Equipment

Ultra-High Vacuum Transmission Electron Microscope (UHVTEM)

The ultra-high-vacuum transmission electron microscope (UHVTEM, Hitachi H-9000, operates at 300 kV and a base pressure of 2×10^-10 Torr. For context, this is three orders of magnitude higher than typical TEM vacuum levels. This UHV environment enables the preparation of atomically-clean surfaces as well as growth of reactive or easily oxidizable materials. Gases such as disilane, digerman, arsine and trimethylgallium can be inserted to the sample through leak valves. This allows chemical vapor deposition of semiconductor systems such as Si, Ge and GaAs to be carried out during TEM imaging, creating real-time atomic resolution “movies” of nucleation and growth.

The system has also been modified to include a series of connected side chambers. Samples can be transferred between the UHVTEM and side chambers without breaking the vacuum through a series of transfer rods. In the side chambers we can clean samples, heat chips, and deposit metals and semiconductors in both thermal and electron beam sources. To date, electron beam and thermal evaporators have allowed us to deposit a wide range of metals and semiconductors (Au, Ag, Ti, Nb, Cu, Ge) on cleaned 2D material substrates (Gr, hBN, MoS2, WSE2). The UHV environment, due to its absence of carbonaceous contamination and other impurities, provides an ideal playground to study nucleation and groth kinetics in its pure form. This technique is particularly beneficial in studies of nanoisland and nanowire nucleation and growth, thin film epitaxy, diffusion (both surface and interdiffusion, as well as surface reconstructions and oxidation.

The Thermo Fisher Scientific (TFS) Themis Z G3 aberration-corrected scanning transmission electron microscope (STEM) achieves < 0.6 Å resolution (sample dependent) and is equipped with an optimized monochromator for < 30 meV energy resolution in EELS at 60 kV, a Gatan Continuum electron energy loss spectrometer and image filter, a TFS Super-X energy dispersive x-ray spectrometer system, a segmented STEM detector for fast DPC and iDPC imaging, a Lorentz lens, a 16 megapixel Ceta II camera and a 4D STEM EMPAD camera. Single tilt, double tilt, and tomography holders are available. The instrument can be operated at 60, 200, and 300 kV for the flexibility to accommodate a range of electron beam sensitive materials.

Our group members often use the equipment in the Materials Research Laboratory Shared Experimental Facilties. Particularly important is the JEOL 2011 TEM, in which we carry out our liquid cell experiments. In this photo, Serin is performing a liquid cell experiment using a Hummingbird electrochemical liquid cell holder. The liquid cell consists of two unltrathin silicon membranes that sandwich a think liquid layer when clamped together in the sample holder. The electron beam passes through the liquid cell and goes into the camera underneath, allowing us to record nanoscale events in real time. The liquid cell is integrated with microfluidic channels and wires to enable liquid flow and external electrical manipulation.

This MonoCL3+ is attached to the JEOL 2011 TEM and is available to measure cathodoluminescience from TEM samples. A mirror can be inserted/extracted to the TEM column to collect the light emitted from the sample and reflect it to a detector. Two detectors (photomultiplier and CCD) are available.

This photo shows the liquid cell holder. Liquid is introduced into the liquid cell via a flow tube connected to a syringe pump. Separate electronics is used to apply external stimuli to the liquid cell ship. Heating via a resistance heater is controlled using a sourcemeter, and biasing is controlled using a potentiostat.

Optical microscope and micromanipulator for transfer of 2D materials: 5x, 10x, 20x, 50x and 100x objective lenses are available with dual BF-DF modes. Heating and vacuum stage are equipped for transfer process. The micromanipulator can precisely move in x/y/z directions to fabricate vdW heterostructures and to transfer them to a TEM grid.

Dell desktop with NVidia GPU for S/TEM image processing, simulation, and data analysis.