. These data are essential for piezoelectric thin film process specification and the design and qualification of microelectromechanical systems devices.     

Electrical,morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells

Molybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in “substrate configuration” thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films.     

Synthesis of biomaterial thin films by pulsed laser technologies: Electrochemical evaluation of bioactive glass-based nanocomposite coatings for biomedical applications

The surface of biomedical titanium implants has been covered with thin films of bioactive glass and bioactive glass + poly(methyl methacrylate nanocomposite) in order to increase the resistance to corrosion and improve the bioactivity of their area in contact with bone tissue. To this purpose Pulsed Laser Deposition and Matrix Assisted Pulsed Laser Evaporation with an excimer laser source have been applied.The layer assessments under conditions that simulate their biological interaction with the human body fluids and resistance to degradation have been studied by electrochemical polarization and electrochemical impedance spectroscopy. The poly(methyl methacrylate) addition to bioglass has reduced the bone ability to bond but resulted in a significant increase of the shielding efficiency against corrosion of the applied coatings.The obtained results support the application of bioactive glass and composite bioactive glass + poly(methyl methacrylate) coatings for the development of advanced highly stable implants and prostheses that cannot be affected by corrosion.     

Deposition and characterization of reactive magnetron sputtered aluminum nitride thin films for film bulk acoustic wave resonator

This work studies the relationship between the deposition process parameters and the properties of sputtered c-axis-oriented aluminum nitride (AlN) thin films. AlN films were deposited on a Pt electrode by reactive magnetron sputtering under various deposition conditions. The films were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). A polycrystalline AlN film with highly c-axis-preferred orientation was achieved. The XRD rocking curve was 2.7°. The FESEM photographs also show that the AlN film has a dense hexagonal surface texture with uniform grain size and a highly ordered column structure.