Figure 1

(a) Schematic diagram of the graphene FET based on the reversible switching of AL of electrons. The device consists of H-graphene as a channel between the source and the drain, and the ${\mathrm{NH}}_3$ gas at pressure $P_{\mathrm{NH}3}$ as the proton acceptor in contact with the channel. The conductance of the channel is controlled by applying the perpendicular external electric fields to the graphene (denoted by arrows). The top and bottom electrodes (not shown here) for the generation of the applied fields are electrically isolated from the rest of the device. In the device setup, only the upper side of the graphene is accessible by H atoms and ${\mathrm{NH}}_3$. Depending on the electric-field strength $E_{\mathrm{ext}}$, temperature $T$, and $P_{\mathrm{NH}3}$, the H atoms exist either as the isolated monomers attached to graphene (denoted by yellow circles) or as part of the $\mathrm{NH}_4{}^{+}$ ions (a red dashed circle). (b) The demonstration of the field-induced switching between the high-resistance ($R$) state and the low-$R$ state for a given $P_{\mathrm{NH}3}$. Here, the absolute value of $R$ depends on the size of the graphene channel in Ref. 11. However, the field effect on $R$ is qualitatively valid regardless of the sample size.Reuse & Permissions

Figure 2

Proton donor-acceptor reaction on hydrogenated graphene. (a) The DFT energy curves for the adsorption of ${\mathrm{NH}}_3$ on H-graphene (filled squares) and for the adsorption of $\mathrm{NH}_4{}^{+}$ on bare graphene (filled circles) as a function of the height ($h_{\mathrm{N}}$) of the N atom in an adsorbate from the graphene sheet. The energy of the lowest-energy state (denoted by $\mathbf{e}$) is set to zero. For the adsorption curve of ${\mathrm{NH}}_3$, spin-polarized calculations were done to describe the magnetic state associated with ${\mathrm{H}}_{\mathrm{monomer}}$. (b)–(e) Atomic structures of the important steps in the adsorption of ${\mathrm{NH}}_3$ denoted by $\mathbf{b}$, $\mathbf{c}$, $\mathbf{d}$, and $\mathbf{e}$ in (a); (b) ${\mathrm{NH}}_3$ well separated from ${\mathrm{H}}_{\mathrm{monomer}}$ (${\mathrm{NH}}_3$ is not shown here). (c) The metastable ${\mathrm{NH}}_3\mathrm{\text{−}}{\mathrm{H}}_{\mathrm{monomer}}$ state where ${\mathrm{NH}}_3$ is weakly physisorbed on the H-graphene. (d) The saddle-point geometry of the transition from the metastable state $\mathbf{c}$ to the lowest energy state $\mathbf{e}$, which involves the proton transfer from ${\mathrm{H}}_{\mathrm{monomer}}$ to ${\mathrm{NH}}_3$. (e) The adsorption geometry of $\mathrm{NH}_4{}^{+}$ on graphene ($\mathrm{NH}_4{}^{+}\mathrm{\text{−}}{\mathrm{\text{graphene}}}^{-}$). The adsorption of ${\mathrm{NH}}_3$ on H-graphene [i.e., the PDA reaction in Eq. (1)] occurs in a sequence of $\mathbf{b}$, $\mathbf{c}$, $\mathbf{d}$, and $\mathbf{e}$, with the adsorption energy $E_{\mathrm{ads}}=0.41\mathrm{eV}$. The open boxes in (a) were obtained from the linearly interpolated configurations between the states $\mathbf{d}$ and $\mathbf{e}$, showing a downhill reaction. The reverse reaction leads to the removal of ${\mathrm{NH}}_3$ and recovery of ${\mathrm{H}}_{\mathrm{monomer}}$, while the direct desorption of $\mathrm{NH}_4{}^{+}$ (filled circles) is energetically unfavorable.Reuse & Permissions

Figure 3

Electric field-induced control of the adsorption or desorption of H atoms on graphene. (a) The adsorption energy ($E_{\mathrm{ads}}$) of ${\mathrm{NH}}_3$ on H-graphene versus the external electric fields ($E_{\mathrm{ext}}$) (closed circles for the PBE results and open circles for the vdW-DF calculation results). (b) The $P_{\mathrm{NH}3}\mathrm{\text{−}}T$ relation for the thermodynamic condition $\Delta G=0$ of the PDA reaction in Eq. (1) at different $E_{\mathrm{ext}}$, where $P_{\mathrm{NH}3}$ is ${\mathrm{NH}}_3$ pressure and $T$ is temperature. (c)–(d) Field-induced tuning of the density of the H monomers (${\mathrm{H}}_{\mathrm{monomer}}$) in H-graphene. The ratio $n_{\mathrm{Hmonomer}}/n_{\mathrm{H}}{}^{\mathrm{tot}}$ as a function of $E_{\mathrm{ext}}$ for different $P_{\mathrm{NH}3}$ at (c) $T=300$ and (d) 210 K. $n_{\mathrm{H}}{}^{\mathrm{tot}}$ is the total density of H atoms on graphene.Reuse & Permissions