Error using Tikz matrix inside of subfloat

Question

Possible Duplicate:
Problem with defining shortcuts for TikZ matrices.

I'm getting a the following error using subfloat and tikz matrix together: ERROR: Package pgfbasematrix Error: Single ampersand used with wrong catcode. Commenting out the subfloat lines results in no errors. Thanks in advance for any suggestions.

\documentclass{article}
%% For drawing
\usepackage{tikz}
\usetikzlibrary{arrows,positioning}

%% For subfloat
\usepackage{subfig}

%% Drawing
\def\linkaba{stealth'-stealth'}
\def\linkab{-stealth'}
\def\linkba{stealth'-}
\newcommand{\directedtriangle}[4]{
  \node (A) at (0,0) [nd] {}; % Lower Left
  \node (B) at +(1,0) [nd] {}; % Lower Right
  \node (C) at +(0.5,0.75) [nd] {}; % Top
  \draw[#1] (A)--(B);
  \draw[#2] (A)--(C);
  \draw[#3] (B)--(C);
  \node [below] at +(0.5,-0.1) {\footnotesize (#4)};
}
\newcommand{\directedwedge}[3]{
  \node (A) at (0,0) [nd] {}; % Lower Left
  \node (B) at +(1,0) [nd] {}; % Lower Right
  \node (C) at +(0.5,0.75) [nd] {}; % Top
  \draw[#1] (A)--(C);
  \draw[#2] (B)--(C);
  \node [below] at +(0.5,-0.1) {\footnotesize (#3)};
}


\begin{document}
\begin{figure}[t]
\subfloat[Wedges]{
  \begin{tikzpicture}[nd/.style={circle,draw,fill=black!50,inner sep=2pt}]    
    \matrix[column sep=0.4cm, row sep=0cm]
    {
      \directedwedge{\linkba}{\linkba}{i} &
      \directedwedge{\linkab}{\linkba}{ii} &
      \directedwedge{\linkab}{\linkab}{iii} \\
      \directedwedge{\linkaba}{\linkab}{iv} &
      \directedwedge{\linkaba}{\linkba}{v} &
      \directedwedge{\linkaba}{\linkaba}{vi} \\
    };
  \end{tikzpicture}}

\subfloat[Triangles]{
  \begin{tikzpicture}[nd/.style={circle,draw,fill=black!50,inner sep=2pt}]    
    \matrix[column sep=0.4cm, row sep=0cm]
    {
      \directedtriangle{\linkab}{\linkba}{\linkba}{a} &
      \directedtriangle{\linkab}{\linkba}{\linkab}{b} &
      \directedtriangle{\linkaba}{\linkba}{\linkba}{c} &
      \directedtriangle{\linkaba}{\linkab}{\linkba}{d} \\
      \directedtriangle{\linkaba}{\linkab}{\linkab}{e} &
      \directedtriangle{\linkaba}{\linkaba}{\linkba}{f} &
      \directedtriangle{\linkaba}{\linkaba}{\linkaba}{g}\\
    };
  \end{tikzpicture}}
  \vspace{-0.5cm}
  \caption{All different directed wedges and triangles}
  \label{fig:dwedge}
\end{figure}


\end{document}