L=1
V0=1

V1x[x_]=V0 Sin[(( 2π)/L)x]

Plot[ V1x[x],{x,-1,1}]

V1xz[x_,z_]=V0  Sin[(((2π)/L) )x] Exp[-(((2π)/L))z]

Plot3D[ V1xz[x,z],{x,-1,1},{z,0,1},PlotRange->{-1,1}]

Plot3D[ V1xz[x,z],{x,-1,1},{z,0,1},PlotRange->{-0.1,0.1}]