D.-L. Liu

Metal-coated Si springs: Nanoelectromechanical actuators

We demonstrated a nanoscale electromechanical actuator operation using an isolated nanoscale spring. The four-turn Si nanosprings were grown using the oblique angle deposition technique with substrate rotation, and were rendered conductive by coating with a 10-nm-thick Co layer using chemical vapor deposition. The electromechanical actuation of a nanospring was performed by passing through a dc current using a conductive atomic force microscope (AFM) tip. The electromagnetic force leads to spring compression, which is measured with the same AFM tip. The spring constant was determined from these measurements and was consistent with that obtained from a finite element analysis.

Magnetic properties of Co nanocolumns fabricated by oblique-angle deposition

The magnetic properties of columnar Co films on SiO2 substrates fabricated by oblique-angle incident thermal evaporation at room temperature were systematically examined by multiple techniques, including magnetic force microscopy (MFM), magneto-optical Kerr effect (MOKE), and scanning electron microscopy (SEM). Films with thickness ranging from 50 to 500 nm were deposited at the incident angles θ (with respect to substrate normal) from 0° to 85°. For films with thickness of ∼500 nm, the SEM shows the column tilt angle β increases as the θ angle increases and β 60° . The result implies that for θ>60°, the axis parallel to the incident beam behaves more like the in-plane easy axis. These magnetic anisotropies are correlated to the angular-dependent columnar structure of Co films.The magnetic properties of columnar Co films on SiO2 substrates fabricated by oblique-angle incident thermal evaporation at room temperature were systematically examined by multiple techniques, including magnetic force microscopy (MFM), magneto-optical Kerr effect (MOKE), and scanning electron microscopy (SEM). Films with thickness ranging from 50 to 500 nm were deposited at the incident angles θ (with respect to substrate normal) from 0° to 85°. For films with thickness of ∼500 nm, the SEM shows the column tilt angle β increases as the θ angle increases and β<θ. The MFM images show that for 55°<θ<75°, stripe domains are formed and are nearly parallel to the direction of incident vapor beam. The hysteresis loops obtained from MOKE show that along the direction perpendicular to the incident vapor beam the coercivity Hc stays almost constant for all θ angles and the squareness decreases as the θ increases. This is in contrast to the increase of Hc and the increase of squareness in the direction parallel to ...

Physical properties of nanostructures grown by oblique angle deposition

Isolated three-dimensional nanostructures were grown on templated or flat substrates by oblique angle deposition with or without substrate rotation where the physical shadowing effect dominates and controls the structures. The mechanical and electromechanical properties of Si springs and Co coated Si springs were measured by atomic force microscopy. The electrical property of β-phase W nanorods were measured by scanning tunneling microscopy. Examples of measurements of the elastic property of springs, electromechanical actuation, field emission of electrons, and field ionization of argon gas are presented. Potential applications and improvements of growth of uniform nanostructures are discussed.

Molecular Caulking A Pore Sealing CVD Polymer for Ultralow k Dielectrics

Porosity has been introduced in existing low-k interlayer dielectrics to further reduce their dielectric constant. It is desirable to deposit a metallic layer on top of the porous dielectric by chemical vapor deposition (CVD). However this presents the challenge of preventing the precursor from penetrating into the porous dielectric and depositing metal within this insulating layer. In the present paper a low-k CVD polymer capping (Molecular Caulking) is deposited at room temperature onto the porous ultralow k dielectric methyl silsesquioxane. Experiments show that the Molecular Caulking prevents precursor penetration during subsequent metallorganic CVD. In addition, while the Molecular Caulking itself slightly penetrates into the methyl silsesquioxane, it does not appreciably increase surface roughness or film dielectric constant.

Size effect and strain rate sensitivity in benzocyclobutene film

The mechanical properties of benzocyclobutene film are investigated at the nanoscale by nano-indentation using atomic force microscopy (AFM). The force versus indentation depth data were collected with two different AFM tips of radii ∼20 and ∼380nm. A strong size effect of the plastic flow stress was observed as the radius of the indenter tip was reduced. More important, the material exhibited pronounced strain rate sensitivity when probed at the nanoscale, while it was rate insensitive at larger scales. These two size effects were quantified by analytic and finite element modeling.