of the microscope to adjust the wavelength. This latter

can now be done to great accuracy in most modern STEM

equipment.

 The advantage of having all of one type of line

passing directly through the center of the pattern is

explained below. If it were possible to have all of one

line type (the (9311 lines for a B =(114)pattern) in the

center of the pattern, a reference microscope operating

potential could then be defined for that particular

lattice parameter. For a material of different lattice

parameter, the difference in accelerating potential

required to bring the lines to the center of the pattern

compared to the reference would be proportional to the

difference in lattice parameter between the two materials

(Steeds, 1979). To measure a change in lattice parameter

in this way, one would merely note the change in

accelerating potential required to achieve identical

patterns in the central disc.

 To more rigorously solve the effect of beam

convergence on HOLZ line formation, the Bragg angle and

the actual angle the beam makes with each specific HOLZ

diffracting plane must be determined. For example, for B

= (114>, a = 3.56, and R = 27.07 (100 kV electrons), the

calculated value for h2+k2+12 using equation (1) is

90.713. Because this number is not an integer, the Bragg

condition in the first order zone is not satisfied for B =

(114>. Consider a second beam direction B'. If B' were