Structural Collapse targets only the player. The player can sacrifice an artifact or land with hexproof, for example.

The target player needn't control an artifact or a land. Structural Collapse will still deal 2 damage to that player.

If the player controls an artifact land, he or she can't choose to sacrifice that permanent for both the artifact and the land. If that's the only artifact the player controls, he or she must sacrifice another land. If it's the only land the player controls, he or she must sacrifice another artifact. If it's the only artifact and the only land the player controls, he or she sacrifices just that permanent.