Abstract: A holder for a flat substrate, such as for example a semiconductor wafer or a glass slide, has a fixture with a sample insertion groove for holding the flat substrate, or multiple sample insertion grooves for holding multiple flat substrates. The fixture also has a channel milled perpendicular to the sample insertion groove. The channel may be machined such that two portions of the channel open to opposite sides of the fixture. Positioned in the channel of the fixture is a cantilever spring for securing the flat substrate in the sample insertion groove. The channel may contain a single cantilever spring that extends an entire length of the channel, or multiple cantilever springs. The fixture may include a post, dove tail, screw, or clamp for mounting the holder on a stage inside a vacuum chamber of an instrument.