N. J. Ianno

Characterization of pulsed laser deposited zinc oxide

Abstract The pulsed laser deposition of zinc oxide films (ZnO) has been studied as a function of laser wavelength, and substrate temperature. Optical emission spectroscopy of the laser produced plume was used to characterize the deposition process. The deposited films were characterized by X-ray diffractometry, Auger electron spectroscopy, and scanning electron microscopy. Highly textured (002) ZnO films deposited at substrate temperatures of 300 °C with laser wavelengths of 532 nm and 248 nm. However, the energy fluence of 248 nm radiation controls the degree of texturing, allowing highly textured films to be deposited at room temperature.

Deposition of diamond-like carbon on a titanium biomedical alloy

Abstract Much of the orthopedic community now believe that the long-term failure of total hip and knee prostheses is directly or indirectly due to the production of wear particles, particularly polyethylene wear particles which are produced at the articulating interface between the metal component and the high molecular weight plastic component. Therefore, a friction and wear reducing coating on the metal component, which is also biocompatible, should reduce the production of the polyethylene wear particles and dramatically extend hip-implant life. Diamond-like carbon (DLC), with its extreme smoothness, hardness, low coefficient of friction, and biocompatibility is an excellent candidate for such an application. One of the key issues that may limit the utility of DLC in this application is the adhesion of this material to common biomedical alloys. We will show that high adhesion strength between sputter-deposited DLC and a silicon-coated titanium biomedical alloy can be easily achieved.

Thermochromic VO2 sputtered by control of a vanadium-oxygen emission ratio

Abstract The objective of this work is to deposit and characterize coatings containing primarily the VO 2 phase. This phase has a thermochromic semiconductor to metal transition at 68°C. The VO 2 thus becomes more reflective and conductive above the transition temperature. One application uses the change in infrared optical properties for thermal switches near room temperature. Precise stoichiometry is required to deposit VO 2 coatings because of competition from other oxide phases. To achieve this stoichiometric control we deposited VO 2 by controlling a plasma emission ratio of vanadium and oxygen. The emission ratio was processed in real time for feedback control. The feedback involved increasing or decreasing the oxygen flow to maintain a desired ratio. Direct current reactive magnetron sputtering was used with a constant current power supply. We varied the deposition temperature between 350 and 650°C and the amount of oxygen injected into the system from 3.0–3.8 sccm. X-Ray, resistance and reflectance measurements verified that the majority phase of the coatings was VO 2 . The resistance results showed a change of about three orders of magnitude due to the semiconductor to metal transition. The reflectance results showed emittance changes in the infrared between 61.2 and 90%, so this is an excellent material for a thermal switch. Space simulation exposures showed that these films could withstand between 3.7 and 37.2 years in space without forming other phases but that their emittance would degrade during this time.

Formation of pyrite (FeS2) thin films by thermal sulfurization of dc magnetron sputtered iron

Iron films deposited by direct current magnetron sputtering onto glass substrates were converted into FeS2 films by thermal sulfurization. Experiments were carried out to optimize the sulfurization process, and the formation of FeS2 thin films was investigated under different annealing temperatures and times. High quality FeS2 films were fabricated using this process, and single phase pyrite films were obtained after sulfurization in a sulfur and nitrogen atmosphere at 450 °C for 1 h. Film crystallinity and phase identification were determined by using x-ray diffraction. The cubic phase pyrite films prepared were p-type, and scanning electron microscopy studies exhibited a homogeneous surface of pyrite. The authors have found that the best Ohmic contact for their pyrite thin films, using inexpensive metals, was Ni. The following were chosen for the study: Al, Mo, Fe, and Ni, and the one that led to the lowest resistance, 333 Ω, was Ni.

Highly oriented Tl2Ba2Ca2Cu3O10 thin films by pulsed laser evaporation

We have fabricated superconducting thin films on MgO(100) substrates with nearly pure Tl2Ba2Ca2Cu3O10 (2:2:2:3) phase using pulsed laser evaporation and post‐annealing. The films had c axes perpendicular to the substrates. Superconducting films with onset temperatures of 125 K and zero resistance at 110 K were obtained. X‐ray microprobe fluorescence measurements indicate that a typical composition of films is Tl0.66Ba1.77Ca1.46Cu3Ox, which is low in Tl compared to that expected for the 2:2:2:3 phase. A typical grain size is greater than 10 μm as revealed by scanning electron microscopy.

