A measured force resolution of 5.6×10−18 N/Hz at 4.8 K in vacuum using a single-crystal silicon cantilever only 600 Å thick is demonstrated. The spring constant of this cantilever was 6.5×10−6 N/m, or more than 1000 times smaller than that of typical atomic force microscope cantilevers. The cantilever fabrication includes the integration of in-line tips so that the cantilever can be oriented perpendicular to a sample surface. This orientation helps suppress cantilever snap-in so that high force sensitivity can be realized for tip-sample distances less than 100 Å.
A magnetic resonance force microscope with a “tip-on-cantilever” configuration was used to compare imaging characteristics of paramagnetic and ferromagnetic samples. Three-dimensional electron paramagnetic resonance (EPR) imaging of diphenylpicrylhydrazil (DPPH) particles was accomplished by scanning the sample in two dimensions while stepping an external field. The EPR force map showed broad response reflecting the size and shape of the sample, allowing a three-dimensional real-space magnetization image to be successfully reconstructed. In contrast to the EPR case, ferromagnetic resonance imaging of a micron-scale yttrium iron garnet sample showed no significant line broadening despite the strong field gradient (∼10 G/μm). Two-dimensional force maps revealed spatial dependence of magnetostatic and magnetoelastic modes.
Advantages of superconducting quantum interference device-detected magnetic resonance over conventional high-frequency electron paramagnetic resonance for characterization of nanomagnetic materials
We propose a novel strategy to integrate the nanoimprint lithography (NIL) technique with directed self-assembly (DSA) of block copolymer (BCP) for providing a robust, high-yield, and low-defect-density path to sub-20 nm dense patterning. Through this new NIL-DSA method, UV nanoimprint resist is used as the DSA copolymer pre-pattern to expedite the DSA process. This method was successfully used to fabricate a 1.0 Td in(-2) servo-integrated nanoimprint template for bit-patterned media (BPM) application. The fabricated template was used for UV-cure NIL on a 2.5-inch disk. The imprint resist patterns were further transferred into the underlying CoCrPt magnetic layer through a carbon hard mask using ion beam etching. The successful integration of the NIL technique with the DSA process provides us with a new route to BPM nanofabrication, which includes the following three major advantages: (1) a simpler and faster way to implement DSA for high-density BPM patterning; (2) a novel method for fabricating a high-quality dot pattern template through an iterative imprint-DSA-template procedure; and (3) an uncomplicated integration scheme for implementing non-periodic servo features with BCP patterns, thus accelerating the transition of moving the DSA technique from laboratory research to the BPM manufacturing environment.
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