Multilayers For Applications Research Articles

Vertical Electrical Conductivity of ZnO/GaN Multilayers for Application in Distributed Bragg Reflectors

We have demonstrated an electrically conductive ZnO/GaN multilayer structure using hybrid plasma-assisted molecular beam epitaxy. Electrical I-V characteristics were measured through the top three pairs of a six pair ZnO/GaN sample. The total measured resistance was dominated by lateral and contact resistances, setting an upper limit of similar to 10(-4) Omega.cm(2) for the vertical specific series resistance of the stack. A strong contribution to the low resistance is the cancellation of spontaneous and piezoelectric polarization that occurs in the in- plane strained ZnO/GaN sample, as shown by electrical simulations. In addition, the simulations show that the actual vertical resistance of the sample could in fact be three orders of magnitude lower and that ZnO/GaN structures with thicknesses fulfilling the Bragg condition should have similar resistance. Our results suggest that ZnO/GaN distributed Bragg reflectors (DBRs) are a promising alternative to pure III-nitride DBRs in GaN-based vertical-cavity surface-emitting lasers.

Cr/Sc/Mo multilayer for condenser optics in water window microscopes

We developed a high-reflectance wide-reflection-band multilayer for application in condenser optics in microscopes working in the water window soft X-ray region. Grazing incidence 20 period Cr/Sc multilayers suffered damage when they were deposited on toroidal substrates, possibly because of the compressive stress of the thick Sc layers present in them. To avoid such damages, we minimized the Sc layer thickness by using a Cr/Sc/Mo 10 tri-layer structure. The resulting multilayer had a periodic thickness of 9.8nm to reflect 310eV soft X-ray at an angle of incidence of 77.2°. The multilayers were successfully deposited on Si wafers and concave BK7 substrates by ion beam sputtering with no damage. The peak height, angular acceptance, and spectral width of the measured reflectance of the Cr/Sc/Mo 10 tri-layer were 27.4%, 1.5°, and 35eV, respectively, showing that it was suitable for condenser optics of broadband high-Z plasma soft X-ray sources.

Study and characterization of W/Si and W/B4C multilayer for applications in hard X-rays mirror

Multilayer thin films with 2.3 nm-7.6 nm of d-spacing were deposited on fusion glass and float glass substrates by magnetron sputtering. Multilayer thin film with a lower interface roughness was deposited at an abnormal discharge region of I-V characteristic curve in DC glow discharge, compared to normal discharge region. Interface roughness of periodical multilayer in general depends on layer thickness, but in this study interface roughness was controlled by adjusting deposition conditions regardless of layer thickness. But interface roughness and X-ray reflectivity (XRR) of multilayer react sensitively to surface roughness of substrate. Multilayer thin film with 2.3 nm d-spacing shoes 42% of characteristic X-ray reflectivity(Cu Kα, λ=∼0.154 nm), while 3.6 nm d-spacing shows 80% of reflectivity. XRR, transmission electron microscope (TEM) and atomic force microscopy (AFM) were used to analyze the interface roughness (σ), surface roughness and d-spacing.

Numerical modeling of self-propagating reactions in Ru/Al nanoscale multilayer foils

The Ru/Al system integrates high energy density and high product ductility and serves as an alternative for utilization as nanoscale reactive multilayer. We present a modeling study that relates the Ru-Al phase transformations occurring during self-propagating reactions with macroscopic reaction parameters such as net front velocity and reaction temperature. We coupled equations for mass and thermal transport and used a numerical scheme to solve the differential equations. We calculated the temporal evolution of the temperature distribution in the reaction front as a function of the multilayer bilayer thickness. The calculated net velocities were between 4.2 m/s and 10.8 m/s, and maximal reaction temperatures were up to 2171 K, in good agreement with measured data. Interfacial premixing, estimated to be around 4 nm, had a large influence on reaction velocities and temperature at smaller bilayer thicknesses. Finally, the theoretical results of the present study help to explain the experimental findings and guide tailoring of reactive properties of Ru/Al multilayers for applications.

TiOx/Ag/TiOx multilayer for application as a transparent conductive electrode and heat mirror

Amorphous TiOx films and Ag layer were deposited by electron-beam evaporation on soda-lime glass at room temperature. The details regarding the structure, surface morphology, and optical properties of the as-prepared TiOx films were examined by X-ray diffraction, scanning electron microscopy, and ultra-violet (UV) -visible-near-infrared (NIR) spectrometry. The TiOx films exhibit amorphous phase with an optical band gap of 3.35 eV. The polygrains oriented along the (111) and (200) directions in the Ag films were adopted to supply carriers into the TiOx film and lower the sheet resistance of the stacked layer. The multilayer exhibited a sufficiently large Ag thickness (>15 nm), low resistance, high UV transmittance, visible transmittance, and high NIR reflection. Dependence of Ag thickness, TiOx bottom-layer, and TiOx overlayer on the optical and electrical properties of TiOx/Ag/TiOx were explored. A figure of merit (FOM) was used to find an optimal structure for a multilayer with superior conductivity and visible transparency. An FOM of 9.8 × 10−2 (Ω−1) at the visible wavelength of 550 nm for a TiOx/Ag/TiOx stacked layer with an 18-nm-thick Ag and a 20-nm-thick TiOx was achieved. The TiOx/Ag/TiOx sample annealed at 500 °C 10 min also shows a good thermal stability.

