Methods for depositing material onto microfeature workpieces in reaction chambers and systems for depositing materials onto microfeature workpieces are disclosed herein. In one embodiment, a method includes depositing molecules of a gas onto a microfeature workpiece in the reaction chamber and selectively irradiating a first portion of the molecules on the microfeature workpiece in the reaction chamber with a selected radiation without irradiating a second portion of the molecules on the workpiece with the selected radiation. The first portion of the molecules can be irradiated to activate the portion of the molecules or desorb the portion of the molecules from the workpiece. The first portion of the molecules can be selectively irradiated by impinging the first portion of the molecules with a laser beam or other energy source.