The image shows a scanning electron micrograph of GaAs nanowires on a silicon substrate. These self-catalyzed GaAs wires were grown from the gallium droplets that can be seen on the wire tips.
For this sample and many others, SEM is a proven technique for resolving the topography of the nanomaterials while displaying excellent contrast between the various constituents. However, acquiring such materials contrast can be daunting when those materials are insulators, exhibit sensitivity to electron beams, or are similar in composition. In these cases, it is a challenge to achieve this contrast quickly, at TV-rate scanning, with low noise and at short working distance, or from a tilted perspective.
To solve all these challenges associated with materials contrast imaging, FEI recently launched the all-new Apreo SEM, featuring a unique in-lens backscatter detector (T1). Apreo’s T1 detector captures backscatter signal as soon as the beam is switched on. Because it is positioned at the bottom of the column, intense materials contrast is available all the way from navigation to imaging the smallest details. With sensitivity to beam currents as low as only a few pA, it is ideal for imaging sensitive samples that would otherwise be damaged.
Apreo further improves materials contrast with a novel compound electrostatic-magnetic final lens. Compound lens filtering was used in this image to enhance the contrast between two materials that are very close in average atomic weight (Ga and GaAs). Moreover, the compound lens filter can be used to filter out charging signal, enabling charge-free imaging on insulators in cases where excellent low-beam energy and low-current performance are not enough.
Combined with a range of features that make the microscope versatile, effective, and easy to use, Apreo’s excellent detection gives researchers the contrast they need to advance scientific discovery.
Sample courtesy of David Fuster, Andrés Raya, Álvaro San Paulo and María Ujue González in the group “MBE: quantum nanostructure for optoelectronics” at “IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC)”.