Characterization and Measurement Facilities

The characterization and measurement facilities hosted by the Physics Department at Emory University include a biophotonic imaging system, 3D confocal microscopy imaging system, a variable pressure scanning electron microscope, an atomic force microscope, a Static and Dynamic Light Scattering System, a diffraction-limited bright/darkfield DIC optical microscope, a magnetoelectronic property characterization system, a microwave spectroscopy system, a Vibrating Sample Magnetometer, and a MOKE Magnetometer.

Atomic Force Microscope (AFM) for biological studies

Atomic force microscopy (AFM) is a type of scanning probe microscopy primarily used to produce topological images of surfaces with nanometer-scale resolution. A cantilever with a sharp tip scans an atomically flat surface over which a biological sample is deposited. The deflection of the cantilever that occurs when the tip encounters the sample is recorded and converted to an analog signal that is mapped to the corresponding coordinates to construct topological images. AFM imaging allows for non-destructive characterization of specimens ranging from living cells to single molecules under conditions close to physiological.

AFM can also be used to study the sample response to forces in force spectroscopy/sample manipulation applications.

Equipment

Bruker Nano MultiMode 8

Imaging Modes

PeakForce Tapping™ Mode, PeakForce Tapping™ Mode with ScanAsyst™, Force Spectroscopy, Tapping Mode, Contact Mode, Phase Imaging, Quantitative Nanomechanical Measurements

Capabilities

- Scans up to 10 microns laterally and 2.5 microns vertically

- Stage accommodates samples up to 12 mm x 12 mm

- All modes operate in both air and fluid (at ambient temperature only)

Magnetic Tweezers

Magnetic Tweezers (MT) facilitate the observation and manipulation of micrometer-scale objects.  Commercially available ferromagnetic micro-particles (e.g. Dynabeads®) are coupled to an object of interest, these particles act as magnetic handles with which forces can be exerted.  Once attached, the micro-particle system is added to a custom flow chamber mounted on a motorized magnetic rotor-equipped inverted microscope.  Calibrated force and torque can be applied to the micro-particles, while, simultaneously, real-time 3D particle tracking software allows measurement of the particles translational response.  Typical applications include force-spectroscopy of macromolecular systems such as force-extension and torque-extension measurements of DNA (see figure inset); however, our system is highly adaptable and can be used for a variety of other systems.  

Tethered Particle Microscopy (TPM)

Two TPM systems are available.

The first is based on a Leica differential interference contrast (DIC) DM LB-100 microscope (Leica Microsystems, Wetzlar, Germany) with oil-immersion objectives (100, NA 1.2–1.4 or 63, NA 0.6–1.4). DIC has a high signal/ noise ratio and allows short 1 ms exposures with no significant blurring due to the motion of the beads. Standard interlaced videos at 50 Hz from a CV-A60 CCD camera (JAI, Copenhagen, Denmark) are digitized with an IMAQ PCI-1409 frame grabber (National Instruments, Austin, TX) and analyzed in real time using custom Lab View (National Instruments) routines. The routine accurately tracks multiple beads in real time on a personal computer with 512 MB of 133 MHz RAM and an AMD Sempron 3100þ processor operating at 1.8 GHz.

A second multiplexed TPM microscope is equipped with a larger pixel format camera with data transfer fast enough for video steaming to disk storage in real-time. In this system, a Gigabit Ethernet (gigE) camera (CM-140GE, JAI, Copenhagen, Denmark) is used to acquire images with 1390 X 1040 resolution at 30 frames per second from either DIC or dark field setups. Labview with NI Vision Acquisition Software (National Instruments, Austin, TX) is utilized to grab, display and record the video stream. Using a custom Labview routine, video streams are recorded as uncompressed avi files to the hard drive.  Post-processing methods are employed in order to prevent frame dropping that may occur during real-time analysis.

Biophotonic Imaging System

The system is based on the Olympus IX71 Inverted Microscope equipped with a Spectra Physics Tsunami ultra fast mode locked, TI:S laser pumped by Spectra Physics Millennia Nd:YAG Laser. The system is capable of optical spectrometry, two-photon fluorescence, lifetime imaging and fluorescence correlation spectroscopy.

