An x-ray window includes a mount with a support frame and an aperture. A window film has a stack of layers including: a thin film layer comprising a material selected from the group consisting of diamond, graphene, diamond-like carbon, beryllium, and combinations thereof; a boron hydride layer; and a polymer layer. The window film, including the thin film layer, the boron hydride layer, and the polymer layer, extends across the aperture and is supported by the support frame. The window film is attached to the support frame, defining a sealed joint. The layers are capable of withstanding a differential pressure of at least 1 atmosphere. The window film is substantially transmissive to x-rays having an energy in the range of 100-20,000 electronvolts.