Investigation of the rf and dc hollow cathode plasma-jet sputtering systems for the deposition of silicon thin films

Abstract Both rf and dc hollow cathode plasma-jet sputtering systems have been investigated for thin film semiconductor deposition. These systems were studied as a modification of the well-known rf hollow cathode plasma jet system. The aim of this modification was to provide low temperature deposition of semiconductor silicon and silicon-based alloys as thin films with these plasma jet systems. As a first step, the deposition of an already well explored, hydrogenated amorphous silicon material, a-Si:H, was chosen for experimentation. Plasma erosion of single crystal silicon nozzles in an Ar and H2 working gas mixture was utilized for this purpose. A comparison of both dc and rf hollow cathode plasma jets has been made and correlated to the a-Si:H thin film properties. As a preliminary result, large differences between the properties of a-Si:H thin films deposited using dc and rf plasmas have been found. Monohydride Si:H composition was found for a-Si:H films fabricated using the dc plasma jet system under certain experimental conditions. However, predominantly di-hydride and multi-hydride structures and strong oxidization were found for the a-Si:H films deposited using rf plasma excitation. The sputtering efficiencies of both the rf and dc jet sources for silicon films have been found to be similar.

Aluminum oxynitride coatings for oxidation resistance of epoxy films

Abstract Aluminum nitride (AlN) and aluminum oxynitride (AlNO) films were sputter deposited onto epoxy coated silicon substrates. The films were characterized by: electron microscopy; atomic force microscopy; θ-2θ X-ray diffractometry; and profilometry. The surface morphology of the films was a function of the feed gas oxygen content. Amorphous aluminum oxynitride films formed with oxygen flows of more than 0.5 sccm yielded smooth, continuous coatings over the epoxy. The oxynitride/epoxy/silicon structure was exposed in an electron cyclotron resonance low Earth orbit simulator, and showed 2–3 nm roughening up to the maximum fluence of 2.4×1022 atoms/cm2. This is equivalent to 94–940 days in low Earth orbit, depending on orbit height.

Deposition of electronic quality amorphous silicon, a-Si:H, thin films by a hollow cathode plasma-jet reactive sputtering system

High quality hydrogenated amorphous silicon, a-Si:H, thin films were deposited by means of a dc hollow cathode plasma-jet with magnetic field confinement. Single-crystal silicon nozzles were reactively sputtered in a high density hollow cathode discharge. Only nontoxic gases, argon and hydrogen, were used for this purpose. Different configurations of the dc hollow cathode were used for the deposition process. Electronic quality a-Si:H thin films were achieved with light to dark conductivity ratios >106, with light conductivity near 10−5 S/cm and dark conductivity between 10−11 and 10−12 S/cm. This was accomplished with a specific configuration of the hollow cathode discharge in the silicon nozzle. Our best films have a Tauc band gap near 1.8 eV and an atomic hydrogen concentration of about 14%. The growth rate achieved for the electronic quality a-Si:H films was in the range of 2–3 μm/h.

Ellipsometry study of non-uniform lateral growth of ZnO thin films

Abstract Ellipsometry is normally used to characterize layered structures which have a uniform properties laterally across the area of the probe beam. Ex situ ellipsometry was used to study the lateral variation in film thickness introduced purposely in ZnO films grown by magnetron sputtering.

In situ spectroscopic ellipsometry studies of electron cyclotron resonance (ECR) plasma etching of oxides of silicon and GaAs

Abstract In situ spectroscopic ellipsometry (SE) covering the spectral range from 280 to 1000 nm was performed during RF bias assisted electron cyclotron resonance (ECR) etching of SiO 2 , GaAs oxide, silicon, and GaAs by a CCl 2 F 2 /O 2 mixture. The etch rate of SiO 2 /Si samples as a function of RF bias power, and total pressure was then measured, in situ, for a constant ECR power of 175 W, and CCl 2 F 2 /O 2 flow rate ratio of 1 3 by performing SE at selected wavelengths most sensitive to changes in SiO 2 thickness. A wide range of etch parameters can be investigated without changing samples by employing a relatively thick SiO 2 layer. This allows rapid optimization of the etch parameters, and can also provide accurate endpoint detection in the face of a time-dependent etch rate. Ellipsometric monitoring of bulk silicon and GaAs samples cannot provide in situ etch rates, however, insight into the etch mechanism may be gained by observing the effect of the etch process on the native oxide layer, surface roughness, and in the case of GaAs, on the surface stoichiometry.