Memory junk when pointing a pointer

Question

In an attempt to implement an adjacent matrix graph, I created the function to create a new "matrix" in which the contents of the graph would be copied to it by adding the new positions. However, when calling this function and printing the new graph, the output contains several memory junk. Where is the error?

class GrafosMatriz{
    public:
     int *grafo;
     int tam;

GrafosMatriz(int tam){
    this->tam = tam;
    grafo = new int[tam*tam];
        for(int i = 0 ; i < tam*tam; i++)
                grafo[i] = 0;

}
void criarVertice(){
    tam++;
    int *aux = new int[tam*tam]; //matriz aux declarada com n+1
        for(int i = 0 ; i < tam*tam; i++){
            aux[i] = 0;
        }

        for(int i = 0,  j = 0; i < tam*tam - tam; i++){ //Passar pela matriz nova de tamanho n+1, sem passar na ultima linha
            if(i%tam != 0){  // pular a ultima coluna da matriz
                j++;
               aux[i] = grafo[j];
            }
        }

        grafo = aux;
        delete aux;

}