A Tomahawk dunk can be performed with one or two hands, and when two hands are used, it is called a backscratcher. During the jump, the ball is raised above, and often behind the player's head for a wind-up before slamming the ball down into the net at the apex of the jump. Due to the undemanding body mechanics involved in execution, the tomahawk is employed by players of all sizes and jumping abilities.[citation needed] Because of the ball-security provided by the use of both hands, the two-handed tomahawk is a staple of game situations—frequently employed in alley-oops and in offense-rebound put-back dunks.
Technique Tip: Determining how far out in front of you to place your front foot may require some trial and error. At the bottom of the motion, your front knee should be somewhere above your heel to mid foot. If your knee is behind your heel, your foot is too far forward; if it’s out over your toes, step out further. One trick to find the right distance is to start in the bottom position and adjust your stance from there. Then stand up and have someone hand you the dumbbells.
Strength exercises include slow, controlled movements like squats, lunges, and weighted step-ups.  Power exercises require explosive, quick moves like those needed for plyometrics and power cleans. Plyometrics are explosive bounding, hopping and jumping drills that blend strength and speed. Finally, practicing maximum vertical jump will increase vertical jump.
A great summary of what it takes to improve vertical jumping ability Joe. There is definitely an art and science to optimizing vertical jump height. I actually just completed a huge post on the topic of How To Jump Higher which your readers may find complements this post nicely. It is a long read (12000+ words) but for those of your readers who want to learn more about the art of jumping they may find it helpful. Keep up the great work!

The method described above is the most common and simplest way to measure one's vertical jump, but other more scientifically accurate methods have been devised. A pressure pad can be used to measure the time it takes for an athlete to complete a jump, and then using a kinematics equation (h = g × t2/8),[4] the computer can calculate his or her vertical jump based on the time in the air.