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,
Sunbeam City is a anticapitalist, antifascist solarpunk instance that is run collectively.