Graphene field effect transistors with ferroelectric gating

Recent experiments on ferroelectric gating have introduced a novel functionality, i.e. nonvolatility, in graphene field effect transistors. A comprehensive understanding in the non-linear, hysteretic ferroelectric gating and an effective way to control it are still absent. In this letter, we quantitatively characterize the hysteretic ferroelectric gating using the reference of an independent background doping (nBG) provided by normal dielectric gating. More importantly, we prove that nBG can be used to control the ferroelectric gating by unidirectionally shifting the hysteretic ferroelectric doping in graphene. Utilizing this electrostatic effect, we demonstrate symmetrical bit writing in graphene-ferroelectric FETs with resistance change over 500% and reproducible no-volatile switching over 10^5 cycles.Comment: 5 Pages; 4 figures; two column forma

Albuminuria as pre-screening tool for better risk prediction

Cardiovascular disease (CVD) and chronic kidney disease (CKD) are common health problems and originates predominantly from generalized atherosclerosis. Diabetes, hypertension, and hypercholesterolemia are well known risk factors for atherosclerosis. Screening for and treatment of these risk factors is the cornerstone for prevention of CVD and CKD. Elevated albuminuria has increasingly been recognized as first evidence of generalized atherosclerosis. Testing for albuminuria is thus far advocated only in case of the presence of the abovementioned risk factors. In this thesis, that is a part of the PREVEND study, it is investigated, whether pre-screening for albuminuria followed by screening for diabetes, hypertension and hypercholesterolemia only in those subjects with elevated albuminuria may be of help to improve the effectiveness of screening for and treatment of CVD and CKD. It was found that in subjects with elevated albuminuria the prevalence of yet undiagnosed CV risk factors is high. The identification of subjects with elevated albuminuria and a newly diagnosed risk factor is important, because these subjects were shown to be at increased risk for both CVD and progressive CKD, especially in subjects ≥55 years of age. In addition, the start of statin treatment in hypercholesterolaemic subjects with elevated albuminuria was associated with a better risk reduction in CV event rate. In conclusion, this thesis shows that pre-screening for albuminuria will make screening to identify subjects at high risk for CVD and progressive CKD more efficient. Those with elevated albuminuria should be invited for further screening for risk factors, and should be treated according to the current guidelines

van der Waals Bonded Co/h-BN Contacts to Ultrathin Black Phosphorus Devices

Due to the chemical inertness of 2D hexagonal-Boron Nitride (h-BN), few atomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals such as Black Phosphorus (BP). However, the effects of h-BN on Schottky barrier height, doping and contact resistance are not well known. Here, we investigate these effects by fabricating h-BN encapsulated BP transistors with cobalt (Co) contacts. In sharp contrast to directly Co contacted p-type BP devices, we observe strong n-type conduction upon insertion of the h-BN at the Co/BP interface. First principles calculations show that this difference arises from the much larger interface dipole at the Co/h-BN interface compared to the Co/BP interface, which reduces the work function of the Co/h-BN contact. The Co/h-BN contacts exhibit low contact resistances (~ 4.5 k-ohm), and are Schottky barrier free. This allows us to probe high electron mobilities (4,200 cm2/Vs) and observe insulator-metal transitions even under two-terminal measurement geometry