Surface Science and Nanostructures Laboratory
Prof. Goldfarb is mainly interested in self-assembled and self-organized growth of epitaxial nanostructures inside STM. One way to self-assemble nanostructures is to introduce strain into the growing layer by carefully controlling the mismatch between the crystalline lattices of the layer and the substrate (heteroepitaxy). Relaxation of mismatch strain drives the self-assembled formation of nanocrystal arrays [1-4], which can be used in quantum-dot and -wire devices, provided the size and shape distribution of the nanocrystals in the array is sufficiently narrow, and their degree of crystalline perfection is high. Nanostructure ordering can be achieved by self-organization on naturally provided mesas, such as periodic step-bunches on vicinal surfaces . Since self-assembly and self-ordering of nanostructures are thermodynamically and/or kinetically determined, only deep understanding of these tendencies (that occur naturally during growth) can provide the means to control them and hence tailor-on-demand. Therefore, the projects carried out in the laboratory are aimed at exploring epitaxial materials systems with varying mismatch and ability to order, such as Ge/Si [1-3] and Co/Si , as well as other refractory metal silicides, and compound semiconductors, e.g., In/CdZnTe  (see the figure below). The goal is to gain a sufficient degree of understanding of the nanostructure-surface interactions for developing a generic approach for controlling the nanostructure behavior on surfaces, towards implementation in realistic devices. One of the strengths of the laboratory is the rare ability to observe the evolution of the growing epilayers in real-space and -time by STM, due to state-of-the-art UHV SPM Microlab where the deposition flux is incident upon the sample while it is being scanned and continuously imaged during growth. Furthermore, bias-dependent STM imaging and scanning tunneling spectroscopy (STS) have been instrumental in studying the nanostructure electronic properties, such as their local density of states (LDOS), for exploration of the observed quantum size effects (QSE’s).
Scanning tunneling microscopy (STM) micrograph of self-assembled pyramidal Ge/Si(001) nano-huts (left) [1-3], self-organized CoSi2/Si(111) nano-islands (middle) , and their LDOS (right). Rightmost image on the black background: In(Te) nanocontacts on a CdZnTe(110) substrate .