Neil R. Murphy

Tunable stoichiometry of BCxNy thin films through multitarget pulsed laser deposition monitored via in situ ellipsometry

Abstract. Pulsed laser deposition is an energetic deposition technique in which thin films are deposited when a laser pulse at 248-nm wavelength strikes a target and material is subsequently deposited onto a substrate with ideally the same stoichiometry. By synchronizing a high-speed mirror system with the pulsing of the laser, and using two separate targets, thin films having tunable stoichiometry have been deposited. Depositions were performed in a high vacuum environment to obtain as much kinetic energy as possible during growth. Typically, some 150 pulses at 300u2009u2009mJ/pulse were required to deposit 1 nm. Island growth must occur on a per pulse basis since over 100 pulses are required to deposit a 1 nm film thickness. Films were deposited to ∼100-nm thickness, and in situ ellipsometry data were modeled to calculate thickness, n and k. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy (AFM) were all performed on each of the films. XPS demonstrated change in film composition with change in laser pulse ratio; ellipsometry displayed thickness from the model generated as well as the optical properties from 370 to 1690 nm. AFM thickness measurements were in agreement with independently modeled ellipsometry thickness values.

Tunable Stoichiometry of SiOx-BaTiOy-BOz Fabricated by Multitarget Pulsed Laser Deposition

Abstract. Oxide materials of desired stoichiometry are challenging to make in small quantities. Nanostructured thin films of multiple oxide materials were obtained by using pulsed laser deposition and multiple independent targets consisting of Si, BaTiO3, and B. Programmable stoichiometry of nanostructured thin films was achieved by synchronizing a 248-nm krypton fluoride excimer laser at an energy of 300u2009u2009mJ/pulse, a galvanometer mirror system, and the three independent target materials with a background pressure of oxygen. Island growth occurred on a per pulse basis; some 500 pulses are required to deposit 1 nm of material. The number of pulses on each target was programmed with a high degree of precision. Trends in material properties were systematically identified by varying the stoichiometry of multiple nanostructured thin films and comparing the resulting properties measured using in situ spectroscopic ellipsometry, capacitance measurements including relative permittivity and loss, and energy dispersive spectroscopy (EDS). Films were deposited ∼150 to 907 nm thickness, and in situ ellipsometry data were modeled to calculate thickness n and k. A representative atomic force microscopy measurement was also collected. EDS, ellipsometry, and capacitance measurements were all performed on each of the samples, with one sample having a calculated permittivity greater than 20,000 at 1 kHz.

Optical Multichannel Imaging of Pulsed Laser Deposition of ZnO

Pulsed laser deposition is an efficient technique to obtain stoichiometric material transfer from target to substrate and has been used by researchers and in industry for depositing materials for use in applications ranging from hard coatings and superconductors to optical materials. The images detailed here will demonstrate the unique plume evolution that occurs and the high-speed ionic species, and slow-speed neutral and molecular species that travel from target material to substrate.

Spectral coherent emission of thermal radiation in the far-field from a truncated resonator

The spectral radiative properties of coherent thermal emission in the mid- and far-IR from two metal-semiconductor resonating structures were demonstrated experimentally. Using an efficient implementation of Rigorous Coupled-Wave Analysis, a truncated resonator was designed to selectively emit at mid-IR and far-IR wavelengths. A High Impulse Power Magnetron Sputtering deposition technique was used to fabricate two Ag-Ge-Ag resonating structures with layer thicknesses of 6-240-160 nm for one sample and 6-700-200 nm for the other. Reflectance measurements demonstrated spectrally selective absorption at the designed mid- and far-IR wavelengths whose general behavior was largely unaffected by a wide range of incident angles. Further, radiance measurements were taken at various high temperatures, up to 601 K, where spectrally selective emission was achieved through wave interference effects due to thermally excited surface waves. From these radiance measurements, spectral emittance was directly derived and compared to the emittance inferred from reflectance measurements. It was established that inferring emittance through Kirchhoff’s law can help to approximate the expected emission from a structure, but it is not an exact method of determining the actual emittance of a thermal source at higher temperatures due to the temperature dependence of material parameters.

Electron-Beam Induced Activation of Catalyst Supports for CNT Growth

The widespread use of carbon nanotubes (CNTs) in numerous practical applications has motivated multi-parameter studies using many support systems, growth conditions and synthesis methods. Among the most widely used support systems in electronics, sapphire is known to be catalytically inactive for CNT growth. Previously, our group demonstrated that the use of ionic bombardment can lead to an increase in CNT growth yield at the irradiated surface of catalytically inactive sapphire.[1] The engineering process was observed to reduce catalyst particle size and extend catalytic activity via the tuning of support stoichiometry and roughness. Therein, activation selectivity could be achieved by means of physically placing a micron-scale mask to impede growth on masked regions. Other studies have also demonstrated the use of ionic bombardment for selective growth of CNTs on slots and pits in other support systems.[2-3] We expand on the use of ionic species for patterned growth by conducting local and selective activation of c-cut sapphire using electron beam (e-beam) irradiation. We demonstrate that we can modify the surface stoichiometry and roughness thus activating the support surface. Exposing the activated sapphire to typical CNT growth conditions resulted in selective growth of vertically aligned CNTs in the activated regions. By varying the irradiation conditions, the process can be tuned to enhance catalytic activity and achieve patterned growth with high-precision.

Modeling and simulation of reactive magnetron co-sputtering for mixed oxide coatings

This work details the development and validation of a variant of the “Berg model for reactive sputtering” that is capable of predicting the chemical valence state of reactively co-sputtered Mo-Ge-O thin films.

High Transparent Conductive Aluminum-Doped Zinc Oxide Thin Films by Reactive Co-Sputtering (Postprint)

Al-doped ZnO films were fabricated using reactive magnetron sputtering simultaneously using separate Zn and Al targets. The AZO films showed high transparency in the visible region and low transmittance in the near IR regions.

Publisher’s note: Tunable stoichiometry of BCxNy thin films through multitarget pulsed laser deposition monitored via in situ ellipsometry

This article [J. Nanophoton.. 8, (1 ), 083890 ( Feb 5 , 2014)] mistakenly appeared in the Special Section on Metamaterials and Photonic Nanostructures. It was republished in the Special Section on Nanostructured Thin Films VI with a corrected CID on 10 February 2014. The updated citation is shown below:

ZnO/Ag Multilayer Stacks for Induced Transmission Filters

ZnO and Ag thin films were deposited using pulsed laser deposition and magnetron sputtering, respectively. Aperiodic ZnO/Ag multilayer stacks exhibited high transmittance in the visible range while blocking UV and IR radition.

Deposition of Metallic and Dielectric Molybdenum Films via Modulated Pulse Power Magnetron Sputtering

The frequency and magnitude of the applied voltage pulses were varied under constant oxygen/argon flow rates to obtain alternating layers of molybdenum trioxide (MoO3) and metallic molybdenum (Mo) using a single Mo target.