Atomic layer deposition of Al_2O_3 and TiO_2 multilayers for applications as bandpass filters and antireflection coatings

Al(2)O(3) and TiO(2) thin films have been deposited on Si wafers, quartz, BK7 glass, and polycarbonate substrates by atomic layer deposition (ALD). The refractive indices and growth rates of the materials have been determined by spectroscopic ellipsometry and transmission electron microscopy. The influence of substrate temperature and precursor on the refractive indices has been investigated. The refractive index of TiO(2) significantly increases with temperature, whereas the Al(2)O(3) films are temperature insensitive. The films deposited using H(2)O(2) as oxygen source show a slightly higher refractive index than the films prepared with H(2)O. Multilayer narrow-bandpass filters and broadband antireflective coatings have been designed and produced by ALD.

Pure Nuclear Reflection fromnaturalFeN0.7/57FeN0.7Multilayer

Amorphous alloy of Fe–N with ∼40 at.% N has been prepared by reactive ion-beam sputtering. A systematic study of the growth behaviour, thermal stability, atomic diffusion and the magnetic properties of the alloy has been done. Deposition characteristics of the film have been studied using the x-ray reflectivity and the atomic force microscopy techniques. The results suggest that it is a suitable system for preparing isotopic multilayers for application as the nuclear Bragg monochromator. Pure nuclear Bragg reflections have been observed from an isotopic multilayer of composition: float glass (substrate)/[ nat FeN 0.7 (30 A)/ 57 FeN 0.7 (20 A)] ×10 / nat FeN 0.7 (30 A). A nuclear Bragg peak because of isotopic periodicity is observed at an angle of 0.55°. where the electronic scattering is of the order of 10 -3 . A nuclear reflectivity of 2.5% has been obtained at the first Bragg peak.

Mo/Si multilayers for EUV lithography by ion beam sputter deposition

Mo/Si multilayers for applications in extreme ultraviolet (EUV) lithography have been prepared on Si wafer substrates using ion beam deposition. The multilayers were characterised by transmission electron microscopy, secondary ion mass spectroscopy, atomic force microscopy, photoelectron spectroscopy, X-ray reflectometry at grazing incidence, and EUV-reflectivity measurements at nearly normal incidence. The surface and the interfaces of the multilayers are rather smooth with only small roughness. The material properties of the layers are characterised by some intermixing and silicide formation at the Mo–Si interfaces and a polycrystalline grain structure of the Mo layers, which is in agreement with prior studies. Appearance of multilayer diffraction spots, well-resolved Kiessig fringes and other diffraction evidence indicate very good coherence of the wave fields and in this manner a good reproducibility of the multilayer period of 6.7 nm. Normal incidence peak reflectivities of 64–65% in the EUV spectral range were routinely obtained at 13.4 nm wavelength. This reflectivity value and the formation of an EUV standing wave field are confirmed using photoelectron spectroscopy, and an application for defect particle analysis is proposed. The obtained results are discussed in comparison to literature data of multilayers prepared by other deposition techniques and considering new attempts of interface engineering.

Magnetic thin films for high-density recording

Magnetic and magneto-optic recording technologies are continuing to evolve at a rapid pace resulting in longer playing times and more data being stored in ever decreasing volumes. Thin-film media are playing an important role in this process. Three different type of thin-film media are discussed here, namely, a hard disk application for data recording, metal-evaporated tape for audio/video applications and CoNi/ Pt multilayer for application as a magneto-optic media for blue laser recording. The relationship between deposition parameters (evaporation and sputtering), structural parameters and magnetic and recording behaviour are discussed.

Design and manufacture of sputtered multilayers for applications to soft X-ray optics

Des muticouches nanometriques ont ete deposees par pulverisation diode rf ultravide dans une chambre equipee d'ellipsometres in situ. L'influence de la composition, de la rugosite, de la presence d'une couche d'interface et du nombre de periodes a ete estimee afin d'optimiser les empilements pour la reflexion de rayons X mous. Le comportement de ces structures sous recuit thermique a ete observe. Enfin des reseaux ont ete realises avec succes

Manufacture and performances of rhodium/carbon multilayer x-ray mirrors

A diode rf-sputtering technique was used to produce Rh/C multilayers for application in the soft-x-ray domain. In situ kinetic ellipsometry is used to calibrate the deposition rates and to analyze precisely the interface structure formation. Grazing x-ray reflectivity at the Cu-Kα line (1.54 Å), and absolute soft-x-ray reflectivity at the Cu-Lα line (13.33 Å) and at the C-Kα line (44.7 Å) are also measured on the same multilayers. A model which assumes a quasi-sharp C-Rh interface (4 Å thick) and a diffused Rh-C interface (22 Å) in the stack is used to fit the reflectivity curves at the three experimental wavelengths. Reflectivities as high as 22% at 13.3 Å and 24% at 44.7 Å were measured on a 17-period multilayer structure having a period of ≂69 Å.

Characterization of Ultrathin Multilayers for Applications in X-Ray Optics

Ultrathin multilayers have unique physical properties which are of great practical importance. Our interest here is in layer systems suitable for X-ray optical devices, in particular for X-ray mirrors. Optimization of device performance depends upon such factors as the layer uniformity (thickness and composition), interface roughness, and structural irregularities. Techniques such as Rutherford backscattering, X-ray diffraction and Auger profile analysis provide valuable structural information but averaged over comparatively large specimen regions. High-resolution electron microscopy has been used in the present study to gain complementary insight into the local microstructure of various layer systems, based on combinations of Rh,W,C,B4C, grown by diode rf-sputtering. Samples suitable for electron microscopy were prepared in cross-section using standard grinding, dimpling and argon ion-milling techniques. Most observations were made with a JEM-4000EX HREM operated at 400kV, with selected area electron diffraction (SAED) to determine the average bilayer thickness by reference to the diffraction pattern of the Si (110) substrate. Optical diffractograms (ODMs) and digital processing were used for accurate measurement of the lattice spacings visible in the multilayers.