Add a schematic overview of the lithography and FIB milling.

Author: jvdoorn

chapters/method.tex

@@ -32,11 +32,27 @@ \section{On-chip design}
     \label{tab:sample-dimensions}
 \end{SCtable}
 
-\subsection{Nanofabrication}
+\subsection{Nano fabrication}
 \label{subsec:nanofabrication}
-A \qty{9}{\mm} by \qty{5}{\mm} undoped \ce{Si} wafer of \qty{500}{\um} thick is used as a substrate. The substrate is spincoated at \qty{2000}{\rpm} with positive resist AR-P 662.06 and baked at \qty{150}{\celsius} for \qty{3}{\min}. This step is then repeated in order to coat 2 layers in total resulting in a total thickness of \qty{1}{\um}. A lithography step is performed using the Raith 100 EBPG exposing the resist to \qty{400}{\micro\coulomb\per\square\cm}. The resist is developed using a 1:3 mixture of MIBK and isopropanol for \qty{45}{\s}, the development is stopped using isopropanol. The Z-407 sputtering machine deposits a \qty{5}{\nm} \ce{MoSi} sticking layer followed by a \qty{500}{\nm} \ce{Au} layer. The lift-off is performed in acetone and anisole.
+A \qty{9}{\mm} by \qty{5}{\mm} undoped \ce{Si} wafer of \qty{500}{\um} thick is used as a substrate. The substrate is spincoated at \qty{2000}{\rpm} with positive resist AR-P 662.06 and baked at \qty{150}{\celsius} for \qty{3}{\min}. This step is then repeated in order to coat 2 layers in total resulting in a total thickness of \qty{1}{\um}. A lithography step is performed using the Raith 100 EBPG exposing the resist to \qty{400}{\micro\coulomb\per\square\cm}. The resist is developed using a 1:3 mixture of MIBK and isopropanol for \qty{45}{\s}, the development is stopped using isopropanol. The Z-407 sputtering machine deposits a \qty{5}{\nm} \ce{MoSi} sticking layer followed by a \qty{500}{\nm} \ce{Au} layer. The lift-off is performed in acetone and anisole. For an overview of the lithography process refer to \autoref{fig:lithography}.
 
-Inside the inner loop of the coil, we mill a hole of roughly \qty{15}{\um} deep with a diameter of \qty{100}{\um} in the \ce{Si} substrate using a \ce{Ga+} focussed ion beam (Aquilos 2 Cryo-FIB). A similar hole is also made in a microscope coverslip. To aid this process a very thin (\qty{5}{\nano\meter}) \ce{Pt} layer is deposited on the glass. Using a micromanipulator a \ce{NdFeB} particle of \qty{12}{\um} is placed inside the \ce{Si} hole. The easiest way to do so is by sticking the particle to the bottom of the needle and then scraping the particle off on the sides of the \ce{Si} hole. The coverslip is placed on top of the \ce{Si} substrate. The holes are carefully aligned by moving the coverslip using a micromanipulator. The coverslip is then glued to the \ce{Si} substrate using an epoxy. The coverslip creates a enclosed environment for the particle to move in. This prevents the particle from escaping the trap. The particle is magnetized by putting the whole sample in a magnetic field of approximately \qty{1.3}{\tesla} for several minutes at room temperature and pressure. \autoref{fig:optical-microscope-image-sample} shows an optical microscope image of the sample.
+\begin{figure}[h]
+    \centering
+    \includegraphics{figures/lithography.pdf}
+    \caption{A schematic overview of the lithography process: the resist is exposed to an electron beam (a); the exposed resist is developed (b); a thin sticking layer and \qty{500}{\nano\meter} of \ce{Au} are deposited (c); acetone/anisole dissolves the resist and lifts off the \ce{Au} layer (d).}
+    \label{fig:lithography}
+\end{figure}
+
+Inside the inner loop of the coil, we mill a hole of roughly \qty{15}{\um} deep with a diameter of \qty{100}{\um} in the \ce{Si} substrate using a \ce{Ga+} focussed ion beam (Aquilos 2 Cryo-FIB). A similar hole is also made in a microscope coverslip. To aid this process a very thin (\qty{5}{\nano\meter}) \ce{Pt} layer is deposited on the glass. \autoref{fig:FIB} shows a schematic overview of the milling process in the wafer.
+
+\begin{figure}[h]
+    \centering
+    \includegraphics{figures/FIB.pdf}
+    \caption{A schematic overview of the FIB milling process in the \ce{Si}-wafer: the \ce{Ga+} ions are focussed on the sample and mill a hole bounded by the tracks (a); the resulting hole after the milling (b).}
+    \label{fig:FIB}
+\end{figure}
+
+Using a micromanipulator a \ce{NdFeB} particle of \qty{12}{\um} is placed inside the \ce{Si} hole. The easiest way to do so is by sticking the particle to the bottom of the needle and then scraping the particle off on the sides of the \ce{Si} hole. The coverslip is placed on top of the \ce{Si} substrate. The holes are carefully aligned by moving the coverslip using a micromanipulator. The coverslip is then glued to the \ce{Si} substrate using an epoxy. The coverslip creates a enclosed environment for the particle to move in. This prevents the particle from escaping the trap. The particle is magnetized by putting the whole sample in a magnetic field of approximately \qty{1.3}{\tesla} for several minutes at room temperature and pressure. \autoref{fig:optical-microscope-image-sample} shows an optical microscope image of the sample.
 
 \begin{figure}
     \centering