Equipment & Techniques
The Elmitec LEEM V is a field-emission low energy electron microscope
for in-situ microscopy of dynamic surface processes. The microscope is
capable of micro-low energy electron diffraction (u-LEED). In contrast to
conventional LEED optics that average over a large area of the sample
u-LEED can yield diffraction patterns of different micron-sized regions of
the sample surface. While imaging the sample can be heated to 1500K
and exposed to certain gases at pressures up to 10-3 Torr. The system has
a separate preparation chamber that includes a load lock, sputter ion gun, Auger electron spectrometer and an additional heating stage. In LEEM the resolution is 5.5nm on Pb on Mo(100) and in PEEM the resolution is 9.5nm on Pb on Mo(100).
In contrast to other imaging techniques such as scanning probe microscopy and scanning electron microscopy, this full-field microscope allows for real-time imaging of the sample without the need to raster across the surface. Unlike TEM and SEM that can cause beam damage on the sample due to high accelerating voltages, the electrons in LEEM are slowed down to a few eV or a few tenths of an eV before they reach the surface of the sample or can even be reflected off the surface with little interaction (negative potential). One of the most common uses of the instrument is to study real-time film growth, changes in the phase or crystallinity, or work function changes of samples under various conditions (pressure, temperature, environment, etcetera).
We have plans of adding IRRAS or RAIRS capabilities that can be performed simultaneously with LEEM.
Sample Requirements:
1) The sample must be smaller than 10mm x 10mm in length and width and larger than 3mm x 3mm.
2) Sample thickness should be anywhere between ~0.5mm to 2mm.
3) The sample surface should be conductive or at a minimum semiconducting. Insulating samples will not work. As an example, a ~50-100nm thick conductive film (Au) on an insulating support (mica) will "usually" work. The important part is that the surface needs to be conducting or semiconducting. Si wafers need to be doped to prevent charging and must only contain the native oxide that is approximately ~90nm thick (it will be silver or blue in color). Si wafers with a deep blue or puple color contain a ~300nm oxide that is not suitable.
4) For samples prepared ex-situ, they will need to be degassed for a minimum of 1-2 hours at the highest temperature possible in the LEEM prep chamber prior to imaging.
5) Samples cannot have sharp edges or cracks as these will likely cause an arc and possibly destroy the sample.
Contact Samuel Tenney (stenney@bnl.gov) to discuss your planned experiment(s)in more detail.
Elmitec LEEM V
Elmitec LEEM V system for in-situ low energy electron microscopy (LEEM), photoemission electron microscopy (PEEM) and micro-low energy electron diffraction (u-LEED).
ScientaOmicron 4-Point Nanoprobe
Nanoprobe system capable of performing scanning electron microscopy (SEM), scanning Auger spectromicroscopy (nanoSAM), 4-point probe measurments, and low energy electron diffraction (LEED).
Omicron Nanotechnology 4-Point Nanoprobe system capable of performing scanning electron microscopy (SEM), scanning Auger spectromicroscopy (nanoSAM), and low energy electron diffraction (LEED).
The sample stage utilizes the common "flag" style sample holders and can be cooled to below 120K with liquid nitrogen under the SEM column. Samples can be transferred to the preparation chamber for sputtering, annealing (>1000K), deposition, and LEED. The system can accommodate numerous samples at a time and is designed for high sample throughput.
Contact Samuel Tenney (stenney@bnl.gov) to discuss your planned experiment(s)in more detail.
Bruker NanoIR3-s
Combined AFM and laser system for nanoscale infrared spectromicroscopy (nanoIR) and scattering-type scanning near-nield optical microscopy (s-SNOM)
The nanoIR combines an atomic force microscope with infrared lasers to perform infrared spectroscopy and scattering type scanning near field optical microscopy (s-SNOM) with a spatial resolution of 10-50nm. The instrument can also perform nano thermal analysis (nanoTA) of samples to look at melt characteristics and phase transitions with spatial resolution on the order of tens of nanometers. The lasers cover the region from ~850cm-1 to ~2250cm-1. The system typically operates at ambient, but the environmental enclosure can be employed to control humidity and gas composition around the sample and tip. The s-SNOM setup utilizes a liquid nitrogen cooled MCT detector.
The unit is currently equipped with 6 quantum cascade lasers (QCLs) spanning a range from ~850-2247 wavenumbers. 5 of the 6 QCLs can operate in both pulsed and CW mode, with the laser spanning 1230-1478 wavenumbers only being capable of pulsed mode operation.
Sample Requirements:
An ideal sample for all techniques would be a very flat sample with a size of ~10mmx10mm in length/width. Smaller samples would also work,
however larger samples may lead to some additional limitations, but could potentially be accommodated.
For PTIR mode the sample needs to be thick enough that the IR excitation of the material causes enough expansion that it can be measured with the cantilever. There are a few papers pertaining to the minimum thickness required for a detectable signal. Organic materials should be thicker than 100nm, however thinner samples have been successfully measured. Materials with a large coefficient of thermal expansion (PMMA, polystyrene, etc) work quite well. In PTIR mode you can use contact or tapping mode tips. Contact mode = more signal and ~50nm spatial resolution, whereas tapping mode = less signal, but better spatial resolution (~10nm).
For s-SNOM the sample of interest needs to be placed on a highly reflective and ultraflat surface (e.g. Au). Si wafers can be used, but may have some limitations as silica does absorb in certain infrared ranges. The sample of interest must also be no more than 300nm in height above the reference substrate. The sample of interest and the highly reflective substrate must be present within the same field of view (currently 50um x 50um).
Please provide an AFM image (alternatively an SEM image) as well as an IR (ATR, trasmission, reflection) spectrum of your sample(s) prior to your session to make the best use of the valuable time on the instrument.
Contact Samuel Tenney (stenney@bnl.gov) to discuss your planned experiment(s) in more detail and whether contact mode or tapping mode is needed among other details.
Photothermal Spectroscopy Corp. mIRage (O-PTIR + Raman)
The mIRage optical-photothermal infrared (O-PTIR) plus Raman instrument provides sub-500nm spatially resolved infrared and Raman spectra on the same spot at the same time with the same spatial resolution. The instrument can perform hyperspectral imaging and chemical imaging as well as point spectroscopy.
The mIRage O-PTIR + Raman is equipped with one 532nm laser and four IR quantum cascade lasers spanning the range from 758 to 1806 wavenumbers. The unit is equipped with 3 detectors for different configurations. Two standard detectors for reflection and transmission as well as 3rd detector for beam sensitive samples (high sensitivity, low light detector). Samples should be mounted on a mircoscope slide. Alternative sample mounts can be accommodated, but should be discussed in advance.
Contact Samuel Tenney (stenney@bnl.gov) to discuss your planned experiment(s)in more detail.