to provide accurate quantification of structural properties at the atomic level. Most university research groups, for example, require permission to use such high-end electron microscopes at national lab facilities, which requires excessive time commitment. Universal challenges mainly involve becoming accustomed to the programming language desired and writing software that can tackle the very specific problems for a given material system. For example, one can imagine how a different analysis technique, and thus a separate image processing algorithm, is necessary for studying ideal cubic versus complex monoclinic structures. Other STEM techniques Specialized sample holders or modifications to the microscope can allow a number of additional techniques to be performed in STEM. Some examples are described below. STEM tomography STEM tomography allows the complete three-dimensional internal and external structure of a specimen to be reconstructed from a tilt-series of 2D projection images of the specimen acquired at incremental tilts. High angle ADF STEM is a particularly useful imaging mode for electron tomography because the intensity of high angle ADF-STEM images varies only with the projected mass-thickness of the sample, and the atomic number of atoms in the sample. This yields highly interpretable three dimensional reconstructions. Cryo-STEM Cryogenic electron microscopy in STEM (Cryo-STEM) allows specimens to be held in the microscope at liquid nitrogen or liquid helium temperatures. This is useful for imaging specimens that would be volatile in high vacuum at room temperature. Cryo-STEM has been used to study vitrified biological samples, vitrified solid-liquid interfaces in material specimens, and specimens containing elemental sulfur, which is prone to sublimation in electron microscopes at room temperature. In situ/environmental STEM In order to study the reactions of particles in gaseous environments, a STEM may be modified with a differentially pumped sample chamber to allow gas flow around the sample, whilst a specialized holder is used to control the reaction temperature. Alternatively a holder mounted with an enclosed gas flow cell may be used. Nanoparticles and biological cells have been studied in liquid environments using liquid-phase electron microscopy in STEM, accomplished by mounting a microfluidic enclosure in the specimen holder. Low-voltage STEM A low-voltage electron microscope (LVEM) is an electron microscope that is designed to operate at relatively low electron accelerating voltages of between 0.5 and 30 kV. Some LVEMs can function as an SEM, a TEM, and a STEM in a single compact instrument. Using a low beam voltage increases image contrast which is especially