Al2O3 films were deposited by atomic layer deposition (ALD) at temperatures as low as 33 °C in a viscous-flow reactor using alternating exposures of Al(CH3)3 (trimethylaluminum [TMA]) and H2O. Low-temperature Al2O3 ALD films have the potential to coat thermally fragile substrates such as organic, polymeric, or biological materials. The properties of low-temperature Al2O3 ALD films were investigated versus growth temperature by depositing films on Si(100) substrates and quartz crystal microbalance (QCM) sensors. Al2O3 film thicknesses, growth rates, densities, and optical properties were determined using surface profilometry, atomic force microscopy (AFM), QCM, and spectroscopic ellipsometry. Al2O3 film densities were lower at lower deposition temperatures. Al2O3 ALD film densities were 3.0 g/cm3 at 177 °C and 2.5 g/cm3 at 33 °C. AFM images showed that Al2O3 ALD films grown at low temperatures were very smooth with a root-mean-squared (RMS) roughness of only 4 ± 1 Å. Current−voltage and capacitance−voltage measurements showed good electrical properties of the low-temperature Al2O3 ALD films. Elemental analysis of the films using forward recoil spectrometry revealed hydrogen concentrations that increased with decreasing growth temperature. No other elements were observed by Rutherford backscattering spectrometry except the parent aluminum and oxygen concentrations. Low-temperature Al2O3 ALD at 58 °C was demonstrated for the first time on a poly(ethylene terephthalate) (PET) polymeric substrate. Al2O3 ALD coatings on PET bottles resulted in reduced CO2 gas permeabilities.

A chemical reactor was constructed for growing thin films using atomic layer deposition (ALD) techniques. This reactor utilizes a viscous flow of inert carrier gas to transport the reactants to the sample substrates and to sweep the unused reactants and reaction products out of the reaction zone. A gas pulse switching method is employed for introducing the reactants. An in situ quartz crystal microbalance (QCM) in the reaction zone is used for monitoring the ALD film growth. By modifying a commercially available QCM housing and using polished QCM sensors, quantitative thickness measurements of the thin films grown by ALD are obtained in real time. The QCM is employed to characterize the performance of the viscous flow reactor during Al2O3 ALD.

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In order to employ Li-ion batteries (LIBs) in next-generation hybrid electric and/or plug-in hybrid electric vehicles (HEVs and PHEVs), LIBs must satisfy many requirements: electrodes with long lifetimes (fabricated from inexpensive environmentally benign materials), stability over a wide temperature range, high energy density, and high rate capability. Establishing long-term durability while operating at realistic temperatures (5000 charge-depleting cycles, 15 year calendar life, and a range from À46 8C to þ66 8C) for a battery that does not fail catastrophically remains a significant challenge. [1] Recently, surface modifications of electrode materials have been explored as viable paths to improve the performance of LIBs for vehicular applications.[2] The cycle life and safety issues have been largely satisfied for Li x MO 2 (M ¼ Co, Ni, Mn, etc.) cathodes by coating the active material particles with a metal oxide and/or metal phosphate. [2a,2b,3] For anode, state-of-the-art materials such as Si suffer from significant volume expansion/contraction during charge-discharge leading to rapid capacity fade.[4] Natural graphite (NG) is a realistic candidate anode, for vehicular applications, due to its high reversible capacity, low and flat potential relative to Li/Li þ , moderate volume change, and low cost.[5] In previous reports, the performance of NG was improved by surface modifications with mild oxidation, [6] coating with amorphous carbon,[5c] metal oxides (Al 2 O 3 , ZrO 2 ), [5a,7] and metal phosphate (AlPO 4 ).[5b] These efforts were performed in order to mitigate the solid electrolyte interphase (SEI) [8] that is formed on the NG surface by reductive decomposition of the electrolyte during initial charge-discharge especially at elevated temperatures. The decomposition of the SEI at elevated temperature ($80 8C) is exothermic and initiates thermal runaway. [9] In most previous reports films of metal oxides and metal phosphates have been deposited on powder electrode materials with 'sol-gel' wet-chemical methods.

Ultrathin atomic layer deposition (ALD) coatings enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that LiCoO2 cathode powders coated with metal oxides with thicknesses of ∼100 to 1000Å grown using wet chemical techniques improved LIB performance. In this study, LiCoO2 powders were coated with conformal Al2normalO3 ALD films with thicknesses of only ∼3 to 4Å established using two ALD cycles. The coated LiCoO2 powders exhibited a capacity retention of 89% after 120 charge–discharge cycles in the 3.3–4.5 V (vs Li/Li+ ) range. In contrast, the bare LiCoO2 powders displayed only a 45% capacity retention. Al2normalO3 ALD films coated directly on the composite electrode also produced improved capacity retention. This dramatic improvement may result from the ultrathin Al2normalO3 ALD film acting to minimize Co dissolution or reduce surface electrolyte reactions. Similar experiments with ultrathin ZnO ALD films did not display enhanced performance.