Browsing by Subject "Scanning probe microscopy."

Now showing 1 - 7 of 7

Open Access
Fabrication and characterization of GaAs and InAs hall sensors
(2004) Özdemir, Serdar
Scanning Hall Probe Microscopy has become a widely used method for magnetic field measurements in the last decade. For Scanning Hall Probe Microscopy, low noise Hall sensors are fabricated from GaAs and InAs structures using optical lithography techniques. Noise analysis of both types of sensors are done at 77 K and 300 K for various Hall currents. Minimum detectable magnetic fields are calculated from these noise measurements. The range of the Hall currents that makes the sensors work most efficiently are also calculated.
Open Access
Grating loaded integrated optical cantilevers
(2010) Karademir, Ertuğrul
Cantilever beams are the most important parts of standard scanning probe microscopy. In this work, an integrated optical approach to sense the deflection of a cantilever beam is suggested and realized. A grating coupler loaded on the upper surface of the cantilever beam couples the incident light to the chip, which is then conveyed through a taper structure to a waveguide to be detected by a photodiode. Deflections of the cantilever beam change the optical path and hence the total transmitted intensity. Finally an optical signal is produced and this signal is measured. Resonance peak of 27.2 Q factor is obtained, which could be further enhanced by proper vibration isolation and employment of vacuum environment.
Open Access
Integrated optical displacement sensors for scanning force microscopies
(2003) Kocabaş, Coşkun
In this thesis, we have studied the use of integrated optical waveguide devices acting as integrated displacement sensors on cantilevers for scanning probe microscopes. These displacement sensors include integrated optical waveguide devices such as Bragg gratings, ring resonators, race track resonators and waveguide Michelson interferometers fabricated on a cantilever to measure the displacement of the cantilever tip due to the forces between surface and the tip. The displacement of the cantilever tip is measured directly from the change of the transmission characteristics of the optical device. As the cantilever tip displaces, the stress on the cantilever surface changes the refractive index of the materials that make up the integrated optical device which cause variations in its optical transmission characteristics. We have also studied an optical waveguide grating coupler fabricated on the cantilever for the same purpose. In two different embodiments of this device, light is either coupled in or out of the waveguide via the waveguide grating coupler. The displacement of the cantilever alters the direction of the scattered light and measuring the power of the scattered light with a position sensitive detector allows for the detection of cantilever i tip displacement. The novel design proposed in this work provides very high displacement sensitivity of the order of 10−4˚A−1 .
Open Access
Investigation of lateral forces in dynamic mode using combined AFM/STM
(2007) Atabak, Mehrdad
In this Ph.D. work, we constructed a ¯ber optic interferometer based non-contact Atomic Force Microscope (nc-AFM) combined with Scanning Tunneling Micro- scope(STM) to study lateral force interactions on Si(111)-(77) surface. The in- terferometer has been built in such a way that its sensitivity surpasses that of the earlier versions used in normal force measurements. The improvement in the resolution of the interferometer has allowed us to use sub-Angstrom oscillation amplitudes to obtain quantitative lateral force measurements. We have observed single and double atomic steps on Si(111)-(77) surface in topography and lat- eral sti®ness images. This information allowed us to measure the lateral forces directly and quantitatively. We have also carried out lateral force-distance spec- troscopy experiments, in which we simultaneously measured the force gradient and tunneling current, as the sample is approached towards the tip. The lateral force?distance curves exhibit a sharp increase of the force gradient, just after the tunnel current starts to increase, while the sample is approaching to the tip. We observed only positive force gradients. In separate experiments, we imaged the Cu-TBPP molecules deposited on Cu(100) surface in normal and torsional mode in dynamic force microscope us- ing STM feedback, with a homemade tungsten cantilever. Our experiments have shown the possibility of manipulating molecules on surface using a vibrating can- tilever. However the forces involved in these experiments are not quantitatively measured due to limitations of the method.
Open Access
Investigation of the magnetic properties of BSCCO superconductors with scanning Hall probe microscope
(2002) Dede, Münir
A low temperature scanning Hall probe microscope (LT-SHPM) with low noise GaAs/AlGaAs 2DEG Hall probes is used to investigate the magnetic properties of a Ag-sheathed BSCCO-2223 tape and a single crystal BSCCO-2212 superconductor. The Hall probes are micro fabricated with 1 µm wide Hall bars which have ∼0.85 µm electrical width. The magnetization behavior, vortex structures and the vortex lattice melting are observed at 77 K. Flux penetration into the BSCCO-2212 single crystal is also observed and imaged with single vortex resolution.
Open Access
Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback
(2005) Ürkmen, Koray
Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of ~50nm & 7mG/ Hz at room temperature. In the SHPM technique, Scanning Tunneling Microscope (STM) or Atomic Force Microscope (AFM) feedback is usually used for bringing the Hall sensor into close proximity of the sample. In the latter, the Hall probe has to be integrated with an AFM cantilever in a complicated microfabrication process. In this work, we have eliminated the difficult cantileverHall probe integration process; a Hall sensor is simply glued at the end of Quartz crystals, which are used as a force sensor. The sensor assembly is dithered at the resonance frequency and the quartz force sensor output is detected with a Lock-in and PLL system. SHPM electronics is modified to detect AFM topography and the phase, along with the magnetic field image. NIST MIRS (Magnetic Referance Sample) (Hard Disk) sample, 100 MB high capacity zip disk and Garnet sample are imaged with the Quartz Crystal AFM feedback and the performance is found to be comparable with the SHPM using STM feedback. Quartz Crystal AFM feedback offers a very simple sensor fabrication and operation in SHPM. This method eliminates the necessity of conducting samples for SHPM.
Open Access
Scanning probe microscopy for optoelectronic characterization at the nanoscale
(2010) Ürel, Mustafa
In this work, we propose methods for electrical characterization of nanostructured surfaces using electrostatic force and tunneling current measurements in scanning probe microscopy. Resolution smaller than 10 nm in electrostatic force microscopy (EFM) is attained and reasons for this attainment is explained in terms of the tip-sample capacitance and mechanical vibrations of tip design. Dynamic measurements are done in EFM using a lumped model for tip-sample electrostatic interaction instead of a simple tip-sample capacitance model. Surface photovoltage measurements are done and assured in EFM using frequency response techniques. Also, combining tunneling current measurements by EFM measurements, optoelectonic properties of graphene/graphene oxide samples are characterized.