diff --git a/src/main.py b/src/main.py
index d3994fd..5832970 100644
--- a/src/main.py
+++ b/src/main.py
@@ -382,7 +382,7 @@ def make_nexus_schema_dictionary(substrate_object, layers):
     return pld_fabrication
 
 
-def build_nexus_file(pld_fabrication, output_path, rheed_osc=None):
+def build_nexus_file(pld_fabrication, output_path, rheed_osc=None, heatmap_matrix=None):
     # NOTE: look at the mail attachment from Emiliano...
     with h5py.File(output_path, "w") as f:
         nx_pld_entry = f.create_group("pld_fabrication")
@@ -645,10 +645,10 @@ def build_nexus_file(pld_fabrication, output_path, rheed_osc=None):
             raise TypeError(te)
 
         # RHEED data section
-        if rheed_osc is not None:
-            nx_rheed = nx_pld_entry.create_group("rheed_data")
-            nx_rheed.attrs["NX_class"] = "NXdata"
+        nx_rheed = nx_pld_entry.create_group("rheed_data")
+        nx_rheed.attrs["NX_class"] = "NXdata"
 
+        if rheed_osc is not None:
             # Asse temporale
             t_ds = nx_rheed.create_dataset("time", data=rheed_osc["time"])
             t_ds.attrs["units"] = "s"
@@ -682,6 +682,14 @@ def build_nexus_file(pld_fabrication, output_path, rheed_osc=None):
             # nx_rheed.attrs["layer_indices"] = [0]  # asse layer
             # nx_rheed.attrs["time_indices"] = [1]   # asse tempo
             # nx_rheed.attrs["channel_indices"] = [2]
+        if heatmap_matrix is not None:
+            heatmap = nx_rheed.create_dataset("diffraction_image", data=heatmap_matrix)
+            heatmap.attrs["long_name"] = "Diffraction Image"
+            heatmap.attrs["units"] = "a.u."
+            # this is of my own initiative. good???
+            heatmap.attrs["interpretation"] = "spectrum"
+            # suggested by DeepSeek, useful?
+            heatmap.attrs["suggested_colormap"] = "viridis"
     return
 
 
@@ -721,9 +729,12 @@ if __name__ == "__main__":
     # TO-DO: make it format-agnostic. If not possible, make it PNG-only.
     if os.path.isfile("tests/LAO_16min50s_736C_STO.bmp"):  # if BMP
         # if os.path.isfile("tests/LAO_16min50s_736C_STO.png"): # if PNG
-        with open() as img:
-            img = Image.open("tests/LAO_16min50s_736C_STO.bmp").convert("L")
-            mx = np.array(img, dtype=np.uint8)
+        img = Image.open("tests/LAO_16min50s_736C_STO.bmp").convert("L")
+        mx = np.array(img, dtype=np.uint8)
+        normalized_mx = mx.astype(np.float32) / 255.0  # consider deleting???
     build_nexus_file(
-        result, output_path=f"output/sample-{sample_name}-nexus.h5", rheed_osc=rheed_osc
+        result,
+        output_path=f"output/sample-{sample_name}-nexus.h5",
+        rheed_osc=rheed_osc,
+        heatmap_matrix=normalized_mx,
     )