How to change the font size in icon in vis-network node

Question

 {
    id: 7,
    label: "dataType",
    shape: "dot",
    icon: {
         face:'Arial',          
         code: "\u0074\u0078\u0074",      // "txt"       
         },        
    value: 28
  }, 

I want to add an icon to the dot type node, But no matter I increase size:40 or font:{size:40}, I cannot change the size of the unicode characters. How can I adjust the display size of unicode characters without changing the node value?