creating a new folder and a text file inside that folder

I wanna create a new folder named log and inside that folder i want to create a textfile named log.txt and this is the path i want to create D:\New Folder

i have tried this to create a new folder named log

string FilePathSave = Folder.ToString() + System.IO.Directory.CreateDirectory(@"D:\New Folder\Log");

And i have created a text file using this

string FilePathSave = Folder.ToString() +"log.txt";
File.WriteAllText(FilePathSave, TextBox1.Text);                

But i cant create like D:\New Folder\Log\log.txt...any suggestion??