Experiments in NMR Force Microscopy*

We report details of the construction and use of three nuclear magnetic resonance force microscopy (NMRFM) probes, as well as the development of control systems for three-dimensional nanoscale imaging and spectroscopy. Our variable temperature probe performed position-dependent $^{1}$H NMR force measurements on a 25x15x7 $\mu $m$^{3}$ single crystal of ammonium sulfate (NH$_{4})_{2}$SO$_{4}$ at room temperature in a sample-on-oscillator geometry. Force signals were detected with a signal-to-noise ratio of 6, and 12 $\mu $m resolution, in a one-dimensional scan. Measurements of NMR relaxation times T$_{2}^{\ast }$=1.5$\pm $0.2 $\mu $s, T$_{2}$= 44$\pm $2 $\mu $s, and T$_{1}$=5.6$\pm $0.7 s were obtained. We describe the upgrade of our $^{3}$He NMRFM probe for measurements towards the base temperature of 0.3K for investigation of nanoscale structures and metal oxide interfaces using the iOSCAR technique and perpendicular-cantilever geometry. Force-detected $^{11}$B NMR signals in a 30 $\mu $m crystal of superconductor MgB$_{2}$ have also been achieved using this probe. Efforts in the development of our NMRFM probe for the study of biological samples in liquid media are reported. Magnetic field effects on micromagnet films on cantilevers are being studied for the characterization of the mechanical sensors to be used in these liquid experiments.