In order for CaSTL to achieve its mission of understanding fundamental chemical processes by probing single events in chemistry, photophysics, and nanocatalysis, the Center continues to develop state-of-the-art instrumentation. This instrument is pushing the joint space-time limits of resolution relevant to chemistry.
The combined AFM/STM/NLO is an inverted Olympus microscope frame with a commercial scanning probe AFM/STM microscope attached that is capable to scan by sample or by head. The latter is crucial for laser tip alignment. The instrument allows for simultaneous Raman and backscatter imaging through the microscope objective, along with time-resolved measurements using vector light.
The Ultrafast Single Molecule Imager is an optical far-field microscope interfaced with an ultrafast laser light source. This system was built for the purpose to interrogate the ultrafast optical response of single molecular systems. The instrument derives its high sensitivity from several unique features. First, the laser system, a synchronously pumped femtosecond optical parametric oscillator has a very wide tunable spectral range from the visible to the mid-IR. Second, the imaging unit is equipped with three different kinds of sensitive photodectors. Besides three separate photomulitplier tubes, the microscope incorporates a low noise CCD camera and a fast photodiode for detecting modulated signals in real time. Taken together, this instrument is one of the world’s most sensitive all-optical imaging tools.
This system was designed for time-resolved STM measurements at cryogenic (5K) temperatures, and under ultrahigh vacuum (10-11 torr) conditions. A unique feature of this system is the parabolic collector (right panel), which can be aligned at cryogenic temperatures and UHV conditions to precisely match its focus with the STM tip apex. The system is coupled to a two-color fs laser, with pulse widths of 20 fs and repetition rate of 250 kHz.
This home-built SFG spectroscopy set up is interfaced with a 90-fs, 2 kHz femtosecond laser system and consists of 1) a 100-fs OPA tunable from 3 to 10 µm; 2) a grating-slit pulse shaper for generating picosecond visible pulses; 3) a local oscillator (LO) generation unit using a LiNbO3 crystal; and 4) a focusing unit to generate SFG signals; and 5) a detection unit consisting of a spectrograph and MCT and PMT detectors. The capabilities of the set up include homodyne fs-IR/ps-vis frequency-domain experiments, heterodyne fs-IR/ps-vis frequency-domain experiments, as well as heterodyne fs-IR/fs-vis time-domain experiments.
This homebuilt system includes a femtosecond laser setup (A), a leak detector, an evaporator load lock (B), and a sample load lock (C). The laser setup has a harmonic generator (foreground in A) and a femtosecond oscillator (background in A) that provides wavelengths from 210 nm to 1040 nm, with a gap from 520 nm to 690 nm. This laser system is coupled to an adjacent low temperature STM. The evaporator load lock enables rapid turnaround of metal and molecular dosers that can be made without venting the vacuum chamber containing the STM, thus allowing rapid screening of atoms and molecules for dosing onto the sample. The sample load locks enables rapid turnaround of samples and STM tips that can be made without venting the vacuum chamber containing the STM, thus allowing rapid exchange of samples and tips.
The CaSTL TIRF-AFM system combines single molecule TIRF microscopy with a moveable, field-enhancing AFM probe in order to enable a variety of new imaging modes. On top of the light microscope, with 1.45 NA TIRF objective for single molecule fluorescence work, is mounted an AFM. It is outfitted with a high-resolution CCD camera for wide field imaging and a UV-enhanced Si avalanche photodetector for photon counting experiments.
The ultrafast system for SE-FSRS and ultrafast TERS studies consists of a high repetition-rate amplifier seeded by a broadband oscillator, which generates 8 µJ, 30 fs pulses with repetition rates from 100 to 250 kHz. Half of the amplifier output is directed to a narrow band pass filter for spontaneous and stimulated Raman pumping. Photoexcitation is performed using pulses from a visible optical parametric oscillator or fundamental doubling. A supercontinuum white light source is available for transient absorption or for stimulating femtosecond Raman spectroscopy. High-speed detection is enabled by a 1 kHz CCD (Princeton Instruments PIXIS 100F) and imaging spectrograph. This system is can perform sub-100-fs transient absorption and femtosecond stimulated Raman experiments in either a transmissive or reflective geometry.
A home-built multi-chamber UHV system is available for atomic scale STM imaging and optical microscopy. This system prepares pristine surfaces and characterizes them at the atomic scale, with temperature control between 10 K and 400 K, with the option of performing feedback controlled nanolithography. For TERS studies, lasers at 405 nm, 532 nm, 633 nm, and 785 nm are available.
A custom optical microscope was fabricated for STM-TERS. Excitation at laser wavelengths given above is performed with a polarization-maintaining single-mode fiber and is focused with an achromatic lens. Inelastically scattered light from the tip-sample junction is collected through a fiber bundle and analyzed. The STM stage is controlled by the electronics system equipped with a custom approach interface. This system allows correlated TERS and STM imaging and tip-sample TERS intensity distance dependence from Au or Ag tips on any conducting substrate. Due to its ambient nature, efficient optimization of the tip preparation procedure and TERS enhancement factor can be performed on this instrument.
A Rennishaw InVia Cofocal Raman Microscope with excitation wavelengths 785 nm, 532 nm and 405 nm was funded by an NSF MRI-R2 Award (PI: Apkarian). The instrument is fitted with options for making a 2-dimensional Raman image of the sample, and the sample cell can be cooled to 75 K and heated to 600 ºC.
The FEI Quanta 3D FEG is a scanning electron microscope (SEM)/focused ion beam (FIB) dual-beam instrument for 2D and 3D material characterization and analysis. Various capabilities include high-resolution imaging (1.2 nm at 30 kV), low kV high contrast imaging, micromachining, Pt deposition, chemical composition analysis and mapping, crystal structure determination and orientation mapping.
The Department of Chemistry Modeling Facility is a multi-user facility that provides cutting-edge resources for performing computational simulations of chemical systems, spanning quantum-mechanical electronic structure of molecules and materials to molecular dynamics of large biomolecules and membranes. Calculations are primarily performed on a 110+ node cluster "Greenplanet", with each node having 2 quad-core 2.8Ghz Intel Xeon X5560 processors, 12-24GB 1333MHz DDR3 RAM, and 160GB-1TB local storage, and each being connected to a 40 Gigabit/s QDR Infiniband high-speed network and a 150TB disk array.