For the high level serving technique:
The racket head must rise up while in contact with the ball for top spin and kick serves.
The racket also rises up for flat and slice serves, but not as much.
This can be directly observed in high speed videos. It appears to involve
ulnar deviation, a wrist joint motion.
These composite gifs and pictures were created by Toly.
Slice serve gif. 3 frames shows racket positions before, during and after impact.
Slice serve. The 3 frames from above. Note rise of racket vs baseline.
Kick serve gif.
Kick serve. The 3 frames from above. Note racket rise vs baseline.
Flat serve. Use the
period & comma keys to single frame. Time scale counts down to impact at "0" milliseconds.
Observe and compare all angles for the composite gifs, pictures and the video. All at impact - Arm angle tilt, forearm-to-racket-shaft angle, average direction of racket strings contacting ball vs vertical.
In order to record videos like these you need:
1) 240 fps
2) small motion blur (fast shutter)
3) bright sunny day
4) camera placement. (these were looking along the ball's trajectory)
Countdown time scale, processing & analysis was done on Kinovea. Kinovea is a free open source application that has many capabilities for video analysis and display.
The direction of the racket strings tend to be perpendicular to the spin axes shown in this ball diagram. The match would not be perfect because the racket head is on a curved path and the collision adds complications. Also, the ball spin diagram was made by studying elite players and the above images are from one pro player. But the racket string direction for the kick serve looks closer to the horizontal direction than the flat and slice serves. Print the ball diagram, draw perpendiculars to the 3 spin axes and see how close they might be. (I believe that the top spin serve has a different spin axis than the kick serve.)
If the OP does not have a high level serve technique, the OP is on his own.