David E. Golden

Effect of growth conditions on surface morphology and photoelectric work function characteristics of iridium oxide thin films

The effect of thermal growth conditions on the morphology and surface work function of iridium oxide thin films grown by annealing Ir thin films in an O2 ambient is presented. The samples were analyzed using x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and photoelectric work function measurements. It is found that, with increasing temperature, IrO2 changes from (110) oriented to a mixture of (110) and (200) during the oxide growth. This is manifested as a sharpening of the photoelectric energy distributions at 800 °C. The surface work function was determined to be 4.23 eV using ultraviolet photoelectron spectroscopy. X-ray photoelectron spectroscopy analysis shows that IrO2 starts to form at 600 °C accompanied by surface roughening. Annealing the Ir film at 900 °C in O2 ambient leads to almost complete desorption of the film.

Field emission characteristics of iridium oxide tips

An important issue in field emission vacuum microelectronics is the stability of the field emitters with the residual ambient gas. Particularly important is that the field emitter tips made of refractory metals like molybdenum, niobium and tungsten are susceptible to oxidation. The corresponding metal oxides are insulating and adversely affect the emission current characteristic by increasing the width of the effective tunneling barrier. With this perspective, we studied iridium oxide field emitters to evaluate the characteristics of conductive oxide tips. We studied the field emission characteristics of iridium and thermally prepared iridium oxide field emitters using field emission microscopy and current–voltage measurements. We found that, upon oxidation, the voltage required to achieve the desired emission current desire dropped significantly. In addition, oxidation led to a decrease of emission current fluctuations. The development of stable conductive oxide field emitters should improve the performa...

Effect of average grain size on the work function of diamond films

The work function of hydrogen-terminated polycrystalline diamond films deposited by electrophoresis on molybdenum was studied using ultraviolet photoelectron spectroscopy with 21.2 eV photons for average grain sizes ranging from 0.32 to 108 μm. The work function has a maximum of about 5.1 eV at 0.32 μm, then decreases with increasing grain size to a minimum of about 3.2 eV at an average grain size of about 4 μm and then increases to a value of about 4.8 eV at a grain size of 108 μm. The results are consistent with a model in which the work function is controlled by the work function of single crystal diamond (111) at the larger grain sizes, graphitic carbon at the smaller grain sizes, and by a negative electron affinity that increases with decreasing grain size due to defects near diamond (111) crystallite edges for the intervening grain sizes. The large change in work function (almost a factor of 2) could be useful to make conductors with different work functions for microelectronic gate structures.

Field emission from molybdenum carbide

The thermal stability and the resiliency of molybdenum carbide field-emission tips deposited at room temperature by electrophoresis have been studied. The field emission from Mo2C films deposited on Mo tips does not change after being heated to 800 °C while exposed to 360 L of air, although MoO2, MoO3, and possibly MoO, are present in the films. The field-emission thresholds agree with photoelectric work functions determined from photoelectron spectroscopy measurements of similarly grown flat samples. These films are found to exist in three distinct phases as a function of temperature after formation by room-temperature electrophoresis. From room temperature to 500 °C, MoO3 is the dominant oxide, from 500 to 775 °C, MoC2 is the dominant oxide, and above 825 °C both oxides have virtually disappeared.

VARIATION OF FIELD EMISSION AND PHOTOELECTRIC THRESHOLDS OF DIAMOND FILMS WITH AVERAGE GRAIN SIZE

We report a decrease in field emission threshold from 3.8 to 3.4 eV for room temperature electrophoresis grown polycrystalline diamond films on molybdenum tips as the diamond average grain size increases from 0.25 to 6 μm. The field emission thresholds agree with photoelectric work functions determined from photoelectron spectroscopy measurements of similarly grown flat samples. In addition, diamond surface states are observed at 0.4, 0.9, and 1.8 eV above the valence band. The results are consistent with an increasing negative electron affinity with grain size due to increased surface hydrogen bonding and with perhaps a contribution from surface defect states.

