The ordination of deacons - "in order to serve"
"At a lower level of the hierarchy are to be found deacons, who receive the imposition of hands 'not unto the priesthood, but unto the ministry."' At an ordination to the diaconate only the bishop lays hands on the candidate, thus signifying the deacon's special attachment to the bishop in the tasks of his "diakonia."
Source: Catechism of the Catholic Church (Vatican.va)