Can we create sheet of neutron I want to know are there any theory or technology to create a neutron matter like neutron star on earth. Even a tiny thin sheet like graphene
And how heavy it is if we create 1x1 sqmm of neutron sheet. Can it catch/detect/harvest neutrino and other kind of particle?
 A: No, to create stable neutron matter, you need some binding mechanism, that opposes the decay due to the weak interaction ($\beta$-decay). In neutron stars this is gravity and the pressure generated by gravity. One can explain this inhibition of $\beta$-decay because there is a degenerate electron gas (i.e. all states below the Fermi energy are occupied), therefore $\beta$-decay is forbidden by the Pauli principle, because the electron's target states are occupied. In conclusion, only heavy stars get neutron stars at the end of their life. Lighter stars become white dwarfs (where the degeneracy pressure of electrons determines the radius). Only when the collapsed core of a star is more massive than approximately $1.39 M_\odot$ (the Chandrasekhar limit) it forms a neutron star. So to form a sheet of neutron matter you would have to use a device that generates a comparable pressure as the neutron star by its weight (and this is obviously far out of our technological reach, probably even altogether impossible).
Also, the nature of the matter in neutron stars is debated. Is is possible their cores are not degenerate neutron-matter, but some kind of "quark matter", possibly strange matter (consisting of up, down and strange quarks). The term Quark star is used to describe such an object.
A: If you tried to build a neutron sheet, you would start with a single atom and start adding neutrons to it to build a sheet. Although this is possible, when you add a few neutrons to the atom, it becomes unstable. The more neutrons you add to the atom, the shorter its half life becomes. You might be able to add 3 or 4 neutrons before it becomes unstable and breaks apart. This sometimes happens in neutron stars. It becomes a supernova.
