At this moment and At once

At once and at this moment are semantically related in presently topic. In some cases you can use "At once" instead the phrase "At this moment" as an adjective or an adverb, when it comes to topics like instantaneous.

At once adverb - Without delay or hesitation; with no time intervening.

At this moment and at once are semantically related in presently topic. Sometimes you can use "At this moment" instead the phrase "At once" as an adjective or an adverb, if it concerns topics such as instantaneous.