P. Terrence Murray

Growth of TiC thin films by pulsed laser evaporation

Abstract Thin films of TiC have been grown on Si (100) substrates by pulsed laser evaporation. Analysis by X-ray photoelectron spectroscopy and by Auger sputter depth profiles indicates that the films grown between RT and 500° C are stoichiometric TiC. Film/ substrate interdiffusion is observed at higher substrate temperatures.

Growth of yttria-stabilized cubic zirconia films on GaAs (100) by pulsed laser evaporation

Abstract Thin films of yttria-stabilized cubic zirconia have been grown on GaAs (100) substrates by pulsed laser evaporation at room temperature. The films deposited at laser power densities of 5 × 10 7 W/cm 2 show little evidence of target splashing. Energy dispersiv X-ray analysis and Auger analysis indicate the target stoichiometry to be maintained in the films. Analysis by Raman spectroscopy shows the films to grow primarily in the cubic phase.

Deposition and characterization of SiC and cordierite thin films grown by pulsed laser evaporation

Thin films of SiC and cordierite were deposited on Si (100) by pulsed laser evaporation (PLE) technique at various substrate temperatures. Auger, X-ray photoelectron spectroscopy, and grazing incidence X-ray diffraction were used to investigate the stoichiometry, chemistry, and structure of the PLE-deposited films. The results indicate that properties of SiC films were affected by the substrate temperature. The SiC films grown at 25 °C were amorphous and were a physical mixture of silicon, carbon and very little SiC. The films deposited at 500 and 900 °C substrate temperature were polycrystalline SiC. The as-deposited cordierite films were stoichiometric crystalline.

Laser–plasma interactions in 532 nm ablation of Si

Single-crystal Si was ablated by pulsed 532 nm laser radiation, and the volume of removed material and the time-resolved current of ejected ions were measured. These data were used to determine the ion fraction of ejected material. The ion fractions provide direct evidence that the break point is due to the laser-plasma interaction. This is confirmed by the speed distributions of the positive ions and from the integrated intensities of the low-speed ion component.

Pulsed-Laser Deposited Transition-Metal Carbides for Field-Emission Cathode Coatings

Thin films of transition-metal carbides ZrC, HfC, and TiC were deposited by pulsed-laser deposition under vacuum. The surface chemistry of the films was characterized with ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy in situ. X-ray diffraction was used to characterize the film structure. TiC was shown to be nearly stoichiometric and polycrystalline. The TiC was applied to a vertically aligned carbon nanotube sample and characterized by field emission. Field-emission results showed enhanced current and current density at a film thickness, 5 nm, not previously reported in the literature. Emission from TiC films was also shown to be less affected by adsorbates during field emission. Pulsed-laser deposition of TiC offers a distinct advantage over other techniques in that high-quality films can be obtained under ultrahigh vacuum conditions without the use of a reactive background gas or excessively high annealing temperatures. The application of TiC by pulsed-laser deposition as a cathode coating shows potential for integration into a fabrication process.

Memristor-based pattern recognition for image processing: an adaptive coded aperture imaging and sensing opportunity

Adaptive coded aperture (diffraction) sensing, an emerging technology enabling real-time, wide-area IR/visible sensing and imaging, could benefit from new high performance biologically inspired image processing architectures. The memristor, a novel two terminal passive device can enable significantly powerful biologically inspired processing architectures. This device was first theorized by Dr. Leon Chua in 1971. In 2008, HP Labs successfully fabricated the first memristor devices. Due to its unique properties, the memristor can be used to implement neuromorphic functions as its dynamics closely model those of a synapse, and can thus be utilized in biologically inspired processing architectures. This paper uses existing device models to determine how device parameters can be tuned for the memristor to be used in neuromorphic circuit design. Specifically, the relation between the different models and the number of states the device can hold are examined.

