Charge State Of Nitrogen-vacancy Centers Research Articles

Super-Resolution Diamond Magnetic Microscopy of Superparamagnetic Nanoparticles.

Scanning-probe and wide-field magnetic microscopes based on nitrogen-vacancy (NV) centers in diamond have enabled advances in the study of biology and materials, but each method has drawbacks. Here, we implement an alternative method for nanoscale magnetic microscopy based on optical control of the charge state of NV centers in a dense layer near the diamond surface. By combining a donut-beam super-resolution technique with optically detected magnetic resonance spectroscopy, we imaged the magnetic fields produced by single 30 nm iron-oxide nanoparticles. The magnetic microscope has a lateral spatial resolution of ∼100 nm, and it resolves the individual magnetic dipole features from clusters of nanoparticles with interparticle spacings down to ∼190 nm. The magnetic feature amplitudes are more than an order of magnitude larger than those obtained by confocal magnetic microscopy due to the narrower optical point-spread function and the shallow depth of NV centers. We analyze the magnetic nanoparticle images and sensitivity as a function of the microscope's spatial resolution and show that the signal-to-noise ratio for nanoparticle detection does not degrade as the spatial resolution improves. We identify sources of background fluorescence that limit the present performance, including diamond second-order Raman emission and imperfect NV charge state control. Our method, which uses <10 mW laser power and can be parallelized by patterned illumination, introduces a promising format for nanoscale magnetic imaging.

Change in charge state of NV center caused by monovacancy formation

Effects of monovacancy formation on the charge states of nitrogen vacancy (NV) centers in nitrogen-doped diamond single crystal were investigated. Monovacancies are formed using high-energy electron beam irradiation. The ratio of the concentration of negatively charged nitrogen vacancy (NV−) centers to the total concentration of NV− centers and neutral nitrogen vacancy (NV0) centers decreases with increased concentration of monovacancies. This decrease occurs because of the reduction of the concentration of neutral substitutional nitrogen [Ns0] donating electrons to NV0 centers. Findings indicate that numerous electrons of Ns0 are transferred preferentially to monovacancies, not to NV0 centers.

Charge states of nitrogen-vacancy centers in Fermi level controlled diamond n-i-n junctions

Control of the charge state of the nitrogen-vacancy (NV) center is crucial because of its instability and its transitions between the negative (NV–) and neutral (NV0) NV charge states under laser irradiation In this study, we fabricated an n-i-n junction, with an i-layer sandwiched between two phosphorus-doped n-layers; then, we measured the charge state of NV centers under steady state and laser irradiation in a known band structure where the Fermi energy changes gradually. The steady-state charge state measured by a nondestructive single shot exhibited stable NV– and NV0 signals when the Fermi level was even slightly above and below the transition level, respectively. This result indicates that the charge state can be significantly stabilized through band engineering. Both charge-state populations were observed only when the Fermi level was close to the transition level. Under continuous green laser irradiation, the ratio of NV– measured by the photoluminescence spectra changed gradually with the Fermi level in the depletion layer because of the balance between excitation from the laser and the supply of charge from the band. This outcome agrees reasonably with the calculated bands. Furthermore, we measured the PL spectra of the ensemble NV centers and discovered that their charge state can be well-controlled, as in the single NV center. The charge state of the i-layer at the interface can be stabilized by depositing a thin n-layer on the surface. These results would contribute significantly to improve sensor performance.

Equilibrium charge state of NV centers in diamond

We investigated charge states of nitrogen vacancy (NV) centers in diamond single crystals. The charge states were evaluated using concentrations of both negatively charged (NV−) and neutral-state (NV0) NV centers. This study specifically examines diamond crystals containing mainly neutral substitutional nitrogen (N0s), NV− centers, and NV0 centers. Results show that the charged states of NV centers evaluated for this study depended on concentrations of both neutral substitutional nitrogen (N0s) and NVT centers, which is a sum of [NV−] and [NV0]. The NV centers were fully negatively charged when the ratio of [NVT] to [N0s] was 1%–20% in our diamond crystals. When [NVT]/[N0s] is larger than 20%–30%, NV0 centers appeared gradually. The concentration ratio between NV− centers and NV0 centers was described using an equilibrium equation.

