title: Graphical parameters in ggplot2: How to change axis/tick thickness
body: <p>I just started using 'ggplot2', and am running into some problems with the graphical usability.</p>
  
  <p>I wanted to do a simple regression biplot. However, I am not quite convinced by the themes offered by 'ggplot2' and 'ggthemes'.</p>
  
  <p>My code thus far is as follows:</p>
  
  <pre><code>    ggplot(data, aes(APE.15N, APE.13C)) +
          geom_point(size=3) +
          geom_smooth(method="lm", se=F, col="black") +
          theme_light(base_size = 20) + 
          annotate("text", x=.9, y=1.35, label="R²=0.3192, p&lt;0.001", size=6.5) +
          coord_cartesian(xlim = c(.25, 1.1), ylim = c(1.05, 2.55)) +
          ylab(expression(paste('APE '^{13}, "C", sep = ""))) +
          xlab(expression(paste('APE '^{15}, "N", sep = ""))) 
  </code></pre>
  
  <p>...which gives me the following plot:</p>
  
  <p><a href="https://i.stack.imgur.com/PWUks.png" rel="noreferrer">ouput from R with ggplot2</a></p>
  
  <p>Now, I would like to increase the axis-line thickness as well as the tick thickness to at least 2 points, add minor ticks, get rid of the background grid, and change the axis colour to black.</p>
  
  <p>I just can't figure out how...</p>
  
  <p>I would imagine the result as in the following graph:</p>
  
  <p><a href="https://i.stack.imgur.com/9NSdf.png" rel="noreferrer">example graph</a></p>
  
  <p>Thank you,
  your help is very much appreciated</p>