Fabrication and testing of memristive devices

As semiconductor devices have shrunk further into the nanoscale regime, a new device, the memristor, has been discovered that has the potential to transform neuromorphic computing systems. This device is considered as the fourth fundamental circuit element. It was first theorized by Dr. Leon Chua in 1971 and has been discovered by HP labs in 2008. This paper describes initial efforts at fabricating the memristor devices and examining their properties. Two versions of memristor devices have been fabricated at the University of Dayton and the Air Force Research Laboratory utilizing varying thicknesses of the TiO2 dielectric layers. Our results show that the devices do exhibit the characteristic hysteresis loop in their I-V plots. Further refinement in the devices to achieve stronger hysteresis will be carried out as future work.

Synthesis of Ag Nanoparticles by Through Thin Film Ablation

There are several applications that require a thin layer of nanoparticles that are spread uniformly and without agglomeration over a surface. Among these applications are carbon nanotube synthesis and the development of fuel cells, advanced sensors, and optoelectronic devices. There is a need for improved processes of forming these nanoparticles. Among the numerous methods that have been developed, pulsed laser ablation has proved (ElShall et al., 1995; Burr et al., 1997, Seraphin et al., 1997, Geohegan et al., 1998; Lowndes et al, 1998, Makimura et al., 1998; Becker et al., 1998; Lowndes et al., 1999; Makino et al., 1999; Link and El-Sayed, 2000; Mafune et al., 2000; Mafune et al., 2001; Ogawa et al., 2000; Tang et al., 2001; Ozawa et al., 2001; Hata et al., 2001; Barnes et al., 2002) to be especially effective because of the potential for congruent ablation, the ability to produce nanoparticles of high purity, the ability to deposit nanoparticles on room temperature substrates, and the relative simplicity of the process. One problem with conventional pulsed laser ablation is the observation that the deposited material, in addition to containing nanoparticles, also contains large, m-sized particles. These are formed through a process denoted splashing (Ready, 1963), which occurs when a transient liquid layer is formed in the irradiated volume of the target; liquid droplets can be ejected from the target by the recoil pressure of the expanding gas on the transient liquid layer. Traditionally, splashing has been minimized (but not eliminated) by ablating very smooth targets or by using low laser energy densities. Target splashing is an issue in nanoparticle synthesis since the deposition of large particles within a field of nanoparticles makes it considerably more difficult to exploit the unique properties of isolated, non-agglomerated nanoparticles. Target splashing is also an issue because it represents material waste. There is, therefore, a need for a laser ablation process that further reduces or, ideally, eliminates splashing in nanoparticle synthesis. In addition, there is the further need for a process that minimizes nanoparticle agglomeration

Synthesis of oxidation resistant lead nanoparticle films by modified pulsed laser ablation

Thin layers of lead nanoparticles have been produced by a modified pulsed laser ablation (PLA) process in which smaller nanoparticles were swept out of the ablation chamber by a stream of flowing Ar. Large (μm-sized) particles, which are usually deposited during the standard PLA process, were successfully eliminated from the deposit. The nanoparticles deposited on room temperature substrates were well distributed, and the most probable particle diameter was in the order of 30 nm. Since lead is highly reactive, the nanoparticles formed in Ar were quickly oxidized upon exposure to air. A small partial pressure of H2S gas was subsequently added to the effluent, downstream from the ablation chamber, and this resulted in the formation of nanoparticle deposits that were surprisingly oxidation resistant. The properties of the nanoparticle films (as determined by transmission electron microscopy, scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and conductivity measurements) are ...

Memristor fabrication and characterization: an adaptive coded aperture imaging and sensing opportunity

The memristor, experimentally verified for the first time in 2008, is one of four fundamental passive circuit elements (the others being resistors, capacitors, and inductors). Development and characterization of memristor devices and the design of novel computing architectures based on these devices can potentially provide significant advances in intelligence processing systems for a variety of applications including image processing, robotics, and machine learning. In particular, adaptive coded aperture (diffraction) sensing, an emerging technology enabling real-time, wide-area IR/visible sensing and imaging, could benefit from new high performance biologically inspired image processing architectures based on memristors. In this paper, we present results from the fabrication and characterization of memristor devices utilizing titanium oxide dielectric layers in a parallel plate conuration. Two versions of memristor devices have been fabricated at the University of Dayton and the Air Force Research Laboratory utilizing varying thicknesses of the TiO2 dielectric layers. Our results show that the devices do exhibit the characteristic hysteresis loop in their I-V plots.