Study of ion-implanted nitrogen related defects in diamond Schottky barrier diode by transient photocapacitance and photoluminescence spectroscopy

The study of nitrogen-vacancy (NV) centers in diamond are growing attractive in the application of quantum devices. Here, electrical control of NV charge state and defects induced by nitrogen ions implantation in diamond were investigated by transient photocapacitance (TPC) spectroscopy and photoluminescence (PL) spectroscopy. The experiments show that thresholds of 1.2 eV appeared in TPC spectra are probably due to the presence of excited defect energy levels related to vacancy or NV center. Alternatively, the 2.2 eV defect observed in the TPC spectrum is probably attributed to NV centers. The variation of TPC and PL spectra with different applied voltages suggests that bias voltages control the charge state of NV centers since their effect on the Fermi level shifting in the depletion region. Furthermore, the steady-state photocapacitance indicates that the 2.2 eV deep trap slows down the process of photocapacitance rise and fall, and these processes can be enhanced by a higher electrical field.

NV Center Charge State Controlled Graphene-on-Diamond Field Effect Transistor Actions With Multi-Wavelength Optical Inputs

We demonstrate graphene-on-diamond field effect transistor (FET) actions modulated by optically excited charge state of nitrogen-vacancy (NV) centers in diamond. Palladium (Pd) metal contacts on graphene serve as the source and the drain. Negative charge state NV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> center in diamond serves as the gate with diamond being the gate dielectric and produces an electric field to enhance the hole concentration in the graphene channel. The conductivity of graphene varies with negative charge state NV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> center, resulting in differential conductance. The negative gate bias is removed when a NV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> center is converted to an NV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> center. P-type graphene channel exhibits positive differential conductance under illumination by a blue (405 nm) laser beam while on the contrary negative differential conductance by a red (633 nm) laser beam. Furthermore, by simultaneous illumination of both blue and red laser beams, effects on differential conductance decrease according to the relative intensity of the two laser beams. Graphene FETs with wavelength dependent multiple optical inputs and one electrical output in response to the charge state of NV centers in diamond has been reported.

Analysis of the charge state of nitrogen-vacancy centers in diamond driven by an infrared laser field

The methods of controlling the charge state of nitrogen–vacancy centers using pulsed infrared laser field are studied. The effect of radiation intensity at a wavelength of about 1 μm on the ionization of these color centers was shown. The obtained results can be useful for multiphoton microscopy of biological objects, high-resolution microscopy and sensory applications.

Electrical control of deep NV centers in diamond by means of sub-superficial graphitic micro-electrodes

The control of the charge state of nitrogen-vacancy (NV) centers in diamond is of primary importance for the stabilization of their quantum-optical properties, in applications ranging from quantum sensing to quantum computing. In this work buried current-injecting graphitic micro-electrodes were fabricated in bulk diamond by means of a 6 MeV C3+ scanning micro-beam. The electrodes were exploited to control the variation in the relative population of the negative (NV−) and neutral (NV0) charge states of a sub-superficial NV centers ensemble located in the inter-electrode gap region. Photoluminescence spectra exhibited an electrically-induced increase up to 40% in the NV− population at the expense of the NV0 charge state, with a linear dependence from the injected current at applied biases smaller than 350 V, and was interpreted as the result of electron trapping at NV sites. An abrupt current increase at ∼350 V bias resulted in a strong electroluminescence from the NV0 centers, in addition to two spectrally sharp emission lines at 563.5 nm and 580 nm, not visible under optical excitation and attributed to self-interstitial defects. These results disclose new possibilities in the electrical control of the charge state of NV centers located in the diamond bulk, which are characterized by longer spin coherence times.