3D Confocal Microscopy Imaging System

The system is based on a VT-Eye confocal microscope attached to a Leica inverted microscope. It is capable of capturing 30 images per second at 512 x 512 pixel resolution, and up to 400 images/s with a reduced field of view. 3D acquisition can be performed at 256 x 256 x 100 pixel resolution at rate of 1 image per second.

Scanning Electron Microscope

E-beam lithography system is based on the variable-pressure Zeiss EVO MA10 scanning electron microscope with Lab6/W electron source. The highest resolution is 3 nm. Patterning is controlled by the NPGS 9.0 e-beam lithography package.

Atomic Force Microscope

Veeco Dimension 5000 atomic force microscope features a large sample stage that accepts up to 8" samples. It has a full acoustic enclosure and pneumatic vibration isolation.

Static and Dynamic Light Scattering System

The CGS3 compact goniometer system is equipped with a 22 mW HeNe laser, a single photon counting module from Perkin Elmer, and an ALV digital correlator. The system is capable of performing both static and dynamic light scattering experiments with an angular coverage of 17° to 150° at an angular resolution of 0.025°.

Pulsed-Electron Paramagnetic Resonance (EPR) Spectrometer

The home-constructed pulsed-EPR spectrometer operates continuously over X-band (8.2-12.4 GHz) and Ku-band (12.4-18.0 GHz) microwave frequencies. Folded half wave resonators and a modified Varian X-band cavity (TE) resonator are used to achieve different microwave frequencies and optimize different experiments. The detection bandwidth is ≤500 MHz and the pulse timing resolution is ≤1.6 ns. Sample temperatures from <2 K to 295 K are maintained by a Janis cryostat. Electron spin-echo (ESE) experiments are typically performed at 6-30 K. All operations are controlled via GPIB/IEEE-488 PC-device interfaces by using Matlab software.

Optical Microscope

Olympus Provis AX-70 research microscope features brightfield/darkfield illumination modes, a large sample stage, ultrawide view 10x eyepieces, 5x, 10x, 20x, 50x, and 100x Uplan objectives on a motorized turret, an insertable 2x magnifier, a Nomarski differential contrast observation mode, a cube system, and an Olympus DP12 digital camera system.

Magnetoelectronic Characterization System

The home-built variable-temperature magnetoelectronic property measurement system utilizes a closed-cycle Advanced Research Systems cryostat. It operates at temperatures between 4 K and 350 K, and . The magnetic field of up to 5 kOe can be rotated by 360 degrees by a computer-controlled mechanism. Low-noise dc and ac electronic transport measurements are performed with a Signal Recovery 7265 lock-in amplifier, Keithley 6221 current source, and Keithley 6430 sub-femto sourcemeter. The system is fully computer controlled through a Labview-based interface.

Continuous-Wave Electron Paramagnetic Resonance (EPR) Spectrometer

A Bruker E500 spectrometer is used to perform continuous-wave EPR and electron-nuclear double resonance (ENDOR) experiments at X-band (~9.4 GHz) and Q-band (~31 GHz). Different cryostats allow EPR and ENDOR experiments to be performed from 4 K to room temperature.

Microwave Spectroscopy System

The home-built electronic microwave setup features a 4-350 K closed cycle ARS cryostat wired with two 26 GHz microwave signal lines and a 1.5 Tesla GMW Model 5402 electromagnet with in-plane rotation mechanism. An additional home-built magnet allows three-dimensional computer-controlled rotation of the magnetic field. The system is equipped with a 20 GHz Anritsu microwave signal generator, a 20 GHz Anritsu spectrum analyzer, a lock-in amplifier, and Keithley sourcemeter for simultaneous dc electronic and microwave measurements. The system is fully computer controlled through a Labview-based interface.

Vibrating Sample Magnetometer

This magnetometer takes fully computer-controlled measurements, has an innovative permanent magnet-based field source (1.6 kOe limit). It also uses a Signal Recovery 7265 lock-in amplifier with a sensitivity of better than 1E-5 emu, which can accomodate samples up to 1/4".

MOKE Magnetometer

This MOKE Magnetometer uses variable temperature continuous flow cryostat, 1.5-350K range. It is also has a home-built 2.5kG electromagnet and is compatible with longitudinal, transverse, and polar measurement geometries. An additional small 25 Gauss electromagnet built is into the sample stage enabling transverse and longitudinal ac susceptibility measurements at frequencies of up to 20kHz. Full digital control of all functions is accomplished via a Labview-based interface.