This thing is called a 5D optical data storage crystal. It's a little piece of fused quartz, etched to remarkable precision using a femtosecond ultraviolet laser.
The "5D" part of the name is just a marketing gimmick (it only has three dimensions, obviously), but it's impressive anyway. Using current technology, these little things can store 360 terabytes of data. Once written, these crystals can survive temperatures up to 1000°C, and could theoretically last for billions of years.
A betavoltaic device uses beta particles from radioactive decay to generate electricity. Basically, it works like a solar cell, but using radiation instead of light.
Hypothetically, this could be used to make batteries which last a long time. Using thin layers of radioactive carbon-14 sandwiched between layers of semiconductive diamond (which would also keep the radioactivity contained), tiny batteries like these could supply small amounts of power for thousands of years. Prototypes have been made using nickel-63 as the energy source,
@InvaderXan @FuchsiaShock i looked into this too a while back! the trouble is that betavoltaic cells have power output typically in the range of tens to hundreds of microwatts, which can be useful for low draw hard-to-reach applications, but many orders of magnitude lower than what a phone battery puts out (on the order of 1-10W). for that you'd need something more like a SNAP RTG, using the decay heat from a slug of plutonium to drive thermocouples. smaller slug in this case and thus cooler running, since it just needs a few watts and not the hundreds that space rated RTGs produce, but i don't know any other passive nuclear process that has power density comparable with lithium batteries. (and plutonium is also pretty hazardous, less for its alpha emissions than because it's a toxic heavy metal and also occasionally pyrophoric. idk how i'd feel about carrying that around in my pocket, however well shielded)
(also as someone who literally has an "atomkraft? ja, bitte!" sticker on her laptop i feel bound to note that we could probably most easily produce beta sources at industrial scale via neutron activation in a running reactor, the same way a lot of medical isotopes are made)
Sunbeam City is a anticapitalist, antifascist solarpunk instance that is run collectively.