Addressing Single Nitrogen-Vacancy Centers in Diamond with Transparent in-Plane Gate Structures

For many applications of the nitrogen-vacancy (NV) center in diamond, the understanding and active control of its charge state is highly desired. In this work, we demonstrate the reversible manipulation of the charge state of a single NV center from NV(-) across NV(0) to a nonfluorescent, dark state by using an all-diamond in-plane gate nanostructure. Applying a voltage to the in-plane gate structure can influence the energy band bending sufficiently for charge state conversion of NV centers. These diamond in-plane structures can function as transparent top gates, enabling the distant control of the charge state of NV centers tens of micrometers away from the nanostructure.

Optical manipulation of the charge state of nitrogen-vacancy center in diamond

The conversion between two nitrogen vacancy (NV) center charge states (NV0 and NV−) was experimentally studied with laser in the range from 378 to 492 nm. The wavelength and power dependent charge state conversion was proved to be single-photon process at short wavelength and two-photon process at long wavelength. Also, the presence of metastable state in NV− significantly affected the conversion process, which can be used to increase NV− population from 72.5% to 80.5% by applying a magnetic field under 532 nm excitation. The method can be used for improving the fidelity of charge state polarization and subsequently optimizing the quantum control with NV center and resolution in the magnetometric and biological sensoring.

Surface and size effects on the charge state of NV center in nanodiamonds

Electronic structures and stability of nitrogen–vacancy (NV) centers doped in nanodiamonds (NDs) have been investigated with large-scale density functional theory (DFT) calculations. Spin polarized defect states are not affected by the particle sizes and surface decorations, while the band gap is sensitive to these effects. Induced by the spherical surface electric dipole layer, surface functionalization has a long-ranged impact on the stability of charged NV centers doped in NDs. NV− center doped in DNs is more favorable for n-type fluorinated diamond, while NV0 is preferred for p-type hydrogenated NDs. Therefore, surface decoration provides a useful way for defect state engineering.

Tunable light emission from nitrogen-vacancy centers in single crystal diamond PIN diodes

Charge-states modulation of nitrogen-vacancy (NV) centers incorporated into single crystal diamond films attracts increasing attention for solid-state qubits applications. Here, we discuss the electro- and photoluminescence emission properties of NV centers incorporated by gas phase nitrogen delta-doping of the intrinsic diamond layer of a positive-intrinsic-negative (PIN) junction diode. The experiments show that the charge state of NV centers can be intentionally controlled by applying well-defined external bias voltages. It can be switched from the negatively charged state NV− to the neutral charged state NV0 when a strong forward bias potential is applied. This can be switched back by application of reverse potentials. These results will be discussed assuming basic electronic properties of diamond PIN diodes, including the variation of spectral properties as well as the dynamics of charge state transitions.

Nondecaying long range effect of surface decoration on the charge state of NV center in diamond

On the basis of density functional theory, stability and electronic structure of nitrogen-vacancy (NV) centers in surface modified diamond have been studied. Surface decoration is traditionally expected to only have influence on those NV centers close to the surface. However, our calculations indicate that its effect to charged NV centers is nondecaying and long-range, where the formation energy of the charged NV center converges to a value typically different for different types of surface decoration. Such a nondecaying long range effect is due to the electrostatic potential shift induced by the surface dipole layer, and it leads to the preference of NV(-) center for oxygen saturated diamond and NV(0) for hydrogenated one. Our work demonstrates that surface functionalization can be used to modify the relative stabilities of differently charged defects in nonmetallic materials.

Chemical control of the charge state of nitrogen-vacancy centers in diamond

We investigate the effect of surface termination on the charge state of nitrogen vacancy centers, which have been ion-implanted few nanometers below the surface of diamond. We find that, when changing the surface termination from oxygen to hydrogen, previously stable NV- centers convert into NV0 and, subsequently, into an unknown non-fluorescent state. This effect is found to depend strongly on the implantation dose. Simulations of the electronic band structure confirm the dissappearance of NV- in the vicinity of the hydrogen-terminated surface. The band bending, which induces a p-type surface conductive layer leads to a depletion of electrons in the nitrogen vacancies close to the surface. Therefore, hydrogen surface termination provides a chemical way for the control of the charge state of nitrogen-vacancy centers in diamond. Furthermore, it opens the way to an electrostatic control of the charge state with the use of an external gate electrode.