  Let $S\subset\mathbb{R}^3$ be a $C^4$-smooth relatively compact orientable
surface with a sufficiently regular boundary. For $\beta\in\mathbb{R}_+$, let
$E_j(\beta)$ denote the $j$th negative eigenvalue of the operator associated
with the quadratic form \[ H^1(\mathbb{R}^3)\ni u\mapsto \iiint_{\mathbb{R}^3}
|\nabla u|^2dx -\beta \iint_S |u|^2d\sigma, \] where $\sigma$ is the
two-dimensional Hausdorff measure on $S$. We show that for each fixed $j$ one
has the asymptotic expansion \[ E_j(\beta)=-\dfrac{\beta^2}{4}+\mu^D_j+ o(1)
\;\text{ as }\; \beta\to+\infty\,, \] where $\mu_j^D$ is the $j$th eigenvalue
of the operator $-\Delta_S+K-M^2$ on $L^2(S)$, in which $K$ and $M$ are the
Gauss and mean curvatures, respectively, and $-\Delta_S$ is the
Laplace-Beltrami operator with the Dirichlet condition at the boundary of $S$.
If, in addition, the boundary of $S$ is $C^2$-smooth, then the remainder
estimate can be improved to ${\mathcal O}(\beta^{-1}\log\beta)$.
