We present X-ray photoelectron spectroscopy data which show that the chemisorbed oxygen previously observed to be on the surface of thin AlO x layers formed by room temperature thermal oxidation is bound by oxygen vacancies in the oxide. Increasing the electric field across the oxide, either by over-coating with a metallic electrode, or by electron bombardment, drives this surface chemisorbed oxygen into the vacancy sites. Due to the low bonding energies of these oxygen sites, subsequent oxygen exposures draw these

Cyanate esters are a class of thermal resistant polymers widely used as thermal resistant and electrical insulating materials for electric devices and structural composite applications. In this article, the effect of 2,2Ј-diallyl bisphenol A (DBA) on catalyzing the thermal curing of cyanate ester resins was studied. The curing behavior, thermal resistance, and thermal mechanical properties of these DBA catalyzed cyanate ester resins were characterized. The results show that DBA is especially suitable for catalyzing the polymerization of the novolac cyanate ester resin (HF-5), as it acts as both the curing catalyst through depressing the exothermic peak temperature (T exo ) by nearly 100°C and the toughening agent of the novolac cyanate ester resin by slightly reducing the elastic modulus at the glassy state. The thermogravimetric analysis and dynamic mechanical thermal analysis show that the 5 wt % DBA-catalyzed novolac cyanate ester resin exhibits good thermal resistance with T d 5 of 410°C and the char yield at 900°C of 58% and can retain its mechanical strength up to 250°C.

Cyanate esters are a class of important thermally resistant polymers. To tailor their processability and thermomechanical properties, a series of cyanate ester blends based on a trifunctional novolac cyanate ester (HF-5), a difunctional bisphenol E cyanate ester (HF-9), and a reactive catalyst [2,2 0 -diallyl bisphenol A (DBA)] were formulated. The effect of the blend composition on the rheology and curing behavior of these cyanate ester blends and the corresponding thermal and mechanical properties of the cured cyanate ester blends was studied. The results showed that HF-5 contributed to good mechanical property retention at high temperatures because of its trifunctionality, whereas HF-9 imparted processability by reducing the viscosity and extending the pot life of the formulated cyanate ester blends at the processing temperature. On the basis of the results, an optimal cyanate ester blend suitable for resin transfer molding was determined: the HF-5/HF-9/DBA weight ratio of 80 : 15 : 5 exhibited good processability and thermomechanical properties.

We report scanning tunneling microscopy and ballistic electron emission microscopy studies of the electronic states of the uncovered and chemisorbed-oxygen covered surface of AlOx tunnel barrier layers. These states change when chemisorbed oxygen ions are moved into the oxide by either flood gun electron bombardment or by thermal annealing. The former, if sufficiently energetic, results in locally well defined conduction band onsets at ∼ 1 V, while the latter results in a progressively higher local conduction band onset, exceeding 2.3 V for 500 and 600 C thermal anneals.The prevalence of aluminum oxide layers formed by room temperature oxidation as the barrier in Josephson junctions (JJ) 1 and magnetic tunnel junctions (MTJs) 2 continues to motivate efforts to better understand and control its electronic structure. While bulk, stoichiometric Al 2 O 3 has a band gap of ∼ 8.8 eV, 3 for amorphous AlO x films grown at ∼ 20 C it is a much smaller. This is beneficial as thin, transparent barriers provide the high critical current densities (JJs) and low specific impedance levels (MTJs) required by many applications, but band tails, localized states, and spatial inhomogeneities that may also be found in amorphous AlO x 4,5,6 can be very detrimental for high performance, low noise applications. 7,8 Indeed, conducting atomic force microscopy studies of AlO x layers have shown inhomogeneous current distributions at the nanoscale, attributed to either a variation in local barrier heights 9 or in barrier thickness 10 . However, a serious challenge for such surface spectroscopy studies of the electronic properties of AlO x is that the surface is invariably covered, even in ultra-high vacuum (UHV), with chemisorbed oxygen bound by positively charged oxygen vacancies in the oxide, with the degree of coverage depending on oxide thickness. 6,11 We report the use of scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM) to examine the density of states (DOS) of the AlO x surface, and to determine how these states change when chemisorbed oxygen ions are moved into the oxide by either flood-gun electron-bombardment (FGEB), or by thermal annealing. Both treatments greatly reduce, if not eliminate, low energy band tail states and narrow the DOS distribution over an oxide area. However FGEB, which we argue has similarities in effect to depositing a metallic over-layer with a high work function φ, causes different changes in the DOS than annealing. The former, if sufficiently energetic, results in locally well defined conduction band onsets at ∼ 1 V, while the latter results in a progressively higher local conduction band onset, exceeding 2.3 V for 500 and 600 C anneals.We fabricated the samples for this study via thin film thermal evaporation and post-growth processing in UHV. For most samples, we deposited 12 nm of Au on hydrogen terminated (111) Si to form a high quality Schottky barrier (SB) to serve as the BEEM detector. This was followed by a 1.2 nm buffer layer of Cu, 1.2 nm Co, and finally 1 nm Al,...

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