A compact electron energy analyzer for measuring field emission energy distributions

A simple instrument to determine field emission tip work functions and shape functions from simultaneous current–voltage (I–V) characteristics and field emission energy distributions of field emitter tips and tip arrays is described. This instrument uses a cylindrical energy analyzer with a few correcting elements to simulate a hemispherical analyzer and provides a low cost and more compact alternative to a commercial hemispherical spectrometer. I–V curves and energy distributions may be automatically obtained as a function of time to study field emission tip degradation with usage and/or exposure to gases of interest.

Say It Straight Training with Mothers in Chemical Dependency Treatment.

ABSTRACT Effectiveness of Say It Straight communication training as a treatment component was evaluated with 36 mothers in residential chemical dependency treatment. All were indigent, 32 had previous criminal offenses and 14 were on probation or parole at the time of treatment. Self-reported, disempowering behaviors showed highly significant decreases after SIS training (p < 0.001). Empowering behaviors, quality of family and group life showed significant increases (p = 0.001, p = 0.008, p = 0.015, respectively). Self-esteem, assessed with one group of eight mothers, showed a highly significant increase after training (p = 0.009). Statistically significant differences between mothers in treatment an average of 40 days compared to those in treatment 141 days prior to training disappeared after 10-16 hours of training, although the latter group also showed positive changes. Reports regarding training effectiveness were very positive. Results indicate this training is an important addition to treatment and may have implication for shortened treatment time, increased treatment retention and reduction in relapse/recidivism.

Dynamic stability of field emission from molybdenum microtips exposed to oxygen

The emission current in a molybdenum field emission array can decrease by 50% in 1000 s at an oxygen pressure of 10−6 Torr. To overcome this disadvantage of molybdenum microtips, the effectiveness of dynamic surface cleaning has been investigated in a single-aperture gated-diode configuration. For dynamic surface cleaning, tip surface oxide buildup is balanced by tip oxide removal due to sputtering by ions created in ionizing collisions with field-emitted electrons. The present results demonstrate stable dynamic cleaning with clean and partially oxidized molybdenum tips for currents ranging from 10−11 to 10−9 A with oxygen exposures of up to 1000 L. For currents above 10−9 A, ion bombardment causes the tip shape to become unstable leading to failure with increasing oxygen exposure.

Photoelectric workfunctions of metals oxide films and emission characteristics of molybdenum emitter tips with oxide coatings

Photoelectric work functions of flat thin metal oxides of interest as potential field emission sources for field emission displays have been measured using ultraviolet photoelectron spectroscopy. The samples which include molybdenum, lanthanum strontium cobalt oxide, lead zirconium titanate, lead niobium zirconium titanate have also been characterized with X-ray photoelectron spectroscopy and X-ray diffraction spectroscopy. In addition, field emission measurements have been made with molybdenum and molybdenum coated field emission tips using single tip-gated aperture diodes mounted on a micromechanical motion control system. In these measurements, an electron decelerating lens and a hemispherical electron spectrometer is positioned behind the gated aperture so field emitted electrons passing through the aperture may be decelerated and their energy distribution measured. The emission characteristics and electron energy distributions were measured at different electric field strengths to determine the range of validity of the Fowler-Nordheim equation for the various emitter surfaces.

Effect of SP 3 /( SP 2 + SP 3 ) Carbon Fraction on the Photoelectric Threshold and Electron Affinity of Diamond Films

We report a significant decrease in the photoelectric threshold of chemical vapor deposition grown diamond films as the fraction of sp 3 carbon to sp 2 plus sp 3 carbon in the films decreases. Raman spectroscopy and x-ray photoelectron spectroscopy are used to characterize the different forms of carbon in the films and the sp 3 /( sp 2 + sp 3 ) carbon fraction at the surface. We observe a decrease in the photoelectric threshold from 4.5 eV to 3.9 eV as the sp 3 /( sp 2 + sp 3 ) carbon fraction at the surface decreases from 71% to 55%. Ultraviolet photoelectron spectroscopy of the films shows that they have a negative electron affinity surface. Therefore, the work function of the films decreases from 4.5 eV to 3.9 eV. We propose that the decrease in photoelectric threshold is due to a decrease in the band gap of sp 2 - sp 3 carbon networks at the grain boundaries. The observed decrease in photoelectric threshold can be used to tailor the electronic properties of diamond films for specific applications.