A sample and selective support structure mounted on a platform in a scanning tunneling microscope includes a double spring support with the springs overlapped to reduce overall length of the support. In a preferred embodiment, a rigid support structure supports a first platform. A second platform is positioned around and spaced from the first platform and includes a plurality of support members extending therefrom. A first set of springs is attached to the rigid support structure and to the second platform for supporting the second platform, and a second set of springs is attached to the second platform and to the first platform for supporting the first platform. By attaching the second set of springs to the rigid members extending from the second platform, the first and second sets of springs can be overlapped, thereby reducing the overall length of the spring support without reducing the effective length of the springs. A lock mechanism is provided for locking the first and second platforms when not in use, and includes a rod that engages holes in two members depending from the first and second platforms. The lock mechanism further includes first and second rigid arms pivotally attached to the rod and supported whereby the rigid arms extend from and retract to the rod when the rod is translated. When the rigid arms are extended from the rod, the arms engage lock mechanisms depending from the first platform, thereby achieving a rigid lock in six axes of motion.