Geotiffwrite doesn't show any image

Hi, I was making a script to extract xyz data from surface figure and write it into geotiff file. The script works and create an image, however when i opened it windows preview said it's corrupted and if i opened it in global mapper the file only show a single color image but with the right coordinates. Here is the script

ch=gcf;
ch = findobj(ch,'Type','surface');
ch=get(gca,'ch');
x=get(ch,'Xdata');
y=get(ch,'Ydata');
z=get(ch,'Zdata');
z{1,1}=[];

z1=cell2mat(z);
yin=min(cell2mat(y));
yax=max(cell2mat(y));
xin=min(cell2mat(x));
xax=max(cell2mat(x));

xmin=min(xin(:));
xmax=max(xax(:));
ymin=min(yin(:));
ymax=max(yax(:));

s=size(z1);
R = georefcells([ymin,ymax],[xmin,xmax],s);

tiffile='11test.tif' ;
geotiffwrite(tiffile,z1,R)
[z1,R] = geotiffread(tiffile);

Here is the screenshot of the image in GlobalMapper: