Rochael J. Collins

Synthesis and characterization of TiO2 thin films on organic self-assembled monolayers: part I. Film formation from aqueous solutions

Self-assembled monolayers (SAMs) bearing sulfonate (-SO 3 H) surface functional groups, on single-crystal Si wafers, were used as substrates for the deposition of TiO 2 thin films from aqueous solutions. Polycrystalline TiO 2 thin films over 50 nm thick formed in 2 h by hydrolysis of TiCl 4 in aqueous HCI solutions at 80 °C. The films were pore-free, showed excellent adherence and uniformity, and consisted of anatase crystallites 2–4 nm in diameter. Annealing at temperatures up to 600 °C caused coarsening of the anatase grains, but no loss of adherence or structural integrity.

Performance Impact of Monolayer Coating of Polysilicon Micromotors

This paper reports the impact on performance of flange-bearing polysilicon micromotors for different self-assembled monolayer coatings on the surface of released motors. Octadecyltrichlorosilane (OTS) and (3,3,3-trifluoropropyl) trichlorosilane (TFP) are found to be promising as they significantly improve micromotor performance. Micromotors coated with OTS show a stable rotor speed and minimum operating voltage during a nine-month testing period. The experiments on gear ratio as a function of wobble cycles indicate that wear in a bearing without OTS coating is significant and results in changes in the gear ratio from the start of micromotor operation by as much as 40%, while the change of gear ratio is within 4% for near 80 million wobble cycles over a nine-month testing period for motors with OTS coating. For motors coated with TFP, no stiction and no significant change of the gear ratio are observed for the testing duration. However, the study of gear ratio as a function of wobble cycles shows that the rotor speed fluctuates in the beginning and then stabilizes for wobble micromotors coated with TFP. OTS coating is found to decrease the flange frictional force/torque by a factor of about 1.5. This net reduction of the flange friction force/torque comes about from the combined action of increasing the frictional coefficient from 0.36 to 0.55 and decreasing the normal contact force associated with the rotor/flange contact friction from near 0.8 μN to near 0.3 μN

Low temperature deposition of patterned TiO2 thin films using photopatterned self‐assembled monolayers

Patterned thin films of TiO2 were deposited from aqueous solution onto photopatterned self‐assembled monolayer (SAM) films on Si substrates. Regions of the SAM containing sulfonate surface functionality were created by the photo‐oxidation of initially deposited thioacetate groups through a mask. The nanocrystalline TiO2‐on‐SAM films were deposited selectively on the photolyzed regions of the SAM. The electrical properties of such films were assessed for potential microelectronic device applications. Current–voltage and capacitance–voltage measurements made on nonpatterned TiO2 films yielded values of relative permittivity ranging from 24 to 57, film resistivities of 1.0–1.5×109 Ω cm and breakdown voltages in excess of 1 MV/cm.

Synthesis and characterization of TiO 2 thin films on organic self-assembled monolayers: Part II. Film formation via an organometallic route

Crystalline, uniform, adherent, ultrathin films of TiO 2 were deposited onto OH-functionalized organic self-assembled monolayers (SAMs) on single-crystalline Si at low-temperature ( 2 by x-ray photoelectron spectroscopy, electron diffraction, and energy-dispersive x-ray microanalysis. Transmission electron microscopy showed the films to be uniform in thickness (2 ± 0.5 nm) and continuous. On bare Si, in contrast, there was no evidence of TiO 2 deposition under identical conditions. Unlike the anatase films deposited on SAMs from aqueous solutions (described in the preceding paper), the electron diffraction patterns of the films deposited from alkoxide solutions suggest that they were the rutile phase. It is suggested that the functionalized SAMs enable the anchoring of the Ti alkoxide and initiate the formation of an adherent oxide film, and that they are sufficiently uniform that the resulting film is continuous and uniform in thickness.

Deposition of oxide thin films on silicon using organic self-assembled monolayers

Crystalline oxide thin films have been synthesized at low temperatures from aqueous liquid solutions. A key element of the approach is the use of organic self-assembled monolayers (SAMs) on the substrate to promote the growth of adherent inorganic films. A SAM is a close- packed, highly ordered array of long-chain hydrocarbon molecules, anchored to the substrate by covalent bonds. The terminating functional group on the SAM surface is chosen so as to initiate and help sustain the formation of the oxide film when the substrate is immersed in the oxide precursor solution. Synthesis, microstructural characterization, and properties of TiO2, ZrO2, SiO2, and Y2O3 films are surveyed. Crystalline films were formed either directly from solution, or through subsequent heat treatments at temperatures that in most cases were lower than typical sol-gel or vapor phase deposition processes. All depositions were from aqueous solutions onto single-crystal (100) silicon. The ability to produce patterned films on a micron scale has been demonstrated, taking advantage of the selective deposition characteristics towards different surface functional groups of the SAM. The role of the SAM in oxide film formation is discussed.